diff --git a/Android.bp b/Android.bp
new file mode 100644
index 0000000..45e7681
--- /dev/null
+++ b/Android.bp
@@ -0,0 +1,62 @@
+// This file is generated by cargo_embargo.
+// Do not modify this file after the first "rust_*" or "genrule" module
+// because the changes will be overridden on upgrade.
+// Content before the first "rust_*" or "genrule" module is preserved.
+
+package {
+    default_applicable_licenses: ["external_rust_crates_libhyper_license"],
+}
+
+license {
+    name: "external_rust_crates_libhyper_license",
+    visibility: [":__subpackages__"],
+    license_kinds: ["SPDX-license-identifier-MIT"],
+    license_text: ["LICENSE"],
+}
+
+rust_library {
+    name: "libhyper",
+    host_supported: true,
+    crate_name: "hyper",
+    cargo_env_compat: true,
+    cargo_pkg_version: "0.14.28",
+    crate_root: "src/lib.rs",
+    edition: "2018",
+    features: [
+        "client",
+        "default",
+        "full",
+        "h2",
+        "http1",
+        "http2",
+        "runtime",
+        "server",
+        "socket2",
+        "stream",
+        "tcp",
+    ],
+    rustlibs: [
+        "libbytes",
+        "libfutures_channel",
+        "libfutures_core",
+        "libfutures_util",
+        "libh2",
+        "libhttp",
+        "libhttp_body",
+        "libhttparse",
+        "libhttpdate",
+        "libitoa",
+        "libpin_project_lite",
+        "libsocket2",
+        "libtokio",
+        "libtower_service",
+        "libtracing",
+        "libwant",
+    ],
+    apex_available: [
+        "//apex_available:platform",
+        "//apex_available:anyapex",
+    ],
+    product_available: true,
+    vendor_available: true,
+}
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..1ceb406
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,334 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies.
+#
+# If you are reading this file be aware that the original Cargo.toml
+# will likely look very different (and much more reasonable).
+# See Cargo.toml.orig for the original contents.
+
+[package]
+edition = "2018"
+name = "hyper"
+version = "0.14.28"
+authors = ["Sean McArthur <sean@seanmonstar.com>"]
+include = [
+    "Cargo.toml",
+    "LICENSE",
+    "src/**/*",
+]
+description = "A fast and correct HTTP library."
+homepage = "https://hyper.rs"
+documentation = "https://docs.rs/hyper"
+readme = "README.md"
+keywords = [
+    "http",
+    "hyper",
+    "hyperium",
+]
+categories = [
+    "network-programming",
+    "web-programming::http-client",
+    "web-programming::http-server",
+]
+license = "MIT"
+repository = "https://github.com/hyperium/hyper"
+
+[package.metadata.docs.rs]
+features = [
+    "ffi",
+    "full",
+]
+rustdoc-args = [
+    "--cfg",
+    "docsrs",
+    "--cfg",
+    "hyper_unstable_ffi",
+]
+
+[package.metadata.playground]
+features = ["full"]
+
+[profile.bench]
+codegen-units = 1
+incremental = false
+
+[profile.release]
+codegen-units = 1
+incremental = false
+
+[[example]]
+name = "client"
+path = "examples/client.rs"
+required-features = ["full"]
+
+[[example]]
+name = "client_json"
+path = "examples/client_json.rs"
+required-features = ["full"]
+
+[[example]]
+name = "echo"
+path = "examples/echo.rs"
+required-features = ["full"]
+
+[[example]]
+name = "gateway"
+path = "examples/gateway.rs"
+required-features = ["full"]
+
+[[example]]
+name = "hello"
+path = "examples/hello.rs"
+required-features = ["full"]
+
+[[example]]
+name = "http_proxy"
+path = "examples/http_proxy.rs"
+required-features = ["full"]
+
+[[example]]
+name = "multi_server"
+path = "examples/multi_server.rs"
+required-features = ["full"]
+
+[[example]]
+name = "params"
+path = "examples/params.rs"
+required-features = ["full"]
+
+[[example]]
+name = "send_file"
+path = "examples/send_file.rs"
+required-features = ["full"]
+
+[[example]]
+name = "service_struct_impl"
+path = "examples/service_struct_impl.rs"
+required-features = ["full"]
+
+[[example]]
+name = "single_threaded"
+path = "examples/single_threaded.rs"
+required-features = ["full"]
+
+[[example]]
+name = "state"
+path = "examples/state.rs"
+required-features = ["full"]
+
+[[example]]
+name = "tower_client"
+path = "examples/tower_client.rs"
+required-features = [
+    "full",
+    "backports",
+]
+
+[[example]]
+name = "tower_server"
+path = "examples/tower_server.rs"
+required-features = ["full"]
+
+[[example]]
+name = "upgrades"
+path = "examples/upgrades.rs"
+required-features = ["full"]
+
+[[example]]
+name = "web_api"
+path = "examples/web_api.rs"
+required-features = ["full"]
+
+[[test]]
+name = "client"
+path = "tests/client.rs"
+required-features = ["full"]
+
+[[test]]
+name = "integration"
+path = "tests/integration.rs"
+required-features = ["full"]
+
+[[test]]
+name = "server"
+path = "tests/server.rs"
+required-features = ["full"]
+
+[[bench]]
+name = "body"
+path = "benches/body.rs"
+required-features = ["full"]
+
+[[bench]]
+name = "connect"
+path = "benches/connect.rs"
+required-features = ["full"]
+
+[[bench]]
+name = "end_to_end"
+path = "benches/end_to_end.rs"
+required-features = ["full"]
+
+[[bench]]
+name = "pipeline"
+path = "benches/pipeline.rs"
+required-features = ["full"]
+
+[[bench]]
+name = "server"
+path = "benches/server.rs"
+required-features = ["full"]
+
+[dependencies.bytes]
+version = "1"
+
+[dependencies.futures-channel]
+version = "0.3"
+
+[dependencies.futures-core]
+version = "0.3"
+default-features = false
+
+[dependencies.futures-util]
+version = "0.3"
+default-features = false
+
+[dependencies.h2]
+version = "0.3.17"
+optional = true
+
+[dependencies.http]
+version = "0.2"
+
+[dependencies.http-body]
+version = "0.4"
+
+[dependencies.httparse]
+version = "1.8"
+
+[dependencies.httpdate]
+version = "1.0"
+
+[dependencies.itoa]
+version = "1"
+
+[dependencies.libc]
+version = "0.2"
+optional = true
+
+[dependencies.pin-project-lite]
+version = "0.2.4"
+
+[dependencies.socket2]
+version = ">=0.4.7, <0.6.0"
+features = ["all"]
+optional = true
+
+[dependencies.tokio]
+version = "1"
+features = ["sync"]
+
+[dependencies.tower-service]
+version = "0.3"
+
+[dependencies.tracing]
+version = "0.1"
+features = ["std"]
+default-features = false
+
+[dependencies.want]
+version = "0.3"
+
+[dev-dependencies.futures-util]
+version = "0.3"
+features = ["alloc"]
+default-features = false
+
+[dev-dependencies.matches]
+version = "0.1"
+
+[dev-dependencies.num_cpus]
+version = "1.0"
+
+[dev-dependencies.pretty_env_logger]
+version = "0.4"
+
+[dev-dependencies.serde]
+version = "1.0"
+features = ["derive"]
+
+[dev-dependencies.serde_json]
+version = "1.0"
+
+[dev-dependencies.spmc]
+version = "0.3"
+
+[dev-dependencies.tokio]
+version = "1"
+features = [
+    "fs",
+    "macros",
+    "io-std",
+    "io-util",
+    "rt",
+    "rt-multi-thread",
+    "sync",
+    "time",
+    "test-util",
+]
+
+[dev-dependencies.tokio-test]
+version = "0.4"
+
+[dev-dependencies.tokio-util]
+version = "0.7"
+features = ["codec"]
+
+[dev-dependencies.tower]
+version = "0.4"
+features = [
+    "make",
+    "util",
+]
+default-features = false
+
+[dev-dependencies.url]
+version = "2.2"
+
+[features]
+__internal_happy_eyeballs_tests = []
+backports = []
+client = []
+default = []
+deprecated = []
+ffi = ["libc"]
+full = [
+    "client",
+    "http1",
+    "http2",
+    "server",
+    "stream",
+    "runtime",
+]
+http1 = []
+http2 = ["h2"]
+nightly = []
+runtime = [
+    "tcp",
+    "tokio/rt",
+    "tokio/time",
+]
+server = []
+stream = []
+tcp = [
+    "socket2",
+    "tokio/net",
+    "tokio/rt",
+    "tokio/time",
+]
+
+[target."cfg(any(target_os = \"linux\", target_os = \"macos\"))".dev-dependencies.pnet_datalink]
+version = "0.27.2"
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
new file mode 100644
index 0000000..088b600
--- /dev/null
+++ b/Cargo.toml.orig
@@ -0,0 +1,258 @@
+[package]
+name = "hyper"
+version = "0.14.28"
+description = "A fast and correct HTTP library."
+readme = "README.md"
+homepage = "https://hyper.rs"
+documentation = "https://docs.rs/hyper"
+repository = "https://github.com/hyperium/hyper"
+license = "MIT"
+authors = ["Sean McArthur <sean@seanmonstar.com>"]
+keywords = ["http", "hyper", "hyperium"]
+categories = ["network-programming", "web-programming::http-client", "web-programming::http-server"]
+edition = "2018"
+
+include = [
+  "Cargo.toml",
+  "LICENSE",
+  "src/**/*",
+  #"build.rs",
+]
+
+[dependencies]
+bytes = "1"
+futures-core = { version = "0.3", default-features = false }
+futures-channel = "0.3"
+futures-util = { version = "0.3", default-features = false }
+http = "0.2"
+http-body = "0.4"
+httpdate = "1.0"
+httparse = "1.8"
+h2 = { version = "0.3.17", optional = true }
+itoa = "1"
+tracing = { version = "0.1", default-features = false, features = ["std"] }
+pin-project-lite = "0.2.4"
+tower-service = "0.3"
+tokio = { version = "1", features = ["sync"] }
+want = "0.3"
+
+# Optional
+
+libc = { version = "0.2", optional = true }
+socket2 = { version = ">=0.4.7, <0.6.0", optional = true, features = ["all"] }
+
+[dev-dependencies]
+futures-util = { version = "0.3", default-features = false, features = ["alloc"] }
+matches = "0.1"
+num_cpus = "1.0"
+pretty_env_logger = "0.4"
+spmc = "0.3"
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+tokio = { version = "1", features = [
+    "fs",
+    "macros",
+    "io-std",
+    "io-util",
+    "rt",
+    "rt-multi-thread", # so examples can use #[tokio::main]
+    "sync",
+    "time",
+    "test-util",
+] }
+tokio-test = "0.4"
+tokio-util = { version = "0.7", features = ["codec"] }
+tower = { version = "0.4", default-features = false, features = ["make", "util"] }
+url = "2.2"
+
+[target.'cfg(any(target_os = "linux", target_os = "macos"))'.dev-dependencies]
+pnet_datalink = "0.27.2"
+
+[features]
+# Nothing by default
+default = []
+
+# Easily turn it all on
+full = [
+    "client",
+    "http1",
+    "http2",
+    "server",
+    "stream",
+    "runtime",
+]
+
+# HTTP versions
+http1 = []
+http2 = ["h2"]
+
+# Client/Server
+client = []
+server = []
+
+# `impl Stream` for things
+stream = []
+
+# Tokio support
+runtime = [
+    "tcp",
+    "tokio/rt",
+    "tokio/time",
+]
+tcp = [
+    "socket2",
+    "tokio/net",
+    "tokio/rt",
+    "tokio/time",
+]
+
+# C-API support (currently unstable (no semver))
+ffi = ["libc"]
+
+# enable 1.0 backports
+backports = []
+
+# whether or not to display deprecation warnings
+deprecated = []
+
+# internal features used in CI
+nightly = []
+__internal_happy_eyeballs_tests = []
+
+[package.metadata.docs.rs]
+features = ["ffi", "full"]
+rustdoc-args = ["--cfg", "docsrs", "--cfg", "hyper_unstable_ffi"]
+
+[package.metadata.playground]
+features = ["full"]
+
+[profile.release]
+codegen-units = 1
+incremental = false
+
+[profile.bench]
+codegen-units = 1
+incremental = false
+
+[[example]]
+name = "client"
+path = "examples/client.rs"
+required-features = ["full"]
+
+[[example]]
+name = "client_json"
+path = "examples/client_json.rs"
+required-features = ["full"]
+
+[[example]]
+name = "echo"
+path = "examples/echo.rs"
+required-features = ["full"]
+
+[[example]]
+name = "gateway"
+path = "examples/gateway.rs"
+required-features = ["full"]
+
+[[example]]
+name = "hello"
+path = "examples/hello.rs"
+required-features = ["full"]
+
+[[example]]
+name = "http_proxy"
+path = "examples/http_proxy.rs"
+required-features = ["full"]
+
+[[example]]
+name = "multi_server"
+path = "examples/multi_server.rs"
+required-features = ["full"]
+
+[[example]]
+name = "params"
+path = "examples/params.rs"
+required-features = ["full"]
+
+[[example]]
+name = "send_file"
+path = "examples/send_file.rs"
+required-features = ["full"]
+
+[[example]]
+name = "service_struct_impl"
+path = "examples/service_struct_impl.rs"
+required-features = ["full"]
+
+[[example]]
+name = "single_threaded"
+path = "examples/single_threaded.rs"
+required-features = ["full"]
+
+[[example]]
+name = "state"
+path = "examples/state.rs"
+required-features = ["full"]
+
+[[example]]
+name = "tower_client"
+path = "examples/tower_client.rs"
+required-features = ["full", "backports"]
+
+[[example]]
+name = "tower_server"
+path = "examples/tower_server.rs"
+required-features = ["full"]
+
+[[example]]
+name = "upgrades"
+path = "examples/upgrades.rs"
+required-features = ["full"]
+
+
+[[example]]
+name = "web_api"
+path = "examples/web_api.rs"
+required-features = ["full"]
+
+
+[[bench]]
+name = "body"
+path = "benches/body.rs"
+required-features = ["full"]
+
+[[bench]]
+name = "connect"
+path = "benches/connect.rs"
+required-features = ["full"]
+
+[[bench]]
+name = "end_to_end"
+path = "benches/end_to_end.rs"
+required-features = ["full"]
+
+[[bench]]
+name = "pipeline"
+path = "benches/pipeline.rs"
+required-features = ["full"]
+
+[[bench]]
+name = "server"
+path = "benches/server.rs"
+required-features = ["full"]
+
+
+[[test]]
+name = "client"
+path = "tests/client.rs"
+required-features = ["full"]
+
+[[test]]
+name = "integration"
+path = "tests/integration.rs"
+required-features = ["full"]
+
+[[test]]
+name = "server"
+path = "tests/server.rs"
+required-features = ["full"]
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..bc1e966
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,19 @@
+Copyright (c) 2014-2021 Sean McArthur
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
diff --git a/METADATA b/METADATA
new file mode 100644
index 0000000..6dbe029
--- /dev/null
+++ b/METADATA
@@ -0,0 +1,20 @@
+name: "hyper"
+description: "A fast and correct HTTP library."
+third_party {
+  identifier {
+    type: "crates.io"
+    value: "hyper"
+  }
+  identifier {
+    type: "Archive"
+    value: "https://static.crates.io/crates/hyper/hyper-0.14.28.crate"
+    primary_source: true
+  }
+  version: "0.14.28"
+  license_type: NOTICE
+  last_upgrade_date {
+    year: 2024
+    month: 6
+    day: 3
+  }
+}
diff --git a/MODULE_LICENSE_MIT b/MODULE_LICENSE_MIT
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/MODULE_LICENSE_MIT
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..48bea6e
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1,2 @@
+# Bug component: 688011
+include platform/prebuilts/rust:main:/OWNERS
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..328f47b
--- /dev/null
+++ b/README.md
@@ -0,0 +1,41 @@
+# [hyper](https://hyper.rs)
+
+[![crates.io](https://img.shields.io/crates/v/hyper.svg)](https://crates.io/crates/hyper)
+[![Released API docs](https://docs.rs/hyper/badge.svg)](https://docs.rs/hyper)
+[![MIT licensed](https://img.shields.io/badge/license-MIT-blue.svg)](./LICENSE)
+[![CI](https://github.com/hyperium/hyper/workflows/CI/badge.svg)](https://github.com/hyperium/hyper/actions?query=workflow%3ACI)
+[![Discord chat][discord-badge]][discord-url]
+
+A **fast** and **correct** HTTP implementation for Rust.
+
+- HTTP/1 and HTTP/2
+- Asynchronous design
+- Leading in performance
+- Tested and **correct**
+- Extensive production use
+- Client and Server APIs
+
+**Get started** by looking over the [guides](https://hyper.rs/guides).
+
+## "Low-level"
+
+hyper is a relatively low-level library, meant to be a building block for
+libraries and applications.
+
+If you are looking for a convenient HTTP client, then you may wish to consider
+[reqwest](https://github.com/seanmonstar/reqwest). If you are looking for a
+convenient HTTP server, then you may wish to consider [Axum](https://github.com/tokio-rs/tokio).
+Both are built on top of this library.
+
+## Contributing
+
+To get involved, take a look at [CONTRIBUTING](CONTRIBUTING.md).
+
+If you prefer chatting, there is an active community in the [Discord server][discord-url].
+
+## License
+
+hyper is provided under the MIT license. See [LICENSE](LICENSE).
+
+[discord-badge]: https://img.shields.io/discord/500028886025895936.svg?logo=discord
+[discord-url]: https://discord.gg/kkwpueZ
diff --git a/cargo_embargo.json b/cargo_embargo.json
new file mode 100644
index 0000000..0ea1d13
--- /dev/null
+++ b/cargo_embargo.json
@@ -0,0 +1,16 @@
+{
+  "features": [
+    "client",
+    "default",
+    "full",
+    "h2",
+    "http1",
+    "http2",
+    "runtime",
+    "server",
+    "socket2",
+    "stream",
+    "tcp"
+  ],
+  "run_cargo": false
+}
diff --git a/src/body/aggregate.rs b/src/body/aggregate.rs
new file mode 100644
index 0000000..4bce176
--- /dev/null
+++ b/src/body/aggregate.rs
@@ -0,0 +1,38 @@
+use bytes::Buf;
+
+use super::HttpBody;
+use crate::common::buf::BufList;
+
+/// Aggregate the data buffers from a body asynchronously.
+///
+/// The returned `impl Buf` groups the `Buf`s from the `HttpBody` without
+/// copying them. This is ideal if you don't require a contiguous buffer.
+///
+/// # Note
+///
+/// Care needs to be taken if the remote is untrusted. The function doesn't implement any length
+/// checks and an malicious peer might make it consume arbitrary amounts of memory. Checking the
+/// `Content-Length` is a possibility, but it is not strictly mandated to be present.
+#[cfg_attr(
+    feature = "deprecated",
+    deprecated(
+        note = "This function has been replaced by a method on the `hyper::body::HttpBody` trait. Use `.collect().await?.aggregate()` instead."
+    )
+)]
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+pub async fn aggregate<T>(body: T) -> Result<impl Buf, T::Error>
+where
+    T: HttpBody,
+{
+    let mut bufs = BufList::new();
+
+    futures_util::pin_mut!(body);
+    while let Some(buf) = body.data().await {
+        let buf = buf?;
+        if buf.has_remaining() {
+            bufs.push(buf);
+        }
+    }
+
+    Ok(bufs)
+}
diff --git a/src/body/body.rs b/src/body/body.rs
new file mode 100644
index 0000000..7df8740
--- /dev/null
+++ b/src/body/body.rs
@@ -0,0 +1,791 @@
+use std::borrow::Cow;
+#[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
+use std::convert::Infallible;
+#[cfg(feature = "stream")]
+use std::error::Error as StdError;
+use std::fmt;
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use bytes::Bytes;
+use futures_channel::mpsc;
+use futures_channel::oneshot;
+use futures_core::Stream; // for mpsc::Receiver
+#[cfg(feature = "stream")]
+use futures_util::TryStreamExt;
+use http::HeaderMap;
+use http_body::{Body as HttpBody, SizeHint};
+
+use super::DecodedLength;
+#[cfg(feature = "stream")]
+use crate::common::sync_wrapper::SyncWrapper;
+use crate::common::watch;
+#[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
+use crate::proto::h2::ping;
+
+type BodySender = mpsc::Sender<Result<Bytes, crate::Error>>;
+type TrailersSender = oneshot::Sender<HeaderMap>;
+
+/// A stream of `Bytes`, used when receiving bodies.
+///
+/// A good default [`HttpBody`](crate::body::HttpBody) to use in many
+/// applications.
+///
+/// Note: To read the full body, use [`body::to_bytes`](crate::body::to_bytes())
+/// or [`body::aggregate`](crate::body::aggregate()).
+#[must_use = "streams do nothing unless polled"]
+pub struct Body {
+    kind: Kind,
+    /// Keep the extra bits in an `Option<Box<Extra>>`, so that
+    /// Body stays small in the common case (no extras needed).
+    extra: Option<Box<Extra>>,
+}
+
+enum Kind {
+    Once(Option<Bytes>),
+    Chan {
+        content_length: DecodedLength,
+        want_tx: watch::Sender,
+        data_rx: mpsc::Receiver<Result<Bytes, crate::Error>>,
+        trailers_rx: oneshot::Receiver<HeaderMap>,
+    },
+    #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
+    H2 {
+        ping: ping::Recorder,
+        content_length: DecodedLength,
+        recv: h2::RecvStream,
+    },
+    #[cfg(feature = "ffi")]
+    Ffi(crate::ffi::UserBody),
+    #[cfg(feature = "stream")]
+    Wrapped(
+        SyncWrapper<
+            Pin<Box<dyn Stream<Item = Result<Bytes, Box<dyn StdError + Send + Sync>>> + Send>>,
+        >,
+    ),
+}
+
+struct Extra {
+    /// Allow the client to pass a future to delay the `Body` from returning
+    /// EOF. This allows the `Client` to try to put the idle connection
+    /// back into the pool before the body is "finished".
+    ///
+    /// The reason for this is so that creating a new request after finishing
+    /// streaming the body of a response could sometimes result in creating
+    /// a brand new connection, since the pool didn't know about the idle
+    /// connection yet.
+    delayed_eof: Option<DelayEof>,
+}
+
+#[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
+type DelayEofUntil = oneshot::Receiver<Infallible>;
+
+enum DelayEof {
+    /// Initial state, stream hasn't seen EOF yet.
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "client")]
+    NotEof(DelayEofUntil),
+    /// Transitions to this state once we've seen `poll` try to
+    /// return EOF (`None`). This future is then polled, and
+    /// when it completes, the Body finally returns EOF (`None`).
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "client")]
+    Eof(DelayEofUntil),
+}
+
+/// A sender half created through [`Body::channel()`].
+///
+/// Useful when wanting to stream chunks from another thread.
+///
+/// ## Body Closing
+///
+/// Note that the request body will always be closed normally when the sender is dropped (meaning
+/// that the empty terminating chunk will be sent to the remote). If you desire to close the
+/// connection with an incomplete response (e.g. in the case of an error during asynchronous
+/// processing), call the [`Sender::abort()`] method to abort the body in an abnormal fashion.
+///
+/// [`Body::channel()`]: struct.Body.html#method.channel
+/// [`Sender::abort()`]: struct.Sender.html#method.abort
+#[must_use = "Sender does nothing unless sent on"]
+pub struct Sender {
+    want_rx: watch::Receiver,
+    data_tx: BodySender,
+    trailers_tx: Option<TrailersSender>,
+}
+
+const WANT_PENDING: usize = 1;
+const WANT_READY: usize = 2;
+
+impl Body {
+    /// Create an empty `Body` stream.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use hyper::{Body, Request};
+    ///
+    /// // create a `GET /` request
+    /// let get = Request::new(Body::empty());
+    /// ```
+    #[inline]
+    pub fn empty() -> Body {
+        Body::new(Kind::Once(None))
+    }
+
+    /// Create a `Body` stream with an associated sender half.
+    ///
+    /// Useful when wanting to stream chunks from another thread.
+    #[inline]
+    pub fn channel() -> (Sender, Body) {
+        Self::new_channel(DecodedLength::CHUNKED, /*wanter =*/ false)
+    }
+
+    pub(crate) fn new_channel(content_length: DecodedLength, wanter: bool) -> (Sender, Body) {
+        let (data_tx, data_rx) = mpsc::channel(0);
+        let (trailers_tx, trailers_rx) = oneshot::channel();
+
+        // If wanter is true, `Sender::poll_ready()` won't becoming ready
+        // until the `Body` has been polled for data once.
+        let want = if wanter { WANT_PENDING } else { WANT_READY };
+
+        let (want_tx, want_rx) = watch::channel(want);
+
+        let tx = Sender {
+            want_rx,
+            data_tx,
+            trailers_tx: Some(trailers_tx),
+        };
+        let rx = Body::new(Kind::Chan {
+            content_length,
+            want_tx,
+            data_rx,
+            trailers_rx,
+        });
+
+        (tx, rx)
+    }
+
+    /// Wrap a futures `Stream` in a box inside `Body`.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use hyper::Body;
+    /// let chunks: Vec<Result<_, std::io::Error>> = vec![
+    ///     Ok("hello"),
+    ///     Ok(" "),
+    ///     Ok("world"),
+    /// ];
+    ///
+    /// let stream = futures_util::stream::iter(chunks);
+    ///
+    /// let body = Body::wrap_stream(stream);
+    /// ```
+    ///
+    /// # Optional
+    ///
+    /// This function requires enabling the `stream` feature in your
+    /// `Cargo.toml`.
+    #[cfg(feature = "stream")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "stream")))]
+    pub fn wrap_stream<S, O, E>(stream: S) -> Body
+    where
+        S: Stream<Item = Result<O, E>> + Send + 'static,
+        O: Into<Bytes> + 'static,
+        E: Into<Box<dyn StdError + Send + Sync>> + 'static,
+    {
+        let mapped = stream.map_ok(Into::into).map_err(Into::into);
+        Body::new(Kind::Wrapped(SyncWrapper::new(Box::pin(mapped))))
+    }
+
+    fn new(kind: Kind) -> Body {
+        Body { kind, extra: None }
+    }
+
+    #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
+    pub(crate) fn h2(
+        recv: h2::RecvStream,
+        mut content_length: DecodedLength,
+        ping: ping::Recorder,
+    ) -> Self {
+        // If the stream is already EOS, then the "unknown length" is clearly
+        // actually ZERO.
+        if !content_length.is_exact() && recv.is_end_stream() {
+            content_length = DecodedLength::ZERO;
+        }
+        let body = Body::new(Kind::H2 {
+            ping,
+            content_length,
+            recv,
+        });
+
+        body
+    }
+
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "client")]
+    pub(crate) fn delayed_eof(&mut self, fut: DelayEofUntil) {
+        self.extra_mut().delayed_eof = Some(DelayEof::NotEof(fut));
+    }
+
+    fn take_delayed_eof(&mut self) -> Option<DelayEof> {
+        self.extra
+            .as_mut()
+            .and_then(|extra| extra.delayed_eof.take())
+    }
+
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    fn extra_mut(&mut self) -> &mut Extra {
+        self.extra
+            .get_or_insert_with(|| Box::new(Extra { delayed_eof: None }))
+    }
+
+    fn poll_eof(&mut self, cx: &mut Context<'_>) -> Poll<Option<crate::Result<Bytes>>> {
+        match self.take_delayed_eof() {
+            #[cfg(any(feature = "http1", feature = "http2"))]
+            #[cfg(feature = "client")]
+            Some(DelayEof::NotEof(mut delay)) => match self.poll_inner(cx) {
+                ok @ Poll::Ready(Some(Ok(..))) | ok @ Poll::Pending => {
+                    self.extra_mut().delayed_eof = Some(DelayEof::NotEof(delay));
+                    ok
+                }
+                Poll::Ready(None) => match Pin::new(&mut delay).poll(cx) {
+                    Poll::Ready(Ok(never)) => match never {},
+                    Poll::Pending => {
+                        self.extra_mut().delayed_eof = Some(DelayEof::Eof(delay));
+                        Poll::Pending
+                    }
+                    Poll::Ready(Err(_done)) => Poll::Ready(None),
+                },
+                Poll::Ready(Some(Err(e))) => Poll::Ready(Some(Err(e))),
+            },
+            #[cfg(any(feature = "http1", feature = "http2"))]
+            #[cfg(feature = "client")]
+            Some(DelayEof::Eof(mut delay)) => match Pin::new(&mut delay).poll(cx) {
+                Poll::Ready(Ok(never)) => match never {},
+                Poll::Pending => {
+                    self.extra_mut().delayed_eof = Some(DelayEof::Eof(delay));
+                    Poll::Pending
+                }
+                Poll::Ready(Err(_done)) => Poll::Ready(None),
+            },
+            #[cfg(any(
+                not(any(feature = "http1", feature = "http2")),
+                not(feature = "client")
+            ))]
+            Some(delay_eof) => match delay_eof {},
+            None => self.poll_inner(cx),
+        }
+    }
+
+    #[cfg(feature = "ffi")]
+    pub(crate) fn as_ffi_mut(&mut self) -> &mut crate::ffi::UserBody {
+        match self.kind {
+            Kind::Ffi(ref mut body) => return body,
+            _ => {
+                self.kind = Kind::Ffi(crate::ffi::UserBody::new());
+            }
+        }
+
+        match self.kind {
+            Kind::Ffi(ref mut body) => body,
+            _ => unreachable!(),
+        }
+    }
+
+    fn poll_inner(&mut self, cx: &mut Context<'_>) -> Poll<Option<crate::Result<Bytes>>> {
+        match self.kind {
+            Kind::Once(ref mut val) => Poll::Ready(val.take().map(Ok)),
+            Kind::Chan {
+                content_length: ref mut len,
+                ref mut data_rx,
+                ref mut want_tx,
+                ..
+            } => {
+                want_tx.send(WANT_READY);
+
+                match ready!(Pin::new(data_rx).poll_next(cx)?) {
+                    Some(chunk) => {
+                        len.sub_if(chunk.len() as u64);
+                        Poll::Ready(Some(Ok(chunk)))
+                    }
+                    None => Poll::Ready(None),
+                }
+            }
+            #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
+            Kind::H2 {
+                ref ping,
+                recv: ref mut h2,
+                content_length: ref mut len,
+            } => match ready!(h2.poll_data(cx)) {
+                Some(Ok(bytes)) => {
+                    let _ = h2.flow_control().release_capacity(bytes.len());
+                    len.sub_if(bytes.len() as u64);
+                    ping.record_data(bytes.len());
+                    Poll::Ready(Some(Ok(bytes)))
+                }
+                Some(Err(e)) => match e.reason() {
+                    // These reasons should cause stop of body reading, but nor fail it.
+                    // The same logic as for `AsyncRead for H2Upgraded` is applied here.
+                    Some(h2::Reason::NO_ERROR) | Some(h2::Reason::CANCEL) => Poll::Ready(None),
+                    _ => Poll::Ready(Some(Err(crate::Error::new_body(e)))),
+                },
+                None => Poll::Ready(None),
+            },
+
+            #[cfg(feature = "ffi")]
+            Kind::Ffi(ref mut body) => body.poll_data(cx),
+
+            #[cfg(feature = "stream")]
+            Kind::Wrapped(ref mut s) => match ready!(s.get_mut().as_mut().poll_next(cx)) {
+                Some(res) => Poll::Ready(Some(res.map_err(crate::Error::new_body))),
+                None => Poll::Ready(None),
+            },
+        }
+    }
+
+    #[cfg(feature = "http1")]
+    pub(super) fn take_full_data(&mut self) -> Option<Bytes> {
+        if let Kind::Once(ref mut chunk) = self.kind {
+            chunk.take()
+        } else {
+            None
+        }
+    }
+}
+
+impl Default for Body {
+    /// Returns `Body::empty()`.
+    #[inline]
+    fn default() -> Body {
+        Body::empty()
+    }
+}
+
+impl HttpBody for Body {
+    type Data = Bytes;
+    type Error = crate::Error;
+
+    fn poll_data(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<Self::Data, Self::Error>>> {
+        self.poll_eof(cx)
+    }
+
+    fn poll_trailers(
+        #[cfg_attr(not(feature = "http2"), allow(unused_mut))] mut self: Pin<&mut Self>,
+        #[cfg_attr(not(feature = "http2"), allow(unused))] cx: &mut Context<'_>,
+    ) -> Poll<Result<Option<HeaderMap>, Self::Error>> {
+        match self.kind {
+            #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
+            Kind::H2 {
+                recv: ref mut h2,
+                ref ping,
+                ..
+            } => match ready!(h2.poll_trailers(cx)) {
+                Ok(t) => {
+                    ping.record_non_data();
+                    Poll::Ready(Ok(t))
+                }
+                Err(e) => Poll::Ready(Err(crate::Error::new_h2(e))),
+            },
+            Kind::Chan {
+                ref mut trailers_rx,
+                ..
+            } => match ready!(Pin::new(trailers_rx).poll(cx)) {
+                Ok(t) => Poll::Ready(Ok(Some(t))),
+                Err(_) => Poll::Ready(Ok(None)),
+            },
+            #[cfg(feature = "ffi")]
+            Kind::Ffi(ref mut body) => body.poll_trailers(cx),
+            _ => Poll::Ready(Ok(None)),
+        }
+    }
+
+    fn is_end_stream(&self) -> bool {
+        match self.kind {
+            Kind::Once(ref val) => val.is_none(),
+            Kind::Chan { content_length, .. } => content_length == DecodedLength::ZERO,
+            #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
+            Kind::H2 { recv: ref h2, .. } => h2.is_end_stream(),
+            #[cfg(feature = "ffi")]
+            Kind::Ffi(..) => false,
+            #[cfg(feature = "stream")]
+            Kind::Wrapped(..) => false,
+        }
+    }
+
+    fn size_hint(&self) -> SizeHint {
+        macro_rules! opt_len {
+            ($content_length:expr) => {{
+                let mut hint = SizeHint::default();
+
+                if let Some(content_length) = $content_length.into_opt() {
+                    hint.set_exact(content_length);
+                }
+
+                hint
+            }};
+        }
+
+        match self.kind {
+            Kind::Once(Some(ref val)) => SizeHint::with_exact(val.len() as u64),
+            Kind::Once(None) => SizeHint::with_exact(0),
+            #[cfg(feature = "stream")]
+            Kind::Wrapped(..) => SizeHint::default(),
+            Kind::Chan { content_length, .. } => opt_len!(content_length),
+            #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
+            Kind::H2 { content_length, .. } => opt_len!(content_length),
+            #[cfg(feature = "ffi")]
+            Kind::Ffi(..) => SizeHint::default(),
+        }
+    }
+}
+
+impl fmt::Debug for Body {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        #[derive(Debug)]
+        struct Streaming;
+        #[derive(Debug)]
+        struct Empty;
+        #[derive(Debug)]
+        struct Full<'a>(&'a Bytes);
+
+        let mut builder = f.debug_tuple("Body");
+        match self.kind {
+            Kind::Once(None) => builder.field(&Empty),
+            Kind::Once(Some(ref chunk)) => builder.field(&Full(chunk)),
+            _ => builder.field(&Streaming),
+        };
+
+        builder.finish()
+    }
+}
+
+/// # Optional
+///
+/// This function requires enabling the `stream` feature in your
+/// `Cargo.toml`.
+#[cfg(feature = "stream")]
+impl Stream for Body {
+    type Item = crate::Result<Bytes>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        HttpBody::poll_data(self, cx)
+    }
+}
+
+/// # Optional
+///
+/// This function requires enabling the `stream` feature in your
+/// `Cargo.toml`.
+#[cfg(feature = "stream")]
+impl From<Box<dyn Stream<Item = Result<Bytes, Box<dyn StdError + Send + Sync>>> + Send>> for Body {
+    #[inline]
+    fn from(
+        stream: Box<dyn Stream<Item = Result<Bytes, Box<dyn StdError + Send + Sync>>> + Send>,
+    ) -> Body {
+        Body::new(Kind::Wrapped(SyncWrapper::new(stream.into())))
+    }
+}
+
+impl From<Bytes> for Body {
+    #[inline]
+    fn from(chunk: Bytes) -> Body {
+        if chunk.is_empty() {
+            Body::empty()
+        } else {
+            Body::new(Kind::Once(Some(chunk)))
+        }
+    }
+}
+
+impl From<Vec<u8>> for Body {
+    #[inline]
+    fn from(vec: Vec<u8>) -> Body {
+        Body::from(Bytes::from(vec))
+    }
+}
+
+impl From<&'static [u8]> for Body {
+    #[inline]
+    fn from(slice: &'static [u8]) -> Body {
+        Body::from(Bytes::from(slice))
+    }
+}
+
+impl From<Cow<'static, [u8]>> for Body {
+    #[inline]
+    fn from(cow: Cow<'static, [u8]>) -> Body {
+        match cow {
+            Cow::Borrowed(b) => Body::from(b),
+            Cow::Owned(o) => Body::from(o),
+        }
+    }
+}
+
+impl From<String> for Body {
+    #[inline]
+    fn from(s: String) -> Body {
+        Body::from(Bytes::from(s.into_bytes()))
+    }
+}
+
+impl From<&'static str> for Body {
+    #[inline]
+    fn from(slice: &'static str) -> Body {
+        Body::from(Bytes::from(slice.as_bytes()))
+    }
+}
+
+impl From<Cow<'static, str>> for Body {
+    #[inline]
+    fn from(cow: Cow<'static, str>) -> Body {
+        match cow {
+            Cow::Borrowed(b) => Body::from(b),
+            Cow::Owned(o) => Body::from(o),
+        }
+    }
+}
+
+impl Sender {
+    /// Check to see if this `Sender` can send more data.
+    pub fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        // Check if the receiver end has tried polling for the body yet
+        ready!(self.poll_want(cx)?);
+        self.data_tx
+            .poll_ready(cx)
+            .map_err(|_| crate::Error::new_closed())
+    }
+
+    fn poll_want(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        match self.want_rx.load(cx) {
+            WANT_READY => Poll::Ready(Ok(())),
+            WANT_PENDING => Poll::Pending,
+            watch::CLOSED => Poll::Ready(Err(crate::Error::new_closed())),
+            unexpected => unreachable!("want_rx value: {}", unexpected),
+        }
+    }
+
+    async fn ready(&mut self) -> crate::Result<()> {
+        futures_util::future::poll_fn(|cx| self.poll_ready(cx)).await
+    }
+
+    /// Send data on data channel when it is ready.
+    pub async fn send_data(&mut self, chunk: Bytes) -> crate::Result<()> {
+        self.ready().await?;
+        self.data_tx
+            .try_send(Ok(chunk))
+            .map_err(|_| crate::Error::new_closed())
+    }
+
+    /// Send trailers on trailers channel.
+    pub async fn send_trailers(&mut self, trailers: HeaderMap) -> crate::Result<()> {
+        let tx = match self.trailers_tx.take() {
+            Some(tx) => tx,
+            None => return Err(crate::Error::new_closed()),
+        };
+        tx.send(trailers).map_err(|_| crate::Error::new_closed())
+    }
+
+    /// Try to send data on this channel.
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err(Bytes)` if the channel could not (currently) accept
+    /// another `Bytes`.
+    ///
+    /// # Note
+    ///
+    /// This is mostly useful for when trying to send from some other thread
+    /// that doesn't have an async context. If in an async context, prefer
+    /// `send_data()` instead.
+    pub fn try_send_data(&mut self, chunk: Bytes) -> Result<(), Bytes> {
+        self.data_tx
+            .try_send(Ok(chunk))
+            .map_err(|err| err.into_inner().expect("just sent Ok"))
+    }
+
+    /// Aborts the body in an abnormal fashion.
+    pub fn abort(mut self) {
+        self.send_error(crate::Error::new_body_write_aborted());
+    }
+
+    pub(crate) fn send_error(&mut self, err: crate::Error) {
+        let _ = self
+            .data_tx
+            // clone so the send works even if buffer is full
+            .clone()
+            .try_send(Err(err));
+    }
+}
+
+impl fmt::Debug for Sender {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        #[derive(Debug)]
+        struct Open;
+        #[derive(Debug)]
+        struct Closed;
+
+        let mut builder = f.debug_tuple("Sender");
+        match self.want_rx.peek() {
+            watch::CLOSED => builder.field(&Closed),
+            _ => builder.field(&Open),
+        };
+
+        builder.finish()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::mem;
+    use std::task::Poll;
+
+    use super::{Body, DecodedLength, HttpBody, Sender, SizeHint};
+
+    #[test]
+    fn test_size_of() {
+        // These are mostly to help catch *accidentally* increasing
+        // the size by too much.
+
+        let body_size = mem::size_of::<Body>();
+        let body_expected_size = mem::size_of::<u64>() * 6;
+        assert!(
+            body_size <= body_expected_size,
+            "Body size = {} <= {}",
+            body_size,
+            body_expected_size,
+        );
+
+        assert_eq!(body_size, mem::size_of::<Option<Body>>(), "Option<Body>");
+
+        assert_eq!(
+            mem::size_of::<Sender>(),
+            mem::size_of::<usize>() * 5,
+            "Sender"
+        );
+
+        assert_eq!(
+            mem::size_of::<Sender>(),
+            mem::size_of::<Option<Sender>>(),
+            "Option<Sender>"
+        );
+    }
+
+    #[test]
+    fn size_hint() {
+        fn eq(body: Body, b: SizeHint, note: &str) {
+            let a = body.size_hint();
+            assert_eq!(a.lower(), b.lower(), "lower for {:?}", note);
+            assert_eq!(a.upper(), b.upper(), "upper for {:?}", note);
+        }
+
+        eq(Body::from("Hello"), SizeHint::with_exact(5), "from str");
+
+        eq(Body::empty(), SizeHint::with_exact(0), "empty");
+
+        eq(Body::channel().1, SizeHint::new(), "channel");
+
+        eq(
+            Body::new_channel(DecodedLength::new(4), /*wanter =*/ false).1,
+            SizeHint::with_exact(4),
+            "channel with length",
+        );
+    }
+
+    #[tokio::test]
+    async fn channel_abort() {
+        let (tx, mut rx) = Body::channel();
+
+        tx.abort();
+
+        let err = rx.data().await.unwrap().unwrap_err();
+        assert!(err.is_body_write_aborted(), "{:?}", err);
+    }
+
+    #[tokio::test]
+    async fn channel_abort_when_buffer_is_full() {
+        let (mut tx, mut rx) = Body::channel();
+
+        tx.try_send_data("chunk 1".into()).expect("send 1");
+        // buffer is full, but can still send abort
+        tx.abort();
+
+        let chunk1 = rx.data().await.expect("item 1").expect("chunk 1");
+        assert_eq!(chunk1, "chunk 1");
+
+        let err = rx.data().await.unwrap().unwrap_err();
+        assert!(err.is_body_write_aborted(), "{:?}", err);
+    }
+
+    #[test]
+    fn channel_buffers_one() {
+        let (mut tx, _rx) = Body::channel();
+
+        tx.try_send_data("chunk 1".into()).expect("send 1");
+
+        // buffer is now full
+        let chunk2 = tx.try_send_data("chunk 2".into()).expect_err("send 2");
+        assert_eq!(chunk2, "chunk 2");
+    }
+
+    #[tokio::test]
+    async fn channel_empty() {
+        let (_, mut rx) = Body::channel();
+
+        assert!(rx.data().await.is_none());
+    }
+
+    #[test]
+    fn channel_ready() {
+        let (mut tx, _rx) = Body::new_channel(DecodedLength::CHUNKED, /*wanter = */ false);
+
+        let mut tx_ready = tokio_test::task::spawn(tx.ready());
+
+        assert!(tx_ready.poll().is_ready(), "tx is ready immediately");
+    }
+
+    #[test]
+    fn channel_wanter() {
+        let (mut tx, mut rx) = Body::new_channel(DecodedLength::CHUNKED, /*wanter = */ true);
+
+        let mut tx_ready = tokio_test::task::spawn(tx.ready());
+        let mut rx_data = tokio_test::task::spawn(rx.data());
+
+        assert!(
+            tx_ready.poll().is_pending(),
+            "tx isn't ready before rx has been polled"
+        );
+
+        assert!(rx_data.poll().is_pending(), "poll rx.data");
+        assert!(tx_ready.is_woken(), "rx poll wakes tx");
+
+        assert!(
+            tx_ready.poll().is_ready(),
+            "tx is ready after rx has been polled"
+        );
+    }
+
+    #[test]
+    fn channel_notices_closure() {
+        let (mut tx, rx) = Body::new_channel(DecodedLength::CHUNKED, /*wanter = */ true);
+
+        let mut tx_ready = tokio_test::task::spawn(tx.ready());
+
+        assert!(
+            tx_ready.poll().is_pending(),
+            "tx isn't ready before rx has been polled"
+        );
+
+        drop(rx);
+        assert!(tx_ready.is_woken(), "dropping rx wakes tx");
+
+        match tx_ready.poll() {
+            Poll::Ready(Err(ref e)) if e.is_closed() => (),
+            unexpected => panic!("tx poll ready unexpected: {:?}", unexpected),
+        }
+    }
+}
diff --git a/src/body/length.rs b/src/body/length.rs
new file mode 100644
index 0000000..e2bbee8
--- /dev/null
+++ b/src/body/length.rs
@@ -0,0 +1,123 @@
+use std::fmt;
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub(crate) struct DecodedLength(u64);
+
+#[cfg(any(feature = "http1", feature = "http2"))]
+impl From<Option<u64>> for DecodedLength {
+    fn from(len: Option<u64>) -> Self {
+        len.and_then(|len| {
+            // If the length is u64::MAX, oh well, just reported chunked.
+            Self::checked_new(len).ok()
+        })
+        .unwrap_or(DecodedLength::CHUNKED)
+    }
+}
+
+#[cfg(any(feature = "http1", feature = "http2", test))]
+const MAX_LEN: u64 = std::u64::MAX - 2;
+
+impl DecodedLength {
+    pub(crate) const CLOSE_DELIMITED: DecodedLength = DecodedLength(::std::u64::MAX);
+    pub(crate) const CHUNKED: DecodedLength = DecodedLength(::std::u64::MAX - 1);
+    pub(crate) const ZERO: DecodedLength = DecodedLength(0);
+
+    #[cfg(test)]
+    pub(crate) fn new(len: u64) -> Self {
+        debug_assert!(len <= MAX_LEN);
+        DecodedLength(len)
+    }
+
+    /// Takes the length as a content-length without other checks.
+    ///
+    /// Should only be called if previously confirmed this isn't
+    /// CLOSE_DELIMITED or CHUNKED.
+    #[inline]
+    #[cfg(feature = "http1")]
+    pub(crate) fn danger_len(self) -> u64 {
+        debug_assert!(self.0 < Self::CHUNKED.0);
+        self.0
+    }
+
+    /// Converts to an Option<u64> representing a Known or Unknown length.
+    pub(crate) fn into_opt(self) -> Option<u64> {
+        match self {
+            DecodedLength::CHUNKED | DecodedLength::CLOSE_DELIMITED => None,
+            DecodedLength(known) => Some(known),
+        }
+    }
+
+    /// Checks the `u64` is within the maximum allowed for content-length.
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    pub(crate) fn checked_new(len: u64) -> Result<Self, crate::error::Parse> {
+        use tracing::warn;
+
+        if len <= MAX_LEN {
+            Ok(DecodedLength(len))
+        } else {
+            warn!("content-length bigger than maximum: {} > {}", len, MAX_LEN);
+            Err(crate::error::Parse::TooLarge)
+        }
+    }
+
+    pub(crate) fn sub_if(&mut self, amt: u64) {
+        match *self {
+            DecodedLength::CHUNKED | DecodedLength::CLOSE_DELIMITED => (),
+            DecodedLength(ref mut known) => {
+                *known -= amt;
+            }
+        }
+    }
+
+    /// Returns whether this represents an exact length.
+    ///
+    /// This includes 0, which of course is an exact known length.
+    ///
+    /// It would return false if "chunked" or otherwise size-unknown.
+    #[cfg(feature = "http2")]
+    pub(crate) fn is_exact(&self) -> bool {
+        self.0 <= MAX_LEN
+    }
+}
+
+impl fmt::Debug for DecodedLength {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            DecodedLength::CLOSE_DELIMITED => f.write_str("CLOSE_DELIMITED"),
+            DecodedLength::CHUNKED => f.write_str("CHUNKED"),
+            DecodedLength(n) => f.debug_tuple("DecodedLength").field(&n).finish(),
+        }
+    }
+}
+
+impl fmt::Display for DecodedLength {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            DecodedLength::CLOSE_DELIMITED => f.write_str("close-delimited"),
+            DecodedLength::CHUNKED => f.write_str("chunked encoding"),
+            DecodedLength::ZERO => f.write_str("empty"),
+            DecodedLength(n) => write!(f, "content-length ({} bytes)", n),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn sub_if_known() {
+        let mut len = DecodedLength::new(30);
+        len.sub_if(20);
+
+        assert_eq!(len.0, 10);
+    }
+
+    #[test]
+    fn sub_if_chunked() {
+        let mut len = DecodedLength::CHUNKED;
+        len.sub_if(20);
+
+        assert_eq!(len, DecodedLength::CHUNKED);
+    }
+}
diff --git a/src/body/mod.rs b/src/body/mod.rs
new file mode 100644
index 0000000..109b1e6
--- /dev/null
+++ b/src/body/mod.rs
@@ -0,0 +1,67 @@
+//! Streaming bodies for Requests and Responses
+//!
+//! For both [Clients](crate::client) and [Servers](crate::server), requests and
+//! responses use streaming bodies, instead of complete buffering. This
+//! allows applications to not use memory they don't need, and allows exerting
+//! back-pressure on connections by only reading when asked.
+//!
+//! There are two pieces to this in hyper:
+//!
+//! - **The [`HttpBody`](HttpBody) trait** describes all possible bodies.
+//!   hyper allows any body type that implements `HttpBody`, allowing
+//!   applications to have fine-grained control over their streaming.
+//! - **The [`Body`](Body) concrete type**, which is an implementation of
+//!   `HttpBody`, and returned by hyper as a "receive stream" (so, for server
+//!   requests and client responses). It is also a decent default implementation
+//!   if you don't have very custom needs of your send streams.
+
+pub use bytes::{Buf, Bytes};
+pub use http_body::Body as HttpBody;
+pub use http_body::SizeHint;
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+pub use self::aggregate::aggregate;
+pub use self::body::{Body, Sender};
+pub(crate) use self::length::DecodedLength;
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+pub use self::to_bytes::to_bytes;
+
+mod aggregate;
+mod body;
+mod length;
+mod to_bytes;
+
+/// An optimization to try to take a full body if immediately available.
+///
+/// This is currently limited to *only* `hyper::Body`s.
+#[cfg(feature = "http1")]
+pub(crate) fn take_full_data<T: HttpBody + 'static>(body: &mut T) -> Option<T::Data> {
+    use std::any::{Any, TypeId};
+
+    // This static type check can be optimized at compile-time.
+    if TypeId::of::<T>() == TypeId::of::<Body>() {
+        let mut full = (body as &mut dyn Any)
+            .downcast_mut::<Body>()
+            .expect("must be Body")
+            .take_full_data();
+        // This second cast is required to make the type system happy.
+        // Without it, the compiler cannot reason that the type is actually
+        // `T::Data`. Oh wells.
+        //
+        // It's still a measurable win!
+        (&mut full as &mut dyn Any)
+            .downcast_mut::<Option<T::Data>>()
+            .expect("must be T::Data")
+            .take()
+    } else {
+        None
+    }
+}
+
+fn _assert_send_sync() {
+    fn _assert_send<T: Send>() {}
+    fn _assert_sync<T: Sync>() {}
+
+    _assert_send::<Body>();
+    _assert_sync::<Body>();
+}
diff --git a/src/body/to_bytes.rs b/src/body/to_bytes.rs
new file mode 100644
index 0000000..2e398d2
--- /dev/null
+++ b/src/body/to_bytes.rs
@@ -0,0 +1,89 @@
+use bytes::{Buf, BufMut, Bytes};
+
+use super::HttpBody;
+
+/// Concatenate the buffers from a body into a single `Bytes` asynchronously.
+///
+/// This may require copying the data into a single buffer. If you don't need
+/// a contiguous buffer, prefer the [`aggregate`](crate::body::aggregate())
+/// function.
+///
+/// # Note
+///
+/// Care needs to be taken if the remote is untrusted. The function doesn't implement any length
+/// checks and an malicious peer might make it consume arbitrary amounts of memory. Checking the
+/// `Content-Length` is a possibility, but it is not strictly mandated to be present.
+///
+/// # Example
+///
+/// ```
+/// # #[cfg(all(feature = "client", feature = "tcp", any(feature = "http1", feature = "http2")))]
+/// # async fn doc() -> hyper::Result<()> {
+/// use hyper::{body::HttpBody};
+///
+/// # let request = hyper::Request::builder()
+/// #        .method(hyper::Method::POST)
+/// #        .uri("http://httpbin.org/post")
+/// #        .header("content-type", "application/json")
+/// #        .body(hyper::Body::from(r#"{"library":"hyper"}"#)).unwrap();
+/// # let client = hyper::Client::new();
+/// let response = client.request(request).await?;
+///
+/// const MAX_ALLOWED_RESPONSE_SIZE: u64 = 1024;
+///
+/// let response_content_length = match response.body().size_hint().upper() {
+///     Some(v) => v,
+///     None => MAX_ALLOWED_RESPONSE_SIZE + 1 // Just to protect ourselves from a malicious response
+/// };
+///
+/// if response_content_length < MAX_ALLOWED_RESPONSE_SIZE {
+///     let body_bytes = hyper::body::to_bytes(response.into_body()).await?;
+///     println!("body: {:?}", body_bytes);
+/// }
+///
+/// # Ok(())
+/// # }
+/// ```
+#[cfg_attr(
+    feature = "deprecated",
+    deprecated(
+        note = "This function has been replaced by a method on the `hyper::body::HttpBody` trait. Use `.collect().await?.to_bytes()` instead."
+    )
+)]
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+pub async fn to_bytes<T>(body: T) -> Result<Bytes, T::Error>
+where
+    T: HttpBody,
+{
+    futures_util::pin_mut!(body);
+
+    // If there's only 1 chunk, we can just return Buf::to_bytes()
+    let mut first = if let Some(buf) = body.data().await {
+        buf?
+    } else {
+        return Ok(Bytes::new());
+    };
+
+    let second = if let Some(buf) = body.data().await {
+        buf?
+    } else {
+        return Ok(first.copy_to_bytes(first.remaining()));
+    };
+
+    // Don't pre-emptively reserve *too* much.
+    let rest = (body.size_hint().lower() as usize).min(1024 * 16);
+    let cap = first
+        .remaining()
+        .saturating_add(second.remaining())
+        .saturating_add(rest);
+    // With more than 1 buf, we gotta flatten into a Vec first.
+    let mut vec = Vec::with_capacity(cap);
+    vec.put(first);
+    vec.put(second);
+
+    while let Some(buf) = body.data().await {
+        vec.put(buf?);
+    }
+
+    Ok(vec.into())
+}
diff --git a/src/cfg.rs b/src/cfg.rs
new file mode 100644
index 0000000..71a5351
--- /dev/null
+++ b/src/cfg.rs
@@ -0,0 +1,44 @@
+macro_rules! cfg_feature {
+    (
+        #![$meta:meta]
+        $($item:item)*
+    ) => {
+        $(
+            #[cfg($meta)]
+            #[cfg_attr(docsrs, doc(cfg($meta)))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_proto {
+    ($($item:item)*) => {
+        cfg_feature! {
+            #![all(
+                any(feature = "http1", feature = "http2"),
+                any(feature = "client", feature = "server"),
+            )]
+            $($item)*
+        }
+    }
+}
+
+cfg_proto! {
+    macro_rules! cfg_client {
+        ($($item:item)*) => {
+            cfg_feature! {
+                #![feature = "client"]
+                $($item)*
+            }
+        }
+    }
+
+    macro_rules! cfg_server {
+        ($($item:item)*) => {
+            cfg_feature! {
+                #![feature = "server"]
+                $($item)*
+            }
+        }
+    }
+}
diff --git a/src/client/client.rs b/src/client/client.rs
new file mode 100644
index 0000000..8195554
--- /dev/null
+++ b/src/client/client.rs
@@ -0,0 +1,1525 @@
+use std::error::Error as StdError;
+use std::fmt;
+use std::future::Future;
+use std::marker::Unpin;
+use std::mem;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::time::Duration;
+
+use futures_channel::oneshot;
+use futures_util::future::{self, Either, FutureExt as _, TryFutureExt as _};
+use http::header::{HeaderValue, HOST};
+use http::uri::{Port, Scheme};
+use http::{Method, Request, Response, Uri, Version};
+use tracing::{debug, trace, warn};
+
+use crate::body::{Body, HttpBody};
+use crate::client::connect::CaptureConnectionExtension;
+use crate::common::{exec::BoxSendFuture, lazy as hyper_lazy, sync_wrapper::SyncWrapper, Lazy};
+#[cfg(feature = "http2")]
+use crate::ext::Protocol;
+use crate::rt::Executor;
+
+use super::conn;
+use super::connect::{self, sealed::Connect, Alpn, Connected, Connection};
+use super::pool::{
+    self, CheckoutIsClosedError, Key as PoolKey, Pool, Poolable, Pooled, Reservation,
+};
+#[cfg(feature = "tcp")]
+use super::HttpConnector;
+
+/// A Client to make outgoing HTTP requests.
+///
+/// `Client` is cheap to clone and cloning is the recommended way to share a `Client`. The
+/// underlying connection pool will be reused.
+#[cfg_attr(docsrs, doc(cfg(any(feature = "http1", feature = "http2"))))]
+pub struct Client<C, B = Body> {
+    config: Config,
+    #[cfg_attr(feature = "deprecated", allow(deprecated))]
+    conn_builder: conn::Builder,
+    connector: C,
+    pool: Pool<PoolClient<B>>,
+}
+
+#[derive(Clone, Copy, Debug)]
+struct Config {
+    retry_canceled_requests: bool,
+    set_host: bool,
+    ver: Ver,
+}
+
+/// A `Future` that will resolve to an HTTP Response.
+///
+/// This is returned by `Client::request` (and `Client::get`).
+#[must_use = "futures do nothing unless polled"]
+pub struct ResponseFuture {
+    inner: SyncWrapper<Pin<Box<dyn Future<Output = crate::Result<Response<Body>>> + Send>>>,
+}
+
+// ===== impl Client =====
+
+#[cfg(feature = "tcp")]
+impl Client<HttpConnector, Body> {
+    /// Create a new Client with the default [config](Builder).
+    ///
+    /// # Note
+    ///
+    /// The default connector does **not** handle TLS. Speaking to `https`
+    /// destinations will require [configuring a connector that implements
+    /// TLS](https://hyper.rs/guides/client/configuration).
+    #[cfg_attr(docsrs, doc(cfg(feature = "tcp")))]
+    #[inline]
+    pub fn new() -> Client<HttpConnector, Body> {
+        Builder::default().build_http()
+    }
+}
+
+#[cfg(feature = "tcp")]
+impl Default for Client<HttpConnector, Body> {
+    fn default() -> Client<HttpConnector, Body> {
+        Client::new()
+    }
+}
+
+impl Client<(), Body> {
+    /// Create a builder to configure a new `Client`.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # #[cfg(feature  = "runtime")]
+    /// # fn run () {
+    /// use std::time::Duration;
+    /// use hyper::Client;
+    ///
+    /// let client = Client::builder()
+    ///     .pool_idle_timeout(Duration::from_secs(30))
+    ///     .http2_only(true)
+    ///     .build_http();
+    /// # let infer: Client<_, hyper::Body> = client;
+    /// # drop(infer);
+    /// # }
+    /// # fn main() {}
+    /// ```
+    #[inline]
+    pub fn builder() -> Builder {
+        Builder::default()
+    }
+}
+
+impl<C, B> Client<C, B>
+where
+    C: Connect + Clone + Send + Sync + 'static,
+    B: HttpBody + Send + 'static,
+    B::Data: Send,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    /// Send a `GET` request to the supplied `Uri`.
+    ///
+    /// # Note
+    ///
+    /// This requires that the `HttpBody` type have a `Default` implementation.
+    /// It *should* return an "empty" version of itself, such that
+    /// `HttpBody::is_end_stream` is `true`.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # #[cfg(feature  = "runtime")]
+    /// # fn run () {
+    /// use hyper::{Client, Uri};
+    ///
+    /// let client = Client::new();
+    ///
+    /// let future = client.get(Uri::from_static("http://httpbin.org/ip"));
+    /// # }
+    /// # fn main() {}
+    /// ```
+    pub fn get(&self, uri: Uri) -> ResponseFuture
+    where
+        B: Default,
+    {
+        let body = B::default();
+        if !body.is_end_stream() {
+            warn!("default HttpBody used for get() does not return true for is_end_stream");
+        }
+
+        let mut req = Request::new(body);
+        *req.uri_mut() = uri;
+        self.request(req)
+    }
+
+    /// Send a constructed `Request` using this `Client`.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # #[cfg(feature  = "runtime")]
+    /// # fn run () {
+    /// use hyper::{Body, Method, Client, Request};
+    ///
+    /// let client = Client::new();
+    ///
+    /// let req = Request::builder()
+    ///     .method(Method::POST)
+    ///     .uri("http://httpbin.org/post")
+    ///     .body(Body::from("Hallo!"))
+    ///     .expect("request builder");
+    ///
+    /// let future = client.request(req);
+    /// # }
+    /// # fn main() {}
+    /// ```
+    pub fn request(&self, mut req: Request<B>) -> ResponseFuture {
+        let is_http_connect = req.method() == Method::CONNECT;
+        match req.version() {
+            Version::HTTP_11 => (),
+            Version::HTTP_10 => {
+                if is_http_connect {
+                    warn!("CONNECT is not allowed for HTTP/1.0");
+                    return ResponseFuture::new(future::err(
+                        crate::Error::new_user_unsupported_request_method(),
+                    ));
+                }
+            }
+            Version::HTTP_2 => (),
+            // completely unsupported HTTP version (like HTTP/0.9)!
+            other => return ResponseFuture::error_version(other),
+        };
+
+        let pool_key = match extract_domain(req.uri_mut(), is_http_connect) {
+            Ok(s) => s,
+            Err(err) => {
+                return ResponseFuture::new(future::err(err));
+            }
+        };
+
+        ResponseFuture::new(self.clone().retryably_send_request(req, pool_key))
+    }
+
+    async fn retryably_send_request(
+        self,
+        mut req: Request<B>,
+        pool_key: PoolKey,
+    ) -> crate::Result<Response<Body>> {
+        let uri = req.uri().clone();
+
+        loop {
+            req = match self.send_request(req, pool_key.clone()).await {
+                Ok(resp) => return Ok(resp),
+                Err(ClientError::Normal(err)) => return Err(err),
+                Err(ClientError::Canceled {
+                    connection_reused,
+                    mut req,
+                    reason,
+                }) => {
+                    if !self.config.retry_canceled_requests || !connection_reused {
+                        // if client disabled, don't retry
+                        // a fresh connection means we definitely can't retry
+                        return Err(reason);
+                    }
+
+                    trace!(
+                        "unstarted request canceled, trying again (reason={:?})",
+                        reason
+                    );
+                    *req.uri_mut() = uri.clone();
+                    req
+                }
+            }
+        }
+    }
+
+    async fn send_request(
+        &self,
+        mut req: Request<B>,
+        pool_key: PoolKey,
+    ) -> Result<Response<Body>, ClientError<B>> {
+        let mut pooled = match self.connection_for(pool_key).await {
+            Ok(pooled) => pooled,
+            Err(ClientConnectError::Normal(err)) => return Err(ClientError::Normal(err)),
+            Err(ClientConnectError::H2CheckoutIsClosed(reason)) => {
+                return Err(ClientError::Canceled {
+                    connection_reused: true,
+                    req,
+                    reason,
+                })
+            }
+        };
+        req.extensions_mut()
+            .get_mut::<CaptureConnectionExtension>()
+            .map(|conn| conn.set(&pooled.conn_info));
+        if pooled.is_http1() {
+            if req.version() == Version::HTTP_2 {
+                warn!("Connection is HTTP/1, but request requires HTTP/2");
+                return Err(ClientError::Normal(
+                    crate::Error::new_user_unsupported_version()
+                        .with_client_connect_info(pooled.conn_info.clone()),
+                ));
+            }
+
+            if self.config.set_host {
+                let uri = req.uri().clone();
+                req.headers_mut().entry(HOST).or_insert_with(|| {
+                    let hostname = uri.host().expect("authority implies host");
+                    if let Some(port) = get_non_default_port(&uri) {
+                        let s = format!("{}:{}", hostname, port);
+                        HeaderValue::from_str(&s)
+                    } else {
+                        HeaderValue::from_str(hostname)
+                    }
+                    .expect("uri host is valid header value")
+                });
+            }
+
+            // CONNECT always sends authority-form, so check it first...
+            if req.method() == Method::CONNECT {
+                authority_form(req.uri_mut());
+            } else if pooled.conn_info.is_proxied {
+                absolute_form(req.uri_mut());
+            } else {
+                origin_form(req.uri_mut());
+            }
+        } else if req.method() == Method::CONNECT {
+            #[cfg(not(feature = "http2"))]
+            authority_form(req.uri_mut());
+
+            #[cfg(feature = "http2")]
+            if req.extensions().get::<Protocol>().is_none() {
+                authority_form(req.uri_mut());
+            }
+        }
+
+        let mut res = match pooled.send_request_retryable(req).await {
+            Err((err, orig_req)) => {
+                return Err(ClientError::map_with_reused(pooled.is_reused())((
+                    err.with_client_connect_info(pooled.conn_info.clone()),
+                    orig_req,
+                )));
+            }
+            Ok(res) => res,
+        };
+
+        // If the Connector included 'extra' info, add to Response...
+        if let Some(extra) = &pooled.conn_info.extra {
+            extra.set(res.extensions_mut());
+        }
+
+        // As of futures@0.1.21, there is a race condition in the mpsc
+        // channel, such that sending when the receiver is closing can
+        // result in the message being stuck inside the queue. It won't
+        // ever notify until the Sender side is dropped.
+        //
+        // To counteract this, we must check if our senders 'want' channel
+        // has been closed after having tried to send. If so, error out...
+        if pooled.is_closed() {
+            return Ok(res);
+        }
+
+        // If pooled is HTTP/2, we can toss this reference immediately.
+        //
+        // when pooled is dropped, it will try to insert back into the
+        // pool. To delay that, spawn a future that completes once the
+        // sender is ready again.
+        //
+        // This *should* only be once the related `Connection` has polled
+        // for a new request to start.
+        //
+        // It won't be ready if there is a body to stream.
+        if pooled.is_http2() || !pooled.is_pool_enabled() || pooled.is_ready() {
+            drop(pooled);
+        } else if !res.body().is_end_stream() {
+            let (delayed_tx, delayed_rx) = oneshot::channel();
+            res.body_mut().delayed_eof(delayed_rx);
+            let on_idle = future::poll_fn(move |cx| pooled.poll_ready(cx)).map(move |_| {
+                // At this point, `pooled` is dropped, and had a chance
+                // to insert into the pool (if conn was idle)
+                drop(delayed_tx);
+            });
+
+            #[cfg_attr(feature = "deprecated", allow(deprecated))]
+            self.conn_builder.exec.execute(on_idle);
+        } else {
+            // There's no body to delay, but the connection isn't
+            // ready yet. Only re-insert when it's ready
+            let on_idle = future::poll_fn(move |cx| pooled.poll_ready(cx)).map(|_| ());
+
+            #[cfg_attr(feature = "deprecated", allow(deprecated))]
+            self.conn_builder.exec.execute(on_idle);
+        }
+
+        Ok(res)
+    }
+
+    async fn connection_for(
+        &self,
+        pool_key: PoolKey,
+    ) -> Result<Pooled<PoolClient<B>>, ClientConnectError> {
+        // This actually races 2 different futures to try to get a ready
+        // connection the fastest, and to reduce connection churn.
+        //
+        // - If the pool has an idle connection waiting, that's used
+        //   immediately.
+        // - Otherwise, the Connector is asked to start connecting to
+        //   the destination Uri.
+        // - Meanwhile, the pool Checkout is watching to see if any other
+        //   request finishes and tries to insert an idle connection.
+        // - If a new connection is started, but the Checkout wins after
+        //   (an idle connection became available first), the started
+        //   connection future is spawned into the runtime to complete,
+        //   and then be inserted into the pool as an idle connection.
+        let checkout = self.pool.checkout(pool_key.clone());
+        let connect = self.connect_to(pool_key);
+        let is_ver_h2 = self.config.ver == Ver::Http2;
+
+        // The order of the `select` is depended on below...
+
+        match future::select(checkout, connect).await {
+            // Checkout won, connect future may have been started or not.
+            //
+            // If it has, let it finish and insert back into the pool,
+            // so as to not waste the socket...
+            Either::Left((Ok(checked_out), connecting)) => {
+                // This depends on the `select` above having the correct
+                // order, such that if the checkout future were ready
+                // immediately, the connect future will never have been
+                // started.
+                //
+                // If it *wasn't* ready yet, then the connect future will
+                // have been started...
+                if connecting.started() {
+                    let bg = connecting
+                        .map_err(|err| {
+                            trace!("background connect error: {}", err);
+                        })
+                        .map(|_pooled| {
+                            // dropping here should just place it in
+                            // the Pool for us...
+                        });
+                    // An execute error here isn't important, we're just trying
+                    // to prevent a waste of a socket...
+                    #[cfg_attr(feature = "deprecated", allow(deprecated))]
+                    self.conn_builder.exec.execute(bg);
+                }
+                Ok(checked_out)
+            }
+            // Connect won, checkout can just be dropped.
+            Either::Right((Ok(connected), _checkout)) => Ok(connected),
+            // Either checkout or connect could get canceled:
+            //
+            // 1. Connect is canceled if this is HTTP/2 and there is
+            //    an outstanding HTTP/2 connecting task.
+            // 2. Checkout is canceled if the pool cannot deliver an
+            //    idle connection reliably.
+            //
+            // In both cases, we should just wait for the other future.
+            Either::Left((Err(err), connecting)) => {
+                if err.is_canceled() {
+                    connecting.await.map_err(ClientConnectError::Normal)
+                } else {
+                    Err(ClientConnectError::Normal(err))
+                }
+            }
+            Either::Right((Err(err), checkout)) => {
+                if err.is_canceled() {
+                    checkout.await.map_err(move |err| {
+                        if is_ver_h2
+                            && err.is_canceled()
+                            && err.find_source::<CheckoutIsClosedError>().is_some()
+                        {
+                            ClientConnectError::H2CheckoutIsClosed(err)
+                        } else {
+                            ClientConnectError::Normal(err)
+                        }
+                    })
+                } else {
+                    Err(ClientConnectError::Normal(err))
+                }
+            }
+        }
+    }
+
+    fn connect_to(
+        &self,
+        pool_key: PoolKey,
+    ) -> impl Lazy<Output = crate::Result<Pooled<PoolClient<B>>>> + Unpin {
+        #[cfg_attr(feature = "deprecated", allow(deprecated))]
+        let executor = self.conn_builder.exec.clone();
+        let pool = self.pool.clone();
+        #[cfg(not(feature = "http2"))]
+        let conn_builder = self.conn_builder.clone();
+        #[cfg(feature = "http2")]
+        let mut conn_builder = self.conn_builder.clone();
+        let ver = self.config.ver;
+        let is_ver_h2 = ver == Ver::Http2;
+        let connector = self.connector.clone();
+        let dst = domain_as_uri(pool_key.clone());
+        hyper_lazy(move || {
+            // Try to take a "connecting lock".
+            //
+            // If the pool_key is for HTTP/2, and there is already a
+            // connection being established, then this can't take a
+            // second lock. The "connect_to" future is Canceled.
+            let connecting = match pool.connecting(&pool_key, ver) {
+                Some(lock) => lock,
+                None => {
+                    let canceled =
+                        crate::Error::new_canceled().with("HTTP/2 connection in progress");
+                    return Either::Right(future::err(canceled));
+                }
+            };
+            Either::Left(
+                connector
+                    .connect(connect::sealed::Internal, dst)
+                    .map_err(crate::Error::new_connect)
+                    .and_then(move |io| {
+                        let connected = io.connected();
+                        // If ALPN is h2 and we aren't http2_only already,
+                        // then we need to convert our pool checkout into
+                        // a single HTTP2 one.
+                        let connecting = if connected.alpn == Alpn::H2 && !is_ver_h2 {
+                            match connecting.alpn_h2(&pool) {
+                                Some(lock) => {
+                                    trace!("ALPN negotiated h2, updating pool");
+                                    lock
+                                }
+                                None => {
+                                    // Another connection has already upgraded,
+                                    // the pool checkout should finish up for us.
+                                    let canceled = crate::Error::new_canceled()
+                                        .with("ALPN upgraded to HTTP/2");
+                                    return Either::Right(future::err(canceled));
+                                }
+                            }
+                        } else {
+                            connecting
+                        };
+
+                        #[cfg_attr(not(feature = "http2"), allow(unused))]
+                        let is_h2 = is_ver_h2 || connected.alpn == Alpn::H2;
+                        #[cfg(feature = "http2")]
+                        {
+                            conn_builder.http2_only(is_h2);
+                        }
+
+                        Either::Left(Box::pin(async move {
+                            let (tx, conn) = conn_builder.handshake(io).await?;
+
+                            trace!("handshake complete, spawning background dispatcher task");
+                            executor.execute(
+                                conn.map_err(|e| debug!("client connection error: {}", e))
+                                    .map(|_| ()),
+                            );
+
+                            // Wait for 'conn' to ready up before we
+                            // declare this tx as usable
+                            let tx = tx.when_ready().await?;
+
+                            let tx = {
+                                #[cfg(feature = "http2")]
+                                {
+                                    if is_h2 {
+                                        PoolTx::Http2(tx.into_http2())
+                                    } else {
+                                        PoolTx::Http1(tx)
+                                    }
+                                }
+                                #[cfg(not(feature = "http2"))]
+                                PoolTx::Http1(tx)
+                            };
+
+                            Ok(pool.pooled(
+                                connecting,
+                                PoolClient {
+                                    conn_info: connected,
+                                    tx,
+                                },
+                            ))
+                        }))
+                    }),
+            )
+        })
+    }
+}
+
+impl<C, B> tower_service::Service<Request<B>> for Client<C, B>
+where
+    C: Connect + Clone + Send + Sync + 'static,
+    B: HttpBody + Send + 'static,
+    B::Data: Send,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type Response = Response<Body>;
+    type Error = crate::Error;
+    type Future = ResponseFuture;
+
+    fn poll_ready(&mut self, _: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: Request<B>) -> Self::Future {
+        self.request(req)
+    }
+}
+
+impl<C, B> tower_service::Service<Request<B>> for &'_ Client<C, B>
+where
+    C: Connect + Clone + Send + Sync + 'static,
+    B: HttpBody + Send + 'static,
+    B::Data: Send,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type Response = Response<Body>;
+    type Error = crate::Error;
+    type Future = ResponseFuture;
+
+    fn poll_ready(&mut self, _: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: Request<B>) -> Self::Future {
+        self.request(req)
+    }
+}
+
+impl<C: Clone, B> Clone for Client<C, B> {
+    fn clone(&self) -> Client<C, B> {
+        Client {
+            config: self.config.clone(),
+            conn_builder: self.conn_builder.clone(),
+            connector: self.connector.clone(),
+            pool: self.pool.clone(),
+        }
+    }
+}
+
+impl<C, B> fmt::Debug for Client<C, B> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Client").finish()
+    }
+}
+
+// ===== impl ResponseFuture =====
+
+impl ResponseFuture {
+    fn new<F>(value: F) -> Self
+    where
+        F: Future<Output = crate::Result<Response<Body>>> + Send + 'static,
+    {
+        Self {
+            inner: SyncWrapper::new(Box::pin(value)),
+        }
+    }
+
+    fn error_version(ver: Version) -> Self {
+        warn!("Request has unsupported version \"{:?}\"", ver);
+        ResponseFuture::new(Box::pin(future::err(
+            crate::Error::new_user_unsupported_version(),
+        )))
+    }
+}
+
+impl fmt::Debug for ResponseFuture {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("Future<Response>")
+    }
+}
+
+impl Future for ResponseFuture {
+    type Output = crate::Result<Response<Body>>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.inner.get_mut().as_mut().poll(cx)
+    }
+}
+
+// ===== impl PoolClient =====
+
+// FIXME: allow() required due to `impl Trait` leaking types to this lint
+#[allow(missing_debug_implementations)]
+struct PoolClient<B> {
+    conn_info: Connected,
+    tx: PoolTx<B>,
+}
+
+enum PoolTx<B> {
+    #[cfg_attr(feature = "deprecated", allow(deprecated))]
+    Http1(conn::SendRequest<B>),
+    #[cfg(feature = "http2")]
+    Http2(conn::Http2SendRequest<B>),
+}
+
+impl<B> PoolClient<B> {
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        match self.tx {
+            PoolTx::Http1(ref mut tx) => tx.poll_ready(cx),
+            #[cfg(feature = "http2")]
+            PoolTx::Http2(_) => Poll::Ready(Ok(())),
+        }
+    }
+
+    fn is_http1(&self) -> bool {
+        !self.is_http2()
+    }
+
+    fn is_http2(&self) -> bool {
+        match self.tx {
+            PoolTx::Http1(_) => false,
+            #[cfg(feature = "http2")]
+            PoolTx::Http2(_) => true,
+        }
+    }
+
+    fn is_ready(&self) -> bool {
+        match self.tx {
+            PoolTx::Http1(ref tx) => tx.is_ready(),
+            #[cfg(feature = "http2")]
+            PoolTx::Http2(ref tx) => tx.is_ready(),
+        }
+    }
+
+    fn is_closed(&self) -> bool {
+        match self.tx {
+            PoolTx::Http1(ref tx) => tx.is_closed(),
+            #[cfg(feature = "http2")]
+            PoolTx::Http2(ref tx) => tx.is_closed(),
+        }
+    }
+}
+
+impl<B: HttpBody + 'static> PoolClient<B> {
+    fn send_request_retryable(
+        &mut self,
+        req: Request<B>,
+    ) -> impl Future<Output = Result<Response<Body>, (crate::Error, Option<Request<B>>)>>
+    where
+        B: Send,
+    {
+        match self.tx {
+            #[cfg(not(feature = "http2"))]
+            PoolTx::Http1(ref mut tx) => tx.send_request_retryable(req),
+            #[cfg(feature = "http2")]
+            PoolTx::Http1(ref mut tx) => Either::Left(tx.send_request_retryable(req)),
+            #[cfg(feature = "http2")]
+            PoolTx::Http2(ref mut tx) => Either::Right(tx.send_request_retryable(req)),
+        }
+    }
+}
+
+impl<B> Poolable for PoolClient<B>
+where
+    B: Send + 'static,
+{
+    fn is_open(&self) -> bool {
+        if self.conn_info.poisoned.poisoned() {
+            trace!(
+                "marking {:?} as closed because it was poisoned",
+                self.conn_info
+            );
+            return false;
+        }
+        match self.tx {
+            PoolTx::Http1(ref tx) => tx.is_ready(),
+            #[cfg(feature = "http2")]
+            PoolTx::Http2(ref tx) => tx.is_ready(),
+        }
+    }
+
+    fn reserve(self) -> Reservation<Self> {
+        match self.tx {
+            PoolTx::Http1(tx) => Reservation::Unique(PoolClient {
+                conn_info: self.conn_info,
+                tx: PoolTx::Http1(tx),
+            }),
+            #[cfg(feature = "http2")]
+            PoolTx::Http2(tx) => {
+                let b = PoolClient {
+                    conn_info: self.conn_info.clone(),
+                    tx: PoolTx::Http2(tx.clone()),
+                };
+                let a = PoolClient {
+                    conn_info: self.conn_info,
+                    tx: PoolTx::Http2(tx),
+                };
+                Reservation::Shared(a, b)
+            }
+        }
+    }
+
+    fn can_share(&self) -> bool {
+        self.is_http2()
+    }
+}
+
+// ===== impl ClientError =====
+
+// FIXME: allow() required due to `impl Trait` leaking types to this lint
+#[allow(missing_debug_implementations)]
+enum ClientError<B> {
+    Normal(crate::Error),
+    Canceled {
+        connection_reused: bool,
+        req: Request<B>,
+        reason: crate::Error,
+    },
+}
+
+impl<B> ClientError<B> {
+    fn map_with_reused(conn_reused: bool) -> impl Fn((crate::Error, Option<Request<B>>)) -> Self {
+        move |(err, orig_req)| {
+            if let Some(req) = orig_req {
+                ClientError::Canceled {
+                    connection_reused: conn_reused,
+                    reason: err,
+                    req,
+                }
+            } else {
+                ClientError::Normal(err)
+            }
+        }
+    }
+}
+
+enum ClientConnectError {
+    Normal(crate::Error),
+    H2CheckoutIsClosed(crate::Error),
+}
+
+/// A marker to identify what version a pooled connection is.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+pub(super) enum Ver {
+    Auto,
+    Http2,
+}
+
+fn origin_form(uri: &mut Uri) {
+    let path = match uri.path_and_query() {
+        Some(path) if path.as_str() != "/" => {
+            let mut parts = ::http::uri::Parts::default();
+            parts.path_and_query = Some(path.clone());
+            Uri::from_parts(parts).expect("path is valid uri")
+        }
+        _none_or_just_slash => {
+            debug_assert!(Uri::default() == "/");
+            Uri::default()
+        }
+    };
+    *uri = path
+}
+
+fn absolute_form(uri: &mut Uri) {
+    debug_assert!(uri.scheme().is_some(), "absolute_form needs a scheme");
+    debug_assert!(
+        uri.authority().is_some(),
+        "absolute_form needs an authority"
+    );
+    // If the URI is to HTTPS, and the connector claimed to be a proxy,
+    // then it *should* have tunneled, and so we don't want to send
+    // absolute-form in that case.
+    if uri.scheme() == Some(&Scheme::HTTPS) {
+        origin_form(uri);
+    }
+}
+
+fn authority_form(uri: &mut Uri) {
+    if let Some(path) = uri.path_and_query() {
+        // `https://hyper.rs` would parse with `/` path, don't
+        // annoy people about that...
+        if path != "/" {
+            warn!("HTTP/1.1 CONNECT request stripping path: {:?}", path);
+        }
+    }
+    *uri = match uri.authority() {
+        Some(auth) => {
+            let mut parts = ::http::uri::Parts::default();
+            parts.authority = Some(auth.clone());
+            Uri::from_parts(parts).expect("authority is valid")
+        }
+        None => {
+            unreachable!("authority_form with relative uri");
+        }
+    };
+}
+
+fn extract_domain(uri: &mut Uri, is_http_connect: bool) -> crate::Result<PoolKey> {
+    let uri_clone = uri.clone();
+    match (uri_clone.scheme(), uri_clone.authority()) {
+        (Some(scheme), Some(auth)) => Ok((scheme.clone(), auth.clone())),
+        (None, Some(auth)) if is_http_connect => {
+            let scheme = match auth.port_u16() {
+                Some(443) => {
+                    set_scheme(uri, Scheme::HTTPS);
+                    Scheme::HTTPS
+                }
+                _ => {
+                    set_scheme(uri, Scheme::HTTP);
+                    Scheme::HTTP
+                }
+            };
+            Ok((scheme, auth.clone()))
+        }
+        _ => {
+            debug!("Client requires absolute-form URIs, received: {:?}", uri);
+            Err(crate::Error::new_user_absolute_uri_required())
+        }
+    }
+}
+
+fn domain_as_uri((scheme, auth): PoolKey) -> Uri {
+    http::uri::Builder::new()
+        .scheme(scheme)
+        .authority(auth)
+        .path_and_query("/")
+        .build()
+        .expect("domain is valid Uri")
+}
+
+fn set_scheme(uri: &mut Uri, scheme: Scheme) {
+    debug_assert!(
+        uri.scheme().is_none(),
+        "set_scheme expects no existing scheme"
+    );
+    let old = mem::replace(uri, Uri::default());
+    let mut parts: ::http::uri::Parts = old.into();
+    parts.scheme = Some(scheme);
+    parts.path_and_query = Some("/".parse().expect("slash is a valid path"));
+    *uri = Uri::from_parts(parts).expect("scheme is valid");
+}
+
+fn get_non_default_port(uri: &Uri) -> Option<Port<&str>> {
+    match (uri.port().map(|p| p.as_u16()), is_schema_secure(uri)) {
+        (Some(443), true) => None,
+        (Some(80), false) => None,
+        _ => uri.port(),
+    }
+}
+
+fn is_schema_secure(uri: &Uri) -> bool {
+    uri.scheme_str()
+        .map(|scheme_str| matches!(scheme_str, "wss" | "https"))
+        .unwrap_or_default()
+}
+
+/// A builder to configure a new [`Client`](Client).
+///
+/// # Example
+///
+/// ```
+/// # #[cfg(feature  = "runtime")]
+/// # fn run () {
+/// use std::time::Duration;
+/// use hyper::Client;
+///
+/// let client = Client::builder()
+///     .pool_idle_timeout(Duration::from_secs(30))
+///     .http2_only(true)
+///     .build_http();
+/// # let infer: Client<_, hyper::Body> = client;
+/// # drop(infer);
+/// # }
+/// # fn main() {}
+/// ```
+#[cfg_attr(docsrs, doc(cfg(any(feature = "http1", feature = "http2"))))]
+#[derive(Clone)]
+pub struct Builder {
+    client_config: Config,
+    #[cfg_attr(feature = "deprecated", allow(deprecated))]
+    conn_builder: conn::Builder,
+    pool_config: pool::Config,
+}
+
+impl Default for Builder {
+    fn default() -> Self {
+        Self {
+            client_config: Config {
+                retry_canceled_requests: true,
+                set_host: true,
+                ver: Ver::Auto,
+            },
+            #[cfg_attr(feature = "deprecated", allow(deprecated))]
+            conn_builder: conn::Builder::new(),
+            pool_config: pool::Config {
+                idle_timeout: Some(Duration::from_secs(90)),
+                max_idle_per_host: std::usize::MAX,
+            },
+        }
+    }
+}
+
+impl Builder {
+    #[doc(hidden)]
+    #[deprecated(
+        note = "name is confusing, to disable the connection pool, call pool_max_idle_per_host(0)"
+    )]
+    pub fn keep_alive(&mut self, val: bool) -> &mut Self {
+        if !val {
+            // disable
+            self.pool_max_idle_per_host(0)
+        } else if self.pool_config.max_idle_per_host == 0 {
+            // enable
+            self.pool_max_idle_per_host(std::usize::MAX)
+        } else {
+            // already enabled
+            self
+        }
+    }
+
+    #[doc(hidden)]
+    #[deprecated(note = "renamed to `pool_idle_timeout`")]
+    pub fn keep_alive_timeout<D>(&mut self, val: D) -> &mut Self
+    where
+        D: Into<Option<Duration>>,
+    {
+        self.pool_idle_timeout(val)
+    }
+
+    /// Set an optional timeout for idle sockets being kept-alive.
+    ///
+    /// Pass `None` to disable timeout.
+    ///
+    /// Default is 90 seconds.
+    pub fn pool_idle_timeout<D>(&mut self, val: D) -> &mut Self
+    where
+        D: Into<Option<Duration>>,
+    {
+        self.pool_config.idle_timeout = val.into();
+        self
+    }
+
+    #[doc(hidden)]
+    #[deprecated(note = "renamed to `pool_max_idle_per_host`")]
+    pub fn max_idle_per_host(&mut self, max_idle: usize) -> &mut Self {
+        self.pool_config.max_idle_per_host = max_idle;
+        self
+    }
+
+    /// Sets the maximum idle connection per host allowed in the pool.
+    ///
+    /// Default is `usize::MAX` (no limit).
+    pub fn pool_max_idle_per_host(&mut self, max_idle: usize) -> &mut Self {
+        self.pool_config.max_idle_per_host = max_idle;
+        self
+    }
+
+    // HTTP/1 options
+
+    /// Sets the exact size of the read buffer to *always* use.
+    ///
+    /// Note that setting this option unsets the `http1_max_buf_size` option.
+    ///
+    /// Default is an adaptive read buffer.
+    pub fn http1_read_buf_exact_size(&mut self, sz: usize) -> &mut Self {
+        self.conn_builder.http1_read_buf_exact_size(Some(sz));
+        self
+    }
+
+    /// Set the maximum buffer size for the connection.
+    ///
+    /// Default is ~400kb.
+    ///
+    /// Note that setting this option unsets the `http1_read_exact_buf_size` option.
+    ///
+    /// # Panics
+    ///
+    /// The minimum value allowed is 8192. This method panics if the passed `max` is less than the minimum.
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn http1_max_buf_size(&mut self, max: usize) -> &mut Self {
+        self.conn_builder.http1_max_buf_size(max);
+        self
+    }
+
+    /// Set whether HTTP/1 connections will accept spaces between header names
+    /// and the colon that follow them in responses.
+    ///
+    /// Newline codepoints (`\r` and `\n`) will be transformed to spaces when
+    /// parsing.
+    ///
+    /// You probably don't need this, here is what [RFC 7230 Section 3.2.4.] has
+    /// to say about it:
+    ///
+    /// > No whitespace is allowed between the header field-name and colon. In
+    /// > the past, differences in the handling of such whitespace have led to
+    /// > security vulnerabilities in request routing and response handling. A
+    /// > server MUST reject any received request message that contains
+    /// > whitespace between a header field-name and colon with a response code
+    /// > of 400 (Bad Request). A proxy MUST remove any such whitespace from a
+    /// > response message before forwarding the message downstream.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    ///
+    /// [RFC 7230 Section 3.2.4.]: https://tools.ietf.org/html/rfc7230#section-3.2.4
+    pub fn http1_allow_spaces_after_header_name_in_responses(&mut self, val: bool) -> &mut Self {
+        self.conn_builder
+            .http1_allow_spaces_after_header_name_in_responses(val);
+        self
+    }
+
+    /// Set whether HTTP/1 connections will accept obsolete line folding for
+    /// header values.
+    ///
+    /// You probably don't need this, here is what [RFC 7230 Section 3.2.4.] has
+    /// to say about it:
+    ///
+    /// > A server that receives an obs-fold in a request message that is not
+    /// > within a message/http container MUST either reject the message by
+    /// > sending a 400 (Bad Request), preferably with a representation
+    /// > explaining that obsolete line folding is unacceptable, or replace
+    /// > each received obs-fold with one or more SP octets prior to
+    /// > interpreting the field value or forwarding the message downstream.
+    ///
+    /// > A proxy or gateway that receives an obs-fold in a response message
+    /// > that is not within a message/http container MUST either discard the
+    /// > message and replace it with a 502 (Bad Gateway) response, preferably
+    /// > with a representation explaining that unacceptable line folding was
+    /// > received, or replace each received obs-fold with one or more SP
+    /// > octets prior to interpreting the field value or forwarding the
+    /// > message downstream.
+    ///
+    /// > A user agent that receives an obs-fold in a response message that is
+    /// > not within a message/http container MUST replace each received
+    /// > obs-fold with one or more SP octets prior to interpreting the field
+    /// > value.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    ///
+    /// [RFC 7230 Section 3.2.4.]: https://tools.ietf.org/html/rfc7230#section-3.2.4
+    pub fn http1_allow_obsolete_multiline_headers_in_responses(&mut self, val: bool) -> &mut Self {
+        self.conn_builder
+            .http1_allow_obsolete_multiline_headers_in_responses(val);
+        self
+    }
+
+    /// Sets whether invalid header lines should be silently ignored in HTTP/1 responses.
+    ///
+    /// This mimicks the behaviour of major browsers. You probably don't want this.
+    /// You should only want this if you are implementing a proxy whose main
+    /// purpose is to sit in front of browsers whose users access arbitrary content
+    /// which may be malformed, and they expect everything that works without
+    /// the proxy to keep working with the proxy.
+    ///
+    /// This option will prevent Hyper's client from returning an error encountered
+    /// when parsing a header, except if the error was caused by the character NUL
+    /// (ASCII code 0), as Chrome specifically always reject those.
+    ///
+    /// The ignorable errors are:
+    /// * empty header names;
+    /// * characters that are not allowed in header names, except for `\0` and `\r`;
+    /// * when `allow_spaces_after_header_name_in_responses` is not enabled,
+    ///   spaces and tabs between the header name and the colon;
+    /// * missing colon between header name and colon;
+    /// * characters that are not allowed in header values except for `\0` and `\r`.
+    ///
+    /// If an ignorable error is encountered, the parser tries to find the next
+    /// line in the input to resume parsing the rest of the headers. An error
+    /// will be emitted nonetheless if it finds `\0` or a lone `\r` while
+    /// looking for the next line.
+    pub fn http1_ignore_invalid_headers_in_responses(&mut self, val: bool) -> &mut Builder {
+        self.conn_builder
+            .http1_ignore_invalid_headers_in_responses(val);
+        self
+    }
+
+    /// Set whether HTTP/1 connections should try to use vectored writes,
+    /// or always flatten into a single buffer.
+    ///
+    /// Note that setting this to false may mean more copies of body data,
+    /// but may also improve performance when an IO transport doesn't
+    /// support vectored writes well, such as most TLS implementations.
+    ///
+    /// Setting this to true will force hyper to use queued strategy
+    /// which may eliminate unnecessary cloning on some TLS backends
+    ///
+    /// Default is `auto`. In this mode hyper will try to guess which
+    /// mode to use
+    pub fn http1_writev(&mut self, enabled: bool) -> &mut Builder {
+        self.conn_builder.http1_writev(enabled);
+        self
+    }
+
+    /// Set whether HTTP/1 connections will write header names as title case at
+    /// the socket level.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    pub fn http1_title_case_headers(&mut self, val: bool) -> &mut Self {
+        self.conn_builder.http1_title_case_headers(val);
+        self
+    }
+
+    /// Set whether to support preserving original header cases.
+    ///
+    /// Currently, this will record the original cases received, and store them
+    /// in a private extension on the `Response`. It will also look for and use
+    /// such an extension in any provided `Request`.
+    ///
+    /// Since the relevant extension is still private, there is no way to
+    /// interact with the original cases. The only effect this can have now is
+    /// to forward the cases in a proxy-like fashion.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    pub fn http1_preserve_header_case(&mut self, val: bool) -> &mut Self {
+        self.conn_builder.http1_preserve_header_case(val);
+        self
+    }
+
+    /// Set whether HTTP/0.9 responses should be tolerated.
+    ///
+    /// Default is false.
+    pub fn http09_responses(&mut self, val: bool) -> &mut Self {
+        self.conn_builder.http09_responses(val);
+        self
+    }
+
+    /// Set whether the connection **must** use HTTP/2.
+    ///
+    /// The destination must either allow HTTP2 Prior Knowledge, or the
+    /// `Connect` should be configured to do use ALPN to upgrade to `h2`
+    /// as part of the connection process. This will not make the `Client`
+    /// utilize ALPN by itself.
+    ///
+    /// Note that setting this to true prevents HTTP/1 from being allowed.
+    ///
+    /// Default is false.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_only(&mut self, val: bool) -> &mut Self {
+        self.client_config.ver = if val { Ver::Http2 } else { Ver::Auto };
+        self
+    }
+
+    /// Sets the [`SETTINGS_INITIAL_WINDOW_SIZE`][spec] option for HTTP2
+    /// stream-level flow control.
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    ///
+    /// [spec]: https://http2.github.io/http2-spec/#SETTINGS_INITIAL_WINDOW_SIZE
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_initial_stream_window_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
+        self.conn_builder
+            .http2_initial_stream_window_size(sz.into());
+        self
+    }
+
+    /// Sets the max connection-level flow control for HTTP2
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_initial_connection_window_size(
+        &mut self,
+        sz: impl Into<Option<u32>>,
+    ) -> &mut Self {
+        self.conn_builder
+            .http2_initial_connection_window_size(sz.into());
+        self
+    }
+
+    /// Sets whether to use an adaptive flow control.
+    ///
+    /// Enabling this will override the limits set in
+    /// `http2_initial_stream_window_size` and
+    /// `http2_initial_connection_window_size`.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_adaptive_window(&mut self, enabled: bool) -> &mut Self {
+        self.conn_builder.http2_adaptive_window(enabled);
+        self
+    }
+
+    /// Sets the maximum frame size to use for HTTP2.
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_frame_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
+        self.conn_builder.http2_max_frame_size(sz);
+        self
+    }
+
+    /// Sets an interval for HTTP2 Ping frames should be sent to keep a
+    /// connection alive.
+    ///
+    /// Pass `None` to disable HTTP2 keep-alive.
+    ///
+    /// Default is currently disabled.
+    ///
+    /// # Cargo Feature
+    ///
+    /// Requires the `runtime` cargo feature to be enabled.
+    #[cfg(feature = "runtime")]
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_keep_alive_interval(
+        &mut self,
+        interval: impl Into<Option<Duration>>,
+    ) -> &mut Self {
+        self.conn_builder.http2_keep_alive_interval(interval);
+        self
+    }
+
+    /// Sets a timeout for receiving an acknowledgement of the keep-alive ping.
+    ///
+    /// If the ping is not acknowledged within the timeout, the connection will
+    /// be closed. Does nothing if `http2_keep_alive_interval` is disabled.
+    ///
+    /// Default is 20 seconds.
+    ///
+    /// # Cargo Feature
+    ///
+    /// Requires the `runtime` cargo feature to be enabled.
+    #[cfg(feature = "runtime")]
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_keep_alive_timeout(&mut self, timeout: Duration) -> &mut Self {
+        self.conn_builder.http2_keep_alive_timeout(timeout);
+        self
+    }
+
+    /// Sets whether HTTP2 keep-alive should apply while the connection is idle.
+    ///
+    /// If disabled, keep-alive pings are only sent while there are open
+    /// request/responses streams. If enabled, pings are also sent when no
+    /// streams are active. Does nothing if `http2_keep_alive_interval` is
+    /// disabled.
+    ///
+    /// Default is `false`.
+    ///
+    /// # Cargo Feature
+    ///
+    /// Requires the `runtime` cargo feature to be enabled.
+    #[cfg(feature = "runtime")]
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_keep_alive_while_idle(&mut self, enabled: bool) -> &mut Self {
+        self.conn_builder.http2_keep_alive_while_idle(enabled);
+        self
+    }
+
+    /// Sets the maximum number of HTTP2 concurrent locally reset streams.
+    ///
+    /// See the documentation of [`h2::client::Builder::max_concurrent_reset_streams`] for more
+    /// details.
+    ///
+    /// The default value is determined by the `h2` crate.
+    ///
+    /// [`h2::client::Builder::max_concurrent_reset_streams`]: https://docs.rs/h2/client/struct.Builder.html#method.max_concurrent_reset_streams
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_concurrent_reset_streams(&mut self, max: usize) -> &mut Self {
+        self.conn_builder.http2_max_concurrent_reset_streams(max);
+        self
+    }
+
+    /// Set the maximum write buffer size for each HTTP/2 stream.
+    ///
+    /// Default is currently 1MB, but may change.
+    ///
+    /// # Panics
+    ///
+    /// The value must be no larger than `u32::MAX`.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_send_buf_size(&mut self, max: usize) -> &mut Self {
+        self.conn_builder.http2_max_send_buf_size(max);
+        self
+    }
+
+    /// Set whether to retry requests that get disrupted before ever starting
+    /// to write.
+    ///
+    /// This means a request that is queued, and gets given an idle, reused
+    /// connection, and then encounters an error immediately as the idle
+    /// connection was found to be unusable.
+    ///
+    /// When this is set to `false`, the related `ResponseFuture` would instead
+    /// resolve to an `Error::Cancel`.
+    ///
+    /// Default is `true`.
+    #[inline]
+    pub fn retry_canceled_requests(&mut self, val: bool) -> &mut Self {
+        self.client_config.retry_canceled_requests = val;
+        self
+    }
+
+    /// Set whether to automatically add the `Host` header to requests.
+    ///
+    /// If true, and a request does not include a `Host` header, one will be
+    /// added automatically, derived from the authority of the `Uri`.
+    ///
+    /// Default is `true`.
+    #[inline]
+    pub fn set_host(&mut self, val: bool) -> &mut Self {
+        self.client_config.set_host = val;
+        self
+    }
+
+    /// Provide an executor to execute background `Connection` tasks.
+    pub fn executor<E>(&mut self, exec: E) -> &mut Self
+    where
+        E: Executor<BoxSendFuture> + Send + Sync + 'static,
+    {
+        self.conn_builder.executor(exec);
+        self
+    }
+
+    /// Builder a client with this configuration and the default `HttpConnector`.
+    #[cfg(feature = "tcp")]
+    pub fn build_http<B>(&self) -> Client<HttpConnector, B>
+    where
+        B: HttpBody + Send,
+        B::Data: Send,
+    {
+        let mut connector = HttpConnector::new();
+        if self.pool_config.is_enabled() {
+            connector.set_keepalive(self.pool_config.idle_timeout);
+        }
+        self.build(connector)
+    }
+
+    /// Combine the configuration of this builder with a connector to create a `Client`.
+    pub fn build<C, B>(&self, connector: C) -> Client<C, B>
+    where
+        C: Connect + Clone,
+        B: HttpBody + Send,
+        B::Data: Send,
+    {
+        #[cfg_attr(feature = "deprecated", allow(deprecated))]
+        Client {
+            config: self.client_config,
+            conn_builder: self.conn_builder.clone(),
+            connector,
+            pool: Pool::new(self.pool_config, &self.conn_builder.exec),
+        }
+    }
+}
+
+impl fmt::Debug for Builder {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Builder")
+            .field("client_config", &self.client_config)
+            .field("conn_builder", &self.conn_builder)
+            .field("pool_config", &self.pool_config)
+            .finish()
+    }
+}
+
+#[cfg(test)]
+mod unit_tests {
+    use super::*;
+
+    #[test]
+    fn response_future_is_sync() {
+        fn assert_sync<T: Sync>() {}
+        assert_sync::<ResponseFuture>();
+    }
+
+    #[test]
+    fn set_relative_uri_with_implicit_path() {
+        let mut uri = "http://hyper.rs".parse().unwrap();
+        origin_form(&mut uri);
+        assert_eq!(uri.to_string(), "/");
+    }
+
+    #[test]
+    fn test_origin_form() {
+        let mut uri = "http://hyper.rs/guides".parse().unwrap();
+        origin_form(&mut uri);
+        assert_eq!(uri.to_string(), "/guides");
+
+        let mut uri = "http://hyper.rs/guides?foo=bar".parse().unwrap();
+        origin_form(&mut uri);
+        assert_eq!(uri.to_string(), "/guides?foo=bar");
+    }
+
+    #[test]
+    fn test_absolute_form() {
+        let mut uri = "http://hyper.rs/guides".parse().unwrap();
+        absolute_form(&mut uri);
+        assert_eq!(uri.to_string(), "http://hyper.rs/guides");
+
+        let mut uri = "https://hyper.rs/guides".parse().unwrap();
+        absolute_form(&mut uri);
+        assert_eq!(uri.to_string(), "/guides");
+    }
+
+    #[test]
+    fn test_authority_form() {
+        let _ = pretty_env_logger::try_init();
+
+        let mut uri = "http://hyper.rs".parse().unwrap();
+        authority_form(&mut uri);
+        assert_eq!(uri.to_string(), "hyper.rs");
+
+        let mut uri = "hyper.rs".parse().unwrap();
+        authority_form(&mut uri);
+        assert_eq!(uri.to_string(), "hyper.rs");
+    }
+
+    #[test]
+    fn test_extract_domain_connect_no_port() {
+        let mut uri = "hyper.rs".parse().unwrap();
+        let (scheme, host) = extract_domain(&mut uri, true).expect("extract domain");
+        assert_eq!(scheme, *"http");
+        assert_eq!(host, "hyper.rs");
+    }
+
+    #[test]
+    fn test_is_secure() {
+        assert_eq!(
+            is_schema_secure(&"http://hyper.rs".parse::<Uri>().unwrap()),
+            false
+        );
+        assert_eq!(is_schema_secure(&"hyper.rs".parse::<Uri>().unwrap()), false);
+        assert_eq!(
+            is_schema_secure(&"wss://hyper.rs".parse::<Uri>().unwrap()),
+            true
+        );
+        assert_eq!(
+            is_schema_secure(&"ws://hyper.rs".parse::<Uri>().unwrap()),
+            false
+        );
+    }
+
+    #[test]
+    fn test_get_non_default_port() {
+        assert!(get_non_default_port(&"http://hyper.rs".parse::<Uri>().unwrap()).is_none());
+        assert!(get_non_default_port(&"http://hyper.rs:80".parse::<Uri>().unwrap()).is_none());
+        assert!(get_non_default_port(&"https://hyper.rs:443".parse::<Uri>().unwrap()).is_none());
+        assert!(get_non_default_port(&"hyper.rs:80".parse::<Uri>().unwrap()).is_none());
+
+        assert_eq!(
+            get_non_default_port(&"http://hyper.rs:123".parse::<Uri>().unwrap())
+                .unwrap()
+                .as_u16(),
+            123
+        );
+        assert_eq!(
+            get_non_default_port(&"https://hyper.rs:80".parse::<Uri>().unwrap())
+                .unwrap()
+                .as_u16(),
+            80
+        );
+        assert_eq!(
+            get_non_default_port(&"hyper.rs:123".parse::<Uri>().unwrap())
+                .unwrap()
+                .as_u16(),
+            123
+        );
+    }
+}
diff --git a/src/client/conn.rs b/src/client/conn.rs
new file mode 100644
index 0000000..8da457d
--- /dev/null
+++ b/src/client/conn.rs
@@ -0,0 +1,1154 @@
+//! Lower-level client connection API.
+//!
+//! The types in this module are to provide a lower-level API based around a
+//! single connection. Connecting to a host, pooling connections, and the like
+//! are not handled at this level. This module provides the building blocks to
+//! customize those things externally.
+//!
+//! If don't have need to manage connections yourself, consider using the
+//! higher-level [Client](super) API.
+//!
+//! ## Example
+//! A simple example that uses the `SendRequest` struct to talk HTTP over a Tokio TCP stream
+//! ```no_run
+//! # #[cfg(all(feature = "client", feature = "http1", feature = "runtime"))]
+//! # mod rt {
+//! use tower::ServiceExt;
+//! use http::{Request, StatusCode};
+//! use hyper::{client::conn, Body};
+//! use tokio::net::TcpStream;
+//!
+//! #[tokio::main]
+//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
+//!     let target_stream = TcpStream::connect("example.com:80").await?;
+//!
+//!     let (mut request_sender, connection) = conn::handshake(target_stream).await?;
+//!
+//!     // spawn a task to poll the connection and drive the HTTP state
+//!     tokio::spawn(async move {
+//!         if let Err(e) = connection.await {
+//!             eprintln!("Error in connection: {}", e);
+//!         }
+//!     });
+//!
+//!     let request = Request::builder()
+//!         // We need to manually add the host header because SendRequest does not
+//!         .header("Host", "example.com")
+//!         .method("GET")
+//!         .body(Body::from(""))?;
+//!     let response = request_sender.send_request(request).await?;
+//!     assert!(response.status() == StatusCode::OK);
+//!
+//!     // To send via the same connection again, it may not work as it may not be ready,
+//!     // so we have to wait until the request_sender becomes ready.
+//!     request_sender.ready().await?;
+//!     let request = Request::builder()
+//!         .header("Host", "example.com")
+//!         .method("GET")
+//!         .body(Body::from(""))?;
+//!     let response = request_sender.send_request(request).await?;
+//!     assert!(response.status() == StatusCode::OK);
+//!     Ok(())
+//! }
+//!
+//! # }
+//! ```
+
+#[cfg(all(feature = "backports", feature = "http1"))]
+pub mod http1;
+#[cfg(all(feature = "backports", feature = "http2"))]
+pub mod http2;
+
+#[cfg(not(all(feature = "http1", feature = "http2")))]
+use std::convert::Infallible;
+use std::error::Error as StdError;
+use std::fmt;
+use std::future::Future;
+#[cfg(not(all(feature = "http1", feature = "http2")))]
+use std::marker::PhantomData;
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::sync::Arc;
+use std::task::{Context, Poll};
+#[cfg(all(feature = "runtime", feature = "http2"))]
+use std::time::Duration;
+
+use bytes::Bytes;
+use futures_util::future::{self, Either, FutureExt as _};
+use httparse::ParserConfig;
+use pin_project_lite::pin_project;
+use tokio::io::{AsyncRead, AsyncWrite};
+use tower_service::Service;
+use tracing::{debug, trace};
+
+use super::dispatch;
+use crate::body::HttpBody;
+use crate::common::exec::{BoxSendFuture, Exec};
+use crate::proto;
+use crate::rt::Executor;
+#[cfg(feature = "http1")]
+use crate::upgrade::Upgraded;
+use crate::{Body, Request, Response};
+
+#[cfg(feature = "http1")]
+type Http1Dispatcher<T, B> =
+    proto::dispatch::Dispatcher<proto::dispatch::Client<B>, B, T, proto::h1::ClientTransaction>;
+
+#[cfg(not(feature = "http1"))]
+type Http1Dispatcher<T, B> = (Infallible, PhantomData<(T, Pin<Box<B>>)>);
+
+#[cfg(feature = "http2")]
+type Http2ClientTask<B> = proto::h2::ClientTask<B>;
+
+#[cfg(not(feature = "http2"))]
+type Http2ClientTask<B> = (Infallible, PhantomData<Pin<Box<B>>>);
+
+pin_project! {
+    #[project = ProtoClientProj]
+    enum ProtoClient<T, B>
+    where
+        B: HttpBody,
+    {
+        H1 {
+            #[pin]
+            h1: Http1Dispatcher<T, B>,
+        },
+        H2 {
+            #[pin]
+            h2: Http2ClientTask<B>,
+        },
+    }
+}
+
+/// Returns a handshake future over some IO.
+///
+/// This is a shortcut for `Builder::new().handshake(io)`.
+/// See [`client::conn`](crate::client::conn) for more.
+#[cfg_attr(
+    feature = "deprecated",
+    deprecated(
+        note = "This function will be replaced with `client::conn::http1::handshake` and `client::conn::http2::handshake` in 1.0, enable the \"backports\" feature to use them now."
+    )
+)]
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+pub async fn handshake<T>(
+    io: T,
+) -> crate::Result<(SendRequest<crate::Body>, Connection<T, crate::Body>)>
+where
+    T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+{
+    #[allow(deprecated)]
+    Builder::new().handshake(io).await
+}
+
+/// The sender side of an established connection.
+#[cfg_attr(
+    feature = "deprecated",
+    deprecated(
+        note = "This type will be replaced with `client::conn::http1::SendRequest` and `client::conn::http2::SendRequest` in 1.0, enable the \"backports\" feature to use them now."
+    )
+)]
+pub struct SendRequest<B> {
+    dispatch: dispatch::Sender<Request<B>, Response<Body>>,
+}
+
+/// A future that processes all HTTP state for the IO object.
+///
+/// In most cases, this should just be spawned into an executor, so that it
+/// can process incoming and outgoing messages, notice hangups, and the like.
+#[must_use = "futures do nothing unless polled"]
+#[cfg_attr(
+    feature = "deprecated",
+    deprecated(
+        note = "This type will be replaced with `client::conn::http1::Connection` and `client::conn::http2::Connection` in 1.0, enable the \"backports\" feature to use them now."
+    )
+)]
+pub struct Connection<T, B>
+where
+    T: AsyncRead + AsyncWrite + Send + 'static,
+    B: HttpBody + 'static,
+{
+    inner: Option<ProtoClient<T, B>>,
+}
+
+/// A builder to configure an HTTP connection.
+///
+/// After setting options, the builder is used to create a handshake future.
+#[derive(Clone, Debug)]
+#[cfg_attr(
+    feature = "deprecated",
+    deprecated(
+        note = "This type will be replaced with `client::conn::http1::Builder` and `client::conn::http2::Builder` in 1.0, enable the \"backports\" feature to use them now."
+    )
+)]
+pub struct Builder {
+    pub(super) exec: Exec,
+    h09_responses: bool,
+    h1_parser_config: ParserConfig,
+    h1_writev: Option<bool>,
+    h1_title_case_headers: bool,
+    h1_preserve_header_case: bool,
+    #[cfg(feature = "ffi")]
+    h1_preserve_header_order: bool,
+    h1_read_buf_exact_size: Option<usize>,
+    h1_max_buf_size: Option<usize>,
+    #[cfg(feature = "ffi")]
+    h1_headers_raw: bool,
+    #[cfg(feature = "http2")]
+    h2_builder: proto::h2::client::Config,
+    version: Proto,
+}
+
+#[derive(Clone, Debug)]
+enum Proto {
+    #[cfg(feature = "http1")]
+    Http1,
+    #[cfg(feature = "http2")]
+    Http2,
+}
+
+/// A future returned by `SendRequest::send_request`.
+///
+/// Yields a `Response` if successful.
+#[must_use = "futures do nothing unless polled"]
+pub struct ResponseFuture {
+    inner: ResponseFutureState,
+}
+
+enum ResponseFutureState {
+    Waiting(dispatch::Promise<Response<Body>>),
+    // Option is to be able to `take()` it in `poll`
+    Error(Option<crate::Error>),
+}
+
+/// Deconstructed parts of a `Connection`.
+///
+/// This allows taking apart a `Connection` at a later time, in order to
+/// reclaim the IO object, and additional related pieces.
+#[derive(Debug)]
+pub struct Parts<T> {
+    /// The original IO object used in the handshake.
+    pub io: T,
+    /// A buffer of bytes that have been read but not processed as HTTP.
+    ///
+    /// For instance, if the `Connection` is used for an HTTP upgrade request,
+    /// it is possible the server sent back the first bytes of the new protocol
+    /// along with the response upgrade.
+    ///
+    /// You will want to check for any existing bytes if you plan to continue
+    /// communicating on the IO object.
+    pub read_buf: Bytes,
+    _inner: (),
+}
+
+// ========== internal client api
+
+// A `SendRequest` that can be cloned to send HTTP2 requests.
+// private for now, probably not a great idea of a type...
+#[must_use = "futures do nothing unless polled"]
+#[cfg(feature = "http2")]
+pub(super) struct Http2SendRequest<B> {
+    dispatch: dispatch::UnboundedSender<Request<B>, Response<Body>>,
+}
+
+// ===== impl SendRequest
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+impl<B> SendRequest<B> {
+    /// Polls to determine whether this sender can be used yet for a request.
+    ///
+    /// If the associated connection is closed, this returns an Error.
+    pub fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        self.dispatch.poll_ready(cx)
+    }
+
+    pub(super) async fn when_ready(self) -> crate::Result<Self> {
+        let mut me = Some(self);
+        future::poll_fn(move |cx| {
+            ready!(me.as_mut().unwrap().poll_ready(cx))?;
+            Poll::Ready(Ok(me.take().unwrap()))
+        })
+        .await
+    }
+
+    pub(super) fn is_ready(&self) -> bool {
+        self.dispatch.is_ready()
+    }
+
+    pub(super) fn is_closed(&self) -> bool {
+        self.dispatch.is_closed()
+    }
+
+    #[cfg(feature = "http2")]
+    pub(super) fn into_http2(self) -> Http2SendRequest<B> {
+        Http2SendRequest {
+            dispatch: self.dispatch.unbound(),
+        }
+    }
+}
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+impl<B> SendRequest<B>
+where
+    B: HttpBody + 'static,
+{
+    /// Sends a `Request` on the associated connection.
+    ///
+    /// Returns a future that if successful, yields the `Response`.
+    ///
+    /// # Note
+    ///
+    /// There are some key differences in what automatic things the `Client`
+    /// does for you that will not be done here:
+    ///
+    /// - `Client` requires absolute-form `Uri`s, since the scheme and
+    ///   authority are needed to connect. They aren't required here.
+    /// - Since the `Client` requires absolute-form `Uri`s, it can add
+    ///   the `Host` header based on it. You must add a `Host` header yourself
+    ///   before calling this method.
+    /// - Since absolute-form `Uri`s are not required, if received, they will
+    ///   be serialized as-is.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use http::header::HOST;
+    /// # use hyper::client::conn::SendRequest;
+    /// # use hyper::Body;
+    /// use hyper::Request;
+    ///
+    /// # async fn doc(mut tx: SendRequest<Body>) -> hyper::Result<()> {
+    /// // build a Request
+    /// let req = Request::builder()
+    ///     .uri("/foo/bar")
+    ///     .header(HOST, "hyper.rs")
+    ///     .body(Body::empty())
+    ///     .unwrap();
+    ///
+    /// // send it and await a Response
+    /// let res = tx.send_request(req).await?;
+    /// // assert the Response
+    /// assert!(res.status().is_success());
+    /// # Ok(())
+    /// # }
+    /// # fn main() {}
+    /// ```
+    pub fn send_request(&mut self, req: Request<B>) -> ResponseFuture {
+        let inner = match self.dispatch.send(req) {
+            Ok(rx) => ResponseFutureState::Waiting(rx),
+            Err(_req) => {
+                debug!("connection was not ready");
+                let err = crate::Error::new_canceled().with("connection was not ready");
+                ResponseFutureState::Error(Some(err))
+            }
+        };
+
+        ResponseFuture { inner }
+    }
+
+    pub(super) fn send_request_retryable(
+        &mut self,
+        req: Request<B>,
+    ) -> impl Future<Output = Result<Response<Body>, (crate::Error, Option<Request<B>>)>> + Unpin
+    where
+        B: Send,
+    {
+        match self.dispatch.try_send(req) {
+            Ok(rx) => {
+                Either::Left(rx.then(move |res| {
+                    match res {
+                        Ok(Ok(res)) => future::ok(res),
+                        Ok(Err(err)) => future::err(err),
+                        // this is definite bug if it happens, but it shouldn't happen!
+                        Err(_) => panic!("dispatch dropped without returning error"),
+                    }
+                }))
+            }
+            Err(req) => {
+                debug!("connection was not ready");
+                let err = crate::Error::new_canceled().with("connection was not ready");
+                Either::Right(future::err((err, Some(req))))
+            }
+        }
+    }
+}
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+impl<B> Service<Request<B>> for SendRequest<B>
+where
+    B: HttpBody + 'static,
+{
+    type Response = Response<Body>;
+    type Error = crate::Error;
+    type Future = ResponseFuture;
+
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.poll_ready(cx)
+    }
+
+    fn call(&mut self, req: Request<B>) -> Self::Future {
+        self.send_request(req)
+    }
+}
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+impl<B> fmt::Debug for SendRequest<B> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SendRequest").finish()
+    }
+}
+
+// ===== impl Http2SendRequest
+
+#[cfg(feature = "http2")]
+impl<B> Http2SendRequest<B> {
+    pub(super) fn is_ready(&self) -> bool {
+        self.dispatch.is_ready()
+    }
+
+    pub(super) fn is_closed(&self) -> bool {
+        self.dispatch.is_closed()
+    }
+}
+
+#[cfg(feature = "http2")]
+impl<B> Http2SendRequest<B>
+where
+    B: HttpBody + 'static,
+{
+    pub(super) fn send_request_retryable(
+        &mut self,
+        req: Request<B>,
+    ) -> impl Future<Output = Result<Response<Body>, (crate::Error, Option<Request<B>>)>>
+    where
+        B: Send,
+    {
+        match self.dispatch.try_send(req) {
+            Ok(rx) => {
+                Either::Left(rx.then(move |res| {
+                    match res {
+                        Ok(Ok(res)) => future::ok(res),
+                        Ok(Err(err)) => future::err(err),
+                        // this is definite bug if it happens, but it shouldn't happen!
+                        Err(_) => panic!("dispatch dropped without returning error"),
+                    }
+                }))
+            }
+            Err(req) => {
+                debug!("connection was not ready");
+                let err = crate::Error::new_canceled().with("connection was not ready");
+                Either::Right(future::err((err, Some(req))))
+            }
+        }
+    }
+}
+
+#[cfg(feature = "http2")]
+impl<B> fmt::Debug for Http2SendRequest<B> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Http2SendRequest").finish()
+    }
+}
+
+#[cfg(feature = "http2")]
+impl<B> Clone for Http2SendRequest<B> {
+    fn clone(&self) -> Self {
+        Http2SendRequest {
+            dispatch: self.dispatch.clone(),
+        }
+    }
+}
+
+// ===== impl Connection
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+impl<T, B> Connection<T, B>
+where
+    T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    B: HttpBody + Unpin + Send + 'static,
+    B::Data: Send,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    /// Return the inner IO object, and additional information.
+    ///
+    /// Only works for HTTP/1 connections. HTTP/2 connections will panic.
+    pub fn into_parts(self) -> Parts<T> {
+        match self.inner.expect("already upgraded") {
+            #[cfg(feature = "http1")]
+            ProtoClient::H1 { h1 } => {
+                let (io, read_buf, _) = h1.into_inner();
+                Parts {
+                    io,
+                    read_buf,
+                    _inner: (),
+                }
+            }
+            ProtoClient::H2 { .. } => {
+                panic!("http2 cannot into_inner");
+            }
+
+            #[cfg(not(feature = "http1"))]
+            ProtoClient::H1 { h1 } => match h1.0 {},
+        }
+    }
+
+    /// Poll the connection for completion, but without calling `shutdown`
+    /// on the underlying IO.
+    ///
+    /// This is useful to allow running a connection while doing an HTTP
+    /// upgrade. Once the upgrade is completed, the connection would be "done",
+    /// but it is not desired to actually shutdown the IO object. Instead you
+    /// would take it back using `into_parts`.
+    ///
+    /// Use [`poll_fn`](https://docs.rs/futures/0.1.25/futures/future/fn.poll_fn.html)
+    /// and [`try_ready!`](https://docs.rs/futures/0.1.25/futures/macro.try_ready.html)
+    /// to work with this function; or use the `without_shutdown` wrapper.
+    pub fn poll_without_shutdown(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        match *self.inner.as_mut().expect("already upgraded") {
+            #[cfg(feature = "http1")]
+            ProtoClient::H1 { ref mut h1 } => h1.poll_without_shutdown(cx),
+            #[cfg(feature = "http2")]
+            ProtoClient::H2 { ref mut h2, .. } => Pin::new(h2).poll(cx).map_ok(|_| ()),
+
+            #[cfg(not(feature = "http1"))]
+            ProtoClient::H1 { ref mut h1 } => match h1.0 {},
+            #[cfg(not(feature = "http2"))]
+            ProtoClient::H2 { ref mut h2, .. } => match h2.0 {},
+        }
+    }
+
+    /// Prevent shutdown of the underlying IO object at the end of service the request,
+    /// instead run `into_parts`. This is a convenience wrapper over `poll_without_shutdown`.
+    pub fn without_shutdown(self) -> impl Future<Output = crate::Result<Parts<T>>> {
+        let mut conn = Some(self);
+        future::poll_fn(move |cx| -> Poll<crate::Result<Parts<T>>> {
+            ready!(conn.as_mut().unwrap().poll_without_shutdown(cx))?;
+            Poll::Ready(Ok(conn.take().unwrap().into_parts()))
+        })
+    }
+
+    /// Returns whether the [extended CONNECT protocol][1] is enabled or not.
+    ///
+    /// This setting is configured by the server peer by sending the
+    /// [`SETTINGS_ENABLE_CONNECT_PROTOCOL` parameter][2] in a `SETTINGS` frame.
+    /// This method returns the currently acknowledged value received from the
+    /// remote.
+    ///
+    /// [1]: https://datatracker.ietf.org/doc/html/rfc8441#section-4
+    /// [2]: https://datatracker.ietf.org/doc/html/rfc8441#section-3
+    #[cfg(feature = "http2")]
+    pub fn http2_is_extended_connect_protocol_enabled(&self) -> bool {
+        match self.inner.as_ref().unwrap() {
+            ProtoClient::H1 { .. } => false,
+            ProtoClient::H2 { h2 } => h2.is_extended_connect_protocol_enabled(),
+        }
+    }
+}
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+impl<T, B> Future for Connection<T, B>
+where
+    T: AsyncRead + AsyncWrite + Unpin + Send,
+    B: HttpBody + Send + 'static,
+    B::Data: Send,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type Output = crate::Result<()>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match ready!(Pin::new(self.inner.as_mut().unwrap()).poll(cx))? {
+            proto::Dispatched::Shutdown => Poll::Ready(Ok(())),
+            #[cfg(feature = "http1")]
+            proto::Dispatched::Upgrade(pending) => match self.inner.take() {
+                Some(ProtoClient::H1 { h1 }) => {
+                    let (io, buf, _) = h1.into_inner();
+                    pending.fulfill(Upgraded::new(io, buf));
+                    Poll::Ready(Ok(()))
+                }
+                _ => {
+                    drop(pending);
+                    unreachable!("Upgrade expects h1");
+                }
+            },
+        }
+    }
+}
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+impl<T, B> fmt::Debug for Connection<T, B>
+where
+    T: AsyncRead + AsyncWrite + fmt::Debug + Send + 'static,
+    B: HttpBody + 'static,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Connection").finish()
+    }
+}
+
+// ===== impl Builder
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+impl Builder {
+    /// Creates a new connection builder.
+    #[inline]
+    pub fn new() -> Builder {
+        Builder {
+            exec: Exec::Default,
+            h09_responses: false,
+            h1_writev: None,
+            h1_read_buf_exact_size: None,
+            h1_parser_config: Default::default(),
+            h1_title_case_headers: false,
+            h1_preserve_header_case: false,
+            #[cfg(feature = "ffi")]
+            h1_preserve_header_order: false,
+            h1_max_buf_size: None,
+            #[cfg(feature = "ffi")]
+            h1_headers_raw: false,
+            #[cfg(feature = "http2")]
+            h2_builder: Default::default(),
+            #[cfg(feature = "http1")]
+            version: Proto::Http1,
+            #[cfg(not(feature = "http1"))]
+            version: Proto::Http2,
+        }
+    }
+
+    /// Provide an executor to execute background HTTP2 tasks.
+    pub fn executor<E>(&mut self, exec: E) -> &mut Builder
+    where
+        E: Executor<BoxSendFuture> + Send + Sync + 'static,
+    {
+        self.exec = Exec::Executor(Arc::new(exec));
+        self
+    }
+
+    /// Set whether HTTP/0.9 responses should be tolerated.
+    ///
+    /// Default is false.
+    pub fn http09_responses(&mut self, enabled: bool) -> &mut Builder {
+        self.h09_responses = enabled;
+        self
+    }
+
+    /// Set whether HTTP/1 connections will accept spaces between header names
+    /// and the colon that follow them in responses.
+    ///
+    /// You probably don't need this, here is what [RFC 7230 Section 3.2.4.] has
+    /// to say about it:
+    ///
+    /// > No whitespace is allowed between the header field-name and colon. In
+    /// > the past, differences in the handling of such whitespace have led to
+    /// > security vulnerabilities in request routing and response handling. A
+    /// > server MUST reject any received request message that contains
+    /// > whitespace between a header field-name and colon with a response code
+    /// > of 400 (Bad Request). A proxy MUST remove any such whitespace from a
+    /// > response message before forwarding the message downstream.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    ///
+    /// [RFC 7230 Section 3.2.4.]: https://tools.ietf.org/html/rfc7230#section-3.2.4
+    pub fn http1_allow_spaces_after_header_name_in_responses(
+        &mut self,
+        enabled: bool,
+    ) -> &mut Builder {
+        self.h1_parser_config
+            .allow_spaces_after_header_name_in_responses(enabled);
+        self
+    }
+
+    /// Set whether HTTP/1 connections will accept obsolete line folding for
+    /// header values.
+    ///
+    /// Newline codepoints (`\r` and `\n`) will be transformed to spaces when
+    /// parsing.
+    ///
+    /// You probably don't need this, here is what [RFC 7230 Section 3.2.4.] has
+    /// to say about it:
+    ///
+    /// > A server that receives an obs-fold in a request message that is not
+    /// > within a message/http container MUST either reject the message by
+    /// > sending a 400 (Bad Request), preferably with a representation
+    /// > explaining that obsolete line folding is unacceptable, or replace
+    /// > each received obs-fold with one or more SP octets prior to
+    /// > interpreting the field value or forwarding the message downstream.
+    ///
+    /// > A proxy or gateway that receives an obs-fold in a response message
+    /// > that is not within a message/http container MUST either discard the
+    /// > message and replace it with a 502 (Bad Gateway) response, preferably
+    /// > with a representation explaining that unacceptable line folding was
+    /// > received, or replace each received obs-fold with one or more SP
+    /// > octets prior to interpreting the field value or forwarding the
+    /// > message downstream.
+    ///
+    /// > A user agent that receives an obs-fold in a response message that is
+    /// > not within a message/http container MUST replace each received
+    /// > obs-fold with one or more SP octets prior to interpreting the field
+    /// > value.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    ///
+    /// [RFC 7230 Section 3.2.4.]: https://tools.ietf.org/html/rfc7230#section-3.2.4
+    pub fn http1_allow_obsolete_multiline_headers_in_responses(
+        &mut self,
+        enabled: bool,
+    ) -> &mut Builder {
+        self.h1_parser_config
+            .allow_obsolete_multiline_headers_in_responses(enabled);
+        self
+    }
+
+    /// Set whether HTTP/1 connections will silently ignored malformed header lines.
+    ///
+    /// If this is enabled and and a header line does not start with a valid header
+    /// name, or does not include a colon at all, the line will be silently ignored
+    /// and no error will be reported.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    pub fn http1_ignore_invalid_headers_in_responses(&mut self, enabled: bool) -> &mut Builder {
+        self.h1_parser_config
+            .ignore_invalid_headers_in_responses(enabled);
+        self
+    }
+
+    /// Set whether HTTP/1 connections should try to use vectored writes,
+    /// or always flatten into a single buffer.
+    ///
+    /// Note that setting this to false may mean more copies of body data,
+    /// but may also improve performance when an IO transport doesn't
+    /// support vectored writes well, such as most TLS implementations.
+    ///
+    /// Setting this to true will force hyper to use queued strategy
+    /// which may eliminate unnecessary cloning on some TLS backends
+    ///
+    /// Default is `auto`. In this mode hyper will try to guess which
+    /// mode to use
+    pub fn http1_writev(&mut self, enabled: bool) -> &mut Builder {
+        self.h1_writev = Some(enabled);
+        self
+    }
+
+    /// Set whether HTTP/1 connections will write header names as title case at
+    /// the socket level.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    pub fn http1_title_case_headers(&mut self, enabled: bool) -> &mut Builder {
+        self.h1_title_case_headers = enabled;
+        self
+    }
+
+    /// Set whether to support preserving original header cases.
+    ///
+    /// Currently, this will record the original cases received, and store them
+    /// in a private extension on the `Response`. It will also look for and use
+    /// such an extension in any provided `Request`.
+    ///
+    /// Since the relevant extension is still private, there is no way to
+    /// interact with the original cases. The only effect this can have now is
+    /// to forward the cases in a proxy-like fashion.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    pub fn http1_preserve_header_case(&mut self, enabled: bool) -> &mut Builder {
+        self.h1_preserve_header_case = enabled;
+        self
+    }
+
+    /// Set whether to support preserving original header order.
+    ///
+    /// Currently, this will record the order in which headers are received, and store this
+    /// ordering in a private extension on the `Response`. It will also look for and use
+    /// such an extension in any provided `Request`.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    #[cfg(feature = "ffi")]
+    pub fn http1_preserve_header_order(&mut self, enabled: bool) -> &mut Builder {
+        self.h1_preserve_header_order = enabled;
+        self
+    }
+
+    /// Sets the exact size of the read buffer to *always* use.
+    ///
+    /// Note that setting this option unsets the `http1_max_buf_size` option.
+    ///
+    /// Default is an adaptive read buffer.
+    pub fn http1_read_buf_exact_size(&mut self, sz: Option<usize>) -> &mut Builder {
+        self.h1_read_buf_exact_size = sz;
+        self.h1_max_buf_size = None;
+        self
+    }
+
+    /// Set the maximum buffer size for the connection.
+    ///
+    /// Default is ~400kb.
+    ///
+    /// Note that setting this option unsets the `http1_read_exact_buf_size` option.
+    ///
+    /// # Panics
+    ///
+    /// The minimum value allowed is 8192. This method panics if the passed `max` is less than the minimum.
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn http1_max_buf_size(&mut self, max: usize) -> &mut Self {
+        assert!(
+            max >= proto::h1::MINIMUM_MAX_BUFFER_SIZE,
+            "the max_buf_size cannot be smaller than the minimum that h1 specifies."
+        );
+
+        self.h1_max_buf_size = Some(max);
+        self.h1_read_buf_exact_size = None;
+        self
+    }
+
+    #[cfg(feature = "ffi")]
+    pub(crate) fn http1_headers_raw(&mut self, enabled: bool) -> &mut Self {
+        self.h1_headers_raw = enabled;
+        self
+    }
+
+    /// Sets whether HTTP2 is required.
+    ///
+    /// Default is false.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_only(&mut self, enabled: bool) -> &mut Builder {
+        if enabled {
+            self.version = Proto::Http2
+        }
+        self
+    }
+
+    /// Sets the [`SETTINGS_INITIAL_WINDOW_SIZE`][spec] option for HTTP2
+    /// stream-level flow control.
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    ///
+    /// [spec]: https://http2.github.io/http2-spec/#SETTINGS_INITIAL_WINDOW_SIZE
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_initial_stream_window_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
+        if let Some(sz) = sz.into() {
+            self.h2_builder.adaptive_window = false;
+            self.h2_builder.initial_stream_window_size = sz;
+        }
+        self
+    }
+
+    /// Sets the max connection-level flow control for HTTP2
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_initial_connection_window_size(
+        &mut self,
+        sz: impl Into<Option<u32>>,
+    ) -> &mut Self {
+        if let Some(sz) = sz.into() {
+            self.h2_builder.adaptive_window = false;
+            self.h2_builder.initial_conn_window_size = sz;
+        }
+        self
+    }
+
+    /// Sets whether to use an adaptive flow control.
+    ///
+    /// Enabling this will override the limits set in
+    /// `http2_initial_stream_window_size` and
+    /// `http2_initial_connection_window_size`.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_adaptive_window(&mut self, enabled: bool) -> &mut Self {
+        use proto::h2::SPEC_WINDOW_SIZE;
+
+        self.h2_builder.adaptive_window = enabled;
+        if enabled {
+            self.h2_builder.initial_conn_window_size = SPEC_WINDOW_SIZE;
+            self.h2_builder.initial_stream_window_size = SPEC_WINDOW_SIZE;
+        }
+        self
+    }
+
+    /// Sets the maximum frame size to use for HTTP2.
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_frame_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
+        if let Some(sz) = sz.into() {
+            self.h2_builder.max_frame_size = sz;
+        }
+        self
+    }
+
+    /// Sets an interval for HTTP2 Ping frames should be sent to keep a
+    /// connection alive.
+    ///
+    /// Pass `None` to disable HTTP2 keep-alive.
+    ///
+    /// Default is currently disabled.
+    ///
+    /// # Cargo Feature
+    ///
+    /// Requires the `runtime` cargo feature to be enabled.
+    #[cfg(feature = "runtime")]
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_keep_alive_interval(
+        &mut self,
+        interval: impl Into<Option<Duration>>,
+    ) -> &mut Self {
+        self.h2_builder.keep_alive_interval = interval.into();
+        self
+    }
+
+    /// Sets a timeout for receiving an acknowledgement of the keep-alive ping.
+    ///
+    /// If the ping is not acknowledged within the timeout, the connection will
+    /// be closed. Does nothing if `http2_keep_alive_interval` is disabled.
+    ///
+    /// Default is 20 seconds.
+    ///
+    /// # Cargo Feature
+    ///
+    /// Requires the `runtime` cargo feature to be enabled.
+    #[cfg(feature = "runtime")]
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_keep_alive_timeout(&mut self, timeout: Duration) -> &mut Self {
+        self.h2_builder.keep_alive_timeout = timeout;
+        self
+    }
+
+    /// Sets whether HTTP2 keep-alive should apply while the connection is idle.
+    ///
+    /// If disabled, keep-alive pings are only sent while there are open
+    /// request/responses streams. If enabled, pings are also sent when no
+    /// streams are active. Does nothing if `http2_keep_alive_interval` is
+    /// disabled.
+    ///
+    /// Default is `false`.
+    ///
+    /// # Cargo Feature
+    ///
+    /// Requires the `runtime` cargo feature to be enabled.
+    #[cfg(feature = "runtime")]
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_keep_alive_while_idle(&mut self, enabled: bool) -> &mut Self {
+        self.h2_builder.keep_alive_while_idle = enabled;
+        self
+    }
+
+    /// Sets the maximum number of HTTP2 concurrent locally reset streams.
+    ///
+    /// See the documentation of [`h2::client::Builder::max_concurrent_reset_streams`] for more
+    /// details.
+    ///
+    /// The default value is determined by the `h2` crate.
+    ///
+    /// [`h2::client::Builder::max_concurrent_reset_streams`]: https://docs.rs/h2/client/struct.Builder.html#method.max_concurrent_reset_streams
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_concurrent_reset_streams(&mut self, max: usize) -> &mut Self {
+        self.h2_builder.max_concurrent_reset_streams = Some(max);
+        self
+    }
+
+    /// Set the maximum write buffer size for each HTTP/2 stream.
+    ///
+    /// Default is currently 1MB, but may change.
+    ///
+    /// # Panics
+    ///
+    /// The value must be no larger than `u32::MAX`.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_send_buf_size(&mut self, max: usize) -> &mut Self {
+        assert!(max <= std::u32::MAX as usize);
+        self.h2_builder.max_send_buffer_size = max;
+        self
+    }
+
+    /// Constructs a connection with the configured options and IO.
+    /// See [`client::conn`](crate::client::conn) for more.
+    ///
+    /// Note, if [`Connection`] is not `await`-ed, [`SendRequest`] will
+    /// do nothing.
+    pub fn handshake<T, B>(
+        &self,
+        io: T,
+    ) -> impl Future<Output = crate::Result<(SendRequest<B>, Connection<T, B>)>>
+    where
+        T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+        B: HttpBody + 'static,
+        B::Data: Send,
+        B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    {
+        let opts = self.clone();
+
+        async move {
+            trace!("client handshake {:?}", opts.version);
+
+            let (tx, rx) = dispatch::channel();
+            let proto = match opts.version {
+                #[cfg(feature = "http1")]
+                Proto::Http1 => {
+                    let mut conn = proto::Conn::new(io);
+                    conn.set_h1_parser_config(opts.h1_parser_config);
+                    if let Some(writev) = opts.h1_writev {
+                        if writev {
+                            conn.set_write_strategy_queue();
+                        } else {
+                            conn.set_write_strategy_flatten();
+                        }
+                    }
+                    if opts.h1_title_case_headers {
+                        conn.set_title_case_headers();
+                    }
+                    if opts.h1_preserve_header_case {
+                        conn.set_preserve_header_case();
+                    }
+                    #[cfg(feature = "ffi")]
+                    if opts.h1_preserve_header_order {
+                        conn.set_preserve_header_order();
+                    }
+                    if opts.h09_responses {
+                        conn.set_h09_responses();
+                    }
+
+                    #[cfg(feature = "ffi")]
+                    conn.set_raw_headers(opts.h1_headers_raw);
+
+                    if let Some(sz) = opts.h1_read_buf_exact_size {
+                        conn.set_read_buf_exact_size(sz);
+                    }
+                    if let Some(max) = opts.h1_max_buf_size {
+                        conn.set_max_buf_size(max);
+                    }
+                    let cd = proto::h1::dispatch::Client::new(rx);
+                    let dispatch = proto::h1::Dispatcher::new(cd, conn);
+                    ProtoClient::H1 { h1: dispatch }
+                }
+                #[cfg(feature = "http2")]
+                Proto::Http2 => {
+                    let h2 =
+                        proto::h2::client::handshake(io, rx, &opts.h2_builder, opts.exec.clone())
+                            .await?;
+                    ProtoClient::H2 { h2 }
+                }
+            };
+
+            Ok((
+                SendRequest { dispatch: tx },
+                Connection { inner: Some(proto) },
+            ))
+        }
+    }
+}
+
+// ===== impl ResponseFuture
+
+impl Future for ResponseFuture {
+    type Output = crate::Result<Response<Body>>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match self.inner {
+            ResponseFutureState::Waiting(ref mut rx) => {
+                Pin::new(rx).poll(cx).map(|res| match res {
+                    Ok(Ok(resp)) => Ok(resp),
+                    Ok(Err(err)) => Err(err),
+                    // this is definite bug if it happens, but it shouldn't happen!
+                    Err(_canceled) => panic!("dispatch dropped without returning error"),
+                })
+            }
+            ResponseFutureState::Error(ref mut err) => {
+                Poll::Ready(Err(err.take().expect("polled after ready")))
+            }
+        }
+    }
+}
+
+impl fmt::Debug for ResponseFuture {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("ResponseFuture").finish()
+    }
+}
+
+// ===== impl ProtoClient
+
+impl<T, B> Future for ProtoClient<T, B>
+where
+    T: AsyncRead + AsyncWrite + Send + Unpin + 'static,
+    B: HttpBody + Send + 'static,
+    B::Data: Send,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type Output = crate::Result<proto::Dispatched>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match self.project() {
+            #[cfg(feature = "http1")]
+            ProtoClientProj::H1 { h1 } => h1.poll(cx),
+            #[cfg(feature = "http2")]
+            ProtoClientProj::H2 { h2, .. } => h2.poll(cx),
+
+            #[cfg(not(feature = "http1"))]
+            ProtoClientProj::H1 { h1 } => match h1.0 {},
+            #[cfg(not(feature = "http2"))]
+            ProtoClientProj::H2 { h2, .. } => match h2.0 {},
+        }
+    }
+}
+
+// assert trait markers
+
+trait AssertSend: Send {}
+trait AssertSendSync: Send + Sync {}
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+#[doc(hidden)]
+impl<B: Send> AssertSendSync for SendRequest<B> {}
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+#[doc(hidden)]
+impl<T: Send, B: Send> AssertSend for Connection<T, B>
+where
+    T: AsyncRead + AsyncWrite + Send + 'static,
+    B: HttpBody + 'static,
+    B::Data: Send,
+{
+}
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+#[doc(hidden)]
+impl<T: Send + Sync, B: Send + Sync> AssertSendSync for Connection<T, B>
+where
+    T: AsyncRead + AsyncWrite + Send + 'static,
+    B: HttpBody + 'static,
+    B::Data: Send + Sync + 'static,
+{
+}
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+#[doc(hidden)]
+impl AssertSendSync for Builder {}
+
+#[doc(hidden)]
+impl AssertSend for ResponseFuture {}
diff --git a/src/client/conn/http1.rs b/src/client/conn/http1.rs
new file mode 100644
index 0000000..37eda04
--- /dev/null
+++ b/src/client/conn/http1.rs
@@ -0,0 +1,541 @@
+//! HTTP/1 client connections
+
+use std::error::Error as StdError;
+use std::fmt;
+use std::future::Future;
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use bytes::Bytes;
+use http::{Request, Response};
+use httparse::ParserConfig;
+use tokio::io::{AsyncRead, AsyncWrite};
+
+use super::super::dispatch;
+use crate::body::{Body as IncomingBody, HttpBody as Body};
+use crate::proto;
+use crate::upgrade::Upgraded;
+
+type Dispatcher<T, B> =
+    proto::dispatch::Dispatcher<proto::dispatch::Client<B>, B, T, proto::h1::ClientTransaction>;
+
+/// The sender side of an established connection.
+pub struct SendRequest<B> {
+    dispatch: dispatch::Sender<Request<B>, Response<IncomingBody>>,
+}
+
+/// Deconstructed parts of a `Connection`.
+///
+/// This allows taking apart a `Connection` at a later time, in order to
+/// reclaim the IO object, and additional related pieces.
+#[derive(Debug)]
+pub struct Parts<T> {
+    /// The original IO object used in the handshake.
+    pub io: T,
+    /// A buffer of bytes that have been read but not processed as HTTP.
+    ///
+    /// For instance, if the `Connection` is used for an HTTP upgrade request,
+    /// it is possible the server sent back the first bytes of the new protocol
+    /// along with the response upgrade.
+    ///
+    /// You will want to check for any existing bytes if you plan to continue
+    /// communicating on the IO object.
+    pub read_buf: Bytes,
+    _inner: (),
+}
+
+/// A future that processes all HTTP state for the IO object.
+///
+/// In most cases, this should just be spawned into an executor, so that it
+/// can process incoming and outgoing messages, notice hangups, and the like.
+#[must_use = "futures do nothing unless polled"]
+pub struct Connection<T, B>
+where
+    T: AsyncRead + AsyncWrite + Send + 'static,
+    B: Body + 'static,
+{
+    inner: Option<Dispatcher<T, B>>,
+}
+
+impl<T, B> Connection<T, B>
+where
+    T: AsyncRead + AsyncWrite + Send + Unpin + 'static,
+    B: Body + 'static,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    /// Return the inner IO object, and additional information.
+    ///
+    /// Only works for HTTP/1 connections. HTTP/2 connections will panic.
+    pub fn into_parts(self) -> Parts<T> {
+        let (io, read_buf, _) = self.inner.expect("already upgraded").into_inner();
+        Parts {
+            io,
+            read_buf,
+            _inner: (),
+        }
+    }
+
+    /// Poll the connection for completion, but without calling `shutdown`
+    /// on the underlying IO.
+    ///
+    /// This is useful to allow running a connection while doing an HTTP
+    /// upgrade. Once the upgrade is completed, the connection would be "done",
+    /// but it is not desired to actually shutdown the IO object. Instead you
+    /// would take it back using `into_parts`.
+    ///
+    /// Use [`poll_fn`](https://docs.rs/futures/0.1.25/futures/future/fn.poll_fn.html)
+    /// and [`try_ready!`](https://docs.rs/futures/0.1.25/futures/macro.try_ready.html)
+    /// to work with this function; or use the `without_shutdown` wrapper.
+    pub fn poll_without_shutdown(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        self.inner
+            .as_mut()
+            .expect("algready upgraded")
+            .poll_without_shutdown(cx)
+    }
+
+    /// Prevent shutdown of the underlying IO object at the end of service the request,
+    /// instead run `into_parts`. This is a convenience wrapper over `poll_without_shutdown`.
+    pub fn without_shutdown(self) -> impl Future<Output = crate::Result<Parts<T>>> {
+        let mut conn = Some(self);
+        futures_util::future::poll_fn(move |cx| -> Poll<crate::Result<Parts<T>>> {
+            ready!(conn.as_mut().unwrap().poll_without_shutdown(cx))?;
+            Poll::Ready(Ok(conn.take().unwrap().into_parts()))
+        })
+    }
+}
+
+/// A builder to configure an HTTP connection.
+///
+/// After setting options, the builder is used to create a handshake future.
+#[derive(Clone, Debug)]
+pub struct Builder {
+    h09_responses: bool,
+    h1_parser_config: ParserConfig,
+    h1_writev: Option<bool>,
+    h1_title_case_headers: bool,
+    h1_preserve_header_case: bool,
+    #[cfg(feature = "ffi")]
+    h1_preserve_header_order: bool,
+    h1_read_buf_exact_size: Option<usize>,
+    h1_max_buf_size: Option<usize>,
+}
+
+/// Returns a handshake future over some IO.
+///
+/// This is a shortcut for `Builder::new().handshake(io)`.
+/// See [`client::conn`](crate::client::conn) for more.
+pub async fn handshake<T, B>(io: T) -> crate::Result<(SendRequest<B>, Connection<T, B>)>
+where
+    T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    B: Body + 'static,
+    B::Data: Send,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    Builder::new().handshake(io).await
+}
+
+// ===== impl SendRequest
+
+impl<B> SendRequest<B> {
+    /// Polls to determine whether this sender can be used yet for a request.
+    ///
+    /// If the associated connection is closed, this returns an Error.
+    pub fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        self.dispatch.poll_ready(cx)
+    }
+
+    /// Waits until the dispatcher is ready
+    ///
+    /// If the associated connection is closed, this returns an Error.
+    pub async fn ready(&mut self) -> crate::Result<()> {
+        futures_util::future::poll_fn(|cx| self.poll_ready(cx)).await
+    }
+
+    /*
+    pub(super) async fn when_ready(self) -> crate::Result<Self> {
+        let mut me = Some(self);
+        future::poll_fn(move |cx| {
+            ready!(me.as_mut().unwrap().poll_ready(cx))?;
+            Poll::Ready(Ok(me.take().unwrap()))
+        })
+        .await
+    }
+
+    pub(super) fn is_ready(&self) -> bool {
+        self.dispatch.is_ready()
+    }
+
+    pub(super) fn is_closed(&self) -> bool {
+        self.dispatch.is_closed()
+    }
+    */
+}
+
+impl<B> SendRequest<B>
+where
+    B: Body + 'static,
+{
+    /// Sends a `Request` on the associated connection.
+    ///
+    /// Returns a future that if successful, yields the `Response`.
+    ///
+    /// # Note
+    ///
+    /// There are some key differences in what automatic things the `Client`
+    /// does for you that will not be done here:
+    ///
+    /// - `Client` requires absolute-form `Uri`s, since the scheme and
+    ///   authority are needed to connect. They aren't required here.
+    /// - Since the `Client` requires absolute-form `Uri`s, it can add
+    ///   the `Host` header based on it. You must add a `Host` header yourself
+    ///   before calling this method.
+    /// - Since absolute-form `Uri`s are not required, if received, they will
+    ///   be serialized as-is.
+    pub fn send_request(
+        &mut self,
+        req: Request<B>,
+    ) -> impl Future<Output = crate::Result<Response<IncomingBody>>> {
+        let sent = self.dispatch.send(req);
+
+        async move {
+            match sent {
+                Ok(rx) => match rx.await {
+                    Ok(Ok(resp)) => Ok(resp),
+                    Ok(Err(err)) => Err(err),
+                    // this is definite bug if it happens, but it shouldn't happen!
+                    Err(_canceled) => panic!("dispatch dropped without returning error"),
+                },
+                Err(_req) => {
+                    tracing::debug!("connection was not ready");
+
+                    Err(crate::Error::new_canceled().with("connection was not ready"))
+                }
+            }
+        }
+    }
+
+    /*
+    pub(super) fn send_request_retryable(
+        &mut self,
+        req: Request<B>,
+    ) -> impl Future<Output = Result<Response<Body>, (crate::Error, Option<Request<B>>)>> + Unpin
+    where
+        B: Send,
+    {
+        match self.dispatch.try_send(req) {
+            Ok(rx) => {
+                Either::Left(rx.then(move |res| {
+                    match res {
+                        Ok(Ok(res)) => future::ok(res),
+                        Ok(Err(err)) => future::err(err),
+                        // this is definite bug if it happens, but it shouldn't happen!
+                        Err(_) => panic!("dispatch dropped without returning error"),
+                    }
+                }))
+            }
+            Err(req) => {
+                tracing::debug!("connection was not ready");
+                let err = crate::Error::new_canceled().with("connection was not ready");
+                Either::Right(future::err((err, Some(req))))
+            }
+        }
+    }
+    */
+}
+
+impl<B> fmt::Debug for SendRequest<B> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SendRequest").finish()
+    }
+}
+
+// ===== impl Connection
+
+impl<T, B> fmt::Debug for Connection<T, B>
+where
+    T: AsyncRead + AsyncWrite + fmt::Debug + Send + 'static,
+    B: Body + 'static,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Connection").finish()
+    }
+}
+
+impl<T, B> Future for Connection<T, B>
+where
+    T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    B: Body + Send + 'static,
+    B::Data: Send,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type Output = crate::Result<()>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match ready!(Pin::new(self.inner.as_mut().unwrap()).poll(cx))? {
+            proto::Dispatched::Shutdown => Poll::Ready(Ok(())),
+            proto::Dispatched::Upgrade(pending) => match self.inner.take() {
+                Some(h1) => {
+                    let (io, buf, _) = h1.into_inner();
+                    pending.fulfill(Upgraded::new(io, buf));
+                    Poll::Ready(Ok(()))
+                }
+                _ => {
+                    drop(pending);
+                    unreachable!("Upgraded twice");
+                }
+            },
+        }
+    }
+}
+
+// ===== impl Builder
+
+impl Builder {
+    /// Creates a new connection builder.
+    #[inline]
+    pub fn new() -> Builder {
+        Builder {
+            h09_responses: false,
+            h1_writev: None,
+            h1_read_buf_exact_size: None,
+            h1_parser_config: Default::default(),
+            h1_title_case_headers: false,
+            h1_preserve_header_case: false,
+            #[cfg(feature = "ffi")]
+            h1_preserve_header_order: false,
+            h1_max_buf_size: None,
+        }
+    }
+
+    /// Set whether HTTP/0.9 responses should be tolerated.
+    ///
+    /// Default is false.
+    pub fn http09_responses(&mut self, enabled: bool) -> &mut Builder {
+        self.h09_responses = enabled;
+        self
+    }
+
+    /// Set whether HTTP/1 connections will accept spaces between header names
+    /// and the colon that follow them in responses.
+    ///
+    /// You probably don't need this, here is what [RFC 7230 Section 3.2.4.] has
+    /// to say about it:
+    ///
+    /// > No whitespace is allowed between the header field-name and colon. In
+    /// > the past, differences in the handling of such whitespace have led to
+    /// > security vulnerabilities in request routing and response handling. A
+    /// > server MUST reject any received request message that contains
+    /// > whitespace between a header field-name and colon with a response code
+    /// > of 400 (Bad Request). A proxy MUST remove any such whitespace from a
+    /// > response message before forwarding the message downstream.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    ///
+    /// [RFC 7230 Section 3.2.4.]: https://tools.ietf.org/html/rfc7230#section-3.2.4
+    pub fn allow_spaces_after_header_name_in_responses(&mut self, enabled: bool) -> &mut Builder {
+        self.h1_parser_config
+            .allow_spaces_after_header_name_in_responses(enabled);
+        self
+    }
+
+    /// Set whether HTTP/1 connections will accept obsolete line folding for
+    /// header values.
+    ///
+    /// Newline codepoints (`\r` and `\n`) will be transformed to spaces when
+    /// parsing.
+    ///
+    /// You probably don't need this, here is what [RFC 7230 Section 3.2.4.] has
+    /// to say about it:
+    ///
+    /// > A server that receives an obs-fold in a request message that is not
+    /// > within a message/http container MUST either reject the message by
+    /// > sending a 400 (Bad Request), preferably with a representation
+    /// > explaining that obsolete line folding is unacceptable, or replace
+    /// > each received obs-fold with one or more SP octets prior to
+    /// > interpreting the field value or forwarding the message downstream.
+    ///
+    /// > A proxy or gateway that receives an obs-fold in a response message
+    /// > that is not within a message/http container MUST either discard the
+    /// > message and replace it with a 502 (Bad Gateway) response, preferably
+    /// > with a representation explaining that unacceptable line folding was
+    /// > received, or replace each received obs-fold with one or more SP
+    /// > octets prior to interpreting the field value or forwarding the
+    /// > message downstream.
+    ///
+    /// > A user agent that receives an obs-fold in a response message that is
+    /// > not within a message/http container MUST replace each received
+    /// > obs-fold with one or more SP octets prior to interpreting the field
+    /// > value.
+    ///
+    /// Default is false.
+    ///
+    /// [RFC 7230 Section 3.2.4.]: https://tools.ietf.org/html/rfc7230#section-3.2.4
+    pub fn allow_obsolete_multiline_headers_in_responses(&mut self, enabled: bool) -> &mut Builder {
+        self.h1_parser_config
+            .allow_obsolete_multiline_headers_in_responses(enabled);
+        self
+    }
+
+    /// Set whether HTTP/1 connections will silently ignored malformed header lines.
+    ///
+    /// If this is enabled and and a header line does not start with a valid header
+    /// name, or does not include a colon at all, the line will be silently ignored
+    /// and no error will be reported.
+    ///
+    /// Default is false.
+    pub fn ignore_invalid_headers_in_responses(&mut self, enabled: bool) -> &mut Builder {
+        self.h1_parser_config
+            .ignore_invalid_headers_in_responses(enabled);
+        self
+    }
+
+    /// Set whether HTTP/1 connections should try to use vectored writes,
+    /// or always flatten into a single buffer.
+    ///
+    /// Note that setting this to false may mean more copies of body data,
+    /// but may also improve performance when an IO transport doesn't
+    /// support vectored writes well, such as most TLS implementations.
+    ///
+    /// Setting this to true will force hyper to use queued strategy
+    /// which may eliminate unnecessary cloning on some TLS backends
+    ///
+    /// Default is `auto`. In this mode hyper will try to guess which
+    /// mode to use
+    pub fn writev(&mut self, enabled: bool) -> &mut Builder {
+        self.h1_writev = Some(enabled);
+        self
+    }
+
+    /// Set whether HTTP/1 connections will write header names as title case at
+    /// the socket level.
+    ///
+    /// Default is false.
+    pub fn title_case_headers(&mut self, enabled: bool) -> &mut Builder {
+        self.h1_title_case_headers = enabled;
+        self
+    }
+
+    /// Set whether to support preserving original header cases.
+    ///
+    /// Currently, this will record the original cases received, and store them
+    /// in a private extension on the `Response`. It will also look for and use
+    /// such an extension in any provided `Request`.
+    ///
+    /// Since the relevant extension is still private, there is no way to
+    /// interact with the original cases. The only effect this can have now is
+    /// to forward the cases in a proxy-like fashion.
+    ///
+    /// Default is false.
+    pub fn preserve_header_case(&mut self, enabled: bool) -> &mut Builder {
+        self.h1_preserve_header_case = enabled;
+        self
+    }
+
+    /// Set whether to support preserving original header order.
+    ///
+    /// Currently, this will record the order in which headers are received, and store this
+    /// ordering in a private extension on the `Response`. It will also look for and use
+    /// such an extension in any provided `Request`.
+    ///
+    /// Default is false.
+    #[cfg(feature = "ffi")]
+    pub fn preserve_header_order(&mut self, enabled: bool) -> &mut Builder {
+        self.h1_preserve_header_order = enabled;
+        self
+    }
+
+    /// Sets the exact size of the read buffer to *always* use.
+    ///
+    /// Note that setting this option unsets the `max_buf_size` option.
+    ///
+    /// Default is an adaptive read buffer.
+    pub fn read_buf_exact_size(&mut self, sz: Option<usize>) -> &mut Builder {
+        self.h1_read_buf_exact_size = sz;
+        self.h1_max_buf_size = None;
+        self
+    }
+
+    /// Set the maximum buffer size for the connection.
+    ///
+    /// Default is ~400kb.
+    ///
+    /// Note that setting this option unsets the `read_exact_buf_size` option.
+    ///
+    /// # Panics
+    ///
+    /// The minimum value allowed is 8192. This method panics if the passed `max` is less than the minimum.
+    pub fn max_buf_size(&mut self, max: usize) -> &mut Self {
+        assert!(
+            max >= proto::h1::MINIMUM_MAX_BUFFER_SIZE,
+            "the max_buf_size cannot be smaller than the minimum that h1 specifies."
+        );
+
+        self.h1_max_buf_size = Some(max);
+        self.h1_read_buf_exact_size = None;
+        self
+    }
+
+    /// Constructs a connection with the configured options and IO.
+    /// See [`client::conn`](crate::client::conn) for more.
+    ///
+    /// Note, if [`Connection`] is not `await`-ed, [`SendRequest`] will
+    /// do nothing.
+    pub fn handshake<T, B>(
+        &self,
+        io: T,
+    ) -> impl Future<Output = crate::Result<(SendRequest<B>, Connection<T, B>)>>
+    where
+        T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+        B: Body + 'static,
+        B::Data: Send,
+        B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    {
+        let opts = self.clone();
+
+        async move {
+            tracing::trace!("client handshake HTTP/1");
+
+            let (tx, rx) = dispatch::channel();
+            let mut conn = proto::Conn::new(io);
+            conn.set_h1_parser_config(opts.h1_parser_config);
+            if let Some(writev) = opts.h1_writev {
+                if writev {
+                    conn.set_write_strategy_queue();
+                } else {
+                    conn.set_write_strategy_flatten();
+                }
+            }
+            if opts.h1_title_case_headers {
+                conn.set_title_case_headers();
+            }
+            if opts.h1_preserve_header_case {
+                conn.set_preserve_header_case();
+            }
+            #[cfg(feature = "ffi")]
+            if opts.h1_preserve_header_order {
+                conn.set_preserve_header_order();
+            }
+
+            if opts.h09_responses {
+                conn.set_h09_responses();
+            }
+
+            if let Some(sz) = opts.h1_read_buf_exact_size {
+                conn.set_read_buf_exact_size(sz);
+            }
+            if let Some(max) = opts.h1_max_buf_size {
+                conn.set_max_buf_size(max);
+            }
+            let cd = proto::h1::dispatch::Client::new(rx);
+            let proto = proto::h1::Dispatcher::new(cd, conn);
+
+            Ok((
+                SendRequest { dispatch: tx },
+                Connection { inner: Some(proto) },
+            ))
+        }
+    }
+}
diff --git a/src/client/conn/http2.rs b/src/client/conn/http2.rs
new file mode 100644
index 0000000..5697e9e
--- /dev/null
+++ b/src/client/conn/http2.rs
@@ -0,0 +1,420 @@
+//! HTTP/2 client connections
+
+use std::error::Error as StdError;
+use std::fmt;
+use std::future::Future;
+use std::marker::PhantomData;
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::sync::Arc;
+use std::task::{Context, Poll};
+use std::time::Duration;
+
+use http::{Request, Response};
+use tokio::io::{AsyncRead, AsyncWrite};
+
+use super::super::dispatch;
+use crate::body::{Body as IncomingBody, HttpBody as Body};
+use crate::common::exec::{BoxSendFuture, Exec};
+use crate::proto;
+use crate::rt::Executor;
+
+/// The sender side of an established connection.
+pub struct SendRequest<B> {
+    dispatch: dispatch::UnboundedSender<Request<B>, Response<IncomingBody>>,
+}
+
+impl<B> Clone for SendRequest<B> {
+    fn clone(&self) -> SendRequest<B> {
+        SendRequest {
+            dispatch: self.dispatch.clone(),
+        }
+    }
+}
+
+/// A future that processes all HTTP state for the IO object.
+///
+/// In most cases, this should just be spawned into an executor, so that it
+/// can process incoming and outgoing messages, notice hangups, and the like.
+#[must_use = "futures do nothing unless polled"]
+pub struct Connection<T, B>
+where
+    T: AsyncRead + AsyncWrite + Send + 'static,
+    B: Body + 'static,
+{
+    inner: (PhantomData<T>, proto::h2::ClientTask<B>),
+}
+
+/// A builder to configure an HTTP connection.
+///
+/// After setting options, the builder is used to create a handshake future.
+#[derive(Clone, Debug)]
+pub struct Builder {
+    pub(super) exec: Exec,
+    h2_builder: proto::h2::client::Config,
+}
+
+/// Returns a handshake future over some IO.
+///
+/// This is a shortcut for `Builder::new().handshake(io)`.
+/// See [`client::conn`](crate::client::conn) for more.
+pub async fn handshake<E, T, B>(exec: E, io: T) -> crate::Result<(SendRequest<B>, Connection<T, B>)>
+where
+    E: Executor<BoxSendFuture> + Send + Sync + 'static,
+    T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    B: Body + 'static,
+    B::Data: Send,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    Builder::new(exec).handshake(io).await
+}
+
+// ===== impl SendRequest
+
+impl<B> SendRequest<B> {
+    /// Polls to determine whether this sender can be used yet for a request.
+    ///
+    /// If the associated connection is closed, this returns an Error.
+    pub fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        if self.is_closed() {
+            Poll::Ready(Err(crate::Error::new_closed()))
+        } else {
+            Poll::Ready(Ok(()))
+        }
+    }
+
+    /// Waits until the dispatcher is ready
+    ///
+    /// If the associated connection is closed, this returns an Error.
+    pub async fn ready(&mut self) -> crate::Result<()> {
+        futures_util::future::poll_fn(|cx| self.poll_ready(cx)).await
+    }
+
+    /*
+    pub(super) async fn when_ready(self) -> crate::Result<Self> {
+        let mut me = Some(self);
+        future::poll_fn(move |cx| {
+            ready!(me.as_mut().unwrap().poll_ready(cx))?;
+            Poll::Ready(Ok(me.take().unwrap()))
+        })
+        .await
+    }
+
+    pub(super) fn is_ready(&self) -> bool {
+        self.dispatch.is_ready()
+    }
+    */
+
+    pub(super) fn is_closed(&self) -> bool {
+        self.dispatch.is_closed()
+    }
+}
+
+impl<B> SendRequest<B>
+where
+    B: Body + 'static,
+{
+    /// Sends a `Request` on the associated connection.
+    ///
+    /// Returns a future that if successful, yields the `Response`.
+    ///
+    /// # Note
+    ///
+    /// There are some key differences in what automatic things the `Client`
+    /// does for you that will not be done here:
+    ///
+    /// - `Client` requires absolute-form `Uri`s, since the scheme and
+    ///   authority are needed to connect. They aren't required here.
+    /// - Since the `Client` requires absolute-form `Uri`s, it can add
+    ///   the `Host` header based on it. You must add a `Host` header yourself
+    ///   before calling this method.
+    /// - Since absolute-form `Uri`s are not required, if received, they will
+    ///   be serialized as-is.
+    pub fn send_request(
+        &mut self,
+        req: Request<B>,
+    ) -> impl Future<Output = crate::Result<Response<IncomingBody>>> {
+        let sent = self.dispatch.send(req);
+
+        async move {
+            match sent {
+                Ok(rx) => match rx.await {
+                    Ok(Ok(resp)) => Ok(resp),
+                    Ok(Err(err)) => Err(err),
+                    // this is definite bug if it happens, but it shouldn't happen!
+                    Err(_canceled) => panic!("dispatch dropped without returning error"),
+                },
+                Err(_req) => {
+                    tracing::debug!("connection was not ready");
+
+                    Err(crate::Error::new_canceled().with("connection was not ready"))
+                }
+            }
+        }
+    }
+
+    /*
+    pub(super) fn send_request_retryable(
+        &mut self,
+        req: Request<B>,
+    ) -> impl Future<Output = Result<Response<Body>, (crate::Error, Option<Request<B>>)>> + Unpin
+    where
+        B: Send,
+    {
+        match self.dispatch.try_send(req) {
+            Ok(rx) => {
+                Either::Left(rx.then(move |res| {
+                    match res {
+                        Ok(Ok(res)) => future::ok(res),
+                        Ok(Err(err)) => future::err(err),
+                        // this is definite bug if it happens, but it shouldn't happen!
+                        Err(_) => panic!("dispatch dropped without returning error"),
+                    }
+                }))
+            }
+            Err(req) => {
+                tracing::debug!("connection was not ready");
+                let err = crate::Error::new_canceled().with("connection was not ready");
+                Either::Right(future::err((err, Some(req))))
+            }
+        }
+    }
+    */
+}
+
+impl<B> fmt::Debug for SendRequest<B> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SendRequest").finish()
+    }
+}
+
+// ===== impl Connection
+
+impl<T, B> Connection<T, B>
+where
+    T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    B: Body + Unpin + Send + 'static,
+    B::Data: Send,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    /// Returns whether the [extended CONNECT protocol][1] is enabled or not.
+    ///
+    /// This setting is configured by the server peer by sending the
+    /// [`SETTINGS_ENABLE_CONNECT_PROTOCOL` parameter][2] in a `SETTINGS` frame.
+    /// This method returns the currently acknowledged value received from the
+    /// remote.
+    ///
+    /// [1]: https://datatracker.ietf.org/doc/html/rfc8441#section-4
+    /// [2]: https://datatracker.ietf.org/doc/html/rfc8441#section-3
+    pub fn is_extended_connect_protocol_enabled(&self) -> bool {
+        self.inner.1.is_extended_connect_protocol_enabled()
+    }
+}
+
+impl<T, B> fmt::Debug for Connection<T, B>
+where
+    T: AsyncRead + AsyncWrite + fmt::Debug + Send + 'static,
+    B: Body + 'static,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Connection").finish()
+    }
+}
+
+impl<T, B> Future for Connection<T, B>
+where
+    T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    B: Body + Send + 'static,
+    B::Data: Send,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type Output = crate::Result<()>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match ready!(Pin::new(&mut self.inner.1).poll(cx))? {
+            proto::Dispatched::Shutdown => Poll::Ready(Ok(())),
+            #[cfg(feature = "http1")]
+            proto::Dispatched::Upgrade(_pending) => unreachable!("http2 cannot upgrade"),
+        }
+    }
+}
+
+// ===== impl Builder
+
+impl Builder {
+    /// Creates a new connection builder.
+    #[inline]
+    pub fn new<E>(exec: E) -> Builder
+    where
+        E: Executor<BoxSendFuture> + Send + Sync + 'static,
+    {
+        use std::sync::Arc;
+        Builder {
+            exec: Exec::Executor(Arc::new(exec)),
+            h2_builder: Default::default(),
+        }
+    }
+
+    /// Provide an executor to execute background HTTP2 tasks.
+    pub fn executor<E>(&mut self, exec: E) -> &mut Builder
+    where
+        E: Executor<BoxSendFuture> + Send + Sync + 'static,
+    {
+        self.exec = Exec::Executor(Arc::new(exec));
+        self
+    }
+
+    /// Sets the [`SETTINGS_INITIAL_WINDOW_SIZE`][spec] option for HTTP2
+    /// stream-level flow control.
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    ///
+    /// [spec]: https://http2.github.io/http2-spec/#SETTINGS_INITIAL_WINDOW_SIZE
+    pub fn initial_stream_window_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
+        if let Some(sz) = sz.into() {
+            self.h2_builder.adaptive_window = false;
+            self.h2_builder.initial_stream_window_size = sz;
+        }
+        self
+    }
+
+    /// Sets the max connection-level flow control for HTTP2
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    pub fn initial_connection_window_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
+        if let Some(sz) = sz.into() {
+            self.h2_builder.adaptive_window = false;
+            self.h2_builder.initial_conn_window_size = sz;
+        }
+        self
+    }
+
+    /// Sets whether to use an adaptive flow control.
+    ///
+    /// Enabling this will override the limits set in
+    /// `initial_stream_window_size` and
+    /// `initial_connection_window_size`.
+    pub fn adaptive_window(&mut self, enabled: bool) -> &mut Self {
+        use proto::h2::SPEC_WINDOW_SIZE;
+
+        self.h2_builder.adaptive_window = enabled;
+        if enabled {
+            self.h2_builder.initial_conn_window_size = SPEC_WINDOW_SIZE;
+            self.h2_builder.initial_stream_window_size = SPEC_WINDOW_SIZE;
+        }
+        self
+    }
+
+    /// Sets the maximum frame size to use for HTTP2.
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    pub fn max_frame_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
+        if let Some(sz) = sz.into() {
+            self.h2_builder.max_frame_size = sz;
+        }
+        self
+    }
+
+    /// Sets an interval for HTTP2 Ping frames should be sent to keep a
+    /// connection alive.
+    ///
+    /// Pass `None` to disable HTTP2 keep-alive.
+    ///
+    /// Default is currently disabled.
+    #[cfg(feature = "runtime")]
+    pub fn keep_alive_interval(&mut self, interval: impl Into<Option<Duration>>) -> &mut Self {
+        self.h2_builder.keep_alive_interval = interval.into();
+        self
+    }
+
+    /// Sets a timeout for receiving an acknowledgement of the keep-alive ping.
+    ///
+    /// If the ping is not acknowledged within the timeout, the connection will
+    /// be closed. Does nothing if `keep_alive_interval` is disabled.
+    ///
+    /// Default is 20 seconds.
+    #[cfg(feature = "runtime")]
+    pub fn keep_alive_timeout(&mut self, timeout: Duration) -> &mut Self {
+        self.h2_builder.keep_alive_timeout = timeout;
+        self
+    }
+
+    /// Sets whether HTTP2 keep-alive should apply while the connection is idle.
+    ///
+    /// If disabled, keep-alive pings are only sent while there are open
+    /// request/responses streams. If enabled, pings are also sent when no
+    /// streams are active. Does nothing if `keep_alive_interval` is
+    /// disabled.
+    ///
+    /// Default is `false`.
+    #[cfg(feature = "runtime")]
+    pub fn keep_alive_while_idle(&mut self, enabled: bool) -> &mut Self {
+        self.h2_builder.keep_alive_while_idle = enabled;
+        self
+    }
+
+    /// Sets the maximum number of HTTP2 concurrent locally reset streams.
+    ///
+    /// See the documentation of [`h2::client::Builder::max_concurrent_reset_streams`] for more
+    /// details.
+    ///
+    /// The default value is determined by the `h2` crate.
+    ///
+    /// [`h2::client::Builder::max_concurrent_reset_streams`]: https://docs.rs/h2/client/struct.Builder.html#method.max_concurrent_reset_streams
+    pub fn max_concurrent_reset_streams(&mut self, max: usize) -> &mut Self {
+        self.h2_builder.max_concurrent_reset_streams = Some(max);
+        self
+    }
+
+    /// Set the maximum write buffer size for each HTTP/2 stream.
+    ///
+    /// Default is currently 1MB, but may change.
+    ///
+    /// # Panics
+    ///
+    /// The value must be no larger than `u32::MAX`.
+    pub fn max_send_buf_size(&mut self, max: usize) -> &mut Self {
+        assert!(max <= std::u32::MAX as usize);
+        self.h2_builder.max_send_buffer_size = max;
+        self
+    }
+
+    /// Constructs a connection with the configured options and IO.
+    /// See [`client::conn`](crate::client::conn) for more.
+    ///
+    /// Note, if [`Connection`] is not `await`-ed, [`SendRequest`] will
+    /// do nothing.
+    pub fn handshake<T, B>(
+        &self,
+        io: T,
+    ) -> impl Future<Output = crate::Result<(SendRequest<B>, Connection<T, B>)>>
+    where
+        T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+        B: Body + 'static,
+        B::Data: Send,
+        B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    {
+        let opts = self.clone();
+
+        async move {
+            tracing::trace!("client handshake HTTP/1");
+
+            let (tx, rx) = dispatch::channel();
+            let h2 = proto::h2::client::handshake(io, rx, &opts.h2_builder, opts.exec).await?;
+            Ok((
+                SendRequest {
+                    dispatch: tx.unbound(),
+                },
+                Connection {
+                    inner: (PhantomData, h2),
+                },
+            ))
+        }
+    }
+}
diff --git a/src/client/connect/dns.rs b/src/client/connect/dns.rs
new file mode 100644
index 0000000..50245de
--- /dev/null
+++ b/src/client/connect/dns.rs
@@ -0,0 +1,427 @@
+//! DNS Resolution used by the `HttpConnector`.
+//!
+//! This module contains:
+//!
+//! - A [`GaiResolver`](GaiResolver) that is the default resolver for the
+//!   `HttpConnector`.
+//! - The `Name` type used as an argument to custom resolvers.
+//!
+//! # Resolvers are `Service`s
+//!
+//! A resolver is just a
+//! `Service<Name, Response = impl Iterator<Item = SocketAddr>>`.
+//!
+//! A simple resolver that ignores the name and always returns a specific
+//! address:
+//!
+//! ```rust,ignore
+//! use std::{convert::Infallible, iter, net::SocketAddr};
+//!
+//! let resolver = tower::service_fn(|_name| async {
+//!     Ok::<_, Infallible>(iter::once(SocketAddr::from(([127, 0, 0, 1], 8080))))
+//! });
+//! ```
+use std::error::Error;
+use std::future::Future;
+use std::net::{Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV6, ToSocketAddrs};
+use std::pin::Pin;
+use std::str::FromStr;
+use std::task::{Context, Poll};
+use std::{fmt, io, vec};
+
+use tokio::task::JoinHandle;
+use tower_service::Service;
+use tracing::debug;
+
+pub(super) use self::sealed::Resolve;
+
+/// A domain name to resolve into IP addresses.
+#[derive(Clone, Hash, Eq, PartialEq)]
+pub struct Name {
+    host: Box<str>,
+}
+
+/// A resolver using blocking `getaddrinfo` calls in a threadpool.
+#[derive(Clone)]
+pub struct GaiResolver {
+    _priv: (),
+}
+
+/// An iterator of IP addresses returned from `getaddrinfo`.
+pub struct GaiAddrs {
+    inner: SocketAddrs,
+}
+
+/// A future to resolve a name returned by `GaiResolver`.
+pub struct GaiFuture {
+    inner: JoinHandle<Result<SocketAddrs, io::Error>>,
+}
+
+impl Name {
+    pub(super) fn new(host: Box<str>) -> Name {
+        Name { host }
+    }
+
+    /// View the hostname as a string slice.
+    pub fn as_str(&self) -> &str {
+        &self.host
+    }
+}
+
+impl fmt::Debug for Name {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&self.host, f)
+    }
+}
+
+impl fmt::Display for Name {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.host, f)
+    }
+}
+
+impl FromStr for Name {
+    type Err = InvalidNameError;
+
+    fn from_str(host: &str) -> Result<Self, Self::Err> {
+        // Possibly add validation later
+        Ok(Name::new(host.into()))
+    }
+}
+
+/// Error indicating a given string was not a valid domain name.
+#[derive(Debug)]
+pub struct InvalidNameError(());
+
+impl fmt::Display for InvalidNameError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("Not a valid domain name")
+    }
+}
+
+impl Error for InvalidNameError {}
+
+impl GaiResolver {
+    /// Construct a new `GaiResolver`.
+    pub fn new() -> Self {
+        GaiResolver { _priv: () }
+    }
+}
+
+impl Service<Name> for GaiResolver {
+    type Response = GaiAddrs;
+    type Error = io::Error;
+    type Future = GaiFuture;
+
+    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, name: Name) -> Self::Future {
+        let blocking = tokio::task::spawn_blocking(move || {
+            debug!("resolving host={:?}", name.host);
+            (&*name.host, 0)
+                .to_socket_addrs()
+                .map(|i| SocketAddrs { iter: i })
+        });
+
+        GaiFuture { inner: blocking }
+    }
+}
+
+impl fmt::Debug for GaiResolver {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("GaiResolver")
+    }
+}
+
+impl Future for GaiFuture {
+    type Output = Result<GaiAddrs, io::Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Pin::new(&mut self.inner).poll(cx).map(|res| match res {
+            Ok(Ok(addrs)) => Ok(GaiAddrs { inner: addrs }),
+            Ok(Err(err)) => Err(err),
+            Err(join_err) => {
+                if join_err.is_cancelled() {
+                    Err(io::Error::new(io::ErrorKind::Interrupted, join_err))
+                } else {
+                    panic!("gai background task failed: {:?}", join_err)
+                }
+            }
+        })
+    }
+}
+
+impl fmt::Debug for GaiFuture {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("GaiFuture")
+    }
+}
+
+impl Drop for GaiFuture {
+    fn drop(&mut self) {
+        self.inner.abort();
+    }
+}
+
+impl Iterator for GaiAddrs {
+    type Item = SocketAddr;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next()
+    }
+}
+
+impl fmt::Debug for GaiAddrs {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("GaiAddrs")
+    }
+}
+
+pub(super) struct SocketAddrs {
+    iter: vec::IntoIter<SocketAddr>,
+}
+
+impl SocketAddrs {
+    pub(super) fn new(addrs: Vec<SocketAddr>) -> Self {
+        SocketAddrs {
+            iter: addrs.into_iter(),
+        }
+    }
+
+    pub(super) fn try_parse(host: &str, port: u16) -> Option<SocketAddrs> {
+        if let Ok(addr) = host.parse::<Ipv4Addr>() {
+            let addr = SocketAddrV4::new(addr, port);
+            return Some(SocketAddrs {
+                iter: vec![SocketAddr::V4(addr)].into_iter(),
+            });
+        }
+        if let Ok(addr) = host.parse::<Ipv6Addr>() {
+            let addr = SocketAddrV6::new(addr, port, 0, 0);
+            return Some(SocketAddrs {
+                iter: vec![SocketAddr::V6(addr)].into_iter(),
+            });
+        }
+        None
+    }
+
+    #[inline]
+    fn filter(self, predicate: impl FnMut(&SocketAddr) -> bool) -> SocketAddrs {
+        SocketAddrs::new(self.iter.filter(predicate).collect())
+    }
+
+    pub(super) fn split_by_preference(
+        self,
+        local_addr_ipv4: Option<Ipv4Addr>,
+        local_addr_ipv6: Option<Ipv6Addr>,
+    ) -> (SocketAddrs, SocketAddrs) {
+        match (local_addr_ipv4, local_addr_ipv6) {
+            (Some(_), None) => (self.filter(SocketAddr::is_ipv4), SocketAddrs::new(vec![])),
+            (None, Some(_)) => (self.filter(SocketAddr::is_ipv6), SocketAddrs::new(vec![])),
+            _ => {
+                let preferring_v6 = self
+                    .iter
+                    .as_slice()
+                    .first()
+                    .map(SocketAddr::is_ipv6)
+                    .unwrap_or(false);
+
+                let (preferred, fallback) = self
+                    .iter
+                    .partition::<Vec<_>, _>(|addr| addr.is_ipv6() == preferring_v6);
+
+                (SocketAddrs::new(preferred), SocketAddrs::new(fallback))
+            }
+        }
+    }
+
+    pub(super) fn is_empty(&self) -> bool {
+        self.iter.as_slice().is_empty()
+    }
+
+    pub(super) fn len(&self) -> usize {
+        self.iter.as_slice().len()
+    }
+}
+
+impl Iterator for SocketAddrs {
+    type Item = SocketAddr;
+    #[inline]
+    fn next(&mut self) -> Option<SocketAddr> {
+        self.iter.next()
+    }
+}
+
+/*
+/// A resolver using `getaddrinfo` calls via the `tokio_executor::threadpool::blocking` API.
+///
+/// Unlike the `GaiResolver` this will not spawn dedicated threads, but only works when running on the
+/// multi-threaded Tokio runtime.
+#[cfg(feature = "runtime")]
+#[derive(Clone, Debug)]
+pub struct TokioThreadpoolGaiResolver(());
+
+/// The future returned by `TokioThreadpoolGaiResolver`.
+#[cfg(feature = "runtime")]
+#[derive(Debug)]
+pub struct TokioThreadpoolGaiFuture {
+    name: Name,
+}
+
+#[cfg(feature = "runtime")]
+impl TokioThreadpoolGaiResolver {
+    /// Creates a new DNS resolver that will use tokio threadpool's blocking
+    /// feature.
+    ///
+    /// **Requires** its futures to be run on the threadpool runtime.
+    pub fn new() -> Self {
+        TokioThreadpoolGaiResolver(())
+    }
+}
+
+#[cfg(feature = "runtime")]
+impl Service<Name> for TokioThreadpoolGaiResolver {
+    type Response = GaiAddrs;
+    type Error = io::Error;
+    type Future = TokioThreadpoolGaiFuture;
+
+    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, name: Name) -> Self::Future {
+        TokioThreadpoolGaiFuture { name }
+    }
+}
+
+#[cfg(feature = "runtime")]
+impl Future for TokioThreadpoolGaiFuture {
+    type Output = Result<GaiAddrs, io::Error>;
+
+    fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match ready!(tokio_executor::threadpool::blocking(|| (
+            self.name.as_str(),
+            0
+        )
+            .to_socket_addrs()))
+        {
+            Ok(Ok(iter)) => Poll::Ready(Ok(GaiAddrs {
+                inner: IpAddrs { iter },
+            })),
+            Ok(Err(e)) => Poll::Ready(Err(e)),
+            // a BlockingError, meaning not on a tokio_executor::threadpool :(
+            Err(e) => Poll::Ready(Err(io::Error::new(io::ErrorKind::Other, e))),
+        }
+    }
+}
+*/
+
+mod sealed {
+    use std::future::Future;
+    use std::task::{Context, Poll};
+
+    use super::{Name, SocketAddr};
+    use tower_service::Service;
+
+    // "Trait alias" for `Service<Name, Response = Addrs>`
+    pub trait Resolve {
+        type Addrs: Iterator<Item = SocketAddr>;
+        type Error: Into<Box<dyn std::error::Error + Send + Sync>>;
+        type Future: Future<Output = Result<Self::Addrs, Self::Error>>;
+
+        fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>;
+        fn resolve(&mut self, name: Name) -> Self::Future;
+    }
+
+    impl<S> Resolve for S
+    where
+        S: Service<Name>,
+        S::Response: Iterator<Item = SocketAddr>,
+        S::Error: Into<Box<dyn std::error::Error + Send + Sync>>,
+    {
+        type Addrs = S::Response;
+        type Error = S::Error;
+        type Future = S::Future;
+
+        fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+            Service::poll_ready(self, cx)
+        }
+
+        fn resolve(&mut self, name: Name) -> Self::Future {
+            Service::call(self, name)
+        }
+    }
+}
+
+pub(super) async fn resolve<R>(resolver: &mut R, name: Name) -> Result<R::Addrs, R::Error>
+where
+    R: Resolve,
+{
+    futures_util::future::poll_fn(|cx| resolver.poll_ready(cx)).await?;
+    resolver.resolve(name).await
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::net::{Ipv4Addr, Ipv6Addr};
+
+    #[test]
+    fn test_ip_addrs_split_by_preference() {
+        let ip_v4 = Ipv4Addr::new(127, 0, 0, 1);
+        let ip_v6 = Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1);
+        let v4_addr = (ip_v4, 80).into();
+        let v6_addr = (ip_v6, 80).into();
+
+        let (mut preferred, mut fallback) = SocketAddrs {
+            iter: vec![v4_addr, v6_addr].into_iter(),
+        }
+        .split_by_preference(None, None);
+        assert!(preferred.next().unwrap().is_ipv4());
+        assert!(fallback.next().unwrap().is_ipv6());
+
+        let (mut preferred, mut fallback) = SocketAddrs {
+            iter: vec![v6_addr, v4_addr].into_iter(),
+        }
+        .split_by_preference(None, None);
+        assert!(preferred.next().unwrap().is_ipv6());
+        assert!(fallback.next().unwrap().is_ipv4());
+
+        let (mut preferred, mut fallback) = SocketAddrs {
+            iter: vec![v4_addr, v6_addr].into_iter(),
+        }
+        .split_by_preference(Some(ip_v4), Some(ip_v6));
+        assert!(preferred.next().unwrap().is_ipv4());
+        assert!(fallback.next().unwrap().is_ipv6());
+
+        let (mut preferred, mut fallback) = SocketAddrs {
+            iter: vec![v6_addr, v4_addr].into_iter(),
+        }
+        .split_by_preference(Some(ip_v4), Some(ip_v6));
+        assert!(preferred.next().unwrap().is_ipv6());
+        assert!(fallback.next().unwrap().is_ipv4());
+
+        let (mut preferred, fallback) = SocketAddrs {
+            iter: vec![v4_addr, v6_addr].into_iter(),
+        }
+        .split_by_preference(Some(ip_v4), None);
+        assert!(preferred.next().unwrap().is_ipv4());
+        assert!(fallback.is_empty());
+
+        let (mut preferred, fallback) = SocketAddrs {
+            iter: vec![v4_addr, v6_addr].into_iter(),
+        }
+        .split_by_preference(None, Some(ip_v6));
+        assert!(preferred.next().unwrap().is_ipv6());
+        assert!(fallback.is_empty());
+    }
+
+    #[test]
+    fn test_name_from_str() {
+        const DOMAIN: &str = "test.example.com";
+        let name = Name::from_str(DOMAIN).expect("Should be a valid domain");
+        assert_eq!(name.as_str(), DOMAIN);
+        assert_eq!(name.to_string(), DOMAIN);
+    }
+}
diff --git a/src/client/connect/http.rs b/src/client/connect/http.rs
new file mode 100644
index 0000000..ee09afe
--- /dev/null
+++ b/src/client/connect/http.rs
@@ -0,0 +1,1012 @@
+use std::error::Error as StdError;
+use std::fmt;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomData;
+use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr};
+use std::pin::Pin;
+use std::sync::Arc;
+use std::task::{self, Poll};
+use std::time::Duration;
+
+use futures_util::future::Either;
+use http::uri::{Scheme, Uri};
+use pin_project_lite::pin_project;
+use tokio::net::{TcpSocket, TcpStream};
+use tokio::time::Sleep;
+use tracing::{debug, trace, warn};
+
+use super::dns::{self, resolve, GaiResolver, Resolve};
+use super::{Connected, Connection};
+//#[cfg(feature = "runtime")] use super::dns::TokioThreadpoolGaiResolver;
+
+/// A connector for the `http` scheme.
+///
+/// Performs DNS resolution in a thread pool, and then connects over TCP.
+///
+/// # Note
+///
+/// Sets the [`HttpInfo`](HttpInfo) value on responses, which includes
+/// transport information such as the remote socket address used.
+#[cfg_attr(docsrs, doc(cfg(feature = "tcp")))]
+#[derive(Clone)]
+pub struct HttpConnector<R = GaiResolver> {
+    config: Arc<Config>,
+    resolver: R,
+}
+
+/// Extra information about the transport when an HttpConnector is used.
+///
+/// # Example
+///
+/// ```
+/// # async fn doc() -> hyper::Result<()> {
+/// use hyper::Uri;
+/// use hyper::client::{Client, connect::HttpInfo};
+///
+/// let client = Client::new();
+/// let uri = Uri::from_static("http://example.com");
+///
+/// let res = client.get(uri).await?;
+/// res
+///     .extensions()
+///     .get::<HttpInfo>()
+///     .map(|info| {
+///         println!("remote addr = {}", info.remote_addr());
+///     });
+/// # Ok(())
+/// # }
+/// ```
+///
+/// # Note
+///
+/// If a different connector is used besides [`HttpConnector`](HttpConnector),
+/// this value will not exist in the extensions. Consult that specific
+/// connector to see what "extra" information it might provide to responses.
+#[derive(Clone, Debug)]
+pub struct HttpInfo {
+    remote_addr: SocketAddr,
+    local_addr: SocketAddr,
+}
+
+#[derive(Clone)]
+struct Config {
+    connect_timeout: Option<Duration>,
+    enforce_http: bool,
+    happy_eyeballs_timeout: Option<Duration>,
+    keep_alive_timeout: Option<Duration>,
+    local_address_ipv4: Option<Ipv4Addr>,
+    local_address_ipv6: Option<Ipv6Addr>,
+    nodelay: bool,
+    reuse_address: bool,
+    send_buffer_size: Option<usize>,
+    recv_buffer_size: Option<usize>,
+}
+
+// ===== impl HttpConnector =====
+
+impl HttpConnector {
+    /// Construct a new HttpConnector.
+    pub fn new() -> HttpConnector {
+        HttpConnector::new_with_resolver(GaiResolver::new())
+    }
+}
+
+/*
+#[cfg(feature = "runtime")]
+impl HttpConnector<TokioThreadpoolGaiResolver> {
+    /// Construct a new HttpConnector using the `TokioThreadpoolGaiResolver`.
+    ///
+    /// This resolver **requires** the threadpool runtime to be used.
+    pub fn new_with_tokio_threadpool_resolver() -> Self {
+        HttpConnector::new_with_resolver(TokioThreadpoolGaiResolver::new())
+    }
+}
+*/
+
+impl<R> HttpConnector<R> {
+    /// Construct a new HttpConnector.
+    ///
+    /// Takes a [`Resolver`](crate::client::connect::dns#resolvers-are-services) to handle DNS lookups.
+    pub fn new_with_resolver(resolver: R) -> HttpConnector<R> {
+        HttpConnector {
+            config: Arc::new(Config {
+                connect_timeout: None,
+                enforce_http: true,
+                happy_eyeballs_timeout: Some(Duration::from_millis(300)),
+                keep_alive_timeout: None,
+                local_address_ipv4: None,
+                local_address_ipv6: None,
+                nodelay: false,
+                reuse_address: false,
+                send_buffer_size: None,
+                recv_buffer_size: None,
+            }),
+            resolver,
+        }
+    }
+
+    /// Option to enforce all `Uri`s have the `http` scheme.
+    ///
+    /// Enabled by default.
+    #[inline]
+    pub fn enforce_http(&mut self, is_enforced: bool) {
+        self.config_mut().enforce_http = is_enforced;
+    }
+
+    /// Set that all sockets have `SO_KEEPALIVE` set with the supplied duration.
+    ///
+    /// If `None`, the option will not be set.
+    ///
+    /// Default is `None`.
+    #[inline]
+    pub fn set_keepalive(&mut self, dur: Option<Duration>) {
+        self.config_mut().keep_alive_timeout = dur;
+    }
+
+    /// Set that all sockets have `SO_NODELAY` set to the supplied value `nodelay`.
+    ///
+    /// Default is `false`.
+    #[inline]
+    pub fn set_nodelay(&mut self, nodelay: bool) {
+        self.config_mut().nodelay = nodelay;
+    }
+
+    /// Sets the value of the SO_SNDBUF option on the socket.
+    #[inline]
+    pub fn set_send_buffer_size(&mut self, size: Option<usize>) {
+        self.config_mut().send_buffer_size = size;
+    }
+
+    /// Sets the value of the SO_RCVBUF option on the socket.
+    #[inline]
+    pub fn set_recv_buffer_size(&mut self, size: Option<usize>) {
+        self.config_mut().recv_buffer_size = size;
+    }
+
+    /// Set that all sockets are bound to the configured address before connection.
+    ///
+    /// If `None`, the sockets will not be bound.
+    ///
+    /// Default is `None`.
+    #[inline]
+    pub fn set_local_address(&mut self, addr: Option<IpAddr>) {
+        let (v4, v6) = match addr {
+            Some(IpAddr::V4(a)) => (Some(a), None),
+            Some(IpAddr::V6(a)) => (None, Some(a)),
+            _ => (None, None),
+        };
+
+        let cfg = self.config_mut();
+
+        cfg.local_address_ipv4 = v4;
+        cfg.local_address_ipv6 = v6;
+    }
+
+    /// Set that all sockets are bound to the configured IPv4 or IPv6 address (depending on host's
+    /// preferences) before connection.
+    #[inline]
+    pub fn set_local_addresses(&mut self, addr_ipv4: Ipv4Addr, addr_ipv6: Ipv6Addr) {
+        let cfg = self.config_mut();
+
+        cfg.local_address_ipv4 = Some(addr_ipv4);
+        cfg.local_address_ipv6 = Some(addr_ipv6);
+    }
+
+    /// Set the connect timeout.
+    ///
+    /// If a domain resolves to multiple IP addresses, the timeout will be
+    /// evenly divided across them.
+    ///
+    /// Default is `None`.
+    #[inline]
+    pub fn set_connect_timeout(&mut self, dur: Option<Duration>) {
+        self.config_mut().connect_timeout = dur;
+    }
+
+    /// Set timeout for [RFC 6555 (Happy Eyeballs)][RFC 6555] algorithm.
+    ///
+    /// If hostname resolves to both IPv4 and IPv6 addresses and connection
+    /// cannot be established using preferred address family before timeout
+    /// elapses, then connector will in parallel attempt connection using other
+    /// address family.
+    ///
+    /// If `None`, parallel connection attempts are disabled.
+    ///
+    /// Default is 300 milliseconds.
+    ///
+    /// [RFC 6555]: https://tools.ietf.org/html/rfc6555
+    #[inline]
+    pub fn set_happy_eyeballs_timeout(&mut self, dur: Option<Duration>) {
+        self.config_mut().happy_eyeballs_timeout = dur;
+    }
+
+    /// Set that all socket have `SO_REUSEADDR` set to the supplied value `reuse_address`.
+    ///
+    /// Default is `false`.
+    #[inline]
+    pub fn set_reuse_address(&mut self, reuse_address: bool) -> &mut Self {
+        self.config_mut().reuse_address = reuse_address;
+        self
+    }
+
+    // private
+
+    fn config_mut(&mut self) -> &mut Config {
+        // If the are HttpConnector clones, this will clone the inner
+        // config. So mutating the config won't ever affect previous
+        // clones.
+        Arc::make_mut(&mut self.config)
+    }
+}
+
+static INVALID_NOT_HTTP: &str = "invalid URL, scheme is not http";
+static INVALID_MISSING_SCHEME: &str = "invalid URL, scheme is missing";
+static INVALID_MISSING_HOST: &str = "invalid URL, host is missing";
+
+// R: Debug required for now to allow adding it to debug output later...
+impl<R: fmt::Debug> fmt::Debug for HttpConnector<R> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("HttpConnector").finish()
+    }
+}
+
+impl<R> tower_service::Service<Uri> for HttpConnector<R>
+where
+    R: Resolve + Clone + Send + Sync + 'static,
+    R::Future: Send,
+{
+    type Response = TcpStream;
+    type Error = ConnectError;
+    type Future = HttpConnecting<R>;
+
+    fn poll_ready(&mut self, cx: &mut task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        ready!(self.resolver.poll_ready(cx)).map_err(ConnectError::dns)?;
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, dst: Uri) -> Self::Future {
+        let mut self_ = self.clone();
+        HttpConnecting {
+            fut: Box::pin(async move { self_.call_async(dst).await }),
+            _marker: PhantomData,
+        }
+    }
+}
+
+fn get_host_port<'u>(config: &Config, dst: &'u Uri) -> Result<(&'u str, u16), ConnectError> {
+    trace!(
+        "Http::connect; scheme={:?}, host={:?}, port={:?}",
+        dst.scheme(),
+        dst.host(),
+        dst.port(),
+    );
+
+    if config.enforce_http {
+        if dst.scheme() != Some(&Scheme::HTTP) {
+            return Err(ConnectError {
+                msg: INVALID_NOT_HTTP.into(),
+                cause: None,
+            });
+        }
+    } else if dst.scheme().is_none() {
+        return Err(ConnectError {
+            msg: INVALID_MISSING_SCHEME.into(),
+            cause: None,
+        });
+    }
+
+    let host = match dst.host() {
+        Some(s) => s,
+        None => {
+            return Err(ConnectError {
+                msg: INVALID_MISSING_HOST.into(),
+                cause: None,
+            })
+        }
+    };
+    let port = match dst.port() {
+        Some(port) => port.as_u16(),
+        None => {
+            if dst.scheme() == Some(&Scheme::HTTPS) {
+                443
+            } else {
+                80
+            }
+        }
+    };
+
+    Ok((host, port))
+}
+
+impl<R> HttpConnector<R>
+where
+    R: Resolve,
+{
+    async fn call_async(&mut self, dst: Uri) -> Result<TcpStream, ConnectError> {
+        let config = &self.config;
+
+        let (host, port) = get_host_port(config, &dst)?;
+        let host = host.trim_start_matches('[').trim_end_matches(']');
+
+        // If the host is already an IP addr (v4 or v6),
+        // skip resolving the dns and start connecting right away.
+        let addrs = if let Some(addrs) = dns::SocketAddrs::try_parse(host, port) {
+            addrs
+        } else {
+            let addrs = resolve(&mut self.resolver, dns::Name::new(host.into()))
+                .await
+                .map_err(ConnectError::dns)?;
+            let addrs = addrs
+                .map(|mut addr| {
+                    addr.set_port(port);
+                    addr
+                })
+                .collect();
+            dns::SocketAddrs::new(addrs)
+        };
+
+        let c = ConnectingTcp::new(addrs, config);
+
+        let sock = c.connect().await?;
+
+        if let Err(e) = sock.set_nodelay(config.nodelay) {
+            warn!("tcp set_nodelay error: {}", e);
+        }
+
+        Ok(sock)
+    }
+}
+
+impl Connection for TcpStream {
+    fn connected(&self) -> Connected {
+        let connected = Connected::new();
+        if let (Ok(remote_addr), Ok(local_addr)) = (self.peer_addr(), self.local_addr()) {
+            connected.extra(HttpInfo {
+                remote_addr,
+                local_addr,
+            })
+        } else {
+            connected
+        }
+    }
+}
+
+impl HttpInfo {
+    /// Get the remote address of the transport used.
+    pub fn remote_addr(&self) -> SocketAddr {
+        self.remote_addr
+    }
+
+    /// Get the local address of the transport used.
+    pub fn local_addr(&self) -> SocketAddr {
+        self.local_addr
+    }
+}
+
+pin_project! {
+    // Not publicly exported (so missing_docs doesn't trigger).
+    //
+    // We return this `Future` instead of the `Pin<Box<dyn Future>>` directly
+    // so that users don't rely on it fitting in a `Pin<Box<dyn Future>>` slot
+    // (and thus we can change the type in the future).
+    #[must_use = "futures do nothing unless polled"]
+    #[allow(missing_debug_implementations)]
+    pub struct HttpConnecting<R> {
+        #[pin]
+        fut: BoxConnecting,
+        _marker: PhantomData<R>,
+    }
+}
+
+type ConnectResult = Result<TcpStream, ConnectError>;
+type BoxConnecting = Pin<Box<dyn Future<Output = ConnectResult> + Send>>;
+
+impl<R: Resolve> Future for HttpConnecting<R> {
+    type Output = ConnectResult;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
+        self.project().fut.poll(cx)
+    }
+}
+
+// Not publicly exported (so missing_docs doesn't trigger).
+pub struct ConnectError {
+    msg: Box<str>,
+    cause: Option<Box<dyn StdError + Send + Sync>>,
+}
+
+impl ConnectError {
+    fn new<S, E>(msg: S, cause: E) -> ConnectError
+    where
+        S: Into<Box<str>>,
+        E: Into<Box<dyn StdError + Send + Sync>>,
+    {
+        ConnectError {
+            msg: msg.into(),
+            cause: Some(cause.into()),
+        }
+    }
+
+    fn dns<E>(cause: E) -> ConnectError
+    where
+        E: Into<Box<dyn StdError + Send + Sync>>,
+    {
+        ConnectError::new("dns error", cause)
+    }
+
+    fn m<S, E>(msg: S) -> impl FnOnce(E) -> ConnectError
+    where
+        S: Into<Box<str>>,
+        E: Into<Box<dyn StdError + Send + Sync>>,
+    {
+        move |cause| ConnectError::new(msg, cause)
+    }
+}
+
+impl fmt::Debug for ConnectError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if let Some(ref cause) = self.cause {
+            f.debug_tuple("ConnectError")
+                .field(&self.msg)
+                .field(cause)
+                .finish()
+        } else {
+            self.msg.fmt(f)
+        }
+    }
+}
+
+impl fmt::Display for ConnectError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.msg)?;
+
+        if let Some(ref cause) = self.cause {
+            write!(f, ": {}", cause)?;
+        }
+
+        Ok(())
+    }
+}
+
+impl StdError for ConnectError {
+    fn source(&self) -> Option<&(dyn StdError + 'static)> {
+        self.cause.as_ref().map(|e| &**e as _)
+    }
+}
+
+struct ConnectingTcp<'a> {
+    preferred: ConnectingTcpRemote,
+    fallback: Option<ConnectingTcpFallback>,
+    config: &'a Config,
+}
+
+impl<'a> ConnectingTcp<'a> {
+    fn new(remote_addrs: dns::SocketAddrs, config: &'a Config) -> Self {
+        if let Some(fallback_timeout) = config.happy_eyeballs_timeout {
+            let (preferred_addrs, fallback_addrs) = remote_addrs
+                .split_by_preference(config.local_address_ipv4, config.local_address_ipv6);
+            if fallback_addrs.is_empty() {
+                return ConnectingTcp {
+                    preferred: ConnectingTcpRemote::new(preferred_addrs, config.connect_timeout),
+                    fallback: None,
+                    config,
+                };
+            }
+
+            ConnectingTcp {
+                preferred: ConnectingTcpRemote::new(preferred_addrs, config.connect_timeout),
+                fallback: Some(ConnectingTcpFallback {
+                    delay: tokio::time::sleep(fallback_timeout),
+                    remote: ConnectingTcpRemote::new(fallback_addrs, config.connect_timeout),
+                }),
+                config,
+            }
+        } else {
+            ConnectingTcp {
+                preferred: ConnectingTcpRemote::new(remote_addrs, config.connect_timeout),
+                fallback: None,
+                config,
+            }
+        }
+    }
+}
+
+struct ConnectingTcpFallback {
+    delay: Sleep,
+    remote: ConnectingTcpRemote,
+}
+
+struct ConnectingTcpRemote {
+    addrs: dns::SocketAddrs,
+    connect_timeout: Option<Duration>,
+}
+
+impl ConnectingTcpRemote {
+    fn new(addrs: dns::SocketAddrs, connect_timeout: Option<Duration>) -> Self {
+        let connect_timeout = connect_timeout
+            .map(|t| t.checked_div(addrs.len() as u32))
+            .flatten();
+
+        Self {
+            addrs,
+            connect_timeout,
+        }
+    }
+}
+
+impl ConnectingTcpRemote {
+    async fn connect(&mut self, config: &Config) -> Result<TcpStream, ConnectError> {
+        let mut err = None;
+        for addr in &mut self.addrs {
+            debug!("connecting to {}", addr);
+            match connect(&addr, config, self.connect_timeout)?.await {
+                Ok(tcp) => {
+                    debug!("connected to {}", addr);
+                    return Ok(tcp);
+                }
+                Err(e) => {
+                    trace!("connect error for {}: {:?}", addr, e);
+                    err = Some(e);
+                }
+            }
+        }
+
+        match err {
+            Some(e) => Err(e),
+            None => Err(ConnectError::new(
+                "tcp connect error",
+                std::io::Error::new(std::io::ErrorKind::NotConnected, "Network unreachable"),
+            )),
+        }
+    }
+}
+
+fn bind_local_address(
+    socket: &socket2::Socket,
+    dst_addr: &SocketAddr,
+    local_addr_ipv4: &Option<Ipv4Addr>,
+    local_addr_ipv6: &Option<Ipv6Addr>,
+) -> io::Result<()> {
+    match (*dst_addr, local_addr_ipv4, local_addr_ipv6) {
+        (SocketAddr::V4(_), Some(addr), _) => {
+            socket.bind(&SocketAddr::new(addr.clone().into(), 0).into())?;
+        }
+        (SocketAddr::V6(_), _, Some(addr)) => {
+            socket.bind(&SocketAddr::new(addr.clone().into(), 0).into())?;
+        }
+        _ => {
+            if cfg!(windows) {
+                // Windows requires a socket be bound before calling connect
+                let any: SocketAddr = match *dst_addr {
+                    SocketAddr::V4(_) => ([0, 0, 0, 0], 0).into(),
+                    SocketAddr::V6(_) => ([0, 0, 0, 0, 0, 0, 0, 0], 0).into(),
+                };
+                socket.bind(&any.into())?;
+            }
+        }
+    }
+
+    Ok(())
+}
+
+fn connect(
+    addr: &SocketAddr,
+    config: &Config,
+    connect_timeout: Option<Duration>,
+) -> Result<impl Future<Output = Result<TcpStream, ConnectError>>, ConnectError> {
+    // TODO(eliza): if Tokio's `TcpSocket` gains support for setting the
+    // keepalive timeout, it would be nice to use that instead of socket2,
+    // and avoid the unsafe `into_raw_fd`/`from_raw_fd` dance...
+    use socket2::{Domain, Protocol, Socket, TcpKeepalive, Type};
+    use std::convert::TryInto;
+
+    let domain = Domain::for_address(*addr);
+    let socket = Socket::new(domain, Type::STREAM, Some(Protocol::TCP))
+        .map_err(ConnectError::m("tcp open error"))?;
+
+    // When constructing a Tokio `TcpSocket` from a raw fd/socket, the user is
+    // responsible for ensuring O_NONBLOCK is set.
+    socket
+        .set_nonblocking(true)
+        .map_err(ConnectError::m("tcp set_nonblocking error"))?;
+
+    if let Some(dur) = config.keep_alive_timeout {
+        let conf = TcpKeepalive::new().with_time(dur);
+        if let Err(e) = socket.set_tcp_keepalive(&conf) {
+            warn!("tcp set_keepalive error: {}", e);
+        }
+    }
+
+    bind_local_address(
+        &socket,
+        addr,
+        &config.local_address_ipv4,
+        &config.local_address_ipv6,
+    )
+    .map_err(ConnectError::m("tcp bind local error"))?;
+
+    #[cfg(unix)]
+    let socket = unsafe {
+        // Safety: `from_raw_fd` is only safe to call if ownership of the raw
+        // file descriptor is transferred. Since we call `into_raw_fd` on the
+        // socket2 socket, it gives up ownership of the fd and will not close
+        // it, so this is safe.
+        use std::os::unix::io::{FromRawFd, IntoRawFd};
+        TcpSocket::from_raw_fd(socket.into_raw_fd())
+    };
+    #[cfg(windows)]
+    let socket = unsafe {
+        // Safety: `from_raw_socket` is only safe to call if ownership of the raw
+        // Windows SOCKET is transferred. Since we call `into_raw_socket` on the
+        // socket2 socket, it gives up ownership of the SOCKET and will not close
+        // it, so this is safe.
+        use std::os::windows::io::{FromRawSocket, IntoRawSocket};
+        TcpSocket::from_raw_socket(socket.into_raw_socket())
+    };
+
+    if config.reuse_address {
+        if let Err(e) = socket.set_reuseaddr(true) {
+            warn!("tcp set_reuse_address error: {}", e);
+        }
+    }
+
+    if let Some(size) = config.send_buffer_size {
+        if let Err(e) = socket.set_send_buffer_size(size.try_into().unwrap_or(std::u32::MAX)) {
+            warn!("tcp set_buffer_size error: {}", e);
+        }
+    }
+
+    if let Some(size) = config.recv_buffer_size {
+        if let Err(e) = socket.set_recv_buffer_size(size.try_into().unwrap_or(std::u32::MAX)) {
+            warn!("tcp set_recv_buffer_size error: {}", e);
+        }
+    }
+
+    let connect = socket.connect(*addr);
+    Ok(async move {
+        match connect_timeout {
+            Some(dur) => match tokio::time::timeout(dur, connect).await {
+                Ok(Ok(s)) => Ok(s),
+                Ok(Err(e)) => Err(e),
+                Err(e) => Err(io::Error::new(io::ErrorKind::TimedOut, e)),
+            },
+            None => connect.await,
+        }
+        .map_err(ConnectError::m("tcp connect error"))
+    })
+}
+
+impl ConnectingTcp<'_> {
+    async fn connect(mut self) -> Result<TcpStream, ConnectError> {
+        match self.fallback {
+            None => self.preferred.connect(self.config).await,
+            Some(mut fallback) => {
+                let preferred_fut = self.preferred.connect(self.config);
+                futures_util::pin_mut!(preferred_fut);
+
+                let fallback_fut = fallback.remote.connect(self.config);
+                futures_util::pin_mut!(fallback_fut);
+
+                let fallback_delay = fallback.delay;
+                futures_util::pin_mut!(fallback_delay);
+
+                let (result, future) =
+                    match futures_util::future::select(preferred_fut, fallback_delay).await {
+                        Either::Left((result, _fallback_delay)) => {
+                            (result, Either::Right(fallback_fut))
+                        }
+                        Either::Right(((), preferred_fut)) => {
+                            // Delay is done, start polling both the preferred and the fallback
+                            futures_util::future::select(preferred_fut, fallback_fut)
+                                .await
+                                .factor_first()
+                        }
+                    };
+
+                if result.is_err() {
+                    // Fallback to the remaining future (could be preferred or fallback)
+                    // if we get an error
+                    future.await
+                } else {
+                    result
+                }
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::io;
+
+    use ::http::Uri;
+
+    use super::super::sealed::{Connect, ConnectSvc};
+    use super::{Config, ConnectError, HttpConnector};
+
+    async fn connect<C>(
+        connector: C,
+        dst: Uri,
+    ) -> Result<<C::_Svc as ConnectSvc>::Connection, <C::_Svc as ConnectSvc>::Error>
+    where
+        C: Connect,
+    {
+        connector.connect(super::super::sealed::Internal, dst).await
+    }
+
+    #[tokio::test]
+    async fn test_errors_enforce_http() {
+        let dst = "https://example.domain/foo/bar?baz".parse().unwrap();
+        let connector = HttpConnector::new();
+
+        let err = connect(connector, dst).await.unwrap_err();
+        assert_eq!(&*err.msg, super::INVALID_NOT_HTTP);
+    }
+
+    #[cfg(any(target_os = "linux", target_os = "macos"))]
+    fn get_local_ips() -> (Option<std::net::Ipv4Addr>, Option<std::net::Ipv6Addr>) {
+        use std::net::{IpAddr, TcpListener};
+
+        let mut ip_v4 = None;
+        let mut ip_v6 = None;
+
+        let ips = pnet_datalink::interfaces()
+            .into_iter()
+            .flat_map(|i| i.ips.into_iter().map(|n| n.ip()));
+
+        for ip in ips {
+            match ip {
+                IpAddr::V4(ip) if TcpListener::bind((ip, 0)).is_ok() => ip_v4 = Some(ip),
+                IpAddr::V6(ip) if TcpListener::bind((ip, 0)).is_ok() => ip_v6 = Some(ip),
+                _ => (),
+            }
+
+            if ip_v4.is_some() && ip_v6.is_some() {
+                break;
+            }
+        }
+
+        (ip_v4, ip_v6)
+    }
+
+    #[tokio::test]
+    async fn test_errors_missing_scheme() {
+        let dst = "example.domain".parse().unwrap();
+        let mut connector = HttpConnector::new();
+        connector.enforce_http(false);
+
+        let err = connect(connector, dst).await.unwrap_err();
+        assert_eq!(&*err.msg, super::INVALID_MISSING_SCHEME);
+    }
+
+    // NOTE: pnet crate that we use in this test doesn't compile on Windows
+    #[cfg(any(target_os = "linux", target_os = "macos"))]
+    #[tokio::test]
+    async fn local_address() {
+        use std::net::{IpAddr, TcpListener};
+        let _ = pretty_env_logger::try_init();
+
+        let (bind_ip_v4, bind_ip_v6) = get_local_ips();
+        let server4 = TcpListener::bind("127.0.0.1:0").unwrap();
+        let port = server4.local_addr().unwrap().port();
+        let server6 = TcpListener::bind(&format!("[::1]:{}", port)).unwrap();
+
+        let assert_client_ip = |dst: String, server: TcpListener, expected_ip: IpAddr| async move {
+            let mut connector = HttpConnector::new();
+
+            match (bind_ip_v4, bind_ip_v6) {
+                (Some(v4), Some(v6)) => connector.set_local_addresses(v4, v6),
+                (Some(v4), None) => connector.set_local_address(Some(v4.into())),
+                (None, Some(v6)) => connector.set_local_address(Some(v6.into())),
+                _ => unreachable!(),
+            }
+
+            connect(connector, dst.parse().unwrap()).await.unwrap();
+
+            let (_, client_addr) = server.accept().unwrap();
+
+            assert_eq!(client_addr.ip(), expected_ip);
+        };
+
+        if let Some(ip) = bind_ip_v4 {
+            assert_client_ip(format!("http://127.0.0.1:{}", port), server4, ip.into()).await;
+        }
+
+        if let Some(ip) = bind_ip_v6 {
+            assert_client_ip(format!("http://[::1]:{}", port), server6, ip.into()).await;
+        }
+    }
+
+    #[test]
+    #[cfg_attr(not(feature = "__internal_happy_eyeballs_tests"), ignore)]
+    fn client_happy_eyeballs() {
+        use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, TcpListener};
+        use std::time::{Duration, Instant};
+
+        use super::dns;
+        use super::ConnectingTcp;
+
+        let _ = pretty_env_logger::try_init();
+        let server4 = TcpListener::bind("127.0.0.1:0").unwrap();
+        let addr = server4.local_addr().unwrap();
+        let _server6 = TcpListener::bind(&format!("[::1]:{}", addr.port())).unwrap();
+        let rt = tokio::runtime::Builder::new_current_thread()
+            .enable_all()
+            .build()
+            .unwrap();
+
+        let local_timeout = Duration::default();
+        let unreachable_v4_timeout = measure_connect(unreachable_ipv4_addr()).1;
+        let unreachable_v6_timeout = measure_connect(unreachable_ipv6_addr()).1;
+        let fallback_timeout = std::cmp::max(unreachable_v4_timeout, unreachable_v6_timeout)
+            + Duration::from_millis(250);
+
+        let scenarios = &[
+            // Fast primary, without fallback.
+            (&[local_ipv4_addr()][..], 4, local_timeout, false),
+            (&[local_ipv6_addr()][..], 6, local_timeout, false),
+            // Fast primary, with (unused) fallback.
+            (
+                &[local_ipv4_addr(), local_ipv6_addr()][..],
+                4,
+                local_timeout,
+                false,
+            ),
+            (
+                &[local_ipv6_addr(), local_ipv4_addr()][..],
+                6,
+                local_timeout,
+                false,
+            ),
+            // Unreachable + fast primary, without fallback.
+            (
+                &[unreachable_ipv4_addr(), local_ipv4_addr()][..],
+                4,
+                unreachable_v4_timeout,
+                false,
+            ),
+            (
+                &[unreachable_ipv6_addr(), local_ipv6_addr()][..],
+                6,
+                unreachable_v6_timeout,
+                false,
+            ),
+            // Unreachable + fast primary, with (unused) fallback.
+            (
+                &[
+                    unreachable_ipv4_addr(),
+                    local_ipv4_addr(),
+                    local_ipv6_addr(),
+                ][..],
+                4,
+                unreachable_v4_timeout,
+                false,
+            ),
+            (
+                &[
+                    unreachable_ipv6_addr(),
+                    local_ipv6_addr(),
+                    local_ipv4_addr(),
+                ][..],
+                6,
+                unreachable_v6_timeout,
+                true,
+            ),
+            // Slow primary, with (used) fallback.
+            (
+                &[slow_ipv4_addr(), local_ipv4_addr(), local_ipv6_addr()][..],
+                6,
+                fallback_timeout,
+                false,
+            ),
+            (
+                &[slow_ipv6_addr(), local_ipv6_addr(), local_ipv4_addr()][..],
+                4,
+                fallback_timeout,
+                true,
+            ),
+            // Slow primary, with (used) unreachable + fast fallback.
+            (
+                &[slow_ipv4_addr(), unreachable_ipv6_addr(), local_ipv6_addr()][..],
+                6,
+                fallback_timeout + unreachable_v6_timeout,
+                false,
+            ),
+            (
+                &[slow_ipv6_addr(), unreachable_ipv4_addr(), local_ipv4_addr()][..],
+                4,
+                fallback_timeout + unreachable_v4_timeout,
+                true,
+            ),
+        ];
+
+        // Scenarios for IPv6 -> IPv4 fallback require that host can access IPv6 network.
+        // Otherwise, connection to "slow" IPv6 address will error-out immediately.
+        let ipv6_accessible = measure_connect(slow_ipv6_addr()).0;
+
+        for &(hosts, family, timeout, needs_ipv6_access) in scenarios {
+            if needs_ipv6_access && !ipv6_accessible {
+                continue;
+            }
+
+            let (start, stream) = rt
+                .block_on(async move {
+                    let addrs = hosts
+                        .iter()
+                        .map(|host| (host.clone(), addr.port()).into())
+                        .collect();
+                    let cfg = Config {
+                        local_address_ipv4: None,
+                        local_address_ipv6: None,
+                        connect_timeout: None,
+                        keep_alive_timeout: None,
+                        happy_eyeballs_timeout: Some(fallback_timeout),
+                        nodelay: false,
+                        reuse_address: false,
+                        enforce_http: false,
+                        send_buffer_size: None,
+                        recv_buffer_size: None,
+                    };
+                    let connecting_tcp = ConnectingTcp::new(dns::SocketAddrs::new(addrs), &cfg);
+                    let start = Instant::now();
+                    Ok::<_, ConnectError>((start, ConnectingTcp::connect(connecting_tcp).await?))
+                })
+                .unwrap();
+            let res = if stream.peer_addr().unwrap().is_ipv4() {
+                4
+            } else {
+                6
+            };
+            let duration = start.elapsed();
+
+            // Allow actual duration to be +/- 150ms off.
+            let min_duration = if timeout >= Duration::from_millis(150) {
+                timeout - Duration::from_millis(150)
+            } else {
+                Duration::default()
+            };
+            let max_duration = timeout + Duration::from_millis(150);
+
+            assert_eq!(res, family);
+            assert!(duration >= min_duration);
+            assert!(duration <= max_duration);
+        }
+
+        fn local_ipv4_addr() -> IpAddr {
+            Ipv4Addr::new(127, 0, 0, 1).into()
+        }
+
+        fn local_ipv6_addr() -> IpAddr {
+            Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1).into()
+        }
+
+        fn unreachable_ipv4_addr() -> IpAddr {
+            Ipv4Addr::new(127, 0, 0, 2).into()
+        }
+
+        fn unreachable_ipv6_addr() -> IpAddr {
+            Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 2).into()
+        }
+
+        fn slow_ipv4_addr() -> IpAddr {
+            // RFC 6890 reserved IPv4 address.
+            Ipv4Addr::new(198, 18, 0, 25).into()
+        }
+
+        fn slow_ipv6_addr() -> IpAddr {
+            // RFC 6890 reserved IPv6 address.
+            Ipv6Addr::new(2001, 2, 0, 0, 0, 0, 0, 254).into()
+        }
+
+        fn measure_connect(addr: IpAddr) -> (bool, Duration) {
+            let start = Instant::now();
+            let result =
+                std::net::TcpStream::connect_timeout(&(addr, 80).into(), Duration::from_secs(1));
+
+            let reachable = result.is_ok() || result.unwrap_err().kind() == io::ErrorKind::TimedOut;
+            let duration = start.elapsed();
+            (reachable, duration)
+        }
+    }
+}
diff --git a/src/client/connect/mod.rs b/src/client/connect/mod.rs
new file mode 100644
index 0000000..4c29dd3
--- /dev/null
+++ b/src/client/connect/mod.rs
@@ -0,0 +1,640 @@
+//! Connectors used by the `Client`.
+//!
+//! This module contains:
+//!
+//! - A default [`HttpConnector`][] that does DNS resolution and establishes
+//!   connections over TCP.
+//! - Types to build custom connectors.
+//!
+//! # Connectors
+//!
+//! A "connector" is a [`Service`][] that takes a [`Uri`][] destination, and
+//! its `Response` is some type implementing [`AsyncRead`][], [`AsyncWrite`][],
+//! and [`Connection`][].
+//!
+//! ## Custom Connectors
+//!
+//! A simple connector that ignores the `Uri` destination and always returns
+//! a TCP connection to the same address could be written like this:
+//!
+//! ```rust,ignore
+//! let connector = tower::service_fn(|_dst| async {
+//!     tokio::net::TcpStream::connect("127.0.0.1:1337")
+//! })
+//! ```
+//!
+//! Or, fully written out:
+//!
+//! ```
+//! # #[cfg(feature = "runtime")]
+//! # mod rt {
+//! use std::{future::Future, net::SocketAddr, pin::Pin, task::{self, Poll}};
+//! use hyper::{service::Service, Uri};
+//! use tokio::net::TcpStream;
+//!
+//! #[derive(Clone)]
+//! struct LocalConnector;
+//!
+//! impl Service<Uri> for LocalConnector {
+//!     type Response = TcpStream;
+//!     type Error = std::io::Error;
+//!     // We can't "name" an `async` generated future.
+//!     type Future = Pin<Box<
+//!         dyn Future<Output = Result<Self::Response, Self::Error>> + Send
+//!     >>;
+//!
+//!     fn poll_ready(&mut self, _: &mut task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+//!         // This connector is always ready, but others might not be.
+//!         Poll::Ready(Ok(()))
+//!     }
+//!
+//!     fn call(&mut self, _: Uri) -> Self::Future {
+//!         Box::pin(TcpStream::connect(SocketAddr::from(([127, 0, 0, 1], 1337))))
+//!     }
+//! }
+//! # }
+//! ```
+//!
+//! It's worth noting that for `TcpStream`s, the [`HttpConnector`][] is a
+//! better starting place to extend from.
+//!
+//! Using either of the above connector examples, it can be used with the
+//! `Client` like this:
+//!
+//! ```
+//! # #[cfg(feature = "runtime")]
+//! # fn rt () {
+//! # let connector = hyper::client::HttpConnector::new();
+//! // let connector = ...
+//!
+//! let client = hyper::Client::builder()
+//!     .build::<_, hyper::Body>(connector);
+//! # }
+//! ```
+//!
+//!
+//! [`HttpConnector`]: HttpConnector
+//! [`Service`]: crate::service::Service
+//! [`Uri`]: ::http::Uri
+//! [`AsyncRead`]: tokio::io::AsyncRead
+//! [`AsyncWrite`]: tokio::io::AsyncWrite
+//! [`Connection`]: Connection
+use std::fmt;
+use std::fmt::{Debug, Formatter};
+use std::ops::Deref;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::Arc;
+
+use ::http::Extensions;
+use tokio::sync::watch;
+
+cfg_feature! {
+    #![feature = "tcp"]
+
+    pub use self::http::{HttpConnector, HttpInfo};
+
+    pub mod dns;
+    mod http;
+}
+
+cfg_feature! {
+    #![any(feature = "http1", feature = "http2")]
+
+    pub use self::sealed::Connect;
+}
+
+/// Describes a type returned by a connector.
+pub trait Connection {
+    /// Return metadata describing the connection.
+    fn connected(&self) -> Connected;
+}
+
+/// Extra information about the connected transport.
+///
+/// This can be used to inform recipients about things like if ALPN
+/// was used, or if connected to an HTTP proxy.
+#[derive(Debug)]
+pub struct Connected {
+    pub(super) alpn: Alpn,
+    pub(super) is_proxied: bool,
+    pub(super) extra: Option<Extra>,
+    pub(super) poisoned: PoisonPill,
+}
+
+#[derive(Clone)]
+pub(crate) struct PoisonPill {
+    poisoned: Arc<AtomicBool>,
+}
+
+impl Debug for PoisonPill {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        // print the address of the pill—this makes debugging issues much easier
+        write!(
+            f,
+            "PoisonPill@{:p} {{ poisoned: {} }}",
+            self.poisoned,
+            self.poisoned.load(Ordering::Relaxed)
+        )
+    }
+}
+
+impl PoisonPill {
+    pub(crate) fn healthy() -> Self {
+        Self {
+            poisoned: Arc::new(AtomicBool::new(false)),
+        }
+    }
+    pub(crate) fn poison(&self) {
+        self.poisoned.store(true, Ordering::Relaxed)
+    }
+
+    pub(crate) fn poisoned(&self) -> bool {
+        self.poisoned.load(Ordering::Relaxed)
+    }
+}
+
+/// [`CaptureConnection`] allows callers to capture [`Connected`] information
+///
+/// To capture a connection for a request, use [`capture_connection`].
+#[derive(Debug, Clone)]
+pub struct CaptureConnection {
+    rx: watch::Receiver<Option<Connected>>,
+}
+
+/// Capture the connection for a given request
+///
+/// When making a request with Hyper, the underlying connection must implement the [`Connection`] trait.
+/// [`capture_connection`] allows a caller to capture the returned [`Connected`] structure as soon
+/// as the connection is established.
+///
+/// *Note*: If establishing a connection fails, [`CaptureConnection::connection_metadata`] will always return none.
+///
+/// # Examples
+///
+/// **Synchronous access**:
+/// The [`CaptureConnection::connection_metadata`] method allows callers to check if a connection has been
+/// established. This is ideal for situations where you are certain the connection has already
+/// been established (e.g. after the response future has already completed).
+/// ```rust
+/// use hyper::client::connect::{capture_connection, CaptureConnection};
+/// let mut request = http::Request::builder()
+///   .uri("http://foo.com")
+///   .body(())
+///   .unwrap();
+///
+/// let captured_connection = capture_connection(&mut request);
+/// // some time later after the request has been sent...
+/// let connection_info = captured_connection.connection_metadata();
+/// println!("we are connected! {:?}", connection_info.as_ref());
+/// ```
+///
+/// **Asynchronous access**:
+/// The [`CaptureConnection::wait_for_connection_metadata`] method returns a future resolves as soon as the
+/// connection is available.
+///
+/// ```rust
+/// # #[cfg(feature  = "runtime")]
+/// # async fn example() {
+/// use hyper::client::connect::{capture_connection, CaptureConnection};
+/// let mut request = http::Request::builder()
+///   .uri("http://foo.com")
+///   .body(hyper::Body::empty())
+///   .unwrap();
+///
+/// let mut captured = capture_connection(&mut request);
+/// tokio::task::spawn(async move {
+///     let connection_info = captured.wait_for_connection_metadata().await;
+///     println!("we are connected! {:?}", connection_info.as_ref());
+/// });
+///
+/// let client = hyper::Client::new();
+/// client.request(request).await.expect("request failed");
+/// # }
+/// ```
+pub fn capture_connection<B>(request: &mut crate::http::Request<B>) -> CaptureConnection {
+    let (tx, rx) = CaptureConnection::new();
+    request.extensions_mut().insert(tx);
+    rx
+}
+
+/// TxSide for [`CaptureConnection`]
+///
+/// This is inserted into `Extensions` to allow Hyper to back channel connection info
+#[derive(Clone)]
+pub(crate) struct CaptureConnectionExtension {
+    tx: Arc<watch::Sender<Option<Connected>>>,
+}
+
+impl CaptureConnectionExtension {
+    pub(crate) fn set(&self, connected: &Connected) {
+        self.tx.send_replace(Some(connected.clone()));
+    }
+}
+
+impl CaptureConnection {
+    /// Internal API to create the tx and rx half of [`CaptureConnection`]
+    pub(crate) fn new() -> (CaptureConnectionExtension, Self) {
+        let (tx, rx) = watch::channel(None);
+        (
+            CaptureConnectionExtension { tx: Arc::new(tx) },
+            CaptureConnection { rx },
+        )
+    }
+
+    /// Retrieve the connection metadata, if available
+    pub fn connection_metadata(&self) -> impl Deref<Target = Option<Connected>> + '_ {
+        self.rx.borrow()
+    }
+
+    /// Wait for the connection to be established
+    ///
+    /// If a connection was established, this will always return `Some(...)`. If the request never
+    /// successfully connected (e.g. DNS resolution failure), this method will never return.
+    pub async fn wait_for_connection_metadata(
+        &mut self,
+    ) -> impl Deref<Target = Option<Connected>> + '_ {
+        if self.rx.borrow().is_some() {
+            return self.rx.borrow();
+        }
+        let _ = self.rx.changed().await;
+        self.rx.borrow()
+    }
+}
+
+pub(super) struct Extra(Box<dyn ExtraInner>);
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub(super) enum Alpn {
+    H2,
+    None,
+}
+
+impl Connected {
+    /// Create new `Connected` type with empty metadata.
+    pub fn new() -> Connected {
+        Connected {
+            alpn: Alpn::None,
+            is_proxied: false,
+            extra: None,
+            poisoned: PoisonPill::healthy(),
+        }
+    }
+
+    /// Set whether the connected transport is to an HTTP proxy.
+    ///
+    /// This setting will affect if HTTP/1 requests written on the transport
+    /// will have the request-target in absolute-form or origin-form:
+    ///
+    /// - When `proxy(false)`:
+    ///
+    /// ```http
+    /// GET /guide HTTP/1.1
+    /// ```
+    ///
+    /// - When `proxy(true)`:
+    ///
+    /// ```http
+    /// GET http://hyper.rs/guide HTTP/1.1
+    /// ```
+    ///
+    /// Default is `false`.
+    pub fn proxy(mut self, is_proxied: bool) -> Connected {
+        self.is_proxied = is_proxied;
+        self
+    }
+
+    /// Determines if the connected transport is to an HTTP proxy.
+    pub fn is_proxied(&self) -> bool {
+        self.is_proxied
+    }
+
+    /// Set extra connection information to be set in the extensions of every `Response`.
+    pub fn extra<T: Clone + Send + Sync + 'static>(mut self, extra: T) -> Connected {
+        if let Some(prev) = self.extra {
+            self.extra = Some(Extra(Box::new(ExtraChain(prev.0, extra))));
+        } else {
+            self.extra = Some(Extra(Box::new(ExtraEnvelope(extra))));
+        }
+        self
+    }
+
+    /// Copies the extra connection information into an `Extensions` map.
+    pub fn get_extras(&self, extensions: &mut Extensions) {
+        if let Some(extra) = &self.extra {
+            extra.set(extensions);
+        }
+    }
+
+    /// Set that the connected transport negotiated HTTP/2 as its next protocol.
+    pub fn negotiated_h2(mut self) -> Connected {
+        self.alpn = Alpn::H2;
+        self
+    }
+
+    /// Determines if the connected transport negotiated HTTP/2 as its next protocol.
+    pub fn is_negotiated_h2(&self) -> bool {
+        self.alpn == Alpn::H2
+    }
+
+    /// Poison this connection
+    ///
+    /// A poisoned connection will not be reused for subsequent requests by the pool
+    pub fn poison(&self) {
+        self.poisoned.poison();
+        tracing::debug!(
+            poison_pill = ?self.poisoned, "connection was poisoned"
+        );
+    }
+
+    // Don't public expose that `Connected` is `Clone`, unsure if we want to
+    // keep that contract...
+    pub(super) fn clone(&self) -> Connected {
+        Connected {
+            alpn: self.alpn.clone(),
+            is_proxied: self.is_proxied,
+            extra: self.extra.clone(),
+            poisoned: self.poisoned.clone(),
+        }
+    }
+}
+
+// ===== impl Extra =====
+
+impl Extra {
+    pub(super) fn set(&self, res: &mut Extensions) {
+        self.0.set(res);
+    }
+}
+
+impl Clone for Extra {
+    fn clone(&self) -> Extra {
+        Extra(self.0.clone_box())
+    }
+}
+
+impl fmt::Debug for Extra {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Extra").finish()
+    }
+}
+
+trait ExtraInner: Send + Sync {
+    fn clone_box(&self) -> Box<dyn ExtraInner>;
+    fn set(&self, res: &mut Extensions);
+}
+
+// This indirection allows the `Connected` to have a type-erased "extra" value,
+// while that type still knows its inner extra type. This allows the correct
+// TypeId to be used when inserting into `res.extensions_mut()`.
+#[derive(Clone)]
+struct ExtraEnvelope<T>(T);
+
+impl<T> ExtraInner for ExtraEnvelope<T>
+where
+    T: Clone + Send + Sync + 'static,
+{
+    fn clone_box(&self) -> Box<dyn ExtraInner> {
+        Box::new(self.clone())
+    }
+
+    fn set(&self, res: &mut Extensions) {
+        res.insert(self.0.clone());
+    }
+}
+
+struct ExtraChain<T>(Box<dyn ExtraInner>, T);
+
+impl<T: Clone> Clone for ExtraChain<T> {
+    fn clone(&self) -> Self {
+        ExtraChain(self.0.clone_box(), self.1.clone())
+    }
+}
+
+impl<T> ExtraInner for ExtraChain<T>
+where
+    T: Clone + Send + Sync + 'static,
+{
+    fn clone_box(&self) -> Box<dyn ExtraInner> {
+        Box::new(self.clone())
+    }
+
+    fn set(&self, res: &mut Extensions) {
+        self.0.set(res);
+        res.insert(self.1.clone());
+    }
+}
+
+#[cfg(any(feature = "http1", feature = "http2"))]
+pub(super) mod sealed {
+    use std::error::Error as StdError;
+    use std::future::Future;
+    use std::marker::Unpin;
+
+    use ::http::Uri;
+    use tokio::io::{AsyncRead, AsyncWrite};
+
+    use super::Connection;
+
+    /// Connect to a destination, returning an IO transport.
+    ///
+    /// A connector receives a [`Uri`](::http::Uri) and returns a `Future` of the
+    /// ready connection.
+    ///
+    /// # Trait Alias
+    ///
+    /// This is really just an *alias* for the `tower::Service` trait, with
+    /// additional bounds set for convenience *inside* hyper. You don't actually
+    /// implement this trait, but `tower::Service<Uri>` instead.
+    // The `Sized` bound is to prevent creating `dyn Connect`, since they cannot
+    // fit the `Connect` bounds because of the blanket impl for `Service`.
+    pub trait Connect: Sealed + Sized {
+        #[doc(hidden)]
+        type _Svc: ConnectSvc;
+        #[doc(hidden)]
+        fn connect(self, internal_only: Internal, dst: Uri) -> <Self::_Svc as ConnectSvc>::Future;
+    }
+
+    #[allow(unreachable_pub)]
+    pub trait ConnectSvc {
+        type Connection: AsyncRead + AsyncWrite + Connection + Unpin + Send + 'static;
+        type Error: Into<Box<dyn StdError + Send + Sync>>;
+        type Future: Future<Output = Result<Self::Connection, Self::Error>> + Unpin + Send + 'static;
+
+        fn connect(self, internal_only: Internal, dst: Uri) -> Self::Future;
+    }
+
+    impl<S, T> Connect for S
+    where
+        S: tower_service::Service<Uri, Response = T> + Send + 'static,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        S::Future: Unpin + Send,
+        T: AsyncRead + AsyncWrite + Connection + Unpin + Send + 'static,
+    {
+        type _Svc = S;
+
+        fn connect(self, _: Internal, dst: Uri) -> crate::service::Oneshot<S, Uri> {
+            crate::service::oneshot(self, dst)
+        }
+    }
+
+    impl<S, T> ConnectSvc for S
+    where
+        S: tower_service::Service<Uri, Response = T> + Send + 'static,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        S::Future: Unpin + Send,
+        T: AsyncRead + AsyncWrite + Connection + Unpin + Send + 'static,
+    {
+        type Connection = T;
+        type Error = S::Error;
+        type Future = crate::service::Oneshot<S, Uri>;
+
+        fn connect(self, _: Internal, dst: Uri) -> Self::Future {
+            crate::service::oneshot(self, dst)
+        }
+    }
+
+    impl<S, T> Sealed for S
+    where
+        S: tower_service::Service<Uri, Response = T> + Send,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        S::Future: Unpin + Send,
+        T: AsyncRead + AsyncWrite + Connection + Unpin + Send + 'static,
+    {
+    }
+
+    pub trait Sealed {}
+    #[allow(missing_debug_implementations)]
+    pub struct Internal;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Connected;
+    use crate::client::connect::CaptureConnection;
+
+    #[derive(Clone, Debug, PartialEq)]
+    struct Ex1(usize);
+
+    #[derive(Clone, Debug, PartialEq)]
+    struct Ex2(&'static str);
+
+    #[derive(Clone, Debug, PartialEq)]
+    struct Ex3(&'static str);
+
+    #[test]
+    fn test_connected_extra() {
+        let c1 = Connected::new().extra(Ex1(41));
+
+        let mut ex = ::http::Extensions::new();
+
+        assert_eq!(ex.get::<Ex1>(), None);
+
+        c1.extra.as_ref().expect("c1 extra").set(&mut ex);
+
+        assert_eq!(ex.get::<Ex1>(), Some(&Ex1(41)));
+    }
+
+    #[test]
+    fn test_connected_extra_chain() {
+        // If a user composes connectors and at each stage, there's "extra"
+        // info to attach, it shouldn't override the previous extras.
+
+        let c1 = Connected::new()
+            .extra(Ex1(45))
+            .extra(Ex2("zoom"))
+            .extra(Ex3("pew pew"));
+
+        let mut ex1 = ::http::Extensions::new();
+
+        assert_eq!(ex1.get::<Ex1>(), None);
+        assert_eq!(ex1.get::<Ex2>(), None);
+        assert_eq!(ex1.get::<Ex3>(), None);
+
+        c1.extra.as_ref().expect("c1 extra").set(&mut ex1);
+
+        assert_eq!(ex1.get::<Ex1>(), Some(&Ex1(45)));
+        assert_eq!(ex1.get::<Ex2>(), Some(&Ex2("zoom")));
+        assert_eq!(ex1.get::<Ex3>(), Some(&Ex3("pew pew")));
+
+        // Just like extensions, inserting the same type overrides previous type.
+        let c2 = Connected::new()
+            .extra(Ex1(33))
+            .extra(Ex2("hiccup"))
+            .extra(Ex1(99));
+
+        let mut ex2 = ::http::Extensions::new();
+
+        c2.extra.as_ref().expect("c2 extra").set(&mut ex2);
+
+        assert_eq!(ex2.get::<Ex1>(), Some(&Ex1(99)));
+        assert_eq!(ex2.get::<Ex2>(), Some(&Ex2("hiccup")));
+    }
+
+    #[test]
+    fn test_sync_capture_connection() {
+        let (tx, rx) = CaptureConnection::new();
+        assert!(
+            rx.connection_metadata().is_none(),
+            "connection has not been set"
+        );
+        tx.set(&Connected::new().proxy(true));
+        assert_eq!(
+            rx.connection_metadata()
+                .as_ref()
+                .expect("connected should be set")
+                .is_proxied(),
+            true
+        );
+
+        // ensure it can be called multiple times
+        assert_eq!(
+            rx.connection_metadata()
+                .as_ref()
+                .expect("connected should be set")
+                .is_proxied(),
+            true
+        );
+    }
+
+    #[tokio::test]
+    async fn async_capture_connection() {
+        let (tx, mut rx) = CaptureConnection::new();
+        assert!(
+            rx.connection_metadata().is_none(),
+            "connection has not been set"
+        );
+        let test_task = tokio::spawn(async move {
+            assert_eq!(
+                rx.wait_for_connection_metadata()
+                    .await
+                    .as_ref()
+                    .expect("connection should be set")
+                    .is_proxied(),
+                true
+            );
+            // can be awaited multiple times
+            assert!(
+                rx.wait_for_connection_metadata().await.is_some(),
+                "should be awaitable multiple times"
+            );
+
+            assert_eq!(rx.connection_metadata().is_some(), true);
+        });
+        // can't be finished, we haven't set the connection yet
+        assert_eq!(test_task.is_finished(), false);
+        tx.set(&Connected::new().proxy(true));
+
+        assert!(test_task.await.is_ok());
+    }
+
+    #[tokio::test]
+    async fn capture_connection_sender_side_dropped() {
+        let (tx, mut rx) = CaptureConnection::new();
+        assert!(
+            rx.connection_metadata().is_none(),
+            "connection has not been set"
+        );
+        drop(tx);
+        assert!(rx.wait_for_connection_metadata().await.is_none());
+    }
+}
diff --git a/src/client/dispatch.rs b/src/client/dispatch.rs
new file mode 100644
index 0000000..a1a93ea
--- /dev/null
+++ b/src/client/dispatch.rs
@@ -0,0 +1,442 @@
+#[cfg(feature = "http2")]
+use std::future::Future;
+use std::marker::Unpin;
+#[cfg(feature = "http2")]
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use futures_util::FutureExt;
+use tokio::sync::{mpsc, oneshot};
+
+pub(crate) type RetryPromise<T, U> = oneshot::Receiver<Result<U, (crate::Error, Option<T>)>>;
+pub(crate) type Promise<T> = oneshot::Receiver<Result<T, crate::Error>>;
+
+pub(crate) fn channel<T, U>() -> (Sender<T, U>, Receiver<T, U>) {
+    let (tx, rx) = mpsc::unbounded_channel();
+    let (giver, taker) = want::new();
+    let tx = Sender {
+        buffered_once: false,
+        giver,
+        inner: tx,
+    };
+    let rx = Receiver { inner: rx, taker };
+    (tx, rx)
+}
+
+/// A bounded sender of requests and callbacks for when responses are ready.
+///
+/// While the inner sender is unbounded, the Giver is used to determine
+/// if the Receiver is ready for another request.
+pub(crate) struct Sender<T, U> {
+    /// One message is always allowed, even if the Receiver hasn't asked
+    /// for it yet. This boolean keeps track of whether we've sent one
+    /// without notice.
+    buffered_once: bool,
+    /// The Giver helps watch that the the Receiver side has been polled
+    /// when the queue is empty. This helps us know when a request and
+    /// response have been fully processed, and a connection is ready
+    /// for more.
+    giver: want::Giver,
+    /// Actually bounded by the Giver, plus `buffered_once`.
+    inner: mpsc::UnboundedSender<Envelope<T, U>>,
+}
+
+/// An unbounded version.
+///
+/// Cannot poll the Giver, but can still use it to determine if the Receiver
+/// has been dropped. However, this version can be cloned.
+#[cfg(feature = "http2")]
+pub(crate) struct UnboundedSender<T, U> {
+    /// Only used for `is_closed`, since mpsc::UnboundedSender cannot be checked.
+    giver: want::SharedGiver,
+    inner: mpsc::UnboundedSender<Envelope<T, U>>,
+}
+
+impl<T, U> Sender<T, U> {
+    pub(crate) fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        self.giver
+            .poll_want(cx)
+            .map_err(|_| crate::Error::new_closed())
+    }
+
+    pub(crate) fn is_ready(&self) -> bool {
+        self.giver.is_wanting()
+    }
+
+    pub(crate) fn is_closed(&self) -> bool {
+        self.giver.is_canceled()
+    }
+
+    fn can_send(&mut self) -> bool {
+        if self.giver.give() || !self.buffered_once {
+            // If the receiver is ready *now*, then of course we can send.
+            //
+            // If the receiver isn't ready yet, but we don't have anything
+            // in the channel yet, then allow one message.
+            self.buffered_once = true;
+            true
+        } else {
+            false
+        }
+    }
+
+    pub(crate) fn try_send(&mut self, val: T) -> Result<RetryPromise<T, U>, T> {
+        if !self.can_send() {
+            return Err(val);
+        }
+        let (tx, rx) = oneshot::channel();
+        self.inner
+            .send(Envelope(Some((val, Callback::Retry(Some(tx))))))
+            .map(move |_| rx)
+            .map_err(|mut e| (e.0).0.take().expect("envelope not dropped").0)
+    }
+
+    pub(crate) fn send(&mut self, val: T) -> Result<Promise<U>, T> {
+        if !self.can_send() {
+            return Err(val);
+        }
+        let (tx, rx) = oneshot::channel();
+        self.inner
+            .send(Envelope(Some((val, Callback::NoRetry(Some(tx))))))
+            .map(move |_| rx)
+            .map_err(|mut e| (e.0).0.take().expect("envelope not dropped").0)
+    }
+
+    #[cfg(feature = "http2")]
+    pub(crate) fn unbound(self) -> UnboundedSender<T, U> {
+        UnboundedSender {
+            giver: self.giver.shared(),
+            inner: self.inner,
+        }
+    }
+}
+
+#[cfg(feature = "http2")]
+impl<T, U> UnboundedSender<T, U> {
+    pub(crate) fn is_ready(&self) -> bool {
+        !self.giver.is_canceled()
+    }
+
+    pub(crate) fn is_closed(&self) -> bool {
+        self.giver.is_canceled()
+    }
+
+    pub(crate) fn try_send(&mut self, val: T) -> Result<RetryPromise<T, U>, T> {
+        let (tx, rx) = oneshot::channel();
+        self.inner
+            .send(Envelope(Some((val, Callback::Retry(Some(tx))))))
+            .map(move |_| rx)
+            .map_err(|mut e| (e.0).0.take().expect("envelope not dropped").0)
+    }
+
+    #[cfg(all(feature = "backports", feature = "http2"))]
+    pub(crate) fn send(&mut self, val: T) -> Result<Promise<U>, T> {
+        let (tx, rx) = oneshot::channel();
+        self.inner
+            .send(Envelope(Some((val, Callback::NoRetry(Some(tx))))))
+            .map(move |_| rx)
+            .map_err(|mut e| (e.0).0.take().expect("envelope not dropped").0)
+    }
+}
+
+#[cfg(feature = "http2")]
+impl<T, U> Clone for UnboundedSender<T, U> {
+    fn clone(&self) -> Self {
+        UnboundedSender {
+            giver: self.giver.clone(),
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+pub(crate) struct Receiver<T, U> {
+    inner: mpsc::UnboundedReceiver<Envelope<T, U>>,
+    taker: want::Taker,
+}
+
+impl<T, U> Receiver<T, U> {
+    pub(crate) fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<(T, Callback<T, U>)>> {
+        match self.inner.poll_recv(cx) {
+            Poll::Ready(item) => {
+                Poll::Ready(item.map(|mut env| env.0.take().expect("envelope not dropped")))
+            }
+            Poll::Pending => {
+                self.taker.want();
+                Poll::Pending
+            }
+        }
+    }
+
+    #[cfg(feature = "http1")]
+    pub(crate) fn close(&mut self) {
+        self.taker.cancel();
+        self.inner.close();
+    }
+
+    #[cfg(feature = "http1")]
+    pub(crate) fn try_recv(&mut self) -> Option<(T, Callback<T, U>)> {
+        match self.inner.recv().now_or_never() {
+            Some(Some(mut env)) => env.0.take(),
+            _ => None,
+        }
+    }
+}
+
+impl<T, U> Drop for Receiver<T, U> {
+    fn drop(&mut self) {
+        // Notify the giver about the closure first, before dropping
+        // the mpsc::Receiver.
+        self.taker.cancel();
+    }
+}
+
+struct Envelope<T, U>(Option<(T, Callback<T, U>)>);
+
+impl<T, U> Drop for Envelope<T, U> {
+    fn drop(&mut self) {
+        if let Some((val, cb)) = self.0.take() {
+            cb.send(Err((
+                crate::Error::new_canceled().with("connection closed"),
+                Some(val),
+            )));
+        }
+    }
+}
+
+pub(crate) enum Callback<T, U> {
+    Retry(Option<oneshot::Sender<Result<U, (crate::Error, Option<T>)>>>),
+    NoRetry(Option<oneshot::Sender<Result<U, crate::Error>>>),
+}
+
+impl<T, U> Drop for Callback<T, U> {
+    fn drop(&mut self) {
+        // FIXME(nox): What errors do we want here?
+        let error = crate::Error::new_user_dispatch_gone().with(if std::thread::panicking() {
+            "user code panicked"
+        } else {
+            "runtime dropped the dispatch task"
+        });
+
+        match self {
+            Callback::Retry(tx) => {
+                if let Some(tx) = tx.take() {
+                    let _ = tx.send(Err((error, None)));
+                }
+            }
+            Callback::NoRetry(tx) => {
+                if let Some(tx) = tx.take() {
+                    let _ = tx.send(Err(error));
+                }
+            }
+        }
+    }
+}
+
+impl<T, U> Callback<T, U> {
+    #[cfg(feature = "http2")]
+    pub(crate) fn is_canceled(&self) -> bool {
+        match *self {
+            Callback::Retry(Some(ref tx)) => tx.is_closed(),
+            Callback::NoRetry(Some(ref tx)) => tx.is_closed(),
+            _ => unreachable!(),
+        }
+    }
+
+    pub(crate) fn poll_canceled(&mut self, cx: &mut Context<'_>) -> Poll<()> {
+        match *self {
+            Callback::Retry(Some(ref mut tx)) => tx.poll_closed(cx),
+            Callback::NoRetry(Some(ref mut tx)) => tx.poll_closed(cx),
+            _ => unreachable!(),
+        }
+    }
+
+    pub(crate) fn send(mut self, val: Result<U, (crate::Error, Option<T>)>) {
+        match self {
+            Callback::Retry(ref mut tx) => {
+                let _ = tx.take().unwrap().send(val);
+            }
+            Callback::NoRetry(ref mut tx) => {
+                let _ = tx.take().unwrap().send(val.map_err(|e| e.0));
+            }
+        }
+    }
+
+    #[cfg(feature = "http2")]
+    pub(crate) async fn send_when(
+        self,
+        mut when: impl Future<Output = Result<U, (crate::Error, Option<T>)>> + Unpin,
+    ) {
+        use futures_util::future;
+        use tracing::trace;
+
+        let mut cb = Some(self);
+
+        // "select" on this callback being canceled, and the future completing
+        future::poll_fn(move |cx| {
+            match Pin::new(&mut when).poll(cx) {
+                Poll::Ready(Ok(res)) => {
+                    cb.take().expect("polled after complete").send(Ok(res));
+                    Poll::Ready(())
+                }
+                Poll::Pending => {
+                    // check if the callback is canceled
+                    ready!(cb.as_mut().unwrap().poll_canceled(cx));
+                    trace!("send_when canceled");
+                    Poll::Ready(())
+                }
+                Poll::Ready(Err(err)) => {
+                    cb.take().expect("polled after complete").send(Err(err));
+                    Poll::Ready(())
+                }
+            }
+        })
+        .await
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[cfg(feature = "nightly")]
+    extern crate test;
+
+    use std::future::Future;
+    use std::pin::Pin;
+    use std::task::{Context, Poll};
+
+    use super::{channel, Callback, Receiver};
+
+    #[derive(Debug)]
+    struct Custom(i32);
+
+    impl<T, U> Future for Receiver<T, U> {
+        type Output = Option<(T, Callback<T, U>)>;
+
+        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+            self.poll_recv(cx)
+        }
+    }
+
+    /// Helper to check if the future is ready after polling once.
+    struct PollOnce<'a, F>(&'a mut F);
+
+    impl<F, T> Future for PollOnce<'_, F>
+    where
+        F: Future<Output = T> + Unpin,
+    {
+        type Output = Option<()>;
+
+        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+            match Pin::new(&mut self.0).poll(cx) {
+                Poll::Ready(_) => Poll::Ready(Some(())),
+                Poll::Pending => Poll::Ready(None),
+            }
+        }
+    }
+
+    #[tokio::test]
+    async fn drop_receiver_sends_cancel_errors() {
+        let _ = pretty_env_logger::try_init();
+
+        let (mut tx, mut rx) = channel::<Custom, ()>();
+
+        // must poll once for try_send to succeed
+        assert!(PollOnce(&mut rx).await.is_none(), "rx empty");
+
+        let promise = tx.try_send(Custom(43)).unwrap();
+        drop(rx);
+
+        let fulfilled = promise.await;
+        let err = fulfilled
+            .expect("fulfilled")
+            .expect_err("promise should error");
+        match (err.0.kind(), err.1) {
+            (&crate::error::Kind::Canceled, Some(_)) => (),
+            e => panic!("expected Error::Cancel(_), found {:?}", e),
+        }
+    }
+
+    #[tokio::test]
+    async fn sender_checks_for_want_on_send() {
+        let (mut tx, mut rx) = channel::<Custom, ()>();
+
+        // one is allowed to buffer, second is rejected
+        let _ = tx.try_send(Custom(1)).expect("1 buffered");
+        tx.try_send(Custom(2)).expect_err("2 not ready");
+
+        assert!(PollOnce(&mut rx).await.is_some(), "rx once");
+
+        // Even though 1 has been popped, only 1 could be buffered for the
+        // lifetime of the channel.
+        tx.try_send(Custom(2)).expect_err("2 still not ready");
+
+        assert!(PollOnce(&mut rx).await.is_none(), "rx empty");
+
+        let _ = tx.try_send(Custom(2)).expect("2 ready");
+    }
+
+    #[cfg(feature = "http2")]
+    #[test]
+    fn unbounded_sender_doesnt_bound_on_want() {
+        let (tx, rx) = channel::<Custom, ()>();
+        let mut tx = tx.unbound();
+
+        let _ = tx.try_send(Custom(1)).unwrap();
+        let _ = tx.try_send(Custom(2)).unwrap();
+        let _ = tx.try_send(Custom(3)).unwrap();
+
+        drop(rx);
+
+        let _ = tx.try_send(Custom(4)).unwrap_err();
+    }
+
+    #[cfg(feature = "nightly")]
+    #[bench]
+    fn giver_queue_throughput(b: &mut test::Bencher) {
+        use crate::{Body, Request, Response};
+
+        let rt = tokio::runtime::Builder::new_current_thread()
+            .enable_all()
+            .build()
+            .unwrap();
+        let (mut tx, mut rx) = channel::<Request<Body>, Response<Body>>();
+
+        b.iter(move || {
+            let _ = tx.send(Request::default()).unwrap();
+            rt.block_on(async {
+                loop {
+                    let poll_once = PollOnce(&mut rx);
+                    let opt = poll_once.await;
+                    if opt.is_none() {
+                        break;
+                    }
+                }
+            });
+        })
+    }
+
+    #[cfg(feature = "nightly")]
+    #[bench]
+    fn giver_queue_not_ready(b: &mut test::Bencher) {
+        let rt = tokio::runtime::Builder::new_current_thread()
+            .enable_all()
+            .build()
+            .unwrap();
+        let (_tx, mut rx) = channel::<i32, ()>();
+        b.iter(move || {
+            rt.block_on(async {
+                let poll_once = PollOnce(&mut rx);
+                assert!(poll_once.await.is_none());
+            });
+        })
+    }
+
+    #[cfg(feature = "nightly")]
+    #[bench]
+    fn giver_queue_cancel(b: &mut test::Bencher) {
+        let (_tx, mut rx) = channel::<i32, ()>();
+
+        b.iter(move || {
+            rx.taker.cancel();
+        })
+    }
+}
diff --git a/src/client/mod.rs b/src/client/mod.rs
new file mode 100644
index 0000000..734bda8
--- /dev/null
+++ b/src/client/mod.rs
@@ -0,0 +1,68 @@
+//! HTTP Client
+//!
+//! There are two levels of APIs provided for construct HTTP clients:
+//!
+//! - The higher-level [`Client`](Client) type.
+//! - The lower-level [`conn`](conn) module.
+//!
+//! # Client
+//!
+//! The [`Client`](Client) is the main way to send HTTP requests to a server.
+//! The default `Client` provides these things on top of the lower-level API:
+//!
+//! - A default **connector**, able to resolve hostnames and connect to
+//!   destinations over plain-text TCP.
+//! - A **pool** of existing connections, allowing better performance when
+//!   making multiple requests to the same hostname.
+//! - Automatic setting of the `Host` header, based on the request `Uri`.
+//! - Automatic request **retries** when a pooled connection is closed by the
+//!   server before any bytes have been written.
+//!
+//! Many of these features can configured, by making use of
+//! [`Client::builder`](Client::builder).
+//!
+//! ## Example
+//!
+//! For a small example program simply fetching a URL, take a look at the
+//! [full client example](https://github.com/hyperium/hyper/blob/master/examples/client.rs).
+//!
+//! ```
+//! # #[cfg(all(feature = "tcp", feature = "client", any(feature = "http1", feature = "http2")))]
+//! # async fn fetch_httpbin() -> hyper::Result<()> {
+//! use hyper::{body::HttpBody as _, Client, Uri};
+//!
+//! let client = Client::new();
+//!
+//! // Make a GET /ip to 'http://httpbin.org'
+//! let res = client.get(Uri::from_static("http://httpbin.org/ip")).await?;
+//!
+//! // And then, if the request gets a response...
+//! println!("status: {}", res.status());
+//!
+//! // Concatenate the body stream into a single buffer...
+//! let buf = hyper::body::to_bytes(res).await?;
+//!
+//! println!("body: {:?}", buf);
+//! # Ok(())
+//! # }
+//! # fn main () {}
+//! ```
+
+#[cfg(feature = "tcp")]
+pub use self::connect::HttpConnector;
+
+pub mod connect;
+#[cfg(all(test, feature = "runtime"))]
+mod tests;
+
+cfg_feature! {
+    #![any(feature = "http1", feature = "http2")]
+
+    pub use self::client::{Builder, Client, ResponseFuture};
+
+    mod client;
+    pub mod conn;
+    pub(super) mod dispatch;
+    mod pool;
+    pub mod service;
+}
diff --git a/src/client/pool.rs b/src/client/pool.rs
new file mode 100644
index 0000000..1dfd6ba
--- /dev/null
+++ b/src/client/pool.rs
@@ -0,0 +1,1048 @@
+use std::collections::{HashMap, HashSet, VecDeque};
+use std::error::Error as StdError;
+use std::fmt;
+use std::future::Future;
+use std::marker::Unpin;
+use std::ops::{Deref, DerefMut};
+use std::pin::Pin;
+use std::sync::{Arc, Mutex, Weak};
+use std::task::{Context, Poll};
+
+#[cfg(not(feature = "runtime"))]
+use std::time::{Duration, Instant};
+
+use futures_channel::oneshot;
+#[cfg(feature = "runtime")]
+use tokio::time::{Duration, Instant, Interval};
+use tracing::{debug, trace};
+
+use super::client::Ver;
+use crate::common::exec::Exec;
+
+// FIXME: allow() required due to `impl Trait` leaking types to this lint
+#[allow(missing_debug_implementations)]
+pub(super) struct Pool<T> {
+    // If the pool is disabled, this is None.
+    inner: Option<Arc<Mutex<PoolInner<T>>>>,
+}
+
+// Before using a pooled connection, make sure the sender is not dead.
+//
+// This is a trait to allow the `client::pool::tests` to work for `i32`.
+//
+// See https://github.com/hyperium/hyper/issues/1429
+pub(super) trait Poolable: Unpin + Send + Sized + 'static {
+    fn is_open(&self) -> bool;
+    /// Reserve this connection.
+    ///
+    /// Allows for HTTP/2 to return a shared reservation.
+    fn reserve(self) -> Reservation<Self>;
+    fn can_share(&self) -> bool;
+}
+
+/// When checking out a pooled connection, it might be that the connection
+/// only supports a single reservation, or it might be usable for many.
+///
+/// Specifically, HTTP/1 requires a unique reservation, but HTTP/2 can be
+/// used for multiple requests.
+// FIXME: allow() required due to `impl Trait` leaking types to this lint
+#[allow(missing_debug_implementations)]
+pub(super) enum Reservation<T> {
+    /// This connection could be used multiple times, the first one will be
+    /// reinserted into the `idle` pool, and the second will be given to
+    /// the `Checkout`.
+    #[cfg(feature = "http2")]
+    Shared(T, T),
+    /// This connection requires unique access. It will be returned after
+    /// use is complete.
+    Unique(T),
+}
+
+/// Simple type alias in case the key type needs to be adjusted.
+pub(super) type Key = (http::uri::Scheme, http::uri::Authority); //Arc<String>;
+
+struct PoolInner<T> {
+    // A flag that a connection is being established, and the connection
+    // should be shared. This prevents making multiple HTTP/2 connections
+    // to the same host.
+    connecting: HashSet<Key>,
+    // These are internal Conns sitting in the event loop in the KeepAlive
+    // state, waiting to receive a new Request to send on the socket.
+    idle: HashMap<Key, Vec<Idle<T>>>,
+    max_idle_per_host: usize,
+    // These are outstanding Checkouts that are waiting for a socket to be
+    // able to send a Request one. This is used when "racing" for a new
+    // connection.
+    //
+    // The Client starts 2 tasks, 1 to connect a new socket, and 1 to wait
+    // for the Pool to receive an idle Conn. When a Conn becomes idle,
+    // this list is checked for any parked Checkouts, and tries to notify
+    // them that the Conn could be used instead of waiting for a brand new
+    // connection.
+    waiters: HashMap<Key, VecDeque<oneshot::Sender<T>>>,
+    // A oneshot channel is used to allow the interval to be notified when
+    // the Pool completely drops. That way, the interval can cancel immediately.
+    #[cfg(feature = "runtime")]
+    idle_interval_ref: Option<oneshot::Sender<std::convert::Infallible>>,
+    #[cfg(feature = "runtime")]
+    exec: Exec,
+    timeout: Option<Duration>,
+}
+
+// This is because `Weak::new()` *allocates* space for `T`, even if it
+// doesn't need it!
+struct WeakOpt<T>(Option<Weak<T>>);
+
+#[derive(Clone, Copy, Debug)]
+pub(super) struct Config {
+    pub(super) idle_timeout: Option<Duration>,
+    pub(super) max_idle_per_host: usize,
+}
+
+impl Config {
+    pub(super) fn is_enabled(&self) -> bool {
+        self.max_idle_per_host > 0
+    }
+}
+
+impl<T> Pool<T> {
+    pub(super) fn new(config: Config, __exec: &Exec) -> Pool<T> {
+        let inner = if config.is_enabled() {
+            Some(Arc::new(Mutex::new(PoolInner {
+                connecting: HashSet::new(),
+                idle: HashMap::new(),
+                #[cfg(feature = "runtime")]
+                idle_interval_ref: None,
+                max_idle_per_host: config.max_idle_per_host,
+                waiters: HashMap::new(),
+                #[cfg(feature = "runtime")]
+                exec: __exec.clone(),
+                timeout: config.idle_timeout.filter(|&t| t > Duration::ZERO),
+            })))
+        } else {
+            None
+        };
+
+        Pool { inner }
+    }
+
+    fn is_enabled(&self) -> bool {
+        self.inner.is_some()
+    }
+
+    #[cfg(test)]
+    pub(super) fn no_timer(&self) {
+        // Prevent an actual interval from being created for this pool...
+        #[cfg(feature = "runtime")]
+        {
+            let mut inner = self.inner.as_ref().unwrap().lock().unwrap();
+            assert!(inner.idle_interval_ref.is_none(), "timer already spawned");
+            let (tx, _) = oneshot::channel();
+            inner.idle_interval_ref = Some(tx);
+        }
+    }
+}
+
+impl<T: Poolable> Pool<T> {
+    /// Returns a `Checkout` which is a future that resolves if an idle
+    /// connection becomes available.
+    pub(super) fn checkout(&self, key: Key) -> Checkout<T> {
+        Checkout {
+            key,
+            pool: self.clone(),
+            waiter: None,
+        }
+    }
+
+    /// Ensure that there is only ever 1 connecting task for HTTP/2
+    /// connections. This does nothing for HTTP/1.
+    pub(super) fn connecting(&self, key: &Key, ver: Ver) -> Option<Connecting<T>> {
+        if ver == Ver::Http2 {
+            if let Some(ref enabled) = self.inner {
+                let mut inner = enabled.lock().unwrap();
+                return if inner.connecting.insert(key.clone()) {
+                    let connecting = Connecting {
+                        key: key.clone(),
+                        pool: WeakOpt::downgrade(enabled),
+                    };
+                    Some(connecting)
+                } else {
+                    trace!("HTTP/2 connecting already in progress for {:?}", key);
+                    None
+                };
+            }
+        }
+
+        // else
+        Some(Connecting {
+            key: key.clone(),
+            // in HTTP/1's case, there is never a lock, so we don't
+            // need to do anything in Drop.
+            pool: WeakOpt::none(),
+        })
+    }
+
+    #[cfg(test)]
+    fn locked(&self) -> std::sync::MutexGuard<'_, PoolInner<T>> {
+        self.inner.as_ref().expect("enabled").lock().expect("lock")
+    }
+
+    /* Used in client/tests.rs...
+    #[cfg(feature = "runtime")]
+    #[cfg(test)]
+    pub(super) fn h1_key(&self, s: &str) -> Key {
+        Arc::new(s.to_string())
+    }
+
+    #[cfg(feature = "runtime")]
+    #[cfg(test)]
+    pub(super) fn idle_count(&self, key: &Key) -> usize {
+        self
+            .locked()
+            .idle
+            .get(key)
+            .map(|list| list.len())
+            .unwrap_or(0)
+    }
+    */
+
+    pub(super) fn pooled(
+        &self,
+        #[cfg_attr(not(feature = "http2"), allow(unused_mut))] mut connecting: Connecting<T>,
+        value: T,
+    ) -> Pooled<T> {
+        let (value, pool_ref) = if let Some(ref enabled) = self.inner {
+            match value.reserve() {
+                #[cfg(feature = "http2")]
+                Reservation::Shared(to_insert, to_return) => {
+                    let mut inner = enabled.lock().unwrap();
+                    inner.put(connecting.key.clone(), to_insert, enabled);
+                    // Do this here instead of Drop for Connecting because we
+                    // already have a lock, no need to lock the mutex twice.
+                    inner.connected(&connecting.key);
+                    // prevent the Drop of Connecting from repeating inner.connected()
+                    connecting.pool = WeakOpt::none();
+
+                    // Shared reservations don't need a reference to the pool,
+                    // since the pool always keeps a copy.
+                    (to_return, WeakOpt::none())
+                }
+                Reservation::Unique(value) => {
+                    // Unique reservations must take a reference to the pool
+                    // since they hope to reinsert once the reservation is
+                    // completed
+                    (value, WeakOpt::downgrade(enabled))
+                }
+            }
+        } else {
+            // If pool is not enabled, skip all the things...
+
+            // The Connecting should have had no pool ref
+            debug_assert!(connecting.pool.upgrade().is_none());
+
+            (value, WeakOpt::none())
+        };
+        Pooled {
+            key: connecting.key.clone(),
+            is_reused: false,
+            pool: pool_ref,
+            value: Some(value),
+        }
+    }
+
+    fn reuse(&self, key: &Key, value: T) -> Pooled<T> {
+        debug!("reuse idle connection for {:?}", key);
+        // TODO: unhack this
+        // In Pool::pooled(), which is used for inserting brand new connections,
+        // there's some code that adjusts the pool reference taken depending
+        // on if the Reservation can be shared or is unique. By the time
+        // reuse() is called, the reservation has already been made, and
+        // we just have the final value, without knowledge of if this is
+        // unique or shared. So, the hack is to just assume Ver::Http2 means
+        // shared... :(
+        let mut pool_ref = WeakOpt::none();
+        if !value.can_share() {
+            if let Some(ref enabled) = self.inner {
+                pool_ref = WeakOpt::downgrade(enabled);
+            }
+        }
+
+        Pooled {
+            is_reused: true,
+            key: key.clone(),
+            pool: pool_ref,
+            value: Some(value),
+        }
+    }
+}
+
+/// Pop off this list, looking for a usable connection that hasn't expired.
+struct IdlePopper<'a, T> {
+    key: &'a Key,
+    list: &'a mut Vec<Idle<T>>,
+}
+
+impl<'a, T: Poolable + 'a> IdlePopper<'a, T> {
+    fn pop(self, expiration: &Expiration) -> Option<Idle<T>> {
+        while let Some(entry) = self.list.pop() {
+            // If the connection has been closed, or is older than our idle
+            // timeout, simply drop it and keep looking...
+            if !entry.value.is_open() {
+                trace!("removing closed connection for {:?}", self.key);
+                continue;
+            }
+            // TODO: Actually, since the `idle` list is pushed to the end always,
+            // that would imply that if *this* entry is expired, then anything
+            // "earlier" in the list would *have* to be expired also... Right?
+            //
+            // In that case, we could just break out of the loop and drop the
+            // whole list...
+            if expiration.expires(entry.idle_at) {
+                trace!("removing expired connection for {:?}", self.key);
+                continue;
+            }
+
+            let value = match entry.value.reserve() {
+                #[cfg(feature = "http2")]
+                Reservation::Shared(to_reinsert, to_checkout) => {
+                    self.list.push(Idle {
+                        idle_at: Instant::now(),
+                        value: to_reinsert,
+                    });
+                    to_checkout
+                }
+                Reservation::Unique(unique) => unique,
+            };
+
+            return Some(Idle {
+                idle_at: entry.idle_at,
+                value,
+            });
+        }
+
+        None
+    }
+}
+
+impl<T: Poolable> PoolInner<T> {
+    fn put(&mut self, key: Key, value: T, __pool_ref: &Arc<Mutex<PoolInner<T>>>) {
+        if value.can_share() && self.idle.contains_key(&key) {
+            trace!("put; existing idle HTTP/2 connection for {:?}", key);
+            return;
+        }
+        trace!("put; add idle connection for {:?}", key);
+        let mut remove_waiters = false;
+        let mut value = Some(value);
+        if let Some(waiters) = self.waiters.get_mut(&key) {
+            while let Some(tx) = waiters.pop_front() {
+                if !tx.is_canceled() {
+                    let reserved = value.take().expect("value already sent");
+                    let reserved = match reserved.reserve() {
+                        #[cfg(feature = "http2")]
+                        Reservation::Shared(to_keep, to_send) => {
+                            value = Some(to_keep);
+                            to_send
+                        }
+                        Reservation::Unique(uniq) => uniq,
+                    };
+                    match tx.send(reserved) {
+                        Ok(()) => {
+                            if value.is_none() {
+                                break;
+                            } else {
+                                continue;
+                            }
+                        }
+                        Err(e) => {
+                            value = Some(e);
+                        }
+                    }
+                }
+
+                trace!("put; removing canceled waiter for {:?}", key);
+            }
+            remove_waiters = waiters.is_empty();
+        }
+        if remove_waiters {
+            self.waiters.remove(&key);
+        }
+
+        match value {
+            Some(value) => {
+                // borrow-check scope...
+                {
+                    let idle_list = self.idle.entry(key.clone()).or_insert_with(Vec::new);
+                    if self.max_idle_per_host <= idle_list.len() {
+                        trace!("max idle per host for {:?}, dropping connection", key);
+                        return;
+                    }
+
+                    debug!("pooling idle connection for {:?}", key);
+                    idle_list.push(Idle {
+                        value,
+                        idle_at: Instant::now(),
+                    });
+                }
+
+                #[cfg(feature = "runtime")]
+                {
+                    self.spawn_idle_interval(__pool_ref);
+                }
+            }
+            None => trace!("put; found waiter for {:?}", key),
+        }
+    }
+
+    /// A `Connecting` task is complete. Not necessarily successfully,
+    /// but the lock is going away, so clean up.
+    fn connected(&mut self, key: &Key) {
+        let existed = self.connecting.remove(key);
+        debug_assert!(existed, "Connecting dropped, key not in pool.connecting");
+        // cancel any waiters. if there are any, it's because
+        // this Connecting task didn't complete successfully.
+        // those waiters would never receive a connection.
+        self.waiters.remove(key);
+    }
+
+    #[cfg(feature = "runtime")]
+    fn spawn_idle_interval(&mut self, pool_ref: &Arc<Mutex<PoolInner<T>>>) {
+        let (dur, rx) = {
+            if self.idle_interval_ref.is_some() {
+                return;
+            }
+
+            if let Some(dur) = self.timeout {
+                let (tx, rx) = oneshot::channel();
+                self.idle_interval_ref = Some(tx);
+                (dur, rx)
+            } else {
+                return;
+            }
+        };
+
+        let interval = IdleTask {
+            interval: tokio::time::interval(dur),
+            pool: WeakOpt::downgrade(pool_ref),
+            pool_drop_notifier: rx,
+        };
+
+        self.exec.execute(interval);
+    }
+}
+
+impl<T> PoolInner<T> {
+    /// Any `FutureResponse`s that were created will have made a `Checkout`,
+    /// and possibly inserted into the pool that it is waiting for an idle
+    /// connection. If a user ever dropped that future, we need to clean out
+    /// those parked senders.
+    fn clean_waiters(&mut self, key: &Key) {
+        let mut remove_waiters = false;
+        if let Some(waiters) = self.waiters.get_mut(key) {
+            waiters.retain(|tx| !tx.is_canceled());
+            remove_waiters = waiters.is_empty();
+        }
+        if remove_waiters {
+            self.waiters.remove(key);
+        }
+    }
+}
+
+#[cfg(feature = "runtime")]
+impl<T: Poolable> PoolInner<T> {
+    /// This should *only* be called by the IdleTask
+    fn clear_expired(&mut self) {
+        let dur = self.timeout.expect("interval assumes timeout");
+
+        let now = Instant::now();
+        //self.last_idle_check_at = now;
+
+        self.idle.retain(|key, values| {
+            values.retain(|entry| {
+                if !entry.value.is_open() {
+                    trace!("idle interval evicting closed for {:?}", key);
+                    return false;
+                }
+
+                // Avoid `Instant::sub` to avoid issues like rust-lang/rust#86470.
+                if now.saturating_duration_since(entry.idle_at) > dur {
+                    trace!("idle interval evicting expired for {:?}", key);
+                    return false;
+                }
+
+                // Otherwise, keep this value...
+                true
+            });
+
+            // returning false evicts this key/val
+            !values.is_empty()
+        });
+    }
+}
+
+impl<T> Clone for Pool<T> {
+    fn clone(&self) -> Pool<T> {
+        Pool {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+/// A wrapped poolable value that tries to reinsert to the Pool on Drop.
+// Note: The bounds `T: Poolable` is needed for the Drop impl.
+pub(super) struct Pooled<T: Poolable> {
+    value: Option<T>,
+    is_reused: bool,
+    key: Key,
+    pool: WeakOpt<Mutex<PoolInner<T>>>,
+}
+
+impl<T: Poolable> Pooled<T> {
+    pub(super) fn is_reused(&self) -> bool {
+        self.is_reused
+    }
+
+    pub(super) fn is_pool_enabled(&self) -> bool {
+        self.pool.0.is_some()
+    }
+
+    fn as_ref(&self) -> &T {
+        self.value.as_ref().expect("not dropped")
+    }
+
+    fn as_mut(&mut self) -> &mut T {
+        self.value.as_mut().expect("not dropped")
+    }
+}
+
+impl<T: Poolable> Deref for Pooled<T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        self.as_ref()
+    }
+}
+
+impl<T: Poolable> DerefMut for Pooled<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        self.as_mut()
+    }
+}
+
+impl<T: Poolable> Drop for Pooled<T> {
+    fn drop(&mut self) {
+        if let Some(value) = self.value.take() {
+            if !value.is_open() {
+                // If we *already* know the connection is done here,
+                // it shouldn't be re-inserted back into the pool.
+                return;
+            }
+
+            if let Some(pool) = self.pool.upgrade() {
+                if let Ok(mut inner) = pool.lock() {
+                    inner.put(self.key.clone(), value, &pool);
+                }
+            } else if !value.can_share() {
+                trace!("pool dropped, dropping pooled ({:?})", self.key);
+            }
+            // Ver::Http2 is already in the Pool (or dead), so we wouldn't
+            // have an actual reference to the Pool.
+        }
+    }
+}
+
+impl<T: Poolable> fmt::Debug for Pooled<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Pooled").field("key", &self.key).finish()
+    }
+}
+
+struct Idle<T> {
+    idle_at: Instant,
+    value: T,
+}
+
+// FIXME: allow() required due to `impl Trait` leaking types to this lint
+#[allow(missing_debug_implementations)]
+pub(super) struct Checkout<T> {
+    key: Key,
+    pool: Pool<T>,
+    waiter: Option<oneshot::Receiver<T>>,
+}
+
+#[derive(Debug)]
+pub(super) struct CheckoutIsClosedError;
+
+impl StdError for CheckoutIsClosedError {}
+
+impl fmt::Display for CheckoutIsClosedError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("checked out connection was closed")
+    }
+}
+
+impl<T: Poolable> Checkout<T> {
+    fn poll_waiter(&mut self, cx: &mut Context<'_>) -> Poll<Option<crate::Result<Pooled<T>>>> {
+        if let Some(mut rx) = self.waiter.take() {
+            match Pin::new(&mut rx).poll(cx) {
+                Poll::Ready(Ok(value)) => {
+                    if value.is_open() {
+                        Poll::Ready(Some(Ok(self.pool.reuse(&self.key, value))))
+                    } else {
+                        Poll::Ready(Some(Err(
+                            crate::Error::new_canceled().with(CheckoutIsClosedError)
+                        )))
+                    }
+                }
+                Poll::Pending => {
+                    self.waiter = Some(rx);
+                    Poll::Pending
+                }
+                Poll::Ready(Err(_canceled)) => Poll::Ready(Some(Err(
+                    crate::Error::new_canceled().with("request has been canceled")
+                ))),
+            }
+        } else {
+            Poll::Ready(None)
+        }
+    }
+
+    fn checkout(&mut self, cx: &mut Context<'_>) -> Option<Pooled<T>> {
+        let entry = {
+            let mut inner = self.pool.inner.as_ref()?.lock().unwrap();
+            let expiration = Expiration::new(inner.timeout);
+            let maybe_entry = inner.idle.get_mut(&self.key).and_then(|list| {
+                trace!("take? {:?}: expiration = {:?}", self.key, expiration.0);
+                // A block to end the mutable borrow on list,
+                // so the map below can check is_empty()
+                {
+                    let popper = IdlePopper {
+                        key: &self.key,
+                        list,
+                    };
+                    popper.pop(&expiration)
+                }
+                .map(|e| (e, list.is_empty()))
+            });
+
+            let (entry, empty) = if let Some((e, empty)) = maybe_entry {
+                (Some(e), empty)
+            } else {
+                // No entry found means nuke the list for sure.
+                (None, true)
+            };
+            if empty {
+                //TODO: This could be done with the HashMap::entry API instead.
+                inner.idle.remove(&self.key);
+            }
+
+            if entry.is_none() && self.waiter.is_none() {
+                let (tx, mut rx) = oneshot::channel();
+                trace!("checkout waiting for idle connection: {:?}", self.key);
+                inner
+                    .waiters
+                    .entry(self.key.clone())
+                    .or_insert_with(VecDeque::new)
+                    .push_back(tx);
+
+                // register the waker with this oneshot
+                assert!(Pin::new(&mut rx).poll(cx).is_pending());
+                self.waiter = Some(rx);
+            }
+
+            entry
+        };
+
+        entry.map(|e| self.pool.reuse(&self.key, e.value))
+    }
+}
+
+impl<T: Poolable> Future for Checkout<T> {
+    type Output = crate::Result<Pooled<T>>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        if let Some(pooled) = ready!(self.poll_waiter(cx)?) {
+            return Poll::Ready(Ok(pooled));
+        }
+
+        if let Some(pooled) = self.checkout(cx) {
+            Poll::Ready(Ok(pooled))
+        } else if !self.pool.is_enabled() {
+            Poll::Ready(Err(crate::Error::new_canceled().with("pool is disabled")))
+        } else {
+            // There's a new waiter, already registered in self.checkout()
+            debug_assert!(self.waiter.is_some());
+            Poll::Pending
+        }
+    }
+}
+
+impl<T> Drop for Checkout<T> {
+    fn drop(&mut self) {
+        if self.waiter.take().is_some() {
+            trace!("checkout dropped for {:?}", self.key);
+            if let Some(Ok(mut inner)) = self.pool.inner.as_ref().map(|i| i.lock()) {
+                inner.clean_waiters(&self.key);
+            }
+        }
+    }
+}
+
+// FIXME: allow() required due to `impl Trait` leaking types to this lint
+#[allow(missing_debug_implementations)]
+pub(super) struct Connecting<T: Poolable> {
+    key: Key,
+    pool: WeakOpt<Mutex<PoolInner<T>>>,
+}
+
+impl<T: Poolable> Connecting<T> {
+    pub(super) fn alpn_h2(self, pool: &Pool<T>) -> Option<Self> {
+        debug_assert!(
+            self.pool.0.is_none(),
+            "Connecting::alpn_h2 but already Http2"
+        );
+
+        pool.connecting(&self.key, Ver::Http2)
+    }
+}
+
+impl<T: Poolable> Drop for Connecting<T> {
+    fn drop(&mut self) {
+        if let Some(pool) = self.pool.upgrade() {
+            // No need to panic on drop, that could abort!
+            if let Ok(mut inner) = pool.lock() {
+                inner.connected(&self.key);
+            }
+        }
+    }
+}
+
+struct Expiration(Option<Duration>);
+
+impl Expiration {
+    fn new(dur: Option<Duration>) -> Expiration {
+        Expiration(dur)
+    }
+
+    fn expires(&self, instant: Instant) -> bool {
+        match self.0 {
+            // Avoid `Instant::elapsed` to avoid issues like rust-lang/rust#86470.
+            Some(timeout) => Instant::now().saturating_duration_since(instant) > timeout,
+            None => false,
+        }
+    }
+}
+
+#[cfg(feature = "runtime")]
+pin_project_lite::pin_project! {
+    struct IdleTask<T> {
+        #[pin]
+        interval: Interval,
+        pool: WeakOpt<Mutex<PoolInner<T>>>,
+        // This allows the IdleTask to be notified as soon as the entire
+        // Pool is fully dropped, and shutdown. This channel is never sent on,
+        // but Err(Canceled) will be received when the Pool is dropped.
+        #[pin]
+        pool_drop_notifier: oneshot::Receiver<std::convert::Infallible>,
+    }
+}
+
+#[cfg(feature = "runtime")]
+impl<T: Poolable + 'static> Future for IdleTask<T> {
+    type Output = ();
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+        loop {
+            match this.pool_drop_notifier.as_mut().poll(cx) {
+                Poll::Ready(Ok(n)) => match n {},
+                Poll::Pending => (),
+                Poll::Ready(Err(_canceled)) => {
+                    trace!("pool closed, canceling idle interval");
+                    return Poll::Ready(());
+                }
+            }
+
+            ready!(this.interval.as_mut().poll_tick(cx));
+
+            if let Some(inner) = this.pool.upgrade() {
+                if let Ok(mut inner) = inner.lock() {
+                    trace!("idle interval checking for expired");
+                    inner.clear_expired();
+                    continue;
+                }
+            }
+            return Poll::Ready(());
+        }
+    }
+}
+
+impl<T> WeakOpt<T> {
+    fn none() -> Self {
+        WeakOpt(None)
+    }
+
+    fn downgrade(arc: &Arc<T>) -> Self {
+        WeakOpt(Some(Arc::downgrade(arc)))
+    }
+
+    fn upgrade(&self) -> Option<Arc<T>> {
+        self.0.as_ref().and_then(Weak::upgrade)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::future::Future;
+    use std::pin::Pin;
+    use std::task::Context;
+    use std::task::Poll;
+    use std::time::Duration;
+
+    use super::{Connecting, Key, Pool, Poolable, Reservation, WeakOpt};
+    use crate::common::exec::Exec;
+
+    /// Test unique reservations.
+    #[derive(Debug, PartialEq, Eq)]
+    struct Uniq<T>(T);
+
+    impl<T: Send + 'static + Unpin> Poolable for Uniq<T> {
+        fn is_open(&self) -> bool {
+            true
+        }
+
+        fn reserve(self) -> Reservation<Self> {
+            Reservation::Unique(self)
+        }
+
+        fn can_share(&self) -> bool {
+            false
+        }
+    }
+
+    fn c<T: Poolable>(key: Key) -> Connecting<T> {
+        Connecting {
+            key,
+            pool: WeakOpt::none(),
+        }
+    }
+
+    fn host_key(s: &str) -> Key {
+        (http::uri::Scheme::HTTP, s.parse().expect("host key"))
+    }
+
+    fn pool_no_timer<T>() -> Pool<T> {
+        pool_max_idle_no_timer(::std::usize::MAX)
+    }
+
+    fn pool_max_idle_no_timer<T>(max_idle: usize) -> Pool<T> {
+        let pool = Pool::new(
+            super::Config {
+                idle_timeout: Some(Duration::from_millis(100)),
+                max_idle_per_host: max_idle,
+            },
+            &Exec::Default,
+        );
+        pool.no_timer();
+        pool
+    }
+
+    #[tokio::test]
+    async fn test_pool_checkout_smoke() {
+        let pool = pool_no_timer();
+        let key = host_key("foo");
+        let pooled = pool.pooled(c(key.clone()), Uniq(41));
+
+        drop(pooled);
+
+        match pool.checkout(key).await {
+            Ok(pooled) => assert_eq!(*pooled, Uniq(41)),
+            Err(_) => panic!("not ready"),
+        };
+    }
+
+    /// Helper to check if the future is ready after polling once.
+    struct PollOnce<'a, F>(&'a mut F);
+
+    impl<F, T, U> Future for PollOnce<'_, F>
+    where
+        F: Future<Output = Result<T, U>> + Unpin,
+    {
+        type Output = Option<()>;
+
+        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+            match Pin::new(&mut self.0).poll(cx) {
+                Poll::Ready(Ok(_)) => Poll::Ready(Some(())),
+                Poll::Ready(Err(_)) => Poll::Ready(Some(())),
+                Poll::Pending => Poll::Ready(None),
+            }
+        }
+    }
+
+    #[tokio::test]
+    async fn test_pool_checkout_returns_none_if_expired() {
+        let pool = pool_no_timer();
+        let key = host_key("foo");
+        let pooled = pool.pooled(c(key.clone()), Uniq(41));
+
+        drop(pooled);
+        tokio::time::sleep(pool.locked().timeout.unwrap()).await;
+        let mut checkout = pool.checkout(key);
+        let poll_once = PollOnce(&mut checkout);
+        let is_not_ready = poll_once.await.is_none();
+        assert!(is_not_ready);
+    }
+
+    #[cfg(feature = "runtime")]
+    #[tokio::test]
+    async fn test_pool_checkout_removes_expired() {
+        let pool = pool_no_timer();
+        let key = host_key("foo");
+
+        pool.pooled(c(key.clone()), Uniq(41));
+        pool.pooled(c(key.clone()), Uniq(5));
+        pool.pooled(c(key.clone()), Uniq(99));
+
+        assert_eq!(
+            pool.locked().idle.get(&key).map(|entries| entries.len()),
+            Some(3)
+        );
+        tokio::time::sleep(pool.locked().timeout.unwrap()).await;
+
+        let mut checkout = pool.checkout(key.clone());
+        let poll_once = PollOnce(&mut checkout);
+        // checkout.await should clean out the expired
+        poll_once.await;
+        assert!(pool.locked().idle.get(&key).is_none());
+    }
+
+    #[test]
+    fn test_pool_max_idle_per_host() {
+        let pool = pool_max_idle_no_timer(2);
+        let key = host_key("foo");
+
+        pool.pooled(c(key.clone()), Uniq(41));
+        pool.pooled(c(key.clone()), Uniq(5));
+        pool.pooled(c(key.clone()), Uniq(99));
+
+        // pooled and dropped 3, max_idle should only allow 2
+        assert_eq!(
+            pool.locked().idle.get(&key).map(|entries| entries.len()),
+            Some(2)
+        );
+    }
+
+    #[cfg(feature = "runtime")]
+    #[tokio::test]
+    async fn test_pool_timer_removes_expired() {
+        let _ = pretty_env_logger::try_init();
+        tokio::time::pause();
+
+        let pool = Pool::new(
+            super::Config {
+                idle_timeout: Some(Duration::from_millis(10)),
+                max_idle_per_host: std::usize::MAX,
+            },
+            &Exec::Default,
+        );
+
+        let key = host_key("foo");
+
+        pool.pooled(c(key.clone()), Uniq(41));
+        pool.pooled(c(key.clone()), Uniq(5));
+        pool.pooled(c(key.clone()), Uniq(99));
+
+        assert_eq!(
+            pool.locked().idle.get(&key).map(|entries| entries.len()),
+            Some(3)
+        );
+
+        // Let the timer tick passed the expiration...
+        tokio::time::advance(Duration::from_millis(30)).await;
+        // Yield so the Interval can reap...
+        tokio::task::yield_now().await;
+
+        assert!(pool.locked().idle.get(&key).is_none());
+    }
+
+    #[tokio::test]
+    async fn test_pool_checkout_task_unparked() {
+        use futures_util::future::join;
+        use futures_util::FutureExt;
+
+        let pool = pool_no_timer();
+        let key = host_key("foo");
+        let pooled = pool.pooled(c(key.clone()), Uniq(41));
+
+        let checkout = join(pool.checkout(key), async {
+            // the checkout future will park first,
+            // and then this lazy future will be polled, which will insert
+            // the pooled back into the pool
+            //
+            // this test makes sure that doing so will unpark the checkout
+            drop(pooled);
+        })
+        .map(|(entry, _)| entry);
+
+        assert_eq!(*checkout.await.unwrap(), Uniq(41));
+    }
+
+    #[tokio::test]
+    async fn test_pool_checkout_drop_cleans_up_waiters() {
+        let pool = pool_no_timer::<Uniq<i32>>();
+        let key = host_key("foo");
+
+        let mut checkout1 = pool.checkout(key.clone());
+        let mut checkout2 = pool.checkout(key.clone());
+
+        let poll_once1 = PollOnce(&mut checkout1);
+        let poll_once2 = PollOnce(&mut checkout2);
+
+        // first poll needed to get into Pool's parked
+        poll_once1.await;
+        assert_eq!(pool.locked().waiters.get(&key).unwrap().len(), 1);
+        poll_once2.await;
+        assert_eq!(pool.locked().waiters.get(&key).unwrap().len(), 2);
+
+        // on drop, clean up Pool
+        drop(checkout1);
+        assert_eq!(pool.locked().waiters.get(&key).unwrap().len(), 1);
+
+        drop(checkout2);
+        assert!(pool.locked().waiters.get(&key).is_none());
+    }
+
+    #[derive(Debug)]
+    struct CanClose {
+        #[allow(unused)]
+        val: i32,
+        closed: bool,
+    }
+
+    impl Poolable for CanClose {
+        fn is_open(&self) -> bool {
+            !self.closed
+        }
+
+        fn reserve(self) -> Reservation<Self> {
+            Reservation::Unique(self)
+        }
+
+        fn can_share(&self) -> bool {
+            false
+        }
+    }
+
+    #[test]
+    fn pooled_drop_if_closed_doesnt_reinsert() {
+        let pool = pool_no_timer();
+        let key = host_key("foo");
+        pool.pooled(
+            c(key.clone()),
+            CanClose {
+                val: 57,
+                closed: true,
+            },
+        );
+
+        assert!(!pool.locked().idle.contains_key(&key));
+    }
+}
diff --git a/src/client/service.rs b/src/client/service.rs
new file mode 100644
index 0000000..047dd98
--- /dev/null
+++ b/src/client/service.rs
@@ -0,0 +1,95 @@
+//! Utilities used to interact with the Tower ecosystem.
+//!
+//! This module provides `Connect` which hook-ins into the Tower ecosystem.
+
+use std::error::Error as StdError;
+use std::future::Future;
+use std::marker::PhantomData;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use tracing::debug;
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+use super::conn::{Builder, SendRequest};
+use crate::{
+    body::HttpBody,
+    service::{MakeConnection, Service},
+};
+
+/// Creates a connection via `SendRequest`.
+///
+/// This accepts a `hyper::client::conn::Builder` and provides
+/// a `MakeService` implementation to create connections from some
+/// target `T`.
+#[derive(Debug)]
+pub struct Connect<C, B, T> {
+    inner: C,
+    #[cfg_attr(feature = "deprecated", allow(deprecated))]
+    builder: Builder,
+    _pd: PhantomData<fn(T, B)>,
+}
+
+impl<C, B, T> Connect<C, B, T> {
+    /// Create a new `Connect` with some inner connector `C` and a connection
+    /// builder.
+    #[cfg_attr(feature = "deprecated", allow(deprecated))]
+    pub fn new(inner: C, builder: Builder) -> Self {
+        Self {
+            inner,
+            builder,
+            _pd: PhantomData,
+        }
+    }
+}
+
+impl<C, B, T> Service<T> for Connect<C, B, T>
+where
+    C: MakeConnection<T>,
+    C::Connection: Unpin + Send + 'static,
+    C::Future: Send + 'static,
+    C::Error: Into<Box<dyn StdError + Send + Sync>> + Send,
+    B: HttpBody + Unpin + Send + 'static,
+    B::Data: Send + Unpin,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    #[cfg_attr(feature = "deprecated", allow(deprecated))]
+    type Response = SendRequest<B>;
+    type Error = crate::Error;
+    type Future =
+        Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send + 'static>>;
+
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.inner
+            .poll_ready(cx)
+            .map_err(|e| crate::Error::new(crate::error::Kind::Connect).with(e.into()))
+    }
+
+    fn call(&mut self, req: T) -> Self::Future {
+        let builder = self.builder.clone();
+        let io = self.inner.make_connection(req);
+
+        let fut = async move {
+            match io.await {
+                Ok(io) => match builder.handshake(io).await {
+                    Ok((sr, conn)) => {
+                        #[cfg_attr(feature = "deprecated", allow(deprecated))]
+                        builder.exec.execute(async move {
+                            if let Err(e) = conn.await {
+                                debug!("connection error: {:?}", e);
+                            }
+                        });
+                        Ok(sr)
+                    }
+                    Err(e) => Err(e),
+                },
+                Err(e) => {
+                    let err = crate::Error::new(crate::error::Kind::Connect).with(e.into());
+                    Err(err)
+                }
+            }
+        };
+
+        Box::pin(fut)
+    }
+}
diff --git a/src/client/tests.rs b/src/client/tests.rs
new file mode 100644
index 0000000..0a281a6
--- /dev/null
+++ b/src/client/tests.rs
@@ -0,0 +1,286 @@
+use std::io;
+
+use futures_util::future;
+use tokio::net::TcpStream;
+
+use super::Client;
+
+#[tokio::test]
+async fn client_connect_uri_argument() {
+    let connector = tower::service_fn(|dst: http::Uri| {
+        assert_eq!(dst.scheme(), Some(&http::uri::Scheme::HTTP));
+        assert_eq!(dst.host(), Some("example.local"));
+        assert_eq!(dst.port(), None);
+        assert_eq!(dst.path(), "/", "path should be removed");
+
+        future::err::<TcpStream, _>(io::Error::new(io::ErrorKind::Other, "expect me"))
+    });
+
+    let client = Client::builder().build::<_, crate::Body>(connector);
+    let _ = client
+        .get("http://example.local/and/a/path".parse().unwrap())
+        .await
+        .expect_err("response should fail");
+}
+
+/*
+// FIXME: re-implement tests with `async/await`
+#[test]
+fn retryable_request() {
+    let _ = pretty_env_logger::try_init();
+
+    let mut rt = Runtime::new().expect("new rt");
+    let mut connector = MockConnector::new();
+
+    let sock1 = connector.mock("http://mock.local");
+    let sock2 = connector.mock("http://mock.local");
+
+    let client = Client::builder()
+        .build::<_, crate::Body>(connector);
+
+    client.pool.no_timer();
+
+    {
+
+        let req = Request::builder()
+            .uri("http://mock.local/a")
+            .body(Default::default())
+            .unwrap();
+        let res1 = client.request(req);
+        let srv1 = poll_fn(|| {
+            try_ready!(sock1.read(&mut [0u8; 512]));
+            try_ready!(sock1.write(b"HTTP/1.1 200 OK\r\nContent-Length: 0\r\n\r\n"));
+            Ok(Async::Ready(()))
+        }).map_err(|e: std::io::Error| panic!("srv1 poll_fn error: {}", e));
+        rt.block_on(res1.join(srv1)).expect("res1");
+    }
+    drop(sock1);
+
+    let req = Request::builder()
+        .uri("http://mock.local/b")
+        .body(Default::default())
+        .unwrap();
+    let res2 = client.request(req)
+        .map(|res| {
+            assert_eq!(res.status().as_u16(), 222);
+        });
+    let srv2 = poll_fn(|| {
+        try_ready!(sock2.read(&mut [0u8; 512]));
+        try_ready!(sock2.write(b"HTTP/1.1 222 OK\r\nContent-Length: 0\r\n\r\n"));
+        Ok(Async::Ready(()))
+    }).map_err(|e: std::io::Error| panic!("srv2 poll_fn error: {}", e));
+
+    rt.block_on(res2.join(srv2)).expect("res2");
+}
+
+#[test]
+fn conn_reset_after_write() {
+    let _ = pretty_env_logger::try_init();
+
+    let mut rt = Runtime::new().expect("new rt");
+    let mut connector = MockConnector::new();
+
+    let sock1 = connector.mock("http://mock.local");
+
+    let client = Client::builder()
+        .build::<_, crate::Body>(connector);
+
+    client.pool.no_timer();
+
+    {
+        let req = Request::builder()
+            .uri("http://mock.local/a")
+            .body(Default::default())
+            .unwrap();
+        let res1 = client.request(req);
+        let srv1 = poll_fn(|| {
+            try_ready!(sock1.read(&mut [0u8; 512]));
+            try_ready!(sock1.write(b"HTTP/1.1 200 OK\r\nContent-Length: 0\r\n\r\n"));
+            Ok(Async::Ready(()))
+        }).map_err(|e: std::io::Error| panic!("srv1 poll_fn error: {}", e));
+        rt.block_on(res1.join(srv1)).expect("res1");
+    }
+
+    let req = Request::builder()
+        .uri("http://mock.local/a")
+        .body(Default::default())
+        .unwrap();
+    let res2 = client.request(req);
+    let mut sock1 = Some(sock1);
+    let srv2 = poll_fn(|| {
+        // We purposefully keep the socket open until the client
+        // has written the second request, and THEN disconnect.
+        //
+        // Not because we expect servers to be jerks, but to trigger
+        // state where we write on an assumedly good connection, and
+        // only reset the close AFTER we wrote bytes.
+        try_ready!(sock1.as_mut().unwrap().read(&mut [0u8; 512]));
+        sock1.take();
+        Ok(Async::Ready(()))
+    }).map_err(|e: std::io::Error| panic!("srv2 poll_fn error: {}", e));
+    let err = rt.block_on(res2.join(srv2)).expect_err("res2");
+    assert!(err.is_incomplete_message(), "{:?}", err);
+}
+
+#[test]
+fn checkout_win_allows_connect_future_to_be_pooled() {
+    let _ = pretty_env_logger::try_init();
+
+    let mut rt = Runtime::new().expect("new rt");
+    let mut connector = MockConnector::new();
+
+
+    let (tx, rx) = oneshot::channel::<()>();
+    let sock1 = connector.mock("http://mock.local");
+    let sock2 = connector.mock_fut("http://mock.local", rx);
+
+    let client = Client::builder()
+        .build::<_, crate::Body>(connector);
+
+    client.pool.no_timer();
+
+    let uri = "http://mock.local/a".parse::<crate::Uri>().expect("uri parse");
+
+    // First request just sets us up to have a connection able to be put
+    // back in the pool. *However*, it doesn't insert immediately. The
+    // body has 1 pending byte, and we will only drain in request 2, once
+    // the connect future has been started.
+    let mut body = {
+        let res1 = client.get(uri.clone())
+            .map(|res| res.into_body().concat2());
+        let srv1 = poll_fn(|| {
+            try_ready!(sock1.read(&mut [0u8; 512]));
+            // Chunked is used so as to force 2 body reads.
+            try_ready!(sock1.write(b"\
+                HTTP/1.1 200 OK\r\n\
+                transfer-encoding: chunked\r\n\
+                \r\n\
+                1\r\nx\r\n\
+                0\r\n\r\n\
+            "));
+            Ok(Async::Ready(()))
+        }).map_err(|e: std::io::Error| panic!("srv1 poll_fn error: {}", e));
+
+        rt.block_on(res1.join(srv1)).expect("res1").0
+    };
+
+
+    // The second request triggers the only mocked connect future, but then
+    // the drained body allows the first socket to go back to the pool,
+    // "winning" the checkout race.
+    {
+        let res2 = client.get(uri.clone());
+        let drain = poll_fn(move || {
+            body.poll()
+        });
+        let srv2 = poll_fn(|| {
+            try_ready!(sock1.read(&mut [0u8; 512]));
+            try_ready!(sock1.write(b"HTTP/1.1 200 OK\r\nConnection: close\r\n\r\nx"));
+            Ok(Async::Ready(()))
+        }).map_err(|e: std::io::Error| panic!("srv2 poll_fn error: {}", e));
+
+        rt.block_on(res2.join(drain).join(srv2)).expect("res2");
+    }
+
+    // "Release" the mocked connect future, and let the runtime spin once so
+    // it's all setup...
+    {
+        let mut tx = Some(tx);
+        let client = &client;
+        let key = client.pool.h1_key("http://mock.local");
+        let mut tick_cnt = 0;
+        let fut = poll_fn(move || {
+            tx.take();
+
+            if client.pool.idle_count(&key) == 0 {
+                tick_cnt += 1;
+                assert!(tick_cnt < 10, "ticked too many times waiting for idle");
+                trace!("no idle yet; tick count: {}", tick_cnt);
+                ::futures::task::current().notify();
+                Ok(Async::NotReady)
+            } else {
+                Ok::<_, ()>(Async::Ready(()))
+            }
+        });
+        rt.block_on(fut).unwrap();
+    }
+
+    // Third request just tests out that the "loser" connection was pooled. If
+    // it isn't, this will panic since the MockConnector doesn't have any more
+    // mocks to give out.
+    {
+        let res3 = client.get(uri);
+        let srv3 = poll_fn(|| {
+            try_ready!(sock2.read(&mut [0u8; 512]));
+            try_ready!(sock2.write(b"HTTP/1.1 200 OK\r\nContent-Length: 0\r\n\r\n"));
+            Ok(Async::Ready(()))
+        }).map_err(|e: std::io::Error| panic!("srv3 poll_fn error: {}", e));
+
+        rt.block_on(res3.join(srv3)).expect("res3");
+    }
+}
+
+#[cfg(feature = "nightly")]
+#[bench]
+fn bench_http1_get_0b(b: &mut test::Bencher) {
+    let _ = pretty_env_logger::try_init();
+
+    let mut rt = Runtime::new().expect("new rt");
+    let mut connector = MockConnector::new();
+
+
+    let client = Client::builder()
+        .build::<_, crate::Body>(connector.clone());
+
+    client.pool.no_timer();
+
+    let uri = Uri::from_static("http://mock.local/a");
+
+    b.iter(move || {
+        let sock1 = connector.mock("http://mock.local");
+        let res1 = client
+            .get(uri.clone())
+            .and_then(|res| {
+                res.into_body().for_each(|_| Ok(()))
+            });
+        let srv1 = poll_fn(|| {
+            try_ready!(sock1.read(&mut [0u8; 512]));
+            try_ready!(sock1.write(b"HTTP/1.1 200 OK\r\nContent-Length: 0\r\n\r\n"));
+            Ok(Async::Ready(()))
+        }).map_err(|e: std::io::Error| panic!("srv1 poll_fn error: {}", e));
+        rt.block_on(res1.join(srv1)).expect("res1");
+    });
+}
+
+#[cfg(feature = "nightly")]
+#[bench]
+fn bench_http1_get_10b(b: &mut test::Bencher) {
+    let _ = pretty_env_logger::try_init();
+
+    let mut rt = Runtime::new().expect("new rt");
+    let mut connector = MockConnector::new();
+
+
+    let client = Client::builder()
+        .build::<_, crate::Body>(connector.clone());
+
+    client.pool.no_timer();
+
+    let uri = Uri::from_static("http://mock.local/a");
+
+    b.iter(move || {
+        let sock1 = connector.mock("http://mock.local");
+        let res1 = client
+            .get(uri.clone())
+            .and_then(|res| {
+                res.into_body().for_each(|_| Ok(()))
+            });
+        let srv1 = poll_fn(|| {
+            try_ready!(sock1.read(&mut [0u8; 512]));
+            try_ready!(sock1.write(b"HTTP/1.1 200 OK\r\nContent-Length: 10\r\n\r\n0123456789"));
+            Ok(Async::Ready(()))
+        }).map_err(|e: std::io::Error| panic!("srv1 poll_fn error: {}", e));
+        rt.block_on(res1.join(srv1)).expect("res1");
+    });
+}
+*/
diff --git a/src/common/buf.rs b/src/common/buf.rs
new file mode 100644
index 0000000..64e9333
--- /dev/null
+++ b/src/common/buf.rs
@@ -0,0 +1,151 @@
+use std::collections::VecDeque;
+use std::io::IoSlice;
+
+use bytes::{Buf, BufMut, Bytes, BytesMut};
+
+pub(crate) struct BufList<T> {
+    bufs: VecDeque<T>,
+}
+
+impl<T: Buf> BufList<T> {
+    pub(crate) fn new() -> BufList<T> {
+        BufList {
+            bufs: VecDeque::new(),
+        }
+    }
+
+    #[inline]
+    pub(crate) fn push(&mut self, buf: T) {
+        debug_assert!(buf.has_remaining());
+        self.bufs.push_back(buf);
+    }
+
+    #[inline]
+    #[cfg(feature = "http1")]
+    pub(crate) fn bufs_cnt(&self) -> usize {
+        self.bufs.len()
+    }
+}
+
+impl<T: Buf> Buf for BufList<T> {
+    #[inline]
+    fn remaining(&self) -> usize {
+        self.bufs.iter().map(|buf| buf.remaining()).sum()
+    }
+
+    #[inline]
+    fn chunk(&self) -> &[u8] {
+        self.bufs.front().map(Buf::chunk).unwrap_or_default()
+    }
+
+    #[inline]
+    fn advance(&mut self, mut cnt: usize) {
+        while cnt > 0 {
+            {
+                let front = &mut self.bufs[0];
+                let rem = front.remaining();
+                if rem > cnt {
+                    front.advance(cnt);
+                    return;
+                } else {
+                    front.advance(rem);
+                    cnt -= rem;
+                }
+            }
+            self.bufs.pop_front();
+        }
+    }
+
+    #[inline]
+    fn chunks_vectored<'t>(&'t self, dst: &mut [IoSlice<'t>]) -> usize {
+        if dst.is_empty() {
+            return 0;
+        }
+        let mut vecs = 0;
+        for buf in &self.bufs {
+            vecs += buf.chunks_vectored(&mut dst[vecs..]);
+            if vecs == dst.len() {
+                break;
+            }
+        }
+        vecs
+    }
+
+    #[inline]
+    fn copy_to_bytes(&mut self, len: usize) -> Bytes {
+        // Our inner buffer may have an optimized version of copy_to_bytes, and if the whole
+        // request can be fulfilled by the front buffer, we can take advantage.
+        match self.bufs.front_mut() {
+            Some(front) if front.remaining() == len => {
+                let b = front.copy_to_bytes(len);
+                self.bufs.pop_front();
+                b
+            }
+            Some(front) if front.remaining() > len => front.copy_to_bytes(len),
+            _ => {
+                assert!(len <= self.remaining(), "`len` greater than remaining");
+                let mut bm = BytesMut::with_capacity(len);
+                bm.put(self.take(len));
+                bm.freeze()
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::ptr;
+
+    use super::*;
+
+    fn hello_world_buf() -> BufList<Bytes> {
+        BufList {
+            bufs: vec![Bytes::from("Hello"), Bytes::from(" "), Bytes::from("World")].into(),
+        }
+    }
+
+    #[test]
+    fn to_bytes_shorter() {
+        let mut bufs = hello_world_buf();
+        let old_ptr = bufs.chunk().as_ptr();
+        let start = bufs.copy_to_bytes(4);
+        assert_eq!(start, "Hell");
+        assert!(ptr::eq(old_ptr, start.as_ptr()));
+        assert_eq!(bufs.chunk(), b"o");
+        assert!(ptr::eq(old_ptr.wrapping_add(4), bufs.chunk().as_ptr()));
+        assert_eq!(bufs.remaining(), 7);
+    }
+
+    #[test]
+    fn to_bytes_eq() {
+        let mut bufs = hello_world_buf();
+        let old_ptr = bufs.chunk().as_ptr();
+        let start = bufs.copy_to_bytes(5);
+        assert_eq!(start, "Hello");
+        assert!(ptr::eq(old_ptr, start.as_ptr()));
+        assert_eq!(bufs.chunk(), b" ");
+        assert_eq!(bufs.remaining(), 6);
+    }
+
+    #[test]
+    fn to_bytes_longer() {
+        let mut bufs = hello_world_buf();
+        let start = bufs.copy_to_bytes(7);
+        assert_eq!(start, "Hello W");
+        assert_eq!(bufs.remaining(), 4);
+    }
+
+    #[test]
+    fn one_long_buf_to_bytes() {
+        let mut buf = BufList::new();
+        buf.push(b"Hello World" as &[_]);
+        assert_eq!(buf.copy_to_bytes(5), "Hello");
+        assert_eq!(buf.chunk(), b" World");
+    }
+
+    #[test]
+    #[should_panic(expected = "`len` greater than remaining")]
+    fn buf_to_bytes_too_many() {
+        hello_world_buf().copy_to_bytes(42);
+    }
+}
diff --git a/src/common/date.rs b/src/common/date.rs
new file mode 100644
index 0000000..a436fc0
--- /dev/null
+++ b/src/common/date.rs
@@ -0,0 +1,124 @@
+use std::cell::RefCell;
+use std::fmt::{self, Write};
+use std::str;
+use std::time::{Duration, SystemTime};
+
+#[cfg(feature = "http2")]
+use http::header::HeaderValue;
+use httpdate::HttpDate;
+
+// "Sun, 06 Nov 1994 08:49:37 GMT".len()
+pub(crate) const DATE_VALUE_LENGTH: usize = 29;
+
+#[cfg(feature = "http1")]
+pub(crate) fn extend(dst: &mut Vec<u8>) {
+    CACHED.with(|cache| {
+        dst.extend_from_slice(cache.borrow().buffer());
+    })
+}
+
+#[cfg(feature = "http1")]
+pub(crate) fn update() {
+    CACHED.with(|cache| {
+        cache.borrow_mut().check();
+    })
+}
+
+#[cfg(feature = "http2")]
+pub(crate) fn update_and_header_value() -> HeaderValue {
+    CACHED.with(|cache| {
+        let mut cache = cache.borrow_mut();
+        cache.check();
+        HeaderValue::from_bytes(cache.buffer()).expect("Date format should be valid HeaderValue")
+    })
+}
+
+struct CachedDate {
+    bytes: [u8; DATE_VALUE_LENGTH],
+    pos: usize,
+    next_update: SystemTime,
+}
+
+thread_local!(static CACHED: RefCell<CachedDate> = RefCell::new(CachedDate::new()));
+
+impl CachedDate {
+    fn new() -> Self {
+        let mut cache = CachedDate {
+            bytes: [0; DATE_VALUE_LENGTH],
+            pos: 0,
+            next_update: SystemTime::now(),
+        };
+        cache.update(cache.next_update);
+        cache
+    }
+
+    fn buffer(&self) -> &[u8] {
+        &self.bytes[..]
+    }
+
+    fn check(&mut self) {
+        let now = SystemTime::now();
+        if now > self.next_update {
+            self.update(now);
+        }
+    }
+
+    fn update(&mut self, now: SystemTime) {
+        self.render(now);
+        self.next_update = now + Duration::new(1, 0);
+    }
+
+    fn render(&mut self, now: SystemTime) {
+        self.pos = 0;
+        let _ = write!(self, "{}", HttpDate::from(now));
+        debug_assert!(self.pos == DATE_VALUE_LENGTH);
+    }
+}
+
+impl fmt::Write for CachedDate {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        let len = s.len();
+        self.bytes[self.pos..self.pos + len].copy_from_slice(s.as_bytes());
+        self.pos += len;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[cfg(feature = "nightly")]
+    use test::Bencher;
+
+    #[test]
+    fn test_date_len() {
+        assert_eq!(DATE_VALUE_LENGTH, "Sun, 06 Nov 1994 08:49:37 GMT".len());
+    }
+
+    #[cfg(feature = "nightly")]
+    #[bench]
+    fn bench_date_check(b: &mut Bencher) {
+        let mut date = CachedDate::new();
+        // cache the first update
+        date.check();
+
+        b.iter(|| {
+            date.check();
+        });
+    }
+
+    #[cfg(feature = "nightly")]
+    #[bench]
+    fn bench_date_render(b: &mut Bencher) {
+        let mut date = CachedDate::new();
+        let now = SystemTime::now();
+        date.render(now);
+        b.bytes = date.buffer().len() as u64;
+
+        b.iter(|| {
+            date.render(now);
+            test::black_box(&date);
+        });
+    }
+}
diff --git a/src/common/drain.rs b/src/common/drain.rs
new file mode 100644
index 0000000..c8562d3
--- /dev/null
+++ b/src/common/drain.rs
@@ -0,0 +1,218 @@
+use std::future::Future;
+use std::mem;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use pin_project_lite::pin_project;
+use tokio::sync::watch;
+
+pub(crate) fn channel() -> (Signal, Watch) {
+    let (tx, rx) = watch::channel(());
+    (Signal { tx }, Watch { rx })
+}
+
+pub(crate) struct Signal {
+    tx: watch::Sender<()>,
+}
+
+pub(crate) struct Draining(Pin<Box<dyn Future<Output = ()> + Send + Sync>>);
+
+#[derive(Clone)]
+pub(crate) struct Watch {
+    rx: watch::Receiver<()>,
+}
+
+pin_project! {
+    #[allow(missing_debug_implementations)]
+    pub struct Watching<F, FN> {
+        #[pin]
+        future: F,
+        state: State<FN>,
+        watch: Pin<Box<dyn Future<Output = ()> + Send + Sync>>,
+        _rx: watch::Receiver<()>,
+    }
+}
+
+enum State<F> {
+    Watch(F),
+    Draining,
+}
+
+impl Signal {
+    pub(crate) fn drain(self) -> Draining {
+        let _ = self.tx.send(());
+        Draining(Box::pin(async move { self.tx.closed().await }))
+    }
+}
+
+impl Future for Draining {
+    type Output = ();
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Pin::new(&mut self.as_mut().0).poll(cx)
+    }
+}
+
+impl Watch {
+    pub(crate) fn watch<F, FN>(self, future: F, on_drain: FN) -> Watching<F, FN>
+    where
+        F: Future,
+        FN: FnOnce(Pin<&mut F>),
+    {
+        let Self { mut rx } = self;
+        let _rx = rx.clone();
+        Watching {
+            future,
+            state: State::Watch(on_drain),
+            watch: Box::pin(async move {
+                let _ = rx.changed().await;
+            }),
+            // Keep the receiver alive until the future completes, so that
+            // dropping it can signal that draining has completed.
+            _rx,
+        }
+    }
+}
+
+impl<F, FN> Future for Watching<F, FN>
+where
+    F: Future,
+    FN: FnOnce(Pin<&mut F>),
+{
+    type Output = F::Output;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut me = self.project();
+        loop {
+            match mem::replace(me.state, State::Draining) {
+                State::Watch(on_drain) => {
+                    match Pin::new(&mut me.watch).poll(cx) {
+                        Poll::Ready(()) => {
+                            // Drain has been triggered!
+                            on_drain(me.future.as_mut());
+                        }
+                        Poll::Pending => {
+                            *me.state = State::Watch(on_drain);
+                            return me.future.poll(cx);
+                        }
+                    }
+                }
+                State::Draining => return me.future.poll(cx),
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    struct TestMe {
+        draining: bool,
+        finished: bool,
+        poll_cnt: usize,
+    }
+
+    impl Future for TestMe {
+        type Output = ();
+
+        fn poll(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Self::Output> {
+            self.poll_cnt += 1;
+            if self.finished {
+                Poll::Ready(())
+            } else {
+                Poll::Pending
+            }
+        }
+    }
+
+    #[test]
+    fn watch() {
+        let mut mock = tokio_test::task::spawn(());
+        mock.enter(|cx, _| {
+            let (tx, rx) = channel();
+            let fut = TestMe {
+                draining: false,
+                finished: false,
+                poll_cnt: 0,
+            };
+
+            let mut watch = rx.watch(fut, |mut fut| {
+                fut.draining = true;
+            });
+
+            assert_eq!(watch.future.poll_cnt, 0);
+
+            // First poll should poll the inner future
+            assert!(Pin::new(&mut watch).poll(cx).is_pending());
+            assert_eq!(watch.future.poll_cnt, 1);
+
+            // Second poll should poll the inner future again
+            assert!(Pin::new(&mut watch).poll(cx).is_pending());
+            assert_eq!(watch.future.poll_cnt, 2);
+
+            let mut draining = tx.drain();
+            // Drain signaled, but needs another poll to be noticed.
+            assert!(!watch.future.draining);
+            assert_eq!(watch.future.poll_cnt, 2);
+
+            // Now, poll after drain has been signaled.
+            assert!(Pin::new(&mut watch).poll(cx).is_pending());
+            assert_eq!(watch.future.poll_cnt, 3);
+            assert!(watch.future.draining);
+
+            // Draining is not ready until watcher completes
+            assert!(Pin::new(&mut draining).poll(cx).is_pending());
+
+            // Finishing up the watch future
+            watch.future.finished = true;
+            assert!(Pin::new(&mut watch).poll(cx).is_ready());
+            assert_eq!(watch.future.poll_cnt, 4);
+            drop(watch);
+
+            assert!(Pin::new(&mut draining).poll(cx).is_ready());
+        })
+    }
+
+    #[test]
+    fn watch_clones() {
+        let mut mock = tokio_test::task::spawn(());
+        mock.enter(|cx, _| {
+            let (tx, rx) = channel();
+
+            let fut1 = TestMe {
+                draining: false,
+                finished: false,
+                poll_cnt: 0,
+            };
+            let fut2 = TestMe {
+                draining: false,
+                finished: false,
+                poll_cnt: 0,
+            };
+
+            let watch1 = rx.clone().watch(fut1, |mut fut| {
+                fut.draining = true;
+            });
+            let watch2 = rx.watch(fut2, |mut fut| {
+                fut.draining = true;
+            });
+
+            let mut draining = tx.drain();
+
+            // Still 2 outstanding watchers
+            assert!(Pin::new(&mut draining).poll(cx).is_pending());
+
+            // drop 1 for whatever reason
+            drop(watch1);
+
+            // Still not ready, 1 other watcher still pending
+            assert!(Pin::new(&mut draining).poll(cx).is_pending());
+
+            drop(watch2);
+
+            // Now all watchers are gone, draining is complete
+            assert!(Pin::new(&mut draining).poll(cx).is_ready());
+        });
+    }
+}
diff --git a/src/common/exec.rs b/src/common/exec.rs
new file mode 100644
index 0000000..76f6161
--- /dev/null
+++ b/src/common/exec.rs
@@ -0,0 +1,145 @@
+use std::fmt;
+use std::future::Future;
+use std::pin::Pin;
+use std::sync::Arc;
+
+#[cfg(all(feature = "server", any(feature = "http1", feature = "http2")))]
+use crate::body::Body;
+#[cfg(feature = "server")]
+use crate::body::HttpBody;
+#[cfg(all(feature = "http2", feature = "server"))]
+use crate::proto::h2::server::H2Stream;
+use crate::rt::Executor;
+#[cfg(all(feature = "server", any(feature = "http1", feature = "http2")))]
+use crate::server::server::{new_svc::NewSvcTask, Watcher};
+#[cfg(all(feature = "server", any(feature = "http1", feature = "http2")))]
+use crate::service::HttpService;
+
+#[cfg(feature = "server")]
+pub trait ConnStreamExec<F, B: HttpBody>: Clone {
+    fn execute_h2stream(&mut self, fut: H2Stream<F, B>);
+}
+
+#[cfg(all(feature = "server", any(feature = "http1", feature = "http2")))]
+pub trait NewSvcExec<I, N, S: HttpService<Body>, E, W: Watcher<I, S, E>>: Clone {
+    fn execute_new_svc(&mut self, fut: NewSvcTask<I, N, S, E, W>);
+}
+
+pub(crate) type BoxSendFuture = Pin<Box<dyn Future<Output = ()> + Send>>;
+
+// Either the user provides an executor for background tasks, or we use
+// `tokio::spawn`.
+#[derive(Clone)]
+pub enum Exec {
+    Default,
+    Executor(Arc<dyn Executor<BoxSendFuture> + Send + Sync>),
+}
+
+// ===== impl Exec =====
+
+impl Exec {
+    pub(crate) fn execute<F>(&self, fut: F)
+    where
+        F: Future<Output = ()> + Send + 'static,
+    {
+        match *self {
+            Exec::Default => {
+                #[cfg(feature = "tcp")]
+                {
+                    tokio::task::spawn(fut);
+                }
+                #[cfg(not(feature = "tcp"))]
+                {
+                    // If no runtime, we need an executor!
+                    panic!("executor must be set")
+                }
+            }
+            Exec::Executor(ref e) => {
+                e.execute(Box::pin(fut));
+            }
+        }
+    }
+}
+
+impl fmt::Debug for Exec {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Exec").finish()
+    }
+}
+
+#[cfg(feature = "server")]
+impl<F, B> ConnStreamExec<F, B> for Exec
+where
+    H2Stream<F, B>: Future<Output = ()> + Send + 'static,
+    B: HttpBody,
+{
+    fn execute_h2stream(&mut self, fut: H2Stream<F, B>) {
+        self.execute(fut)
+    }
+}
+
+#[cfg(all(feature = "server", any(feature = "http1", feature = "http2")))]
+impl<I, N, S, E, W> NewSvcExec<I, N, S, E, W> for Exec
+where
+    NewSvcTask<I, N, S, E, W>: Future<Output = ()> + Send + 'static,
+    S: HttpService<Body>,
+    W: Watcher<I, S, E>,
+{
+    fn execute_new_svc(&mut self, fut: NewSvcTask<I, N, S, E, W>) {
+        self.execute(fut)
+    }
+}
+
+// ==== impl Executor =====
+
+#[cfg(feature = "server")]
+impl<E, F, B> ConnStreamExec<F, B> for E
+where
+    E: Executor<H2Stream<F, B>> + Clone,
+    H2Stream<F, B>: Future<Output = ()>,
+    B: HttpBody,
+{
+    fn execute_h2stream(&mut self, fut: H2Stream<F, B>) {
+        self.execute(fut)
+    }
+}
+
+#[cfg(all(feature = "server", any(feature = "http1", feature = "http2")))]
+impl<I, N, S, E, W> NewSvcExec<I, N, S, E, W> for E
+where
+    E: Executor<NewSvcTask<I, N, S, E, W>> + Clone,
+    NewSvcTask<I, N, S, E, W>: Future<Output = ()>,
+    S: HttpService<Body>,
+    W: Watcher<I, S, E>,
+{
+    fn execute_new_svc(&mut self, fut: NewSvcTask<I, N, S, E, W>) {
+        self.execute(fut)
+    }
+}
+
+// If http2 is not enable, we just have a stub here, so that the trait bounds
+// that *would* have been needed are still checked. Why?
+//
+// Because enabling `http2` shouldn't suddenly add new trait bounds that cause
+// a compilation error.
+#[cfg(not(feature = "http2"))]
+#[allow(missing_debug_implementations)]
+pub struct H2Stream<F, B>(std::marker::PhantomData<(F, B)>);
+
+#[cfg(not(feature = "http2"))]
+impl<F, B, E> Future for H2Stream<F, B>
+where
+    F: Future<Output = Result<http::Response<B>, E>>,
+    B: crate::body::HttpBody,
+    B::Error: Into<Box<dyn std::error::Error + Send + Sync>>,
+    E: Into<Box<dyn std::error::Error + Send + Sync>>,
+{
+    type Output = ();
+
+    fn poll(
+        self: Pin<&mut Self>,
+        _cx: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Self::Output> {
+        unreachable!()
+    }
+}
diff --git a/src/common/io/mod.rs b/src/common/io/mod.rs
new file mode 100644
index 0000000..2e6d506
--- /dev/null
+++ b/src/common/io/mod.rs
@@ -0,0 +1,3 @@
+mod rewind;
+
+pub(crate) use self::rewind::Rewind;
diff --git a/src/common/io/rewind.rs b/src/common/io/rewind.rs
new file mode 100644
index 0000000..9ed7c42
--- /dev/null
+++ b/src/common/io/rewind.rs
@@ -0,0 +1,155 @@
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::{cmp, io};
+
+use bytes::{Buf, Bytes};
+use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
+
+/// Combine a buffer with an IO, rewinding reads to use the buffer.
+#[derive(Debug)]
+pub(crate) struct Rewind<T> {
+    pre: Option<Bytes>,
+    inner: T,
+}
+
+impl<T> Rewind<T> {
+    #[cfg(any(all(feature = "http2", feature = "server"), test))]
+    pub(crate) fn new(io: T) -> Self {
+        Rewind {
+            pre: None,
+            inner: io,
+        }
+    }
+
+    pub(crate) fn new_buffered(io: T, buf: Bytes) -> Self {
+        Rewind {
+            pre: Some(buf),
+            inner: io,
+        }
+    }
+
+    #[cfg(any(all(feature = "http1", feature = "http2", feature = "server"), test))]
+    pub(crate) fn rewind(&mut self, bs: Bytes) {
+        debug_assert!(self.pre.is_none());
+        self.pre = Some(bs);
+    }
+
+    pub(crate) fn into_inner(self) -> (T, Bytes) {
+        (self.inner, self.pre.unwrap_or_else(Bytes::new))
+    }
+
+    // pub(crate) fn get_mut(&mut self) -> &mut T {
+    //     &mut self.inner
+    // }
+}
+
+impl<T> AsyncRead for Rewind<T>
+where
+    T: AsyncRead + Unpin,
+{
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        if let Some(mut prefix) = self.pre.take() {
+            // If there are no remaining bytes, let the bytes get dropped.
+            if !prefix.is_empty() {
+                let copy_len = cmp::min(prefix.len(), buf.remaining());
+                // TODO: There should be a way to do following two lines cleaner...
+                buf.put_slice(&prefix[..copy_len]);
+                prefix.advance(copy_len);
+                // Put back what's left
+                if !prefix.is_empty() {
+                    self.pre = Some(prefix);
+                }
+
+                return Poll::Ready(Ok(()));
+            }
+        }
+        Pin::new(&mut self.inner).poll_read(cx, buf)
+    }
+}
+
+impl<T> AsyncWrite for Rewind<T>
+where
+    T: AsyncWrite + Unpin,
+{
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        Pin::new(&mut self.inner).poll_write(cx, buf)
+    }
+
+    fn poll_write_vectored(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        Pin::new(&mut self.inner).poll_write_vectored(cx, bufs)
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.inner).poll_flush(cx)
+    }
+
+    fn poll_shutdown(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.inner).poll_shutdown(cx)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        self.inner.is_write_vectored()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    // FIXME: re-implement tests with `async/await`, this import should
+    // trigger a warning to remind us
+    use super::Rewind;
+    use bytes::Bytes;
+    use tokio::io::AsyncReadExt;
+
+    #[tokio::test]
+    async fn partial_rewind() {
+        let underlying = [104, 101, 108, 108, 111];
+
+        let mock = tokio_test::io::Builder::new().read(&underlying).build();
+
+        let mut stream = Rewind::new(mock);
+
+        // Read off some bytes, ensure we filled o1
+        let mut buf = [0; 2];
+        stream.read_exact(&mut buf).await.expect("read1");
+
+        // Rewind the stream so that it is as if we never read in the first place.
+        stream.rewind(Bytes::copy_from_slice(&buf[..]));
+
+        let mut buf = [0; 5];
+        stream.read_exact(&mut buf).await.expect("read1");
+
+        // At this point we should have read everything that was in the MockStream
+        assert_eq!(&buf, &underlying);
+    }
+
+    #[tokio::test]
+    async fn full_rewind() {
+        let underlying = [104, 101, 108, 108, 111];
+
+        let mock = tokio_test::io::Builder::new().read(&underlying).build();
+
+        let mut stream = Rewind::new(mock);
+
+        let mut buf = [0; 5];
+        stream.read_exact(&mut buf).await.expect("read1");
+
+        // Rewind the stream so that it is as if we never read in the first place.
+        stream.rewind(Bytes::copy_from_slice(&buf[..]));
+
+        let mut buf = [0; 5];
+        stream.read_exact(&mut buf).await.expect("read1");
+    }
+}
diff --git a/src/common/lazy.rs b/src/common/lazy.rs
new file mode 100644
index 0000000..df2c07d
--- /dev/null
+++ b/src/common/lazy.rs
@@ -0,0 +1,79 @@
+use std::future::Future;
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use pin_project_lite::pin_project;
+
+pub(crate) trait Started: Future {
+    fn started(&self) -> bool;
+}
+
+pub(crate) fn lazy<F, R>(func: F) -> Lazy<F, R>
+where
+    F: FnOnce() -> R,
+    R: Future + Unpin,
+{
+    Lazy {
+        inner: Inner::Init { func },
+    }
+}
+
+// FIXME: allow() required due to `impl Trait` leaking types to this lint
+pin_project! {
+    #[allow(missing_debug_implementations)]
+    pub(crate) struct Lazy<F, R> {
+        #[pin]
+        inner: Inner<F, R>,
+    }
+}
+
+pin_project! {
+    #[project = InnerProj]
+    #[project_replace = InnerProjReplace]
+    enum Inner<F, R> {
+        Init { func: F },
+        Fut { #[pin] fut: R },
+        Empty,
+    }
+}
+
+impl<F, R> Started for Lazy<F, R>
+where
+    F: FnOnce() -> R,
+    R: Future,
+{
+    fn started(&self) -> bool {
+        match self.inner {
+            Inner::Init { .. } => false,
+            Inner::Fut { .. } | Inner::Empty => true,
+        }
+    }
+}
+
+impl<F, R> Future for Lazy<F, R>
+where
+    F: FnOnce() -> R,
+    R: Future,
+{
+    type Output = R::Output;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+
+        if let InnerProj::Fut { fut } = this.inner.as_mut().project() {
+            return fut.poll(cx);
+        }
+
+        match this.inner.as_mut().project_replace(Inner::Empty) {
+            InnerProjReplace::Init { func } => {
+                this.inner.set(Inner::Fut { fut: func() });
+                if let InnerProj::Fut { fut } = this.inner.project() {
+                    return fut.poll(cx);
+                }
+                unreachable!()
+            }
+            _ => unreachable!("lazy state wrong"),
+        }
+    }
+}
diff --git a/src/common/mod.rs b/src/common/mod.rs
new file mode 100644
index 0000000..3d83946
--- /dev/null
+++ b/src/common/mod.rs
@@ -0,0 +1,30 @@
+macro_rules! ready {
+    ($e:expr) => {
+        match $e {
+            std::task::Poll::Ready(v) => v,
+            std::task::Poll::Pending => return std::task::Poll::Pending,
+        }
+    };
+}
+
+pub(crate) mod buf;
+#[cfg(all(feature = "server", any(feature = "http1", feature = "http2")))]
+pub(crate) mod date;
+#[cfg(all(feature = "server", any(feature = "http1", feature = "http2")))]
+pub(crate) mod drain;
+#[cfg(any(feature = "http1", feature = "http2", feature = "server"))]
+pub(crate) mod exec;
+pub(crate) mod io;
+#[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
+mod lazy;
+#[cfg(any(
+    feature = "stream",
+    all(feature = "client", any(feature = "http1", feature = "http2"))
+))]
+pub(crate) mod sync_wrapper;
+#[cfg(feature = "http1")]
+pub(crate) mod task;
+pub(crate) mod watch;
+
+#[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
+pub(crate) use self::lazy::{lazy, Started as Lazy};
diff --git a/src/common/sync_wrapper.rs b/src/common/sync_wrapper.rs
new file mode 100644
index 0000000..704d1a6
--- /dev/null
+++ b/src/common/sync_wrapper.rs
@@ -0,0 +1,110 @@
+/*
+ * This is a copy of the sync_wrapper crate.
+ */
+
+/// A mutual exclusion primitive that relies on static type information only
+///
+/// In some cases synchronization can be proven statically: whenever you hold an exclusive `&mut`
+/// reference, the Rust type system ensures that no other part of the program can hold another
+/// reference to the data. Therefore it is safe to access it even if the current thread obtained
+/// this reference via a channel. Whenever this is the case, the overhead of allocating and locking
+/// a [`Mutex`] can be avoided by using this static version.
+///
+/// One example where this is often applicable is [`Future`], which requires an exclusive reference
+/// for its [`poll`] method: While a given `Future` implementation may not be safe to access by
+/// multiple threads concurrently, the executor can only run the `Future` on one thread at any
+/// given time, making it [`Sync`] in practice as long as the implementation is `Send`. You can
+/// therefore use the sync wrapper to prove that your data structure is `Sync` even though it
+/// contains such a `Future`.
+///
+/// # Example
+///
+/// ```ignore
+/// use hyper::common::sync_wrapper::SyncWrapper;
+/// use std::future::Future;
+///
+/// struct MyThing {
+///     future: SyncWrapper<Box<dyn Future<Output = String> + Send>>,
+/// }
+///
+/// impl MyThing {
+///     // all accesses to `self.future` now require an exclusive reference or ownership
+/// }
+///
+/// fn assert_sync<T: Sync>() {}
+///
+/// assert_sync::<MyThing>();
+/// ```
+///
+/// [`Mutex`]: https://doc.rust-lang.org/std/sync/struct.Mutex.html
+/// [`Future`]: https://doc.rust-lang.org/std/future/trait.Future.html
+/// [`poll`]: https://doc.rust-lang.org/std/future/trait.Future.html#method.poll
+/// [`Sync`]: https://doc.rust-lang.org/std/marker/trait.Sync.html
+#[repr(transparent)]
+pub(crate) struct SyncWrapper<T>(T);
+
+impl<T> SyncWrapper<T> {
+    /// Creates a new SyncWrapper containing the given value.
+    ///
+    /// # Examples
+    ///
+    /// ```ignore
+    /// use hyper::common::sync_wrapper::SyncWrapper;
+    ///
+    /// let wrapped = SyncWrapper::new(42);
+    /// ```
+    pub(crate) fn new(value: T) -> Self {
+        Self(value)
+    }
+
+    /// Acquires a reference to the protected value.
+    ///
+    /// This is safe because it requires an exclusive reference to the wrapper. Therefore this method
+    /// neither panics nor does it return an error. This is in contrast to [`Mutex::get_mut`] which
+    /// returns an error if another thread panicked while holding the lock. It is not recommended
+    /// to send an exclusive reference to a potentially damaged value to another thread for further
+    /// processing.
+    ///
+    /// [`Mutex::get_mut`]: https://doc.rust-lang.org/std/sync/struct.Mutex.html#method.get_mut
+    ///
+    /// # Examples
+    ///
+    /// ```ignore
+    /// use hyper::common::sync_wrapper::SyncWrapper;
+    ///
+    /// let mut wrapped = SyncWrapper::new(42);
+    /// let value = wrapped.get_mut();
+    /// *value = 0;
+    /// assert_eq!(*wrapped.get_mut(), 0);
+    /// ```
+    pub(crate) fn get_mut(&mut self) -> &mut T {
+        &mut self.0
+    }
+
+    /// Consumes this wrapper, returning the underlying data.
+    ///
+    /// This is safe because it requires ownership of the wrapper, aherefore this method will neither
+    /// panic nor does it return an error. This is in contrast to [`Mutex::into_inner`] which
+    /// returns an error if another thread panicked while holding the lock. It is not recommended
+    /// to send an exclusive reference to a potentially damaged value to another thread for further
+    /// processing.
+    ///
+    /// [`Mutex::into_inner`]: https://doc.rust-lang.org/std/sync/struct.Mutex.html#method.into_inner
+    ///
+    /// # Examples
+    ///
+    /// ```ignore
+    /// use hyper::common::sync_wrapper::SyncWrapper;
+    ///
+    /// let mut wrapped = SyncWrapper::new(42);
+    /// assert_eq!(wrapped.into_inner(), 42);
+    /// ```
+    #[allow(dead_code)]
+    pub(crate) fn into_inner(self) -> T {
+        self.0
+    }
+}
+
+// this is safe because the only operations permitted on this data structure require exclusive
+// access or ownership
+unsafe impl<T: Send> Sync for SyncWrapper<T> {}
diff --git a/src/common/task.rs b/src/common/task.rs
new file mode 100644
index 0000000..0ac047a
--- /dev/null
+++ b/src/common/task.rs
@@ -0,0 +1,12 @@
+use std::{
+    convert::Infallible,
+    task::{Context, Poll},
+};
+
+/// A function to help "yield" a future, such that it is re-scheduled immediately.
+///
+/// Useful for spin counts, so a future doesn't hog too much time.
+pub(crate) fn yield_now(cx: &mut Context<'_>) -> Poll<Infallible> {
+    cx.waker().wake_by_ref();
+    Poll::Pending
+}
diff --git a/src/common/watch.rs b/src/common/watch.rs
new file mode 100644
index 0000000..ba17d55
--- /dev/null
+++ b/src/common/watch.rs
@@ -0,0 +1,73 @@
+//! An SPSC broadcast channel.
+//!
+//! - The value can only be a `usize`.
+//! - The consumer is only notified if the value is different.
+//! - The value `0` is reserved for closed.
+
+use futures_util::task::AtomicWaker;
+use std::sync::{
+    atomic::{AtomicUsize, Ordering},
+    Arc,
+};
+use std::task;
+
+type Value = usize;
+
+pub(crate) const CLOSED: usize = 0;
+
+pub(crate) fn channel(initial: Value) -> (Sender, Receiver) {
+    debug_assert!(
+        initial != CLOSED,
+        "watch::channel initial state of 0 is reserved"
+    );
+
+    let shared = Arc::new(Shared {
+        value: AtomicUsize::new(initial),
+        waker: AtomicWaker::new(),
+    });
+
+    (
+        Sender {
+            shared: shared.clone(),
+        },
+        Receiver { shared },
+    )
+}
+
+pub(crate) struct Sender {
+    shared: Arc<Shared>,
+}
+
+pub(crate) struct Receiver {
+    shared: Arc<Shared>,
+}
+
+struct Shared {
+    value: AtomicUsize,
+    waker: AtomicWaker,
+}
+
+impl Sender {
+    pub(crate) fn send(&mut self, value: Value) {
+        if self.shared.value.swap(value, Ordering::SeqCst) != value {
+            self.shared.waker.wake();
+        }
+    }
+}
+
+impl Drop for Sender {
+    fn drop(&mut self) {
+        self.send(CLOSED);
+    }
+}
+
+impl Receiver {
+    pub(crate) fn load(&mut self, cx: &mut task::Context<'_>) -> Value {
+        self.shared.waker.register(cx.waker());
+        self.shared.value.load(Ordering::SeqCst)
+    }
+
+    pub(crate) fn peek(&self) -> Value {
+        self.shared.value.load(Ordering::Relaxed)
+    }
+}
diff --git a/src/error.rs b/src/error.rs
new file mode 100644
index 0000000..5beedeb
--- /dev/null
+++ b/src/error.rs
@@ -0,0 +1,663 @@
+//! Error and Result module.
+
+#[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
+use crate::client::connect::Connected;
+use std::error::Error as StdError;
+use std::fmt;
+
+/// Result type often returned from methods that can have hyper `Error`s.
+pub type Result<T> = std::result::Result<T, Error>;
+
+type Cause = Box<dyn StdError + Send + Sync>;
+
+/// Represents errors that can occur handling HTTP streams.
+pub struct Error {
+    inner: Box<ErrorImpl>,
+}
+
+struct ErrorImpl {
+    kind: Kind,
+    cause: Option<Cause>,
+    #[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
+    connect_info: Option<Connected>,
+}
+
+#[derive(Debug)]
+pub(super) enum Kind {
+    Parse(Parse),
+    User(User),
+    /// A message reached EOF, but is not complete.
+    #[allow(unused)]
+    IncompleteMessage,
+    /// A connection received a message (or bytes) when not waiting for one.
+    #[cfg(feature = "http1")]
+    UnexpectedMessage,
+    /// A pending item was dropped before ever being processed.
+    Canceled,
+    /// Indicates a channel (client or body sender) is closed.
+    ChannelClosed,
+    /// An `io::Error` that occurred while trying to read or write to a network stream.
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    Io,
+    /// Error occurred while connecting.
+    #[allow(unused)]
+    Connect,
+    /// Error creating a TcpListener.
+    #[cfg(all(feature = "tcp", feature = "server"))]
+    Listen,
+    /// Error accepting on an Incoming stream.
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "server")]
+    Accept,
+    /// User took too long to send headers
+    #[cfg(all(feature = "http1", feature = "server", feature = "runtime"))]
+    HeaderTimeout,
+    /// Error while reading a body from connection.
+    #[cfg(any(feature = "http1", feature = "http2", feature = "stream"))]
+    Body,
+    /// Error while writing a body to connection.
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    BodyWrite,
+    /// Error calling AsyncWrite::shutdown()
+    #[cfg(feature = "http1")]
+    Shutdown,
+
+    /// A general error from h2.
+    #[cfg(feature = "http2")]
+    Http2,
+}
+
+#[derive(Debug)]
+pub(super) enum Parse {
+    Method,
+    Version,
+    #[cfg(feature = "http1")]
+    VersionH2,
+    Uri,
+    #[cfg_attr(not(all(feature = "http1", feature = "server")), allow(unused))]
+    UriTooLong,
+    Header(Header),
+    TooLarge,
+    Status,
+    #[cfg_attr(debug_assertions, allow(unused))]
+    Internal,
+}
+
+#[derive(Debug)]
+pub(super) enum Header {
+    Token,
+    #[cfg(feature = "http1")]
+    ContentLengthInvalid,
+    #[cfg(all(feature = "http1", feature = "server"))]
+    TransferEncodingInvalid,
+    #[cfg(feature = "http1")]
+    TransferEncodingUnexpected,
+}
+
+#[derive(Debug)]
+pub(super) enum User {
+    /// Error calling user's HttpBody::poll_data().
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    Body,
+    /// The user aborted writing of the outgoing body.
+    BodyWriteAborted,
+    /// Error calling user's MakeService.
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "server")]
+    MakeService,
+    /// Error from future of user's Service.
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    Service,
+    /// User tried to send a certain header in an unexpected context.
+    ///
+    /// For example, sending both `content-length` and `transfer-encoding`.
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "server")]
+    UnexpectedHeader,
+    /// User tried to create a Request with bad version.
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "client")]
+    UnsupportedVersion,
+    /// User tried to create a CONNECT Request with the Client.
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "client")]
+    UnsupportedRequestMethod,
+    /// User tried to respond with a 1xx (not 101) response code.
+    #[cfg(feature = "http1")]
+    #[cfg(feature = "server")]
+    UnsupportedStatusCode,
+    /// User tried to send a Request with Client with non-absolute URI.
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "client")]
+    AbsoluteUriRequired,
+
+    /// User tried polling for an upgrade that doesn't exist.
+    NoUpgrade,
+
+    /// User polled for an upgrade, but low-level API is not using upgrades.
+    #[cfg(feature = "http1")]
+    ManualUpgrade,
+
+    /// User called `server::Connection::without_shutdown()` on an HTTP/2 conn.
+    #[cfg(feature = "server")]
+    WithoutShutdownNonHttp1,
+
+    /// The dispatch task is gone.
+    #[cfg(feature = "client")]
+    DispatchGone,
+
+    /// User aborted in an FFI callback.
+    #[cfg(feature = "ffi")]
+    AbortedByCallback,
+}
+
+// Sentinel type to indicate the error was caused by a timeout.
+#[derive(Debug)]
+pub(super) struct TimedOut;
+
+impl Error {
+    /// Returns true if this was an HTTP parse error.
+    pub fn is_parse(&self) -> bool {
+        matches!(self.inner.kind, Kind::Parse(_))
+    }
+
+    /// Returns true if this was an HTTP parse error caused by a message that was too large.
+    pub fn is_parse_too_large(&self) -> bool {
+        matches!(
+            self.inner.kind,
+            Kind::Parse(Parse::TooLarge) | Kind::Parse(Parse::UriTooLong)
+        )
+    }
+
+    /// Returns true if this was an HTTP parse error caused by an invalid response status code or
+    /// reason phrase.
+    pub fn is_parse_status(&self) -> bool {
+        matches!(self.inner.kind, Kind::Parse(Parse::Status))
+    }
+
+    /// Returns true if this error was caused by user code.
+    pub fn is_user(&self) -> bool {
+        matches!(self.inner.kind, Kind::User(_))
+    }
+
+    /// Returns true if this was about a `Request` that was canceled.
+    pub fn is_canceled(&self) -> bool {
+        matches!(self.inner.kind, Kind::Canceled)
+    }
+
+    /// Returns true if a sender's channel is closed.
+    pub fn is_closed(&self) -> bool {
+        matches!(self.inner.kind, Kind::ChannelClosed)
+    }
+
+    /// Returns true if this was an error from `Connect`.
+    pub fn is_connect(&self) -> bool {
+        matches!(self.inner.kind, Kind::Connect)
+    }
+
+    /// Returns true if the connection closed before a message could complete.
+    pub fn is_incomplete_message(&self) -> bool {
+        matches!(self.inner.kind, Kind::IncompleteMessage)
+    }
+
+    /// Returns true if the body write was aborted.
+    pub fn is_body_write_aborted(&self) -> bool {
+        matches!(self.inner.kind, Kind::User(User::BodyWriteAborted))
+    }
+
+    /// Returns true if the error was caused by a timeout.
+    pub fn is_timeout(&self) -> bool {
+        self.find_source::<TimedOut>().is_some()
+    }
+
+    /// Consumes the error, returning its cause.
+    pub fn into_cause(self) -> Option<Box<dyn StdError + Send + Sync>> {
+        self.inner.cause
+    }
+
+    /// Returns the info of the client connection on which this error occurred.
+    #[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
+    pub fn client_connect_info(&self) -> Option<&Connected> {
+        self.inner.connect_info.as_ref()
+    }
+
+    pub(super) fn new(kind: Kind) -> Error {
+        Error {
+            inner: Box::new(ErrorImpl {
+                kind,
+                cause: None,
+                #[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
+                connect_info: None,
+            }),
+        }
+    }
+
+    pub(super) fn with<C: Into<Cause>>(mut self, cause: C) -> Error {
+        self.inner.cause = Some(cause.into());
+        self
+    }
+
+    #[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
+    pub(super) fn with_client_connect_info(mut self, connect_info: Connected) -> Error {
+        self.inner.connect_info = Some(connect_info);
+        self
+    }
+
+    #[cfg(any(all(feature = "http1", feature = "server"), feature = "ffi"))]
+    pub(super) fn kind(&self) -> &Kind {
+        &self.inner.kind
+    }
+
+    pub(crate) fn find_source<E: StdError + 'static>(&self) -> Option<&E> {
+        let mut cause = self.source();
+        while let Some(err) = cause {
+            if let Some(ref typed) = err.downcast_ref() {
+                return Some(typed);
+            }
+            cause = err.source();
+        }
+
+        // else
+        None
+    }
+
+    #[cfg(feature = "http2")]
+    pub(super) fn h2_reason(&self) -> h2::Reason {
+        // Find an h2::Reason somewhere in the cause stack, if it exists,
+        // otherwise assume an INTERNAL_ERROR.
+        self.find_source::<h2::Error>()
+            .and_then(|h2_err| h2_err.reason())
+            .unwrap_or(h2::Reason::INTERNAL_ERROR)
+    }
+
+    pub(super) fn new_canceled() -> Error {
+        Error::new(Kind::Canceled)
+    }
+
+    #[cfg(feature = "http1")]
+    pub(super) fn new_incomplete() -> Error {
+        Error::new(Kind::IncompleteMessage)
+    }
+
+    #[cfg(feature = "http1")]
+    pub(super) fn new_too_large() -> Error {
+        Error::new(Kind::Parse(Parse::TooLarge))
+    }
+
+    #[cfg(feature = "http1")]
+    pub(super) fn new_version_h2() -> Error {
+        Error::new(Kind::Parse(Parse::VersionH2))
+    }
+
+    #[cfg(feature = "http1")]
+    pub(super) fn new_unexpected_message() -> Error {
+        Error::new(Kind::UnexpectedMessage)
+    }
+
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    pub(super) fn new_io(cause: std::io::Error) -> Error {
+        Error::new(Kind::Io).with(cause)
+    }
+
+    #[cfg(all(feature = "server", feature = "tcp"))]
+    pub(super) fn new_listen<E: Into<Cause>>(cause: E) -> Error {
+        Error::new(Kind::Listen).with(cause)
+    }
+
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "server")]
+    pub(super) fn new_accept<E: Into<Cause>>(cause: E) -> Error {
+        Error::new(Kind::Accept).with(cause)
+    }
+
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "client")]
+    pub(super) fn new_connect<E: Into<Cause>>(cause: E) -> Error {
+        Error::new(Kind::Connect).with(cause)
+    }
+
+    pub(super) fn new_closed() -> Error {
+        Error::new(Kind::ChannelClosed)
+    }
+
+    #[cfg(any(feature = "http1", feature = "http2", feature = "stream"))]
+    pub(super) fn new_body<E: Into<Cause>>(cause: E) -> Error {
+        Error::new(Kind::Body).with(cause)
+    }
+
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    pub(super) fn new_body_write<E: Into<Cause>>(cause: E) -> Error {
+        Error::new(Kind::BodyWrite).with(cause)
+    }
+
+    pub(super) fn new_body_write_aborted() -> Error {
+        Error::new(Kind::User(User::BodyWriteAborted))
+    }
+
+    fn new_user(user: User) -> Error {
+        Error::new(Kind::User(user))
+    }
+
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "server")]
+    pub(super) fn new_user_header() -> Error {
+        Error::new_user(User::UnexpectedHeader)
+    }
+
+    #[cfg(all(feature = "http1", feature = "server", feature = "runtime"))]
+    pub(super) fn new_header_timeout() -> Error {
+        Error::new(Kind::HeaderTimeout)
+    }
+
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "client")]
+    pub(super) fn new_user_unsupported_version() -> Error {
+        Error::new_user(User::UnsupportedVersion)
+    }
+
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "client")]
+    pub(super) fn new_user_unsupported_request_method() -> Error {
+        Error::new_user(User::UnsupportedRequestMethod)
+    }
+
+    #[cfg(feature = "http1")]
+    #[cfg(feature = "server")]
+    pub(super) fn new_user_unsupported_status_code() -> Error {
+        Error::new_user(User::UnsupportedStatusCode)
+    }
+
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "client")]
+    pub(super) fn new_user_absolute_uri_required() -> Error {
+        Error::new_user(User::AbsoluteUriRequired)
+    }
+
+    pub(super) fn new_user_no_upgrade() -> Error {
+        Error::new_user(User::NoUpgrade)
+    }
+
+    #[cfg(feature = "http1")]
+    pub(super) fn new_user_manual_upgrade() -> Error {
+        Error::new_user(User::ManualUpgrade)
+    }
+
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[cfg(feature = "server")]
+    pub(super) fn new_user_make_service<E: Into<Cause>>(cause: E) -> Error {
+        Error::new_user(User::MakeService).with(cause)
+    }
+
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    pub(super) fn new_user_service<E: Into<Cause>>(cause: E) -> Error {
+        Error::new_user(User::Service).with(cause)
+    }
+
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    pub(super) fn new_user_body<E: Into<Cause>>(cause: E) -> Error {
+        Error::new_user(User::Body).with(cause)
+    }
+
+    #[cfg(feature = "server")]
+    pub(super) fn new_without_shutdown_not_h1() -> Error {
+        Error::new(Kind::User(User::WithoutShutdownNonHttp1))
+    }
+
+    #[cfg(feature = "http1")]
+    pub(super) fn new_shutdown(cause: std::io::Error) -> Error {
+        Error::new(Kind::Shutdown).with(cause)
+    }
+
+    #[cfg(feature = "ffi")]
+    pub(super) fn new_user_aborted_by_callback() -> Error {
+        Error::new_user(User::AbortedByCallback)
+    }
+
+    #[cfg(feature = "client")]
+    pub(super) fn new_user_dispatch_gone() -> Error {
+        Error::new(Kind::User(User::DispatchGone))
+    }
+
+    #[cfg(feature = "http2")]
+    pub(super) fn new_h2(cause: ::h2::Error) -> Error {
+        if cause.is_io() {
+            Error::new_io(cause.into_io().expect("h2::Error::is_io"))
+        } else {
+            Error::new(Kind::Http2).with(cause)
+        }
+    }
+
+    /// The error's standalone message, without the message from the source.
+    pub fn message(&self) -> impl fmt::Display + '_ {
+        self.description()
+    }
+
+    fn description(&self) -> &str {
+        match self.inner.kind {
+            Kind::Parse(Parse::Method) => "invalid HTTP method parsed",
+            Kind::Parse(Parse::Version) => "invalid HTTP version parsed",
+            #[cfg(feature = "http1")]
+            Kind::Parse(Parse::VersionH2) => "invalid HTTP version parsed (found HTTP2 preface)",
+            Kind::Parse(Parse::Uri) => "invalid URI",
+            Kind::Parse(Parse::UriTooLong) => "URI too long",
+            Kind::Parse(Parse::Header(Header::Token)) => "invalid HTTP header parsed",
+            #[cfg(feature = "http1")]
+            Kind::Parse(Parse::Header(Header::ContentLengthInvalid)) => {
+                "invalid content-length parsed"
+            }
+            #[cfg(all(feature = "http1", feature = "server"))]
+            Kind::Parse(Parse::Header(Header::TransferEncodingInvalid)) => {
+                "invalid transfer-encoding parsed"
+            }
+            #[cfg(feature = "http1")]
+            Kind::Parse(Parse::Header(Header::TransferEncodingUnexpected)) => {
+                "unexpected transfer-encoding parsed"
+            }
+            Kind::Parse(Parse::TooLarge) => "message head is too large",
+            Kind::Parse(Parse::Status) => "invalid HTTP status-code parsed",
+            Kind::Parse(Parse::Internal) => {
+                "internal error inside Hyper and/or its dependencies, please report"
+            }
+            Kind::IncompleteMessage => "connection closed before message completed",
+            #[cfg(feature = "http1")]
+            Kind::UnexpectedMessage => "received unexpected message from connection",
+            Kind::ChannelClosed => "channel closed",
+            Kind::Connect => "error trying to connect",
+            Kind::Canceled => "operation was canceled",
+            #[cfg(all(feature = "server", feature = "tcp"))]
+            Kind::Listen => "error creating server listener",
+            #[cfg(any(feature = "http1", feature = "http2"))]
+            #[cfg(feature = "server")]
+            Kind::Accept => "error accepting connection",
+            #[cfg(all(feature = "http1", feature = "server", feature = "runtime"))]
+            Kind::HeaderTimeout => "read header from client timeout",
+            #[cfg(any(feature = "http1", feature = "http2", feature = "stream"))]
+            Kind::Body => "error reading a body from connection",
+            #[cfg(any(feature = "http1", feature = "http2"))]
+            Kind::BodyWrite => "error writing a body to connection",
+            #[cfg(feature = "http1")]
+            Kind::Shutdown => "error shutting down connection",
+            #[cfg(feature = "http2")]
+            Kind::Http2 => "http2 error",
+            #[cfg(any(feature = "http1", feature = "http2"))]
+            Kind::Io => "connection error",
+
+            #[cfg(any(feature = "http1", feature = "http2"))]
+            Kind::User(User::Body) => "error from user's HttpBody stream",
+            Kind::User(User::BodyWriteAborted) => "user body write aborted",
+            #[cfg(any(feature = "http1", feature = "http2"))]
+            #[cfg(feature = "server")]
+            Kind::User(User::MakeService) => "error from user's MakeService",
+            #[cfg(any(feature = "http1", feature = "http2"))]
+            Kind::User(User::Service) => "error from user's Service",
+            #[cfg(any(feature = "http1", feature = "http2"))]
+            #[cfg(feature = "server")]
+            Kind::User(User::UnexpectedHeader) => "user sent unexpected header",
+            #[cfg(any(feature = "http1", feature = "http2"))]
+            #[cfg(feature = "client")]
+            Kind::User(User::UnsupportedVersion) => "request has unsupported HTTP version",
+            #[cfg(any(feature = "http1", feature = "http2"))]
+            #[cfg(feature = "client")]
+            Kind::User(User::UnsupportedRequestMethod) => "request has unsupported HTTP method",
+            #[cfg(feature = "http1")]
+            #[cfg(feature = "server")]
+            Kind::User(User::UnsupportedStatusCode) => {
+                "response has 1xx status code, not supported by server"
+            }
+            #[cfg(any(feature = "http1", feature = "http2"))]
+            #[cfg(feature = "client")]
+            Kind::User(User::AbsoluteUriRequired) => "client requires absolute-form URIs",
+            Kind::User(User::NoUpgrade) => "no upgrade available",
+            #[cfg(feature = "http1")]
+            Kind::User(User::ManualUpgrade) => "upgrade expected but low level API in use",
+            #[cfg(feature = "server")]
+            Kind::User(User::WithoutShutdownNonHttp1) => {
+                "without_shutdown() called on a non-HTTP/1 connection"
+            }
+            #[cfg(feature = "client")]
+            Kind::User(User::DispatchGone) => "dispatch task is gone",
+            #[cfg(feature = "ffi")]
+            Kind::User(User::AbortedByCallback) => "operation aborted by an application callback",
+        }
+    }
+}
+
+impl fmt::Debug for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut f = f.debug_tuple("hyper::Error");
+        f.field(&self.inner.kind);
+        if let Some(ref cause) = self.inner.cause {
+            f.field(cause);
+        }
+        f.finish()
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if let Some(ref cause) = self.inner.cause {
+            write!(f, "{}: {}", self.description(), cause)
+        } else {
+            f.write_str(self.description())
+        }
+    }
+}
+
+impl StdError for Error {
+    fn source(&self) -> Option<&(dyn StdError + 'static)> {
+        self.inner
+            .cause
+            .as_ref()
+            .map(|cause| &**cause as &(dyn StdError + 'static))
+    }
+}
+
+#[doc(hidden)]
+impl From<Parse> for Error {
+    fn from(err: Parse) -> Error {
+        Error::new(Kind::Parse(err))
+    }
+}
+
+#[cfg(feature = "http1")]
+impl Parse {
+    pub(crate) fn content_length_invalid() -> Self {
+        Parse::Header(Header::ContentLengthInvalid)
+    }
+
+    #[cfg(all(feature = "http1", feature = "server"))]
+    pub(crate) fn transfer_encoding_invalid() -> Self {
+        Parse::Header(Header::TransferEncodingInvalid)
+    }
+
+    pub(crate) fn transfer_encoding_unexpected() -> Self {
+        Parse::Header(Header::TransferEncodingUnexpected)
+    }
+}
+
+impl From<httparse::Error> for Parse {
+    fn from(err: httparse::Error) -> Parse {
+        match err {
+            httparse::Error::HeaderName
+            | httparse::Error::HeaderValue
+            | httparse::Error::NewLine
+            | httparse::Error::Token => Parse::Header(Header::Token),
+            httparse::Error::Status => Parse::Status,
+            httparse::Error::TooManyHeaders => Parse::TooLarge,
+            httparse::Error::Version => Parse::Version,
+        }
+    }
+}
+
+impl From<http::method::InvalidMethod> for Parse {
+    fn from(_: http::method::InvalidMethod) -> Parse {
+        Parse::Method
+    }
+}
+
+impl From<http::status::InvalidStatusCode> for Parse {
+    fn from(_: http::status::InvalidStatusCode) -> Parse {
+        Parse::Status
+    }
+}
+
+impl From<http::uri::InvalidUri> for Parse {
+    fn from(_: http::uri::InvalidUri) -> Parse {
+        Parse::Uri
+    }
+}
+
+impl From<http::uri::InvalidUriParts> for Parse {
+    fn from(_: http::uri::InvalidUriParts) -> Parse {
+        Parse::Uri
+    }
+}
+
+#[doc(hidden)]
+trait AssertSendSync: Send + Sync + 'static {}
+#[doc(hidden)]
+impl AssertSendSync for Error {}
+
+// ===== impl TimedOut ====
+
+impl fmt::Display for TimedOut {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("operation timed out")
+    }
+}
+
+impl StdError for TimedOut {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::mem;
+
+    #[test]
+    fn error_size_of() {
+        assert_eq!(mem::size_of::<Error>(), mem::size_of::<usize>());
+    }
+
+    #[cfg(feature = "http2")]
+    #[test]
+    fn h2_reason_unknown() {
+        let closed = Error::new_closed();
+        assert_eq!(closed.h2_reason(), h2::Reason::INTERNAL_ERROR);
+    }
+
+    #[cfg(feature = "http2")]
+    #[test]
+    fn h2_reason_one_level() {
+        let body_err = Error::new_user_body(h2::Error::from(h2::Reason::ENHANCE_YOUR_CALM));
+        assert_eq!(body_err.h2_reason(), h2::Reason::ENHANCE_YOUR_CALM);
+    }
+
+    #[cfg(feature = "http2")]
+    #[test]
+    fn h2_reason_nested() {
+        let recvd = Error::new_h2(h2::Error::from(h2::Reason::HTTP_1_1_REQUIRED));
+        // Suppose a user were proxying the received error
+        let svc_err = Error::new_user_service(recvd);
+        assert_eq!(svc_err.h2_reason(), h2::Reason::HTTP_1_1_REQUIRED);
+    }
+}
diff --git a/src/ext.rs b/src/ext.rs
new file mode 100644
index 0000000..224206d
--- /dev/null
+++ b/src/ext.rs
@@ -0,0 +1,228 @@
+//! HTTP extensions.
+
+use bytes::Bytes;
+#[cfg(any(feature = "http1", feature = "ffi"))]
+use http::header::HeaderName;
+#[cfg(feature = "http1")]
+use http::header::{IntoHeaderName, ValueIter};
+use http::HeaderMap;
+#[cfg(feature = "ffi")]
+use std::collections::HashMap;
+#[cfg(feature = "http2")]
+use std::fmt;
+
+#[cfg(any(feature = "http1", feature = "ffi"))]
+mod h1_reason_phrase;
+#[cfg(any(feature = "http1", feature = "ffi"))]
+pub use h1_reason_phrase::ReasonPhrase;
+
+#[cfg(feature = "http2")]
+/// Represents the `:protocol` pseudo-header used by
+/// the [Extended CONNECT Protocol].
+///
+/// [Extended CONNECT Protocol]: https://datatracker.ietf.org/doc/html/rfc8441#section-4
+#[derive(Clone, Eq, PartialEq)]
+pub struct Protocol {
+    inner: h2::ext::Protocol,
+}
+
+#[cfg(feature = "http2")]
+impl Protocol {
+    /// Converts a static string to a protocol name.
+    pub const fn from_static(value: &'static str) -> Self {
+        Self {
+            inner: h2::ext::Protocol::from_static(value),
+        }
+    }
+
+    /// Returns a str representation of the header.
+    pub fn as_str(&self) -> &str {
+        self.inner.as_str()
+    }
+
+    #[cfg(feature = "server")]
+    pub(crate) fn from_inner(inner: h2::ext::Protocol) -> Self {
+        Self { inner }
+    }
+
+    pub(crate) fn into_inner(self) -> h2::ext::Protocol {
+        self.inner
+    }
+}
+
+#[cfg(feature = "http2")]
+impl<'a> From<&'a str> for Protocol {
+    fn from(value: &'a str) -> Self {
+        Self {
+            inner: h2::ext::Protocol::from(value),
+        }
+    }
+}
+
+#[cfg(feature = "http2")]
+impl AsRef<[u8]> for Protocol {
+    fn as_ref(&self) -> &[u8] {
+        self.inner.as_ref()
+    }
+}
+
+#[cfg(feature = "http2")]
+impl fmt::Debug for Protocol {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+/// A map from header names to their original casing as received in an HTTP message.
+///
+/// If an HTTP/1 response `res` is parsed on a connection whose option
+/// [`http1_preserve_header_case`] was set to true and the response included
+/// the following headers:
+///
+/// ```ignore
+/// x-Bread: Baguette
+/// X-BREAD: Pain
+/// x-bread: Ficelle
+/// ```
+///
+/// Then `res.extensions().get::<HeaderCaseMap>()` will return a map with:
+///
+/// ```ignore
+/// HeaderCaseMap({
+///     "x-bread": ["x-Bread", "X-BREAD", "x-bread"],
+/// })
+/// ```
+///
+/// [`http1_preserve_header_case`]: /client/struct.Client.html#method.http1_preserve_header_case
+#[derive(Clone, Debug)]
+pub(crate) struct HeaderCaseMap(HeaderMap<Bytes>);
+
+#[cfg(feature = "http1")]
+impl HeaderCaseMap {
+    /// Returns a view of all spellings associated with that header name,
+    /// in the order they were found.
+    pub(crate) fn get_all<'a>(
+        &'a self,
+        name: &HeaderName,
+    ) -> impl Iterator<Item = impl AsRef<[u8]> + 'a> + 'a {
+        self.get_all_internal(name).into_iter()
+    }
+
+    /// Returns a view of all spellings associated with that header name,
+    /// in the order they were found.
+    pub(crate) fn get_all_internal<'a>(&'a self, name: &HeaderName) -> ValueIter<'_, Bytes> {
+        self.0.get_all(name).into_iter()
+    }
+
+    pub(crate) fn default() -> Self {
+        Self(Default::default())
+    }
+
+    #[cfg(any(test, feature = "ffi"))]
+    pub(crate) fn insert(&mut self, name: HeaderName, orig: Bytes) {
+        self.0.insert(name, orig);
+    }
+
+    pub(crate) fn append<N>(&mut self, name: N, orig: Bytes)
+    where
+        N: IntoHeaderName,
+    {
+        self.0.append(name, orig);
+    }
+}
+
+#[cfg(feature = "ffi")]
+#[derive(Clone, Debug)]
+/// Hashmap<Headername, numheaders with that name>
+pub(crate) struct OriginalHeaderOrder {
+    /// Stores how many entries a Headername maps to. This is used
+    /// for accounting.
+    num_entries: HashMap<HeaderName, usize>,
+    /// Stores the ordering of the headers. ex: `vec[i] = (headerName, idx)`,
+    /// The vector is ordered such that the ith element
+    /// represents the ith header that came in off the line.
+    /// The `HeaderName` and `idx` are then used elsewhere to index into
+    /// the multi map that stores the header values.
+    entry_order: Vec<(HeaderName, usize)>,
+}
+
+#[cfg(all(feature = "http1", feature = "ffi"))]
+impl OriginalHeaderOrder {
+    pub(crate) fn default() -> Self {
+        OriginalHeaderOrder {
+            num_entries: HashMap::new(),
+            entry_order: Vec::new(),
+        }
+    }
+
+    pub(crate) fn insert(&mut self, name: HeaderName) {
+        if !self.num_entries.contains_key(&name) {
+            let idx = 0;
+            self.num_entries.insert(name.clone(), 1);
+            self.entry_order.push((name, idx));
+        }
+        // Replacing an already existing element does not
+        // change ordering, so we only care if its the first
+        // header name encountered
+    }
+
+    pub(crate) fn append<N>(&mut self, name: N)
+    where
+        N: IntoHeaderName + Into<HeaderName> + Clone,
+    {
+        let name: HeaderName = name.into();
+        let idx;
+        if self.num_entries.contains_key(&name) {
+            idx = self.num_entries[&name];
+            *self.num_entries.get_mut(&name).unwrap() += 1;
+        } else {
+            idx = 0;
+            self.num_entries.insert(name.clone(), 1);
+        }
+        self.entry_order.push((name, idx));
+    }
+
+    // No doc test is run here because `RUSTFLAGS='--cfg hyper_unstable_ffi'`
+    // is needed to compile. Once ffi is stablized `no_run` should be removed
+    // here.
+    /// This returns an iterator that provides header names and indexes
+    /// in the original order received.
+    ///
+    /// # Examples
+    /// ```no_run
+    /// use hyper::ext::OriginalHeaderOrder;
+    /// use hyper::header::{HeaderName, HeaderValue, HeaderMap};
+    ///
+    /// let mut h_order = OriginalHeaderOrder::default();
+    /// let mut h_map = Headermap::new();
+    ///
+    /// let name1 = b"Set-CookiE";
+    /// let value1 = b"a=b";
+    /// h_map.append(name1);
+    /// h_order.append(name1);
+    ///
+    /// let name2 = b"Content-Encoding";
+    /// let value2 = b"gzip";
+    /// h_map.append(name2, value2);
+    /// h_order.append(name2);
+    ///
+    /// let name3 = b"SET-COOKIE";
+    /// let value3 = b"c=d";
+    /// h_map.append(name3, value3);
+    /// h_order.append(name3)
+    ///
+    /// let mut iter = h_order.get_in_order()
+    ///
+    /// let (name, idx) = iter.next();
+    /// assert_eq!(b"a=b", h_map.get_all(name).nth(idx).unwrap());
+    ///
+    /// let (name, idx) = iter.next();
+    /// assert_eq!(b"gzip", h_map.get_all(name).nth(idx).unwrap());
+    ///
+    /// let (name, idx) = iter.next();
+    /// assert_eq!(b"c=d", h_map.get_all(name).nth(idx).unwrap());
+    /// ```
+    pub(crate) fn get_in_order(&self) -> impl Iterator<Item = &(HeaderName, usize)> {
+        self.entry_order.iter()
+    }
+}
diff --git a/src/ext/h1_reason_phrase.rs b/src/ext/h1_reason_phrase.rs
new file mode 100644
index 0000000..021b632
--- /dev/null
+++ b/src/ext/h1_reason_phrase.rs
@@ -0,0 +1,221 @@
+use std::convert::TryFrom;
+
+use bytes::Bytes;
+
+/// A reason phrase in an HTTP/1 response.
+///
+/// # Clients
+///
+/// For clients, a `ReasonPhrase` will be present in the extensions of the `http::Response` returned
+/// for a request if the reason phrase is different from the canonical reason phrase for the
+/// response's status code. For example, if a server returns `HTTP/1.1 200 Awesome`, the
+/// `ReasonPhrase` will be present and contain `Awesome`, but if a server returns `HTTP/1.1 200 OK`,
+/// the response will not contain a `ReasonPhrase`.
+///
+/// ```no_run
+/// # #[cfg(all(feature = "tcp", feature = "client", feature = "http1"))]
+/// # async fn fake_fetch() -> hyper::Result<()> {
+/// use hyper::{Client, Uri};
+/// use hyper::ext::ReasonPhrase;
+///
+/// let res = Client::new().get(Uri::from_static("http://example.com/non_canonical_reason")).await?;
+///
+/// // Print out the non-canonical reason phrase, if it has one...
+/// if let Some(reason) = res.extensions().get::<ReasonPhrase>() {
+///     println!("non-canonical reason: {}", std::str::from_utf8(reason.as_bytes()).unwrap());
+/// }
+/// # Ok(())
+/// # }
+/// ```
+///
+/// # Servers
+///
+/// When a `ReasonPhrase` is present in the extensions of the `http::Response` written by a server,
+/// its contents will be written in place of the canonical reason phrase when responding via HTTP/1.
+#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct ReasonPhrase(Bytes);
+
+impl ReasonPhrase {
+    /// Gets the reason phrase as bytes.
+    pub fn as_bytes(&self) -> &[u8] {
+        &self.0
+    }
+
+    /// Converts a static byte slice to a reason phrase.
+    pub fn from_static(reason: &'static [u8]) -> Self {
+        // TODO: this can be made const once MSRV is >= 1.57.0
+        if find_invalid_byte(reason).is_some() {
+            panic!("invalid byte in static reason phrase");
+        }
+        Self(Bytes::from_static(reason))
+    }
+
+    /// Converts a `Bytes` directly into a `ReasonPhrase` without validating.
+    ///
+    /// Use with care; invalid bytes in a reason phrase can cause serious security problems if
+    /// emitted in a response.
+    pub unsafe fn from_bytes_unchecked(reason: Bytes) -> Self {
+        Self(reason)
+    }
+}
+
+impl TryFrom<&[u8]> for ReasonPhrase {
+    type Error = InvalidReasonPhrase;
+
+    fn try_from(reason: &[u8]) -> Result<Self, Self::Error> {
+        if let Some(bad_byte) = find_invalid_byte(reason) {
+            Err(InvalidReasonPhrase { bad_byte })
+        } else {
+            Ok(Self(Bytes::copy_from_slice(reason)))
+        }
+    }
+}
+
+impl TryFrom<Vec<u8>> for ReasonPhrase {
+    type Error = InvalidReasonPhrase;
+
+    fn try_from(reason: Vec<u8>) -> Result<Self, Self::Error> {
+        if let Some(bad_byte) = find_invalid_byte(&reason) {
+            Err(InvalidReasonPhrase { bad_byte })
+        } else {
+            Ok(Self(Bytes::from(reason)))
+        }
+    }
+}
+
+impl TryFrom<String> for ReasonPhrase {
+    type Error = InvalidReasonPhrase;
+
+    fn try_from(reason: String) -> Result<Self, Self::Error> {
+        if let Some(bad_byte) = find_invalid_byte(reason.as_bytes()) {
+            Err(InvalidReasonPhrase { bad_byte })
+        } else {
+            Ok(Self(Bytes::from(reason)))
+        }
+    }
+}
+
+impl TryFrom<Bytes> for ReasonPhrase {
+    type Error = InvalidReasonPhrase;
+
+    fn try_from(reason: Bytes) -> Result<Self, Self::Error> {
+        if let Some(bad_byte) = find_invalid_byte(&reason) {
+            Err(InvalidReasonPhrase { bad_byte })
+        } else {
+            Ok(Self(reason))
+        }
+    }
+}
+
+impl Into<Bytes> for ReasonPhrase {
+    fn into(self) -> Bytes {
+        self.0
+    }
+}
+
+impl AsRef<[u8]> for ReasonPhrase {
+    fn as_ref(&self) -> &[u8] {
+        &self.0
+    }
+}
+
+/// Error indicating an invalid byte when constructing a `ReasonPhrase`.
+///
+/// See [the spec][spec] for details on allowed bytes.
+///
+/// [spec]: https://httpwg.org/http-core/draft-ietf-httpbis-messaging-latest.html#rfc.section.4.p.7
+#[derive(Debug)]
+pub struct InvalidReasonPhrase {
+    bad_byte: u8,
+}
+
+impl std::fmt::Display for InvalidReasonPhrase {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "Invalid byte in reason phrase: {}", self.bad_byte)
+    }
+}
+
+impl std::error::Error for InvalidReasonPhrase {}
+
+const fn is_valid_byte(b: u8) -> bool {
+    // See https://www.rfc-editor.org/rfc/rfc5234.html#appendix-B.1
+    const fn is_vchar(b: u8) -> bool {
+        0x21 <= b && b <= 0x7E
+    }
+
+    // See https://httpwg.org/http-core/draft-ietf-httpbis-semantics-latest.html#fields.values
+    //
+    // The 0xFF comparison is technically redundant, but it matches the text of the spec more
+    // clearly and will be optimized away.
+    #[allow(unused_comparisons)]
+    const fn is_obs_text(b: u8) -> bool {
+        0x80 <= b && b <= 0xFF
+    }
+
+    // See https://httpwg.org/http-core/draft-ietf-httpbis-messaging-latest.html#rfc.section.4.p.7
+    b == b'\t' || b == b' ' || is_vchar(b) || is_obs_text(b)
+}
+
+const fn find_invalid_byte(bytes: &[u8]) -> Option<u8> {
+    let mut i = 0;
+    while i < bytes.len() {
+        let b = bytes[i];
+        if !is_valid_byte(b) {
+            return Some(b);
+        }
+        i += 1;
+    }
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn basic_valid() {
+        const PHRASE: &'static [u8] = b"OK";
+        assert_eq!(ReasonPhrase::from_static(PHRASE).as_bytes(), PHRASE);
+        assert_eq!(ReasonPhrase::try_from(PHRASE).unwrap().as_bytes(), PHRASE);
+    }
+
+    #[test]
+    fn empty_valid() {
+        const PHRASE: &'static [u8] = b"";
+        assert_eq!(ReasonPhrase::from_static(PHRASE).as_bytes(), PHRASE);
+        assert_eq!(ReasonPhrase::try_from(PHRASE).unwrap().as_bytes(), PHRASE);
+    }
+
+    #[test]
+    fn obs_text_valid() {
+        const PHRASE: &'static [u8] = b"hyp\xe9r";
+        assert_eq!(ReasonPhrase::from_static(PHRASE).as_bytes(), PHRASE);
+        assert_eq!(ReasonPhrase::try_from(PHRASE).unwrap().as_bytes(), PHRASE);
+    }
+
+    const NEWLINE_PHRASE: &'static [u8] = b"hyp\ner";
+
+    #[test]
+    #[should_panic]
+    fn newline_invalid_panic() {
+        ReasonPhrase::from_static(NEWLINE_PHRASE);
+    }
+
+    #[test]
+    fn newline_invalid_err() {
+        assert!(ReasonPhrase::try_from(NEWLINE_PHRASE).is_err());
+    }
+
+    const CR_PHRASE: &'static [u8] = b"hyp\rer";
+
+    #[test]
+    #[should_panic]
+    fn cr_invalid_panic() {
+        ReasonPhrase::from_static(CR_PHRASE);
+    }
+
+    #[test]
+    fn cr_invalid_err() {
+        assert!(ReasonPhrase::try_from(CR_PHRASE).is_err());
+    }
+}
diff --git a/src/ffi/body.rs b/src/ffi/body.rs
new file mode 100644
index 0000000..39ba5be
--- /dev/null
+++ b/src/ffi/body.rs
@@ -0,0 +1,229 @@
+use std::ffi::c_void;
+use std::mem::ManuallyDrop;
+use std::ptr;
+use std::task::{Context, Poll};
+
+use http::HeaderMap;
+use libc::{c_int, size_t};
+
+use super::task::{hyper_context, hyper_task, hyper_task_return_type, AsTaskType};
+use super::{UserDataPointer, HYPER_ITER_CONTINUE};
+use crate::body::{Body, Bytes, HttpBody as _};
+
+/// A streaming HTTP body.
+pub struct hyper_body(pub(super) Body);
+
+/// A buffer of bytes that is sent or received on a `hyper_body`.
+pub struct hyper_buf(pub(crate) Bytes);
+
+pub(crate) struct UserBody {
+    data_func: hyper_body_data_callback,
+    userdata: *mut c_void,
+}
+
+// ===== Body =====
+
+type hyper_body_foreach_callback = extern "C" fn(*mut c_void, *const hyper_buf) -> c_int;
+
+type hyper_body_data_callback =
+    extern "C" fn(*mut c_void, *mut hyper_context<'_>, *mut *mut hyper_buf) -> c_int;
+
+ffi_fn! {
+    /// Create a new "empty" body.
+    ///
+    /// If not configured, this body acts as an empty payload.
+    fn hyper_body_new() -> *mut hyper_body {
+        Box::into_raw(Box::new(hyper_body(Body::empty())))
+    } ?= ptr::null_mut()
+}
+
+ffi_fn! {
+    /// Free a `hyper_body *`.
+    fn hyper_body_free(body: *mut hyper_body) {
+        drop(non_null!(Box::from_raw(body) ?= ()));
+    }
+}
+
+ffi_fn! {
+    /// Return a task that will poll the body for the next buffer of data.
+    ///
+    /// The task value may have different types depending on the outcome:
+    ///
+    /// - `HYPER_TASK_BUF`: Success, and more data was received.
+    /// - `HYPER_TASK_ERROR`: An error retrieving the data.
+    /// - `HYPER_TASK_EMPTY`: The body has finished streaming data.
+    ///
+    /// This does not consume the `hyper_body *`, so it may be used to again.
+    /// However, it MUST NOT be used or freed until the related task completes.
+    fn hyper_body_data(body: *mut hyper_body) -> *mut hyper_task {
+        // This doesn't take ownership of the Body, so don't allow destructor
+        let mut body = ManuallyDrop::new(non_null!(Box::from_raw(body) ?= ptr::null_mut()));
+
+        Box::into_raw(hyper_task::boxed(async move {
+            body.0.data().await.map(|res| res.map(hyper_buf))
+        }))
+    } ?= ptr::null_mut()
+}
+
+ffi_fn! {
+    /// Return a task that will poll the body and execute the callback with each
+    /// body chunk that is received.
+    ///
+    /// The `hyper_buf` pointer is only a borrowed reference, it cannot live outside
+    /// the execution of the callback. You must make a copy to retain it.
+    ///
+    /// The callback should return `HYPER_ITER_CONTINUE` to continue iterating
+    /// chunks as they are received, or `HYPER_ITER_BREAK` to cancel.
+    ///
+    /// This will consume the `hyper_body *`, you shouldn't use it anymore or free it.
+    fn hyper_body_foreach(body: *mut hyper_body, func: hyper_body_foreach_callback, userdata: *mut c_void) -> *mut hyper_task {
+        let mut body = non_null!(Box::from_raw(body) ?= ptr::null_mut());
+        let userdata = UserDataPointer(userdata);
+
+        Box::into_raw(hyper_task::boxed(async move {
+            while let Some(item) = body.0.data().await {
+                let chunk = item?;
+                if HYPER_ITER_CONTINUE != func(userdata.0, &hyper_buf(chunk)) {
+                    return Err(crate::Error::new_user_aborted_by_callback());
+                }
+            }
+            Ok(())
+        }))
+    } ?= ptr::null_mut()
+}
+
+ffi_fn! {
+    /// Set userdata on this body, which will be passed to callback functions.
+    fn hyper_body_set_userdata(body: *mut hyper_body, userdata: *mut c_void) {
+        let b = non_null!(&mut *body ?= ());
+        b.0.as_ffi_mut().userdata = userdata;
+    }
+}
+
+ffi_fn! {
+    /// Set the data callback for this body.
+    ///
+    /// The callback is called each time hyper needs to send more data for the
+    /// body. It is passed the value from `hyper_body_set_userdata`.
+    ///
+    /// If there is data available, the `hyper_buf **` argument should be set
+    /// to a `hyper_buf *` containing the data, and `HYPER_POLL_READY` should
+    /// be returned.
+    ///
+    /// Returning `HYPER_POLL_READY` while the `hyper_buf **` argument points
+    /// to `NULL` will indicate the body has completed all data.
+    ///
+    /// If there is more data to send, but it isn't yet available, a
+    /// `hyper_waker` should be saved from the `hyper_context *` argument, and
+    /// `HYPER_POLL_PENDING` should be returned. You must wake the saved waker
+    /// to signal the task when data is available.
+    ///
+    /// If some error has occurred, you can return `HYPER_POLL_ERROR` to abort
+    /// the body.
+    fn hyper_body_set_data_func(body: *mut hyper_body, func: hyper_body_data_callback) {
+        let b = non_null!{ &mut *body ?= () };
+        b.0.as_ffi_mut().data_func = func;
+    }
+}
+
+// ===== impl UserBody =====
+
+impl UserBody {
+    pub(crate) fn new() -> UserBody {
+        UserBody {
+            data_func: data_noop,
+            userdata: std::ptr::null_mut(),
+        }
+    }
+
+    pub(crate) fn poll_data(&mut self, cx: &mut Context<'_>) -> Poll<Option<crate::Result<Bytes>>> {
+        let mut out = std::ptr::null_mut();
+        match (self.data_func)(self.userdata, hyper_context::wrap(cx), &mut out) {
+            super::task::HYPER_POLL_READY => {
+                if out.is_null() {
+                    Poll::Ready(None)
+                } else {
+                    let buf = unsafe { Box::from_raw(out) };
+                    Poll::Ready(Some(Ok(buf.0)))
+                }
+            }
+            super::task::HYPER_POLL_PENDING => Poll::Pending,
+            super::task::HYPER_POLL_ERROR => {
+                Poll::Ready(Some(Err(crate::Error::new_body_write_aborted())))
+            }
+            unexpected => Poll::Ready(Some(Err(crate::Error::new_body_write(format!(
+                "unexpected hyper_body_data_func return code {}",
+                unexpected
+            ))))),
+        }
+    }
+
+    pub(crate) fn poll_trailers(
+        &mut self,
+        _cx: &mut Context<'_>,
+    ) -> Poll<crate::Result<Option<HeaderMap>>> {
+        Poll::Ready(Ok(None))
+    }
+}
+
+/// cbindgen:ignore
+extern "C" fn data_noop(
+    _userdata: *mut c_void,
+    _: *mut hyper_context<'_>,
+    _: *mut *mut hyper_buf,
+) -> c_int {
+    super::task::HYPER_POLL_READY
+}
+
+unsafe impl Send for UserBody {}
+unsafe impl Sync for UserBody {}
+
+// ===== Bytes =====
+
+ffi_fn! {
+    /// Create a new `hyper_buf *` by copying the provided bytes.
+    ///
+    /// This makes an owned copy of the bytes, so the `buf` argument can be
+    /// freed or changed afterwards.
+    ///
+    /// This returns `NULL` if allocating a new buffer fails.
+    fn hyper_buf_copy(buf: *const u8, len: size_t) -> *mut hyper_buf {
+        let slice = unsafe {
+            std::slice::from_raw_parts(buf, len)
+        };
+        Box::into_raw(Box::new(hyper_buf(Bytes::copy_from_slice(slice))))
+    } ?= ptr::null_mut()
+}
+
+ffi_fn! {
+    /// Get a pointer to the bytes in this buffer.
+    ///
+    /// This should be used in conjunction with `hyper_buf_len` to get the length
+    /// of the bytes data.
+    ///
+    /// This pointer is borrowed data, and not valid once the `hyper_buf` is
+    /// consumed/freed.
+    fn hyper_buf_bytes(buf: *const hyper_buf) -> *const u8 {
+        unsafe { (*buf).0.as_ptr() }
+    } ?= ptr::null()
+}
+
+ffi_fn! {
+    /// Get the length of the bytes this buffer contains.
+    fn hyper_buf_len(buf: *const hyper_buf) -> size_t {
+        unsafe { (*buf).0.len() }
+    }
+}
+
+ffi_fn! {
+    /// Free this buffer.
+    fn hyper_buf_free(buf: *mut hyper_buf) {
+        drop(unsafe { Box::from_raw(buf) });
+    }
+}
+
+unsafe impl AsTaskType for hyper_buf {
+    fn as_task_type(&self) -> hyper_task_return_type {
+        hyper_task_return_type::HYPER_TASK_BUF
+    }
+}
diff --git a/src/ffi/client.rs b/src/ffi/client.rs
new file mode 100644
index 0000000..670f77d
--- /dev/null
+++ b/src/ffi/client.rs
@@ -0,0 +1,182 @@
+use std::ptr;
+use std::sync::Arc;
+
+use libc::c_int;
+
+use crate::client::conn;
+use crate::rt::Executor as _;
+
+use super::error::hyper_code;
+use super::http_types::{hyper_request, hyper_response};
+use super::io::hyper_io;
+use super::task::{hyper_executor, hyper_task, hyper_task_return_type, AsTaskType, WeakExec};
+
+/// An options builder to configure an HTTP client connection.
+pub struct hyper_clientconn_options {
+    builder: conn::Builder,
+    /// Use a `Weak` to prevent cycles.
+    exec: WeakExec,
+}
+
+/// An HTTP client connection handle.
+///
+/// These are used to send a request on a single connection. It's possible to
+/// send multiple requests on a single connection, such as when HTTP/1
+/// keep-alive or HTTP/2 is used.
+pub struct hyper_clientconn {
+    tx: conn::SendRequest<crate::Body>,
+}
+
+// ===== impl hyper_clientconn =====
+
+ffi_fn! {
+    /// Starts an HTTP client connection handshake using the provided IO transport
+    /// and options.
+    ///
+    /// Both the `io` and the `options` are consumed in this function call.
+    ///
+    /// The returned `hyper_task *` must be polled with an executor until the
+    /// handshake completes, at which point the value can be taken.
+    fn hyper_clientconn_handshake(io: *mut hyper_io, options: *mut hyper_clientconn_options) -> *mut hyper_task {
+        let options = non_null! { Box::from_raw(options) ?= ptr::null_mut() };
+        let io = non_null! { Box::from_raw(io) ?= ptr::null_mut() };
+
+        Box::into_raw(hyper_task::boxed(async move {
+            options.builder.handshake::<_, crate::Body>(io)
+                .await
+                .map(|(tx, conn)| {
+                    options.exec.execute(Box::pin(async move {
+                        let _ = conn.await;
+                    }));
+                    hyper_clientconn { tx }
+                })
+        }))
+    } ?= std::ptr::null_mut()
+}
+
+ffi_fn! {
+    /// Send a request on the client connection.
+    ///
+    /// Returns a task that needs to be polled until it is ready. When ready, the
+    /// task yields a `hyper_response *`.
+    fn hyper_clientconn_send(conn: *mut hyper_clientconn, req: *mut hyper_request) -> *mut hyper_task {
+        let mut req = non_null! { Box::from_raw(req) ?= ptr::null_mut() };
+
+        // Update request with original-case map of headers
+        req.finalize_request();
+
+        let fut = non_null! { &mut *conn ?= ptr::null_mut() }.tx.send_request(req.0);
+
+        let fut = async move {
+            fut.await.map(hyper_response::wrap)
+        };
+
+        Box::into_raw(hyper_task::boxed(fut))
+    } ?= std::ptr::null_mut()
+}
+
+ffi_fn! {
+    /// Free a `hyper_clientconn *`.
+    fn hyper_clientconn_free(conn: *mut hyper_clientconn) {
+        drop(non_null! { Box::from_raw(conn) ?= () });
+    }
+}
+
+unsafe impl AsTaskType for hyper_clientconn {
+    fn as_task_type(&self) -> hyper_task_return_type {
+        hyper_task_return_type::HYPER_TASK_CLIENTCONN
+    }
+}
+
+// ===== impl hyper_clientconn_options =====
+
+ffi_fn! {
+    /// Creates a new set of HTTP clientconn options to be used in a handshake.
+    fn hyper_clientconn_options_new() -> *mut hyper_clientconn_options {
+        #[allow(deprecated)]
+        let builder = conn::Builder::new();
+
+        Box::into_raw(Box::new(hyper_clientconn_options {
+            builder,
+            exec: WeakExec::new(),
+        }))
+    } ?= std::ptr::null_mut()
+}
+
+ffi_fn! {
+    /// Set the whether or not header case is preserved.
+    ///
+    /// Pass `0` to allow lowercase normalization (default), `1` to retain original case.
+    fn hyper_clientconn_options_set_preserve_header_case(opts: *mut hyper_clientconn_options, enabled: c_int) {
+        let opts = non_null! { &mut *opts ?= () };
+        opts.builder.http1_preserve_header_case(enabled != 0);
+    }
+}
+
+ffi_fn! {
+    /// Set the whether or not header order is preserved.
+    ///
+    /// Pass `0` to allow reordering (default), `1` to retain original ordering.
+    fn hyper_clientconn_options_set_preserve_header_order(opts: *mut hyper_clientconn_options, enabled: c_int) {
+        let opts = non_null! { &mut *opts ?= () };
+        opts.builder.http1_preserve_header_order(enabled != 0);
+    }
+}
+
+ffi_fn! {
+    /// Free a `hyper_clientconn_options *`.
+    fn hyper_clientconn_options_free(opts: *mut hyper_clientconn_options) {
+        drop(non_null! { Box::from_raw(opts) ?= () });
+    }
+}
+
+ffi_fn! {
+    /// Set the client background task executor.
+    ///
+    /// This does not consume the `options` or the `exec`.
+    fn hyper_clientconn_options_exec(opts: *mut hyper_clientconn_options, exec: *const hyper_executor) {
+        let opts = non_null! { &mut *opts ?= () };
+
+        let exec = non_null! { Arc::from_raw(exec) ?= () };
+        let weak_exec = hyper_executor::downgrade(&exec);
+        std::mem::forget(exec);
+
+        opts.builder.executor(weak_exec.clone());
+        opts.exec = weak_exec;
+    }
+}
+
+ffi_fn! {
+    /// Set the whether to use HTTP2.
+    ///
+    /// Pass `0` to disable, `1` to enable.
+    fn hyper_clientconn_options_http2(opts: *mut hyper_clientconn_options, enabled: c_int) -> hyper_code {
+        #[cfg(feature = "http2")]
+        {
+            let opts = non_null! { &mut *opts ?= hyper_code::HYPERE_INVALID_ARG };
+            opts.builder.http2_only(enabled != 0);
+            hyper_code::HYPERE_OK
+        }
+
+        #[cfg(not(feature = "http2"))]
+        {
+            drop(opts);
+            drop(enabled);
+            hyper_code::HYPERE_FEATURE_NOT_ENABLED
+        }
+    }
+}
+
+ffi_fn! {
+    /// Set the whether to include a copy of the raw headers in responses
+    /// received on this connection.
+    ///
+    /// Pass `0` to disable, `1` to enable.
+    ///
+    /// If enabled, see `hyper_response_headers_raw()` for usage.
+    fn hyper_clientconn_options_headers_raw(opts: *mut hyper_clientconn_options, enabled: c_int) -> hyper_code {
+        let opts = non_null! { &mut *opts ?= hyper_code::HYPERE_INVALID_ARG };
+        opts.builder.http1_headers_raw(enabled != 0);
+        hyper_code::HYPERE_OK
+    }
+}
diff --git a/src/ffi/error.rs b/src/ffi/error.rs
new file mode 100644
index 0000000..015e595
--- /dev/null
+++ b/src/ffi/error.rs
@@ -0,0 +1,85 @@
+use libc::size_t;
+
+/// A more detailed error object returned by some hyper functions.
+pub struct hyper_error(crate::Error);
+
+/// A return code for many of hyper's methods.
+#[repr(C)]
+pub enum hyper_code {
+    /// All is well.
+    HYPERE_OK,
+    /// General error, details in the `hyper_error *`.
+    HYPERE_ERROR,
+    /// A function argument was invalid.
+    HYPERE_INVALID_ARG,
+    /// The IO transport returned an EOF when one wasn't expected.
+    ///
+    /// This typically means an HTTP request or response was expected, but the
+    /// connection closed cleanly without sending (all of) it.
+    HYPERE_UNEXPECTED_EOF,
+    /// Aborted by a user supplied callback.
+    HYPERE_ABORTED_BY_CALLBACK,
+    /// An optional hyper feature was not enabled.
+    #[cfg_attr(feature = "http2", allow(unused))]
+    HYPERE_FEATURE_NOT_ENABLED,
+    /// The peer sent an HTTP message that could not be parsed.
+    HYPERE_INVALID_PEER_MESSAGE,
+}
+
+// ===== impl hyper_error =====
+
+impl hyper_error {
+    fn code(&self) -> hyper_code {
+        use crate::error::Kind as ErrorKind;
+        use crate::error::User;
+
+        match self.0.kind() {
+            ErrorKind::Parse(_) => hyper_code::HYPERE_INVALID_PEER_MESSAGE,
+            ErrorKind::IncompleteMessage => hyper_code::HYPERE_UNEXPECTED_EOF,
+            ErrorKind::User(User::AbortedByCallback) => hyper_code::HYPERE_ABORTED_BY_CALLBACK,
+            // TODO: add more variants
+            _ => hyper_code::HYPERE_ERROR,
+        }
+    }
+
+    fn print_to(&self, dst: &mut [u8]) -> usize {
+        use std::io::Write;
+
+        let mut dst = std::io::Cursor::new(dst);
+
+        // A write! error doesn't matter. As much as possible will have been
+        // written, and the Cursor position will know how far that is (even
+        // if that is zero).
+        let _ = write!(dst, "{}", &self.0);
+        dst.position() as usize
+    }
+}
+
+ffi_fn! {
+    /// Frees a `hyper_error`.
+    fn hyper_error_free(err: *mut hyper_error) {
+        drop(non_null!(Box::from_raw(err) ?= ()));
+    }
+}
+
+ffi_fn! {
+    /// Get an equivalent `hyper_code` from this error.
+    fn hyper_error_code(err: *const hyper_error) -> hyper_code {
+        non_null!(&*err ?= hyper_code::HYPERE_INVALID_ARG).code()
+    }
+}
+
+ffi_fn! {
+    /// Print the details of this error to a buffer.
+    ///
+    /// The `dst_len` value must be the maximum length that the buffer can
+    /// store.
+    ///
+    /// The return value is number of bytes that were written to `dst`.
+    fn hyper_error_print(err: *const hyper_error, dst: *mut u8, dst_len: size_t) -> size_t {
+        let dst = unsafe {
+            std::slice::from_raw_parts_mut(dst, dst_len)
+        };
+        non_null!(&*err ?= 0).print_to(dst)
+    }
+}
diff --git a/src/ffi/http_types.rs b/src/ffi/http_types.rs
new file mode 100644
index 0000000..ea10f13
--- /dev/null
+++ b/src/ffi/http_types.rs
@@ -0,0 +1,657 @@
+use bytes::Bytes;
+use libc::{c_int, size_t};
+use std::ffi::c_void;
+
+use super::body::{hyper_body, hyper_buf};
+use super::error::hyper_code;
+use super::task::{hyper_task_return_type, AsTaskType};
+use super::{UserDataPointer, HYPER_ITER_CONTINUE};
+use crate::ext::{HeaderCaseMap, OriginalHeaderOrder, ReasonPhrase};
+use crate::header::{HeaderName, HeaderValue};
+use crate::{Body, HeaderMap, Method, Request, Response, Uri};
+
+/// An HTTP request.
+pub struct hyper_request(pub(super) Request<Body>);
+
+/// An HTTP response.
+pub struct hyper_response(pub(super) Response<Body>);
+
+/// An HTTP header map.
+///
+/// These can be part of a request or response.
+pub struct hyper_headers {
+    pub(super) headers: HeaderMap,
+    orig_casing: HeaderCaseMap,
+    orig_order: OriginalHeaderOrder,
+}
+
+pub(crate) struct RawHeaders(pub(crate) hyper_buf);
+
+pub(crate) struct OnInformational {
+    func: hyper_request_on_informational_callback,
+    data: UserDataPointer,
+}
+
+type hyper_request_on_informational_callback = extern "C" fn(*mut c_void, *mut hyper_response);
+
+// ===== impl hyper_request =====
+
+ffi_fn! {
+    /// Construct a new HTTP request.
+    fn hyper_request_new() -> *mut hyper_request {
+        Box::into_raw(Box::new(hyper_request(Request::new(Body::empty()))))
+    } ?= std::ptr::null_mut()
+}
+
+ffi_fn! {
+    /// Free an HTTP request if not going to send it on a client.
+    fn hyper_request_free(req: *mut hyper_request) {
+        drop(non_null!(Box::from_raw(req) ?= ()));
+    }
+}
+
+ffi_fn! {
+    /// Set the HTTP Method of the request.
+    fn hyper_request_set_method(req: *mut hyper_request, method: *const u8, method_len: size_t) -> hyper_code {
+        let bytes = unsafe {
+            std::slice::from_raw_parts(method, method_len as usize)
+        };
+        let req = non_null!(&mut *req ?= hyper_code::HYPERE_INVALID_ARG);
+        match Method::from_bytes(bytes) {
+            Ok(m) => {
+                *req.0.method_mut() = m;
+                hyper_code::HYPERE_OK
+            },
+            Err(_) => {
+                hyper_code::HYPERE_INVALID_ARG
+            }
+        }
+    }
+}
+
+ffi_fn! {
+    /// Set the URI of the request.
+    ///
+    /// The request's URI is best described as the `request-target` from the RFCs. So in HTTP/1,
+    /// whatever is set will get sent as-is in the first line (GET $uri HTTP/1.1). It
+    /// supports the 4 defined variants, origin-form, absolute-form, authority-form, and
+    /// asterisk-form.
+    ///
+    /// The underlying type was built to efficiently support HTTP/2 where the request-target is
+    /// split over :scheme, :authority, and :path. As such, each part can be set explicitly, or the
+    /// type can parse a single contiguous string and if a scheme is found, that slot is "set". If
+    /// the string just starts with a path, only the path portion is set. All pseudo headers that
+    /// have been parsed/set are sent when the connection type is HTTP/2.
+    ///
+    /// To set each slot explicitly, use `hyper_request_set_uri_parts`.
+    fn hyper_request_set_uri(req: *mut hyper_request, uri: *const u8, uri_len: size_t) -> hyper_code {
+        let bytes = unsafe {
+            std::slice::from_raw_parts(uri, uri_len as usize)
+        };
+        let req = non_null!(&mut *req ?= hyper_code::HYPERE_INVALID_ARG);
+        match Uri::from_maybe_shared(bytes) {
+            Ok(u) => {
+                *req.0.uri_mut() = u;
+                hyper_code::HYPERE_OK
+            },
+            Err(_) => {
+                hyper_code::HYPERE_INVALID_ARG
+            }
+        }
+    }
+}
+
+ffi_fn! {
+    /// Set the URI of the request with separate scheme, authority, and
+    /// path/query strings.
+    ///
+    /// Each of `scheme`, `authority`, and `path_and_query` should either be
+    /// null, to skip providing a component, or point to a UTF-8 encoded
+    /// string. If any string pointer argument is non-null, its corresponding
+    /// `len` parameter must be set to the string's length.
+    fn hyper_request_set_uri_parts(
+        req: *mut hyper_request,
+        scheme: *const u8,
+        scheme_len: size_t,
+        authority: *const u8,
+        authority_len: size_t,
+        path_and_query: *const u8,
+        path_and_query_len: size_t
+    ) -> hyper_code {
+        let mut builder = Uri::builder();
+        if !scheme.is_null() {
+            let scheme_bytes = unsafe {
+                std::slice::from_raw_parts(scheme, scheme_len as usize)
+            };
+            builder = builder.scheme(scheme_bytes);
+        }
+        if !authority.is_null() {
+            let authority_bytes = unsafe {
+                std::slice::from_raw_parts(authority, authority_len as usize)
+            };
+            builder = builder.authority(authority_bytes);
+        }
+        if !path_and_query.is_null() {
+            let path_and_query_bytes = unsafe {
+                std::slice::from_raw_parts(path_and_query, path_and_query_len as usize)
+            };
+            builder = builder.path_and_query(path_and_query_bytes);
+        }
+        match builder.build() {
+            Ok(u) => {
+                *unsafe { &mut *req }.0.uri_mut() = u;
+                hyper_code::HYPERE_OK
+            },
+            Err(_) => {
+                hyper_code::HYPERE_INVALID_ARG
+            }
+        }
+    }
+}
+
+ffi_fn! {
+    /// Set the preferred HTTP version of the request.
+    ///
+    /// The version value should be one of the `HYPER_HTTP_VERSION_` constants.
+    ///
+    /// Note that this won't change the major HTTP version of the connection,
+    /// since that is determined at the handshake step.
+    fn hyper_request_set_version(req: *mut hyper_request, version: c_int) -> hyper_code {
+        use http::Version;
+
+        let req = non_null!(&mut *req ?= hyper_code::HYPERE_INVALID_ARG);
+        *req.0.version_mut() = match version {
+            super::HYPER_HTTP_VERSION_NONE => Version::HTTP_11,
+            super::HYPER_HTTP_VERSION_1_0 => Version::HTTP_10,
+            super::HYPER_HTTP_VERSION_1_1 => Version::HTTP_11,
+            super::HYPER_HTTP_VERSION_2 => Version::HTTP_2,
+            _ => {
+                // We don't know this version
+                return hyper_code::HYPERE_INVALID_ARG;
+            }
+        };
+        hyper_code::HYPERE_OK
+    }
+}
+
+ffi_fn! {
+    /// Gets a reference to the HTTP headers of this request
+    ///
+    /// This is not an owned reference, so it should not be accessed after the
+    /// `hyper_request` has been consumed.
+    fn hyper_request_headers(req: *mut hyper_request) -> *mut hyper_headers {
+        hyper_headers::get_or_default(unsafe { &mut *req }.0.extensions_mut())
+    } ?= std::ptr::null_mut()
+}
+
+ffi_fn! {
+    /// Set the body of the request.
+    ///
+    /// The default is an empty body.
+    ///
+    /// This takes ownership of the `hyper_body *`, you must not use it or
+    /// free it after setting it on the request.
+    fn hyper_request_set_body(req: *mut hyper_request, body: *mut hyper_body) -> hyper_code {
+        let body = non_null!(Box::from_raw(body) ?= hyper_code::HYPERE_INVALID_ARG);
+        let req = non_null!(&mut *req ?= hyper_code::HYPERE_INVALID_ARG);
+        *req.0.body_mut() = body.0;
+        hyper_code::HYPERE_OK
+    }
+}
+
+ffi_fn! {
+    /// Set an informational (1xx) response callback.
+    ///
+    /// The callback is called each time hyper receives an informational (1xx)
+    /// response for this request.
+    ///
+    /// The third argument is an opaque user data pointer, which is passed to
+    /// the callback each time.
+    ///
+    /// The callback is passed the `void *` data pointer, and a
+    /// `hyper_response *` which can be inspected as any other response. The
+    /// body of the response will always be empty.
+    ///
+    /// NOTE: The `hyper_response *` is just borrowed data, and will not
+    /// be valid after the callback finishes. You must copy any data you wish
+    /// to persist.
+    fn hyper_request_on_informational(req: *mut hyper_request, callback: hyper_request_on_informational_callback, data: *mut c_void) -> hyper_code {
+        let ext = OnInformational {
+            func: callback,
+            data: UserDataPointer(data),
+        };
+        let req = non_null!(&mut *req ?= hyper_code::HYPERE_INVALID_ARG);
+        req.0.extensions_mut().insert(ext);
+        hyper_code::HYPERE_OK
+    }
+}
+
+impl hyper_request {
+    pub(super) fn finalize_request(&mut self) {
+        if let Some(headers) = self.0.extensions_mut().remove::<hyper_headers>() {
+            *self.0.headers_mut() = headers.headers;
+            self.0.extensions_mut().insert(headers.orig_casing);
+            self.0.extensions_mut().insert(headers.orig_order);
+        }
+    }
+}
+
+// ===== impl hyper_response =====
+
+ffi_fn! {
+    /// Free an HTTP response after using it.
+    fn hyper_response_free(resp: *mut hyper_response) {
+        drop(non_null!(Box::from_raw(resp) ?= ()));
+    }
+}
+
+ffi_fn! {
+    /// Get the HTTP-Status code of this response.
+    ///
+    /// It will always be within the range of 100-599.
+    fn hyper_response_status(resp: *const hyper_response) -> u16 {
+        non_null!(&*resp ?= 0).0.status().as_u16()
+    }
+}
+
+ffi_fn! {
+    /// Get a pointer to the reason-phrase of this response.
+    ///
+    /// This buffer is not null-terminated.
+    ///
+    /// This buffer is owned by the response, and should not be used after
+    /// the response has been freed.
+    ///
+    /// Use `hyper_response_reason_phrase_len()` to get the length of this
+    /// buffer.
+    fn hyper_response_reason_phrase(resp: *const hyper_response) -> *const u8 {
+        non_null!(&*resp ?= std::ptr::null()).reason_phrase().as_ptr()
+    } ?= std::ptr::null()
+}
+
+ffi_fn! {
+    /// Get the length of the reason-phrase of this response.
+    ///
+    /// Use `hyper_response_reason_phrase()` to get the buffer pointer.
+    fn hyper_response_reason_phrase_len(resp: *const hyper_response) -> size_t {
+        non_null!(&*resp ?= 0).reason_phrase().len()
+    }
+}
+
+ffi_fn! {
+    /// Get a reference to the full raw headers of this response.
+    ///
+    /// You must have enabled `hyper_clientconn_options_headers_raw()`, or this
+    /// will return NULL.
+    ///
+    /// The returned `hyper_buf *` is just a reference, owned by the response.
+    /// You need to make a copy if you wish to use it after freeing the
+    /// response.
+    ///
+    /// The buffer is not null-terminated, see the `hyper_buf` functions for
+    /// getting the bytes and length.
+    fn hyper_response_headers_raw(resp: *const hyper_response) -> *const hyper_buf {
+        let resp = non_null!(&*resp ?= std::ptr::null());
+        match resp.0.extensions().get::<RawHeaders>() {
+            Some(raw) => &raw.0,
+            None => std::ptr::null(),
+        }
+    } ?= std::ptr::null()
+}
+
+ffi_fn! {
+    /// Get the HTTP version used by this response.
+    ///
+    /// The returned value could be:
+    ///
+    /// - `HYPER_HTTP_VERSION_1_0`
+    /// - `HYPER_HTTP_VERSION_1_1`
+    /// - `HYPER_HTTP_VERSION_2`
+    /// - `HYPER_HTTP_VERSION_NONE` if newer (or older).
+    fn hyper_response_version(resp: *const hyper_response) -> c_int {
+        use http::Version;
+
+        match non_null!(&*resp ?= 0).0.version() {
+            Version::HTTP_10 => super::HYPER_HTTP_VERSION_1_0,
+            Version::HTTP_11 => super::HYPER_HTTP_VERSION_1_1,
+            Version::HTTP_2 => super::HYPER_HTTP_VERSION_2,
+            _ => super::HYPER_HTTP_VERSION_NONE,
+        }
+    }
+}
+
+ffi_fn! {
+    /// Gets a reference to the HTTP headers of this response.
+    ///
+    /// This is not an owned reference, so it should not be accessed after the
+    /// `hyper_response` has been freed.
+    fn hyper_response_headers(resp: *mut hyper_response) -> *mut hyper_headers {
+        hyper_headers::get_or_default(unsafe { &mut *resp }.0.extensions_mut())
+    } ?= std::ptr::null_mut()
+}
+
+ffi_fn! {
+    /// Take ownership of the body of this response.
+    ///
+    /// It is safe to free the response even after taking ownership of its body.
+    fn hyper_response_body(resp: *mut hyper_response) -> *mut hyper_body {
+        let body = std::mem::take(non_null!(&mut *resp ?= std::ptr::null_mut()).0.body_mut());
+        Box::into_raw(Box::new(hyper_body(body)))
+    } ?= std::ptr::null_mut()
+}
+
+impl hyper_response {
+    pub(super) fn wrap(mut resp: Response<Body>) -> hyper_response {
+        let headers = std::mem::take(resp.headers_mut());
+        let orig_casing = resp
+            .extensions_mut()
+            .remove::<HeaderCaseMap>()
+            .unwrap_or_else(HeaderCaseMap::default);
+        let orig_order = resp
+            .extensions_mut()
+            .remove::<OriginalHeaderOrder>()
+            .unwrap_or_else(OriginalHeaderOrder::default);
+        resp.extensions_mut().insert(hyper_headers {
+            headers,
+            orig_casing,
+            orig_order,
+        });
+
+        hyper_response(resp)
+    }
+
+    fn reason_phrase(&self) -> &[u8] {
+        if let Some(reason) = self.0.extensions().get::<ReasonPhrase>() {
+            return reason.as_bytes();
+        }
+
+        if let Some(reason) = self.0.status().canonical_reason() {
+            return reason.as_bytes();
+        }
+
+        &[]
+    }
+}
+
+unsafe impl AsTaskType for hyper_response {
+    fn as_task_type(&self) -> hyper_task_return_type {
+        hyper_task_return_type::HYPER_TASK_RESPONSE
+    }
+}
+
+// ===== impl Headers =====
+
+type hyper_headers_foreach_callback =
+    extern "C" fn(*mut c_void, *const u8, size_t, *const u8, size_t) -> c_int;
+
+impl hyper_headers {
+    pub(super) fn get_or_default(ext: &mut http::Extensions) -> &mut hyper_headers {
+        if let None = ext.get_mut::<hyper_headers>() {
+            ext.insert(hyper_headers::default());
+        }
+
+        ext.get_mut::<hyper_headers>().unwrap()
+    }
+}
+
+ffi_fn! {
+    /// Iterates the headers passing each name and value pair to the callback.
+    ///
+    /// The `userdata` pointer is also passed to the callback.
+    ///
+    /// The callback should return `HYPER_ITER_CONTINUE` to keep iterating, or
+    /// `HYPER_ITER_BREAK` to stop.
+    fn hyper_headers_foreach(headers: *const hyper_headers, func: hyper_headers_foreach_callback, userdata: *mut c_void) {
+        let headers = non_null!(&*headers ?= ());
+        // For each header name/value pair, there may be a value in the casemap
+        // that corresponds to the HeaderValue. So, we iterator all the keys,
+        // and for each one, try to pair the originally cased name with the value.
+        //
+        // TODO: consider adding http::HeaderMap::entries() iterator
+        let mut ordered_iter =  headers.orig_order.get_in_order().peekable();
+        if ordered_iter.peek().is_some() {
+            for (name, idx) in ordered_iter {
+                let (name_ptr, name_len) = if let Some(orig_name) = headers.orig_casing.get_all(name).nth(*idx) {
+                    (orig_name.as_ref().as_ptr(), orig_name.as_ref().len())
+                } else {
+                    (
+                    name.as_str().as_bytes().as_ptr(),
+                    name.as_str().as_bytes().len(),
+                    )
+                };
+
+                let val_ptr;
+                let val_len;
+                if let Some(value) = headers.headers.get_all(name).iter().nth(*idx) {
+                    val_ptr = value.as_bytes().as_ptr();
+                    val_len = value.as_bytes().len();
+                } else {
+                    // Stop iterating, something has gone wrong.
+                    return;
+                }
+
+                if HYPER_ITER_CONTINUE != func(userdata, name_ptr, name_len, val_ptr, val_len) {
+                    return;
+                }
+            }
+        } else {
+            for name in headers.headers.keys() {
+                let mut names = headers.orig_casing.get_all(name);
+
+                for value in headers.headers.get_all(name) {
+                    let (name_ptr, name_len) = if let Some(orig_name) = names.next() {
+                        (orig_name.as_ref().as_ptr(), orig_name.as_ref().len())
+                    } else {
+                        (
+                            name.as_str().as_bytes().as_ptr(),
+                            name.as_str().as_bytes().len(),
+                        )
+                    };
+
+                    let val_ptr = value.as_bytes().as_ptr();
+                    let val_len = value.as_bytes().len();
+
+                    if HYPER_ITER_CONTINUE != func(userdata, name_ptr, name_len, val_ptr, val_len) {
+                        return;
+                    }
+                }
+            }
+        }
+    }
+}
+
+ffi_fn! {
+    /// Sets the header with the provided name to the provided value.
+    ///
+    /// This overwrites any previous value set for the header.
+    fn hyper_headers_set(headers: *mut hyper_headers, name: *const u8, name_len: size_t, value: *const u8, value_len: size_t) -> hyper_code {
+        let headers = non_null!(&mut *headers ?= hyper_code::HYPERE_INVALID_ARG);
+        match unsafe { raw_name_value(name, name_len, value, value_len) } {
+            Ok((name, value, orig_name)) => {
+                headers.headers.insert(&name, value);
+                headers.orig_casing.insert(name.clone(), orig_name.clone());
+                headers.orig_order.insert(name);
+                hyper_code::HYPERE_OK
+            }
+            Err(code) => code,
+        }
+    }
+}
+
+ffi_fn! {
+    /// Adds the provided value to the list of the provided name.
+    ///
+    /// If there were already existing values for the name, this will append the
+    /// new value to the internal list.
+    fn hyper_headers_add(headers: *mut hyper_headers, name: *const u8, name_len: size_t, value: *const u8, value_len: size_t) -> hyper_code {
+        let headers = non_null!(&mut *headers ?= hyper_code::HYPERE_INVALID_ARG);
+
+        match unsafe { raw_name_value(name, name_len, value, value_len) } {
+            Ok((name, value, orig_name)) => {
+                headers.headers.append(&name, value);
+                headers.orig_casing.append(&name, orig_name.clone());
+                headers.orig_order.append(name);
+                hyper_code::HYPERE_OK
+            }
+            Err(code) => code,
+        }
+    }
+}
+
+impl Default for hyper_headers {
+    fn default() -> Self {
+        Self {
+            headers: Default::default(),
+            orig_casing: HeaderCaseMap::default(),
+            orig_order: OriginalHeaderOrder::default(),
+        }
+    }
+}
+
+unsafe fn raw_name_value(
+    name: *const u8,
+    name_len: size_t,
+    value: *const u8,
+    value_len: size_t,
+) -> Result<(HeaderName, HeaderValue, Bytes), hyper_code> {
+    let name = std::slice::from_raw_parts(name, name_len);
+    let orig_name = Bytes::copy_from_slice(name);
+    let name = match HeaderName::from_bytes(name) {
+        Ok(name) => name,
+        Err(_) => return Err(hyper_code::HYPERE_INVALID_ARG),
+    };
+    let value = std::slice::from_raw_parts(value, value_len);
+    let value = match HeaderValue::from_bytes(value) {
+        Ok(val) => val,
+        Err(_) => return Err(hyper_code::HYPERE_INVALID_ARG),
+    };
+
+    Ok((name, value, orig_name))
+}
+
+// ===== impl OnInformational =====
+
+impl OnInformational {
+    pub(crate) fn call(&mut self, resp: Response<Body>) {
+        let mut resp = hyper_response::wrap(resp);
+        (self.func)(self.data.0, &mut resp);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_headers_foreach_cases_preserved() {
+        let mut headers = hyper_headers::default();
+
+        let name1 = b"Set-CookiE";
+        let value1 = b"a=b";
+        hyper_headers_add(
+            &mut headers,
+            name1.as_ptr(),
+            name1.len(),
+            value1.as_ptr(),
+            value1.len(),
+        );
+
+        let name2 = b"SET-COOKIE";
+        let value2 = b"c=d";
+        hyper_headers_add(
+            &mut headers,
+            name2.as_ptr(),
+            name2.len(),
+            value2.as_ptr(),
+            value2.len(),
+        );
+
+        let mut vec = Vec::<u8>::new();
+        hyper_headers_foreach(&headers, concat, &mut vec as *mut _ as *mut c_void);
+
+        assert_eq!(vec, b"Set-CookiE: a=b\r\nSET-COOKIE: c=d\r\n");
+
+        extern "C" fn concat(
+            vec: *mut c_void,
+            name: *const u8,
+            name_len: usize,
+            value: *const u8,
+            value_len: usize,
+        ) -> c_int {
+            unsafe {
+                let vec = &mut *(vec as *mut Vec<u8>);
+                let name = std::slice::from_raw_parts(name, name_len);
+                let value = std::slice::from_raw_parts(value, value_len);
+                vec.extend(name);
+                vec.extend(b": ");
+                vec.extend(value);
+                vec.extend(b"\r\n");
+            }
+            HYPER_ITER_CONTINUE
+        }
+    }
+
+    #[cfg(all(feature = "http1", feature = "ffi"))]
+    #[test]
+    fn test_headers_foreach_order_preserved() {
+        let mut headers = hyper_headers::default();
+
+        let name1 = b"Set-CookiE";
+        let value1 = b"a=b";
+        hyper_headers_add(
+            &mut headers,
+            name1.as_ptr(),
+            name1.len(),
+            value1.as_ptr(),
+            value1.len(),
+        );
+
+        let name2 = b"Content-Encoding";
+        let value2 = b"gzip";
+        hyper_headers_add(
+            &mut headers,
+            name2.as_ptr(),
+            name2.len(),
+            value2.as_ptr(),
+            value2.len(),
+        );
+
+        let name3 = b"SET-COOKIE";
+        let value3 = b"c=d";
+        hyper_headers_add(
+            &mut headers,
+            name3.as_ptr(),
+            name3.len(),
+            value3.as_ptr(),
+            value3.len(),
+        );
+
+        let mut vec = Vec::<u8>::new();
+        hyper_headers_foreach(&headers, concat, &mut vec as *mut _ as *mut c_void);
+
+        println!("{}", std::str::from_utf8(&vec).unwrap());
+        assert_eq!(
+            vec,
+            b"Set-CookiE: a=b\r\nContent-Encoding: gzip\r\nSET-COOKIE: c=d\r\n"
+        );
+
+        extern "C" fn concat(
+            vec: *mut c_void,
+            name: *const u8,
+            name_len: usize,
+            value: *const u8,
+            value_len: usize,
+        ) -> c_int {
+            unsafe {
+                let vec = &mut *(vec as *mut Vec<u8>);
+                let name = std::slice::from_raw_parts(name, name_len);
+                let value = std::slice::from_raw_parts(value, value_len);
+                vec.extend(name);
+                vec.extend(b": ");
+                vec.extend(value);
+                vec.extend(b"\r\n");
+            }
+            HYPER_ITER_CONTINUE
+        }
+    }
+}
diff --git a/src/ffi/io.rs b/src/ffi/io.rs
new file mode 100644
index 0000000..bff666d
--- /dev/null
+++ b/src/ffi/io.rs
@@ -0,0 +1,178 @@
+use std::ffi::c_void;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use libc::size_t;
+use tokio::io::{AsyncRead, AsyncWrite};
+
+use super::task::hyper_context;
+
+/// Sentinel value to return from a read or write callback that the operation
+/// is pending.
+pub const HYPER_IO_PENDING: size_t = 0xFFFFFFFF;
+/// Sentinel value to return from a read or write callback that the operation
+/// has errored.
+pub const HYPER_IO_ERROR: size_t = 0xFFFFFFFE;
+
+type hyper_io_read_callback =
+    extern "C" fn(*mut c_void, *mut hyper_context<'_>, *mut u8, size_t) -> size_t;
+type hyper_io_write_callback =
+    extern "C" fn(*mut c_void, *mut hyper_context<'_>, *const u8, size_t) -> size_t;
+
+/// An IO object used to represent a socket or similar concept.
+pub struct hyper_io {
+    read: hyper_io_read_callback,
+    write: hyper_io_write_callback,
+    userdata: *mut c_void,
+}
+
+ffi_fn! {
+    /// Create a new IO type used to represent a transport.
+    ///
+    /// The read and write functions of this transport should be set with
+    /// `hyper_io_set_read` and `hyper_io_set_write`.
+    fn hyper_io_new() -> *mut hyper_io {
+        Box::into_raw(Box::new(hyper_io {
+            read: read_noop,
+            write: write_noop,
+            userdata: std::ptr::null_mut(),
+        }))
+    } ?= std::ptr::null_mut()
+}
+
+ffi_fn! {
+    /// Free an unused `hyper_io *`.
+    ///
+    /// This is typically only useful if you aren't going to pass ownership
+    /// of the IO handle to hyper, such as with `hyper_clientconn_handshake()`.
+    fn hyper_io_free(io: *mut hyper_io) {
+        drop(non_null!(Box::from_raw(io) ?= ()));
+    }
+}
+
+ffi_fn! {
+    /// Set the user data pointer for this IO to some value.
+    ///
+    /// This value is passed as an argument to the read and write callbacks.
+    fn hyper_io_set_userdata(io: *mut hyper_io, data: *mut c_void) {
+        non_null!(&mut *io ?= ()).userdata = data;
+    }
+}
+
+ffi_fn! {
+    /// Set the read function for this IO transport.
+    ///
+    /// Data that is read from the transport should be put in the `buf` pointer,
+    /// up to `buf_len` bytes. The number of bytes read should be the return value.
+    ///
+    /// It is undefined behavior to try to access the bytes in the `buf` pointer,
+    /// unless you have already written them yourself. It is also undefined behavior
+    /// to return that more bytes have been written than actually set on the `buf`.
+    ///
+    /// If there is no data currently available, a waker should be claimed from
+    /// the `ctx` and registered with whatever polling mechanism is used to signal
+    /// when data is available later on. The return value should be
+    /// `HYPER_IO_PENDING`.
+    ///
+    /// If there is an irrecoverable error reading data, then `HYPER_IO_ERROR`
+    /// should be the return value.
+    fn hyper_io_set_read(io: *mut hyper_io, func: hyper_io_read_callback) {
+        non_null!(&mut *io ?= ()).read = func;
+    }
+}
+
+ffi_fn! {
+    /// Set the write function for this IO transport.
+    ///
+    /// Data from the `buf` pointer should be written to the transport, up to
+    /// `buf_len` bytes. The number of bytes written should be the return value.
+    ///
+    /// If no data can currently be written, the `waker` should be cloned and
+    /// registered with whatever polling mechanism is used to signal when data
+    /// is available later on. The return value should be `HYPER_IO_PENDING`.
+    ///
+    /// Yeet.
+    ///
+    /// If there is an irrecoverable error reading data, then `HYPER_IO_ERROR`
+    /// should be the return value.
+    fn hyper_io_set_write(io: *mut hyper_io, func: hyper_io_write_callback) {
+        non_null!(&mut *io ?= ()).write = func;
+    }
+}
+
+/// cbindgen:ignore
+extern "C" fn read_noop(
+    _userdata: *mut c_void,
+    _: *mut hyper_context<'_>,
+    _buf: *mut u8,
+    _buf_len: size_t,
+) -> size_t {
+    0
+}
+
+/// cbindgen:ignore
+extern "C" fn write_noop(
+    _userdata: *mut c_void,
+    _: *mut hyper_context<'_>,
+    _buf: *const u8,
+    _buf_len: size_t,
+) -> size_t {
+    0
+}
+
+impl AsyncRead for hyper_io {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut tokio::io::ReadBuf<'_>,
+    ) -> Poll<std::io::Result<()>> {
+        let buf_ptr = unsafe { buf.unfilled_mut() }.as_mut_ptr() as *mut u8;
+        let buf_len = buf.remaining();
+
+        match (self.read)(self.userdata, hyper_context::wrap(cx), buf_ptr, buf_len) {
+            HYPER_IO_PENDING => Poll::Pending,
+            HYPER_IO_ERROR => Poll::Ready(Err(std::io::Error::new(
+                std::io::ErrorKind::Other,
+                "io error",
+            ))),
+            ok => {
+                // We have to trust that the user's read callback actually
+                // filled in that many bytes... :(
+                unsafe { buf.assume_init(ok) };
+                buf.advance(ok);
+                Poll::Ready(Ok(()))
+            }
+        }
+    }
+}
+
+impl AsyncWrite for hyper_io {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<std::io::Result<usize>> {
+        let buf_ptr = buf.as_ptr();
+        let buf_len = buf.len();
+
+        match (self.write)(self.userdata, hyper_context::wrap(cx), buf_ptr, buf_len) {
+            HYPER_IO_PENDING => Poll::Pending,
+            HYPER_IO_ERROR => Poll::Ready(Err(std::io::Error::new(
+                std::io::ErrorKind::Other,
+                "io error",
+            ))),
+            ok => Poll::Ready(Ok(ok)),
+        }
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<std::io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<std::io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+}
+
+unsafe impl Send for hyper_io {}
+unsafe impl Sync for hyper_io {}
diff --git a/src/ffi/macros.rs b/src/ffi/macros.rs
new file mode 100644
index 0000000..022711b
--- /dev/null
+++ b/src/ffi/macros.rs
@@ -0,0 +1,53 @@
+macro_rules! ffi_fn {
+    ($(#[$doc:meta])* fn $name:ident($($arg:ident: $arg_ty:ty),*) -> $ret:ty $body:block ?= $default:expr) => {
+        $(#[$doc])*
+        #[no_mangle]
+        pub extern fn $name($($arg: $arg_ty),*) -> $ret {
+            use std::panic::{self, AssertUnwindSafe};
+
+            match panic::catch_unwind(AssertUnwindSafe(move || $body)) {
+                Ok(v) => v,
+                Err(_) => {
+                    $default
+                }
+            }
+        }
+    };
+
+    ($(#[$doc:meta])* fn $name:ident($($arg:ident: $arg_ty:ty),*) -> $ret:ty $body:block) => {
+        ffi_fn!($(#[$doc])* fn $name($($arg: $arg_ty),*) -> $ret $body ?= {
+            eprintln!("panic unwind caught, aborting");
+            std::process::abort()
+        });
+    };
+
+    ($(#[$doc:meta])* fn $name:ident($($arg:ident: $arg_ty:ty),*) $body:block ?= $default:expr) => {
+        ffi_fn!($(#[$doc])* fn $name($($arg: $arg_ty),*) -> () $body ?= $default);
+    };
+
+    ($(#[$doc:meta])* fn $name:ident($($arg:ident: $arg_ty:ty),*) $body:block) => {
+        ffi_fn!($(#[$doc])* fn $name($($arg: $arg_ty),*) -> () $body);
+    };
+}
+
+macro_rules! non_null {
+    ($ptr:ident, $eval:expr, $err:expr) => {{
+        debug_assert!(!$ptr.is_null(), "{:?} must not be null", stringify!($ptr));
+        if $ptr.is_null() {
+            return $err;
+        }
+        unsafe { $eval }
+    }};
+    (&*$ptr:ident ?= $err:expr) => {{
+        non_null!($ptr, &*$ptr, $err)
+    }};
+    (&mut *$ptr:ident ?= $err:expr) => {{
+        non_null!($ptr, &mut *$ptr, $err)
+    }};
+    (Box::from_raw($ptr:ident) ?= $err:expr) => {{
+        non_null!($ptr, Box::from_raw($ptr), $err)
+    }};
+    (Arc::from_raw($ptr:ident) ?= $err:expr) => {{
+        non_null!($ptr, Arc::from_raw($ptr), $err)
+    }};
+}
diff --git a/src/ffi/mod.rs b/src/ffi/mod.rs
new file mode 100644
index 0000000..fd67a88
--- /dev/null
+++ b/src/ffi/mod.rs
@@ -0,0 +1,94 @@
+// We have a lot of c-types in here, stop warning about their names!
+#![allow(non_camel_case_types)]
+// fmt::Debug isn't helpful on FFI types
+#![allow(missing_debug_implementations)]
+// unreachable_pub warns `#[no_mangle] pub extern fn` in private mod.
+#![allow(unreachable_pub)]
+
+//! # hyper C API
+//!
+//! This part of the documentation describes the C API for hyper. That is, how
+//! to *use* the hyper library in C code. This is **not** a regular Rust
+//! module, and thus it is not accessible in Rust.
+//!
+//! ## Unstable
+//!
+//! The C API of hyper is currently **unstable**, which means it's not part of
+//! the semver contract as the rest of the Rust API is. Because of that, it's
+//! only accessible if `--cfg hyper_unstable_ffi` is passed to `rustc` when
+//! compiling. The easiest way to do that is setting the `RUSTFLAGS`
+//! environment variable.
+//!
+//! ## Building
+//!
+//! The C API is part of the Rust library, but isn't compiled by default. Using
+//! `cargo`, it can be compiled with the following command:
+//!
+//! ```notrust
+//! RUSTFLAGS="--cfg hyper_unstable_ffi" cargo build --features client,http1,http2,ffi
+//! ```
+
+// We may eventually allow the FFI to be enabled without `client` or `http1`,
+// that is why we don't auto enable them as `ffi = ["client", "http1"]` in
+// the `Cargo.toml`.
+//
+// But for now, give a clear message that this compile error is expected.
+#[cfg(not(all(feature = "client", feature = "http1")))]
+compile_error!("The `ffi` feature currently requires the `client` and `http1` features.");
+
+#[cfg(not(hyper_unstable_ffi))]
+compile_error!(
+    "\
+    The `ffi` feature is unstable, and requires the \
+    `RUSTFLAGS='--cfg hyper_unstable_ffi'` environment variable to be set.\
+"
+);
+
+#[macro_use]
+mod macros;
+
+mod body;
+mod client;
+mod error;
+mod http_types;
+mod io;
+mod task;
+
+pub use self::body::*;
+pub use self::client::*;
+pub use self::error::*;
+pub use self::http_types::*;
+pub use self::io::*;
+pub use self::task::*;
+
+/// Return in iter functions to continue iterating.
+pub const HYPER_ITER_CONTINUE: libc::c_int = 0;
+/// Return in iter functions to stop iterating.
+#[allow(unused)]
+pub const HYPER_ITER_BREAK: libc::c_int = 1;
+
+/// An HTTP Version that is unspecified.
+pub const HYPER_HTTP_VERSION_NONE: libc::c_int = 0;
+/// The HTTP/1.0 version.
+pub const HYPER_HTTP_VERSION_1_0: libc::c_int = 10;
+/// The HTTP/1.1 version.
+pub const HYPER_HTTP_VERSION_1_1: libc::c_int = 11;
+/// The HTTP/2 version.
+pub const HYPER_HTTP_VERSION_2: libc::c_int = 20;
+
+struct UserDataPointer(*mut std::ffi::c_void);
+
+// We don't actually know anything about this pointer, it's up to the user
+// to do the right thing.
+unsafe impl Send for UserDataPointer {}
+unsafe impl Sync for UserDataPointer {}
+
+/// cbindgen:ignore
+static VERSION_CSTR: &str = concat!(env!("CARGO_PKG_VERSION"), "\0");
+
+ffi_fn! {
+    /// Returns a static ASCII (null terminated) string of the hyper version.
+    fn hyper_version() -> *const libc::c_char {
+        VERSION_CSTR.as_ptr() as _
+    } ?= std::ptr::null()
+}
diff --git a/src/ffi/task.rs b/src/ffi/task.rs
new file mode 100644
index 0000000..ef54fe4
--- /dev/null
+++ b/src/ffi/task.rs
@@ -0,0 +1,411 @@
+use std::ffi::c_void;
+use std::future::Future;
+use std::pin::Pin;
+use std::ptr;
+use std::sync::{
+    atomic::{AtomicBool, Ordering},
+    Arc, Mutex, Weak,
+};
+use std::task::{Context, Poll};
+
+use futures_util::stream::{FuturesUnordered, Stream};
+use libc::c_int;
+
+use super::error::hyper_code;
+use super::UserDataPointer;
+
+type BoxFuture<T> = Pin<Box<dyn Future<Output = T> + Send>>;
+type BoxAny = Box<dyn AsTaskType + Send + Sync>;
+
+/// Return in a poll function to indicate it was ready.
+pub const HYPER_POLL_READY: c_int = 0;
+/// Return in a poll function to indicate it is still pending.
+///
+/// The passed in `hyper_waker` should be registered to wake up the task at
+/// some later point.
+pub const HYPER_POLL_PENDING: c_int = 1;
+/// Return in a poll function indicate an error.
+pub const HYPER_POLL_ERROR: c_int = 3;
+
+/// A task executor for `hyper_task`s.
+pub struct hyper_executor {
+    /// The executor of all task futures.
+    ///
+    /// There should never be contention on the mutex, as it is only locked
+    /// to drive the futures. However, we cannot guarantee proper usage from
+    /// `hyper_executor_poll()`, which in C could potentially be called inside
+    /// one of the stored futures. The mutex isn't re-entrant, so doing so
+    /// would result in a deadlock, but that's better than data corruption.
+    driver: Mutex<FuturesUnordered<TaskFuture>>,
+
+    /// The queue of futures that need to be pushed into the `driver`.
+    ///
+    /// This is has a separate mutex since `spawn` could be called from inside
+    /// a future, which would mean the driver's mutex is already locked.
+    spawn_queue: Mutex<Vec<TaskFuture>>,
+
+    /// This is used to track when a future calls `wake` while we are within
+    /// `hyper_executor::poll_next`.
+    is_woken: Arc<ExecWaker>,
+}
+
+#[derive(Clone)]
+pub(crate) struct WeakExec(Weak<hyper_executor>);
+
+struct ExecWaker(AtomicBool);
+
+/// An async task.
+pub struct hyper_task {
+    future: BoxFuture<BoxAny>,
+    output: Option<BoxAny>,
+    userdata: UserDataPointer,
+}
+
+struct TaskFuture {
+    task: Option<Box<hyper_task>>,
+}
+
+/// An async context for a task that contains the related waker.
+pub struct hyper_context<'a>(Context<'a>);
+
+/// A waker that is saved and used to waken a pending task.
+pub struct hyper_waker {
+    waker: std::task::Waker,
+}
+
+/// A descriptor for what type a `hyper_task` value is.
+#[repr(C)]
+pub enum hyper_task_return_type {
+    /// The value of this task is null (does not imply an error).
+    HYPER_TASK_EMPTY,
+    /// The value of this task is `hyper_error *`.
+    HYPER_TASK_ERROR,
+    /// The value of this task is `hyper_clientconn *`.
+    HYPER_TASK_CLIENTCONN,
+    /// The value of this task is `hyper_response *`.
+    HYPER_TASK_RESPONSE,
+    /// The value of this task is `hyper_buf *`.
+    HYPER_TASK_BUF,
+}
+
+pub(crate) unsafe trait AsTaskType {
+    fn as_task_type(&self) -> hyper_task_return_type;
+}
+
+pub(crate) trait IntoDynTaskType {
+    fn into_dyn_task_type(self) -> BoxAny;
+}
+
+// ===== impl hyper_executor =====
+
+impl hyper_executor {
+    fn new() -> Arc<hyper_executor> {
+        Arc::new(hyper_executor {
+            driver: Mutex::new(FuturesUnordered::new()),
+            spawn_queue: Mutex::new(Vec::new()),
+            is_woken: Arc::new(ExecWaker(AtomicBool::new(false))),
+        })
+    }
+
+    pub(crate) fn downgrade(exec: &Arc<hyper_executor>) -> WeakExec {
+        WeakExec(Arc::downgrade(exec))
+    }
+
+    fn spawn(&self, task: Box<hyper_task>) {
+        self.spawn_queue
+            .lock()
+            .unwrap()
+            .push(TaskFuture { task: Some(task) });
+    }
+
+    fn poll_next(&self) -> Option<Box<hyper_task>> {
+        // Drain the queue first.
+        self.drain_queue();
+
+        let waker = futures_util::task::waker_ref(&self.is_woken);
+        let mut cx = Context::from_waker(&waker);
+
+        loop {
+            match Pin::new(&mut *self.driver.lock().unwrap()).poll_next(&mut cx) {
+                Poll::Ready(val) => return val,
+                Poll::Pending => {
+                    // Check if any of the pending tasks tried to spawn
+                    // some new tasks. If so, drain into the driver and loop.
+                    if self.drain_queue() {
+                        continue;
+                    }
+
+                    // If the driver called `wake` while we were polling,
+                    // we should poll again immediately!
+                    if self.is_woken.0.swap(false, Ordering::SeqCst) {
+                        continue;
+                    }
+
+                    return None;
+                }
+            }
+        }
+    }
+
+    fn drain_queue(&self) -> bool {
+        let mut queue = self.spawn_queue.lock().unwrap();
+        if queue.is_empty() {
+            return false;
+        }
+
+        let driver = self.driver.lock().unwrap();
+
+        for task in queue.drain(..) {
+            driver.push(task);
+        }
+
+        true
+    }
+}
+
+impl futures_util::task::ArcWake for ExecWaker {
+    fn wake_by_ref(me: &Arc<ExecWaker>) {
+        me.0.store(true, Ordering::SeqCst);
+    }
+}
+
+// ===== impl WeakExec =====
+
+impl WeakExec {
+    pub(crate) fn new() -> Self {
+        WeakExec(Weak::new())
+    }
+}
+
+impl crate::rt::Executor<BoxFuture<()>> for WeakExec {
+    fn execute(&self, fut: BoxFuture<()>) {
+        if let Some(exec) = self.0.upgrade() {
+            exec.spawn(hyper_task::boxed(fut));
+        }
+    }
+}
+
+ffi_fn! {
+    /// Creates a new task executor.
+    fn hyper_executor_new() -> *const hyper_executor {
+        Arc::into_raw(hyper_executor::new())
+    } ?= ptr::null()
+}
+
+ffi_fn! {
+    /// Frees an executor and any incomplete tasks still part of it.
+    fn hyper_executor_free(exec: *const hyper_executor) {
+        drop(non_null!(Arc::from_raw(exec) ?= ()));
+    }
+}
+
+ffi_fn! {
+    /// Push a task onto the executor.
+    ///
+    /// The executor takes ownership of the task, it should not be accessed
+    /// again unless returned back to the user with `hyper_executor_poll`.
+    fn hyper_executor_push(exec: *const hyper_executor, task: *mut hyper_task) -> hyper_code {
+        let exec = non_null!(&*exec ?= hyper_code::HYPERE_INVALID_ARG);
+        let task = non_null!(Box::from_raw(task) ?= hyper_code::HYPERE_INVALID_ARG);
+        exec.spawn(task);
+        hyper_code::HYPERE_OK
+    }
+}
+
+ffi_fn! {
+    /// Polls the executor, trying to make progress on any tasks that have notified
+    /// that they are ready again.
+    ///
+    /// If ready, returns a task from the executor that has completed.
+    ///
+    /// If there are no ready tasks, this returns `NULL`.
+    fn hyper_executor_poll(exec: *const hyper_executor) -> *mut hyper_task {
+        let exec = non_null!(&*exec ?= ptr::null_mut());
+        match exec.poll_next() {
+            Some(task) => Box::into_raw(task),
+            None => ptr::null_mut(),
+        }
+    } ?= ptr::null_mut()
+}
+
+// ===== impl hyper_task =====
+
+impl hyper_task {
+    pub(crate) fn boxed<F>(fut: F) -> Box<hyper_task>
+    where
+        F: Future + Send + 'static,
+        F::Output: IntoDynTaskType + Send + Sync + 'static,
+    {
+        Box::new(hyper_task {
+            future: Box::pin(async move { fut.await.into_dyn_task_type() }),
+            output: None,
+            userdata: UserDataPointer(ptr::null_mut()),
+        })
+    }
+
+    fn output_type(&self) -> hyper_task_return_type {
+        match self.output {
+            None => hyper_task_return_type::HYPER_TASK_EMPTY,
+            Some(ref val) => val.as_task_type(),
+        }
+    }
+}
+
+impl Future for TaskFuture {
+    type Output = Box<hyper_task>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match Pin::new(&mut self.task.as_mut().unwrap().future).poll(cx) {
+            Poll::Ready(val) => {
+                let mut task = self.task.take().unwrap();
+                task.output = Some(val);
+                Poll::Ready(task)
+            }
+            Poll::Pending => Poll::Pending,
+        }
+    }
+}
+
+ffi_fn! {
+    /// Free a task.
+    fn hyper_task_free(task: *mut hyper_task) {
+        drop(non_null!(Box::from_raw(task) ?= ()));
+    }
+}
+
+ffi_fn! {
+    /// Takes the output value of this task.
+    ///
+    /// This must only be called once polling the task on an executor has finished
+    /// this task.
+    ///
+    /// Use `hyper_task_type` to determine the type of the `void *` return value.
+    fn hyper_task_value(task: *mut hyper_task) -> *mut c_void {
+        let task = non_null!(&mut *task ?= ptr::null_mut());
+
+        if let Some(val) = task.output.take() {
+            let p = Box::into_raw(val) as *mut c_void;
+            // protect from returning fake pointers to empty types
+            if p == std::ptr::NonNull::<c_void>::dangling().as_ptr() {
+                ptr::null_mut()
+            } else {
+                p
+            }
+        } else {
+            ptr::null_mut()
+        }
+    } ?= ptr::null_mut()
+}
+
+ffi_fn! {
+    /// Query the return type of this task.
+    fn hyper_task_type(task: *mut hyper_task) -> hyper_task_return_type {
+        // instead of blowing up spectacularly, just say this null task
+        // doesn't have a value to retrieve.
+        non_null!(&*task ?= hyper_task_return_type::HYPER_TASK_EMPTY).output_type()
+    }
+}
+
+ffi_fn! {
+    /// Set a user data pointer to be associated with this task.
+    ///
+    /// This value will be passed to task callbacks, and can be checked later
+    /// with `hyper_task_userdata`.
+    fn hyper_task_set_userdata(task: *mut hyper_task, userdata: *mut c_void) {
+        if task.is_null() {
+            return;
+        }
+
+        unsafe { (*task).userdata = UserDataPointer(userdata) };
+    }
+}
+
+ffi_fn! {
+    /// Retrieve the userdata that has been set via `hyper_task_set_userdata`.
+    fn hyper_task_userdata(task: *mut hyper_task) -> *mut c_void {
+        non_null!(&*task ?= ptr::null_mut()).userdata.0
+    } ?= ptr::null_mut()
+}
+
+// ===== impl AsTaskType =====
+
+unsafe impl AsTaskType for () {
+    fn as_task_type(&self) -> hyper_task_return_type {
+        hyper_task_return_type::HYPER_TASK_EMPTY
+    }
+}
+
+unsafe impl AsTaskType for crate::Error {
+    fn as_task_type(&self) -> hyper_task_return_type {
+        hyper_task_return_type::HYPER_TASK_ERROR
+    }
+}
+
+impl<T> IntoDynTaskType for T
+where
+    T: AsTaskType + Send + Sync + 'static,
+{
+    fn into_dyn_task_type(self) -> BoxAny {
+        Box::new(self)
+    }
+}
+
+impl<T> IntoDynTaskType for crate::Result<T>
+where
+    T: IntoDynTaskType + Send + Sync + 'static,
+{
+    fn into_dyn_task_type(self) -> BoxAny {
+        match self {
+            Ok(val) => val.into_dyn_task_type(),
+            Err(err) => Box::new(err),
+        }
+    }
+}
+
+impl<T> IntoDynTaskType for Option<T>
+where
+    T: IntoDynTaskType + Send + Sync + 'static,
+{
+    fn into_dyn_task_type(self) -> BoxAny {
+        match self {
+            Some(val) => val.into_dyn_task_type(),
+            None => ().into_dyn_task_type(),
+        }
+    }
+}
+
+// ===== impl hyper_context =====
+
+impl hyper_context<'_> {
+    pub(crate) fn wrap<'a, 'b>(cx: &'a mut Context<'b>) -> &'a mut hyper_context<'b> {
+        // A struct with only one field has the same layout as that field.
+        unsafe { std::mem::transmute::<&mut Context<'_>, &mut hyper_context<'_>>(cx) }
+    }
+}
+
+ffi_fn! {
+    /// Copies a waker out of the task context.
+    fn hyper_context_waker(cx: *mut hyper_context<'_>) -> *mut hyper_waker {
+        let waker = non_null!(&mut *cx ?= ptr::null_mut()).0.waker().clone();
+        Box::into_raw(Box::new(hyper_waker { waker }))
+    } ?= ptr::null_mut()
+}
+
+// ===== impl hyper_waker =====
+
+ffi_fn! {
+    /// Free a waker that hasn't been woken.
+    fn hyper_waker_free(waker: *mut hyper_waker) {
+        drop(non_null!(Box::from_raw(waker) ?= ()));
+    }
+}
+
+ffi_fn! {
+    /// Wake up the task associated with a waker.
+    ///
+    /// NOTE: This consumes the waker. You should not use or free the waker afterwards.
+    fn hyper_waker_wake(waker: *mut hyper_waker) {
+        let waker = non_null!(Box::from_raw(waker) ?= ());
+        waker.waker.wake();
+    }
+}
diff --git a/src/headers.rs b/src/headers.rs
new file mode 100644
index 0000000..2e5e5db
--- /dev/null
+++ b/src/headers.rs
@@ -0,0 +1,154 @@
+#[cfg(feature = "http1")]
+use bytes::BytesMut;
+use http::header::CONTENT_LENGTH;
+use http::header::{HeaderValue, ValueIter};
+use http::HeaderMap;
+#[cfg(all(feature = "http2", feature = "client"))]
+use http::Method;
+
+#[cfg(feature = "http1")]
+pub(super) fn connection_keep_alive(value: &HeaderValue) -> bool {
+    connection_has(value, "keep-alive")
+}
+
+#[cfg(feature = "http1")]
+pub(super) fn connection_close(value: &HeaderValue) -> bool {
+    connection_has(value, "close")
+}
+
+#[cfg(feature = "http1")]
+fn connection_has(value: &HeaderValue, needle: &str) -> bool {
+    if let Ok(s) = value.to_str() {
+        for val in s.split(',') {
+            if val.trim().eq_ignore_ascii_case(needle) {
+                return true;
+            }
+        }
+    }
+    false
+}
+
+#[cfg(all(feature = "http1", feature = "server"))]
+pub(super) fn content_length_parse(value: &HeaderValue) -> Option<u64> {
+    from_digits(value.as_bytes())
+}
+
+pub(super) fn content_length_parse_all(headers: &HeaderMap) -> Option<u64> {
+    content_length_parse_all_values(headers.get_all(CONTENT_LENGTH).into_iter())
+}
+
+pub(super) fn content_length_parse_all_values(values: ValueIter<'_, HeaderValue>) -> Option<u64> {
+    // If multiple Content-Length headers were sent, everything can still
+    // be alright if they all contain the same value, and all parse
+    // correctly. If not, then it's an error.
+
+    let mut content_length: Option<u64> = None;
+    for h in values {
+        if let Ok(line) = h.to_str() {
+            for v in line.split(',') {
+                if let Some(n) = from_digits(v.trim().as_bytes()) {
+                    if content_length.is_none() {
+                        content_length = Some(n)
+                    } else if content_length != Some(n) {
+                        return None;
+                    }
+                } else {
+                    return None;
+                }
+            }
+        } else {
+            return None;
+        }
+    }
+
+    content_length
+}
+
+fn from_digits(bytes: &[u8]) -> Option<u64> {
+    // cannot use FromStr for u64, since it allows a signed prefix
+    let mut result = 0u64;
+    const RADIX: u64 = 10;
+
+    if bytes.is_empty() {
+        return None;
+    }
+
+    for &b in bytes {
+        // can't use char::to_digit, since we haven't verified these bytes
+        // are utf-8.
+        match b {
+            b'0'..=b'9' => {
+                result = result.checked_mul(RADIX)?;
+                result = result.checked_add((b - b'0') as u64)?;
+            }
+            _ => {
+                // not a DIGIT, get outta here!
+                return None;
+            }
+        }
+    }
+
+    Some(result)
+}
+
+#[cfg(all(feature = "http2", feature = "client"))]
+pub(super) fn method_has_defined_payload_semantics(method: &Method) -> bool {
+    match *method {
+        Method::GET | Method::HEAD | Method::DELETE | Method::CONNECT => false,
+        _ => true,
+    }
+}
+
+#[cfg(feature = "http2")]
+pub(super) fn set_content_length_if_missing(headers: &mut HeaderMap, len: u64) {
+    headers
+        .entry(CONTENT_LENGTH)
+        .or_insert_with(|| HeaderValue::from(len));
+}
+
+#[cfg(feature = "http1")]
+pub(super) fn transfer_encoding_is_chunked(headers: &HeaderMap) -> bool {
+    is_chunked(headers.get_all(http::header::TRANSFER_ENCODING).into_iter())
+}
+
+#[cfg(feature = "http1")]
+pub(super) fn is_chunked(mut encodings: ValueIter<'_, HeaderValue>) -> bool {
+    // chunked must always be the last encoding, according to spec
+    if let Some(line) = encodings.next_back() {
+        return is_chunked_(line);
+    }
+
+    false
+}
+
+#[cfg(feature = "http1")]
+pub(super) fn is_chunked_(value: &HeaderValue) -> bool {
+    // chunked must always be the last encoding, according to spec
+    if let Ok(s) = value.to_str() {
+        if let Some(encoding) = s.rsplit(',').next() {
+            return encoding.trim().eq_ignore_ascii_case("chunked");
+        }
+    }
+
+    false
+}
+
+#[cfg(feature = "http1")]
+pub(super) fn add_chunked(mut entry: http::header::OccupiedEntry<'_, HeaderValue>) {
+    const CHUNKED: &str = "chunked";
+
+    if let Some(line) = entry.iter_mut().next_back() {
+        // + 2 for ", "
+        let new_cap = line.as_bytes().len() + CHUNKED.len() + 2;
+        let mut buf = BytesMut::with_capacity(new_cap);
+        buf.extend_from_slice(line.as_bytes());
+        buf.extend_from_slice(b", ");
+        buf.extend_from_slice(CHUNKED.as_bytes());
+
+        *line = HeaderValue::from_maybe_shared(buf.freeze())
+            .expect("original header value plus ascii is valid");
+        return;
+    }
+
+    entry.insert(HeaderValue::from_static(CHUNKED));
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..e5e4cfc
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,111 @@
+#![deny(missing_docs)]
+#![deny(missing_debug_implementations)]
+#![cfg_attr(test, deny(rust_2018_idioms))]
+#![cfg_attr(all(test, feature = "full"), deny(unreachable_pub))]
+#![cfg_attr(all(test, feature = "full"), deny(warnings))]
+#![cfg_attr(all(test, feature = "nightly"), feature(test))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
+
+//! # hyper
+//!
+//! hyper is a **fast** and **correct** HTTP implementation written in and for Rust.
+//!
+//! ## Features
+//!
+//! - HTTP/1 and HTTP/2
+//! - Asynchronous design
+//! - Leading in performance
+//! - Tested and **correct**
+//! - Extensive production use
+//! - [Client](client/index.html) and [Server](server/index.html) APIs
+//!
+//! If just starting out, **check out the [Guides](https://hyper.rs/guides)
+//! first.**
+//!
+//! ## "Low-level"
+//!
+//! hyper is a lower-level HTTP library, meant to be a building block
+//! for libraries and applications.
+//!
+//! If looking for just a convenient HTTP client, consider the
+//! [reqwest](https://crates.io/crates/reqwest) crate.
+//!
+//! # Optional Features
+//!
+//! hyper uses a set of [feature flags] to reduce the amount of compiled code.
+//! It is possible to just enable certain features over others. By default,
+//! hyper does not enable any features but allows one to enable a subset for
+//! their use case. Below is a list of the available feature flags. You may
+//! also notice above each function, struct and trait there is listed one or
+//! more feature flags that are required for that item to be used.
+//!
+//! If you are new to hyper it is possible to enable the `full` feature flag
+//! which will enable all public APIs. Beware though that this will pull in
+//! many extra dependencies that you may not need.
+//!
+//! The following optional features are available:
+//!
+//! - `http1`: Enables HTTP/1 support.
+//! - `http2`: Enables HTTP/2 support.
+//! - `client`: Enables the HTTP `client`.
+//! - `server`: Enables the HTTP `server`.
+//! - `runtime`: Enables convenient integration with `tokio`, providing
+//!   connectors and acceptors for TCP, and a default executor.
+//! - `tcp`: Enables convenient implementations over TCP (using tokio).
+//! - `stream`: Provides `futures::Stream` capabilities.
+//! - `backports`: 1.0 functionality backported to 0.14.
+//! - `deprecated`: opt-in to deprecation warnings to prepare you for 1.0.
+//!
+//! [feature flags]: https://doc.rust-lang.org/cargo/reference/manifest.html#the-features-section
+
+#[doc(hidden)]
+pub use http;
+
+#[cfg(all(test, feature = "nightly"))]
+extern crate test;
+
+pub use crate::http::{header, Method, Request, Response, StatusCode, Uri, Version};
+
+#[doc(no_inline)]
+pub use crate::http::HeaderMap;
+
+pub use crate::body::Body;
+pub use crate::error::{Error, Result};
+
+#[macro_use]
+mod cfg;
+#[macro_use]
+mod common;
+pub mod body;
+mod error;
+pub mod ext;
+#[cfg(test)]
+mod mock;
+pub mod rt;
+pub mod service;
+pub mod upgrade;
+
+#[cfg(feature = "ffi")]
+pub mod ffi;
+
+cfg_proto! {
+    mod headers;
+    mod proto;
+}
+
+cfg_feature! {
+    #![feature = "client"]
+
+    pub mod client;
+    #[cfg(any(feature = "http1", feature = "http2"))]
+    #[doc(no_inline)]
+    pub use crate::client::Client;
+}
+
+cfg_feature! {
+    #![feature = "server"]
+
+    pub mod server;
+    #[doc(no_inline)]
+    pub use crate::server::Server;
+}
diff --git a/src/mock.rs b/src/mock.rs
new file mode 100644
index 0000000..1dd57de
--- /dev/null
+++ b/src/mock.rs
@@ -0,0 +1,235 @@
+// FIXME: re-implement tests with `async/await`
+/*
+#[cfg(feature = "runtime")]
+use std::collections::HashMap;
+use std::cmp;
+use std::io::{self, Read, Write};
+#[cfg(feature = "runtime")]
+use std::sync::{Arc, Mutex};
+
+use bytes::Buf;
+use futures::{Async, Poll};
+#[cfg(feature = "runtime")]
+use futures::Future;
+use futures::task::{self, Task};
+use tokio_io::{AsyncRead, AsyncWrite};
+
+#[cfg(feature = "runtime")]
+use crate::client::connect::{Connect, Connected, Destination};
+
+
+
+#[cfg(feature = "runtime")]
+pub struct Duplex {
+    inner: Arc<Mutex<DuplexInner>>,
+}
+
+#[cfg(feature = "runtime")]
+struct DuplexInner {
+    handle_read_task: Option<Task>,
+    read: AsyncIo<MockCursor>,
+    write: AsyncIo<MockCursor>,
+}
+
+#[cfg(feature = "runtime")]
+impl Duplex {
+    pub(crate) fn channel() -> (Duplex, DuplexHandle) {
+        let mut inner = DuplexInner {
+            handle_read_task: None,
+            read: AsyncIo::new_buf(Vec::new(), 0),
+            write: AsyncIo::new_buf(Vec::new(), std::usize::MAX),
+        };
+
+        inner.read.park_tasks(true);
+        inner.write.park_tasks(true);
+
+        let inner = Arc::new(Mutex::new(inner));
+
+        let duplex = Duplex {
+            inner: inner.clone(),
+        };
+        let handle = DuplexHandle {
+            inner: inner,
+        };
+
+        (duplex, handle)
+    }
+}
+
+#[cfg(feature = "runtime")]
+impl Read for Duplex {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        self.inner.lock().unwrap().read.read(buf)
+    }
+}
+
+#[cfg(feature = "runtime")]
+impl Write for Duplex {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        let mut inner = self.inner.lock().unwrap();
+        let ret = inner.write.write(buf);
+        if let Some(task) = inner.handle_read_task.take() {
+            trace!("waking DuplexHandle read");
+            task.notify();
+        }
+        ret
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        self.inner.lock().unwrap().write.flush()
+    }
+}
+
+#[cfg(feature = "runtime")]
+impl AsyncRead for Duplex {
+}
+
+#[cfg(feature = "runtime")]
+impl AsyncWrite for Duplex {
+    fn shutdown(&mut self) -> Poll<(), io::Error> {
+        Ok(().into())
+    }
+
+    fn write_buf<B: Buf>(&mut self, buf: &mut B) -> Poll<usize, io::Error> {
+        let mut inner = self.inner.lock().unwrap();
+        if let Some(task) = inner.handle_read_task.take() {
+            task.notify();
+        }
+        inner.write.write_buf(buf)
+    }
+}
+
+#[cfg(feature = "runtime")]
+pub struct DuplexHandle {
+    inner: Arc<Mutex<DuplexInner>>,
+}
+
+#[cfg(feature = "runtime")]
+impl DuplexHandle {
+    pub fn read(&self, buf: &mut [u8]) -> Poll<usize, io::Error> {
+        let mut inner = self.inner.lock().unwrap();
+        assert!(buf.len() >= inner.write.inner.len());
+        if inner.write.inner.is_empty() {
+            trace!("DuplexHandle read parking");
+            inner.handle_read_task = Some(task::current());
+            return Ok(Async::NotReady);
+        }
+        inner.write.read(buf).map(Async::Ready)
+    }
+
+    pub fn write(&self, bytes: &[u8]) -> Poll<usize, io::Error> {
+        let mut inner = self.inner.lock().unwrap();
+        assert_eq!(inner.read.inner.pos, 0);
+        assert_eq!(inner.read.inner.vec.len(), 0, "write but read isn't empty");
+        inner
+            .read
+            .inner
+            .vec
+            .extend(bytes);
+        inner.read.block_in(bytes.len());
+        Ok(Async::Ready(bytes.len()))
+    }
+}
+
+#[cfg(feature = "runtime")]
+impl Drop for DuplexHandle {
+    fn drop(&mut self) {
+        trace!("mock duplex handle drop");
+        if !::std::thread::panicking() {
+            let mut inner = self.inner.lock().unwrap();
+            inner.read.close();
+            inner.write.close();
+        }
+    }
+}
+
+#[cfg(feature = "runtime")]
+type BoxedConnectFut = Box<dyn Future<Item=(Duplex, Connected), Error=io::Error> + Send>;
+
+#[cfg(feature = "runtime")]
+#[derive(Clone)]
+pub struct MockConnector {
+    mocks: Arc<Mutex<MockedConnections>>,
+}
+
+#[cfg(feature = "runtime")]
+struct MockedConnections(HashMap<String, Vec<BoxedConnectFut>>);
+
+#[cfg(feature = "runtime")]
+impl MockConnector {
+    pub fn new() -> MockConnector {
+        MockConnector {
+            mocks: Arc::new(Mutex::new(MockedConnections(HashMap::new()))),
+        }
+    }
+
+    pub fn mock(&mut self, key: &str) -> DuplexHandle {
+        use futures::future;
+        self.mock_fut(key, future::ok::<_, ()>(()))
+    }
+
+    pub fn mock_fut<F>(&mut self, key: &str, fut: F) -> DuplexHandle
+    where
+        F: Future + Send + 'static,
+    {
+        self.mock_opts(key, Connected::new(), fut)
+    }
+
+    pub fn mock_opts<F>(&mut self, key: &str, connected: Connected, fut: F) -> DuplexHandle
+    where
+        F: Future + Send + 'static,
+    {
+        let key = key.to_owned();
+
+        let (duplex, handle) = Duplex::channel();
+
+        let fut = Box::new(fut.then(move |_| {
+            trace!("MockConnector mocked fut ready");
+            Ok((duplex, connected))
+        }));
+        self.mocks.lock().unwrap().0.entry(key)
+            .or_insert(Vec::new())
+            .push(fut);
+
+        handle
+    }
+}
+
+#[cfg(feature = "runtime")]
+impl Connect for MockConnector {
+    type Transport = Duplex;
+    type Error = io::Error;
+    type Future = BoxedConnectFut;
+
+    fn connect(&self, dst: Destination) -> Self::Future {
+        trace!("mock connect: {:?}", dst);
+        let key = format!("{}://{}{}", dst.scheme(), dst.host(), if let Some(port) = dst.port() {
+            format!(":{}", port)
+        } else {
+            "".to_owned()
+        });
+        let mut mocks = self.mocks.lock().unwrap();
+        let mocks = mocks.0.get_mut(&key)
+            .expect(&format!("unknown mocks uri: {}", key));
+        assert!(!mocks.is_empty(), "no additional mocks for {}", key);
+        mocks.remove(0)
+    }
+}
+
+
+#[cfg(feature = "runtime")]
+impl Drop for MockedConnections {
+    fn drop(&mut self) {
+        if !::std::thread::panicking() {
+            for (key, mocks) in self.0.iter() {
+                assert_eq!(
+                    mocks.len(),
+                    0,
+                    "not all mocked connects for {:?} were used",
+                    key,
+                );
+            }
+        }
+    }
+}
+*/
diff --git a/src/proto/h1/conn.rs b/src/proto/h1/conn.rs
new file mode 100644
index 0000000..5ab72f2
--- /dev/null
+++ b/src/proto/h1/conn.rs
@@ -0,0 +1,1424 @@
+use std::fmt;
+use std::io;
+use std::marker::PhantomData;
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+#[cfg(all(feature = "server", feature = "runtime"))]
+use std::time::Duration;
+
+use bytes::{Buf, Bytes};
+use http::header::{HeaderValue, CONNECTION};
+use http::{HeaderMap, Method, Version};
+use httparse::ParserConfig;
+use tokio::io::{AsyncRead, AsyncWrite};
+#[cfg(all(feature = "server", feature = "runtime"))]
+use tokio::time::Sleep;
+use tracing::{debug, error, trace};
+
+use super::io::Buffered;
+use super::{Decoder, Encode, EncodedBuf, Encoder, Http1Transaction, ParseContext, Wants};
+use crate::body::DecodedLength;
+use crate::headers::connection_keep_alive;
+use crate::proto::{BodyLength, MessageHead};
+
+const H2_PREFACE: &[u8] = b"PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n";
+
+/// This handles a connection, which will have been established over an
+/// `AsyncRead + AsyncWrite` (like a socket), and will likely include multiple
+/// `Transaction`s over HTTP.
+///
+/// The connection will determine when a message begins and ends as well as
+/// determine if this connection can be kept alive after the message,
+/// or if it is complete.
+pub(crate) struct Conn<I, B, T> {
+    io: Buffered<I, EncodedBuf<B>>,
+    state: State,
+    _marker: PhantomData<fn(T)>,
+}
+
+impl<I, B, T> Conn<I, B, T>
+where
+    I: AsyncRead + AsyncWrite + Unpin,
+    B: Buf,
+    T: Http1Transaction,
+{
+    pub(crate) fn new(io: I) -> Conn<I, B, T> {
+        Conn {
+            io: Buffered::new(io),
+            state: State {
+                allow_half_close: false,
+                cached_headers: None,
+                error: None,
+                keep_alive: KA::Busy,
+                method: None,
+                h1_parser_config: ParserConfig::default(),
+                #[cfg(all(feature = "server", feature = "runtime"))]
+                h1_header_read_timeout: None,
+                #[cfg(all(feature = "server", feature = "runtime"))]
+                h1_header_read_timeout_fut: None,
+                #[cfg(all(feature = "server", feature = "runtime"))]
+                h1_header_read_timeout_running: false,
+                preserve_header_case: false,
+                #[cfg(feature = "ffi")]
+                preserve_header_order: false,
+                title_case_headers: false,
+                h09_responses: false,
+                #[cfg(feature = "ffi")]
+                on_informational: None,
+                #[cfg(feature = "ffi")]
+                raw_headers: false,
+                notify_read: false,
+                reading: Reading::Init,
+                writing: Writing::Init,
+                upgrade: None,
+                // We assume a modern world where the remote speaks HTTP/1.1.
+                // If they tell us otherwise, we'll downgrade in `read_head`.
+                version: Version::HTTP_11,
+            },
+            _marker: PhantomData,
+        }
+    }
+
+    #[cfg(feature = "server")]
+    pub(crate) fn set_flush_pipeline(&mut self, enabled: bool) {
+        self.io.set_flush_pipeline(enabled);
+    }
+
+    pub(crate) fn set_write_strategy_queue(&mut self) {
+        self.io.set_write_strategy_queue();
+    }
+
+    pub(crate) fn set_max_buf_size(&mut self, max: usize) {
+        self.io.set_max_buf_size(max);
+    }
+
+    #[cfg(feature = "client")]
+    pub(crate) fn set_read_buf_exact_size(&mut self, sz: usize) {
+        self.io.set_read_buf_exact_size(sz);
+    }
+
+    pub(crate) fn set_write_strategy_flatten(&mut self) {
+        self.io.set_write_strategy_flatten();
+    }
+
+    #[cfg(feature = "client")]
+    pub(crate) fn set_h1_parser_config(&mut self, parser_config: ParserConfig) {
+        self.state.h1_parser_config = parser_config;
+    }
+
+    pub(crate) fn set_title_case_headers(&mut self) {
+        self.state.title_case_headers = true;
+    }
+
+    pub(crate) fn set_preserve_header_case(&mut self) {
+        self.state.preserve_header_case = true;
+    }
+
+    #[cfg(feature = "ffi")]
+    pub(crate) fn set_preserve_header_order(&mut self) {
+        self.state.preserve_header_order = true;
+    }
+
+    #[cfg(feature = "client")]
+    pub(crate) fn set_h09_responses(&mut self) {
+        self.state.h09_responses = true;
+    }
+
+    #[cfg(all(feature = "server", feature = "runtime"))]
+    pub(crate) fn set_http1_header_read_timeout(&mut self, val: Duration) {
+        self.state.h1_header_read_timeout = Some(val);
+    }
+
+    #[cfg(feature = "server")]
+    pub(crate) fn set_allow_half_close(&mut self) {
+        self.state.allow_half_close = true;
+    }
+
+    #[cfg(feature = "ffi")]
+    pub(crate) fn set_raw_headers(&mut self, enabled: bool) {
+        self.state.raw_headers = enabled;
+    }
+
+    pub(crate) fn into_inner(self) -> (I, Bytes) {
+        self.io.into_inner()
+    }
+
+    pub(crate) fn pending_upgrade(&mut self) -> Option<crate::upgrade::Pending> {
+        self.state.upgrade.take()
+    }
+
+    pub(crate) fn is_read_closed(&self) -> bool {
+        self.state.is_read_closed()
+    }
+
+    pub(crate) fn is_write_closed(&self) -> bool {
+        self.state.is_write_closed()
+    }
+
+    pub(crate) fn can_read_head(&self) -> bool {
+        if !matches!(self.state.reading, Reading::Init) {
+            return false;
+        }
+
+        if T::should_read_first() {
+            return true;
+        }
+
+        !matches!(self.state.writing, Writing::Init)
+    }
+
+    pub(crate) fn can_read_body(&self) -> bool {
+        match self.state.reading {
+            Reading::Body(..) | Reading::Continue(..) => true,
+            _ => false,
+        }
+    }
+
+    fn should_error_on_eof(&self) -> bool {
+        // If we're idle, it's probably just the connection closing gracefully.
+        T::should_error_on_parse_eof() && !self.state.is_idle()
+    }
+
+    fn has_h2_prefix(&self) -> bool {
+        let read_buf = self.io.read_buf();
+        read_buf.len() >= 24 && read_buf[..24] == *H2_PREFACE
+    }
+
+    pub(super) fn poll_read_head(
+        &mut self,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<crate::Result<(MessageHead<T::Incoming>, DecodedLength, Wants)>>> {
+        debug_assert!(self.can_read_head());
+        trace!("Conn::read_head");
+
+        let msg = match ready!(self.io.parse::<T>(
+            cx,
+            ParseContext {
+                cached_headers: &mut self.state.cached_headers,
+                req_method: &mut self.state.method,
+                h1_parser_config: self.state.h1_parser_config.clone(),
+                #[cfg(all(feature = "server", feature = "runtime"))]
+                h1_header_read_timeout: self.state.h1_header_read_timeout,
+                #[cfg(all(feature = "server", feature = "runtime"))]
+                h1_header_read_timeout_fut: &mut self.state.h1_header_read_timeout_fut,
+                #[cfg(all(feature = "server", feature = "runtime"))]
+                h1_header_read_timeout_running: &mut self.state.h1_header_read_timeout_running,
+                preserve_header_case: self.state.preserve_header_case,
+                #[cfg(feature = "ffi")]
+                preserve_header_order: self.state.preserve_header_order,
+                h09_responses: self.state.h09_responses,
+                #[cfg(feature = "ffi")]
+                on_informational: &mut self.state.on_informational,
+                #[cfg(feature = "ffi")]
+                raw_headers: self.state.raw_headers,
+            }
+        )) {
+            Ok(msg) => msg,
+            Err(e) => return self.on_read_head_error(e),
+        };
+
+        // Note: don't deconstruct `msg` into local variables, it appears
+        // the optimizer doesn't remove the extra copies.
+
+        debug!("incoming body is {}", msg.decode);
+
+        // Prevent accepting HTTP/0.9 responses after the initial one, if any.
+        self.state.h09_responses = false;
+
+        // Drop any OnInformational callbacks, we're done there!
+        #[cfg(feature = "ffi")]
+        {
+            self.state.on_informational = None;
+        }
+
+        self.state.busy();
+        self.state.keep_alive &= msg.keep_alive;
+        self.state.version = msg.head.version;
+
+        let mut wants = if msg.wants_upgrade {
+            Wants::UPGRADE
+        } else {
+            Wants::EMPTY
+        };
+
+        if msg.decode == DecodedLength::ZERO {
+            if msg.expect_continue {
+                debug!("ignoring expect-continue since body is empty");
+            }
+            self.state.reading = Reading::KeepAlive;
+            if !T::should_read_first() {
+                self.try_keep_alive(cx);
+            }
+        } else if msg.expect_continue {
+            self.state.reading = Reading::Continue(Decoder::new(msg.decode));
+            wants = wants.add(Wants::EXPECT);
+        } else {
+            self.state.reading = Reading::Body(Decoder::new(msg.decode));
+        }
+
+        Poll::Ready(Some(Ok((msg.head, msg.decode, wants))))
+    }
+
+    fn on_read_head_error<Z>(&mut self, e: crate::Error) -> Poll<Option<crate::Result<Z>>> {
+        // If we are currently waiting on a message, then an empty
+        // message should be reported as an error. If not, it is just
+        // the connection closing gracefully.
+        let must_error = self.should_error_on_eof();
+        self.close_read();
+        self.io.consume_leading_lines();
+        let was_mid_parse = e.is_parse() || !self.io.read_buf().is_empty();
+        if was_mid_parse || must_error {
+            // We check if the buf contains the h2 Preface
+            debug!(
+                "parse error ({}) with {} bytes",
+                e,
+                self.io.read_buf().len()
+            );
+            match self.on_parse_error(e) {
+                Ok(()) => Poll::Pending, // XXX: wat?
+                Err(e) => Poll::Ready(Some(Err(e))),
+            }
+        } else {
+            debug!("read eof");
+            self.close_write();
+            Poll::Ready(None)
+        }
+    }
+
+    pub(crate) fn poll_read_body(
+        &mut self,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<io::Result<Bytes>>> {
+        debug_assert!(self.can_read_body());
+
+        let (reading, ret) = match self.state.reading {
+            Reading::Body(ref mut decoder) => {
+                match ready!(decoder.decode(cx, &mut self.io)) {
+                    Ok(slice) => {
+                        let (reading, chunk) = if decoder.is_eof() {
+                            debug!("incoming body completed");
+                            (
+                                Reading::KeepAlive,
+                                if !slice.is_empty() {
+                                    Some(Ok(slice))
+                                } else {
+                                    None
+                                },
+                            )
+                        } else if slice.is_empty() {
+                            error!("incoming body unexpectedly ended");
+                            // This should be unreachable, since all 3 decoders
+                            // either set eof=true or return an Err when reading
+                            // an empty slice...
+                            (Reading::Closed, None)
+                        } else {
+                            return Poll::Ready(Some(Ok(slice)));
+                        };
+                        (reading, Poll::Ready(chunk))
+                    }
+                    Err(e) => {
+                        debug!("incoming body decode error: {}", e);
+                        (Reading::Closed, Poll::Ready(Some(Err(e))))
+                    }
+                }
+            }
+            Reading::Continue(ref decoder) => {
+                // Write the 100 Continue if not already responded...
+                if let Writing::Init = self.state.writing {
+                    trace!("automatically sending 100 Continue");
+                    let cont = b"HTTP/1.1 100 Continue\r\n\r\n";
+                    self.io.headers_buf().extend_from_slice(cont);
+                }
+
+                // And now recurse once in the Reading::Body state...
+                self.state.reading = Reading::Body(decoder.clone());
+                return self.poll_read_body(cx);
+            }
+            _ => unreachable!("poll_read_body invalid state: {:?}", self.state.reading),
+        };
+
+        self.state.reading = reading;
+        self.try_keep_alive(cx);
+        ret
+    }
+
+    pub(crate) fn wants_read_again(&mut self) -> bool {
+        let ret = self.state.notify_read;
+        self.state.notify_read = false;
+        ret
+    }
+
+    pub(crate) fn poll_read_keep_alive(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        debug_assert!(!self.can_read_head() && !self.can_read_body());
+
+        if self.is_read_closed() {
+            Poll::Pending
+        } else if self.is_mid_message() {
+            self.mid_message_detect_eof(cx)
+        } else {
+            self.require_empty_read(cx)
+        }
+    }
+
+    fn is_mid_message(&self) -> bool {
+        !matches!(
+            (&self.state.reading, &self.state.writing),
+            (&Reading::Init, &Writing::Init)
+        )
+    }
+
+    // This will check to make sure the io object read is empty.
+    //
+    // This should only be called for Clients wanting to enter the idle
+    // state.
+    fn require_empty_read(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        debug_assert!(!self.can_read_head() && !self.can_read_body() && !self.is_read_closed());
+        debug_assert!(!self.is_mid_message());
+        debug_assert!(T::is_client());
+
+        if !self.io.read_buf().is_empty() {
+            debug!("received an unexpected {} bytes", self.io.read_buf().len());
+            return Poll::Ready(Err(crate::Error::new_unexpected_message()));
+        }
+
+        let num_read = ready!(self.force_io_read(cx)).map_err(crate::Error::new_io)?;
+
+        if num_read == 0 {
+            let ret = if self.should_error_on_eof() {
+                trace!("found unexpected EOF on busy connection: {:?}", self.state);
+                Poll::Ready(Err(crate::Error::new_incomplete()))
+            } else {
+                trace!("found EOF on idle connection, closing");
+                Poll::Ready(Ok(()))
+            };
+
+            // order is important: should_error needs state BEFORE close_read
+            self.state.close_read();
+            return ret;
+        }
+
+        debug!(
+            "received unexpected {} bytes on an idle connection",
+            num_read
+        );
+        Poll::Ready(Err(crate::Error::new_unexpected_message()))
+    }
+
+    fn mid_message_detect_eof(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        debug_assert!(!self.can_read_head() && !self.can_read_body() && !self.is_read_closed());
+        debug_assert!(self.is_mid_message());
+
+        if self.state.allow_half_close || !self.io.read_buf().is_empty() {
+            return Poll::Pending;
+        }
+
+        let num_read = ready!(self.force_io_read(cx)).map_err(crate::Error::new_io)?;
+
+        if num_read == 0 {
+            trace!("found unexpected EOF on busy connection: {:?}", self.state);
+            self.state.close_read();
+            Poll::Ready(Err(crate::Error::new_incomplete()))
+        } else {
+            Poll::Ready(Ok(()))
+        }
+    }
+
+    fn force_io_read(&mut self, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
+        debug_assert!(!self.state.is_read_closed());
+
+        let result = ready!(self.io.poll_read_from_io(cx));
+        Poll::Ready(result.map_err(|e| {
+            trace!("force_io_read; io error = {:?}", e);
+            self.state.close();
+            e
+        }))
+    }
+
+    fn maybe_notify(&mut self, cx: &mut Context<'_>) {
+        // its possible that we returned NotReady from poll() without having
+        // exhausted the underlying Io. We would have done this when we
+        // determined we couldn't keep reading until we knew how writing
+        // would finish.
+
+        match self.state.reading {
+            Reading::Continue(..) | Reading::Body(..) | Reading::KeepAlive | Reading::Closed => {
+                return
+            }
+            Reading::Init => (),
+        };
+
+        match self.state.writing {
+            Writing::Body(..) => return,
+            Writing::Init | Writing::KeepAlive | Writing::Closed => (),
+        }
+
+        if !self.io.is_read_blocked() {
+            if self.io.read_buf().is_empty() {
+                match self.io.poll_read_from_io(cx) {
+                    Poll::Ready(Ok(n)) => {
+                        if n == 0 {
+                            trace!("maybe_notify; read eof");
+                            if self.state.is_idle() {
+                                self.state.close();
+                            } else {
+                                self.close_read()
+                            }
+                            return;
+                        }
+                    }
+                    Poll::Pending => {
+                        trace!("maybe_notify; read_from_io blocked");
+                        return;
+                    }
+                    Poll::Ready(Err(e)) => {
+                        trace!("maybe_notify; read_from_io error: {}", e);
+                        self.state.close();
+                        self.state.error = Some(crate::Error::new_io(e));
+                    }
+                }
+            }
+            self.state.notify_read = true;
+        }
+    }
+
+    fn try_keep_alive(&mut self, cx: &mut Context<'_>) {
+        self.state.try_keep_alive::<T>();
+        self.maybe_notify(cx);
+    }
+
+    pub(crate) fn can_write_head(&self) -> bool {
+        if !T::should_read_first() && matches!(self.state.reading, Reading::Closed) {
+            return false;
+        }
+
+        match self.state.writing {
+            Writing::Init => self.io.can_headers_buf(),
+            _ => false,
+        }
+    }
+
+    pub(crate) fn can_write_body(&self) -> bool {
+        match self.state.writing {
+            Writing::Body(..) => true,
+            Writing::Init | Writing::KeepAlive | Writing::Closed => false,
+        }
+    }
+
+    pub(crate) fn can_buffer_body(&self) -> bool {
+        self.io.can_buffer()
+    }
+
+    pub(crate) fn write_head(&mut self, head: MessageHead<T::Outgoing>, body: Option<BodyLength>) {
+        if let Some(encoder) = self.encode_head(head, body) {
+            self.state.writing = if !encoder.is_eof() {
+                Writing::Body(encoder)
+            } else if encoder.is_last() {
+                Writing::Closed
+            } else {
+                Writing::KeepAlive
+            };
+        }
+    }
+
+    pub(crate) fn write_full_msg(&mut self, head: MessageHead<T::Outgoing>, body: B) {
+        if let Some(encoder) =
+            self.encode_head(head, Some(BodyLength::Known(body.remaining() as u64)))
+        {
+            let is_last = encoder.is_last();
+            // Make sure we don't write a body if we weren't actually allowed
+            // to do so, like because its a HEAD request.
+            if !encoder.is_eof() {
+                encoder.danger_full_buf(body, self.io.write_buf());
+            }
+            self.state.writing = if is_last {
+                Writing::Closed
+            } else {
+                Writing::KeepAlive
+            }
+        }
+    }
+
+    fn encode_head(
+        &mut self,
+        mut head: MessageHead<T::Outgoing>,
+        body: Option<BodyLength>,
+    ) -> Option<Encoder> {
+        debug_assert!(self.can_write_head());
+
+        if !T::should_read_first() {
+            self.state.busy();
+        }
+
+        self.enforce_version(&mut head);
+
+        let buf = self.io.headers_buf();
+        match super::role::encode_headers::<T>(
+            Encode {
+                head: &mut head,
+                body,
+                #[cfg(feature = "server")]
+                keep_alive: self.state.wants_keep_alive(),
+                req_method: &mut self.state.method,
+                title_case_headers: self.state.title_case_headers,
+            },
+            buf,
+        ) {
+            Ok(encoder) => {
+                debug_assert!(self.state.cached_headers.is_none());
+                debug_assert!(head.headers.is_empty());
+                self.state.cached_headers = Some(head.headers);
+
+                #[cfg(feature = "ffi")]
+                {
+                    self.state.on_informational =
+                        head.extensions.remove::<crate::ffi::OnInformational>();
+                }
+
+                Some(encoder)
+            }
+            Err(err) => {
+                self.state.error = Some(err);
+                self.state.writing = Writing::Closed;
+                None
+            }
+        }
+    }
+
+    // Fix keep-alive when Connection: keep-alive header is not present
+    fn fix_keep_alive(&mut self, head: &mut MessageHead<T::Outgoing>) {
+        let outgoing_is_keep_alive = head
+            .headers
+            .get(CONNECTION)
+            .map(connection_keep_alive)
+            .unwrap_or(false);
+
+        if !outgoing_is_keep_alive {
+            match head.version {
+                // If response is version 1.0 and keep-alive is not present in the response,
+                // disable keep-alive so the server closes the connection
+                Version::HTTP_10 => self.state.disable_keep_alive(),
+                // If response is version 1.1 and keep-alive is wanted, add
+                // Connection: keep-alive header when not present
+                Version::HTTP_11 => {
+                    if self.state.wants_keep_alive() {
+                        head.headers
+                            .insert(CONNECTION, HeaderValue::from_static("keep-alive"));
+                    }
+                }
+                _ => (),
+            }
+        }
+    }
+
+    // If we know the remote speaks an older version, we try to fix up any messages
+    // to work with our older peer.
+    fn enforce_version(&mut self, head: &mut MessageHead<T::Outgoing>) {
+        if let Version::HTTP_10 = self.state.version {
+            // Fixes response or connection when keep-alive header is not present
+            self.fix_keep_alive(head);
+            // If the remote only knows HTTP/1.0, we should force ourselves
+            // to do only speak HTTP/1.0 as well.
+            head.version = Version::HTTP_10;
+        }
+        // If the remote speaks HTTP/1.1, then it *should* be fine with
+        // both HTTP/1.0 and HTTP/1.1 from us. So again, we just let
+        // the user's headers be.
+    }
+
+    pub(crate) fn write_body(&mut self, chunk: B) {
+        debug_assert!(self.can_write_body() && self.can_buffer_body());
+        // empty chunks should be discarded at Dispatcher level
+        debug_assert!(chunk.remaining() != 0);
+
+        let state = match self.state.writing {
+            Writing::Body(ref mut encoder) => {
+                self.io.buffer(encoder.encode(chunk));
+
+                if !encoder.is_eof() {
+                    return;
+                }
+
+                if encoder.is_last() {
+                    Writing::Closed
+                } else {
+                    Writing::KeepAlive
+                }
+            }
+            _ => unreachable!("write_body invalid state: {:?}", self.state.writing),
+        };
+
+        self.state.writing = state;
+    }
+
+    pub(crate) fn write_body_and_end(&mut self, chunk: B) {
+        debug_assert!(self.can_write_body() && self.can_buffer_body());
+        // empty chunks should be discarded at Dispatcher level
+        debug_assert!(chunk.remaining() != 0);
+
+        let state = match self.state.writing {
+            Writing::Body(ref encoder) => {
+                let can_keep_alive = encoder.encode_and_end(chunk, self.io.write_buf());
+                if can_keep_alive {
+                    Writing::KeepAlive
+                } else {
+                    Writing::Closed
+                }
+            }
+            _ => unreachable!("write_body invalid state: {:?}", self.state.writing),
+        };
+
+        self.state.writing = state;
+    }
+
+    pub(crate) fn end_body(&mut self) -> crate::Result<()> {
+        debug_assert!(self.can_write_body());
+
+        let encoder = match self.state.writing {
+            Writing::Body(ref mut enc) => enc,
+            _ => return Ok(()),
+        };
+
+        // end of stream, that means we should try to eof
+        match encoder.end() {
+            Ok(end) => {
+                if let Some(end) = end {
+                    self.io.buffer(end);
+                }
+
+                self.state.writing = if encoder.is_last() || encoder.is_close_delimited() {
+                    Writing::Closed
+                } else {
+                    Writing::KeepAlive
+                };
+
+                Ok(())
+            }
+            Err(not_eof) => {
+                self.state.writing = Writing::Closed;
+                Err(crate::Error::new_body_write_aborted().with(not_eof))
+            }
+        }
+    }
+
+    // When we get a parse error, depending on what side we are, we might be able
+    // to write a response before closing the connection.
+    //
+    // - Client: there is nothing we can do
+    // - Server: if Response hasn't been written yet, we can send a 4xx response
+    fn on_parse_error(&mut self, err: crate::Error) -> crate::Result<()> {
+        if let Writing::Init = self.state.writing {
+            if self.has_h2_prefix() {
+                return Err(crate::Error::new_version_h2());
+            }
+            if let Some(msg) = T::on_error(&err) {
+                // Drop the cached headers so as to not trigger a debug
+                // assert in `write_head`...
+                self.state.cached_headers.take();
+                self.write_head(msg, None);
+                self.state.error = Some(err);
+                return Ok(());
+            }
+        }
+
+        // fallback is pass the error back up
+        Err(err)
+    }
+
+    pub(crate) fn poll_flush(&mut self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        ready!(Pin::new(&mut self.io).poll_flush(cx))?;
+        self.try_keep_alive(cx);
+        trace!("flushed({}): {:?}", T::LOG, self.state);
+        Poll::Ready(Ok(()))
+    }
+
+    pub(crate) fn poll_shutdown(&mut self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        match ready!(Pin::new(self.io.io_mut()).poll_shutdown(cx)) {
+            Ok(()) => {
+                trace!("shut down IO complete");
+                Poll::Ready(Ok(()))
+            }
+            Err(e) => {
+                debug!("error shutting down IO: {}", e);
+                Poll::Ready(Err(e))
+            }
+        }
+    }
+
+    /// If the read side can be cheaply drained, do so. Otherwise, close.
+    pub(super) fn poll_drain_or_close_read(&mut self, cx: &mut Context<'_>) {
+        if let Reading::Continue(ref decoder) = self.state.reading {
+            // skip sending the 100-continue
+            // just move forward to a read, in case a tiny body was included
+            self.state.reading = Reading::Body(decoder.clone());
+        }
+
+        let _ = self.poll_read_body(cx);
+
+        // If still in Reading::Body, just give up
+        match self.state.reading {
+            Reading::Init | Reading::KeepAlive => trace!("body drained"),
+            _ => self.close_read(),
+        }
+    }
+
+    pub(crate) fn close_read(&mut self) {
+        self.state.close_read();
+    }
+
+    pub(crate) fn close_write(&mut self) {
+        self.state.close_write();
+    }
+
+    #[cfg(feature = "server")]
+    pub(crate) fn disable_keep_alive(&mut self) {
+        if self.state.is_idle() {
+            trace!("disable_keep_alive; closing idle connection");
+            self.state.close();
+        } else {
+            trace!("disable_keep_alive; in-progress connection");
+            self.state.disable_keep_alive();
+        }
+    }
+
+    pub(crate) fn take_error(&mut self) -> crate::Result<()> {
+        if let Some(err) = self.state.error.take() {
+            Err(err)
+        } else {
+            Ok(())
+        }
+    }
+
+    pub(super) fn on_upgrade(&mut self) -> crate::upgrade::OnUpgrade {
+        trace!("{}: prepare possible HTTP upgrade", T::LOG);
+        self.state.prepare_upgrade()
+    }
+}
+
+impl<I, B: Buf, T> fmt::Debug for Conn<I, B, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Conn")
+            .field("state", &self.state)
+            .field("io", &self.io)
+            .finish()
+    }
+}
+
+// B and T are never pinned
+impl<I: Unpin, B, T> Unpin for Conn<I, B, T> {}
+
+struct State {
+    allow_half_close: bool,
+    /// Re-usable HeaderMap to reduce allocating new ones.
+    cached_headers: Option<HeaderMap>,
+    /// If an error occurs when there wasn't a direct way to return it
+    /// back to the user, this is set.
+    error: Option<crate::Error>,
+    /// Current keep-alive status.
+    keep_alive: KA,
+    /// If mid-message, the HTTP Method that started it.
+    ///
+    /// This is used to know things such as if the message can include
+    /// a body or not.
+    method: Option<Method>,
+    h1_parser_config: ParserConfig,
+    #[cfg(all(feature = "server", feature = "runtime"))]
+    h1_header_read_timeout: Option<Duration>,
+    #[cfg(all(feature = "server", feature = "runtime"))]
+    h1_header_read_timeout_fut: Option<Pin<Box<Sleep>>>,
+    #[cfg(all(feature = "server", feature = "runtime"))]
+    h1_header_read_timeout_running: bool,
+    preserve_header_case: bool,
+    #[cfg(feature = "ffi")]
+    preserve_header_order: bool,
+    title_case_headers: bool,
+    h09_responses: bool,
+    /// If set, called with each 1xx informational response received for
+    /// the current request. MUST be unset after a non-1xx response is
+    /// received.
+    #[cfg(feature = "ffi")]
+    on_informational: Option<crate::ffi::OnInformational>,
+    #[cfg(feature = "ffi")]
+    raw_headers: bool,
+    /// Set to true when the Dispatcher should poll read operations
+    /// again. See the `maybe_notify` method for more.
+    notify_read: bool,
+    /// State of allowed reads
+    reading: Reading,
+    /// State of allowed writes
+    writing: Writing,
+    /// An expected pending HTTP upgrade.
+    upgrade: Option<crate::upgrade::Pending>,
+    /// Either HTTP/1.0 or 1.1 connection
+    version: Version,
+}
+
+#[derive(Debug)]
+enum Reading {
+    Init,
+    Continue(Decoder),
+    Body(Decoder),
+    KeepAlive,
+    Closed,
+}
+
+enum Writing {
+    Init,
+    Body(Encoder),
+    KeepAlive,
+    Closed,
+}
+
+impl fmt::Debug for State {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut builder = f.debug_struct("State");
+        builder
+            .field("reading", &self.reading)
+            .field("writing", &self.writing)
+            .field("keep_alive", &self.keep_alive);
+
+        // Only show error field if it's interesting...
+        if let Some(ref error) = self.error {
+            builder.field("error", error);
+        }
+
+        if self.allow_half_close {
+            builder.field("allow_half_close", &true);
+        }
+
+        // Purposefully leaving off other fields..
+
+        builder.finish()
+    }
+}
+
+impl fmt::Debug for Writing {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            Writing::Init => f.write_str("Init"),
+            Writing::Body(ref enc) => f.debug_tuple("Body").field(enc).finish(),
+            Writing::KeepAlive => f.write_str("KeepAlive"),
+            Writing::Closed => f.write_str("Closed"),
+        }
+    }
+}
+
+impl std::ops::BitAndAssign<bool> for KA {
+    fn bitand_assign(&mut self, enabled: bool) {
+        if !enabled {
+            trace!("remote disabling keep-alive");
+            *self = KA::Disabled;
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+enum KA {
+    Idle,
+    Busy,
+    Disabled,
+}
+
+impl Default for KA {
+    fn default() -> KA {
+        KA::Busy
+    }
+}
+
+impl KA {
+    fn idle(&mut self) {
+        *self = KA::Idle;
+    }
+
+    fn busy(&mut self) {
+        *self = KA::Busy;
+    }
+
+    fn disable(&mut self) {
+        *self = KA::Disabled;
+    }
+
+    fn status(&self) -> KA {
+        *self
+    }
+}
+
+impl State {
+    fn close(&mut self) {
+        trace!("State::close()");
+        self.reading = Reading::Closed;
+        self.writing = Writing::Closed;
+        self.keep_alive.disable();
+    }
+
+    fn close_read(&mut self) {
+        trace!("State::close_read()");
+        self.reading = Reading::Closed;
+        self.keep_alive.disable();
+    }
+
+    fn close_write(&mut self) {
+        trace!("State::close_write()");
+        self.writing = Writing::Closed;
+        self.keep_alive.disable();
+    }
+
+    fn wants_keep_alive(&self) -> bool {
+        if let KA::Disabled = self.keep_alive.status() {
+            false
+        } else {
+            true
+        }
+    }
+
+    fn try_keep_alive<T: Http1Transaction>(&mut self) {
+        match (&self.reading, &self.writing) {
+            (&Reading::KeepAlive, &Writing::KeepAlive) => {
+                if let KA::Busy = self.keep_alive.status() {
+                    self.idle::<T>();
+                } else {
+                    trace!(
+                        "try_keep_alive({}): could keep-alive, but status = {:?}",
+                        T::LOG,
+                        self.keep_alive
+                    );
+                    self.close();
+                }
+            }
+            (&Reading::Closed, &Writing::KeepAlive) | (&Reading::KeepAlive, &Writing::Closed) => {
+                self.close()
+            }
+            _ => (),
+        }
+    }
+
+    fn disable_keep_alive(&mut self) {
+        self.keep_alive.disable()
+    }
+
+    fn busy(&mut self) {
+        if let KA::Disabled = self.keep_alive.status() {
+            return;
+        }
+        self.keep_alive.busy();
+    }
+
+    fn idle<T: Http1Transaction>(&mut self) {
+        debug_assert!(!self.is_idle(), "State::idle() called while idle");
+
+        self.method = None;
+        self.keep_alive.idle();
+
+        if !self.is_idle() {
+            self.close();
+            return;
+        }
+
+        self.reading = Reading::Init;
+        self.writing = Writing::Init;
+
+        // !T::should_read_first() means Client.
+        //
+        // If Client connection has just gone idle, the Dispatcher
+        // should try the poll loop one more time, so as to poll the
+        // pending requests stream.
+        if !T::should_read_first() {
+            self.notify_read = true;
+        }
+    }
+
+    fn is_idle(&self) -> bool {
+        matches!(self.keep_alive.status(), KA::Idle)
+    }
+
+    fn is_read_closed(&self) -> bool {
+        matches!(self.reading, Reading::Closed)
+    }
+
+    fn is_write_closed(&self) -> bool {
+        matches!(self.writing, Writing::Closed)
+    }
+
+    fn prepare_upgrade(&mut self) -> crate::upgrade::OnUpgrade {
+        let (tx, rx) = crate::upgrade::pending();
+        self.upgrade = Some(tx);
+        rx
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[cfg(feature = "nightly")]
+    #[bench]
+    fn bench_read_head_short(b: &mut ::test::Bencher) {
+        use super::*;
+        let s = b"GET / HTTP/1.1\r\nHost: localhost:8080\r\n\r\n";
+        let len = s.len();
+        b.bytes = len as u64;
+
+        // an empty IO, we'll be skipping and using the read buffer anyways
+        let io = tokio_test::io::Builder::new().build();
+        let mut conn = Conn::<_, bytes::Bytes, crate::proto::h1::ServerTransaction>::new(io);
+        *conn.io.read_buf_mut() = ::bytes::BytesMut::from(&s[..]);
+        conn.state.cached_headers = Some(HeaderMap::with_capacity(2));
+
+        let rt = tokio::runtime::Builder::new_current_thread()
+            .enable_all()
+            .build()
+            .unwrap();
+
+        b.iter(|| {
+            rt.block_on(futures_util::future::poll_fn(|cx| {
+                match conn.poll_read_head(cx) {
+                    Poll::Ready(Some(Ok(x))) => {
+                        ::test::black_box(&x);
+                        let mut headers = x.0.headers;
+                        headers.clear();
+                        conn.state.cached_headers = Some(headers);
+                    }
+                    f => panic!("expected Ready(Some(Ok(..))): {:?}", f),
+                }
+
+                conn.io.read_buf_mut().reserve(1);
+                unsafe {
+                    conn.io.read_buf_mut().set_len(len);
+                }
+                conn.state.reading = Reading::Init;
+                Poll::Ready(())
+            }));
+        });
+    }
+
+    /*
+    //TODO: rewrite these using dispatch... someday...
+    use futures::{Async, Future, Stream, Sink};
+    use futures::future;
+
+    use proto::{self, ClientTransaction, MessageHead, ServerTransaction};
+    use super::super::Encoder;
+    use mock::AsyncIo;
+
+    use super::{Conn, Decoder, Reading, Writing};
+    use ::uri::Uri;
+
+    use std::str::FromStr;
+
+    #[test]
+    fn test_conn_init_read() {
+        let good_message = b"GET / HTTP/1.1\r\n\r\n".to_vec();
+        let len = good_message.len();
+        let io = AsyncIo::new_buf(good_message, len);
+        let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+
+        match conn.poll().unwrap() {
+            Async::Ready(Some(Frame::Message { message, body: false })) => {
+                assert_eq!(message, MessageHead {
+                    subject: ::proto::RequestLine(::Get, Uri::from_str("/").unwrap()),
+                    .. MessageHead::default()
+                })
+            },
+            f => panic!("frame is not Frame::Message: {:?}", f)
+        }
+    }
+
+    #[test]
+    fn test_conn_parse_partial() {
+        let _: Result<(), ()> = future::lazy(|| {
+            let good_message = b"GET / HTTP/1.1\r\nHost: foo.bar\r\n\r\n".to_vec();
+            let io = AsyncIo::new_buf(good_message, 10);
+            let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+            assert!(conn.poll().unwrap().is_not_ready());
+            conn.io.io_mut().block_in(50);
+            let async = conn.poll().unwrap();
+            assert!(async.is_ready());
+            match async {
+                Async::Ready(Some(Frame::Message { .. })) => (),
+                f => panic!("frame is not Message: {:?}", f),
+            }
+            Ok(())
+        }).wait();
+    }
+
+    #[test]
+    fn test_conn_init_read_eof_idle() {
+        let io = AsyncIo::new_buf(vec![], 1);
+        let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+        conn.state.idle();
+
+        match conn.poll().unwrap() {
+            Async::Ready(None) => {},
+            other => panic!("frame is not None: {:?}", other)
+        }
+    }
+
+    #[test]
+    fn test_conn_init_read_eof_idle_partial_parse() {
+        let io = AsyncIo::new_buf(b"GET / HTTP/1.1".to_vec(), 100);
+        let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+        conn.state.idle();
+
+        match conn.poll() {
+            Err(ref err) if err.kind() == std::io::ErrorKind::UnexpectedEof => {},
+            other => panic!("unexpected frame: {:?}", other)
+        }
+    }
+
+    #[test]
+    fn test_conn_init_read_eof_busy() {
+        let _: Result<(), ()> = future::lazy(|| {
+            // server ignores
+            let io = AsyncIo::new_eof();
+            let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+            conn.state.busy();
+
+            match conn.poll().unwrap() {
+                Async::Ready(None) => {},
+                other => panic!("unexpected frame: {:?}", other)
+            }
+
+            // client
+            let io = AsyncIo::new_eof();
+            let mut conn = Conn::<_, proto::Bytes, ClientTransaction>::new(io);
+            conn.state.busy();
+
+            match conn.poll() {
+                Err(ref err) if err.kind() == std::io::ErrorKind::UnexpectedEof => {},
+                other => panic!("unexpected frame: {:?}", other)
+            }
+            Ok(())
+        }).wait();
+    }
+
+    #[test]
+    fn test_conn_body_finish_read_eof() {
+        let _: Result<(), ()> = future::lazy(|| {
+            let io = AsyncIo::new_eof();
+            let mut conn = Conn::<_, proto::Bytes, ClientTransaction>::new(io);
+            conn.state.busy();
+            conn.state.writing = Writing::KeepAlive;
+            conn.state.reading = Reading::Body(Decoder::length(0));
+
+            match conn.poll() {
+                Ok(Async::Ready(Some(Frame::Body { chunk: None }))) => (),
+                other => panic!("unexpected frame: {:?}", other)
+            }
+
+            // conn eofs, but tokio-proto will call poll() again, before calling flush()
+            // the conn eof in this case is perfectly fine
+
+            match conn.poll() {
+                Ok(Async::Ready(None)) => (),
+                other => panic!("unexpected frame: {:?}", other)
+            }
+            Ok(())
+        }).wait();
+    }
+
+    #[test]
+    fn test_conn_message_empty_body_read_eof() {
+        let _: Result<(), ()> = future::lazy(|| {
+            let io = AsyncIo::new_buf(b"HTTP/1.1 200 OK\r\nContent-Length: 0\r\n\r\n".to_vec(), 1024);
+            let mut conn = Conn::<_, proto::Bytes, ClientTransaction>::new(io);
+            conn.state.busy();
+            conn.state.writing = Writing::KeepAlive;
+
+            match conn.poll() {
+                Ok(Async::Ready(Some(Frame::Message { body: false, .. }))) => (),
+                other => panic!("unexpected frame: {:?}", other)
+            }
+
+            // conn eofs, but tokio-proto will call poll() again, before calling flush()
+            // the conn eof in this case is perfectly fine
+
+            match conn.poll() {
+                Ok(Async::Ready(None)) => (),
+                other => panic!("unexpected frame: {:?}", other)
+            }
+            Ok(())
+        }).wait();
+    }
+
+    #[test]
+    fn test_conn_read_body_end() {
+        let _: Result<(), ()> = future::lazy(|| {
+            let io = AsyncIo::new_buf(b"POST / HTTP/1.1\r\nContent-Length: 5\r\n\r\n12345".to_vec(), 1024);
+            let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+            conn.state.busy();
+
+            match conn.poll() {
+                Ok(Async::Ready(Some(Frame::Message { body: true, .. }))) => (),
+                other => panic!("unexpected frame: {:?}", other)
+            }
+
+            match conn.poll() {
+                Ok(Async::Ready(Some(Frame::Body { chunk: Some(_) }))) => (),
+                other => panic!("unexpected frame: {:?}", other)
+            }
+
+            // When the body is done, `poll` MUST return a `Body` frame with chunk set to `None`
+            match conn.poll() {
+                Ok(Async::Ready(Some(Frame::Body { chunk: None }))) => (),
+                other => panic!("unexpected frame: {:?}", other)
+            }
+
+            match conn.poll() {
+                Ok(Async::NotReady) => (),
+                other => panic!("unexpected frame: {:?}", other)
+            }
+            Ok(())
+        }).wait();
+    }
+
+    #[test]
+    fn test_conn_closed_read() {
+        let io = AsyncIo::new_buf(vec![], 0);
+        let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+        conn.state.close();
+
+        match conn.poll().unwrap() {
+            Async::Ready(None) => {},
+            other => panic!("frame is not None: {:?}", other)
+        }
+    }
+
+    #[test]
+    fn test_conn_body_write_length() {
+        let _ = pretty_env_logger::try_init();
+        let _: Result<(), ()> = future::lazy(|| {
+            let io = AsyncIo::new_buf(vec![], 0);
+            let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+            let max = super::super::io::DEFAULT_MAX_BUFFER_SIZE + 4096;
+            conn.state.writing = Writing::Body(Encoder::length((max * 2) as u64));
+
+            assert!(conn.start_send(Frame::Body { chunk: Some(vec![b'a'; max].into()) }).unwrap().is_ready());
+            assert!(!conn.can_buffer_body());
+
+            assert!(conn.start_send(Frame::Body { chunk: Some(vec![b'b'; 1024 * 8].into()) }).unwrap().is_not_ready());
+
+            conn.io.io_mut().block_in(1024 * 3);
+            assert!(conn.poll_complete().unwrap().is_not_ready());
+            conn.io.io_mut().block_in(1024 * 3);
+            assert!(conn.poll_complete().unwrap().is_not_ready());
+            conn.io.io_mut().block_in(max * 2);
+            assert!(conn.poll_complete().unwrap().is_ready());
+
+            assert!(conn.start_send(Frame::Body { chunk: Some(vec![b'c'; 1024 * 8].into()) }).unwrap().is_ready());
+            Ok(())
+        }).wait();
+    }
+
+    #[test]
+    fn test_conn_body_write_chunked() {
+        let _: Result<(), ()> = future::lazy(|| {
+            let io = AsyncIo::new_buf(vec![], 4096);
+            let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+            conn.state.writing = Writing::Body(Encoder::chunked());
+
+            assert!(conn.start_send(Frame::Body { chunk: Some("headers".into()) }).unwrap().is_ready());
+            assert!(conn.start_send(Frame::Body { chunk: Some(vec![b'x'; 8192].into()) }).unwrap().is_ready());
+            Ok(())
+        }).wait();
+    }
+
+    #[test]
+    fn test_conn_body_flush() {
+        let _: Result<(), ()> = future::lazy(|| {
+            let io = AsyncIo::new_buf(vec![], 1024 * 1024 * 5);
+            let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+            conn.state.writing = Writing::Body(Encoder::length(1024 * 1024));
+            assert!(conn.start_send(Frame::Body { chunk: Some(vec![b'a'; 1024 * 1024].into()) }).unwrap().is_ready());
+            assert!(!conn.can_buffer_body());
+            conn.io.io_mut().block_in(1024 * 1024 * 5);
+            assert!(conn.poll_complete().unwrap().is_ready());
+            assert!(conn.can_buffer_body());
+            assert!(conn.io.io_mut().flushed());
+
+            Ok(())
+        }).wait();
+    }
+
+    #[test]
+    fn test_conn_parking() {
+        use std::sync::Arc;
+        use futures::executor::Notify;
+        use futures::executor::NotifyHandle;
+
+        struct Car {
+            permit: bool,
+        }
+        impl Notify for Car {
+            fn notify(&self, _id: usize) {
+                assert!(self.permit, "unparked without permit");
+            }
+        }
+
+        fn car(permit: bool) -> NotifyHandle {
+            Arc::new(Car {
+                permit: permit,
+            }).into()
+        }
+
+        // test that once writing is done, unparks
+        let f = future::lazy(|| {
+            let io = AsyncIo::new_buf(vec![], 4096);
+            let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+            conn.state.reading = Reading::KeepAlive;
+            assert!(conn.poll().unwrap().is_not_ready());
+
+            conn.state.writing = Writing::KeepAlive;
+            assert!(conn.poll_complete().unwrap().is_ready());
+            Ok::<(), ()>(())
+        });
+        ::futures::executor::spawn(f).poll_future_notify(&car(true), 0).unwrap();
+
+
+        // test that flushing when not waiting on read doesn't unpark
+        let f = future::lazy(|| {
+            let io = AsyncIo::new_buf(vec![], 4096);
+            let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+            conn.state.writing = Writing::KeepAlive;
+            assert!(conn.poll_complete().unwrap().is_ready());
+            Ok::<(), ()>(())
+        });
+        ::futures::executor::spawn(f).poll_future_notify(&car(false), 0).unwrap();
+
+
+        // test that flushing and writing isn't done doesn't unpark
+        let f = future::lazy(|| {
+            let io = AsyncIo::new_buf(vec![], 4096);
+            let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+            conn.state.reading = Reading::KeepAlive;
+            assert!(conn.poll().unwrap().is_not_ready());
+            conn.state.writing = Writing::Body(Encoder::length(5_000));
+            assert!(conn.poll_complete().unwrap().is_ready());
+            Ok::<(), ()>(())
+        });
+        ::futures::executor::spawn(f).poll_future_notify(&car(false), 0).unwrap();
+    }
+
+    #[test]
+    fn test_conn_closed_write() {
+        let io = AsyncIo::new_buf(vec![], 0);
+        let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+        conn.state.close();
+
+        match conn.start_send(Frame::Body { chunk: Some(b"foobar".to_vec().into()) }) {
+            Err(_e) => {},
+            other => panic!("did not return Err: {:?}", other)
+        }
+
+        assert!(conn.state.is_write_closed());
+    }
+
+    #[test]
+    fn test_conn_write_empty_chunk() {
+        let io = AsyncIo::new_buf(vec![], 0);
+        let mut conn = Conn::<_, proto::Bytes, ServerTransaction>::new(io);
+        conn.state.writing = Writing::KeepAlive;
+
+        assert!(conn.start_send(Frame::Body { chunk: None }).unwrap().is_ready());
+        assert!(conn.start_send(Frame::Body { chunk: Some(Vec::new().into()) }).unwrap().is_ready());
+        conn.start_send(Frame::Body { chunk: Some(vec![b'a'].into()) }).unwrap_err();
+    }
+    */
+}
diff --git a/src/proto/h1/decode.rs b/src/proto/h1/decode.rs
new file mode 100644
index 0000000..6752d58
--- /dev/null
+++ b/src/proto/h1/decode.rs
@@ -0,0 +1,838 @@
+use std::error::Error as StdError;
+use std::fmt;
+use std::io;
+use std::task::{Context, Poll};
+use std::usize;
+
+use bytes::Bytes;
+use tracing::{debug, trace};
+
+use super::io::MemRead;
+use super::DecodedLength;
+
+use self::Kind::{Chunked, Eof, Length};
+
+/// Maximum amount of bytes allowed in chunked extensions.
+///
+/// This limit is currentlty applied for the entire body, not per chunk.
+const CHUNKED_EXTENSIONS_LIMIT: u64 = 1024 * 16;
+
+/// Decoders to handle different Transfer-Encodings.
+///
+/// If a message body does not include a Transfer-Encoding, it *should*
+/// include a Content-Length header.
+#[derive(Clone, PartialEq)]
+pub(crate) struct Decoder {
+    kind: Kind,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+enum Kind {
+    /// A Reader used when a Content-Length header is passed with a positive integer.
+    Length(u64),
+    /// A Reader used when Transfer-Encoding is `chunked`.
+    Chunked {
+        state: ChunkedState,
+        chunk_len: u64,
+        extensions_cnt: u64,
+    },
+    /// A Reader used for responses that don't indicate a length or chunked.
+    ///
+    /// The bool tracks when EOF is seen on the transport.
+    ///
+    /// Note: This should only used for `Response`s. It is illegal for a
+    /// `Request` to be made with both `Content-Length` and
+    /// `Transfer-Encoding: chunked` missing, as explained from the spec:
+    ///
+    /// > If a Transfer-Encoding header field is present in a response and
+    /// > the chunked transfer coding is not the final encoding, the
+    /// > message body length is determined by reading the connection until
+    /// > it is closed by the server.  If a Transfer-Encoding header field
+    /// > is present in a request and the chunked transfer coding is not
+    /// > the final encoding, the message body length cannot be determined
+    /// > reliably; the server MUST respond with the 400 (Bad Request)
+    /// > status code and then close the connection.
+    Eof(bool),
+}
+
+#[derive(Debug, PartialEq, Clone, Copy)]
+enum ChunkedState {
+    Start,
+    Size,
+    SizeLws,
+    Extension,
+    SizeLf,
+    Body,
+    BodyCr,
+    BodyLf,
+    Trailer,
+    TrailerLf,
+    EndCr,
+    EndLf,
+    End,
+}
+
+impl Decoder {
+    // constructors
+
+    pub(crate) fn length(x: u64) -> Decoder {
+        Decoder {
+            kind: Kind::Length(x),
+        }
+    }
+
+    pub(crate) fn chunked() -> Decoder {
+        Decoder {
+            kind: Kind::Chunked {
+                state: ChunkedState::new(),
+                chunk_len: 0,
+                extensions_cnt: 0,
+            },
+        }
+    }
+
+    pub(crate) fn eof() -> Decoder {
+        Decoder {
+            kind: Kind::Eof(false),
+        }
+    }
+
+    pub(super) fn new(len: DecodedLength) -> Self {
+        match len {
+            DecodedLength::CHUNKED => Decoder::chunked(),
+            DecodedLength::CLOSE_DELIMITED => Decoder::eof(),
+            length => Decoder::length(length.danger_len()),
+        }
+    }
+
+    // methods
+
+    pub(crate) fn is_eof(&self) -> bool {
+        matches!(
+            self.kind,
+            Length(0)
+                | Chunked {
+                    state: ChunkedState::End,
+                    ..
+                }
+                | Eof(true)
+        )
+    }
+
+    pub(crate) fn decode<R: MemRead>(
+        &mut self,
+        cx: &mut Context<'_>,
+        body: &mut R,
+    ) -> Poll<Result<Bytes, io::Error>> {
+        trace!("decode; state={:?}", self.kind);
+        match self.kind {
+            Length(ref mut remaining) => {
+                if *remaining == 0 {
+                    Poll::Ready(Ok(Bytes::new()))
+                } else {
+                    let to_read = *remaining as usize;
+                    let buf = ready!(body.read_mem(cx, to_read))?;
+                    let num = buf.as_ref().len() as u64;
+                    if num > *remaining {
+                        *remaining = 0;
+                    } else if num == 0 {
+                        return Poll::Ready(Err(io::Error::new(
+                            io::ErrorKind::UnexpectedEof,
+                            IncompleteBody,
+                        )));
+                    } else {
+                        *remaining -= num;
+                    }
+                    Poll::Ready(Ok(buf))
+                }
+            }
+            Chunked {
+                ref mut state,
+                ref mut chunk_len,
+                ref mut extensions_cnt,
+            } => {
+                loop {
+                    let mut buf = None;
+                    // advances the chunked state
+                    *state = ready!(state.step(cx, body, chunk_len, extensions_cnt, &mut buf))?;
+                    if *state == ChunkedState::End {
+                        trace!("end of chunked");
+                        return Poll::Ready(Ok(Bytes::new()));
+                    }
+                    if let Some(buf) = buf {
+                        return Poll::Ready(Ok(buf));
+                    }
+                }
+            }
+            Eof(ref mut is_eof) => {
+                if *is_eof {
+                    Poll::Ready(Ok(Bytes::new()))
+                } else {
+                    // 8192 chosen because its about 2 packets, there probably
+                    // won't be that much available, so don't have MemReaders
+                    // allocate buffers to big
+                    body.read_mem(cx, 8192).map_ok(|slice| {
+                        *is_eof = slice.is_empty();
+                        slice
+                    })
+                }
+            }
+        }
+    }
+
+    #[cfg(test)]
+    async fn decode_fut<R: MemRead>(&mut self, body: &mut R) -> Result<Bytes, io::Error> {
+        futures_util::future::poll_fn(move |cx| self.decode(cx, body)).await
+    }
+}
+
+impl fmt::Debug for Decoder {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&self.kind, f)
+    }
+}
+
+macro_rules! byte (
+    ($rdr:ident, $cx:expr) => ({
+        let buf = ready!($rdr.read_mem($cx, 1))?;
+        if !buf.is_empty() {
+            buf[0]
+        } else {
+            return Poll::Ready(Err(io::Error::new(io::ErrorKind::UnexpectedEof,
+                                      "unexpected EOF during chunk size line")));
+        }
+    })
+);
+
+macro_rules! or_overflow {
+    ($e:expr) => (
+        match $e {
+            Some(val) => val,
+            None => return Poll::Ready(Err(io::Error::new(
+                io::ErrorKind::InvalidData,
+                "invalid chunk size: overflow",
+            ))),
+        }
+    )
+}
+
+impl ChunkedState {
+    fn new() -> ChunkedState {
+        ChunkedState::Start
+    }
+    fn step<R: MemRead>(
+        &self,
+        cx: &mut Context<'_>,
+        body: &mut R,
+        size: &mut u64,
+        extensions_cnt: &mut u64,
+        buf: &mut Option<Bytes>,
+    ) -> Poll<Result<ChunkedState, io::Error>> {
+        use self::ChunkedState::*;
+        match *self {
+            Start => ChunkedState::read_start(cx, body, size),
+            Size => ChunkedState::read_size(cx, body, size),
+            SizeLws => ChunkedState::read_size_lws(cx, body),
+            Extension => ChunkedState::read_extension(cx, body, extensions_cnt),
+            SizeLf => ChunkedState::read_size_lf(cx, body, *size),
+            Body => ChunkedState::read_body(cx, body, size, buf),
+            BodyCr => ChunkedState::read_body_cr(cx, body),
+            BodyLf => ChunkedState::read_body_lf(cx, body),
+            Trailer => ChunkedState::read_trailer(cx, body),
+            TrailerLf => ChunkedState::read_trailer_lf(cx, body),
+            EndCr => ChunkedState::read_end_cr(cx, body),
+            EndLf => ChunkedState::read_end_lf(cx, body),
+            End => Poll::Ready(Ok(ChunkedState::End)),
+        }
+    }
+
+    fn read_start<R: MemRead>(
+        cx: &mut Context<'_>,
+        rdr: &mut R,
+        size: &mut u64,
+    ) -> Poll<Result<ChunkedState, io::Error>> {
+        trace!("Read chunk start");
+
+        let radix = 16;
+        match byte!(rdr, cx) {
+            b @ b'0'..=b'9' => {
+                *size = or_overflow!(size.checked_mul(radix));
+                *size = or_overflow!(size.checked_add((b - b'0') as u64));
+            }
+            b @ b'a'..=b'f' => {
+                *size = or_overflow!(size.checked_mul(radix));
+                *size = or_overflow!(size.checked_add((b + 10 - b'a') as u64));
+            }
+            b @ b'A'..=b'F' => {
+                *size = or_overflow!(size.checked_mul(radix));
+                *size = or_overflow!(size.checked_add((b + 10 - b'A') as u64));
+            }
+            _ => {
+                return Poll::Ready(Err(io::Error::new(
+                    io::ErrorKind::InvalidInput,
+                    "Invalid chunk size line: missing size digit",
+                )));
+            }
+        }
+
+        Poll::Ready(Ok(ChunkedState::Size))
+    }
+
+    fn read_size<R: MemRead>(
+        cx: &mut Context<'_>,
+        rdr: &mut R,
+        size: &mut u64,
+    ) -> Poll<Result<ChunkedState, io::Error>> {
+        trace!("Read chunk hex size");
+
+        let radix = 16;
+        match byte!(rdr, cx) {
+            b @ b'0'..=b'9' => {
+                *size = or_overflow!(size.checked_mul(radix));
+                *size = or_overflow!(size.checked_add((b - b'0') as u64));
+            }
+            b @ b'a'..=b'f' => {
+                *size = or_overflow!(size.checked_mul(radix));
+                *size = or_overflow!(size.checked_add((b + 10 - b'a') as u64));
+            }
+            b @ b'A'..=b'F' => {
+                *size = or_overflow!(size.checked_mul(radix));
+                *size = or_overflow!(size.checked_add((b + 10 - b'A') as u64));
+            }
+            b'\t' | b' ' => return Poll::Ready(Ok(ChunkedState::SizeLws)),
+            b';' => return Poll::Ready(Ok(ChunkedState::Extension)),
+            b'\r' => return Poll::Ready(Ok(ChunkedState::SizeLf)),
+            _ => {
+                return Poll::Ready(Err(io::Error::new(
+                    io::ErrorKind::InvalidInput,
+                    "Invalid chunk size line: Invalid Size",
+                )));
+            }
+        }
+        Poll::Ready(Ok(ChunkedState::Size))
+    }
+    fn read_size_lws<R: MemRead>(
+        cx: &mut Context<'_>,
+        rdr: &mut R,
+    ) -> Poll<Result<ChunkedState, io::Error>> {
+        trace!("read_size_lws");
+        match byte!(rdr, cx) {
+            // LWS can follow the chunk size, but no more digits can come
+            b'\t' | b' ' => Poll::Ready(Ok(ChunkedState::SizeLws)),
+            b';' => Poll::Ready(Ok(ChunkedState::Extension)),
+            b'\r' => Poll::Ready(Ok(ChunkedState::SizeLf)),
+            _ => Poll::Ready(Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "Invalid chunk size linear white space",
+            ))),
+        }
+    }
+    fn read_extension<R: MemRead>(
+        cx: &mut Context<'_>,
+        rdr: &mut R,
+        extensions_cnt: &mut u64,
+    ) -> Poll<Result<ChunkedState, io::Error>> {
+        trace!("read_extension");
+        // We don't care about extensions really at all. Just ignore them.
+        // They "end" at the next CRLF.
+        //
+        // However, some implementations may not check for the CR, so to save
+        // them from themselves, we reject extensions containing plain LF as
+        // well.
+        match byte!(rdr, cx) {
+            b'\r' => Poll::Ready(Ok(ChunkedState::SizeLf)),
+            b'\n' => Poll::Ready(Err(io::Error::new(
+                io::ErrorKind::InvalidData,
+                "invalid chunk extension contains newline",
+            ))),
+            _ => {
+                *extensions_cnt += 1;
+                if *extensions_cnt >= CHUNKED_EXTENSIONS_LIMIT {
+                    Poll::Ready(Err(io::Error::new(
+                        io::ErrorKind::InvalidData,
+                        "chunk extensions over limit",
+                    )))
+                } else {
+                    Poll::Ready(Ok(ChunkedState::Extension))
+                }
+            } // no supported extensions
+        }
+    }
+    fn read_size_lf<R: MemRead>(
+        cx: &mut Context<'_>,
+        rdr: &mut R,
+        size: u64,
+    ) -> Poll<Result<ChunkedState, io::Error>> {
+        trace!("Chunk size is {:?}", size);
+        match byte!(rdr, cx) {
+            b'\n' => {
+                if size == 0 {
+                    Poll::Ready(Ok(ChunkedState::EndCr))
+                } else {
+                    debug!("incoming chunked header: {0:#X} ({0} bytes)", size);
+                    Poll::Ready(Ok(ChunkedState::Body))
+                }
+            }
+            _ => Poll::Ready(Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "Invalid chunk size LF",
+            ))),
+        }
+    }
+
+    fn read_body<R: MemRead>(
+        cx: &mut Context<'_>,
+        rdr: &mut R,
+        rem: &mut u64,
+        buf: &mut Option<Bytes>,
+    ) -> Poll<Result<ChunkedState, io::Error>> {
+        trace!("Chunked read, remaining={:?}", rem);
+
+        // cap remaining bytes at the max capacity of usize
+        let rem_cap = match *rem {
+            r if r > usize::MAX as u64 => usize::MAX,
+            r => r as usize,
+        };
+
+        let to_read = rem_cap;
+        let slice = ready!(rdr.read_mem(cx, to_read))?;
+        let count = slice.len();
+
+        if count == 0 {
+            *rem = 0;
+            return Poll::Ready(Err(io::Error::new(
+                io::ErrorKind::UnexpectedEof,
+                IncompleteBody,
+            )));
+        }
+        *buf = Some(slice);
+        *rem -= count as u64;
+
+        if *rem > 0 {
+            Poll::Ready(Ok(ChunkedState::Body))
+        } else {
+            Poll::Ready(Ok(ChunkedState::BodyCr))
+        }
+    }
+    fn read_body_cr<R: MemRead>(
+        cx: &mut Context<'_>,
+        rdr: &mut R,
+    ) -> Poll<Result<ChunkedState, io::Error>> {
+        match byte!(rdr, cx) {
+            b'\r' => Poll::Ready(Ok(ChunkedState::BodyLf)),
+            _ => Poll::Ready(Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "Invalid chunk body CR",
+            ))),
+        }
+    }
+    fn read_body_lf<R: MemRead>(
+        cx: &mut Context<'_>,
+        rdr: &mut R,
+    ) -> Poll<Result<ChunkedState, io::Error>> {
+        match byte!(rdr, cx) {
+            b'\n' => Poll::Ready(Ok(ChunkedState::Size)),
+            _ => Poll::Ready(Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "Invalid chunk body LF",
+            ))),
+        }
+    }
+
+    fn read_trailer<R: MemRead>(
+        cx: &mut Context<'_>,
+        rdr: &mut R,
+    ) -> Poll<Result<ChunkedState, io::Error>> {
+        trace!("read_trailer");
+        match byte!(rdr, cx) {
+            b'\r' => Poll::Ready(Ok(ChunkedState::TrailerLf)),
+            _ => Poll::Ready(Ok(ChunkedState::Trailer)),
+        }
+    }
+    fn read_trailer_lf<R: MemRead>(
+        cx: &mut Context<'_>,
+        rdr: &mut R,
+    ) -> Poll<Result<ChunkedState, io::Error>> {
+        match byte!(rdr, cx) {
+            b'\n' => Poll::Ready(Ok(ChunkedState::EndCr)),
+            _ => Poll::Ready(Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "Invalid trailer end LF",
+            ))),
+        }
+    }
+
+    fn read_end_cr<R: MemRead>(
+        cx: &mut Context<'_>,
+        rdr: &mut R,
+    ) -> Poll<Result<ChunkedState, io::Error>> {
+        match byte!(rdr, cx) {
+            b'\r' => Poll::Ready(Ok(ChunkedState::EndLf)),
+            _ => Poll::Ready(Ok(ChunkedState::Trailer)),
+        }
+    }
+    fn read_end_lf<R: MemRead>(
+        cx: &mut Context<'_>,
+        rdr: &mut R,
+    ) -> Poll<Result<ChunkedState, io::Error>> {
+        match byte!(rdr, cx) {
+            b'\n' => Poll::Ready(Ok(ChunkedState::End)),
+            _ => Poll::Ready(Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "Invalid chunk end LF",
+            ))),
+        }
+    }
+}
+
+#[derive(Debug)]
+struct IncompleteBody;
+
+impl fmt::Display for IncompleteBody {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "end of file before message length reached")
+    }
+}
+
+impl StdError for IncompleteBody {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::pin::Pin;
+    use std::time::Duration;
+    use tokio::io::{AsyncRead, ReadBuf};
+
+    impl<'a> MemRead for &'a [u8] {
+        fn read_mem(&mut self, _: &mut Context<'_>, len: usize) -> Poll<io::Result<Bytes>> {
+            let n = std::cmp::min(len, self.len());
+            if n > 0 {
+                let (a, b) = self.split_at(n);
+                let buf = Bytes::copy_from_slice(a);
+                *self = b;
+                Poll::Ready(Ok(buf))
+            } else {
+                Poll::Ready(Ok(Bytes::new()))
+            }
+        }
+    }
+
+    impl<'a> MemRead for &'a mut (dyn AsyncRead + Unpin) {
+        fn read_mem(&mut self, cx: &mut Context<'_>, len: usize) -> Poll<io::Result<Bytes>> {
+            let mut v = vec![0; len];
+            let mut buf = ReadBuf::new(&mut v);
+            ready!(Pin::new(self).poll_read(cx, &mut buf)?);
+            Poll::Ready(Ok(Bytes::copy_from_slice(&buf.filled())))
+        }
+    }
+
+    impl MemRead for Bytes {
+        fn read_mem(&mut self, _: &mut Context<'_>, len: usize) -> Poll<io::Result<Bytes>> {
+            let n = std::cmp::min(len, self.len());
+            let ret = self.split_to(n);
+            Poll::Ready(Ok(ret))
+        }
+    }
+
+    /*
+    use std::io;
+    use std::io::Write;
+    use super::Decoder;
+    use super::ChunkedState;
+    use futures::{Async, Poll};
+    use bytes::{BytesMut, Bytes};
+    use crate::mock::AsyncIo;
+    */
+
+    #[tokio::test]
+    async fn test_read_chunk_size() {
+        use std::io::ErrorKind::{InvalidData, InvalidInput, UnexpectedEof};
+
+        async fn read(s: &str) -> u64 {
+            let mut state = ChunkedState::new();
+            let rdr = &mut s.as_bytes();
+            let mut size = 0;
+            let mut ext_cnt = 0;
+            loop {
+                let result = futures_util::future::poll_fn(|cx| {
+                    state.step(cx, rdr, &mut size, &mut ext_cnt, &mut None)
+                })
+                .await;
+                let desc = format!("read_size failed for {:?}", s);
+                state = result.expect(desc.as_str());
+                if state == ChunkedState::Body || state == ChunkedState::EndCr {
+                    break;
+                }
+            }
+            size
+        }
+
+        async fn read_err(s: &str, expected_err: io::ErrorKind) {
+            let mut state = ChunkedState::new();
+            let rdr = &mut s.as_bytes();
+            let mut size = 0;
+            let mut ext_cnt = 0;
+            loop {
+                let result = futures_util::future::poll_fn(|cx| {
+                    state.step(cx, rdr, &mut size, &mut ext_cnt, &mut None)
+                })
+                .await;
+                state = match result {
+                    Ok(s) => s,
+                    Err(e) => {
+                        assert!(
+                            expected_err == e.kind(),
+                            "Reading {:?}, expected {:?}, but got {:?}",
+                            s,
+                            expected_err,
+                            e.kind()
+                        );
+                        return;
+                    }
+                };
+                if state == ChunkedState::Body || state == ChunkedState::End {
+                    panic!("Was Ok. Expected Err for {:?}", s);
+                }
+            }
+        }
+
+        assert_eq!(1, read("1\r\n").await);
+        assert_eq!(1, read("01\r\n").await);
+        assert_eq!(0, read("0\r\n").await);
+        assert_eq!(0, read("00\r\n").await);
+        assert_eq!(10, read("A\r\n").await);
+        assert_eq!(10, read("a\r\n").await);
+        assert_eq!(255, read("Ff\r\n").await);
+        assert_eq!(255, read("Ff   \r\n").await);
+        // Missing LF or CRLF
+        read_err("F\rF", InvalidInput).await;
+        read_err("F", UnexpectedEof).await;
+        // Missing digit
+        read_err("\r\n\r\n", InvalidInput).await;
+        read_err("\r\n", InvalidInput).await;
+        // Invalid hex digit
+        read_err("X\r\n", InvalidInput).await;
+        read_err("1X\r\n", InvalidInput).await;
+        read_err("-\r\n", InvalidInput).await;
+        read_err("-1\r\n", InvalidInput).await;
+        // Acceptable (if not fully valid) extensions do not influence the size
+        assert_eq!(1, read("1;extension\r\n").await);
+        assert_eq!(10, read("a;ext name=value\r\n").await);
+        assert_eq!(1, read("1;extension;extension2\r\n").await);
+        assert_eq!(1, read("1;;;  ;\r\n").await);
+        assert_eq!(2, read("2; extension...\r\n").await);
+        assert_eq!(3, read("3   ; extension=123\r\n").await);
+        assert_eq!(3, read("3   ;\r\n").await);
+        assert_eq!(3, read("3   ;   \r\n").await);
+        // Invalid extensions cause an error
+        read_err("1 invalid extension\r\n", InvalidInput).await;
+        read_err("1 A\r\n", InvalidInput).await;
+        read_err("1;no CRLF", UnexpectedEof).await;
+        read_err("1;reject\nnewlines\r\n", InvalidData).await;
+        // Overflow
+        read_err("f0000000000000003\r\n", InvalidData).await;
+    }
+
+    #[tokio::test]
+    async fn test_read_sized_early_eof() {
+        let mut bytes = &b"foo bar"[..];
+        let mut decoder = Decoder::length(10);
+        assert_eq!(decoder.decode_fut(&mut bytes).await.unwrap().len(), 7);
+        let e = decoder.decode_fut(&mut bytes).await.unwrap_err();
+        assert_eq!(e.kind(), io::ErrorKind::UnexpectedEof);
+    }
+
+    #[tokio::test]
+    async fn test_read_chunked_early_eof() {
+        let mut bytes = &b"\
+            9\r\n\
+            foo bar\
+        "[..];
+        let mut decoder = Decoder::chunked();
+        assert_eq!(decoder.decode_fut(&mut bytes).await.unwrap().len(), 7);
+        let e = decoder.decode_fut(&mut bytes).await.unwrap_err();
+        assert_eq!(e.kind(), io::ErrorKind::UnexpectedEof);
+    }
+
+    #[tokio::test]
+    async fn test_read_chunked_single_read() {
+        let mut mock_buf = &b"10\r\n1234567890abcdef\r\n0\r\n"[..];
+        let buf = Decoder::chunked()
+            .decode_fut(&mut mock_buf)
+            .await
+            .expect("decode");
+        assert_eq!(16, buf.len());
+        let result = String::from_utf8(buf.as_ref().to_vec()).expect("decode String");
+        assert_eq!("1234567890abcdef", &result);
+    }
+
+    #[tokio::test]
+    async fn test_read_chunked_extensions_over_limit() {
+        // construct a chunked body where each individual chunked extension
+        // is totally fine, but combined is over the limit.
+        let per_chunk = super::CHUNKED_EXTENSIONS_LIMIT * 2 / 3;
+        let mut scratch = vec![];
+        for _ in 0..2 {
+            scratch.extend(b"1;");
+            scratch.extend(b"x".repeat(per_chunk as usize));
+            scratch.extend(b"\r\nA\r\n");
+        }
+        scratch.extend(b"0\r\n\r\n");
+        let mut mock_buf = Bytes::from(scratch);
+
+        let mut decoder = Decoder::chunked();
+        let buf1 = decoder.decode_fut(&mut mock_buf).await.expect("decode1");
+        assert_eq!(&buf1[..], b"A");
+
+        let err = decoder
+            .decode_fut(&mut mock_buf)
+            .await
+            .expect_err("decode2");
+        assert_eq!(err.kind(), io::ErrorKind::InvalidData);
+        assert_eq!(err.to_string(), "chunk extensions over limit");
+    }
+
+    #[cfg(not(miri))]
+    #[tokio::test]
+    async fn test_read_chunked_trailer_with_missing_lf() {
+        let mut mock_buf = &b"10\r\n1234567890abcdef\r\n0\r\nbad\r\r\n"[..];
+        let mut decoder = Decoder::chunked();
+        decoder.decode_fut(&mut mock_buf).await.expect("decode");
+        let e = decoder.decode_fut(&mut mock_buf).await.unwrap_err();
+        assert_eq!(e.kind(), io::ErrorKind::InvalidInput);
+    }
+
+    #[tokio::test]
+    async fn test_read_chunked_after_eof() {
+        let mut mock_buf = &b"10\r\n1234567890abcdef\r\n0\r\n\r\n"[..];
+        let mut decoder = Decoder::chunked();
+
+        // normal read
+        let buf = decoder.decode_fut(&mut mock_buf).await.unwrap();
+        assert_eq!(16, buf.len());
+        let result = String::from_utf8(buf.as_ref().to_vec()).expect("decode String");
+        assert_eq!("1234567890abcdef", &result);
+
+        // eof read
+        let buf = decoder.decode_fut(&mut mock_buf).await.expect("decode");
+        assert_eq!(0, buf.len());
+
+        // ensure read after eof also returns eof
+        let buf = decoder.decode_fut(&mut mock_buf).await.expect("decode");
+        assert_eq!(0, buf.len());
+    }
+
+    // perform an async read using a custom buffer size and causing a blocking
+    // read at the specified byte
+    async fn read_async(mut decoder: Decoder, content: &[u8], block_at: usize) -> String {
+        let mut outs = Vec::new();
+
+        let mut ins = if block_at == 0 {
+            tokio_test::io::Builder::new()
+                .wait(Duration::from_millis(10))
+                .read(content)
+                .build()
+        } else {
+            tokio_test::io::Builder::new()
+                .read(&content[..block_at])
+                .wait(Duration::from_millis(10))
+                .read(&content[block_at..])
+                .build()
+        };
+
+        let mut ins = &mut ins as &mut (dyn AsyncRead + Unpin);
+
+        loop {
+            let buf = decoder
+                .decode_fut(&mut ins)
+                .await
+                .expect("unexpected decode error");
+            if buf.is_empty() {
+                break; // eof
+            }
+            outs.extend(buf.as_ref());
+        }
+
+        String::from_utf8(outs).expect("decode String")
+    }
+
+    // iterate over the different ways that this async read could go.
+    // tests blocking a read at each byte along the content - The shotgun approach
+    async fn all_async_cases(content: &str, expected: &str, decoder: Decoder) {
+        let content_len = content.len();
+        for block_at in 0..content_len {
+            let actual = read_async(decoder.clone(), content.as_bytes(), block_at).await;
+            assert_eq!(expected, &actual) //, "Failed async. Blocking at {}", block_at);
+        }
+    }
+
+    #[tokio::test]
+    async fn test_read_length_async() {
+        let content = "foobar";
+        all_async_cases(content, content, Decoder::length(content.len() as u64)).await;
+    }
+
+    #[tokio::test]
+    async fn test_read_chunked_async() {
+        let content = "3\r\nfoo\r\n3\r\nbar\r\n0\r\n\r\n";
+        let expected = "foobar";
+        all_async_cases(content, expected, Decoder::chunked()).await;
+    }
+
+    #[tokio::test]
+    async fn test_read_eof_async() {
+        let content = "foobar";
+        all_async_cases(content, content, Decoder::eof()).await;
+    }
+
+    #[cfg(feature = "nightly")]
+    #[bench]
+    fn bench_decode_chunked_1kb(b: &mut test::Bencher) {
+        let rt = new_runtime();
+
+        const LEN: usize = 1024;
+        let mut vec = Vec::new();
+        vec.extend(format!("{:x}\r\n", LEN).as_bytes());
+        vec.extend(&[0; LEN][..]);
+        vec.extend(b"\r\n");
+        let content = Bytes::from(vec);
+
+        b.bytes = LEN as u64;
+
+        b.iter(|| {
+            let mut decoder = Decoder::chunked();
+            rt.block_on(async {
+                let mut raw = content.clone();
+                let chunk = decoder.decode_fut(&mut raw).await.unwrap();
+                assert_eq!(chunk.len(), LEN);
+            });
+        });
+    }
+
+    #[cfg(feature = "nightly")]
+    #[bench]
+    fn bench_decode_length_1kb(b: &mut test::Bencher) {
+        let rt = new_runtime();
+
+        const LEN: usize = 1024;
+        let content = Bytes::from(&[0; LEN][..]);
+        b.bytes = LEN as u64;
+
+        b.iter(|| {
+            let mut decoder = Decoder::length(LEN as u64);
+            rt.block_on(async {
+                let mut raw = content.clone();
+                let chunk = decoder.decode_fut(&mut raw).await.unwrap();
+                assert_eq!(chunk.len(), LEN);
+            });
+        });
+    }
+
+    #[cfg(feature = "nightly")]
+    fn new_runtime() -> tokio::runtime::Runtime {
+        tokio::runtime::Builder::new_current_thread()
+            .enable_all()
+            .build()
+            .expect("rt build")
+    }
+}
diff --git a/src/proto/h1/dispatch.rs b/src/proto/h1/dispatch.rs
new file mode 100644
index 0000000..3516d7a
--- /dev/null
+++ b/src/proto/h1/dispatch.rs
@@ -0,0 +1,761 @@
+use std::error::Error as StdError;
+use std::future::Future;
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use bytes::{Buf, Bytes};
+use http::Request;
+use tokio::io::{AsyncRead, AsyncWrite};
+use tracing::{debug, trace};
+
+use super::{Http1Transaction, Wants};
+use crate::body::{Body, DecodedLength, HttpBody};
+use crate::common;
+use crate::proto::{BodyLength, Conn, Dispatched, MessageHead, RequestHead};
+use crate::upgrade::OnUpgrade;
+
+pub(crate) struct Dispatcher<D, Bs: HttpBody, I, T> {
+    conn: Conn<I, Bs::Data, T>,
+    dispatch: D,
+    body_tx: Option<crate::body::Sender>,
+    body_rx: Pin<Box<Option<Bs>>>,
+    is_closing: bool,
+}
+
+pub(crate) trait Dispatch {
+    type PollItem;
+    type PollBody;
+    type PollError;
+    type RecvItem;
+    fn poll_msg(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<(Self::PollItem, Self::PollBody), Self::PollError>>>;
+    fn recv_msg(&mut self, msg: crate::Result<(Self::RecvItem, Body)>) -> crate::Result<()>;
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), ()>>;
+    fn should_poll(&self) -> bool;
+}
+
+cfg_server! {
+    use crate::service::HttpService;
+
+    pub(crate) struct Server<S: HttpService<B>, B> {
+        in_flight: Pin<Box<Option<S::Future>>>,
+        pub(crate) service: S,
+    }
+}
+
+cfg_client! {
+    pin_project_lite::pin_project! {
+        pub(crate) struct Client<B> {
+            callback: Option<crate::client::dispatch::Callback<Request<B>, http::Response<Body>>>,
+            #[pin]
+            rx: ClientRx<B>,
+            rx_closed: bool,
+        }
+    }
+
+    type ClientRx<B> = crate::client::dispatch::Receiver<Request<B>, http::Response<Body>>;
+}
+
+impl<D, Bs, I, T> Dispatcher<D, Bs, I, T>
+where
+    D: Dispatch<
+            PollItem = MessageHead<T::Outgoing>,
+            PollBody = Bs,
+            RecvItem = MessageHead<T::Incoming>,
+        > + Unpin,
+    D::PollError: Into<Box<dyn StdError + Send + Sync>>,
+    I: AsyncRead + AsyncWrite + Unpin,
+    T: Http1Transaction + Unpin,
+    Bs: HttpBody + 'static,
+    Bs::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    pub(crate) fn new(dispatch: D, conn: Conn<I, Bs::Data, T>) -> Self {
+        Dispatcher {
+            conn,
+            dispatch,
+            body_tx: None,
+            body_rx: Box::pin(None),
+            is_closing: false,
+        }
+    }
+
+    #[cfg(feature = "server")]
+    pub(crate) fn disable_keep_alive(&mut self) {
+        self.conn.disable_keep_alive();
+        if self.conn.is_write_closed() {
+            self.close();
+        }
+    }
+
+    pub(crate) fn into_inner(self) -> (I, Bytes, D) {
+        let (io, buf) = self.conn.into_inner();
+        (io, buf, self.dispatch)
+    }
+
+    /// Run this dispatcher until HTTP says this connection is done,
+    /// but don't call `AsyncWrite::shutdown` on the underlying IO.
+    ///
+    /// This is useful for old-style HTTP upgrades, but ignores
+    /// newer-style upgrade API.
+    pub(crate) fn poll_without_shutdown(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>>
+    where
+        Self: Unpin,
+    {
+        Pin::new(self).poll_catch(cx, false).map_ok(|ds| {
+            if let Dispatched::Upgrade(pending) = ds {
+                pending.manual();
+            }
+        })
+    }
+
+    fn poll_catch(
+        &mut self,
+        cx: &mut Context<'_>,
+        should_shutdown: bool,
+    ) -> Poll<crate::Result<Dispatched>> {
+        Poll::Ready(ready!(self.poll_inner(cx, should_shutdown)).or_else(|e| {
+            // Be sure to alert a streaming body of the failure.
+            if let Some(mut body) = self.body_tx.take() {
+                body.send_error(crate::Error::new_body("connection error"));
+            }
+            // An error means we're shutting down either way.
+            // We just try to give the error to the user,
+            // and close the connection with an Ok. If we
+            // cannot give it to the user, then return the Err.
+            self.dispatch.recv_msg(Err(e))?;
+            Ok(Dispatched::Shutdown)
+        }))
+    }
+
+    fn poll_inner(
+        &mut self,
+        cx: &mut Context<'_>,
+        should_shutdown: bool,
+    ) -> Poll<crate::Result<Dispatched>> {
+        T::update_date();
+
+        ready!(self.poll_loop(cx))?;
+
+        if self.is_done() {
+            if let Some(pending) = self.conn.pending_upgrade() {
+                self.conn.take_error()?;
+                return Poll::Ready(Ok(Dispatched::Upgrade(pending)));
+            } else if should_shutdown {
+                ready!(self.conn.poll_shutdown(cx)).map_err(crate::Error::new_shutdown)?;
+            }
+            self.conn.take_error()?;
+            Poll::Ready(Ok(Dispatched::Shutdown))
+        } else {
+            Poll::Pending
+        }
+    }
+
+    fn poll_loop(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        // Limit the looping on this connection, in case it is ready far too
+        // often, so that other futures don't starve.
+        //
+        // 16 was chosen arbitrarily, as that is number of pipelined requests
+        // benchmarks often use. Perhaps it should be a config option instead.
+        for _ in 0..16 {
+            let _ = self.poll_read(cx)?;
+            let _ = self.poll_write(cx)?;
+            let _ = self.poll_flush(cx)?;
+
+            // This could happen if reading paused before blocking on IO,
+            // such as getting to the end of a framed message, but then
+            // writing/flushing set the state back to Init. In that case,
+            // if the read buffer still had bytes, we'd want to try poll_read
+            // again, or else we wouldn't ever be woken up again.
+            //
+            // Using this instead of task::current() and notify() inside
+            // the Conn is noticeably faster in pipelined benchmarks.
+            if !self.conn.wants_read_again() {
+                //break;
+                return Poll::Ready(Ok(()));
+            }
+        }
+
+        trace!("poll_loop yielding (self = {:p})", self);
+
+        common::task::yield_now(cx).map(|never| match never {})
+    }
+
+    fn poll_read(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        loop {
+            if self.is_closing {
+                return Poll::Ready(Ok(()));
+            } else if self.conn.can_read_head() {
+                ready!(self.poll_read_head(cx))?;
+            } else if let Some(mut body) = self.body_tx.take() {
+                if self.conn.can_read_body() {
+                    match body.poll_ready(cx) {
+                        Poll::Ready(Ok(())) => (),
+                        Poll::Pending => {
+                            self.body_tx = Some(body);
+                            return Poll::Pending;
+                        }
+                        Poll::Ready(Err(_canceled)) => {
+                            // user doesn't care about the body
+                            // so we should stop reading
+                            trace!("body receiver dropped before eof, draining or closing");
+                            self.conn.poll_drain_or_close_read(cx);
+                            continue;
+                        }
+                    }
+                    match self.conn.poll_read_body(cx) {
+                        Poll::Ready(Some(Ok(chunk))) => match body.try_send_data(chunk) {
+                            Ok(()) => {
+                                self.body_tx = Some(body);
+                            }
+                            Err(_canceled) => {
+                                if self.conn.can_read_body() {
+                                    trace!("body receiver dropped before eof, closing");
+                                    self.conn.close_read();
+                                }
+                            }
+                        },
+                        Poll::Ready(None) => {
+                            // just drop, the body will close automatically
+                        }
+                        Poll::Pending => {
+                            self.body_tx = Some(body);
+                            return Poll::Pending;
+                        }
+                        Poll::Ready(Some(Err(e))) => {
+                            body.send_error(crate::Error::new_body(e));
+                        }
+                    }
+                } else {
+                    // just drop, the body will close automatically
+                }
+            } else {
+                return self.conn.poll_read_keep_alive(cx);
+            }
+        }
+    }
+
+    fn poll_read_head(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        // can dispatch receive, or does it still care about, an incoming message?
+        match ready!(self.dispatch.poll_ready(cx)) {
+            Ok(()) => (),
+            Err(()) => {
+                trace!("dispatch no longer receiving messages");
+                self.close();
+                return Poll::Ready(Ok(()));
+            }
+        }
+        // dispatch is ready for a message, try to read one
+        match ready!(self.conn.poll_read_head(cx)) {
+            Some(Ok((mut head, body_len, wants))) => {
+                let body = match body_len {
+                    DecodedLength::ZERO => Body::empty(),
+                    other => {
+                        let (tx, rx) = Body::new_channel(other, wants.contains(Wants::EXPECT));
+                        self.body_tx = Some(tx);
+                        rx
+                    }
+                };
+                if wants.contains(Wants::UPGRADE) {
+                    let upgrade = self.conn.on_upgrade();
+                    debug_assert!(!upgrade.is_none(), "empty upgrade");
+                    debug_assert!(
+                        head.extensions.get::<OnUpgrade>().is_none(),
+                        "OnUpgrade already set"
+                    );
+                    head.extensions.insert(upgrade);
+                }
+                self.dispatch.recv_msg(Ok((head, body)))?;
+                Poll::Ready(Ok(()))
+            }
+            Some(Err(err)) => {
+                debug!("read_head error: {}", err);
+                self.dispatch.recv_msg(Err(err))?;
+                // if here, the dispatcher gave the user the error
+                // somewhere else. we still need to shutdown, but
+                // not as a second error.
+                self.close();
+                Poll::Ready(Ok(()))
+            }
+            None => {
+                // read eof, the write side will have been closed too unless
+                // allow_read_close was set to true, in which case just do
+                // nothing...
+                debug_assert!(self.conn.is_read_closed());
+                if self.conn.is_write_closed() {
+                    self.close();
+                }
+                Poll::Ready(Ok(()))
+            }
+        }
+    }
+
+    fn poll_write(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        loop {
+            if self.is_closing {
+                return Poll::Ready(Ok(()));
+            } else if self.body_rx.is_none()
+                && self.conn.can_write_head()
+                && self.dispatch.should_poll()
+            {
+                if let Some(msg) = ready!(Pin::new(&mut self.dispatch).poll_msg(cx)) {
+                    let (head, mut body) = msg.map_err(crate::Error::new_user_service)?;
+
+                    // Check if the body knows its full data immediately.
+                    //
+                    // If so, we can skip a bit of bookkeeping that streaming
+                    // bodies need to do.
+                    if let Some(full) = crate::body::take_full_data(&mut body) {
+                        self.conn.write_full_msg(head, full);
+                        return Poll::Ready(Ok(()));
+                    }
+
+                    let body_type = if body.is_end_stream() {
+                        self.body_rx.set(None);
+                        None
+                    } else {
+                        let btype = body
+                            .size_hint()
+                            .exact()
+                            .map(BodyLength::Known)
+                            .or_else(|| Some(BodyLength::Unknown));
+                        self.body_rx.set(Some(body));
+                        btype
+                    };
+                    self.conn.write_head(head, body_type);
+                } else {
+                    self.close();
+                    return Poll::Ready(Ok(()));
+                }
+            } else if !self.conn.can_buffer_body() {
+                ready!(self.poll_flush(cx))?;
+            } else {
+                // A new scope is needed :(
+                if let (Some(mut body), clear_body) =
+                    OptGuard::new(self.body_rx.as_mut()).guard_mut()
+                {
+                    debug_assert!(!*clear_body, "opt guard defaults to keeping body");
+                    if !self.conn.can_write_body() {
+                        trace!(
+                            "no more write body allowed, user body is_end_stream = {}",
+                            body.is_end_stream(),
+                        );
+                        *clear_body = true;
+                        continue;
+                    }
+
+                    let item = ready!(body.as_mut().poll_data(cx));
+                    if let Some(item) = item {
+                        let chunk = item.map_err(|e| {
+                            *clear_body = true;
+                            crate::Error::new_user_body(e)
+                        })?;
+                        let eos = body.is_end_stream();
+                        if eos {
+                            *clear_body = true;
+                            if chunk.remaining() == 0 {
+                                trace!("discarding empty chunk");
+                                self.conn.end_body()?;
+                            } else {
+                                self.conn.write_body_and_end(chunk);
+                            }
+                        } else {
+                            if chunk.remaining() == 0 {
+                                trace!("discarding empty chunk");
+                                continue;
+                            }
+                            self.conn.write_body(chunk);
+                        }
+                    } else {
+                        *clear_body = true;
+                        self.conn.end_body()?;
+                    }
+                } else {
+                    // If there's no body_rx, end the body
+                    if self.conn.can_write_body() {
+                        self.conn.end_body()?;
+                    } else {
+                        return Poll::Pending;
+                    }
+                }
+            }
+        }
+    }
+
+    fn poll_flush(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        self.conn.poll_flush(cx).map_err(|err| {
+            debug!("error writing: {}", err);
+            crate::Error::new_body_write(err)
+        })
+    }
+
+    fn close(&mut self) {
+        self.is_closing = true;
+        self.conn.close_read();
+        self.conn.close_write();
+    }
+
+    fn is_done(&self) -> bool {
+        if self.is_closing {
+            return true;
+        }
+
+        let read_done = self.conn.is_read_closed();
+
+        if !T::should_read_first() && read_done {
+            // a client that cannot read may was well be done.
+            true
+        } else {
+            let write_done = self.conn.is_write_closed()
+                || (!self.dispatch.should_poll() && self.body_rx.is_none());
+            read_done && write_done
+        }
+    }
+}
+
+impl<D, Bs, I, T> Future for Dispatcher<D, Bs, I, T>
+where
+    D: Dispatch<
+            PollItem = MessageHead<T::Outgoing>,
+            PollBody = Bs,
+            RecvItem = MessageHead<T::Incoming>,
+        > + Unpin,
+    D::PollError: Into<Box<dyn StdError + Send + Sync>>,
+    I: AsyncRead + AsyncWrite + Unpin,
+    T: Http1Transaction + Unpin,
+    Bs: HttpBody + 'static,
+    Bs::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type Output = crate::Result<Dispatched>;
+
+    #[inline]
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.poll_catch(cx, true)
+    }
+}
+
+// ===== impl OptGuard =====
+
+/// A drop guard to allow a mutable borrow of an Option while being able to
+/// set whether the `Option` should be cleared on drop.
+struct OptGuard<'a, T>(Pin<&'a mut Option<T>>, bool);
+
+impl<'a, T> OptGuard<'a, T> {
+    fn new(pin: Pin<&'a mut Option<T>>) -> Self {
+        OptGuard(pin, false)
+    }
+
+    fn guard_mut(&mut self) -> (Option<Pin<&mut T>>, &mut bool) {
+        (self.0.as_mut().as_pin_mut(), &mut self.1)
+    }
+}
+
+impl<'a, T> Drop for OptGuard<'a, T> {
+    fn drop(&mut self) {
+        if self.1 {
+            self.0.set(None);
+        }
+    }
+}
+
+// ===== impl Server =====
+
+cfg_server! {
+    impl<S, B> Server<S, B>
+    where
+        S: HttpService<B>,
+    {
+        pub(crate) fn new(service: S) -> Server<S, B> {
+            Server {
+                in_flight: Box::pin(None),
+                service,
+            }
+        }
+
+        pub(crate) fn into_service(self) -> S {
+            self.service
+        }
+    }
+
+    // Service is never pinned
+    impl<S: HttpService<B>, B> Unpin for Server<S, B> {}
+
+    impl<S, Bs> Dispatch for Server<S, Body>
+    where
+        S: HttpService<Body, ResBody = Bs>,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        Bs: HttpBody,
+    {
+        type PollItem = MessageHead<http::StatusCode>;
+        type PollBody = Bs;
+        type PollError = S::Error;
+        type RecvItem = RequestHead;
+
+        fn poll_msg(
+            mut self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+        ) -> Poll<Option<Result<(Self::PollItem, Self::PollBody), Self::PollError>>> {
+            let mut this = self.as_mut();
+            let ret = if let Some(ref mut fut) = this.in_flight.as_mut().as_pin_mut() {
+                let resp = ready!(fut.as_mut().poll(cx)?);
+                let (parts, body) = resp.into_parts();
+                let head = MessageHead {
+                    version: parts.version,
+                    subject: parts.status,
+                    headers: parts.headers,
+                    extensions: parts.extensions,
+                };
+                Poll::Ready(Some(Ok((head, body))))
+            } else {
+                unreachable!("poll_msg shouldn't be called if no inflight");
+            };
+
+            // Since in_flight finished, remove it
+            this.in_flight.set(None);
+            ret
+        }
+
+        fn recv_msg(&mut self, msg: crate::Result<(Self::RecvItem, Body)>) -> crate::Result<()> {
+            let (msg, body) = msg?;
+            let mut req = Request::new(body);
+            *req.method_mut() = msg.subject.0;
+            *req.uri_mut() = msg.subject.1;
+            *req.headers_mut() = msg.headers;
+            *req.version_mut() = msg.version;
+            *req.extensions_mut() = msg.extensions;
+            let fut = self.service.call(req);
+            self.in_flight.set(Some(fut));
+            Ok(())
+        }
+
+        fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), ()>> {
+            if self.in_flight.is_some() {
+                Poll::Pending
+            } else {
+                self.service.poll_ready(cx).map_err(|_e| {
+                    // FIXME: return error value.
+                    trace!("service closed");
+                })
+            }
+        }
+
+        fn should_poll(&self) -> bool {
+            self.in_flight.is_some()
+        }
+    }
+}
+
+// ===== impl Client =====
+
+cfg_client! {
+    impl<B> Client<B> {
+        pub(crate) fn new(rx: ClientRx<B>) -> Client<B> {
+            Client {
+                callback: None,
+                rx,
+                rx_closed: false,
+            }
+        }
+    }
+
+    impl<B> Dispatch for Client<B>
+    where
+        B: HttpBody,
+    {
+        type PollItem = RequestHead;
+        type PollBody = B;
+        type PollError = std::convert::Infallible;
+        type RecvItem = crate::proto::ResponseHead;
+
+        fn poll_msg(
+            mut self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+        ) -> Poll<Option<Result<(Self::PollItem, Self::PollBody), Self::PollError>>> {
+            let mut this = self.as_mut();
+            debug_assert!(!this.rx_closed);
+            match this.rx.poll_recv(cx) {
+                Poll::Ready(Some((req, mut cb))) => {
+                    // check that future hasn't been canceled already
+                    match cb.poll_canceled(cx) {
+                        Poll::Ready(()) => {
+                            trace!("request canceled");
+                            Poll::Ready(None)
+                        }
+                        Poll::Pending => {
+                            let (parts, body) = req.into_parts();
+                            let head = RequestHead {
+                                version: parts.version,
+                                subject: crate::proto::RequestLine(parts.method, parts.uri),
+                                headers: parts.headers,
+                                extensions: parts.extensions,
+                            };
+                            this.callback = Some(cb);
+                            Poll::Ready(Some(Ok((head, body))))
+                        }
+                    }
+                }
+                Poll::Ready(None) => {
+                    // user has dropped sender handle
+                    trace!("client tx closed");
+                    this.rx_closed = true;
+                    Poll::Ready(None)
+                }
+                Poll::Pending => Poll::Pending,
+            }
+        }
+
+        fn recv_msg(&mut self, msg: crate::Result<(Self::RecvItem, Body)>) -> crate::Result<()> {
+            match msg {
+                Ok((msg, body)) => {
+                    if let Some(cb) = self.callback.take() {
+                        let res = msg.into_response(body);
+                        cb.send(Ok(res));
+                        Ok(())
+                    } else {
+                        // Getting here is likely a bug! An error should have happened
+                        // in Conn::require_empty_read() before ever parsing a
+                        // full message!
+                        Err(crate::Error::new_unexpected_message())
+                    }
+                }
+                Err(err) => {
+                    if let Some(cb) = self.callback.take() {
+                        cb.send(Err((err, None)));
+                        Ok(())
+                    } else if !self.rx_closed {
+                        self.rx.close();
+                        if let Some((req, cb)) = self.rx.try_recv() {
+                            trace!("canceling queued request with connection error: {}", err);
+                            // in this case, the message was never even started, so it's safe to tell
+                            // the user that the request was completely canceled
+                            cb.send(Err((crate::Error::new_canceled().with(err), Some(req))));
+                            Ok(())
+                        } else {
+                            Err(err)
+                        }
+                    } else {
+                        Err(err)
+                    }
+                }
+            }
+        }
+
+        fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), ()>> {
+            match self.callback {
+                Some(ref mut cb) => match cb.poll_canceled(cx) {
+                    Poll::Ready(()) => {
+                        trace!("callback receiver has dropped");
+                        Poll::Ready(Err(()))
+                    }
+                    Poll::Pending => Poll::Ready(Ok(())),
+                },
+                None => Poll::Ready(Err(())),
+            }
+        }
+
+        fn should_poll(&self) -> bool {
+            self.callback.is_none()
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::proto::h1::ClientTransaction;
+    use std::time::Duration;
+
+    #[test]
+    fn client_read_bytes_before_writing_request() {
+        let _ = pretty_env_logger::try_init();
+
+        tokio_test::task::spawn(()).enter(|cx, _| {
+            let (io, mut handle) = tokio_test::io::Builder::new().build_with_handle();
+
+            // Block at 0 for now, but we will release this response before
+            // the request is ready to write later...
+            let (mut tx, rx) = crate::client::dispatch::channel();
+            let conn = Conn::<_, bytes::Bytes, ClientTransaction>::new(io);
+            let mut dispatcher = Dispatcher::new(Client::new(rx), conn);
+
+            // First poll is needed to allow tx to send...
+            assert!(Pin::new(&mut dispatcher).poll(cx).is_pending());
+
+            // Unblock our IO, which has a response before we've sent request!
+            //
+            handle.read(b"HTTP/1.1 200 OK\r\n\r\n");
+
+            let mut res_rx = tx
+                .try_send(crate::Request::new(crate::Body::empty()))
+                .unwrap();
+
+            tokio_test::assert_ready_ok!(Pin::new(&mut dispatcher).poll(cx));
+            let err = tokio_test::assert_ready_ok!(Pin::new(&mut res_rx).poll(cx))
+                .expect_err("callback should send error");
+
+            match (err.0.kind(), err.1) {
+                (&crate::error::Kind::Canceled, Some(_)) => (),
+                other => panic!("expected Canceled, got {:?}", other),
+            }
+        });
+    }
+
+    #[tokio::test]
+    async fn client_flushing_is_not_ready_for_next_request() {
+        let _ = pretty_env_logger::try_init();
+
+        let (io, _handle) = tokio_test::io::Builder::new()
+            .write(b"POST / HTTP/1.1\r\ncontent-length: 4\r\n\r\n")
+            .read(b"HTTP/1.1 200 OK\r\ncontent-length: 0\r\n\r\n")
+            .wait(std::time::Duration::from_secs(2))
+            .build_with_handle();
+
+        let (mut tx, rx) = crate::client::dispatch::channel();
+        let mut conn = Conn::<_, bytes::Bytes, ClientTransaction>::new(io);
+        conn.set_write_strategy_queue();
+
+        let dispatcher = Dispatcher::new(Client::new(rx), conn);
+        let _dispatcher = tokio::spawn(async move { dispatcher.await });
+
+        let req = crate::Request::builder()
+            .method("POST")
+            .body(crate::Body::from("reee"))
+            .unwrap();
+
+        let res = tx.try_send(req).unwrap().await.expect("response");
+        drop(res);
+
+        assert!(!tx.is_ready());
+    }
+
+    #[tokio::test]
+    async fn body_empty_chunks_ignored() {
+        let _ = pretty_env_logger::try_init();
+
+        let io = tokio_test::io::Builder::new()
+            // no reading or writing, just be blocked for the test...
+            .wait(Duration::from_secs(5))
+            .build();
+
+        let (mut tx, rx) = crate::client::dispatch::channel();
+        let conn = Conn::<_, bytes::Bytes, ClientTransaction>::new(io);
+        let mut dispatcher = tokio_test::task::spawn(Dispatcher::new(Client::new(rx), conn));
+
+        // First poll is needed to allow tx to send...
+        assert!(dispatcher.poll().is_pending());
+
+        let body = {
+            let (mut tx, body) = crate::Body::channel();
+            tx.try_send_data("".into()).unwrap();
+            body
+        };
+
+        let _res_rx = tx.try_send(crate::Request::new(body)).unwrap();
+
+        // Ensure conn.write_body wasn't called with the empty chunk.
+        // If it is, it will trigger an assertion.
+        assert!(dispatcher.poll().is_pending());
+    }
+}
diff --git a/src/proto/h1/encode.rs b/src/proto/h1/encode.rs
new file mode 100644
index 0000000..f0aa261
--- /dev/null
+++ b/src/proto/h1/encode.rs
@@ -0,0 +1,439 @@
+use std::fmt;
+use std::io::IoSlice;
+
+use bytes::buf::{Chain, Take};
+use bytes::Buf;
+use tracing::trace;
+
+use super::io::WriteBuf;
+
+type StaticBuf = &'static [u8];
+
+/// Encoders to handle different Transfer-Encodings.
+#[derive(Debug, Clone, PartialEq)]
+pub(crate) struct Encoder {
+    kind: Kind,
+    is_last: bool,
+}
+
+#[derive(Debug)]
+pub(crate) struct EncodedBuf<B> {
+    kind: BufKind<B>,
+}
+
+#[derive(Debug)]
+pub(crate) struct NotEof(u64);
+
+#[derive(Debug, PartialEq, Clone)]
+enum Kind {
+    /// An Encoder for when Transfer-Encoding includes `chunked`.
+    Chunked,
+    /// An Encoder for when Content-Length is set.
+    ///
+    /// Enforces that the body is not longer than the Content-Length header.
+    Length(u64),
+    /// An Encoder for when neither Content-Length nor Chunked encoding is set.
+    ///
+    /// This is mostly only used with HTTP/1.0 with a length. This kind requires
+    /// the connection to be closed when the body is finished.
+    #[cfg(feature = "server")]
+    CloseDelimited,
+}
+
+#[derive(Debug)]
+enum BufKind<B> {
+    Exact(B),
+    Limited(Take<B>),
+    Chunked(Chain<Chain<ChunkSize, B>, StaticBuf>),
+    ChunkedEnd(StaticBuf),
+}
+
+impl Encoder {
+    fn new(kind: Kind) -> Encoder {
+        Encoder {
+            kind,
+            is_last: false,
+        }
+    }
+    pub(crate) fn chunked() -> Encoder {
+        Encoder::new(Kind::Chunked)
+    }
+
+    pub(crate) fn length(len: u64) -> Encoder {
+        Encoder::new(Kind::Length(len))
+    }
+
+    #[cfg(feature = "server")]
+    pub(crate) fn close_delimited() -> Encoder {
+        Encoder::new(Kind::CloseDelimited)
+    }
+
+    pub(crate) fn is_eof(&self) -> bool {
+        matches!(self.kind, Kind::Length(0))
+    }
+
+    #[cfg(feature = "server")]
+    pub(crate) fn set_last(mut self, is_last: bool) -> Self {
+        self.is_last = is_last;
+        self
+    }
+
+    pub(crate) fn is_last(&self) -> bool {
+        self.is_last
+    }
+
+    pub(crate) fn is_close_delimited(&self) -> bool {
+        match self.kind {
+            #[cfg(feature = "server")]
+            Kind::CloseDelimited => true,
+            _ => false,
+        }
+    }
+
+    pub(crate) fn end<B>(&self) -> Result<Option<EncodedBuf<B>>, NotEof> {
+        match self.kind {
+            Kind::Length(0) => Ok(None),
+            Kind::Chunked => Ok(Some(EncodedBuf {
+                kind: BufKind::ChunkedEnd(b"0\r\n\r\n"),
+            })),
+            #[cfg(feature = "server")]
+            Kind::CloseDelimited => Ok(None),
+            Kind::Length(n) => Err(NotEof(n)),
+        }
+    }
+
+    pub(crate) fn encode<B>(&mut self, msg: B) -> EncodedBuf<B>
+    where
+        B: Buf,
+    {
+        let len = msg.remaining();
+        debug_assert!(len > 0, "encode() called with empty buf");
+
+        let kind = match self.kind {
+            Kind::Chunked => {
+                trace!("encoding chunked {}B", len);
+                let buf = ChunkSize::new(len)
+                    .chain(msg)
+                    .chain(b"\r\n" as &'static [u8]);
+                BufKind::Chunked(buf)
+            }
+            Kind::Length(ref mut remaining) => {
+                trace!("sized write, len = {}", len);
+                if len as u64 > *remaining {
+                    let limit = *remaining as usize;
+                    *remaining = 0;
+                    BufKind::Limited(msg.take(limit))
+                } else {
+                    *remaining -= len as u64;
+                    BufKind::Exact(msg)
+                }
+            }
+            #[cfg(feature = "server")]
+            Kind::CloseDelimited => {
+                trace!("close delimited write {}B", len);
+                BufKind::Exact(msg)
+            }
+        };
+        EncodedBuf { kind }
+    }
+
+    pub(super) fn encode_and_end<B>(&self, msg: B, dst: &mut WriteBuf<EncodedBuf<B>>) -> bool
+    where
+        B: Buf,
+    {
+        let len = msg.remaining();
+        debug_assert!(len > 0, "encode() called with empty buf");
+
+        match self.kind {
+            Kind::Chunked => {
+                trace!("encoding chunked {}B", len);
+                let buf = ChunkSize::new(len)
+                    .chain(msg)
+                    .chain(b"\r\n0\r\n\r\n" as &'static [u8]);
+                dst.buffer(buf);
+                !self.is_last
+            }
+            Kind::Length(remaining) => {
+                use std::cmp::Ordering;
+
+                trace!("sized write, len = {}", len);
+                match (len as u64).cmp(&remaining) {
+                    Ordering::Equal => {
+                        dst.buffer(msg);
+                        !self.is_last
+                    }
+                    Ordering::Greater => {
+                        dst.buffer(msg.take(remaining as usize));
+                        !self.is_last
+                    }
+                    Ordering::Less => {
+                        dst.buffer(msg);
+                        false
+                    }
+                }
+            }
+            #[cfg(feature = "server")]
+            Kind::CloseDelimited => {
+                trace!("close delimited write {}B", len);
+                dst.buffer(msg);
+                false
+            }
+        }
+    }
+
+    /// Encodes the full body, without verifying the remaining length matches.
+    ///
+    /// This is used in conjunction with HttpBody::__hyper_full_data(), which
+    /// means we can trust that the buf has the correct size (the buf itself
+    /// was checked to make the headers).
+    pub(super) fn danger_full_buf<B>(self, msg: B, dst: &mut WriteBuf<EncodedBuf<B>>)
+    where
+        B: Buf,
+    {
+        debug_assert!(msg.remaining() > 0, "encode() called with empty buf");
+        debug_assert!(
+            match self.kind {
+                Kind::Length(len) => len == msg.remaining() as u64,
+                _ => true,
+            },
+            "danger_full_buf length mismatches"
+        );
+
+        match self.kind {
+            Kind::Chunked => {
+                let len = msg.remaining();
+                trace!("encoding chunked {}B", len);
+                let buf = ChunkSize::new(len)
+                    .chain(msg)
+                    .chain(b"\r\n0\r\n\r\n" as &'static [u8]);
+                dst.buffer(buf);
+            }
+            _ => {
+                dst.buffer(msg);
+            }
+        }
+    }
+}
+
+impl<B> Buf for EncodedBuf<B>
+where
+    B: Buf,
+{
+    #[inline]
+    fn remaining(&self) -> usize {
+        match self.kind {
+            BufKind::Exact(ref b) => b.remaining(),
+            BufKind::Limited(ref b) => b.remaining(),
+            BufKind::Chunked(ref b) => b.remaining(),
+            BufKind::ChunkedEnd(ref b) => b.remaining(),
+        }
+    }
+
+    #[inline]
+    fn chunk(&self) -> &[u8] {
+        match self.kind {
+            BufKind::Exact(ref b) => b.chunk(),
+            BufKind::Limited(ref b) => b.chunk(),
+            BufKind::Chunked(ref b) => b.chunk(),
+            BufKind::ChunkedEnd(ref b) => b.chunk(),
+        }
+    }
+
+    #[inline]
+    fn advance(&mut self, cnt: usize) {
+        match self.kind {
+            BufKind::Exact(ref mut b) => b.advance(cnt),
+            BufKind::Limited(ref mut b) => b.advance(cnt),
+            BufKind::Chunked(ref mut b) => b.advance(cnt),
+            BufKind::ChunkedEnd(ref mut b) => b.advance(cnt),
+        }
+    }
+
+    #[inline]
+    fn chunks_vectored<'t>(&'t self, dst: &mut [IoSlice<'t>]) -> usize {
+        match self.kind {
+            BufKind::Exact(ref b) => b.chunks_vectored(dst),
+            BufKind::Limited(ref b) => b.chunks_vectored(dst),
+            BufKind::Chunked(ref b) => b.chunks_vectored(dst),
+            BufKind::ChunkedEnd(ref b) => b.chunks_vectored(dst),
+        }
+    }
+}
+
+#[cfg(target_pointer_width = "32")]
+const USIZE_BYTES: usize = 4;
+
+#[cfg(target_pointer_width = "64")]
+const USIZE_BYTES: usize = 8;
+
+// each byte will become 2 hex
+const CHUNK_SIZE_MAX_BYTES: usize = USIZE_BYTES * 2;
+
+#[derive(Clone, Copy)]
+struct ChunkSize {
+    bytes: [u8; CHUNK_SIZE_MAX_BYTES + 2],
+    pos: u8,
+    len: u8,
+}
+
+impl ChunkSize {
+    fn new(len: usize) -> ChunkSize {
+        use std::fmt::Write;
+        let mut size = ChunkSize {
+            bytes: [0; CHUNK_SIZE_MAX_BYTES + 2],
+            pos: 0,
+            len: 0,
+        };
+        write!(&mut size, "{:X}\r\n", len).expect("CHUNK_SIZE_MAX_BYTES should fit any usize");
+        size
+    }
+}
+
+impl Buf for ChunkSize {
+    #[inline]
+    fn remaining(&self) -> usize {
+        (self.len - self.pos).into()
+    }
+
+    #[inline]
+    fn chunk(&self) -> &[u8] {
+        &self.bytes[self.pos.into()..self.len.into()]
+    }
+
+    #[inline]
+    fn advance(&mut self, cnt: usize) {
+        assert!(cnt <= self.remaining());
+        self.pos += cnt as u8; // just asserted cnt fits in u8
+    }
+}
+
+impl fmt::Debug for ChunkSize {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("ChunkSize")
+            .field("bytes", &&self.bytes[..self.len.into()])
+            .field("pos", &self.pos)
+            .finish()
+    }
+}
+
+impl fmt::Write for ChunkSize {
+    fn write_str(&mut self, num: &str) -> fmt::Result {
+        use std::io::Write;
+        (&mut self.bytes[self.len.into()..])
+            .write_all(num.as_bytes())
+            .expect("&mut [u8].write() cannot error");
+        self.len += num.len() as u8; // safe because bytes is never bigger than 256
+        Ok(())
+    }
+}
+
+impl<B: Buf> From<B> for EncodedBuf<B> {
+    fn from(buf: B) -> Self {
+        EncodedBuf {
+            kind: BufKind::Exact(buf),
+        }
+    }
+}
+
+impl<B: Buf> From<Take<B>> for EncodedBuf<B> {
+    fn from(buf: Take<B>) -> Self {
+        EncodedBuf {
+            kind: BufKind::Limited(buf),
+        }
+    }
+}
+
+impl<B: Buf> From<Chain<Chain<ChunkSize, B>, StaticBuf>> for EncodedBuf<B> {
+    fn from(buf: Chain<Chain<ChunkSize, B>, StaticBuf>) -> Self {
+        EncodedBuf {
+            kind: BufKind::Chunked(buf),
+        }
+    }
+}
+
+impl fmt::Display for NotEof {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "early end, expected {} more bytes", self.0)
+    }
+}
+
+impl std::error::Error for NotEof {}
+
+#[cfg(test)]
+mod tests {
+    use bytes::BufMut;
+
+    use super::super::io::Cursor;
+    use super::Encoder;
+
+    #[test]
+    fn chunked() {
+        let mut encoder = Encoder::chunked();
+        let mut dst = Vec::new();
+
+        let msg1 = b"foo bar".as_ref();
+        let buf1 = encoder.encode(msg1);
+        dst.put(buf1);
+        assert_eq!(dst, b"7\r\nfoo bar\r\n");
+
+        let msg2 = b"baz quux herp".as_ref();
+        let buf2 = encoder.encode(msg2);
+        dst.put(buf2);
+
+        assert_eq!(dst, b"7\r\nfoo bar\r\nD\r\nbaz quux herp\r\n");
+
+        let end = encoder.end::<Cursor<Vec<u8>>>().unwrap().unwrap();
+        dst.put(end);
+
+        assert_eq!(
+            dst,
+            b"7\r\nfoo bar\r\nD\r\nbaz quux herp\r\n0\r\n\r\n".as_ref()
+        );
+    }
+
+    #[test]
+    fn length() {
+        let max_len = 8;
+        let mut encoder = Encoder::length(max_len as u64);
+        let mut dst = Vec::new();
+
+        let msg1 = b"foo bar".as_ref();
+        let buf1 = encoder.encode(msg1);
+        dst.put(buf1);
+
+        assert_eq!(dst, b"foo bar");
+        assert!(!encoder.is_eof());
+        encoder.end::<()>().unwrap_err();
+
+        let msg2 = b"baz".as_ref();
+        let buf2 = encoder.encode(msg2);
+        dst.put(buf2);
+
+        assert_eq!(dst.len(), max_len);
+        assert_eq!(dst, b"foo barb");
+        assert!(encoder.is_eof());
+        assert!(encoder.end::<()>().unwrap().is_none());
+    }
+
+    #[test]
+    fn eof() {
+        let mut encoder = Encoder::close_delimited();
+        let mut dst = Vec::new();
+
+        let msg1 = b"foo bar".as_ref();
+        let buf1 = encoder.encode(msg1);
+        dst.put(buf1);
+
+        assert_eq!(dst, b"foo bar");
+        assert!(!encoder.is_eof());
+        encoder.end::<()>().unwrap();
+
+        let msg2 = b"baz".as_ref();
+        let buf2 = encoder.encode(msg2);
+        dst.put(buf2);
+
+        assert_eq!(dst, b"foo barbaz");
+        assert!(!encoder.is_eof());
+        encoder.end::<()>().unwrap();
+    }
+}
diff --git a/src/proto/h1/io.rs b/src/proto/h1/io.rs
new file mode 100644
index 0000000..02d8a4a
--- /dev/null
+++ b/src/proto/h1/io.rs
@@ -0,0 +1,1000 @@
+use std::cmp;
+use std::fmt;
+#[cfg(all(feature = "server", feature = "runtime"))]
+use std::future::Future;
+use std::io::{self, IoSlice};
+use std::marker::Unpin;
+use std::mem::MaybeUninit;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+#[cfg(all(feature = "server", feature = "runtime"))]
+use std::time::Duration;
+
+use bytes::{Buf, BufMut, Bytes, BytesMut};
+use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
+#[cfg(all(feature = "server", feature = "runtime"))]
+use tokio::time::Instant;
+use tracing::{debug, trace};
+
+use super::{Http1Transaction, ParseContext, ParsedMessage};
+use crate::common::buf::BufList;
+
+/// The initial buffer size allocated before trying to read from IO.
+pub(crate) const INIT_BUFFER_SIZE: usize = 8192;
+
+/// The minimum value that can be set to max buffer size.
+pub(crate) const MINIMUM_MAX_BUFFER_SIZE: usize = INIT_BUFFER_SIZE;
+
+/// The default maximum read buffer size. If the buffer gets this big and
+/// a message is still not complete, a `TooLarge` error is triggered.
+// Note: if this changes, update server::conn::Http::max_buf_size docs.
+pub(crate) const DEFAULT_MAX_BUFFER_SIZE: usize = 8192 + 4096 * 100;
+
+/// The maximum number of distinct `Buf`s to hold in a list before requiring
+/// a flush. Only affects when the buffer strategy is to queue buffers.
+///
+/// Note that a flush can happen before reaching the maximum. This simply
+/// forces a flush if the queue gets this big.
+const MAX_BUF_LIST_BUFFERS: usize = 16;
+
+pub(crate) struct Buffered<T, B> {
+    flush_pipeline: bool,
+    io: T,
+    read_blocked: bool,
+    read_buf: BytesMut,
+    read_buf_strategy: ReadStrategy,
+    write_buf: WriteBuf<B>,
+}
+
+impl<T, B> fmt::Debug for Buffered<T, B>
+where
+    B: Buf,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Buffered")
+            .field("read_buf", &self.read_buf)
+            .field("write_buf", &self.write_buf)
+            .finish()
+    }
+}
+
+impl<T, B> Buffered<T, B>
+where
+    T: AsyncRead + AsyncWrite + Unpin,
+    B: Buf,
+{
+    pub(crate) fn new(io: T) -> Buffered<T, B> {
+        let strategy = if io.is_write_vectored() {
+            WriteStrategy::Queue
+        } else {
+            WriteStrategy::Flatten
+        };
+        let write_buf = WriteBuf::new(strategy);
+        Buffered {
+            flush_pipeline: false,
+            io,
+            read_blocked: false,
+            read_buf: BytesMut::with_capacity(0),
+            read_buf_strategy: ReadStrategy::default(),
+            write_buf,
+        }
+    }
+
+    #[cfg(feature = "server")]
+    pub(crate) fn set_flush_pipeline(&mut self, enabled: bool) {
+        debug_assert!(!self.write_buf.has_remaining());
+        self.flush_pipeline = enabled;
+        if enabled {
+            self.set_write_strategy_flatten();
+        }
+    }
+
+    pub(crate) fn set_max_buf_size(&mut self, max: usize) {
+        assert!(
+            max >= MINIMUM_MAX_BUFFER_SIZE,
+            "The max_buf_size cannot be smaller than {}.",
+            MINIMUM_MAX_BUFFER_SIZE,
+        );
+        self.read_buf_strategy = ReadStrategy::with_max(max);
+        self.write_buf.max_buf_size = max;
+    }
+
+    #[cfg(feature = "client")]
+    pub(crate) fn set_read_buf_exact_size(&mut self, sz: usize) {
+        self.read_buf_strategy = ReadStrategy::Exact(sz);
+    }
+
+    pub(crate) fn set_write_strategy_flatten(&mut self) {
+        // this should always be called only at construction time,
+        // so this assert is here to catch myself
+        debug_assert!(self.write_buf.queue.bufs_cnt() == 0);
+        self.write_buf.set_strategy(WriteStrategy::Flatten);
+    }
+
+    pub(crate) fn set_write_strategy_queue(&mut self) {
+        // this should always be called only at construction time,
+        // so this assert is here to catch myself
+        debug_assert!(self.write_buf.queue.bufs_cnt() == 0);
+        self.write_buf.set_strategy(WriteStrategy::Queue);
+    }
+
+    pub(crate) fn read_buf(&self) -> &[u8] {
+        self.read_buf.as_ref()
+    }
+
+    #[cfg(test)]
+    #[cfg(feature = "nightly")]
+    pub(super) fn read_buf_mut(&mut self) -> &mut BytesMut {
+        &mut self.read_buf
+    }
+
+    /// Return the "allocated" available space, not the potential space
+    /// that could be allocated in the future.
+    fn read_buf_remaining_mut(&self) -> usize {
+        self.read_buf.capacity() - self.read_buf.len()
+    }
+
+    /// Return whether we can append to the headers buffer.
+    ///
+    /// Reasons we can't:
+    /// - The write buf is in queue mode, and some of the past body is still
+    ///   needing to be flushed.
+    pub(crate) fn can_headers_buf(&self) -> bool {
+        !self.write_buf.queue.has_remaining()
+    }
+
+    pub(crate) fn headers_buf(&mut self) -> &mut Vec<u8> {
+        let buf = self.write_buf.headers_mut();
+        &mut buf.bytes
+    }
+
+    pub(super) fn write_buf(&mut self) -> &mut WriteBuf<B> {
+        &mut self.write_buf
+    }
+
+    pub(crate) fn buffer<BB: Buf + Into<B>>(&mut self, buf: BB) {
+        self.write_buf.buffer(buf)
+    }
+
+    pub(crate) fn can_buffer(&self) -> bool {
+        self.flush_pipeline || self.write_buf.can_buffer()
+    }
+
+    pub(crate) fn consume_leading_lines(&mut self) {
+        if !self.read_buf.is_empty() {
+            let mut i = 0;
+            while i < self.read_buf.len() {
+                match self.read_buf[i] {
+                    b'\r' | b'\n' => i += 1,
+                    _ => break,
+                }
+            }
+            self.read_buf.advance(i);
+        }
+    }
+
+    pub(super) fn parse<S>(
+        &mut self,
+        cx: &mut Context<'_>,
+        parse_ctx: ParseContext<'_>,
+    ) -> Poll<crate::Result<ParsedMessage<S::Incoming>>>
+    where
+        S: Http1Transaction,
+    {
+        loop {
+            match super::role::parse_headers::<S>(
+                &mut self.read_buf,
+                ParseContext {
+                    cached_headers: parse_ctx.cached_headers,
+                    req_method: parse_ctx.req_method,
+                    h1_parser_config: parse_ctx.h1_parser_config.clone(),
+                    #[cfg(all(feature = "server", feature = "runtime"))]
+                    h1_header_read_timeout: parse_ctx.h1_header_read_timeout,
+                    #[cfg(all(feature = "server", feature = "runtime"))]
+                    h1_header_read_timeout_fut: parse_ctx.h1_header_read_timeout_fut,
+                    #[cfg(all(feature = "server", feature = "runtime"))]
+                    h1_header_read_timeout_running: parse_ctx.h1_header_read_timeout_running,
+                    preserve_header_case: parse_ctx.preserve_header_case,
+                    #[cfg(feature = "ffi")]
+                    preserve_header_order: parse_ctx.preserve_header_order,
+                    h09_responses: parse_ctx.h09_responses,
+                    #[cfg(feature = "ffi")]
+                    on_informational: parse_ctx.on_informational,
+                    #[cfg(feature = "ffi")]
+                    raw_headers: parse_ctx.raw_headers,
+                },
+            )? {
+                Some(msg) => {
+                    debug!("parsed {} headers", msg.head.headers.len());
+
+                    #[cfg(all(feature = "server", feature = "runtime"))]
+                    {
+                        *parse_ctx.h1_header_read_timeout_running = false;
+
+                        if let Some(h1_header_read_timeout_fut) =
+                            parse_ctx.h1_header_read_timeout_fut
+                        {
+                            // Reset the timer in order to avoid woken up when the timeout finishes
+                            h1_header_read_timeout_fut
+                                .as_mut()
+                                .reset(Instant::now() + Duration::from_secs(30 * 24 * 60 * 60));
+                        }
+                    }
+                    return Poll::Ready(Ok(msg));
+                }
+                None => {
+                    let max = self.read_buf_strategy.max();
+                    if self.read_buf.len() >= max {
+                        debug!("max_buf_size ({}) reached, closing", max);
+                        return Poll::Ready(Err(crate::Error::new_too_large()));
+                    }
+
+                    #[cfg(all(feature = "server", feature = "runtime"))]
+                    if *parse_ctx.h1_header_read_timeout_running {
+                        if let Some(h1_header_read_timeout_fut) =
+                            parse_ctx.h1_header_read_timeout_fut
+                        {
+                            if Pin::new(h1_header_read_timeout_fut).poll(cx).is_ready() {
+                                *parse_ctx.h1_header_read_timeout_running = false;
+
+                                tracing::warn!("read header from client timeout");
+                                return Poll::Ready(Err(crate::Error::new_header_timeout()));
+                            }
+                        }
+                    }
+                }
+            }
+            if ready!(self.poll_read_from_io(cx)).map_err(crate::Error::new_io)? == 0 {
+                trace!("parse eof");
+                return Poll::Ready(Err(crate::Error::new_incomplete()));
+            }
+        }
+    }
+
+    pub(crate) fn poll_read_from_io(&mut self, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
+        self.read_blocked = false;
+        let next = self.read_buf_strategy.next();
+        if self.read_buf_remaining_mut() < next {
+            self.read_buf.reserve(next);
+        }
+
+        let dst = self.read_buf.chunk_mut();
+        let dst = unsafe { &mut *(dst as *mut _ as *mut [MaybeUninit<u8>]) };
+        let mut buf = ReadBuf::uninit(dst);
+        match Pin::new(&mut self.io).poll_read(cx, &mut buf) {
+            Poll::Ready(Ok(_)) => {
+                let n = buf.filled().len();
+                trace!("received {} bytes", n);
+                unsafe {
+                    // Safety: we just read that many bytes into the
+                    // uninitialized part of the buffer, so this is okay.
+                    // @tokio pls give me back `poll_read_buf` thanks
+                    self.read_buf.advance_mut(n);
+                }
+                self.read_buf_strategy.record(n);
+                Poll::Ready(Ok(n))
+            }
+            Poll::Pending => {
+                self.read_blocked = true;
+                Poll::Pending
+            }
+            Poll::Ready(Err(e)) => Poll::Ready(Err(e)),
+        }
+    }
+
+    pub(crate) fn into_inner(self) -> (T, Bytes) {
+        (self.io, self.read_buf.freeze())
+    }
+
+    pub(crate) fn io_mut(&mut self) -> &mut T {
+        &mut self.io
+    }
+
+    pub(crate) fn is_read_blocked(&self) -> bool {
+        self.read_blocked
+    }
+
+    pub(crate) fn poll_flush(&mut self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        if self.flush_pipeline && !self.read_buf.is_empty() {
+            Poll::Ready(Ok(()))
+        } else if self.write_buf.remaining() == 0 {
+            Pin::new(&mut self.io).poll_flush(cx)
+        } else {
+            if let WriteStrategy::Flatten = self.write_buf.strategy {
+                return self.poll_flush_flattened(cx);
+            }
+
+            const MAX_WRITEV_BUFS: usize = 64;
+            loop {
+                let n = {
+                    let mut iovs = [IoSlice::new(&[]); MAX_WRITEV_BUFS];
+                    let len = self.write_buf.chunks_vectored(&mut iovs);
+                    ready!(Pin::new(&mut self.io).poll_write_vectored(cx, &iovs[..len]))?
+                };
+                // TODO(eliza): we have to do this manually because
+                // `poll_write_buf` doesn't exist in Tokio 0.3 yet...when
+                // `poll_write_buf` comes back, the manual advance will need to leave!
+                self.write_buf.advance(n);
+                debug!("flushed {} bytes", n);
+                if self.write_buf.remaining() == 0 {
+                    break;
+                } else if n == 0 {
+                    trace!(
+                        "write returned zero, but {} bytes remaining",
+                        self.write_buf.remaining()
+                    );
+                    return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
+                }
+            }
+            Pin::new(&mut self.io).poll_flush(cx)
+        }
+    }
+
+    /// Specialized version of `flush` when strategy is Flatten.
+    ///
+    /// Since all buffered bytes are flattened into the single headers buffer,
+    /// that skips some bookkeeping around using multiple buffers.
+    fn poll_flush_flattened(&mut self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        loop {
+            let n = ready!(Pin::new(&mut self.io).poll_write(cx, self.write_buf.headers.chunk()))?;
+            debug!("flushed {} bytes", n);
+            self.write_buf.headers.advance(n);
+            if self.write_buf.headers.remaining() == 0 {
+                self.write_buf.headers.reset();
+                break;
+            } else if n == 0 {
+                trace!(
+                    "write returned zero, but {} bytes remaining",
+                    self.write_buf.remaining()
+                );
+                return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
+            }
+        }
+        Pin::new(&mut self.io).poll_flush(cx)
+    }
+
+    #[cfg(test)]
+    fn flush<'a>(&'a mut self) -> impl std::future::Future<Output = io::Result<()>> + 'a {
+        futures_util::future::poll_fn(move |cx| self.poll_flush(cx))
+    }
+}
+
+// The `B` is a `Buf`, we never project a pin to it
+impl<T: Unpin, B> Unpin for Buffered<T, B> {}
+
+// TODO: This trait is old... at least rename to PollBytes or something...
+pub(crate) trait MemRead {
+    fn read_mem(&mut self, cx: &mut Context<'_>, len: usize) -> Poll<io::Result<Bytes>>;
+}
+
+impl<T, B> MemRead for Buffered<T, B>
+where
+    T: AsyncRead + AsyncWrite + Unpin,
+    B: Buf,
+{
+    fn read_mem(&mut self, cx: &mut Context<'_>, len: usize) -> Poll<io::Result<Bytes>> {
+        if !self.read_buf.is_empty() {
+            let n = std::cmp::min(len, self.read_buf.len());
+            Poll::Ready(Ok(self.read_buf.split_to(n).freeze()))
+        } else {
+            let n = ready!(self.poll_read_from_io(cx))?;
+            Poll::Ready(Ok(self.read_buf.split_to(::std::cmp::min(len, n)).freeze()))
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+enum ReadStrategy {
+    Adaptive {
+        decrease_now: bool,
+        next: usize,
+        max: usize,
+    },
+    #[cfg(feature = "client")]
+    Exact(usize),
+}
+
+impl ReadStrategy {
+    fn with_max(max: usize) -> ReadStrategy {
+        ReadStrategy::Adaptive {
+            decrease_now: false,
+            next: INIT_BUFFER_SIZE,
+            max,
+        }
+    }
+
+    fn next(&self) -> usize {
+        match *self {
+            ReadStrategy::Adaptive { next, .. } => next,
+            #[cfg(feature = "client")]
+            ReadStrategy::Exact(exact) => exact,
+        }
+    }
+
+    fn max(&self) -> usize {
+        match *self {
+            ReadStrategy::Adaptive { max, .. } => max,
+            #[cfg(feature = "client")]
+            ReadStrategy::Exact(exact) => exact,
+        }
+    }
+
+    fn record(&mut self, bytes_read: usize) {
+        match *self {
+            ReadStrategy::Adaptive {
+                ref mut decrease_now,
+                ref mut next,
+                max,
+                ..
+            } => {
+                if bytes_read >= *next {
+                    *next = cmp::min(incr_power_of_two(*next), max);
+                    *decrease_now = false;
+                } else {
+                    let decr_to = prev_power_of_two(*next);
+                    if bytes_read < decr_to {
+                        if *decrease_now {
+                            *next = cmp::max(decr_to, INIT_BUFFER_SIZE);
+                            *decrease_now = false;
+                        } else {
+                            // Decreasing is a two "record" process.
+                            *decrease_now = true;
+                        }
+                    } else {
+                        // A read within the current range should cancel
+                        // a potential decrease, since we just saw proof
+                        // that we still need this size.
+                        *decrease_now = false;
+                    }
+                }
+            }
+            #[cfg(feature = "client")]
+            ReadStrategy::Exact(_) => (),
+        }
+    }
+}
+
+fn incr_power_of_two(n: usize) -> usize {
+    n.saturating_mul(2)
+}
+
+fn prev_power_of_two(n: usize) -> usize {
+    // Only way this shift can underflow is if n is less than 4.
+    // (Which would means `usize::MAX >> 64` and underflowed!)
+    debug_assert!(n >= 4);
+    (::std::usize::MAX >> (n.leading_zeros() + 2)) + 1
+}
+
+impl Default for ReadStrategy {
+    fn default() -> ReadStrategy {
+        ReadStrategy::with_max(DEFAULT_MAX_BUFFER_SIZE)
+    }
+}
+
+#[derive(Clone)]
+pub(crate) struct Cursor<T> {
+    bytes: T,
+    pos: usize,
+}
+
+impl<T: AsRef<[u8]>> Cursor<T> {
+    #[inline]
+    pub(crate) fn new(bytes: T) -> Cursor<T> {
+        Cursor { bytes, pos: 0 }
+    }
+}
+
+impl Cursor<Vec<u8>> {
+    /// If we've advanced the position a bit in this cursor, and wish to
+    /// extend the underlying vector, we may wish to unshift the "read" bytes
+    /// off, and move everything else over.
+    fn maybe_unshift(&mut self, additional: usize) {
+        if self.pos == 0 {
+            // nothing to do
+            return;
+        }
+
+        if self.bytes.capacity() - self.bytes.len() >= additional {
+            // there's room!
+            return;
+        }
+
+        self.bytes.drain(0..self.pos);
+        self.pos = 0;
+    }
+
+    fn reset(&mut self) {
+        self.pos = 0;
+        self.bytes.clear();
+    }
+}
+
+impl<T: AsRef<[u8]>> fmt::Debug for Cursor<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Cursor")
+            .field("pos", &self.pos)
+            .field("len", &self.bytes.as_ref().len())
+            .finish()
+    }
+}
+
+impl<T: AsRef<[u8]>> Buf for Cursor<T> {
+    #[inline]
+    fn remaining(&self) -> usize {
+        self.bytes.as_ref().len() - self.pos
+    }
+
+    #[inline]
+    fn chunk(&self) -> &[u8] {
+        &self.bytes.as_ref()[self.pos..]
+    }
+
+    #[inline]
+    fn advance(&mut self, cnt: usize) {
+        debug_assert!(self.pos + cnt <= self.bytes.as_ref().len());
+        self.pos += cnt;
+    }
+}
+
+// an internal buffer to collect writes before flushes
+pub(super) struct WriteBuf<B> {
+    /// Re-usable buffer that holds message headers
+    headers: Cursor<Vec<u8>>,
+    max_buf_size: usize,
+    /// Deque of user buffers if strategy is Queue
+    queue: BufList<B>,
+    strategy: WriteStrategy,
+}
+
+impl<B: Buf> WriteBuf<B> {
+    fn new(strategy: WriteStrategy) -> WriteBuf<B> {
+        WriteBuf {
+            headers: Cursor::new(Vec::with_capacity(INIT_BUFFER_SIZE)),
+            max_buf_size: DEFAULT_MAX_BUFFER_SIZE,
+            queue: BufList::new(),
+            strategy,
+        }
+    }
+}
+
+impl<B> WriteBuf<B>
+where
+    B: Buf,
+{
+    fn set_strategy(&mut self, strategy: WriteStrategy) {
+        self.strategy = strategy;
+    }
+
+    pub(super) fn buffer<BB: Buf + Into<B>>(&mut self, mut buf: BB) {
+        debug_assert!(buf.has_remaining());
+        match self.strategy {
+            WriteStrategy::Flatten => {
+                let head = self.headers_mut();
+
+                head.maybe_unshift(buf.remaining());
+                trace!(
+                    self.len = head.remaining(),
+                    buf.len = buf.remaining(),
+                    "buffer.flatten"
+                );
+                //perf: This is a little faster than <Vec as BufMut>>::put,
+                //but accomplishes the same result.
+                loop {
+                    let adv = {
+                        let slice = buf.chunk();
+                        if slice.is_empty() {
+                            return;
+                        }
+                        head.bytes.extend_from_slice(slice);
+                        slice.len()
+                    };
+                    buf.advance(adv);
+                }
+            }
+            WriteStrategy::Queue => {
+                trace!(
+                    self.len = self.remaining(),
+                    buf.len = buf.remaining(),
+                    "buffer.queue"
+                );
+                self.queue.push(buf.into());
+            }
+        }
+    }
+
+    fn can_buffer(&self) -> bool {
+        match self.strategy {
+            WriteStrategy::Flatten => self.remaining() < self.max_buf_size,
+            WriteStrategy::Queue => {
+                self.queue.bufs_cnt() < MAX_BUF_LIST_BUFFERS && self.remaining() < self.max_buf_size
+            }
+        }
+    }
+
+    fn headers_mut(&mut self) -> &mut Cursor<Vec<u8>> {
+        debug_assert!(!self.queue.has_remaining());
+        &mut self.headers
+    }
+}
+
+impl<B: Buf> fmt::Debug for WriteBuf<B> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("WriteBuf")
+            .field("remaining", &self.remaining())
+            .field("strategy", &self.strategy)
+            .finish()
+    }
+}
+
+impl<B: Buf> Buf for WriteBuf<B> {
+    #[inline]
+    fn remaining(&self) -> usize {
+        self.headers.remaining() + self.queue.remaining()
+    }
+
+    #[inline]
+    fn chunk(&self) -> &[u8] {
+        let headers = self.headers.chunk();
+        if !headers.is_empty() {
+            headers
+        } else {
+            self.queue.chunk()
+        }
+    }
+
+    #[inline]
+    fn advance(&mut self, cnt: usize) {
+        let hrem = self.headers.remaining();
+
+        match hrem.cmp(&cnt) {
+            cmp::Ordering::Equal => self.headers.reset(),
+            cmp::Ordering::Greater => self.headers.advance(cnt),
+            cmp::Ordering::Less => {
+                let qcnt = cnt - hrem;
+                self.headers.reset();
+                self.queue.advance(qcnt);
+            }
+        }
+    }
+
+    #[inline]
+    fn chunks_vectored<'t>(&'t self, dst: &mut [IoSlice<'t>]) -> usize {
+        let n = self.headers.chunks_vectored(dst);
+        self.queue.chunks_vectored(&mut dst[n..]) + n
+    }
+}
+
+#[derive(Debug)]
+enum WriteStrategy {
+    Flatten,
+    Queue,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::time::Duration;
+
+    use tokio_test::io::Builder as Mock;
+
+    // #[cfg(feature = "nightly")]
+    // use test::Bencher;
+
+    /*
+    impl<T: Read> MemRead for AsyncIo<T> {
+        fn read_mem(&mut self, len: usize) -> Poll<Bytes, io::Error> {
+            let mut v = vec![0; len];
+            let n = try_nb!(self.read(v.as_mut_slice()));
+            Ok(Async::Ready(BytesMut::from(&v[..n]).freeze()))
+        }
+    }
+    */
+
+    #[tokio::test]
+    #[ignore]
+    async fn iobuf_write_empty_slice() {
+        // TODO(eliza): can i have writev back pls T_T
+        // // First, let's just check that the Mock would normally return an
+        // // error on an unexpected write, even if the buffer is empty...
+        // let mut mock = Mock::new().build();
+        // futures_util::future::poll_fn(|cx| {
+        //     Pin::new(&mut mock).poll_write_buf(cx, &mut Cursor::new(&[]))
+        // })
+        // .await
+        // .expect_err("should be a broken pipe");
+
+        // // underlying io will return the logic error upon write,
+        // // so we are testing that the io_buf does not trigger a write
+        // // when there is nothing to flush
+        // let mock = Mock::new().build();
+        // let mut io_buf = Buffered::<_, Cursor<Vec<u8>>>::new(mock);
+        // io_buf.flush().await.expect("should short-circuit flush");
+    }
+
+    #[tokio::test]
+    async fn parse_reads_until_blocked() {
+        use crate::proto::h1::ClientTransaction;
+
+        let _ = pretty_env_logger::try_init();
+        let mock = Mock::new()
+            // Split over multiple reads will read all of it
+            .read(b"HTTP/1.1 200 OK\r\n")
+            .read(b"Server: hyper\r\n")
+            // missing last line ending
+            .wait(Duration::from_secs(1))
+            .build();
+
+        let mut buffered = Buffered::<_, Cursor<Vec<u8>>>::new(mock);
+
+        // We expect a `parse` to be not ready, and so can't await it directly.
+        // Rather, this `poll_fn` will wrap the `Poll` result.
+        futures_util::future::poll_fn(|cx| {
+            let parse_ctx = ParseContext {
+                cached_headers: &mut None,
+                req_method: &mut None,
+                h1_parser_config: Default::default(),
+                #[cfg(feature = "runtime")]
+                h1_header_read_timeout: None,
+                #[cfg(feature = "runtime")]
+                h1_header_read_timeout_fut: &mut None,
+                #[cfg(feature = "runtime")]
+                h1_header_read_timeout_running: &mut false,
+                preserve_header_case: false,
+                #[cfg(feature = "ffi")]
+                preserve_header_order: false,
+                h09_responses: false,
+                #[cfg(feature = "ffi")]
+                on_informational: &mut None,
+                #[cfg(feature = "ffi")]
+                raw_headers: false,
+            };
+            assert!(buffered
+                .parse::<ClientTransaction>(cx, parse_ctx)
+                .is_pending());
+            Poll::Ready(())
+        })
+        .await;
+
+        assert_eq!(
+            buffered.read_buf,
+            b"HTTP/1.1 200 OK\r\nServer: hyper\r\n"[..]
+        );
+    }
+
+    #[test]
+    fn read_strategy_adaptive_increments() {
+        let mut strategy = ReadStrategy::default();
+        assert_eq!(strategy.next(), 8192);
+
+        // Grows if record == next
+        strategy.record(8192);
+        assert_eq!(strategy.next(), 16384);
+
+        strategy.record(16384);
+        assert_eq!(strategy.next(), 32768);
+
+        // Enormous records still increment at same rate
+        strategy.record(::std::usize::MAX);
+        assert_eq!(strategy.next(), 65536);
+
+        let max = strategy.max();
+        while strategy.next() < max {
+            strategy.record(max);
+        }
+
+        assert_eq!(strategy.next(), max, "never goes over max");
+        strategy.record(max + 1);
+        assert_eq!(strategy.next(), max, "never goes over max");
+    }
+
+    #[test]
+    fn read_strategy_adaptive_decrements() {
+        let mut strategy = ReadStrategy::default();
+        strategy.record(8192);
+        assert_eq!(strategy.next(), 16384);
+
+        strategy.record(1);
+        assert_eq!(
+            strategy.next(),
+            16384,
+            "first smaller record doesn't decrement yet"
+        );
+        strategy.record(8192);
+        assert_eq!(strategy.next(), 16384, "record was with range");
+
+        strategy.record(1);
+        assert_eq!(
+            strategy.next(),
+            16384,
+            "in-range record should make this the 'first' again"
+        );
+
+        strategy.record(1);
+        assert_eq!(strategy.next(), 8192, "second smaller record decrements");
+
+        strategy.record(1);
+        assert_eq!(strategy.next(), 8192, "first doesn't decrement");
+        strategy.record(1);
+        assert_eq!(strategy.next(), 8192, "doesn't decrement under minimum");
+    }
+
+    #[test]
+    fn read_strategy_adaptive_stays_the_same() {
+        let mut strategy = ReadStrategy::default();
+        strategy.record(8192);
+        assert_eq!(strategy.next(), 16384);
+
+        strategy.record(8193);
+        assert_eq!(
+            strategy.next(),
+            16384,
+            "first smaller record doesn't decrement yet"
+        );
+
+        strategy.record(8193);
+        assert_eq!(
+            strategy.next(),
+            16384,
+            "with current step does not decrement"
+        );
+    }
+
+    #[test]
+    fn read_strategy_adaptive_max_fuzz() {
+        fn fuzz(max: usize) {
+            let mut strategy = ReadStrategy::with_max(max);
+            while strategy.next() < max {
+                strategy.record(::std::usize::MAX);
+            }
+            let mut next = strategy.next();
+            while next > 8192 {
+                strategy.record(1);
+                strategy.record(1);
+                next = strategy.next();
+                assert!(
+                    next.is_power_of_two(),
+                    "decrement should be powers of two: {} (max = {})",
+                    next,
+                    max,
+                );
+            }
+        }
+
+        let mut max = 8192;
+        while max < std::usize::MAX {
+            fuzz(max);
+            max = (max / 2).saturating_mul(3);
+        }
+        fuzz(::std::usize::MAX);
+    }
+
+    #[test]
+    #[should_panic]
+    #[cfg(debug_assertions)] // needs to trigger a debug_assert
+    fn write_buf_requires_non_empty_bufs() {
+        let mock = Mock::new().build();
+        let mut buffered = Buffered::<_, Cursor<Vec<u8>>>::new(mock);
+
+        buffered.buffer(Cursor::new(Vec::new()));
+    }
+
+    /*
+    TODO: needs tokio_test::io to allow configure write_buf calls
+    #[test]
+    fn write_buf_queue() {
+        let _ = pretty_env_logger::try_init();
+
+        let mock = AsyncIo::new_buf(vec![], 1024);
+        let mut buffered = Buffered::<_, Cursor<Vec<u8>>>::new(mock);
+
+
+        buffered.headers_buf().extend(b"hello ");
+        buffered.buffer(Cursor::new(b"world, ".to_vec()));
+        buffered.buffer(Cursor::new(b"it's ".to_vec()));
+        buffered.buffer(Cursor::new(b"hyper!".to_vec()));
+        assert_eq!(buffered.write_buf.queue.bufs_cnt(), 3);
+        buffered.flush().unwrap();
+
+        assert_eq!(buffered.io, b"hello world, it's hyper!");
+        assert_eq!(buffered.io.num_writes(), 1);
+        assert_eq!(buffered.write_buf.queue.bufs_cnt(), 0);
+    }
+    */
+
+    #[tokio::test]
+    async fn write_buf_flatten() {
+        let _ = pretty_env_logger::try_init();
+
+        let mock = Mock::new().write(b"hello world, it's hyper!").build();
+
+        let mut buffered = Buffered::<_, Cursor<Vec<u8>>>::new(mock);
+        buffered.write_buf.set_strategy(WriteStrategy::Flatten);
+
+        buffered.headers_buf().extend(b"hello ");
+        buffered.buffer(Cursor::new(b"world, ".to_vec()));
+        buffered.buffer(Cursor::new(b"it's ".to_vec()));
+        buffered.buffer(Cursor::new(b"hyper!".to_vec()));
+        assert_eq!(buffered.write_buf.queue.bufs_cnt(), 0);
+
+        buffered.flush().await.expect("flush");
+    }
+
+    #[test]
+    fn write_buf_flatten_partially_flushed() {
+        let _ = pretty_env_logger::try_init();
+
+        let b = |s: &str| Cursor::new(s.as_bytes().to_vec());
+
+        let mut write_buf = WriteBuf::<Cursor<Vec<u8>>>::new(WriteStrategy::Flatten);
+
+        write_buf.buffer(b("hello "));
+        write_buf.buffer(b("world, "));
+
+        assert_eq!(write_buf.chunk(), b"hello world, ");
+
+        // advance most of the way, but not all
+        write_buf.advance(11);
+
+        assert_eq!(write_buf.chunk(), b", ");
+        assert_eq!(write_buf.headers.pos, 11);
+        assert_eq!(write_buf.headers.bytes.capacity(), INIT_BUFFER_SIZE);
+
+        // there's still room in the headers buffer, so just push on the end
+        write_buf.buffer(b("it's hyper!"));
+
+        assert_eq!(write_buf.chunk(), b", it's hyper!");
+        assert_eq!(write_buf.headers.pos, 11);
+
+        let rem1 = write_buf.remaining();
+        let cap = write_buf.headers.bytes.capacity();
+
+        // but when this would go over capacity, don't copy the old bytes
+        write_buf.buffer(Cursor::new(vec![b'X'; cap]));
+        assert_eq!(write_buf.remaining(), cap + rem1);
+        assert_eq!(write_buf.headers.pos, 0);
+    }
+
+    #[tokio::test]
+    async fn write_buf_queue_disable_auto() {
+        let _ = pretty_env_logger::try_init();
+
+        let mock = Mock::new()
+            .write(b"hello ")
+            .write(b"world, ")
+            .write(b"it's ")
+            .write(b"hyper!")
+            .build();
+
+        let mut buffered = Buffered::<_, Cursor<Vec<u8>>>::new(mock);
+        buffered.write_buf.set_strategy(WriteStrategy::Queue);
+
+        // we have 4 buffers, and vec IO disabled, but explicitly said
+        // don't try to auto detect (via setting strategy above)
+
+        buffered.headers_buf().extend(b"hello ");
+        buffered.buffer(Cursor::new(b"world, ".to_vec()));
+        buffered.buffer(Cursor::new(b"it's ".to_vec()));
+        buffered.buffer(Cursor::new(b"hyper!".to_vec()));
+        assert_eq!(buffered.write_buf.queue.bufs_cnt(), 3);
+
+        buffered.flush().await.expect("flush");
+
+        assert_eq!(buffered.write_buf.queue.bufs_cnt(), 0);
+    }
+
+    // #[cfg(feature = "nightly")]
+    // #[bench]
+    // fn bench_write_buf_flatten_buffer_chunk(b: &mut Bencher) {
+    //     let s = "Hello, World!";
+    //     b.bytes = s.len() as u64;
+
+    //     let mut write_buf = WriteBuf::<bytes::Bytes>::new();
+    //     write_buf.set_strategy(WriteStrategy::Flatten);
+    //     b.iter(|| {
+    //         let chunk = bytes::Bytes::from(s);
+    //         write_buf.buffer(chunk);
+    //         ::test::black_box(&write_buf);
+    //         write_buf.headers.bytes.clear();
+    //     })
+    // }
+}
diff --git a/src/proto/h1/mod.rs b/src/proto/h1/mod.rs
new file mode 100644
index 0000000..5a2587a
--- /dev/null
+++ b/src/proto/h1/mod.rs
@@ -0,0 +1,122 @@
+#[cfg(all(feature = "server", feature = "runtime"))]
+use std::{pin::Pin, time::Duration};
+
+use bytes::BytesMut;
+use http::{HeaderMap, Method};
+use httparse::ParserConfig;
+#[cfg(all(feature = "server", feature = "runtime"))]
+use tokio::time::Sleep;
+
+use crate::body::DecodedLength;
+use crate::proto::{BodyLength, MessageHead};
+
+pub(crate) use self::conn::Conn;
+pub(crate) use self::decode::Decoder;
+pub(crate) use self::dispatch::Dispatcher;
+pub(crate) use self::encode::{EncodedBuf, Encoder};
+//TODO: move out of h1::io
+pub(crate) use self::io::MINIMUM_MAX_BUFFER_SIZE;
+
+mod conn;
+mod decode;
+pub(crate) mod dispatch;
+mod encode;
+mod io;
+mod role;
+
+cfg_client! {
+    pub(crate) type ClientTransaction = role::Client;
+}
+
+cfg_server! {
+    pub(crate) type ServerTransaction = role::Server;
+}
+
+pub(crate) trait Http1Transaction {
+    type Incoming;
+    type Outgoing: Default;
+    const LOG: &'static str;
+    fn parse(bytes: &mut BytesMut, ctx: ParseContext<'_>) -> ParseResult<Self::Incoming>;
+    fn encode(enc: Encode<'_, Self::Outgoing>, dst: &mut Vec<u8>) -> crate::Result<Encoder>;
+
+    fn on_error(err: &crate::Error) -> Option<MessageHead<Self::Outgoing>>;
+
+    fn is_client() -> bool {
+        !Self::is_server()
+    }
+
+    fn is_server() -> bool {
+        !Self::is_client()
+    }
+
+    fn should_error_on_parse_eof() -> bool {
+        Self::is_client()
+    }
+
+    fn should_read_first() -> bool {
+        Self::is_server()
+    }
+
+    fn update_date() {}
+}
+
+/// Result newtype for Http1Transaction::parse.
+pub(crate) type ParseResult<T> = Result<Option<ParsedMessage<T>>, crate::error::Parse>;
+
+#[derive(Debug)]
+pub(crate) struct ParsedMessage<T> {
+    head: MessageHead<T>,
+    decode: DecodedLength,
+    expect_continue: bool,
+    keep_alive: bool,
+    wants_upgrade: bool,
+}
+
+pub(crate) struct ParseContext<'a> {
+    cached_headers: &'a mut Option<HeaderMap>,
+    req_method: &'a mut Option<Method>,
+    h1_parser_config: ParserConfig,
+    #[cfg(all(feature = "server", feature = "runtime"))]
+    h1_header_read_timeout: Option<Duration>,
+    #[cfg(all(feature = "server", feature = "runtime"))]
+    h1_header_read_timeout_fut: &'a mut Option<Pin<Box<Sleep>>>,
+    #[cfg(all(feature = "server", feature = "runtime"))]
+    h1_header_read_timeout_running: &'a mut bool,
+    preserve_header_case: bool,
+    #[cfg(feature = "ffi")]
+    preserve_header_order: bool,
+    h09_responses: bool,
+    #[cfg(feature = "ffi")]
+    on_informational: &'a mut Option<crate::ffi::OnInformational>,
+    #[cfg(feature = "ffi")]
+    raw_headers: bool,
+}
+
+/// Passed to Http1Transaction::encode
+pub(crate) struct Encode<'a, T> {
+    head: &'a mut MessageHead<T>,
+    body: Option<BodyLength>,
+    #[cfg(feature = "server")]
+    keep_alive: bool,
+    req_method: &'a mut Option<Method>,
+    title_case_headers: bool,
+}
+
+/// Extra flags that a request "wants", like expect-continue or upgrades.
+#[derive(Clone, Copy, Debug)]
+struct Wants(u8);
+
+impl Wants {
+    const EMPTY: Wants = Wants(0b00);
+    const EXPECT: Wants = Wants(0b01);
+    const UPGRADE: Wants = Wants(0b10);
+
+    #[must_use]
+    fn add(self, other: Wants) -> Wants {
+        Wants(self.0 | other.0)
+    }
+
+    fn contains(&self, other: Wants) -> bool {
+        (self.0 & other.0) == other.0
+    }
+}
diff --git a/src/proto/h1/role.rs b/src/proto/h1/role.rs
new file mode 100644
index 0000000..6252207
--- /dev/null
+++ b/src/proto/h1/role.rs
@@ -0,0 +1,2847 @@
+use std::fmt::{self, Write};
+use std::mem::MaybeUninit;
+
+use bytes::Bytes;
+use bytes::BytesMut;
+#[cfg(feature = "server")]
+use http::header::ValueIter;
+use http::header::{self, Entry, HeaderName, HeaderValue};
+use http::{HeaderMap, Method, StatusCode, Version};
+#[cfg(all(feature = "server", feature = "runtime"))]
+use tokio::time::Instant;
+use tracing::{debug, error, trace, trace_span, warn};
+
+use crate::body::DecodedLength;
+#[cfg(feature = "server")]
+use crate::common::date;
+use crate::error::Parse;
+use crate::ext::HeaderCaseMap;
+#[cfg(feature = "ffi")]
+use crate::ext::OriginalHeaderOrder;
+use crate::headers;
+use crate::proto::h1::{
+    Encode, Encoder, Http1Transaction, ParseContext, ParseResult, ParsedMessage,
+};
+use crate::proto::{BodyLength, MessageHead, RequestHead, RequestLine};
+
+const MAX_HEADERS: usize = 100;
+const AVERAGE_HEADER_SIZE: usize = 30; // totally scientific
+#[cfg(feature = "server")]
+const MAX_URI_LEN: usize = (u16::MAX - 1) as usize;
+
+macro_rules! header_name {
+    ($bytes:expr) => {{
+        {
+            match HeaderName::from_bytes($bytes) {
+                Ok(name) => name,
+                Err(e) => maybe_panic!(e),
+            }
+        }
+    }};
+}
+
+macro_rules! header_value {
+    ($bytes:expr) => {{
+        {
+            unsafe { HeaderValue::from_maybe_shared_unchecked($bytes) }
+        }
+    }};
+}
+
+macro_rules! maybe_panic {
+    ($($arg:tt)*) => ({
+        let _err = ($($arg)*);
+        if cfg!(debug_assertions) {
+            panic!("{:?}", _err);
+        } else {
+            error!("Internal Hyper error, please report {:?}", _err);
+            return Err(Parse::Internal)
+        }
+    })
+}
+
+pub(super) fn parse_headers<T>(
+    bytes: &mut BytesMut,
+    ctx: ParseContext<'_>,
+) -> ParseResult<T::Incoming>
+where
+    T: Http1Transaction,
+{
+    // If the buffer is empty, don't bother entering the span, it's just noise.
+    if bytes.is_empty() {
+        return Ok(None);
+    }
+
+    let span = trace_span!("parse_headers");
+    let _s = span.enter();
+
+    #[cfg(all(feature = "server", feature = "runtime"))]
+    if !*ctx.h1_header_read_timeout_running {
+        if let Some(h1_header_read_timeout) = ctx.h1_header_read_timeout {
+            let deadline = Instant::now() + h1_header_read_timeout;
+            *ctx.h1_header_read_timeout_running = true;
+            match ctx.h1_header_read_timeout_fut {
+                Some(h1_header_read_timeout_fut) => {
+                    debug!("resetting h1 header read timeout timer");
+                    h1_header_read_timeout_fut.as_mut().reset(deadline);
+                }
+                None => {
+                    debug!("setting h1 header read timeout timer");
+                    *ctx.h1_header_read_timeout_fut =
+                        Some(Box::pin(tokio::time::sleep_until(deadline)));
+                }
+            }
+        }
+    }
+
+    T::parse(bytes, ctx)
+}
+
+pub(super) fn encode_headers<T>(
+    enc: Encode<'_, T::Outgoing>,
+    dst: &mut Vec<u8>,
+) -> crate::Result<Encoder>
+where
+    T: Http1Transaction,
+{
+    let span = trace_span!("encode_headers");
+    let _s = span.enter();
+    T::encode(enc, dst)
+}
+
+// There are 2 main roles, Client and Server.
+
+#[cfg(feature = "client")]
+pub(crate) enum Client {}
+
+#[cfg(feature = "server")]
+pub(crate) enum Server {}
+
+#[cfg(feature = "server")]
+impl Http1Transaction for Server {
+    type Incoming = RequestLine;
+    type Outgoing = StatusCode;
+    const LOG: &'static str = "{role=server}";
+
+    fn parse(buf: &mut BytesMut, ctx: ParseContext<'_>) -> ParseResult<RequestLine> {
+        debug_assert!(!buf.is_empty(), "parse called with empty buf");
+
+        let mut keep_alive;
+        let is_http_11;
+        let subject;
+        let version;
+        let len;
+        let headers_len;
+
+        // Unsafe: both headers_indices and headers are using uninitialized memory,
+        // but we *never* read any of it until after httparse has assigned
+        // values into it. By not zeroing out the stack memory, this saves
+        // a good ~5% on pipeline benchmarks.
+        let mut headers_indices: [MaybeUninit<HeaderIndices>; MAX_HEADERS] = unsafe {
+            // SAFETY: We can go safely from MaybeUninit array to array of MaybeUninit
+            MaybeUninit::uninit().assume_init()
+        };
+        {
+            /* SAFETY: it is safe to go from MaybeUninit array to array of MaybeUninit */
+            let mut headers: [MaybeUninit<httparse::Header<'_>>; MAX_HEADERS] =
+                unsafe { MaybeUninit::uninit().assume_init() };
+            trace!(bytes = buf.len(), "Request.parse");
+            let mut req = httparse::Request::new(&mut []);
+            let bytes = buf.as_ref();
+            match req.parse_with_uninit_headers(bytes, &mut headers) {
+                Ok(httparse::Status::Complete(parsed_len)) => {
+                    trace!("Request.parse Complete({})", parsed_len);
+                    len = parsed_len;
+                    let uri = req.path.unwrap();
+                    if uri.len() > MAX_URI_LEN {
+                        return Err(Parse::UriTooLong);
+                    }
+                    subject = RequestLine(
+                        Method::from_bytes(req.method.unwrap().as_bytes())?,
+                        uri.parse()?,
+                    );
+                    version = if req.version.unwrap() == 1 {
+                        keep_alive = true;
+                        is_http_11 = true;
+                        Version::HTTP_11
+                    } else {
+                        keep_alive = false;
+                        is_http_11 = false;
+                        Version::HTTP_10
+                    };
+
+                    record_header_indices(bytes, &req.headers, &mut headers_indices)?;
+                    headers_len = req.headers.len();
+                }
+                Ok(httparse::Status::Partial) => return Ok(None),
+                Err(err) => {
+                    return Err(match err {
+                        // if invalid Token, try to determine if for method or path
+                        httparse::Error::Token => {
+                            if req.method.is_none() {
+                                Parse::Method
+                            } else {
+                                debug_assert!(req.path.is_none());
+                                Parse::Uri
+                            }
+                        }
+                        other => other.into(),
+                    });
+                }
+            }
+        };
+
+        let slice = buf.split_to(len).freeze();
+
+        // According to https://tools.ietf.org/html/rfc7230#section-3.3.3
+        // 1. (irrelevant to Request)
+        // 2. (irrelevant to Request)
+        // 3. Transfer-Encoding: chunked has a chunked body.
+        // 4. If multiple differing Content-Length headers or invalid, close connection.
+        // 5. Content-Length header has a sized body.
+        // 6. Length 0.
+        // 7. (irrelevant to Request)
+
+        let mut decoder = DecodedLength::ZERO;
+        let mut expect_continue = false;
+        let mut con_len = None;
+        let mut is_te = false;
+        let mut is_te_chunked = false;
+        let mut wants_upgrade = subject.0 == Method::CONNECT;
+
+        let mut header_case_map = if ctx.preserve_header_case {
+            Some(HeaderCaseMap::default())
+        } else {
+            None
+        };
+
+        #[cfg(feature = "ffi")]
+        let mut header_order = if ctx.preserve_header_order {
+            Some(OriginalHeaderOrder::default())
+        } else {
+            None
+        };
+
+        let mut headers = ctx.cached_headers.take().unwrap_or_else(HeaderMap::new);
+
+        headers.reserve(headers_len);
+
+        for header in &headers_indices[..headers_len] {
+            // SAFETY: array is valid up to `headers_len`
+            let header = unsafe { &*header.as_ptr() };
+            let name = header_name!(&slice[header.name.0..header.name.1]);
+            let value = header_value!(slice.slice(header.value.0..header.value.1));
+
+            match name {
+                header::TRANSFER_ENCODING => {
+                    // https://tools.ietf.org/html/rfc7230#section-3.3.3
+                    // If Transfer-Encoding header is present, and 'chunked' is
+                    // not the final encoding, and this is a Request, then it is
+                    // malformed. A server should respond with 400 Bad Request.
+                    if !is_http_11 {
+                        debug!("HTTP/1.0 cannot have Transfer-Encoding header");
+                        return Err(Parse::transfer_encoding_unexpected());
+                    }
+                    is_te = true;
+                    if headers::is_chunked_(&value) {
+                        is_te_chunked = true;
+                        decoder = DecodedLength::CHUNKED;
+                    } else {
+                        is_te_chunked = false;
+                    }
+                }
+                header::CONTENT_LENGTH => {
+                    if is_te {
+                        continue;
+                    }
+                    let len = headers::content_length_parse(&value)
+                        .ok_or_else(Parse::content_length_invalid)?;
+                    if let Some(prev) = con_len {
+                        if prev != len {
+                            debug!(
+                                "multiple Content-Length headers with different values: [{}, {}]",
+                                prev, len,
+                            );
+                            return Err(Parse::content_length_invalid());
+                        }
+                        // we don't need to append this secondary length
+                        continue;
+                    }
+                    decoder = DecodedLength::checked_new(len)?;
+                    con_len = Some(len);
+                }
+                header::CONNECTION => {
+                    // keep_alive was previously set to default for Version
+                    if keep_alive {
+                        // HTTP/1.1
+                        keep_alive = !headers::connection_close(&value);
+                    } else {
+                        // HTTP/1.0
+                        keep_alive = headers::connection_keep_alive(&value);
+                    }
+                }
+                header::EXPECT => {
+                    // According to https://datatracker.ietf.org/doc/html/rfc2616#section-14.20
+                    // Comparison of expectation values is case-insensitive for unquoted tokens
+                    // (including the 100-continue token)
+                    expect_continue = value.as_bytes().eq_ignore_ascii_case(b"100-continue");
+                }
+                header::UPGRADE => {
+                    // Upgrades are only allowed with HTTP/1.1
+                    wants_upgrade = is_http_11;
+                }
+
+                _ => (),
+            }
+
+            if let Some(ref mut header_case_map) = header_case_map {
+                header_case_map.append(&name, slice.slice(header.name.0..header.name.1));
+            }
+
+            #[cfg(feature = "ffi")]
+            if let Some(ref mut header_order) = header_order {
+                header_order.append(&name);
+            }
+
+            headers.append(name, value);
+        }
+
+        if is_te && !is_te_chunked {
+            debug!("request with transfer-encoding header, but not chunked, bad request");
+            return Err(Parse::transfer_encoding_invalid());
+        }
+
+        let mut extensions = http::Extensions::default();
+
+        if let Some(header_case_map) = header_case_map {
+            extensions.insert(header_case_map);
+        }
+
+        #[cfg(feature = "ffi")]
+        if let Some(header_order) = header_order {
+            extensions.insert(header_order);
+        }
+
+        *ctx.req_method = Some(subject.0.clone());
+
+        Ok(Some(ParsedMessage {
+            head: MessageHead {
+                version,
+                subject,
+                headers,
+                extensions,
+            },
+            decode: decoder,
+            expect_continue,
+            keep_alive,
+            wants_upgrade,
+        }))
+    }
+
+    fn encode(mut msg: Encode<'_, Self::Outgoing>, dst: &mut Vec<u8>) -> crate::Result<Encoder> {
+        trace!(
+            "Server::encode status={:?}, body={:?}, req_method={:?}",
+            msg.head.subject,
+            msg.body,
+            msg.req_method
+        );
+
+        let mut wrote_len = false;
+
+        // hyper currently doesn't support returning 1xx status codes as a Response
+        // This is because Service only allows returning a single Response, and
+        // so if you try to reply with a e.g. 100 Continue, you have no way of
+        // replying with the latter status code response.
+        let (ret, is_last) = if msg.head.subject == StatusCode::SWITCHING_PROTOCOLS {
+            (Ok(()), true)
+        } else if msg.req_method == &Some(Method::CONNECT) && msg.head.subject.is_success() {
+            // Sending content-length or transfer-encoding header on 2xx response
+            // to CONNECT is forbidden in RFC 7231.
+            wrote_len = true;
+            (Ok(()), true)
+        } else if msg.head.subject.is_informational() {
+            warn!("response with 1xx status code not supported");
+            *msg.head = MessageHead::default();
+            msg.head.subject = StatusCode::INTERNAL_SERVER_ERROR;
+            msg.body = None;
+            (Err(crate::Error::new_user_unsupported_status_code()), true)
+        } else {
+            (Ok(()), !msg.keep_alive)
+        };
+
+        // In some error cases, we don't know about the invalid message until already
+        // pushing some bytes onto the `dst`. In those cases, we don't want to send
+        // the half-pushed message, so rewind to before.
+        let orig_len = dst.len();
+
+        let init_cap = 30 + msg.head.headers.len() * AVERAGE_HEADER_SIZE;
+        dst.reserve(init_cap);
+
+        let custom_reason_phrase = msg.head.extensions.get::<crate::ext::ReasonPhrase>();
+
+        if msg.head.version == Version::HTTP_11
+            && msg.head.subject == StatusCode::OK
+            && custom_reason_phrase.is_none()
+        {
+            extend(dst, b"HTTP/1.1 200 OK\r\n");
+        } else {
+            match msg.head.version {
+                Version::HTTP_10 => extend(dst, b"HTTP/1.0 "),
+                Version::HTTP_11 => extend(dst, b"HTTP/1.1 "),
+                Version::HTTP_2 => {
+                    debug!("response with HTTP2 version coerced to HTTP/1.1");
+                    extend(dst, b"HTTP/1.1 ");
+                }
+                other => panic!("unexpected response version: {:?}", other),
+            }
+
+            extend(dst, msg.head.subject.as_str().as_bytes());
+            extend(dst, b" ");
+
+            if let Some(reason) = custom_reason_phrase {
+                extend(dst, reason.as_bytes());
+            } else {
+                // a reason MUST be written, as many parsers will expect it.
+                extend(
+                    dst,
+                    msg.head
+                        .subject
+                        .canonical_reason()
+                        .unwrap_or("<none>")
+                        .as_bytes(),
+                );
+            }
+
+            extend(dst, b"\r\n");
+        }
+
+        let orig_headers;
+        let extensions = std::mem::take(&mut msg.head.extensions);
+        let orig_headers = match extensions.get::<HeaderCaseMap>() {
+            None if msg.title_case_headers => {
+                orig_headers = HeaderCaseMap::default();
+                Some(&orig_headers)
+            }
+            orig_headers => orig_headers,
+        };
+        let encoder = if let Some(orig_headers) = orig_headers {
+            Self::encode_headers_with_original_case(
+                msg,
+                dst,
+                is_last,
+                orig_len,
+                wrote_len,
+                orig_headers,
+            )?
+        } else {
+            Self::encode_headers_with_lower_case(msg, dst, is_last, orig_len, wrote_len)?
+        };
+
+        ret.map(|()| encoder)
+    }
+
+    fn on_error(err: &crate::Error) -> Option<MessageHead<Self::Outgoing>> {
+        use crate::error::Kind;
+        let status = match *err.kind() {
+            Kind::Parse(Parse::Method)
+            | Kind::Parse(Parse::Header(_))
+            | Kind::Parse(Parse::Uri)
+            | Kind::Parse(Parse::Version) => StatusCode::BAD_REQUEST,
+            Kind::Parse(Parse::TooLarge) => StatusCode::REQUEST_HEADER_FIELDS_TOO_LARGE,
+            Kind::Parse(Parse::UriTooLong) => StatusCode::URI_TOO_LONG,
+            _ => return None,
+        };
+
+        debug!("sending automatic response ({}) for parse error", status);
+        let mut msg = MessageHead::default();
+        msg.subject = status;
+        Some(msg)
+    }
+
+    fn is_server() -> bool {
+        true
+    }
+
+    fn update_date() {
+        date::update();
+    }
+}
+
+#[cfg(feature = "server")]
+impl Server {
+    fn can_have_body(method: &Option<Method>, status: StatusCode) -> bool {
+        Server::can_chunked(method, status)
+    }
+
+    fn can_chunked(method: &Option<Method>, status: StatusCode) -> bool {
+        if method == &Some(Method::HEAD) || method == &Some(Method::CONNECT) && status.is_success()
+        {
+            false
+        } else if status.is_informational() {
+            false
+        } else {
+            match status {
+                StatusCode::NO_CONTENT | StatusCode::NOT_MODIFIED => false,
+                _ => true,
+            }
+        }
+    }
+
+    fn can_have_content_length(method: &Option<Method>, status: StatusCode) -> bool {
+        if status.is_informational() || method == &Some(Method::CONNECT) && status.is_success() {
+            false
+        } else {
+            match status {
+                StatusCode::NO_CONTENT | StatusCode::NOT_MODIFIED => false,
+                _ => true,
+            }
+        }
+    }
+
+    fn can_have_implicit_zero_content_length(method: &Option<Method>, status: StatusCode) -> bool {
+        Server::can_have_content_length(method, status) && method != &Some(Method::HEAD)
+    }
+
+    fn encode_headers_with_lower_case(
+        msg: Encode<'_, StatusCode>,
+        dst: &mut Vec<u8>,
+        is_last: bool,
+        orig_len: usize,
+        wrote_len: bool,
+    ) -> crate::Result<Encoder> {
+        struct LowercaseWriter;
+
+        impl HeaderNameWriter for LowercaseWriter {
+            #[inline]
+            fn write_full_header_line(
+                &mut self,
+                dst: &mut Vec<u8>,
+                line: &str,
+                _: (HeaderName, &str),
+            ) {
+                extend(dst, line.as_bytes())
+            }
+
+            #[inline]
+            fn write_header_name_with_colon(
+                &mut self,
+                dst: &mut Vec<u8>,
+                name_with_colon: &str,
+                _: HeaderName,
+            ) {
+                extend(dst, name_with_colon.as_bytes())
+            }
+
+            #[inline]
+            fn write_header_name(&mut self, dst: &mut Vec<u8>, name: &HeaderName) {
+                extend(dst, name.as_str().as_bytes())
+            }
+        }
+
+        Self::encode_headers(msg, dst, is_last, orig_len, wrote_len, LowercaseWriter)
+    }
+
+    #[cold]
+    #[inline(never)]
+    fn encode_headers_with_original_case(
+        msg: Encode<'_, StatusCode>,
+        dst: &mut Vec<u8>,
+        is_last: bool,
+        orig_len: usize,
+        wrote_len: bool,
+        orig_headers: &HeaderCaseMap,
+    ) -> crate::Result<Encoder> {
+        struct OrigCaseWriter<'map> {
+            map: &'map HeaderCaseMap,
+            current: Option<(HeaderName, ValueIter<'map, Bytes>)>,
+            title_case_headers: bool,
+        }
+
+        impl HeaderNameWriter for OrigCaseWriter<'_> {
+            #[inline]
+            fn write_full_header_line(
+                &mut self,
+                dst: &mut Vec<u8>,
+                _: &str,
+                (name, rest): (HeaderName, &str),
+            ) {
+                self.write_header_name(dst, &name);
+                extend(dst, rest.as_bytes());
+            }
+
+            #[inline]
+            fn write_header_name_with_colon(
+                &mut self,
+                dst: &mut Vec<u8>,
+                _: &str,
+                name: HeaderName,
+            ) {
+                self.write_header_name(dst, &name);
+                extend(dst, b": ");
+            }
+
+            #[inline]
+            fn write_header_name(&mut self, dst: &mut Vec<u8>, name: &HeaderName) {
+                let Self {
+                    map,
+                    ref mut current,
+                    title_case_headers,
+                } = *self;
+                if current.as_ref().map_or(true, |(last, _)| last != name) {
+                    *current = None;
+                }
+                let (_, values) =
+                    current.get_or_insert_with(|| (name.clone(), map.get_all_internal(name)));
+
+                if let Some(orig_name) = values.next() {
+                    extend(dst, orig_name);
+                } else if title_case_headers {
+                    title_case(dst, name.as_str().as_bytes());
+                } else {
+                    extend(dst, name.as_str().as_bytes());
+                }
+            }
+        }
+
+        let header_name_writer = OrigCaseWriter {
+            map: orig_headers,
+            current: None,
+            title_case_headers: msg.title_case_headers,
+        };
+
+        Self::encode_headers(msg, dst, is_last, orig_len, wrote_len, header_name_writer)
+    }
+
+    #[inline]
+    fn encode_headers<W>(
+        msg: Encode<'_, StatusCode>,
+        dst: &mut Vec<u8>,
+        mut is_last: bool,
+        orig_len: usize,
+        mut wrote_len: bool,
+        mut header_name_writer: W,
+    ) -> crate::Result<Encoder>
+    where
+        W: HeaderNameWriter,
+    {
+        // In some error cases, we don't know about the invalid message until already
+        // pushing some bytes onto the `dst`. In those cases, we don't want to send
+        // the half-pushed message, so rewind to before.
+        let rewind = |dst: &mut Vec<u8>| {
+            dst.truncate(orig_len);
+        };
+
+        let mut encoder = Encoder::length(0);
+        let mut wrote_date = false;
+        let mut cur_name = None;
+        let mut is_name_written = false;
+        let mut must_write_chunked = false;
+        let mut prev_con_len = None;
+
+        macro_rules! handle_is_name_written {
+            () => {{
+                if is_name_written {
+                    // we need to clean up and write the newline
+                    debug_assert_ne!(
+                        &dst[dst.len() - 2..],
+                        b"\r\n",
+                        "previous header wrote newline but set is_name_written"
+                    );
+
+                    if must_write_chunked {
+                        extend(dst, b", chunked\r\n");
+                    } else {
+                        extend(dst, b"\r\n");
+                    }
+                }
+            }};
+        }
+
+        'headers: for (opt_name, value) in msg.head.headers.drain() {
+            if let Some(n) = opt_name {
+                cur_name = Some(n);
+                handle_is_name_written!();
+                is_name_written = false;
+            }
+            let name = cur_name.as_ref().expect("current header name");
+            match *name {
+                header::CONTENT_LENGTH => {
+                    if wrote_len && !is_name_written {
+                        warn!("unexpected content-length found, canceling");
+                        rewind(dst);
+                        return Err(crate::Error::new_user_header());
+                    }
+                    match msg.body {
+                        Some(BodyLength::Known(known_len)) => {
+                            // The HttpBody claims to know a length, and
+                            // the headers are already set. For performance
+                            // reasons, we are just going to trust that
+                            // the values match.
+                            //
+                            // In debug builds, we'll assert they are the
+                            // same to help developers find bugs.
+                            #[cfg(debug_assertions)]
+                            {
+                                if let Some(len) = headers::content_length_parse(&value) {
+                                    assert!(
+                                        len == known_len,
+                                        "payload claims content-length of {}, custom content-length header claims {}",
+                                        known_len,
+                                        len,
+                                    );
+                                }
+                            }
+
+                            if !is_name_written {
+                                encoder = Encoder::length(known_len);
+                                header_name_writer.write_header_name_with_colon(
+                                    dst,
+                                    "content-length: ",
+                                    header::CONTENT_LENGTH,
+                                );
+                                extend(dst, value.as_bytes());
+                                wrote_len = true;
+                                is_name_written = true;
+                            }
+                            continue 'headers;
+                        }
+                        Some(BodyLength::Unknown) => {
+                            // The HttpBody impl didn't know how long the
+                            // body is, but a length header was included.
+                            // We have to parse the value to return our
+                            // Encoder...
+
+                            if let Some(len) = headers::content_length_parse(&value) {
+                                if let Some(prev) = prev_con_len {
+                                    if prev != len {
+                                        warn!(
+                                            "multiple Content-Length values found: [{}, {}]",
+                                            prev, len
+                                        );
+                                        rewind(dst);
+                                        return Err(crate::Error::new_user_header());
+                                    }
+                                    debug_assert!(is_name_written);
+                                    continue 'headers;
+                                } else {
+                                    // we haven't written content-length yet!
+                                    encoder = Encoder::length(len);
+                                    header_name_writer.write_header_name_with_colon(
+                                        dst,
+                                        "content-length: ",
+                                        header::CONTENT_LENGTH,
+                                    );
+                                    extend(dst, value.as_bytes());
+                                    wrote_len = true;
+                                    is_name_written = true;
+                                    prev_con_len = Some(len);
+                                    continue 'headers;
+                                }
+                            } else {
+                                warn!("illegal Content-Length value: {:?}", value);
+                                rewind(dst);
+                                return Err(crate::Error::new_user_header());
+                            }
+                        }
+                        None => {
+                            // We have no body to actually send,
+                            // but the headers claim a content-length.
+                            // There's only 2 ways this makes sense:
+                            //
+                            // - The header says the length is `0`.
+                            // - This is a response to a `HEAD` request.
+                            if msg.req_method == &Some(Method::HEAD) {
+                                debug_assert_eq!(encoder, Encoder::length(0));
+                            } else {
+                                if value.as_bytes() != b"0" {
+                                    warn!(
+                                        "content-length value found, but empty body provided: {:?}",
+                                        value
+                                    );
+                                }
+                                continue 'headers;
+                            }
+                        }
+                    }
+                    wrote_len = true;
+                }
+                header::TRANSFER_ENCODING => {
+                    if wrote_len && !is_name_written {
+                        warn!("unexpected transfer-encoding found, canceling");
+                        rewind(dst);
+                        return Err(crate::Error::new_user_header());
+                    }
+                    // check that we actually can send a chunked body...
+                    if msg.head.version == Version::HTTP_10
+                        || !Server::can_chunked(msg.req_method, msg.head.subject)
+                    {
+                        continue;
+                    }
+                    wrote_len = true;
+                    // Must check each value, because `chunked` needs to be the
+                    // last encoding, or else we add it.
+                    must_write_chunked = !headers::is_chunked_(&value);
+
+                    if !is_name_written {
+                        encoder = Encoder::chunked();
+                        is_name_written = true;
+                        header_name_writer.write_header_name_with_colon(
+                            dst,
+                            "transfer-encoding: ",
+                            header::TRANSFER_ENCODING,
+                        );
+                        extend(dst, value.as_bytes());
+                    } else {
+                        extend(dst, b", ");
+                        extend(dst, value.as_bytes());
+                    }
+                    continue 'headers;
+                }
+                header::CONNECTION => {
+                    if !is_last && headers::connection_close(&value) {
+                        is_last = true;
+                    }
+                    if !is_name_written {
+                        is_name_written = true;
+                        header_name_writer.write_header_name_with_colon(
+                            dst,
+                            "connection: ",
+                            header::CONNECTION,
+                        );
+                        extend(dst, value.as_bytes());
+                    } else {
+                        extend(dst, b", ");
+                        extend(dst, value.as_bytes());
+                    }
+                    continue 'headers;
+                }
+                header::DATE => {
+                    wrote_date = true;
+                }
+                _ => (),
+            }
+            //TODO: this should perhaps instead combine them into
+            //single lines, as RFC7230 suggests is preferable.
+
+            // non-special write Name and Value
+            debug_assert!(
+                !is_name_written,
+                "{:?} set is_name_written and didn't continue loop",
+                name,
+            );
+            header_name_writer.write_header_name(dst, name);
+            extend(dst, b": ");
+            extend(dst, value.as_bytes());
+            extend(dst, b"\r\n");
+        }
+
+        handle_is_name_written!();
+
+        if !wrote_len {
+            encoder = match msg.body {
+                Some(BodyLength::Unknown) => {
+                    if msg.head.version == Version::HTTP_10
+                        || !Server::can_chunked(msg.req_method, msg.head.subject)
+                    {
+                        Encoder::close_delimited()
+                    } else {
+                        header_name_writer.write_full_header_line(
+                            dst,
+                            "transfer-encoding: chunked\r\n",
+                            (header::TRANSFER_ENCODING, ": chunked\r\n"),
+                        );
+                        Encoder::chunked()
+                    }
+                }
+                None | Some(BodyLength::Known(0)) => {
+                    if Server::can_have_implicit_zero_content_length(
+                        msg.req_method,
+                        msg.head.subject,
+                    ) {
+                        header_name_writer.write_full_header_line(
+                            dst,
+                            "content-length: 0\r\n",
+                            (header::CONTENT_LENGTH, ": 0\r\n"),
+                        )
+                    }
+                    Encoder::length(0)
+                }
+                Some(BodyLength::Known(len)) => {
+                    if !Server::can_have_content_length(msg.req_method, msg.head.subject) {
+                        Encoder::length(0)
+                    } else {
+                        header_name_writer.write_header_name_with_colon(
+                            dst,
+                            "content-length: ",
+                            header::CONTENT_LENGTH,
+                        );
+                        extend(dst, ::itoa::Buffer::new().format(len).as_bytes());
+                        extend(dst, b"\r\n");
+                        Encoder::length(len)
+                    }
+                }
+            };
+        }
+
+        if !Server::can_have_body(msg.req_method, msg.head.subject) {
+            trace!(
+                "server body forced to 0; method={:?}, status={:?}",
+                msg.req_method,
+                msg.head.subject
+            );
+            encoder = Encoder::length(0);
+        }
+
+        // cached date is much faster than formatting every request
+        if !wrote_date {
+            dst.reserve(date::DATE_VALUE_LENGTH + 8);
+            header_name_writer.write_header_name_with_colon(dst, "date: ", header::DATE);
+            date::extend(dst);
+            extend(dst, b"\r\n\r\n");
+        } else {
+            extend(dst, b"\r\n");
+        }
+
+        Ok(encoder.set_last(is_last))
+    }
+}
+
+#[cfg(feature = "server")]
+trait HeaderNameWriter {
+    fn write_full_header_line(
+        &mut self,
+        dst: &mut Vec<u8>,
+        line: &str,
+        name_value_pair: (HeaderName, &str),
+    );
+    fn write_header_name_with_colon(
+        &mut self,
+        dst: &mut Vec<u8>,
+        name_with_colon: &str,
+        name: HeaderName,
+    );
+    fn write_header_name(&mut self, dst: &mut Vec<u8>, name: &HeaderName);
+}
+
+#[cfg(feature = "client")]
+impl Http1Transaction for Client {
+    type Incoming = StatusCode;
+    type Outgoing = RequestLine;
+    const LOG: &'static str = "{role=client}";
+
+    fn parse(buf: &mut BytesMut, ctx: ParseContext<'_>) -> ParseResult<StatusCode> {
+        debug_assert!(!buf.is_empty(), "parse called with empty buf");
+
+        // Loop to skip information status code headers (100 Continue, etc).
+        loop {
+            // Unsafe: see comment in Server Http1Transaction, above.
+            let mut headers_indices: [MaybeUninit<HeaderIndices>; MAX_HEADERS] = unsafe {
+                // SAFETY: We can go safely from MaybeUninit array to array of MaybeUninit
+                MaybeUninit::uninit().assume_init()
+            };
+            let (len, status, reason, version, headers_len) = {
+                // SAFETY: We can go safely from MaybeUninit array to array of MaybeUninit
+                let mut headers: [MaybeUninit<httparse::Header<'_>>; MAX_HEADERS] =
+                    unsafe { MaybeUninit::uninit().assume_init() };
+                trace!(bytes = buf.len(), "Response.parse");
+                let mut res = httparse::Response::new(&mut []);
+                let bytes = buf.as_ref();
+                match ctx.h1_parser_config.parse_response_with_uninit_headers(
+                    &mut res,
+                    bytes,
+                    &mut headers,
+                ) {
+                    Ok(httparse::Status::Complete(len)) => {
+                        trace!("Response.parse Complete({})", len);
+                        let status = StatusCode::from_u16(res.code.unwrap())?;
+
+                        let reason = {
+                            let reason = res.reason.unwrap();
+                            // Only save the reason phrase if it isn't the canonical reason
+                            if Some(reason) != status.canonical_reason() {
+                                Some(Bytes::copy_from_slice(reason.as_bytes()))
+                            } else {
+                                None
+                            }
+                        };
+
+                        let version = if res.version.unwrap() == 1 {
+                            Version::HTTP_11
+                        } else {
+                            Version::HTTP_10
+                        };
+                        record_header_indices(bytes, &res.headers, &mut headers_indices)?;
+                        let headers_len = res.headers.len();
+                        (len, status, reason, version, headers_len)
+                    }
+                    Ok(httparse::Status::Partial) => return Ok(None),
+                    Err(httparse::Error::Version) if ctx.h09_responses => {
+                        trace!("Response.parse accepted HTTP/0.9 response");
+
+                        (0, StatusCode::OK, None, Version::HTTP_09, 0)
+                    }
+                    Err(e) => return Err(e.into()),
+                }
+            };
+
+            let mut slice = buf.split_to(len);
+
+            if ctx
+                .h1_parser_config
+                .obsolete_multiline_headers_in_responses_are_allowed()
+            {
+                for header in &headers_indices[..headers_len] {
+                    // SAFETY: array is valid up to `headers_len`
+                    let header = unsafe { &*header.as_ptr() };
+                    for b in &mut slice[header.value.0..header.value.1] {
+                        if *b == b'\r' || *b == b'\n' {
+                            *b = b' ';
+                        }
+                    }
+                }
+            }
+
+            let slice = slice.freeze();
+
+            let mut headers = ctx.cached_headers.take().unwrap_or_else(HeaderMap::new);
+
+            let mut keep_alive = version == Version::HTTP_11;
+
+            let mut header_case_map = if ctx.preserve_header_case {
+                Some(HeaderCaseMap::default())
+            } else {
+                None
+            };
+
+            #[cfg(feature = "ffi")]
+            let mut header_order = if ctx.preserve_header_order {
+                Some(OriginalHeaderOrder::default())
+            } else {
+                None
+            };
+
+            headers.reserve(headers_len);
+            for header in &headers_indices[..headers_len] {
+                // SAFETY: array is valid up to `headers_len`
+                let header = unsafe { &*header.as_ptr() };
+                let name = header_name!(&slice[header.name.0..header.name.1]);
+                let value = header_value!(slice.slice(header.value.0..header.value.1));
+
+                if let header::CONNECTION = name {
+                    // keep_alive was previously set to default for Version
+                    if keep_alive {
+                        // HTTP/1.1
+                        keep_alive = !headers::connection_close(&value);
+                    } else {
+                        // HTTP/1.0
+                        keep_alive = headers::connection_keep_alive(&value);
+                    }
+                }
+
+                if let Some(ref mut header_case_map) = header_case_map {
+                    header_case_map.append(&name, slice.slice(header.name.0..header.name.1));
+                }
+
+                #[cfg(feature = "ffi")]
+                if let Some(ref mut header_order) = header_order {
+                    header_order.append(&name);
+                }
+
+                headers.append(name, value);
+            }
+
+            let mut extensions = http::Extensions::default();
+
+            if let Some(header_case_map) = header_case_map {
+                extensions.insert(header_case_map);
+            }
+
+            #[cfg(feature = "ffi")]
+            if let Some(header_order) = header_order {
+                extensions.insert(header_order);
+            }
+
+            if let Some(reason) = reason {
+                // Safety: httparse ensures that only valid reason phrase bytes are present in this
+                // field.
+                let reason = unsafe { crate::ext::ReasonPhrase::from_bytes_unchecked(reason) };
+                extensions.insert(reason);
+            }
+
+            #[cfg(feature = "ffi")]
+            if ctx.raw_headers {
+                extensions.insert(crate::ffi::RawHeaders(crate::ffi::hyper_buf(slice)));
+            }
+
+            let head = MessageHead {
+                version,
+                subject: status,
+                headers,
+                extensions,
+            };
+            if let Some((decode, is_upgrade)) = Client::decoder(&head, ctx.req_method)? {
+                return Ok(Some(ParsedMessage {
+                    head,
+                    decode,
+                    expect_continue: false,
+                    // a client upgrade means the connection can't be used
+                    // again, as it is definitely upgrading.
+                    keep_alive: keep_alive && !is_upgrade,
+                    wants_upgrade: is_upgrade,
+                }));
+            }
+
+            #[cfg(feature = "ffi")]
+            if head.subject.is_informational() {
+                if let Some(callback) = ctx.on_informational {
+                    callback.call(head.into_response(crate::Body::empty()));
+                }
+            }
+
+            // Parsing a 1xx response could have consumed the buffer, check if
+            // it is empty now...
+            if buf.is_empty() {
+                return Ok(None);
+            }
+        }
+    }
+
+    fn encode(msg: Encode<'_, Self::Outgoing>, dst: &mut Vec<u8>) -> crate::Result<Encoder> {
+        trace!(
+            "Client::encode method={:?}, body={:?}",
+            msg.head.subject.0,
+            msg.body
+        );
+
+        *msg.req_method = Some(msg.head.subject.0.clone());
+
+        let body = Client::set_length(msg.head, msg.body);
+
+        let init_cap = 30 + msg.head.headers.len() * AVERAGE_HEADER_SIZE;
+        dst.reserve(init_cap);
+
+        extend(dst, msg.head.subject.0.as_str().as_bytes());
+        extend(dst, b" ");
+        //TODO: add API to http::Uri to encode without std::fmt
+        let _ = write!(FastWrite(dst), "{} ", msg.head.subject.1);
+
+        match msg.head.version {
+            Version::HTTP_10 => extend(dst, b"HTTP/1.0"),
+            Version::HTTP_11 => extend(dst, b"HTTP/1.1"),
+            Version::HTTP_2 => {
+                debug!("request with HTTP2 version coerced to HTTP/1.1");
+                extend(dst, b"HTTP/1.1");
+            }
+            other => panic!("unexpected request version: {:?}", other),
+        }
+        extend(dst, b"\r\n");
+
+        if let Some(orig_headers) = msg.head.extensions.get::<HeaderCaseMap>() {
+            write_headers_original_case(
+                &msg.head.headers,
+                orig_headers,
+                dst,
+                msg.title_case_headers,
+            );
+        } else if msg.title_case_headers {
+            write_headers_title_case(&msg.head.headers, dst);
+        } else {
+            write_headers(&msg.head.headers, dst);
+        }
+
+        extend(dst, b"\r\n");
+        msg.head.headers.clear(); //TODO: remove when switching to drain()
+
+        Ok(body)
+    }
+
+    fn on_error(_err: &crate::Error) -> Option<MessageHead<Self::Outgoing>> {
+        // we can't tell the server about any errors it creates
+        None
+    }
+
+    fn is_client() -> bool {
+        true
+    }
+}
+
+#[cfg(feature = "client")]
+impl Client {
+    /// Returns Some(length, wants_upgrade) if successful.
+    ///
+    /// Returns None if this message head should be skipped (like a 100 status).
+    fn decoder(
+        inc: &MessageHead<StatusCode>,
+        method: &mut Option<Method>,
+    ) -> Result<Option<(DecodedLength, bool)>, Parse> {
+        // According to https://tools.ietf.org/html/rfc7230#section-3.3.3
+        // 1. HEAD responses, and Status 1xx, 204, and 304 cannot have a body.
+        // 2. Status 2xx to a CONNECT cannot have a body.
+        // 3. Transfer-Encoding: chunked has a chunked body.
+        // 4. If multiple differing Content-Length headers or invalid, close connection.
+        // 5. Content-Length header has a sized body.
+        // 6. (irrelevant to Response)
+        // 7. Read till EOF.
+
+        match inc.subject.as_u16() {
+            101 => {
+                return Ok(Some((DecodedLength::ZERO, true)));
+            }
+            100 | 102..=199 => {
+                trace!("ignoring informational response: {}", inc.subject.as_u16());
+                return Ok(None);
+            }
+            204 | 304 => return Ok(Some((DecodedLength::ZERO, false))),
+            _ => (),
+        }
+        match *method {
+            Some(Method::HEAD) => {
+                return Ok(Some((DecodedLength::ZERO, false)));
+            }
+            Some(Method::CONNECT) => {
+                if let 200..=299 = inc.subject.as_u16() {
+                    return Ok(Some((DecodedLength::ZERO, true)));
+                }
+            }
+            Some(_) => {}
+            None => {
+                trace!("Client::decoder is missing the Method");
+            }
+        }
+
+        if inc.headers.contains_key(header::TRANSFER_ENCODING) {
+            // https://tools.ietf.org/html/rfc7230#section-3.3.3
+            // If Transfer-Encoding header is present, and 'chunked' is
+            // not the final encoding, and this is a Request, then it is
+            // malformed. A server should respond with 400 Bad Request.
+            if inc.version == Version::HTTP_10 {
+                debug!("HTTP/1.0 cannot have Transfer-Encoding header");
+                Err(Parse::transfer_encoding_unexpected())
+            } else if headers::transfer_encoding_is_chunked(&inc.headers) {
+                Ok(Some((DecodedLength::CHUNKED, false)))
+            } else {
+                trace!("not chunked, read till eof");
+                Ok(Some((DecodedLength::CLOSE_DELIMITED, false)))
+            }
+        } else if let Some(len) = headers::content_length_parse_all(&inc.headers) {
+            Ok(Some((DecodedLength::checked_new(len)?, false)))
+        } else if inc.headers.contains_key(header::CONTENT_LENGTH) {
+            debug!("illegal Content-Length header");
+            Err(Parse::content_length_invalid())
+        } else {
+            trace!("neither Transfer-Encoding nor Content-Length");
+            Ok(Some((DecodedLength::CLOSE_DELIMITED, false)))
+        }
+    }
+    fn set_length(head: &mut RequestHead, body: Option<BodyLength>) -> Encoder {
+        let body = if let Some(body) = body {
+            body
+        } else {
+            head.headers.remove(header::TRANSFER_ENCODING);
+            return Encoder::length(0);
+        };
+
+        // HTTP/1.0 doesn't know about chunked
+        let can_chunked = head.version == Version::HTTP_11;
+        let headers = &mut head.headers;
+
+        // If the user already set specific headers, we should respect them, regardless
+        // of what the HttpBody knows about itself. They set them for a reason.
+
+        // Because of the borrow checker, we can't check the for an existing
+        // Content-Length header while holding an `Entry` for the Transfer-Encoding
+        // header, so unfortunately, we must do the check here, first.
+
+        let existing_con_len = headers::content_length_parse_all(headers);
+        let mut should_remove_con_len = false;
+
+        if !can_chunked {
+            // Chunked isn't legal, so if it is set, we need to remove it.
+            if headers.remove(header::TRANSFER_ENCODING).is_some() {
+                trace!("removing illegal transfer-encoding header");
+            }
+
+            return if let Some(len) = existing_con_len {
+                Encoder::length(len)
+            } else if let BodyLength::Known(len) = body {
+                set_content_length(headers, len)
+            } else {
+                // HTTP/1.0 client requests without a content-length
+                // cannot have any body at all.
+                Encoder::length(0)
+            };
+        }
+
+        // If the user set a transfer-encoding, respect that. Let's just
+        // make sure `chunked` is the final encoding.
+        let encoder = match headers.entry(header::TRANSFER_ENCODING) {
+            Entry::Occupied(te) => {
+                should_remove_con_len = true;
+                if headers::is_chunked(te.iter()) {
+                    Some(Encoder::chunked())
+                } else {
+                    warn!("user provided transfer-encoding does not end in 'chunked'");
+
+                    // There's a Transfer-Encoding, but it doesn't end in 'chunked'!
+                    // An example that could trigger this:
+                    //
+                    //     Transfer-Encoding: gzip
+                    //
+                    // This can be bad, depending on if this is a request or a
+                    // response.
+                    //
+                    // - A request is illegal if there is a `Transfer-Encoding`
+                    //   but it doesn't end in `chunked`.
+                    // - A response that has `Transfer-Encoding` but doesn't
+                    //   end in `chunked` isn't illegal, it just forces this
+                    //   to be close-delimited.
+                    //
+                    // We can try to repair this, by adding `chunked` ourselves.
+
+                    headers::add_chunked(te);
+                    Some(Encoder::chunked())
+                }
+            }
+            Entry::Vacant(te) => {
+                if let Some(len) = existing_con_len {
+                    Some(Encoder::length(len))
+                } else if let BodyLength::Unknown = body {
+                    // GET, HEAD, and CONNECT almost never have bodies.
+                    //
+                    // So instead of sending a "chunked" body with a 0-chunk,
+                    // assume no body here. If you *must* send a body,
+                    // set the headers explicitly.
+                    match head.subject.0 {
+                        Method::GET | Method::HEAD | Method::CONNECT => Some(Encoder::length(0)),
+                        _ => {
+                            te.insert(HeaderValue::from_static("chunked"));
+                            Some(Encoder::chunked())
+                        }
+                    }
+                } else {
+                    None
+                }
+            }
+        };
+
+        // This is because we need a second mutable borrow to remove
+        // content-length header.
+        if let Some(encoder) = encoder {
+            if should_remove_con_len && existing_con_len.is_some() {
+                headers.remove(header::CONTENT_LENGTH);
+            }
+            return encoder;
+        }
+
+        // User didn't set transfer-encoding, AND we know body length,
+        // so we can just set the Content-Length automatically.
+
+        let len = if let BodyLength::Known(len) = body {
+            len
+        } else {
+            unreachable!("BodyLength::Unknown would set chunked");
+        };
+
+        set_content_length(headers, len)
+    }
+}
+
+fn set_content_length(headers: &mut HeaderMap, len: u64) -> Encoder {
+    // At this point, there should not be a valid Content-Length
+    // header. However, since we'll be indexing in anyways, we can
+    // warn the user if there was an existing illegal header.
+    //
+    // Or at least, we can in theory. It's actually a little bit slower,
+    // so perhaps only do that while the user is developing/testing.
+
+    if cfg!(debug_assertions) {
+        match headers.entry(header::CONTENT_LENGTH) {
+            Entry::Occupied(mut cl) => {
+                // Internal sanity check, we should have already determined
+                // that the header was illegal before calling this function.
+                debug_assert!(headers::content_length_parse_all_values(cl.iter()).is_none());
+                // Uh oh, the user set `Content-Length` headers, but set bad ones.
+                // This would be an illegal message anyways, so let's try to repair
+                // with our known good length.
+                error!("user provided content-length header was invalid");
+
+                cl.insert(HeaderValue::from(len));
+                Encoder::length(len)
+            }
+            Entry::Vacant(cl) => {
+                cl.insert(HeaderValue::from(len));
+                Encoder::length(len)
+            }
+        }
+    } else {
+        headers.insert(header::CONTENT_LENGTH, HeaderValue::from(len));
+        Encoder::length(len)
+    }
+}
+
+#[derive(Clone, Copy)]
+struct HeaderIndices {
+    name: (usize, usize),
+    value: (usize, usize),
+}
+
+fn record_header_indices(
+    bytes: &[u8],
+    headers: &[httparse::Header<'_>],
+    indices: &mut [MaybeUninit<HeaderIndices>],
+) -> Result<(), crate::error::Parse> {
+    let bytes_ptr = bytes.as_ptr() as usize;
+
+    for (header, indices) in headers.iter().zip(indices.iter_mut()) {
+        if header.name.len() >= (1 << 16) {
+            debug!("header name larger than 64kb: {:?}", header.name);
+            return Err(crate::error::Parse::TooLarge);
+        }
+        let name_start = header.name.as_ptr() as usize - bytes_ptr;
+        let name_end = name_start + header.name.len();
+        let value_start = header.value.as_ptr() as usize - bytes_ptr;
+        let value_end = value_start + header.value.len();
+
+        // FIXME(maybe_uninit_extra)
+        // FIXME(addr_of)
+        // Currently we don't have `ptr::addr_of_mut` in stable rust or
+        // MaybeUninit::write, so this is some way of assigning into a MaybeUninit
+        // safely
+        let new_header_indices = HeaderIndices {
+            name: (name_start, name_end),
+            value: (value_start, value_end),
+        };
+        *indices = MaybeUninit::new(new_header_indices);
+    }
+
+    Ok(())
+}
+
+// Write header names as title case. The header name is assumed to be ASCII.
+fn title_case(dst: &mut Vec<u8>, name: &[u8]) {
+    dst.reserve(name.len());
+
+    // Ensure first character is uppercased
+    let mut prev = b'-';
+    for &(mut c) in name {
+        if prev == b'-' {
+            c.make_ascii_uppercase();
+        }
+        dst.push(c);
+        prev = c;
+    }
+}
+
+fn write_headers_title_case(headers: &HeaderMap, dst: &mut Vec<u8>) {
+    for (name, value) in headers {
+        title_case(dst, name.as_str().as_bytes());
+        extend(dst, b": ");
+        extend(dst, value.as_bytes());
+        extend(dst, b"\r\n");
+    }
+}
+
+fn write_headers(headers: &HeaderMap, dst: &mut Vec<u8>) {
+    for (name, value) in headers {
+        extend(dst, name.as_str().as_bytes());
+        extend(dst, b": ");
+        extend(dst, value.as_bytes());
+        extend(dst, b"\r\n");
+    }
+}
+
+#[cold]
+fn write_headers_original_case(
+    headers: &HeaderMap,
+    orig_case: &HeaderCaseMap,
+    dst: &mut Vec<u8>,
+    title_case_headers: bool,
+) {
+    // For each header name/value pair, there may be a value in the casemap
+    // that corresponds to the HeaderValue. So, we iterator all the keys,
+    // and for each one, try to pair the originally cased name with the value.
+    //
+    // TODO: consider adding http::HeaderMap::entries() iterator
+    for name in headers.keys() {
+        let mut names = orig_case.get_all(name);
+
+        for value in headers.get_all(name) {
+            if let Some(orig_name) = names.next() {
+                extend(dst, orig_name.as_ref());
+            } else if title_case_headers {
+                title_case(dst, name.as_str().as_bytes());
+            } else {
+                extend(dst, name.as_str().as_bytes());
+            }
+
+            // Wanted for curl test cases that send `X-Custom-Header:\r\n`
+            if value.is_empty() {
+                extend(dst, b":\r\n");
+            } else {
+                extend(dst, b": ");
+                extend(dst, value.as_bytes());
+                extend(dst, b"\r\n");
+            }
+        }
+    }
+}
+
+struct FastWrite<'a>(&'a mut Vec<u8>);
+
+impl<'a> fmt::Write for FastWrite<'a> {
+    #[inline]
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        extend(self.0, s.as_bytes());
+        Ok(())
+    }
+
+    #[inline]
+    fn write_fmt(&mut self, args: fmt::Arguments<'_>) -> fmt::Result {
+        fmt::write(self, args)
+    }
+}
+
+#[inline]
+fn extend(dst: &mut Vec<u8>, data: &[u8]) {
+    dst.extend_from_slice(data);
+}
+
+#[cfg(test)]
+mod tests {
+    use bytes::BytesMut;
+
+    use super::*;
+
+    #[test]
+    fn test_parse_request() {
+        let _ = pretty_env_logger::try_init();
+        let mut raw = BytesMut::from("GET /echo HTTP/1.1\r\nHost: hyper.rs\r\n\r\n");
+        let mut method = None;
+        let msg = Server::parse(
+            &mut raw,
+            ParseContext {
+                cached_headers: &mut None,
+                req_method: &mut method,
+                h1_parser_config: Default::default(),
+                #[cfg(feature = "runtime")]
+                h1_header_read_timeout: None,
+                #[cfg(feature = "runtime")]
+                h1_header_read_timeout_fut: &mut None,
+                #[cfg(feature = "runtime")]
+                h1_header_read_timeout_running: &mut false,
+                preserve_header_case: false,
+                #[cfg(feature = "ffi")]
+                preserve_header_order: false,
+                h09_responses: false,
+                #[cfg(feature = "ffi")]
+                on_informational: &mut None,
+                #[cfg(feature = "ffi")]
+                raw_headers: false,
+            },
+        )
+        .unwrap()
+        .unwrap();
+        assert_eq!(raw.len(), 0);
+        assert_eq!(msg.head.subject.0, crate::Method::GET);
+        assert_eq!(msg.head.subject.1, "/echo");
+        assert_eq!(msg.head.version, crate::Version::HTTP_11);
+        assert_eq!(msg.head.headers.len(), 1);
+        assert_eq!(msg.head.headers["Host"], "hyper.rs");
+        assert_eq!(method, Some(crate::Method::GET));
+    }
+
+    #[test]
+    fn test_parse_response() {
+        let _ = pretty_env_logger::try_init();
+        let mut raw = BytesMut::from("HTTP/1.1 200 OK\r\nContent-Length: 0\r\n\r\n");
+        let ctx = ParseContext {
+            cached_headers: &mut None,
+            req_method: &mut Some(crate::Method::GET),
+            h1_parser_config: Default::default(),
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout: None,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout_fut: &mut None,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout_running: &mut false,
+            preserve_header_case: false,
+            #[cfg(feature = "ffi")]
+            preserve_header_order: false,
+            h09_responses: false,
+            #[cfg(feature = "ffi")]
+            on_informational: &mut None,
+            #[cfg(feature = "ffi")]
+            raw_headers: false,
+        };
+        let msg = Client::parse(&mut raw, ctx).unwrap().unwrap();
+        assert_eq!(raw.len(), 0);
+        assert_eq!(msg.head.subject, crate::StatusCode::OK);
+        assert_eq!(msg.head.version, crate::Version::HTTP_11);
+        assert_eq!(msg.head.headers.len(), 1);
+        assert_eq!(msg.head.headers["Content-Length"], "0");
+    }
+
+    #[test]
+    fn test_parse_request_errors() {
+        let mut raw = BytesMut::from("GET htt:p// HTTP/1.1\r\nHost: hyper.rs\r\n\r\n");
+        let ctx = ParseContext {
+            cached_headers: &mut None,
+            req_method: &mut None,
+            h1_parser_config: Default::default(),
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout: None,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout_fut: &mut None,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout_running: &mut false,
+            preserve_header_case: false,
+            #[cfg(feature = "ffi")]
+            preserve_header_order: false,
+            h09_responses: false,
+            #[cfg(feature = "ffi")]
+            on_informational: &mut None,
+            #[cfg(feature = "ffi")]
+            raw_headers: false,
+        };
+        Server::parse(&mut raw, ctx).unwrap_err();
+    }
+
+    const H09_RESPONSE: &'static str = "Baguettes are super delicious, don't you agree?";
+
+    #[test]
+    fn test_parse_response_h09_allowed() {
+        let _ = pretty_env_logger::try_init();
+        let mut raw = BytesMut::from(H09_RESPONSE);
+        let ctx = ParseContext {
+            cached_headers: &mut None,
+            req_method: &mut Some(crate::Method::GET),
+            h1_parser_config: Default::default(),
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout: None,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout_fut: &mut None,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout_running: &mut false,
+            preserve_header_case: false,
+            #[cfg(feature = "ffi")]
+            preserve_header_order: false,
+            h09_responses: true,
+            #[cfg(feature = "ffi")]
+            on_informational: &mut None,
+            #[cfg(feature = "ffi")]
+            raw_headers: false,
+        };
+        let msg = Client::parse(&mut raw, ctx).unwrap().unwrap();
+        assert_eq!(raw, H09_RESPONSE);
+        assert_eq!(msg.head.subject, crate::StatusCode::OK);
+        assert_eq!(msg.head.version, crate::Version::HTTP_09);
+        assert_eq!(msg.head.headers.len(), 0);
+    }
+
+    #[test]
+    fn test_parse_response_h09_rejected() {
+        let _ = pretty_env_logger::try_init();
+        let mut raw = BytesMut::from(H09_RESPONSE);
+        let ctx = ParseContext {
+            cached_headers: &mut None,
+            req_method: &mut Some(crate::Method::GET),
+            h1_parser_config: Default::default(),
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout: None,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout_fut: &mut None,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout_running: &mut false,
+            preserve_header_case: false,
+            #[cfg(feature = "ffi")]
+            preserve_header_order: false,
+            h09_responses: false,
+            #[cfg(feature = "ffi")]
+            on_informational: &mut None,
+            #[cfg(feature = "ffi")]
+            raw_headers: false,
+        };
+        Client::parse(&mut raw, ctx).unwrap_err();
+        assert_eq!(raw, H09_RESPONSE);
+    }
+
+    const RESPONSE_WITH_WHITESPACE_BETWEEN_HEADER_NAME_AND_COLON: &'static str =
+        "HTTP/1.1 200 OK\r\nAccess-Control-Allow-Credentials : true\r\n\r\n";
+
+    #[test]
+    fn test_parse_allow_response_with_spaces_before_colons() {
+        use httparse::ParserConfig;
+
+        let _ = pretty_env_logger::try_init();
+        let mut raw = BytesMut::from(RESPONSE_WITH_WHITESPACE_BETWEEN_HEADER_NAME_AND_COLON);
+        let mut h1_parser_config = ParserConfig::default();
+        h1_parser_config.allow_spaces_after_header_name_in_responses(true);
+        let ctx = ParseContext {
+            cached_headers: &mut None,
+            req_method: &mut Some(crate::Method::GET),
+            h1_parser_config,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout: None,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout_fut: &mut None,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout_running: &mut false,
+            preserve_header_case: false,
+            #[cfg(feature = "ffi")]
+            preserve_header_order: false,
+            h09_responses: false,
+            #[cfg(feature = "ffi")]
+            on_informational: &mut None,
+            #[cfg(feature = "ffi")]
+            raw_headers: false,
+        };
+        let msg = Client::parse(&mut raw, ctx).unwrap().unwrap();
+        assert_eq!(raw.len(), 0);
+        assert_eq!(msg.head.subject, crate::StatusCode::OK);
+        assert_eq!(msg.head.version, crate::Version::HTTP_11);
+        assert_eq!(msg.head.headers.len(), 1);
+        assert_eq!(msg.head.headers["Access-Control-Allow-Credentials"], "true");
+    }
+
+    #[test]
+    fn test_parse_reject_response_with_spaces_before_colons() {
+        let _ = pretty_env_logger::try_init();
+        let mut raw = BytesMut::from(RESPONSE_WITH_WHITESPACE_BETWEEN_HEADER_NAME_AND_COLON);
+        let ctx = ParseContext {
+            cached_headers: &mut None,
+            req_method: &mut Some(crate::Method::GET),
+            h1_parser_config: Default::default(),
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout: None,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout_fut: &mut None,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout_running: &mut false,
+            preserve_header_case: false,
+            #[cfg(feature = "ffi")]
+            preserve_header_order: false,
+            h09_responses: false,
+            #[cfg(feature = "ffi")]
+            on_informational: &mut None,
+            #[cfg(feature = "ffi")]
+            raw_headers: false,
+        };
+        Client::parse(&mut raw, ctx).unwrap_err();
+    }
+
+    #[test]
+    fn test_parse_preserve_header_case_in_request() {
+        let mut raw =
+            BytesMut::from("GET / HTTP/1.1\r\nHost: hyper.rs\r\nX-BREAD: baguette\r\n\r\n");
+        let ctx = ParseContext {
+            cached_headers: &mut None,
+            req_method: &mut None,
+            h1_parser_config: Default::default(),
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout: None,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout_fut: &mut None,
+            #[cfg(feature = "runtime")]
+            h1_header_read_timeout_running: &mut false,
+            preserve_header_case: true,
+            #[cfg(feature = "ffi")]
+            preserve_header_order: false,
+            h09_responses: false,
+            #[cfg(feature = "ffi")]
+            on_informational: &mut None,
+            #[cfg(feature = "ffi")]
+            raw_headers: false,
+        };
+        let parsed_message = Server::parse(&mut raw, ctx).unwrap().unwrap();
+        let orig_headers = parsed_message
+            .head
+            .extensions
+            .get::<HeaderCaseMap>()
+            .unwrap();
+        assert_eq!(
+            orig_headers
+                .get_all_internal(&HeaderName::from_static("host"))
+                .into_iter()
+                .collect::<Vec<_>>(),
+            vec![&Bytes::from("Host")]
+        );
+        assert_eq!(
+            orig_headers
+                .get_all_internal(&HeaderName::from_static("x-bread"))
+                .into_iter()
+                .collect::<Vec<_>>(),
+            vec![&Bytes::from("X-BREAD")]
+        );
+    }
+
+    #[test]
+    fn test_decoder_request() {
+        fn parse(s: &str) -> ParsedMessage<RequestLine> {
+            let mut bytes = BytesMut::from(s);
+            Server::parse(
+                &mut bytes,
+                ParseContext {
+                    cached_headers: &mut None,
+                    req_method: &mut None,
+                    h1_parser_config: Default::default(),
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout: None,
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout_fut: &mut None,
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout_running: &mut false,
+                    preserve_header_case: false,
+                    #[cfg(feature = "ffi")]
+                    preserve_header_order: false,
+                    h09_responses: false,
+                    #[cfg(feature = "ffi")]
+                    on_informational: &mut None,
+                    #[cfg(feature = "ffi")]
+                    raw_headers: false,
+                },
+            )
+            .expect("parse ok")
+            .expect("parse complete")
+        }
+
+        fn parse_err(s: &str, comment: &str) -> crate::error::Parse {
+            let mut bytes = BytesMut::from(s);
+            Server::parse(
+                &mut bytes,
+                ParseContext {
+                    cached_headers: &mut None,
+                    req_method: &mut None,
+                    h1_parser_config: Default::default(),
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout: None,
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout_fut: &mut None,
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout_running: &mut false,
+                    preserve_header_case: false,
+                    #[cfg(feature = "ffi")]
+                    preserve_header_order: false,
+                    h09_responses: false,
+                    #[cfg(feature = "ffi")]
+                    on_informational: &mut None,
+                    #[cfg(feature = "ffi")]
+                    raw_headers: false,
+                },
+            )
+            .expect_err(comment)
+        }
+
+        // no length or transfer-encoding means 0-length body
+        assert_eq!(
+            parse(
+                "\
+                 GET / HTTP/1.1\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::ZERO
+        );
+
+        assert_eq!(
+            parse(
+                "\
+                 POST / HTTP/1.1\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::ZERO
+        );
+
+        // transfer-encoding: chunked
+        assert_eq!(
+            parse(
+                "\
+                 POST / HTTP/1.1\r\n\
+                 transfer-encoding: chunked\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::CHUNKED
+        );
+
+        assert_eq!(
+            parse(
+                "\
+                 POST / HTTP/1.1\r\n\
+                 transfer-encoding: gzip, chunked\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::CHUNKED
+        );
+
+        assert_eq!(
+            parse(
+                "\
+                 POST / HTTP/1.1\r\n\
+                 transfer-encoding: gzip\r\n\
+                 transfer-encoding: chunked\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::CHUNKED
+        );
+
+        // content-length
+        assert_eq!(
+            parse(
+                "\
+                 POST / HTTP/1.1\r\n\
+                 content-length: 10\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::new(10)
+        );
+
+        // transfer-encoding and content-length = chunked
+        assert_eq!(
+            parse(
+                "\
+                 POST / HTTP/1.1\r\n\
+                 content-length: 10\r\n\
+                 transfer-encoding: chunked\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::CHUNKED
+        );
+
+        assert_eq!(
+            parse(
+                "\
+                 POST / HTTP/1.1\r\n\
+                 transfer-encoding: chunked\r\n\
+                 content-length: 10\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::CHUNKED
+        );
+
+        assert_eq!(
+            parse(
+                "\
+                 POST / HTTP/1.1\r\n\
+                 transfer-encoding: gzip\r\n\
+                 content-length: 10\r\n\
+                 transfer-encoding: chunked\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::CHUNKED
+        );
+
+        // multiple content-lengths of same value are fine
+        assert_eq!(
+            parse(
+                "\
+                 POST / HTTP/1.1\r\n\
+                 content-length: 10\r\n\
+                 content-length: 10\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::new(10)
+        );
+
+        // multiple content-lengths with different values is an error
+        parse_err(
+            "\
+             POST / HTTP/1.1\r\n\
+             content-length: 10\r\n\
+             content-length: 11\r\n\
+             \r\n\
+             ",
+            "multiple content-lengths",
+        );
+
+        // content-length with prefix is not allowed
+        parse_err(
+            "\
+             POST / HTTP/1.1\r\n\
+             content-length: +10\r\n\
+             \r\n\
+             ",
+            "prefixed content-length",
+        );
+
+        // transfer-encoding that isn't chunked is an error
+        parse_err(
+            "\
+             POST / HTTP/1.1\r\n\
+             transfer-encoding: gzip\r\n\
+             \r\n\
+             ",
+            "transfer-encoding but not chunked",
+        );
+
+        parse_err(
+            "\
+             POST / HTTP/1.1\r\n\
+             transfer-encoding: chunked, gzip\r\n\
+             \r\n\
+             ",
+            "transfer-encoding doesn't end in chunked",
+        );
+
+        parse_err(
+            "\
+             POST / HTTP/1.1\r\n\
+             transfer-encoding: chunked\r\n\
+             transfer-encoding: afterlol\r\n\
+             \r\n\
+             ",
+            "transfer-encoding multiple lines doesn't end in chunked",
+        );
+
+        // http/1.0
+
+        assert_eq!(
+            parse(
+                "\
+                 POST / HTTP/1.0\r\n\
+                 content-length: 10\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::new(10)
+        );
+
+        // 1.0 doesn't understand chunked, so its an error
+        parse_err(
+            "\
+             POST / HTTP/1.0\r\n\
+             transfer-encoding: chunked\r\n\
+             \r\n\
+             ",
+            "1.0 chunked",
+        );
+    }
+
+    #[test]
+    fn test_decoder_response() {
+        fn parse(s: &str) -> ParsedMessage<StatusCode> {
+            parse_with_method(s, Method::GET)
+        }
+
+        fn parse_ignores(s: &str) {
+            let mut bytes = BytesMut::from(s);
+            assert!(Client::parse(
+                &mut bytes,
+                ParseContext {
+                    cached_headers: &mut None,
+                    req_method: &mut Some(Method::GET),
+                    h1_parser_config: Default::default(),
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout: None,
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout_fut: &mut None,
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout_running: &mut false,
+                    preserve_header_case: false,
+                    #[cfg(feature = "ffi")]
+                    preserve_header_order: false,
+                    h09_responses: false,
+                    #[cfg(feature = "ffi")]
+                    on_informational: &mut None,
+                    #[cfg(feature = "ffi")]
+                    raw_headers: false,
+                }
+            )
+            .expect("parse ok")
+            .is_none())
+        }
+
+        fn parse_with_method(s: &str, m: Method) -> ParsedMessage<StatusCode> {
+            let mut bytes = BytesMut::from(s);
+            Client::parse(
+                &mut bytes,
+                ParseContext {
+                    cached_headers: &mut None,
+                    req_method: &mut Some(m),
+                    h1_parser_config: Default::default(),
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout: None,
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout_fut: &mut None,
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout_running: &mut false,
+                    preserve_header_case: false,
+                    #[cfg(feature = "ffi")]
+                    preserve_header_order: false,
+                    h09_responses: false,
+                    #[cfg(feature = "ffi")]
+                    on_informational: &mut None,
+                    #[cfg(feature = "ffi")]
+                    raw_headers: false,
+                },
+            )
+            .expect("parse ok")
+            .expect("parse complete")
+        }
+
+        fn parse_err(s: &str) -> crate::error::Parse {
+            let mut bytes = BytesMut::from(s);
+            Client::parse(
+                &mut bytes,
+                ParseContext {
+                    cached_headers: &mut None,
+                    req_method: &mut Some(Method::GET),
+                    h1_parser_config: Default::default(),
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout: None,
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout_fut: &mut None,
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout_running: &mut false,
+                    preserve_header_case: false,
+                    #[cfg(feature = "ffi")]
+                    preserve_header_order: false,
+                    h09_responses: false,
+                    #[cfg(feature = "ffi")]
+                    on_informational: &mut None,
+                    #[cfg(feature = "ffi")]
+                    raw_headers: false,
+                },
+            )
+            .expect_err("parse should err")
+        }
+
+        // no content-length or transfer-encoding means close-delimited
+        assert_eq!(
+            parse(
+                "\
+                 HTTP/1.1 200 OK\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::CLOSE_DELIMITED
+        );
+
+        // 204 and 304 never have a body
+        assert_eq!(
+            parse(
+                "\
+                 HTTP/1.1 204 No Content\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::ZERO
+        );
+
+        assert_eq!(
+            parse(
+                "\
+                 HTTP/1.1 304 Not Modified\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::ZERO
+        );
+
+        // content-length
+        assert_eq!(
+            parse(
+                "\
+                 HTTP/1.1 200 OK\r\n\
+                 content-length: 8\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::new(8)
+        );
+
+        assert_eq!(
+            parse(
+                "\
+                 HTTP/1.1 200 OK\r\n\
+                 content-length: 8\r\n\
+                 content-length: 8\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::new(8)
+        );
+
+        parse_err(
+            "\
+             HTTP/1.1 200 OK\r\n\
+             content-length: 8\r\n\
+             content-length: 9\r\n\
+             \r\n\
+             ",
+        );
+
+        parse_err(
+            "\
+             HTTP/1.1 200 OK\r\n\
+             content-length: +8\r\n\
+             \r\n\
+             ",
+        );
+
+        // transfer-encoding: chunked
+        assert_eq!(
+            parse(
+                "\
+                 HTTP/1.1 200 OK\r\n\
+                 transfer-encoding: chunked\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::CHUNKED
+        );
+
+        // transfer-encoding not-chunked is close-delimited
+        assert_eq!(
+            parse(
+                "\
+                 HTTP/1.1 200 OK\r\n\
+                 transfer-encoding: yolo\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::CLOSE_DELIMITED
+        );
+
+        // transfer-encoding and content-length = chunked
+        assert_eq!(
+            parse(
+                "\
+                 HTTP/1.1 200 OK\r\n\
+                 content-length: 10\r\n\
+                 transfer-encoding: chunked\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::CHUNKED
+        );
+
+        // HEAD can have content-length, but not body
+        assert_eq!(
+            parse_with_method(
+                "\
+                 HTTP/1.1 200 OK\r\n\
+                 content-length: 8\r\n\
+                 \r\n\
+                 ",
+                Method::HEAD
+            )
+            .decode,
+            DecodedLength::ZERO
+        );
+
+        // CONNECT with 200 never has body
+        {
+            let msg = parse_with_method(
+                "\
+                 HTTP/1.1 200 OK\r\n\
+                 \r\n\
+                 ",
+                Method::CONNECT,
+            );
+            assert_eq!(msg.decode, DecodedLength::ZERO);
+            assert!(!msg.keep_alive, "should be upgrade");
+            assert!(msg.wants_upgrade, "should be upgrade");
+        }
+
+        // CONNECT receiving non 200 can have a body
+        assert_eq!(
+            parse_with_method(
+                "\
+                 HTTP/1.1 400 Bad Request\r\n\
+                 \r\n\
+                 ",
+                Method::CONNECT
+            )
+            .decode,
+            DecodedLength::CLOSE_DELIMITED
+        );
+
+        // 1xx status codes
+        parse_ignores(
+            "\
+             HTTP/1.1 100 Continue\r\n\
+             \r\n\
+             ",
+        );
+
+        parse_ignores(
+            "\
+             HTTP/1.1 103 Early Hints\r\n\
+             \r\n\
+             ",
+        );
+
+        // 101 upgrade not supported yet
+        {
+            let msg = parse(
+                "\
+                 HTTP/1.1 101 Switching Protocols\r\n\
+                 \r\n\
+                 ",
+            );
+            assert_eq!(msg.decode, DecodedLength::ZERO);
+            assert!(!msg.keep_alive, "should be last");
+            assert!(msg.wants_upgrade, "should be upgrade");
+        }
+
+        // http/1.0
+        assert_eq!(
+            parse(
+                "\
+                 HTTP/1.0 200 OK\r\n\
+                 \r\n\
+                 "
+            )
+            .decode,
+            DecodedLength::CLOSE_DELIMITED
+        );
+
+        // 1.0 doesn't understand chunked
+        parse_err(
+            "\
+             HTTP/1.0 200 OK\r\n\
+             transfer-encoding: chunked\r\n\
+             \r\n\
+             ",
+        );
+
+        // keep-alive
+        assert!(
+            parse(
+                "\
+                 HTTP/1.1 200 OK\r\n\
+                 content-length: 0\r\n\
+                 \r\n\
+                 "
+            )
+            .keep_alive,
+            "HTTP/1.1 keep-alive is default"
+        );
+
+        assert!(
+            !parse(
+                "\
+                 HTTP/1.1 200 OK\r\n\
+                 content-length: 0\r\n\
+                 connection: foo, close, bar\r\n\
+                 \r\n\
+                 "
+            )
+            .keep_alive,
+            "connection close is always close"
+        );
+
+        assert!(
+            !parse(
+                "\
+                 HTTP/1.0 200 OK\r\n\
+                 content-length: 0\r\n\
+                 \r\n\
+                 "
+            )
+            .keep_alive,
+            "HTTP/1.0 close is default"
+        );
+
+        assert!(
+            parse(
+                "\
+                 HTTP/1.0 200 OK\r\n\
+                 content-length: 0\r\n\
+                 connection: foo, keep-alive, bar\r\n\
+                 \r\n\
+                 "
+            )
+            .keep_alive,
+            "connection keep-alive is always keep-alive"
+        );
+    }
+
+    #[test]
+    fn test_client_request_encode_title_case() {
+        use crate::proto::BodyLength;
+        use http::header::HeaderValue;
+
+        let mut head = MessageHead::default();
+        head.headers
+            .insert("content-length", HeaderValue::from_static("10"));
+        head.headers
+            .insert("content-type", HeaderValue::from_static("application/json"));
+        head.headers.insert("*-*", HeaderValue::from_static("o_o"));
+
+        let mut vec = Vec::new();
+        Client::encode(
+            Encode {
+                head: &mut head,
+                body: Some(BodyLength::Known(10)),
+                keep_alive: true,
+                req_method: &mut None,
+                title_case_headers: true,
+            },
+            &mut vec,
+        )
+        .unwrap();
+
+        assert_eq!(vec, b"GET / HTTP/1.1\r\nContent-Length: 10\r\nContent-Type: application/json\r\n*-*: o_o\r\n\r\n".to_vec());
+    }
+
+    #[test]
+    fn test_client_request_encode_orig_case() {
+        use crate::proto::BodyLength;
+        use http::header::{HeaderValue, CONTENT_LENGTH};
+
+        let mut head = MessageHead::default();
+        head.headers
+            .insert("content-length", HeaderValue::from_static("10"));
+        head.headers
+            .insert("content-type", HeaderValue::from_static("application/json"));
+
+        let mut orig_headers = HeaderCaseMap::default();
+        orig_headers.insert(CONTENT_LENGTH, "CONTENT-LENGTH".into());
+        head.extensions.insert(orig_headers);
+
+        let mut vec = Vec::new();
+        Client::encode(
+            Encode {
+                head: &mut head,
+                body: Some(BodyLength::Known(10)),
+                keep_alive: true,
+                req_method: &mut None,
+                title_case_headers: false,
+            },
+            &mut vec,
+        )
+        .unwrap();
+
+        assert_eq!(
+            &*vec,
+            b"GET / HTTP/1.1\r\nCONTENT-LENGTH: 10\r\ncontent-type: application/json\r\n\r\n"
+                .as_ref(),
+        );
+    }
+    #[test]
+    fn test_client_request_encode_orig_and_title_case() {
+        use crate::proto::BodyLength;
+        use http::header::{HeaderValue, CONTENT_LENGTH};
+
+        let mut head = MessageHead::default();
+        head.headers
+            .insert("content-length", HeaderValue::from_static("10"));
+        head.headers
+            .insert("content-type", HeaderValue::from_static("application/json"));
+
+        let mut orig_headers = HeaderCaseMap::default();
+        orig_headers.insert(CONTENT_LENGTH, "CONTENT-LENGTH".into());
+        head.extensions.insert(orig_headers);
+
+        let mut vec = Vec::new();
+        Client::encode(
+            Encode {
+                head: &mut head,
+                body: Some(BodyLength::Known(10)),
+                keep_alive: true,
+                req_method: &mut None,
+                title_case_headers: true,
+            },
+            &mut vec,
+        )
+        .unwrap();
+
+        assert_eq!(
+            &*vec,
+            b"GET / HTTP/1.1\r\nCONTENT-LENGTH: 10\r\nContent-Type: application/json\r\n\r\n"
+                .as_ref(),
+        );
+    }
+
+    #[test]
+    fn test_server_encode_connect_method() {
+        let mut head = MessageHead::default();
+
+        let mut vec = Vec::new();
+        let encoder = Server::encode(
+            Encode {
+                head: &mut head,
+                body: None,
+                keep_alive: true,
+                req_method: &mut Some(Method::CONNECT),
+                title_case_headers: false,
+            },
+            &mut vec,
+        )
+        .unwrap();
+
+        assert!(encoder.is_last());
+    }
+
+    #[test]
+    fn test_server_response_encode_title_case() {
+        use crate::proto::BodyLength;
+        use http::header::HeaderValue;
+
+        let mut head = MessageHead::default();
+        head.headers
+            .insert("content-length", HeaderValue::from_static("10"));
+        head.headers
+            .insert("content-type", HeaderValue::from_static("application/json"));
+        head.headers
+            .insert("weird--header", HeaderValue::from_static(""));
+
+        let mut vec = Vec::new();
+        Server::encode(
+            Encode {
+                head: &mut head,
+                body: Some(BodyLength::Known(10)),
+                keep_alive: true,
+                req_method: &mut None,
+                title_case_headers: true,
+            },
+            &mut vec,
+        )
+        .unwrap();
+
+        let expected_response =
+            b"HTTP/1.1 200 OK\r\nContent-Length: 10\r\nContent-Type: application/json\r\nWeird--Header: \r\n";
+
+        assert_eq!(&vec[..expected_response.len()], &expected_response[..]);
+    }
+
+    #[test]
+    fn test_server_response_encode_orig_case() {
+        use crate::proto::BodyLength;
+        use http::header::{HeaderValue, CONTENT_LENGTH};
+
+        let mut head = MessageHead::default();
+        head.headers
+            .insert("content-length", HeaderValue::from_static("10"));
+        head.headers
+            .insert("content-type", HeaderValue::from_static("application/json"));
+
+        let mut orig_headers = HeaderCaseMap::default();
+        orig_headers.insert(CONTENT_LENGTH, "CONTENT-LENGTH".into());
+        head.extensions.insert(orig_headers);
+
+        let mut vec = Vec::new();
+        Server::encode(
+            Encode {
+                head: &mut head,
+                body: Some(BodyLength::Known(10)),
+                keep_alive: true,
+                req_method: &mut None,
+                title_case_headers: false,
+            },
+            &mut vec,
+        )
+        .unwrap();
+
+        let expected_response =
+            b"HTTP/1.1 200 OK\r\nCONTENT-LENGTH: 10\r\ncontent-type: application/json\r\ndate: ";
+
+        assert_eq!(&vec[..expected_response.len()], &expected_response[..]);
+    }
+
+    #[test]
+    fn test_server_response_encode_orig_and_title_case() {
+        use crate::proto::BodyLength;
+        use http::header::{HeaderValue, CONTENT_LENGTH};
+
+        let mut head = MessageHead::default();
+        head.headers
+            .insert("content-length", HeaderValue::from_static("10"));
+        head.headers
+            .insert("content-type", HeaderValue::from_static("application/json"));
+
+        let mut orig_headers = HeaderCaseMap::default();
+        orig_headers.insert(CONTENT_LENGTH, "CONTENT-LENGTH".into());
+        head.extensions.insert(orig_headers);
+
+        let mut vec = Vec::new();
+        Server::encode(
+            Encode {
+                head: &mut head,
+                body: Some(BodyLength::Known(10)),
+                keep_alive: true,
+                req_method: &mut None,
+                title_case_headers: true,
+            },
+            &mut vec,
+        )
+        .unwrap();
+
+        let expected_response =
+            b"HTTP/1.1 200 OK\r\nCONTENT-LENGTH: 10\r\nContent-Type: application/json\r\nDate: ";
+
+        assert_eq!(&vec[..expected_response.len()], &expected_response[..]);
+    }
+
+    #[test]
+    fn parse_header_htabs() {
+        let mut bytes = BytesMut::from("HTTP/1.1 200 OK\r\nserver: hello\tworld\r\n\r\n");
+        let parsed = Client::parse(
+            &mut bytes,
+            ParseContext {
+                cached_headers: &mut None,
+                req_method: &mut Some(Method::GET),
+                h1_parser_config: Default::default(),
+                #[cfg(feature = "runtime")]
+                h1_header_read_timeout: None,
+                #[cfg(feature = "runtime")]
+                h1_header_read_timeout_fut: &mut None,
+                #[cfg(feature = "runtime")]
+                h1_header_read_timeout_running: &mut false,
+                preserve_header_case: false,
+                #[cfg(feature = "ffi")]
+                preserve_header_order: false,
+                h09_responses: false,
+                #[cfg(feature = "ffi")]
+                on_informational: &mut None,
+                #[cfg(feature = "ffi")]
+                raw_headers: false,
+            },
+        )
+        .expect("parse ok")
+        .expect("parse complete");
+
+        assert_eq!(parsed.head.headers["server"], "hello\tworld");
+    }
+
+    #[test]
+    fn test_write_headers_orig_case_empty_value() {
+        let mut headers = HeaderMap::new();
+        let name = http::header::HeaderName::from_static("x-empty");
+        headers.insert(&name, "".parse().expect("parse empty"));
+        let mut orig_cases = HeaderCaseMap::default();
+        orig_cases.insert(name, Bytes::from_static(b"X-EmptY"));
+
+        let mut dst = Vec::new();
+        super::write_headers_original_case(&headers, &orig_cases, &mut dst, false);
+
+        assert_eq!(
+            dst, b"X-EmptY:\r\n",
+            "there should be no space between the colon and CRLF"
+        );
+    }
+
+    #[test]
+    fn test_write_headers_orig_case_multiple_entries() {
+        let mut headers = HeaderMap::new();
+        let name = http::header::HeaderName::from_static("x-empty");
+        headers.insert(&name, "a".parse().unwrap());
+        headers.append(&name, "b".parse().unwrap());
+
+        let mut orig_cases = HeaderCaseMap::default();
+        orig_cases.insert(name.clone(), Bytes::from_static(b"X-Empty"));
+        orig_cases.append(name, Bytes::from_static(b"X-EMPTY"));
+
+        let mut dst = Vec::new();
+        super::write_headers_original_case(&headers, &orig_cases, &mut dst, false);
+
+        assert_eq!(dst, b"X-Empty: a\r\nX-EMPTY: b\r\n");
+    }
+
+    #[cfg(feature = "nightly")]
+    use test::Bencher;
+
+    #[cfg(feature = "nightly")]
+    #[bench]
+    fn bench_parse_incoming(b: &mut Bencher) {
+        let mut raw = BytesMut::from(
+            &b"GET /super_long_uri/and_whatever?what_should_we_talk_about/\
+            I_wonder/Hard_to_write_in_an_uri_after_all/you_have_to_make\
+            _up_the_punctuation_yourself/how_fun_is_that?test=foo&test1=\
+            foo1&test2=foo2&test3=foo3&test4=foo4 HTTP/1.1\r\nHost: \
+            hyper.rs\r\nAccept: a lot of things\r\nAccept-Charset: \
+            utf8\r\nAccept-Encoding: *\r\nAccess-Control-Allow-\
+            Credentials: None\r\nAccess-Control-Allow-Origin: None\r\n\
+            Access-Control-Allow-Methods: None\r\nAccess-Control-Allow-\
+            Headers: None\r\nContent-Encoding: utf8\r\nContent-Security-\
+            Policy: None\r\nContent-Type: text/html\r\nOrigin: hyper\
+            \r\nSec-Websocket-Extensions: It looks super important!\r\n\
+            Sec-Websocket-Origin: hyper\r\nSec-Websocket-Version: 4.3\r\
+            \nStrict-Transport-Security: None\r\nUser-Agent: hyper\r\n\
+            X-Content-Duration: None\r\nX-Content-Security-Policy: None\
+            \r\nX-DNSPrefetch-Control: None\r\nX-Frame-Options: \
+            Something important obviously\r\nX-Requested-With: Nothing\
+            \r\n\r\n"[..],
+        );
+        let len = raw.len();
+        let mut headers = Some(HeaderMap::new());
+
+        b.bytes = len as u64;
+        b.iter(|| {
+            let mut msg = Server::parse(
+                &mut raw,
+                ParseContext {
+                    cached_headers: &mut headers,
+                    req_method: &mut None,
+                    h1_parser_config: Default::default(),
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout: None,
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout_fut: &mut None,
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout_running: &mut false,
+                    preserve_header_case: false,
+                    #[cfg(feature = "ffi")]
+                    preserve_header_order: false,
+                    h09_responses: false,
+                    #[cfg(feature = "ffi")]
+                    on_informational: &mut None,
+                    #[cfg(feature = "ffi")]
+                    raw_headers: false,
+                },
+            )
+            .unwrap()
+            .unwrap();
+            ::test::black_box(&msg);
+            msg.head.headers.clear();
+            headers = Some(msg.head.headers);
+            restart(&mut raw, len);
+        });
+
+        fn restart(b: &mut BytesMut, len: usize) {
+            b.reserve(1);
+            unsafe {
+                b.set_len(len);
+            }
+        }
+    }
+
+    #[cfg(feature = "nightly")]
+    #[bench]
+    fn bench_parse_short(b: &mut Bencher) {
+        let s = &b"GET / HTTP/1.1\r\nHost: localhost:8080\r\n\r\n"[..];
+        let mut raw = BytesMut::from(s);
+        let len = raw.len();
+        let mut headers = Some(HeaderMap::new());
+
+        b.bytes = len as u64;
+        b.iter(|| {
+            let mut msg = Server::parse(
+                &mut raw,
+                ParseContext {
+                    cached_headers: &mut headers,
+                    req_method: &mut None,
+                    h1_parser_config: Default::default(),
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout: None,
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout_fut: &mut None,
+                    #[cfg(feature = "runtime")]
+                    h1_header_read_timeout_running: &mut false,
+                    preserve_header_case: false,
+                    #[cfg(feature = "ffi")]
+                    preserve_header_order: false,
+                    h09_responses: false,
+                    #[cfg(feature = "ffi")]
+                    on_informational: &mut None,
+                    #[cfg(feature = "ffi")]
+                    raw_headers: false,
+                },
+            )
+            .unwrap()
+            .unwrap();
+            ::test::black_box(&msg);
+            msg.head.headers.clear();
+            headers = Some(msg.head.headers);
+            restart(&mut raw, len);
+        });
+
+        fn restart(b: &mut BytesMut, len: usize) {
+            b.reserve(1);
+            unsafe {
+                b.set_len(len);
+            }
+        }
+    }
+
+    #[cfg(feature = "nightly")]
+    #[bench]
+    fn bench_server_encode_headers_preset(b: &mut Bencher) {
+        use crate::proto::BodyLength;
+        use http::header::HeaderValue;
+
+        let len = 108;
+        b.bytes = len as u64;
+
+        let mut head = MessageHead::default();
+        let mut headers = HeaderMap::new();
+        headers.insert("content-length", HeaderValue::from_static("10"));
+        headers.insert("content-type", HeaderValue::from_static("application/json"));
+
+        b.iter(|| {
+            let mut vec = Vec::new();
+            head.headers = headers.clone();
+            Server::encode(
+                Encode {
+                    head: &mut head,
+                    body: Some(BodyLength::Known(10)),
+                    keep_alive: true,
+                    req_method: &mut Some(Method::GET),
+                    title_case_headers: false,
+                },
+                &mut vec,
+            )
+            .unwrap();
+            assert_eq!(vec.len(), len);
+            ::test::black_box(vec);
+        })
+    }
+
+    #[cfg(feature = "nightly")]
+    #[bench]
+    fn bench_server_encode_no_headers(b: &mut Bencher) {
+        use crate::proto::BodyLength;
+
+        let len = 76;
+        b.bytes = len as u64;
+
+        let mut head = MessageHead::default();
+        let mut vec = Vec::with_capacity(128);
+
+        b.iter(|| {
+            Server::encode(
+                Encode {
+                    head: &mut head,
+                    body: Some(BodyLength::Known(10)),
+                    keep_alive: true,
+                    req_method: &mut Some(Method::GET),
+                    title_case_headers: false,
+                },
+                &mut vec,
+            )
+            .unwrap();
+            assert_eq!(vec.len(), len);
+            ::test::black_box(&vec);
+
+            vec.clear();
+        })
+    }
+}
diff --git a/src/proto/h2/client.rs b/src/proto/h2/client.rs
new file mode 100644
index 0000000..8c2a4d2
--- /dev/null
+++ b/src/proto/h2/client.rs
@@ -0,0 +1,455 @@
+use std::convert::Infallible;
+use std::error::Error as StdError;
+use std::future::Future;
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+#[cfg(feature = "runtime")]
+use std::time::Duration;
+
+use bytes::Bytes;
+use futures_channel::{mpsc, oneshot};
+use futures_util::future::{self, Either, FutureExt as _, TryFutureExt as _};
+use futures_util::stream::StreamExt as _;
+use h2::client::{Builder, SendRequest};
+use h2::SendStream;
+use http::{Method, StatusCode};
+use tokio::io::{AsyncRead, AsyncWrite};
+use tracing::{debug, trace, warn};
+
+use super::{ping, H2Upgraded, PipeToSendStream, SendBuf};
+use crate::body::HttpBody;
+use crate::client::dispatch::Callback;
+use crate::common::exec::Exec;
+use crate::ext::Protocol;
+use crate::headers;
+use crate::proto::h2::UpgradedSendStream;
+use crate::proto::Dispatched;
+use crate::upgrade::Upgraded;
+use crate::{Body, Request, Response};
+use h2::client::ResponseFuture;
+
+type ClientRx<B> = crate::client::dispatch::Receiver<Request<B>, Response<Body>>;
+
+///// An mpsc channel is used to help notify the `Connection` task when *all*
+///// other handles to it have been dropped, so that it can shutdown.
+type ConnDropRef = mpsc::Sender<Infallible>;
+
+///// A oneshot channel watches the `Connection` task, and when it completes,
+///// the "dispatch" task will be notified and can shutdown sooner.
+type ConnEof = oneshot::Receiver<Infallible>;
+
+// Our defaults are chosen for the "majority" case, which usually are not
+// resource constrained, and so the spec default of 64kb can be too limiting
+// for performance.
+const DEFAULT_CONN_WINDOW: u32 = 1024 * 1024 * 5; // 5mb
+const DEFAULT_STREAM_WINDOW: u32 = 1024 * 1024 * 2; // 2mb
+const DEFAULT_MAX_FRAME_SIZE: u32 = 1024 * 16; // 16kb
+const DEFAULT_MAX_SEND_BUF_SIZE: usize = 1024 * 1024; // 1mb
+
+#[derive(Clone, Debug)]
+pub(crate) struct Config {
+    pub(crate) adaptive_window: bool,
+    pub(crate) initial_conn_window_size: u32,
+    pub(crate) initial_stream_window_size: u32,
+    pub(crate) max_frame_size: u32,
+    #[cfg(feature = "runtime")]
+    pub(crate) keep_alive_interval: Option<Duration>,
+    #[cfg(feature = "runtime")]
+    pub(crate) keep_alive_timeout: Duration,
+    #[cfg(feature = "runtime")]
+    pub(crate) keep_alive_while_idle: bool,
+    pub(crate) max_concurrent_reset_streams: Option<usize>,
+    pub(crate) max_send_buffer_size: usize,
+}
+
+impl Default for Config {
+    fn default() -> Config {
+        Config {
+            adaptive_window: false,
+            initial_conn_window_size: DEFAULT_CONN_WINDOW,
+            initial_stream_window_size: DEFAULT_STREAM_WINDOW,
+            max_frame_size: DEFAULT_MAX_FRAME_SIZE,
+            #[cfg(feature = "runtime")]
+            keep_alive_interval: None,
+            #[cfg(feature = "runtime")]
+            keep_alive_timeout: Duration::from_secs(20),
+            #[cfg(feature = "runtime")]
+            keep_alive_while_idle: false,
+            max_concurrent_reset_streams: None,
+            max_send_buffer_size: DEFAULT_MAX_SEND_BUF_SIZE,
+        }
+    }
+}
+
+fn new_builder(config: &Config) -> Builder {
+    let mut builder = Builder::default();
+    builder
+        .initial_window_size(config.initial_stream_window_size)
+        .initial_connection_window_size(config.initial_conn_window_size)
+        .max_frame_size(config.max_frame_size)
+        .max_send_buffer_size(config.max_send_buffer_size)
+        .enable_push(false);
+    if let Some(max) = config.max_concurrent_reset_streams {
+        builder.max_concurrent_reset_streams(max);
+    }
+    builder
+}
+
+fn new_ping_config(config: &Config) -> ping::Config {
+    ping::Config {
+        bdp_initial_window: if config.adaptive_window {
+            Some(config.initial_stream_window_size)
+        } else {
+            None
+        },
+        #[cfg(feature = "runtime")]
+        keep_alive_interval: config.keep_alive_interval,
+        #[cfg(feature = "runtime")]
+        keep_alive_timeout: config.keep_alive_timeout,
+        #[cfg(feature = "runtime")]
+        keep_alive_while_idle: config.keep_alive_while_idle,
+    }
+}
+
+pub(crate) async fn handshake<T, B>(
+    io: T,
+    req_rx: ClientRx<B>,
+    config: &Config,
+    exec: Exec,
+) -> crate::Result<ClientTask<B>>
+where
+    T: AsyncRead + AsyncWrite + Send + Unpin + 'static,
+    B: HttpBody,
+    B::Data: Send + 'static,
+{
+    let (h2_tx, mut conn) = new_builder(config)
+        .handshake::<_, SendBuf<B::Data>>(io)
+        .await
+        .map_err(crate::Error::new_h2)?;
+
+    // An mpsc channel is used entirely to detect when the
+    // 'Client' has been dropped. This is to get around a bug
+    // in h2 where dropping all SendRequests won't notify a
+    // parked Connection.
+    let (conn_drop_ref, rx) = mpsc::channel(1);
+    let (cancel_tx, conn_eof) = oneshot::channel();
+
+    let conn_drop_rx = rx.into_future().map(|(item, _rx)| {
+        if let Some(never) = item {
+            match never {}
+        }
+    });
+
+    let ping_config = new_ping_config(&config);
+
+    let (conn, ping) = if ping_config.is_enabled() {
+        let pp = conn.ping_pong().expect("conn.ping_pong");
+        let (recorder, mut ponger) = ping::channel(pp, ping_config);
+
+        let conn = future::poll_fn(move |cx| {
+            match ponger.poll(cx) {
+                Poll::Ready(ping::Ponged::SizeUpdate(wnd)) => {
+                    conn.set_target_window_size(wnd);
+                    conn.set_initial_window_size(wnd)?;
+                }
+                #[cfg(feature = "runtime")]
+                Poll::Ready(ping::Ponged::KeepAliveTimedOut) => {
+                    debug!("connection keep-alive timed out");
+                    return Poll::Ready(Ok(()));
+                }
+                Poll::Pending => {}
+            }
+
+            Pin::new(&mut conn).poll(cx)
+        });
+        (Either::Left(conn), recorder)
+    } else {
+        (Either::Right(conn), ping::disabled())
+    };
+    let conn = conn.map_err(|e| debug!("connection error: {}", e));
+
+    exec.execute(conn_task(conn, conn_drop_rx, cancel_tx));
+
+    Ok(ClientTask {
+        ping,
+        conn_drop_ref,
+        conn_eof,
+        executor: exec,
+        h2_tx,
+        req_rx,
+        fut_ctx: None,
+    })
+}
+
+async fn conn_task<C, D>(conn: C, drop_rx: D, cancel_tx: oneshot::Sender<Infallible>)
+where
+    C: Future + Unpin,
+    D: Future<Output = ()> + Unpin,
+{
+    match future::select(conn, drop_rx).await {
+        Either::Left(_) => {
+            // ok or err, the `conn` has finished
+        }
+        Either::Right(((), conn)) => {
+            // mpsc has been dropped, hopefully polling
+            // the connection some more should start shutdown
+            // and then close
+            trace!("send_request dropped, starting conn shutdown");
+            drop(cancel_tx);
+            let _ = conn.await;
+        }
+    }
+}
+
+struct FutCtx<B>
+where
+    B: HttpBody,
+{
+    is_connect: bool,
+    eos: bool,
+    fut: ResponseFuture,
+    body_tx: SendStream<SendBuf<B::Data>>,
+    body: B,
+    cb: Callback<Request<B>, Response<Body>>,
+}
+
+impl<B: HttpBody> Unpin for FutCtx<B> {}
+
+pub(crate) struct ClientTask<B>
+where
+    B: HttpBody,
+{
+    ping: ping::Recorder,
+    conn_drop_ref: ConnDropRef,
+    conn_eof: ConnEof,
+    executor: Exec,
+    h2_tx: SendRequest<SendBuf<B::Data>>,
+    req_rx: ClientRx<B>,
+    fut_ctx: Option<FutCtx<B>>,
+}
+
+impl<B> ClientTask<B>
+where
+    B: HttpBody + 'static,
+{
+    pub(crate) fn is_extended_connect_protocol_enabled(&self) -> bool {
+        self.h2_tx.is_extended_connect_protocol_enabled()
+    }
+}
+
+impl<B> ClientTask<B>
+where
+    B: HttpBody + Send + 'static,
+    B::Data: Send,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    fn poll_pipe(&mut self, f: FutCtx<B>, cx: &mut Context<'_>) {
+        let ping = self.ping.clone();
+        let send_stream = if !f.is_connect {
+            if !f.eos {
+                let mut pipe = Box::pin(PipeToSendStream::new(f.body, f.body_tx)).map(|res| {
+                    if let Err(e) = res {
+                        debug!("client request body error: {}", e);
+                    }
+                });
+
+                // eagerly see if the body pipe is ready and
+                // can thus skip allocating in the executor
+                match Pin::new(&mut pipe).poll(cx) {
+                    Poll::Ready(_) => (),
+                    Poll::Pending => {
+                        let conn_drop_ref = self.conn_drop_ref.clone();
+                        // keep the ping recorder's knowledge of an
+                        // "open stream" alive while this body is
+                        // still sending...
+                        let ping = ping.clone();
+                        let pipe = pipe.map(move |x| {
+                            drop(conn_drop_ref);
+                            drop(ping);
+                            x
+                        });
+                        // Clear send task
+                        self.executor.execute(pipe);
+                    }
+                }
+            }
+
+            None
+        } else {
+            Some(f.body_tx)
+        };
+
+        let fut = f.fut.map(move |result| match result {
+            Ok(res) => {
+                // record that we got the response headers
+                ping.record_non_data();
+
+                let content_length = headers::content_length_parse_all(res.headers());
+                if let (Some(mut send_stream), StatusCode::OK) = (send_stream, res.status()) {
+                    if content_length.map_or(false, |len| len != 0) {
+                        warn!("h2 connect response with non-zero body not supported");
+
+                        send_stream.send_reset(h2::Reason::INTERNAL_ERROR);
+                        return Err((
+                            crate::Error::new_h2(h2::Reason::INTERNAL_ERROR.into()),
+                            None,
+                        ));
+                    }
+                    let (parts, recv_stream) = res.into_parts();
+                    let mut res = Response::from_parts(parts, Body::empty());
+
+                    let (pending, on_upgrade) = crate::upgrade::pending();
+                    let io = H2Upgraded {
+                        ping,
+                        send_stream: unsafe { UpgradedSendStream::new(send_stream) },
+                        recv_stream,
+                        buf: Bytes::new(),
+                    };
+                    let upgraded = Upgraded::new(io, Bytes::new());
+
+                    pending.fulfill(upgraded);
+                    res.extensions_mut().insert(on_upgrade);
+
+                    Ok(res)
+                } else {
+                    let res = res.map(|stream| {
+                        let ping = ping.for_stream(&stream);
+                        crate::Body::h2(stream, content_length.into(), ping)
+                    });
+                    Ok(res)
+                }
+            }
+            Err(err) => {
+                ping.ensure_not_timed_out().map_err(|e| (e, None))?;
+
+                debug!("client response error: {}", err);
+                Err((crate::Error::new_h2(err), None))
+            }
+        });
+        self.executor.execute(f.cb.send_when(fut));
+    }
+}
+
+impl<B> Future for ClientTask<B>
+where
+    B: HttpBody + Send + 'static,
+    B::Data: Send,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type Output = crate::Result<Dispatched>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        loop {
+            match ready!(self.h2_tx.poll_ready(cx)) {
+                Ok(()) => (),
+                Err(err) => {
+                    self.ping.ensure_not_timed_out()?;
+                    return if err.reason() == Some(::h2::Reason::NO_ERROR) {
+                        trace!("connection gracefully shutdown");
+                        Poll::Ready(Ok(Dispatched::Shutdown))
+                    } else {
+                        Poll::Ready(Err(crate::Error::new_h2(err)))
+                    };
+                }
+            };
+
+            match self.fut_ctx.take() {
+                // If we were waiting on pending open
+                // continue where we left off.
+                Some(f) => {
+                    self.poll_pipe(f, cx);
+                    continue;
+                }
+                None => (),
+            }
+
+            match self.req_rx.poll_recv(cx) {
+                Poll::Ready(Some((req, cb))) => {
+                    // check that future hasn't been canceled already
+                    if cb.is_canceled() {
+                        trace!("request callback is canceled");
+                        continue;
+                    }
+                    let (head, body) = req.into_parts();
+                    let mut req = ::http::Request::from_parts(head, ());
+                    super::strip_connection_headers(req.headers_mut(), true);
+                    if let Some(len) = body.size_hint().exact() {
+                        if len != 0 || headers::method_has_defined_payload_semantics(req.method()) {
+                            headers::set_content_length_if_missing(req.headers_mut(), len);
+                        }
+                    }
+
+                    let is_connect = req.method() == Method::CONNECT;
+                    let eos = body.is_end_stream();
+
+                    if is_connect {
+                        if headers::content_length_parse_all(req.headers())
+                            .map_or(false, |len| len != 0)
+                        {
+                            warn!("h2 connect request with non-zero body not supported");
+                            cb.send(Err((
+                                crate::Error::new_h2(h2::Reason::INTERNAL_ERROR.into()),
+                                None,
+                            )));
+                            continue;
+                        }
+                    }
+
+                    if let Some(protocol) = req.extensions_mut().remove::<Protocol>() {
+                        req.extensions_mut().insert(protocol.into_inner());
+                    }
+
+                    let (fut, body_tx) = match self.h2_tx.send_request(req, !is_connect && eos) {
+                        Ok(ok) => ok,
+                        Err(err) => {
+                            debug!("client send request error: {}", err);
+                            cb.send(Err((crate::Error::new_h2(err), None)));
+                            continue;
+                        }
+                    };
+
+                    let f = FutCtx {
+                        is_connect,
+                        eos,
+                        fut,
+                        body_tx,
+                        body,
+                        cb,
+                    };
+
+                    // Check poll_ready() again.
+                    // If the call to send_request() resulted in the new stream being pending open
+                    // we have to wait for the open to complete before accepting new requests.
+                    match self.h2_tx.poll_ready(cx) {
+                        Poll::Pending => {
+                            // Save Context
+                            self.fut_ctx = Some(f);
+                            return Poll::Pending;
+                        }
+                        Poll::Ready(Ok(())) => (),
+                        Poll::Ready(Err(err)) => {
+                            f.cb.send(Err((crate::Error::new_h2(err), None)));
+                            continue;
+                        }
+                    }
+                    self.poll_pipe(f, cx);
+                    continue;
+                }
+
+                Poll::Ready(None) => {
+                    trace!("client::dispatch::Sender dropped");
+                    return Poll::Ready(Ok(Dispatched::Shutdown));
+                }
+
+                Poll::Pending => match ready!(Pin::new(&mut self.conn_eof).poll(cx)) {
+                    Ok(never) => match never {},
+                    Err(_conn_is_eof) => {
+                        trace!("connection task is closed, closing dispatch task");
+                        return Poll::Ready(Ok(Dispatched::Shutdown));
+                    }
+                },
+            }
+        }
+    }
+}
diff --git a/src/proto/h2/mod.rs b/src/proto/h2/mod.rs
new file mode 100644
index 0000000..d50850d
--- /dev/null
+++ b/src/proto/h2/mod.rs
@@ -0,0 +1,470 @@
+use bytes::{Buf, Bytes};
+use h2::{Reason, RecvStream, SendStream};
+use http::header::{HeaderName, CONNECTION, TE, TRAILER, TRANSFER_ENCODING, UPGRADE};
+use http::HeaderMap;
+use pin_project_lite::pin_project;
+use std::error::Error as StdError;
+use std::future::Future;
+use std::io::{self, Cursor, IoSlice};
+use std::mem;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
+use tracing::{debug, trace, warn};
+
+use crate::body::HttpBody;
+use crate::proto::h2::ping::Recorder;
+
+pub(crate) mod ping;
+
+cfg_client! {
+    pub(crate) mod client;
+    pub(crate) use self::client::ClientTask;
+}
+
+cfg_server! {
+    pub(crate) mod server;
+    pub(crate) use self::server::Server;
+}
+
+/// Default initial stream window size defined in HTTP2 spec.
+pub(crate) const SPEC_WINDOW_SIZE: u32 = 65_535;
+
+fn strip_connection_headers(headers: &mut HeaderMap, is_request: bool) {
+    // List of connection headers from:
+    // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Connection
+    //
+    // TE headers are allowed in HTTP/2 requests as long as the value is "trailers", so they're
+    // tested separately.
+    let connection_headers = [
+        HeaderName::from_lowercase(b"keep-alive").unwrap(),
+        HeaderName::from_lowercase(b"proxy-connection").unwrap(),
+        TRAILER,
+        TRANSFER_ENCODING,
+        UPGRADE,
+    ];
+
+    for header in connection_headers.iter() {
+        if headers.remove(header).is_some() {
+            warn!("Connection header illegal in HTTP/2: {}", header.as_str());
+        }
+    }
+
+    if is_request {
+        if headers
+            .get(TE)
+            .map(|te_header| te_header != "trailers")
+            .unwrap_or(false)
+        {
+            warn!("TE headers not set to \"trailers\" are illegal in HTTP/2 requests");
+            headers.remove(TE);
+        }
+    } else if headers.remove(TE).is_some() {
+        warn!("TE headers illegal in HTTP/2 responses");
+    }
+
+    if let Some(header) = headers.remove(CONNECTION) {
+        warn!(
+            "Connection header illegal in HTTP/2: {}",
+            CONNECTION.as_str()
+        );
+        let header_contents = header.to_str().unwrap();
+
+        // A `Connection` header may have a comma-separated list of names of other headers that
+        // are meant for only this specific connection.
+        //
+        // Iterate these names and remove them as headers. Connection-specific headers are
+        // forbidden in HTTP2, as that information has been moved into frame types of the h2
+        // protocol.
+        for name in header_contents.split(',') {
+            let name = name.trim();
+            headers.remove(name);
+        }
+    }
+}
+
+// body adapters used by both Client and Server
+
+pin_project! {
+    struct PipeToSendStream<S>
+    where
+        S: HttpBody,
+    {
+        body_tx: SendStream<SendBuf<S::Data>>,
+        data_done: bool,
+        #[pin]
+        stream: S,
+    }
+}
+
+impl<S> PipeToSendStream<S>
+where
+    S: HttpBody,
+{
+    fn new(stream: S, tx: SendStream<SendBuf<S::Data>>) -> PipeToSendStream<S> {
+        PipeToSendStream {
+            body_tx: tx,
+            data_done: false,
+            stream,
+        }
+    }
+}
+
+impl<S> Future for PipeToSendStream<S>
+where
+    S: HttpBody,
+    S::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type Output = crate::Result<()>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut me = self.project();
+        loop {
+            if !*me.data_done {
+                // we don't have the next chunk of data yet, so just reserve 1 byte to make
+                // sure there's some capacity available. h2 will handle the capacity management
+                // for the actual body chunk.
+                me.body_tx.reserve_capacity(1);
+
+                if me.body_tx.capacity() == 0 {
+                    loop {
+                        match ready!(me.body_tx.poll_capacity(cx)) {
+                            Some(Ok(0)) => {}
+                            Some(Ok(_)) => break,
+                            Some(Err(e)) => {
+                                return Poll::Ready(Err(crate::Error::new_body_write(e)))
+                            }
+                            None => {
+                                // None means the stream is no longer in a
+                                // streaming state, we either finished it
+                                // somehow, or the remote reset us.
+                                return Poll::Ready(Err(crate::Error::new_body_write(
+                                    "send stream capacity unexpectedly closed",
+                                )));
+                            }
+                        }
+                    }
+                } else if let Poll::Ready(reason) = me
+                    .body_tx
+                    .poll_reset(cx)
+                    .map_err(crate::Error::new_body_write)?
+                {
+                    debug!("stream received RST_STREAM: {:?}", reason);
+                    return Poll::Ready(Err(crate::Error::new_body_write(::h2::Error::from(
+                        reason,
+                    ))));
+                }
+
+                match ready!(me.stream.as_mut().poll_data(cx)) {
+                    Some(Ok(chunk)) => {
+                        let is_eos = me.stream.is_end_stream();
+                        trace!(
+                            "send body chunk: {} bytes, eos={}",
+                            chunk.remaining(),
+                            is_eos,
+                        );
+
+                        let buf = SendBuf::Buf(chunk);
+                        me.body_tx
+                            .send_data(buf, is_eos)
+                            .map_err(crate::Error::new_body_write)?;
+
+                        if is_eos {
+                            return Poll::Ready(Ok(()));
+                        }
+                    }
+                    Some(Err(e)) => return Poll::Ready(Err(me.body_tx.on_user_err(e))),
+                    None => {
+                        me.body_tx.reserve_capacity(0);
+                        let is_eos = me.stream.is_end_stream();
+                        if is_eos {
+                            return Poll::Ready(me.body_tx.send_eos_frame());
+                        } else {
+                            *me.data_done = true;
+                            // loop again to poll_trailers
+                        }
+                    }
+                }
+            } else {
+                if let Poll::Ready(reason) = me
+                    .body_tx
+                    .poll_reset(cx)
+                    .map_err(crate::Error::new_body_write)?
+                {
+                    debug!("stream received RST_STREAM: {:?}", reason);
+                    return Poll::Ready(Err(crate::Error::new_body_write(::h2::Error::from(
+                        reason,
+                    ))));
+                }
+
+                match ready!(me.stream.poll_trailers(cx)) {
+                    Ok(Some(trailers)) => {
+                        me.body_tx
+                            .send_trailers(trailers)
+                            .map_err(crate::Error::new_body_write)?;
+                        return Poll::Ready(Ok(()));
+                    }
+                    Ok(None) => {
+                        // There were no trailers, so send an empty DATA frame...
+                        return Poll::Ready(me.body_tx.send_eos_frame());
+                    }
+                    Err(e) => return Poll::Ready(Err(me.body_tx.on_user_err(e))),
+                }
+            }
+        }
+    }
+}
+
+trait SendStreamExt {
+    fn on_user_err<E>(&mut self, err: E) -> crate::Error
+    where
+        E: Into<Box<dyn std::error::Error + Send + Sync>>;
+    fn send_eos_frame(&mut self) -> crate::Result<()>;
+}
+
+impl<B: Buf> SendStreamExt for SendStream<SendBuf<B>> {
+    fn on_user_err<E>(&mut self, err: E) -> crate::Error
+    where
+        E: Into<Box<dyn std::error::Error + Send + Sync>>,
+    {
+        let err = crate::Error::new_user_body(err);
+        debug!("send body user stream error: {}", err);
+        self.send_reset(err.h2_reason());
+        err
+    }
+
+    fn send_eos_frame(&mut self) -> crate::Result<()> {
+        trace!("send body eos");
+        self.send_data(SendBuf::None, true)
+            .map_err(crate::Error::new_body_write)
+    }
+}
+
+#[repr(usize)]
+enum SendBuf<B> {
+    Buf(B),
+    Cursor(Cursor<Box<[u8]>>),
+    None,
+}
+
+impl<B: Buf> Buf for SendBuf<B> {
+    #[inline]
+    fn remaining(&self) -> usize {
+        match *self {
+            Self::Buf(ref b) => b.remaining(),
+            Self::Cursor(ref c) => Buf::remaining(c),
+            Self::None => 0,
+        }
+    }
+
+    #[inline]
+    fn chunk(&self) -> &[u8] {
+        match *self {
+            Self::Buf(ref b) => b.chunk(),
+            Self::Cursor(ref c) => c.chunk(),
+            Self::None => &[],
+        }
+    }
+
+    #[inline]
+    fn advance(&mut self, cnt: usize) {
+        match *self {
+            Self::Buf(ref mut b) => b.advance(cnt),
+            Self::Cursor(ref mut c) => c.advance(cnt),
+            Self::None => {}
+        }
+    }
+
+    fn chunks_vectored<'a>(&'a self, dst: &mut [IoSlice<'a>]) -> usize {
+        match *self {
+            Self::Buf(ref b) => b.chunks_vectored(dst),
+            Self::Cursor(ref c) => c.chunks_vectored(dst),
+            Self::None => 0,
+        }
+    }
+}
+
+struct H2Upgraded<B>
+where
+    B: Buf,
+{
+    ping: Recorder,
+    send_stream: UpgradedSendStream<B>,
+    recv_stream: RecvStream,
+    buf: Bytes,
+}
+
+impl<B> AsyncRead for H2Upgraded<B>
+where
+    B: Buf,
+{
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        read_buf: &mut ReadBuf<'_>,
+    ) -> Poll<Result<(), io::Error>> {
+        if self.buf.is_empty() {
+            self.buf = loop {
+                match ready!(self.recv_stream.poll_data(cx)) {
+                    None => return Poll::Ready(Ok(())),
+                    Some(Ok(buf)) if buf.is_empty() && !self.recv_stream.is_end_stream() => {
+                        continue
+                    }
+                    Some(Ok(buf)) => {
+                        self.ping.record_data(buf.len());
+                        break buf;
+                    }
+                    Some(Err(e)) => {
+                        return Poll::Ready(match e.reason() {
+                            Some(Reason::NO_ERROR) | Some(Reason::CANCEL) => Ok(()),
+                            Some(Reason::STREAM_CLOSED) => {
+                                Err(io::Error::new(io::ErrorKind::BrokenPipe, e))
+                            }
+                            _ => Err(h2_to_io_error(e)),
+                        })
+                    }
+                }
+            };
+        }
+        let cnt = std::cmp::min(self.buf.len(), read_buf.remaining());
+        read_buf.put_slice(&self.buf[..cnt]);
+        self.buf.advance(cnt);
+        let _ = self.recv_stream.flow_control().release_capacity(cnt);
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl<B> AsyncWrite for H2Upgraded<B>
+where
+    B: Buf,
+{
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<Result<usize, io::Error>> {
+        if buf.is_empty() {
+            return Poll::Ready(Ok(0));
+        }
+        self.send_stream.reserve_capacity(buf.len());
+
+        // We ignore all errors returned by `poll_capacity` and `write`, as we
+        // will get the correct from `poll_reset` anyway.
+        let cnt = match ready!(self.send_stream.poll_capacity(cx)) {
+            None => Some(0),
+            Some(Ok(cnt)) => self
+                .send_stream
+                .write(&buf[..cnt], false)
+                .ok()
+                .map(|()| cnt),
+            Some(Err(_)) => None,
+        };
+
+        if let Some(cnt) = cnt {
+            return Poll::Ready(Ok(cnt));
+        }
+
+        Poll::Ready(Err(h2_to_io_error(
+            match ready!(self.send_stream.poll_reset(cx)) {
+                Ok(Reason::NO_ERROR) | Ok(Reason::CANCEL) | Ok(Reason::STREAM_CLOSED) => {
+                    return Poll::Ready(Err(io::ErrorKind::BrokenPipe.into()))
+                }
+                Ok(reason) => reason.into(),
+                Err(e) => e,
+            },
+        )))
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_shutdown(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), io::Error>> {
+        if self.send_stream.write(&[], true).is_ok() {
+            return Poll::Ready(Ok(()));
+        }
+
+        Poll::Ready(Err(h2_to_io_error(
+            match ready!(self.send_stream.poll_reset(cx)) {
+                Ok(Reason::NO_ERROR) => return Poll::Ready(Ok(())),
+                Ok(Reason::CANCEL) | Ok(Reason::STREAM_CLOSED) => {
+                    return Poll::Ready(Err(io::ErrorKind::BrokenPipe.into()))
+                }
+                Ok(reason) => reason.into(),
+                Err(e) => e,
+            },
+        )))
+    }
+}
+
+fn h2_to_io_error(e: h2::Error) -> io::Error {
+    if e.is_io() {
+        e.into_io().unwrap()
+    } else {
+        io::Error::new(io::ErrorKind::Other, e)
+    }
+}
+
+struct UpgradedSendStream<B>(SendStream<SendBuf<Neutered<B>>>);
+
+impl<B> UpgradedSendStream<B>
+where
+    B: Buf,
+{
+    unsafe fn new(inner: SendStream<SendBuf<B>>) -> Self {
+        assert_eq!(mem::size_of::<B>(), mem::size_of::<Neutered<B>>());
+        Self(mem::transmute(inner))
+    }
+
+    fn reserve_capacity(&mut self, cnt: usize) {
+        unsafe { self.as_inner_unchecked().reserve_capacity(cnt) }
+    }
+
+    fn poll_capacity(&mut self, cx: &mut Context<'_>) -> Poll<Option<Result<usize, h2::Error>>> {
+        unsafe { self.as_inner_unchecked().poll_capacity(cx) }
+    }
+
+    fn poll_reset(&mut self, cx: &mut Context<'_>) -> Poll<Result<h2::Reason, h2::Error>> {
+        unsafe { self.as_inner_unchecked().poll_reset(cx) }
+    }
+
+    fn write(&mut self, buf: &[u8], end_of_stream: bool) -> Result<(), io::Error> {
+        let send_buf = SendBuf::Cursor(Cursor::new(buf.into()));
+        unsafe {
+            self.as_inner_unchecked()
+                .send_data(send_buf, end_of_stream)
+                .map_err(h2_to_io_error)
+        }
+    }
+
+    unsafe fn as_inner_unchecked(&mut self) -> &mut SendStream<SendBuf<B>> {
+        &mut *(&mut self.0 as *mut _ as *mut _)
+    }
+}
+
+#[repr(transparent)]
+struct Neutered<B> {
+    _inner: B,
+    impossible: Impossible,
+}
+
+enum Impossible {}
+
+unsafe impl<B> Send for Neutered<B> {}
+
+impl<B> Buf for Neutered<B> {
+    fn remaining(&self) -> usize {
+        match self.impossible {}
+    }
+
+    fn chunk(&self) -> &[u8] {
+        match self.impossible {}
+    }
+
+    fn advance(&mut self, _cnt: usize) {
+        match self.impossible {}
+    }
+}
diff --git a/src/proto/h2/ping.rs b/src/proto/h2/ping.rs
new file mode 100644
index 0000000..d830c93
--- /dev/null
+++ b/src/proto/h2/ping.rs
@@ -0,0 +1,555 @@
+/// HTTP2 Ping usage
+///
+/// hyper uses HTTP2 pings for two purposes:
+///
+/// 1. Adaptive flow control using BDP
+/// 2. Connection keep-alive
+///
+/// Both cases are optional.
+///
+/// # BDP Algorithm
+///
+/// 1. When receiving a DATA frame, if a BDP ping isn't outstanding:
+///   1a. Record current time.
+///   1b. Send a BDP ping.
+/// 2. Increment the number of received bytes.
+/// 3. When the BDP ping ack is received:
+///   3a. Record duration from sent time.
+///   3b. Merge RTT with a running average.
+///   3c. Calculate bdp as bytes/rtt.
+///   3d. If bdp is over 2/3 max, set new max to bdp and update windows.
+
+#[cfg(feature = "runtime")]
+use std::fmt;
+#[cfg(feature = "runtime")]
+use std::future::Future;
+#[cfg(feature = "runtime")]
+use std::pin::Pin;
+use std::sync::{Arc, Mutex};
+use std::task::{self, Poll};
+use std::time::Duration;
+#[cfg(not(feature = "runtime"))]
+use std::time::Instant;
+
+use h2::{Ping, PingPong};
+#[cfg(feature = "runtime")]
+use tokio::time::{Instant, Sleep};
+use tracing::{debug, trace};
+
+type WindowSize = u32;
+
+pub(super) fn disabled() -> Recorder {
+    Recorder { shared: None }
+}
+
+pub(super) fn channel(ping_pong: PingPong, config: Config) -> (Recorder, Ponger) {
+    debug_assert!(
+        config.is_enabled(),
+        "ping channel requires bdp or keep-alive config",
+    );
+
+    let bdp = config.bdp_initial_window.map(|wnd| Bdp {
+        bdp: wnd,
+        max_bandwidth: 0.0,
+        rtt: 0.0,
+        ping_delay: Duration::from_millis(100),
+        stable_count: 0,
+    });
+
+    let (bytes, next_bdp_at) = if bdp.is_some() {
+        (Some(0), Some(Instant::now()))
+    } else {
+        (None, None)
+    };
+
+    #[cfg(feature = "runtime")]
+    let keep_alive = config.keep_alive_interval.map(|interval| KeepAlive {
+        interval,
+        timeout: config.keep_alive_timeout,
+        while_idle: config.keep_alive_while_idle,
+        timer: Box::pin(tokio::time::sleep(interval)),
+        state: KeepAliveState::Init,
+    });
+
+    #[cfg(feature = "runtime")]
+    let last_read_at = keep_alive.as_ref().map(|_| Instant::now());
+
+    let shared = Arc::new(Mutex::new(Shared {
+        bytes,
+        #[cfg(feature = "runtime")]
+        last_read_at,
+        #[cfg(feature = "runtime")]
+        is_keep_alive_timed_out: false,
+        ping_pong,
+        ping_sent_at: None,
+        next_bdp_at,
+    }));
+
+    (
+        Recorder {
+            shared: Some(shared.clone()),
+        },
+        Ponger {
+            bdp,
+            #[cfg(feature = "runtime")]
+            keep_alive,
+            shared,
+        },
+    )
+}
+
+#[derive(Clone)]
+pub(super) struct Config {
+    pub(super) bdp_initial_window: Option<WindowSize>,
+    /// If no frames are received in this amount of time, a PING frame is sent.
+    #[cfg(feature = "runtime")]
+    pub(super) keep_alive_interval: Option<Duration>,
+    /// After sending a keepalive PING, the connection will be closed if
+    /// a pong is not received in this amount of time.
+    #[cfg(feature = "runtime")]
+    pub(super) keep_alive_timeout: Duration,
+    /// If true, sends pings even when there are no active streams.
+    #[cfg(feature = "runtime")]
+    pub(super) keep_alive_while_idle: bool,
+}
+
+#[derive(Clone)]
+pub(crate) struct Recorder {
+    shared: Option<Arc<Mutex<Shared>>>,
+}
+
+pub(super) struct Ponger {
+    bdp: Option<Bdp>,
+    #[cfg(feature = "runtime")]
+    keep_alive: Option<KeepAlive>,
+    shared: Arc<Mutex<Shared>>,
+}
+
+struct Shared {
+    ping_pong: PingPong,
+    ping_sent_at: Option<Instant>,
+
+    // bdp
+    /// If `Some`, bdp is enabled, and this tracks how many bytes have been
+    /// read during the current sample.
+    bytes: Option<usize>,
+    /// We delay a variable amount of time between BDP pings. This allows us
+    /// to send less pings as the bandwidth stabilizes.
+    next_bdp_at: Option<Instant>,
+
+    // keep-alive
+    /// If `Some`, keep-alive is enabled, and the Instant is how long ago
+    /// the connection read the last frame.
+    #[cfg(feature = "runtime")]
+    last_read_at: Option<Instant>,
+
+    #[cfg(feature = "runtime")]
+    is_keep_alive_timed_out: bool,
+}
+
+struct Bdp {
+    /// Current BDP in bytes
+    bdp: u32,
+    /// Largest bandwidth we've seen so far.
+    max_bandwidth: f64,
+    /// Round trip time in seconds
+    rtt: f64,
+    /// Delay the next ping by this amount.
+    ///
+    /// This will change depending on how stable the current bandwidth is.
+    ping_delay: Duration,
+    /// The count of ping round trips where BDP has stayed the same.
+    stable_count: u32,
+}
+
+#[cfg(feature = "runtime")]
+struct KeepAlive {
+    /// If no frames are received in this amount of time, a PING frame is sent.
+    interval: Duration,
+    /// After sending a keepalive PING, the connection will be closed if
+    /// a pong is not received in this amount of time.
+    timeout: Duration,
+    /// If true, sends pings even when there are no active streams.
+    while_idle: bool,
+
+    state: KeepAliveState,
+    timer: Pin<Box<Sleep>>,
+}
+
+#[cfg(feature = "runtime")]
+enum KeepAliveState {
+    Init,
+    Scheduled,
+    PingSent,
+}
+
+pub(super) enum Ponged {
+    SizeUpdate(WindowSize),
+    #[cfg(feature = "runtime")]
+    KeepAliveTimedOut,
+}
+
+#[cfg(feature = "runtime")]
+#[derive(Debug)]
+pub(super) struct KeepAliveTimedOut;
+
+// ===== impl Config =====
+
+impl Config {
+    pub(super) fn is_enabled(&self) -> bool {
+        #[cfg(feature = "runtime")]
+        {
+            self.bdp_initial_window.is_some() || self.keep_alive_interval.is_some()
+        }
+
+        #[cfg(not(feature = "runtime"))]
+        {
+            self.bdp_initial_window.is_some()
+        }
+    }
+}
+
+// ===== impl Recorder =====
+
+impl Recorder {
+    pub(crate) fn record_data(&self, len: usize) {
+        let shared = if let Some(ref shared) = self.shared {
+            shared
+        } else {
+            return;
+        };
+
+        let mut locked = shared.lock().unwrap();
+
+        #[cfg(feature = "runtime")]
+        locked.update_last_read_at();
+
+        // are we ready to send another bdp ping?
+        // if not, we don't need to record bytes either
+
+        if let Some(ref next_bdp_at) = locked.next_bdp_at {
+            if Instant::now() < *next_bdp_at {
+                return;
+            } else {
+                locked.next_bdp_at = None;
+            }
+        }
+
+        if let Some(ref mut bytes) = locked.bytes {
+            *bytes += len;
+        } else {
+            // no need to send bdp ping if bdp is disabled
+            return;
+        }
+
+        if !locked.is_ping_sent() {
+            locked.send_ping();
+        }
+    }
+
+    pub(crate) fn record_non_data(&self) {
+        #[cfg(feature = "runtime")]
+        {
+            let shared = if let Some(ref shared) = self.shared {
+                shared
+            } else {
+                return;
+            };
+
+            let mut locked = shared.lock().unwrap();
+
+            locked.update_last_read_at();
+        }
+    }
+
+    /// If the incoming stream is already closed, convert self into
+    /// a disabled reporter.
+    #[cfg(feature = "client")]
+    pub(super) fn for_stream(self, stream: &h2::RecvStream) -> Self {
+        if stream.is_end_stream() {
+            disabled()
+        } else {
+            self
+        }
+    }
+
+    pub(super) fn ensure_not_timed_out(&self) -> crate::Result<()> {
+        #[cfg(feature = "runtime")]
+        {
+            if let Some(ref shared) = self.shared {
+                let locked = shared.lock().unwrap();
+                if locked.is_keep_alive_timed_out {
+                    return Err(KeepAliveTimedOut.crate_error());
+                }
+            }
+        }
+
+        // else
+        Ok(())
+    }
+}
+
+// ===== impl Ponger =====
+
+impl Ponger {
+    pub(super) fn poll(&mut self, cx: &mut task::Context<'_>) -> Poll<Ponged> {
+        let now = Instant::now();
+        let mut locked = self.shared.lock().unwrap();
+        #[cfg(feature = "runtime")]
+        let is_idle = self.is_idle();
+
+        #[cfg(feature = "runtime")]
+        {
+            if let Some(ref mut ka) = self.keep_alive {
+                ka.schedule(is_idle, &locked);
+                ka.maybe_ping(cx, &mut locked);
+            }
+        }
+
+        if !locked.is_ping_sent() {
+            // XXX: this doesn't register a waker...?
+            return Poll::Pending;
+        }
+
+        match locked.ping_pong.poll_pong(cx) {
+            Poll::Ready(Ok(_pong)) => {
+                let start = locked
+                    .ping_sent_at
+                    .expect("pong received implies ping_sent_at");
+                locked.ping_sent_at = None;
+                let rtt = now - start;
+                trace!("recv pong");
+
+                #[cfg(feature = "runtime")]
+                {
+                    if let Some(ref mut ka) = self.keep_alive {
+                        locked.update_last_read_at();
+                        ka.schedule(is_idle, &locked);
+                    }
+                }
+
+                if let Some(ref mut bdp) = self.bdp {
+                    let bytes = locked.bytes.expect("bdp enabled implies bytes");
+                    locked.bytes = Some(0); // reset
+                    trace!("received BDP ack; bytes = {}, rtt = {:?}", bytes, rtt);
+
+                    let update = bdp.calculate(bytes, rtt);
+                    locked.next_bdp_at = Some(now + bdp.ping_delay);
+                    if let Some(update) = update {
+                        return Poll::Ready(Ponged::SizeUpdate(update));
+                    }
+                }
+            }
+            Poll::Ready(Err(e)) => {
+                debug!("pong error: {}", e);
+            }
+            Poll::Pending => {
+                #[cfg(feature = "runtime")]
+                {
+                    if let Some(ref mut ka) = self.keep_alive {
+                        if let Err(KeepAliveTimedOut) = ka.maybe_timeout(cx) {
+                            self.keep_alive = None;
+                            locked.is_keep_alive_timed_out = true;
+                            return Poll::Ready(Ponged::KeepAliveTimedOut);
+                        }
+                    }
+                }
+            }
+        }
+
+        // XXX: this doesn't register a waker...?
+        Poll::Pending
+    }
+
+    #[cfg(feature = "runtime")]
+    fn is_idle(&self) -> bool {
+        Arc::strong_count(&self.shared) <= 2
+    }
+}
+
+// ===== impl Shared =====
+
+impl Shared {
+    fn send_ping(&mut self) {
+        match self.ping_pong.send_ping(Ping::opaque()) {
+            Ok(()) => {
+                self.ping_sent_at = Some(Instant::now());
+                trace!("sent ping");
+            }
+            Err(err) => {
+                debug!("error sending ping: {}", err);
+            }
+        }
+    }
+
+    fn is_ping_sent(&self) -> bool {
+        self.ping_sent_at.is_some()
+    }
+
+    #[cfg(feature = "runtime")]
+    fn update_last_read_at(&mut self) {
+        if self.last_read_at.is_some() {
+            self.last_read_at = Some(Instant::now());
+        }
+    }
+
+    #[cfg(feature = "runtime")]
+    fn last_read_at(&self) -> Instant {
+        self.last_read_at.expect("keep_alive expects last_read_at")
+    }
+}
+
+// ===== impl Bdp =====
+
+/// Any higher than this likely will be hitting the TCP flow control.
+const BDP_LIMIT: usize = 1024 * 1024 * 16;
+
+impl Bdp {
+    fn calculate(&mut self, bytes: usize, rtt: Duration) -> Option<WindowSize> {
+        // No need to do any math if we're at the limit.
+        if self.bdp as usize == BDP_LIMIT {
+            self.stabilize_delay();
+            return None;
+        }
+
+        // average the rtt
+        let rtt = seconds(rtt);
+        if self.rtt == 0.0 {
+            // First sample means rtt is first rtt.
+            self.rtt = rtt;
+        } else {
+            // Weigh this rtt as 1/8 for a moving average.
+            self.rtt += (rtt - self.rtt) * 0.125;
+        }
+
+        // calculate the current bandwidth
+        let bw = (bytes as f64) / (self.rtt * 1.5);
+        trace!("current bandwidth = {:.1}B/s", bw);
+
+        if bw < self.max_bandwidth {
+            // not a faster bandwidth, so don't update
+            self.stabilize_delay();
+            return None;
+        } else {
+            self.max_bandwidth = bw;
+        }
+
+        // if the current `bytes` sample is at least 2/3 the previous
+        // bdp, increase to double the current sample.
+        if bytes >= self.bdp as usize * 2 / 3 {
+            self.bdp = (bytes * 2).min(BDP_LIMIT) as WindowSize;
+            trace!("BDP increased to {}", self.bdp);
+
+            self.stable_count = 0;
+            self.ping_delay /= 2;
+            Some(self.bdp)
+        } else {
+            self.stabilize_delay();
+            None
+        }
+    }
+
+    fn stabilize_delay(&mut self) {
+        if self.ping_delay < Duration::from_secs(10) {
+            self.stable_count += 1;
+
+            if self.stable_count >= 2 {
+                self.ping_delay *= 4;
+                self.stable_count = 0;
+            }
+        }
+    }
+}
+
+fn seconds(dur: Duration) -> f64 {
+    const NANOS_PER_SEC: f64 = 1_000_000_000.0;
+    let secs = dur.as_secs() as f64;
+    secs + (dur.subsec_nanos() as f64) / NANOS_PER_SEC
+}
+
+// ===== impl KeepAlive =====
+
+#[cfg(feature = "runtime")]
+impl KeepAlive {
+    fn schedule(&mut self, is_idle: bool, shared: &Shared) {
+        match self.state {
+            KeepAliveState::Init => {
+                if !self.while_idle && is_idle {
+                    return;
+                }
+
+                self.state = KeepAliveState::Scheduled;
+                let interval = shared.last_read_at() + self.interval;
+                self.timer.as_mut().reset(interval);
+            }
+            KeepAliveState::PingSent => {
+                if shared.is_ping_sent() {
+                    return;
+                }
+
+                self.state = KeepAliveState::Scheduled;
+                let interval = shared.last_read_at() + self.interval;
+                self.timer.as_mut().reset(interval);
+            }
+            KeepAliveState::Scheduled => (),
+        }
+    }
+
+    fn maybe_ping(&mut self, cx: &mut task::Context<'_>, shared: &mut Shared) {
+        match self.state {
+            KeepAliveState::Scheduled => {
+                if Pin::new(&mut self.timer).poll(cx).is_pending() {
+                    return;
+                }
+                // check if we've received a frame while we were scheduled
+                if shared.last_read_at() + self.interval > self.timer.deadline() {
+                    self.state = KeepAliveState::Init;
+                    cx.waker().wake_by_ref(); // schedule us again
+                    return;
+                }
+                trace!("keep-alive interval ({:?}) reached", self.interval);
+                shared.send_ping();
+                self.state = KeepAliveState::PingSent;
+                let timeout = Instant::now() + self.timeout;
+                self.timer.as_mut().reset(timeout);
+            }
+            KeepAliveState::Init | KeepAliveState::PingSent => (),
+        }
+    }
+
+    fn maybe_timeout(&mut self, cx: &mut task::Context<'_>) -> Result<(), KeepAliveTimedOut> {
+        match self.state {
+            KeepAliveState::PingSent => {
+                if Pin::new(&mut self.timer).poll(cx).is_pending() {
+                    return Ok(());
+                }
+                trace!("keep-alive timeout ({:?}) reached", self.timeout);
+                Err(KeepAliveTimedOut)
+            }
+            KeepAliveState::Init | KeepAliveState::Scheduled => Ok(()),
+        }
+    }
+}
+
+// ===== impl KeepAliveTimedOut =====
+
+#[cfg(feature = "runtime")]
+impl KeepAliveTimedOut {
+    pub(super) fn crate_error(self) -> crate::Error {
+        crate::Error::new(crate::error::Kind::Http2).with(self)
+    }
+}
+
+#[cfg(feature = "runtime")]
+impl fmt::Display for KeepAliveTimedOut {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("keep-alive timed out")
+    }
+}
+
+#[cfg(feature = "runtime")]
+impl std::error::Error for KeepAliveTimedOut {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        Some(&crate::error::TimedOut)
+    }
+}
diff --git a/src/proto/h2/server.rs b/src/proto/h2/server.rs
new file mode 100644
index 0000000..b4e8d68
--- /dev/null
+++ b/src/proto/h2/server.rs
@@ -0,0 +1,554 @@
+use std::error::Error as StdError;
+use std::future::Future;
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+#[cfg(feature = "runtime")]
+use std::time::Duration;
+
+use bytes::Bytes;
+use h2::server::{Connection, Handshake, SendResponse};
+use h2::{Reason, RecvStream};
+use http::{Method, Request};
+use pin_project_lite::pin_project;
+use tokio::io::{AsyncRead, AsyncWrite};
+use tracing::{debug, trace, warn};
+
+use super::{ping, PipeToSendStream, SendBuf};
+use crate::body::HttpBody;
+use crate::common::date;
+use crate::common::exec::ConnStreamExec;
+use crate::ext::Protocol;
+use crate::headers;
+use crate::proto::h2::ping::Recorder;
+use crate::proto::h2::{H2Upgraded, UpgradedSendStream};
+use crate::proto::Dispatched;
+use crate::service::HttpService;
+
+use crate::upgrade::{OnUpgrade, Pending, Upgraded};
+use crate::{Body, Response};
+
+// Our defaults are chosen for the "majority" case, which usually are not
+// resource constrained, and so the spec default of 64kb can be too limiting
+// for performance.
+//
+// At the same time, a server more often has multiple clients connected, and
+// so is more likely to use more resources than a client would.
+const DEFAULT_CONN_WINDOW: u32 = 1024 * 1024; // 1mb
+const DEFAULT_STREAM_WINDOW: u32 = 1024 * 1024; // 1mb
+const DEFAULT_MAX_FRAME_SIZE: u32 = 1024 * 16; // 16kb
+const DEFAULT_MAX_SEND_BUF_SIZE: usize = 1024 * 400; // 400kb
+const DEFAULT_SETTINGS_MAX_HEADER_LIST_SIZE: u32 = 16 << 20; // 16 MB "sane default" taken from golang http2
+
+#[derive(Clone, Debug)]
+pub(crate) struct Config {
+    pub(crate) adaptive_window: bool,
+    pub(crate) initial_conn_window_size: u32,
+    pub(crate) initial_stream_window_size: u32,
+    pub(crate) max_frame_size: u32,
+    pub(crate) enable_connect_protocol: bool,
+    pub(crate) max_concurrent_streams: Option<u32>,
+    pub(crate) max_pending_accept_reset_streams: Option<usize>,
+    #[cfg(feature = "runtime")]
+    pub(crate) keep_alive_interval: Option<Duration>,
+    #[cfg(feature = "runtime")]
+    pub(crate) keep_alive_timeout: Duration,
+    pub(crate) max_send_buffer_size: usize,
+    pub(crate) max_header_list_size: u32,
+}
+
+impl Default for Config {
+    fn default() -> Config {
+        Config {
+            adaptive_window: false,
+            initial_conn_window_size: DEFAULT_CONN_WINDOW,
+            initial_stream_window_size: DEFAULT_STREAM_WINDOW,
+            max_frame_size: DEFAULT_MAX_FRAME_SIZE,
+            enable_connect_protocol: false,
+            max_concurrent_streams: None,
+            max_pending_accept_reset_streams: None,
+            #[cfg(feature = "runtime")]
+            keep_alive_interval: None,
+            #[cfg(feature = "runtime")]
+            keep_alive_timeout: Duration::from_secs(20),
+            max_send_buffer_size: DEFAULT_MAX_SEND_BUF_SIZE,
+            max_header_list_size: DEFAULT_SETTINGS_MAX_HEADER_LIST_SIZE,
+        }
+    }
+}
+
+pin_project! {
+    pub(crate) struct Server<T, S, B, E>
+    where
+        S: HttpService<Body>,
+        B: HttpBody,
+    {
+        exec: E,
+        service: S,
+        state: State<T, B>,
+    }
+}
+
+enum State<T, B>
+where
+    B: HttpBody,
+{
+    Handshaking {
+        ping_config: ping::Config,
+        hs: Handshake<T, SendBuf<B::Data>>,
+    },
+    Serving(Serving<T, B>),
+    Closed,
+}
+
+struct Serving<T, B>
+where
+    B: HttpBody,
+{
+    ping: Option<(ping::Recorder, ping::Ponger)>,
+    conn: Connection<T, SendBuf<B::Data>>,
+    closing: Option<crate::Error>,
+}
+
+impl<T, S, B, E> Server<T, S, B, E>
+where
+    T: AsyncRead + AsyncWrite + Unpin,
+    S: HttpService<Body, ResBody = B>,
+    S::Error: Into<Box<dyn StdError + Send + Sync>>,
+    B: HttpBody + 'static,
+    E: ConnStreamExec<S::Future, B>,
+{
+    pub(crate) fn new(io: T, service: S, config: &Config, exec: E) -> Server<T, S, B, E> {
+        let mut builder = h2::server::Builder::default();
+        builder
+            .initial_window_size(config.initial_stream_window_size)
+            .initial_connection_window_size(config.initial_conn_window_size)
+            .max_frame_size(config.max_frame_size)
+            .max_header_list_size(config.max_header_list_size)
+            .max_send_buffer_size(config.max_send_buffer_size);
+        if let Some(max) = config.max_concurrent_streams {
+            builder.max_concurrent_streams(max);
+        }
+        if let Some(max) = config.max_pending_accept_reset_streams {
+            builder.max_pending_accept_reset_streams(max);
+        }
+        if config.enable_connect_protocol {
+            builder.enable_connect_protocol();
+        }
+        let handshake = builder.handshake(io);
+
+        let bdp = if config.adaptive_window {
+            Some(config.initial_stream_window_size)
+        } else {
+            None
+        };
+
+        let ping_config = ping::Config {
+            bdp_initial_window: bdp,
+            #[cfg(feature = "runtime")]
+            keep_alive_interval: config.keep_alive_interval,
+            #[cfg(feature = "runtime")]
+            keep_alive_timeout: config.keep_alive_timeout,
+            // If keep-alive is enabled for servers, always enabled while
+            // idle, so it can more aggressively close dead connections.
+            #[cfg(feature = "runtime")]
+            keep_alive_while_idle: true,
+        };
+
+        Server {
+            exec,
+            state: State::Handshaking {
+                ping_config,
+                hs: handshake,
+            },
+            service,
+        }
+    }
+
+    pub(crate) fn graceful_shutdown(&mut self) {
+        trace!("graceful_shutdown");
+        match self.state {
+            State::Handshaking { .. } => {
+                // fall-through, to replace state with Closed
+            }
+            State::Serving(ref mut srv) => {
+                if srv.closing.is_none() {
+                    srv.conn.graceful_shutdown();
+                }
+                return;
+            }
+            State::Closed => {
+                return;
+            }
+        }
+        self.state = State::Closed;
+    }
+}
+
+impl<T, S, B, E> Future for Server<T, S, B, E>
+where
+    T: AsyncRead + AsyncWrite + Unpin,
+    S: HttpService<Body, ResBody = B>,
+    S::Error: Into<Box<dyn StdError + Send + Sync>>,
+    B: HttpBody + 'static,
+    E: ConnStreamExec<S::Future, B>,
+{
+    type Output = crate::Result<Dispatched>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let me = &mut *self;
+        loop {
+            let next = match me.state {
+                State::Handshaking {
+                    ref mut hs,
+                    ref ping_config,
+                } => {
+                    let mut conn = ready!(Pin::new(hs).poll(cx).map_err(crate::Error::new_h2))?;
+                    let ping = if ping_config.is_enabled() {
+                        let pp = conn.ping_pong().expect("conn.ping_pong");
+                        Some(ping::channel(pp, ping_config.clone()))
+                    } else {
+                        None
+                    };
+                    State::Serving(Serving {
+                        ping,
+                        conn,
+                        closing: None,
+                    })
+                }
+                State::Serving(ref mut srv) => {
+                    ready!(srv.poll_server(cx, &mut me.service, &mut me.exec))?;
+                    return Poll::Ready(Ok(Dispatched::Shutdown));
+                }
+                State::Closed => {
+                    // graceful_shutdown was called before handshaking finished,
+                    // nothing to do here...
+                    return Poll::Ready(Ok(Dispatched::Shutdown));
+                }
+            };
+            me.state = next;
+        }
+    }
+}
+
+impl<T, B> Serving<T, B>
+where
+    T: AsyncRead + AsyncWrite + Unpin,
+    B: HttpBody + 'static,
+{
+    fn poll_server<S, E>(
+        &mut self,
+        cx: &mut Context<'_>,
+        service: &mut S,
+        exec: &mut E,
+    ) -> Poll<crate::Result<()>>
+    where
+        S: HttpService<Body, ResBody = B>,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        E: ConnStreamExec<S::Future, B>,
+    {
+        if self.closing.is_none() {
+            loop {
+                self.poll_ping(cx);
+
+                // Check that the service is ready to accept a new request.
+                //
+                // - If not, just drive the connection some.
+                // - If ready, try to accept a new request from the connection.
+                match service.poll_ready(cx) {
+                    Poll::Ready(Ok(())) => (),
+                    Poll::Pending => {
+                        // use `poll_closed` instead of `poll_accept`,
+                        // in order to avoid accepting a request.
+                        ready!(self.conn.poll_closed(cx).map_err(crate::Error::new_h2))?;
+                        trace!("incoming connection complete");
+                        return Poll::Ready(Ok(()));
+                    }
+                    Poll::Ready(Err(err)) => {
+                        let err = crate::Error::new_user_service(err);
+                        debug!("service closed: {}", err);
+
+                        let reason = err.h2_reason();
+                        if reason == Reason::NO_ERROR {
+                            // NO_ERROR is only used for graceful shutdowns...
+                            trace!("interpreting NO_ERROR user error as graceful_shutdown");
+                            self.conn.graceful_shutdown();
+                        } else {
+                            trace!("abruptly shutting down with {:?}", reason);
+                            self.conn.abrupt_shutdown(reason);
+                        }
+                        self.closing = Some(err);
+                        break;
+                    }
+                }
+
+                // When the service is ready, accepts an incoming request.
+                match ready!(self.conn.poll_accept(cx)) {
+                    Some(Ok((req, mut respond))) => {
+                        trace!("incoming request");
+                        let content_length = headers::content_length_parse_all(req.headers());
+                        let ping = self
+                            .ping
+                            .as_ref()
+                            .map(|ping| ping.0.clone())
+                            .unwrap_or_else(ping::disabled);
+
+                        // Record the headers received
+                        ping.record_non_data();
+
+                        let is_connect = req.method() == Method::CONNECT;
+                        let (mut parts, stream) = req.into_parts();
+                        let (mut req, connect_parts) = if !is_connect {
+                            (
+                                Request::from_parts(
+                                    parts,
+                                    crate::Body::h2(stream, content_length.into(), ping),
+                                ),
+                                None,
+                            )
+                        } else {
+                            if content_length.map_or(false, |len| len != 0) {
+                                warn!("h2 connect request with non-zero body not supported");
+                                respond.send_reset(h2::Reason::INTERNAL_ERROR);
+                                return Poll::Ready(Ok(()));
+                            }
+                            let (pending, upgrade) = crate::upgrade::pending();
+                            debug_assert!(parts.extensions.get::<OnUpgrade>().is_none());
+                            parts.extensions.insert(upgrade);
+                            (
+                                Request::from_parts(parts, crate::Body::empty()),
+                                Some(ConnectParts {
+                                    pending,
+                                    ping,
+                                    recv_stream: stream,
+                                }),
+                            )
+                        };
+
+                        if let Some(protocol) = req.extensions_mut().remove::<h2::ext::Protocol>() {
+                            req.extensions_mut().insert(Protocol::from_inner(protocol));
+                        }
+
+                        let fut = H2Stream::new(service.call(req), connect_parts, respond);
+                        exec.execute_h2stream(fut);
+                    }
+                    Some(Err(e)) => {
+                        return Poll::Ready(Err(crate::Error::new_h2(e)));
+                    }
+                    None => {
+                        // no more incoming streams...
+                        if let Some((ref ping, _)) = self.ping {
+                            ping.ensure_not_timed_out()?;
+                        }
+
+                        trace!("incoming connection complete");
+                        return Poll::Ready(Ok(()));
+                    }
+                }
+            }
+        }
+
+        debug_assert!(
+            self.closing.is_some(),
+            "poll_server broke loop without closing"
+        );
+
+        ready!(self.conn.poll_closed(cx).map_err(crate::Error::new_h2))?;
+
+        Poll::Ready(Err(self.closing.take().expect("polled after error")))
+    }
+
+    fn poll_ping(&mut self, cx: &mut Context<'_>) {
+        if let Some((_, ref mut estimator)) = self.ping {
+            match estimator.poll(cx) {
+                Poll::Ready(ping::Ponged::SizeUpdate(wnd)) => {
+                    self.conn.set_target_window_size(wnd);
+                    let _ = self.conn.set_initial_window_size(wnd);
+                }
+                #[cfg(feature = "runtime")]
+                Poll::Ready(ping::Ponged::KeepAliveTimedOut) => {
+                    debug!("keep-alive timed out, closing connection");
+                    self.conn.abrupt_shutdown(h2::Reason::NO_ERROR);
+                }
+                Poll::Pending => {}
+            }
+        }
+    }
+}
+
+pin_project! {
+    #[allow(missing_debug_implementations)]
+    pub struct H2Stream<F, B>
+    where
+        B: HttpBody,
+    {
+        reply: SendResponse<SendBuf<B::Data>>,
+        #[pin]
+        state: H2StreamState<F, B>,
+    }
+}
+
+pin_project! {
+    #[project = H2StreamStateProj]
+    enum H2StreamState<F, B>
+    where
+        B: HttpBody,
+    {
+        Service {
+            #[pin]
+            fut: F,
+            connect_parts: Option<ConnectParts>,
+        },
+        Body {
+            #[pin]
+            pipe: PipeToSendStream<B>,
+        },
+    }
+}
+
+struct ConnectParts {
+    pending: Pending,
+    ping: Recorder,
+    recv_stream: RecvStream,
+}
+
+impl<F, B> H2Stream<F, B>
+where
+    B: HttpBody,
+{
+    fn new(
+        fut: F,
+        connect_parts: Option<ConnectParts>,
+        respond: SendResponse<SendBuf<B::Data>>,
+    ) -> H2Stream<F, B> {
+        H2Stream {
+            reply: respond,
+            state: H2StreamState::Service { fut, connect_parts },
+        }
+    }
+}
+
+macro_rules! reply {
+    ($me:expr, $res:expr, $eos:expr) => {{
+        match $me.reply.send_response($res, $eos) {
+            Ok(tx) => tx,
+            Err(e) => {
+                debug!("send response error: {}", e);
+                $me.reply.send_reset(Reason::INTERNAL_ERROR);
+                return Poll::Ready(Err(crate::Error::new_h2(e)));
+            }
+        }
+    }};
+}
+
+impl<F, B, E> H2Stream<F, B>
+where
+    F: Future<Output = Result<Response<B>, E>>,
+    B: HttpBody,
+    B::Data: 'static,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    E: Into<Box<dyn StdError + Send + Sync>>,
+{
+    fn poll2(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        let mut me = self.project();
+        loop {
+            let next = match me.state.as_mut().project() {
+                H2StreamStateProj::Service {
+                    fut: h,
+                    connect_parts,
+                } => {
+                    let res = match h.poll(cx) {
+                        Poll::Ready(Ok(r)) => r,
+                        Poll::Pending => {
+                            // Response is not yet ready, so we want to check if the client has sent a
+                            // RST_STREAM frame which would cancel the current request.
+                            if let Poll::Ready(reason) =
+                                me.reply.poll_reset(cx).map_err(crate::Error::new_h2)?
+                            {
+                                debug!("stream received RST_STREAM: {:?}", reason);
+                                return Poll::Ready(Err(crate::Error::new_h2(reason.into())));
+                            }
+                            return Poll::Pending;
+                        }
+                        Poll::Ready(Err(e)) => {
+                            let err = crate::Error::new_user_service(e);
+                            warn!("http2 service errored: {}", err);
+                            me.reply.send_reset(err.h2_reason());
+                            return Poll::Ready(Err(err));
+                        }
+                    };
+
+                    let (head, body) = res.into_parts();
+                    let mut res = ::http::Response::from_parts(head, ());
+                    super::strip_connection_headers(res.headers_mut(), false);
+
+                    // set Date header if it isn't already set...
+                    res.headers_mut()
+                        .entry(::http::header::DATE)
+                        .or_insert_with(date::update_and_header_value);
+
+                    if let Some(connect_parts) = connect_parts.take() {
+                        if res.status().is_success() {
+                            if headers::content_length_parse_all(res.headers())
+                                .map_or(false, |len| len != 0)
+                            {
+                                warn!("h2 successful response to CONNECT request with body not supported");
+                                me.reply.send_reset(h2::Reason::INTERNAL_ERROR);
+                                return Poll::Ready(Err(crate::Error::new_user_header()));
+                            }
+                            let send_stream = reply!(me, res, false);
+                            connect_parts.pending.fulfill(Upgraded::new(
+                                H2Upgraded {
+                                    ping: connect_parts.ping,
+                                    recv_stream: connect_parts.recv_stream,
+                                    send_stream: unsafe { UpgradedSendStream::new(send_stream) },
+                                    buf: Bytes::new(),
+                                },
+                                Bytes::new(),
+                            ));
+                            return Poll::Ready(Ok(()));
+                        }
+                    }
+
+                    if !body.is_end_stream() {
+                        // automatically set Content-Length from body...
+                        if let Some(len) = body.size_hint().exact() {
+                            headers::set_content_length_if_missing(res.headers_mut(), len);
+                        }
+
+                        let body_tx = reply!(me, res, false);
+                        H2StreamState::Body {
+                            pipe: PipeToSendStream::new(body, body_tx),
+                        }
+                    } else {
+                        reply!(me, res, true);
+                        return Poll::Ready(Ok(()));
+                    }
+                }
+                H2StreamStateProj::Body { pipe } => {
+                    return pipe.poll(cx);
+                }
+            };
+            me.state.set(next);
+        }
+    }
+}
+
+impl<F, B, E> Future for H2Stream<F, B>
+where
+    F: Future<Output = Result<Response<B>, E>>,
+    B: HttpBody,
+    B::Data: 'static,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    E: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type Output = ();
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.poll2(cx).map(|res| {
+            if let Err(e) = res {
+                debug!("stream error: {}", e);
+            }
+        })
+    }
+}
diff --git a/src/proto/mod.rs b/src/proto/mod.rs
new file mode 100644
index 0000000..3628576
--- /dev/null
+++ b/src/proto/mod.rs
@@ -0,0 +1,71 @@
+//! Pieces pertaining to the HTTP message protocol.
+
+cfg_feature! {
+    #![feature = "http1"]
+
+    pub(crate) mod h1;
+
+    pub(crate) use self::h1::Conn;
+
+    #[cfg(feature = "client")]
+    pub(crate) use self::h1::dispatch;
+    #[cfg(feature = "server")]
+    pub(crate) use self::h1::ServerTransaction;
+}
+
+#[cfg(feature = "http2")]
+pub(crate) mod h2;
+
+/// An Incoming Message head. Includes request/status line, and headers.
+#[derive(Debug, Default)]
+pub(crate) struct MessageHead<S> {
+    /// HTTP version of the message.
+    pub(crate) version: http::Version,
+    /// Subject (request line or status line) of Incoming message.
+    pub(crate) subject: S,
+    /// Headers of the Incoming message.
+    pub(crate) headers: http::HeaderMap,
+    /// Extensions.
+    extensions: http::Extensions,
+}
+
+/// An incoming request message.
+#[cfg(feature = "http1")]
+pub(crate) type RequestHead = MessageHead<RequestLine>;
+
+#[derive(Debug, Default, PartialEq)]
+#[cfg(feature = "http1")]
+pub(crate) struct RequestLine(pub(crate) http::Method, pub(crate) http::Uri);
+
+/// An incoming response message.
+#[cfg(all(feature = "http1", feature = "client"))]
+pub(crate) type ResponseHead = MessageHead<http::StatusCode>;
+
+#[derive(Debug)]
+#[cfg(feature = "http1")]
+pub(crate) enum BodyLength {
+    /// Content-Length
+    Known(u64),
+    /// Transfer-Encoding: chunked (if h1)
+    Unknown,
+}
+
+/// Status of when a Dispatcher future completes.
+pub(crate) enum Dispatched {
+    /// Dispatcher completely shutdown connection.
+    Shutdown,
+    /// Dispatcher has pending upgrade, and so did not shutdown.
+    #[cfg(feature = "http1")]
+    Upgrade(crate::upgrade::Pending),
+}
+
+impl MessageHead<http::StatusCode> {
+    fn into_response<B>(self, body: B) -> http::Response<B> {
+        let mut res = http::Response::new(body);
+        *res.status_mut() = self.subject;
+        *res.headers_mut() = self.headers;
+        *res.version_mut() = self.version;
+        *res.extensions_mut() = self.extensions;
+        res
+    }
+}
diff --git a/src/rt.rs b/src/rt.rs
new file mode 100644
index 0000000..2614b59
--- /dev/null
+++ b/src/rt.rs
@@ -0,0 +1,12 @@
+//! Runtime components
+//!
+//! By default, hyper includes the [tokio](https://tokio.rs) runtime.
+//!
+//! If the `runtime` feature is disabled, the types in this module can be used
+//! to plug in other runtimes.
+
+/// An executor of futures.
+pub trait Executor<Fut> {
+    /// Place the future into the executor to be run.
+    fn execute(&self, fut: Fut);
+}
diff --git a/src/server/accept.rs b/src/server/accept.rs
new file mode 100644
index 0000000..07dcd62
--- /dev/null
+++ b/src/server/accept.rs
@@ -0,0 +1,109 @@
+//! The `Accept` trait and supporting types.
+//!
+//! This module contains:
+//!
+//! - The [`Accept`](Accept) trait used to asynchronously accept incoming
+//!   connections.
+//! - Utilities like `poll_fn` to ease creating a custom `Accept`.
+
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+#[cfg(feature = "stream")]
+use futures_core::Stream;
+#[cfg(feature = "stream")]
+use pin_project_lite::pin_project;
+
+/// Asynchronously accept incoming connections.
+pub trait Accept {
+    /// The connection type that can be accepted.
+    type Conn;
+    /// The error type that can occur when accepting a connection.
+    type Error;
+
+    /// Poll to accept the next connection.
+    fn poll_accept(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<Self::Conn, Self::Error>>>;
+}
+
+/// Create an `Accept` with a polling function.
+///
+/// # Example
+///
+/// ```
+/// use std::task::Poll;
+/// use hyper::server::{accept, Server};
+///
+/// # let mock_conn = ();
+/// // If we created some mocked connection...
+/// let mut conn = Some(mock_conn);
+///
+/// // And accept just the mocked conn once...
+/// let once = accept::poll_fn(move |cx| {
+///     Poll::Ready(conn.take().map(Ok::<_, ()>))
+/// });
+///
+/// let builder = Server::builder(once);
+/// ```
+pub fn poll_fn<F, IO, E>(func: F) -> impl Accept<Conn = IO, Error = E>
+where
+    F: FnMut(&mut Context<'_>) -> Poll<Option<Result<IO, E>>>,
+{
+    struct PollFn<F>(F);
+
+    // The closure `F` is never pinned
+    impl<F> Unpin for PollFn<F> {}
+
+    impl<F, IO, E> Accept for PollFn<F>
+    where
+        F: FnMut(&mut Context<'_>) -> Poll<Option<Result<IO, E>>>,
+    {
+        type Conn = IO;
+        type Error = E;
+        fn poll_accept(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+        ) -> Poll<Option<Result<Self::Conn, Self::Error>>> {
+            (self.get_mut().0)(cx)
+        }
+    }
+
+    PollFn(func)
+}
+
+/// Adapt a `Stream` of incoming connections into an `Accept`.
+///
+/// # Optional
+///
+/// This function requires enabling the `stream` feature in your
+/// `Cargo.toml`.
+#[cfg(feature = "stream")]
+pub fn from_stream<S, IO, E>(stream: S) -> impl Accept<Conn = IO, Error = E>
+where
+    S: Stream<Item = Result<IO, E>>,
+{
+    pin_project! {
+        struct FromStream<S> {
+            #[pin]
+            stream: S,
+        }
+    }
+
+    impl<S, IO, E> Accept for FromStream<S>
+    where
+        S: Stream<Item = Result<IO, E>>,
+    {
+        type Conn = IO;
+        type Error = E;
+        fn poll_accept(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+        ) -> Poll<Option<Result<Self::Conn, Self::Error>>> {
+            self.project().stream.poll_next(cx)
+        }
+    }
+
+    FromStream { stream }
+}
diff --git a/src/server/conn.rs b/src/server/conn.rs
new file mode 100644
index 0000000..8ce4c95
--- /dev/null
+++ b/src/server/conn.rs
@@ -0,0 +1,1082 @@
+//! Lower-level Server connection API.
+//!
+//! The types in this module are to provide a lower-level API based around a
+//! single connection. Accepting a connection and binding it with a service
+//! are not handled at this level. This module provides the building blocks to
+//! customize those things externally.
+//!
+//! If you don't have need to manage connections yourself, consider using the
+//! higher-level [Server](super) API.
+//!
+//! ## Example
+//! A simple example that uses the `Http` struct to talk HTTP over a Tokio TCP stream
+//! ```no_run
+//! # #[cfg(all(feature = "http1", feature = "runtime"))]
+//! # mod rt {
+//! use http::{Request, Response, StatusCode};
+//! use hyper::{server::conn::Http, service::service_fn, Body};
+//! use std::{net::SocketAddr, convert::Infallible};
+//! use tokio::net::TcpListener;
+//!
+//! #[tokio::main]
+//! async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
+//!     let addr: SocketAddr = ([127, 0, 0, 1], 8080).into();
+//!
+//!     let mut tcp_listener = TcpListener::bind(addr).await?;
+//!     loop {
+//!         let (tcp_stream, _) = tcp_listener.accept().await?;
+//!         tokio::task::spawn(async move {
+//!             if let Err(http_err) = Http::new()
+//!                     .http1_only(true)
+//!                     .http1_keep_alive(true)
+//!                     .serve_connection(tcp_stream, service_fn(hello))
+//!                     .await {
+//!                 eprintln!("Error while serving HTTP connection: {}", http_err);
+//!             }
+//!         });
+//!     }
+//! }
+//!
+//! async fn hello(_req: Request<Body>) -> Result<Response<Body>, Infallible> {
+//!    Ok(Response::new(Body::from("Hello World!")))
+//! }
+//! # }
+//! ```
+
+#[cfg(all(
+    any(feature = "http1", feature = "http2"),
+    not(all(feature = "http1", feature = "http2"))
+))]
+use std::marker::PhantomData;
+#[cfg(all(any(feature = "http1", feature = "http2"), feature = "runtime"))]
+use std::time::Duration;
+
+#[cfg(feature = "http2")]
+use crate::common::io::Rewind;
+#[cfg(all(feature = "http1", feature = "http2"))]
+use crate::error::{Kind, Parse};
+#[cfg(feature = "http1")]
+use crate::upgrade::Upgraded;
+
+#[cfg(all(feature = "backports", feature = "http1"))]
+pub mod http1;
+#[cfg(all(feature = "backports", feature = "http2"))]
+pub mod http2;
+
+cfg_feature! {
+    #![any(feature = "http1", feature = "http2")]
+
+    use std::error::Error as StdError;
+    use std::fmt;
+    use std::task::{Context, Poll};
+    use std::pin::Pin;
+    use std::future::Future;
+    use std::marker::Unpin;
+    #[cfg(not(all(feature = "http1", feature = "http2")))]
+    use std::convert::Infallible;
+
+    use bytes::Bytes;
+    use pin_project_lite::pin_project;
+    use tokio::io::{AsyncRead, AsyncWrite};
+    use tracing::trace;
+
+    pub use super::server::Connecting;
+    use crate::body::{Body, HttpBody};
+    use crate::common::exec::{ConnStreamExec, Exec};
+    use crate::proto;
+    use crate::service::HttpService;
+
+    pub(super) use self::upgrades::UpgradeableConnection;
+}
+
+#[cfg(feature = "tcp")]
+pub use super::tcp::{AddrIncoming, AddrStream};
+
+/// A lower-level configuration of the HTTP protocol.
+///
+/// This structure is used to configure options for an HTTP server connection.
+///
+/// If you don't have need to manage connections yourself, consider using the
+/// higher-level [Server](super) API.
+#[derive(Clone, Debug)]
+#[cfg(any(feature = "http1", feature = "http2"))]
+#[cfg_attr(docsrs, doc(cfg(any(feature = "http1", feature = "http2"))))]
+#[cfg_attr(
+    feature = "deprecated",
+    deprecated(
+        note = "This struct will be replaced with `server::conn::http1::Builder` and `server::conn::http2::Builder` in 1.0, enable the \"backports\" feature to use them now."
+    )
+)]
+pub struct Http<E = Exec> {
+    pub(crate) exec: E,
+    h1_half_close: bool,
+    h1_keep_alive: bool,
+    h1_title_case_headers: bool,
+    h1_preserve_header_case: bool,
+    #[cfg(all(feature = "http1", feature = "runtime"))]
+    h1_header_read_timeout: Option<Duration>,
+    h1_writev: Option<bool>,
+    #[cfg(feature = "http2")]
+    h2_builder: proto::h2::server::Config,
+    mode: ConnectionMode,
+    max_buf_size: Option<usize>,
+    pipeline_flush: bool,
+}
+
+/// The internal mode of HTTP protocol which indicates the behavior when a parse error occurs.
+#[cfg(any(feature = "http1", feature = "http2"))]
+#[derive(Clone, Debug, PartialEq)]
+enum ConnectionMode {
+    /// Always use HTTP/1 and do not upgrade when a parse error occurs.
+    #[cfg(feature = "http1")]
+    H1Only,
+    /// Always use HTTP/2.
+    #[cfg(feature = "http2")]
+    H2Only,
+    /// Use HTTP/1 and try to upgrade to h2 when a parse error occurs.
+    #[cfg(all(feature = "http1", feature = "http2"))]
+    Fallback,
+}
+
+#[cfg(any(feature = "http1", feature = "http2"))]
+pin_project! {
+    /// A future binding a connection with a Service.
+    ///
+    /// Polling this future will drive HTTP forward.
+    #[must_use = "futures do nothing unless polled"]
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "http1", feature = "http2"))))]
+    pub struct Connection<T, S, E = Exec>
+    where
+        S: HttpService<Body>,
+    {
+        pub(super) conn: Option<ProtoServer<T, S::ResBody, S, E>>,
+        fallback: Fallback<E>,
+    }
+}
+
+#[cfg(feature = "http1")]
+type Http1Dispatcher<T, B, S> =
+    proto::h1::Dispatcher<proto::h1::dispatch::Server<S, Body>, B, T, proto::ServerTransaction>;
+
+#[cfg(all(not(feature = "http1"), feature = "http2"))]
+type Http1Dispatcher<T, B, S> = (Infallible, PhantomData<(T, Box<Pin<B>>, Box<Pin<S>>)>);
+
+#[cfg(feature = "http2")]
+type Http2Server<T, B, S, E> = proto::h2::Server<Rewind<T>, S, B, E>;
+
+#[cfg(all(not(feature = "http2"), feature = "http1"))]
+type Http2Server<T, B, S, E> = (
+    Infallible,
+    PhantomData<(T, Box<Pin<S>>, Box<Pin<B>>, Box<Pin<E>>)>,
+);
+
+#[cfg(any(feature = "http1", feature = "http2"))]
+pin_project! {
+    #[project = ProtoServerProj]
+    pub(super) enum ProtoServer<T, B, S, E = Exec>
+    where
+        S: HttpService<Body>,
+        B: HttpBody,
+    {
+        H1 {
+            #[pin]
+            h1: Http1Dispatcher<T, B, S>,
+        },
+        H2 {
+            #[pin]
+            h2: Http2Server<T, B, S, E>,
+        },
+    }
+}
+
+#[cfg(all(feature = "http1", feature = "http2"))]
+#[derive(Clone, Debug)]
+enum Fallback<E> {
+    ToHttp2(proto::h2::server::Config, E),
+    Http1Only,
+}
+
+#[cfg(all(
+    any(feature = "http1", feature = "http2"),
+    not(all(feature = "http1", feature = "http2"))
+))]
+type Fallback<E> = PhantomData<E>;
+
+#[cfg(all(feature = "http1", feature = "http2"))]
+impl<E> Fallback<E> {
+    fn to_h2(&self) -> bool {
+        match *self {
+            Fallback::ToHttp2(..) => true,
+            Fallback::Http1Only => false,
+        }
+    }
+}
+
+#[cfg(all(feature = "http1", feature = "http2"))]
+impl<E> Unpin for Fallback<E> {}
+
+/// Deconstructed parts of a `Connection`.
+///
+/// This allows taking apart a `Connection` at a later time, in order to
+/// reclaim the IO object, and additional related pieces.
+#[derive(Debug)]
+#[cfg(any(feature = "http1", feature = "http2"))]
+#[cfg_attr(docsrs, doc(cfg(any(feature = "http1", feature = "http2"))))]
+#[cfg_attr(
+    feature = "deprecated",
+    deprecated(
+        note = "This struct will be replaced with `server::conn::http1::Parts` in 1.0, enable the \"backports\" feature to use them now."
+    )
+)]
+pub struct Parts<T, S> {
+    /// The original IO object used in the handshake.
+    pub io: T,
+    /// A buffer of bytes that have been read but not processed as HTTP.
+    ///
+    /// If the client sent additional bytes after its last request, and
+    /// this connection "ended" with an upgrade, the read buffer will contain
+    /// those bytes.
+    ///
+    /// You will want to check for any existing bytes if you plan to continue
+    /// communicating on the IO object.
+    pub read_buf: Bytes,
+    /// The `Service` used to serve this connection.
+    pub service: S,
+    _inner: (),
+}
+
+// ===== impl Http =====
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+#[cfg(any(feature = "http1", feature = "http2"))]
+impl Http {
+    /// Creates a new instance of the HTTP protocol, ready to spawn a server or
+    /// start accepting connections.
+    pub fn new() -> Http {
+        Http {
+            exec: Exec::Default,
+            h1_half_close: false,
+            h1_keep_alive: true,
+            h1_title_case_headers: false,
+            h1_preserve_header_case: false,
+            #[cfg(all(feature = "http1", feature = "runtime"))]
+            h1_header_read_timeout: None,
+            h1_writev: None,
+            #[cfg(feature = "http2")]
+            h2_builder: Default::default(),
+            mode: ConnectionMode::default(),
+            max_buf_size: None,
+            pipeline_flush: false,
+        }
+    }
+}
+
+#[cfg_attr(feature = "deprecated", allow(deprecated))]
+#[cfg(any(feature = "http1", feature = "http2"))]
+impl<E> Http<E> {
+    /// Sets whether HTTP1 is required.
+    ///
+    /// Default is false
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn http1_only(&mut self, val: bool) -> &mut Self {
+        if val {
+            self.mode = ConnectionMode::H1Only;
+        } else {
+            #[cfg(feature = "http2")]
+            {
+                self.mode = ConnectionMode::Fallback;
+            }
+        }
+        self
+    }
+
+    /// Set whether HTTP/1 connections should support half-closures.
+    ///
+    /// Clients can chose to shutdown their write-side while waiting
+    /// for the server to respond. Setting this to `true` will
+    /// prevent closing the connection immediately if `read`
+    /// detects an EOF in the middle of a request.
+    ///
+    /// Default is `false`.
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn http1_half_close(&mut self, val: bool) -> &mut Self {
+        self.h1_half_close = val;
+        self
+    }
+
+    /// Enables or disables HTTP/1 keep-alive.
+    ///
+    /// Default is true.
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn http1_keep_alive(&mut self, val: bool) -> &mut Self {
+        self.h1_keep_alive = val;
+        self
+    }
+
+    /// Set whether HTTP/1 connections will write header names as title case at
+    /// the socket level.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn http1_title_case_headers(&mut self, enabled: bool) -> &mut Self {
+        self.h1_title_case_headers = enabled;
+        self
+    }
+
+    /// Set whether to support preserving original header cases.
+    ///
+    /// Currently, this will record the original cases received, and store them
+    /// in a private extension on the `Request`. It will also look for and use
+    /// such an extension in any provided `Response`.
+    ///
+    /// Since the relevant extension is still private, there is no way to
+    /// interact with the original cases. The only effect this can have now is
+    /// to forward the cases in a proxy-like fashion.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn http1_preserve_header_case(&mut self, enabled: bool) -> &mut Self {
+        self.h1_preserve_header_case = enabled;
+        self
+    }
+
+    /// Set a timeout for reading client request headers. If a client does not
+    /// transmit the entire header within this time, the connection is closed.
+    ///
+    /// Default is None.
+    #[cfg(all(feature = "http1", feature = "runtime"))]
+    #[cfg_attr(docsrs, doc(cfg(all(feature = "http1", feature = "runtime"))))]
+    pub fn http1_header_read_timeout(&mut self, read_timeout: Duration) -> &mut Self {
+        self.h1_header_read_timeout = Some(read_timeout);
+        self
+    }
+
+    /// Set whether HTTP/1 connections should try to use vectored writes,
+    /// or always flatten into a single buffer.
+    ///
+    /// Note that setting this to false may mean more copies of body data,
+    /// but may also improve performance when an IO transport doesn't
+    /// support vectored writes well, such as most TLS implementations.
+    ///
+    /// Setting this to true will force hyper to use queued strategy
+    /// which may eliminate unnecessary cloning on some TLS backends
+    ///
+    /// Default is `auto`. In this mode hyper will try to guess which
+    /// mode to use
+    #[inline]
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn http1_writev(&mut self, val: bool) -> &mut Self {
+        self.h1_writev = Some(val);
+        self
+    }
+
+    /// Sets whether HTTP2 is required.
+    ///
+    /// Default is false
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_only(&mut self, val: bool) -> &mut Self {
+        if val {
+            self.mode = ConnectionMode::H2Only;
+        } else {
+            #[cfg(feature = "http1")]
+            {
+                self.mode = ConnectionMode::Fallback;
+            }
+        }
+        self
+    }
+
+    /// Configures the maximum number of pending reset streams allowed before a GOAWAY will be sent.
+    ///
+    /// This will default to the default value set by the [`h2` crate](https://crates.io/crates/h2).
+    /// As of v0.3.17, it is 20.
+    ///
+    /// See <https://github.com/hyperium/hyper/issues/2877> for more information.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_pending_accept_reset_streams(
+        &mut self,
+        max: impl Into<Option<usize>>,
+    ) -> &mut Self {
+        self.h2_builder.max_pending_accept_reset_streams = max.into();
+
+        self
+    }
+
+    /// Sets the [`SETTINGS_INITIAL_WINDOW_SIZE`][spec] option for HTTP2
+    /// stream-level flow control.
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    ///
+    /// [spec]: https://http2.github.io/http2-spec/#SETTINGS_INITIAL_WINDOW_SIZE
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_initial_stream_window_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
+        if let Some(sz) = sz.into() {
+            self.h2_builder.adaptive_window = false;
+            self.h2_builder.initial_stream_window_size = sz;
+        }
+        self
+    }
+
+    /// Sets the max connection-level flow control for HTTP2.
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_initial_connection_window_size(
+        &mut self,
+        sz: impl Into<Option<u32>>,
+    ) -> &mut Self {
+        if let Some(sz) = sz.into() {
+            self.h2_builder.adaptive_window = false;
+            self.h2_builder.initial_conn_window_size = sz;
+        }
+        self
+    }
+
+    /// Sets whether to use an adaptive flow control.
+    ///
+    /// Enabling this will override the limits set in
+    /// `http2_initial_stream_window_size` and
+    /// `http2_initial_connection_window_size`.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_adaptive_window(&mut self, enabled: bool) -> &mut Self {
+        use proto::h2::SPEC_WINDOW_SIZE;
+
+        self.h2_builder.adaptive_window = enabled;
+        if enabled {
+            self.h2_builder.initial_conn_window_size = SPEC_WINDOW_SIZE;
+            self.h2_builder.initial_stream_window_size = SPEC_WINDOW_SIZE;
+        }
+        self
+    }
+
+    /// Sets the maximum frame size to use for HTTP2.
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_frame_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
+        if let Some(sz) = sz.into() {
+            self.h2_builder.max_frame_size = sz;
+        }
+        self
+    }
+
+    /// Sets the [`SETTINGS_MAX_CONCURRENT_STREAMS`][spec] option for HTTP2
+    /// connections.
+    ///
+    /// Default is no limit (`std::u32::MAX`). Passing `None` will do nothing.
+    ///
+    /// [spec]: https://http2.github.io/http2-spec/#SETTINGS_MAX_CONCURRENT_STREAMS
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_concurrent_streams(&mut self, max: impl Into<Option<u32>>) -> &mut Self {
+        self.h2_builder.max_concurrent_streams = max.into();
+        self
+    }
+
+    /// Sets an interval for HTTP2 Ping frames should be sent to keep a
+    /// connection alive.
+    ///
+    /// Pass `None` to disable HTTP2 keep-alive.
+    ///
+    /// Default is currently disabled.
+    ///
+    /// # Cargo Feature
+    ///
+    /// Requires the `runtime` cargo feature to be enabled.
+    #[cfg(feature = "runtime")]
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_keep_alive_interval(
+        &mut self,
+        interval: impl Into<Option<Duration>>,
+    ) -> &mut Self {
+        self.h2_builder.keep_alive_interval = interval.into();
+        self
+    }
+
+    /// Sets a timeout for receiving an acknowledgement of the keep-alive ping.
+    ///
+    /// If the ping is not acknowledged within the timeout, the connection will
+    /// be closed. Does nothing if `http2_keep_alive_interval` is disabled.
+    ///
+    /// Default is 20 seconds.
+    ///
+    /// # Cargo Feature
+    ///
+    /// Requires the `runtime` cargo feature to be enabled.
+    #[cfg(feature = "runtime")]
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_keep_alive_timeout(&mut self, timeout: Duration) -> &mut Self {
+        self.h2_builder.keep_alive_timeout = timeout;
+        self
+    }
+
+    /// Set the maximum write buffer size for each HTTP/2 stream.
+    ///
+    /// Default is currently ~400KB, but may change.
+    ///
+    /// # Panics
+    ///
+    /// The value must be no larger than `u32::MAX`.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_send_buf_size(&mut self, max: usize) -> &mut Self {
+        assert!(max <= std::u32::MAX as usize);
+        self.h2_builder.max_send_buffer_size = max;
+        self
+    }
+
+    /// Enables the [extended CONNECT protocol].
+    ///
+    /// [extended CONNECT protocol]: https://datatracker.ietf.org/doc/html/rfc8441#section-4
+    #[cfg(feature = "http2")]
+    pub fn http2_enable_connect_protocol(&mut self) -> &mut Self {
+        self.h2_builder.enable_connect_protocol = true;
+        self
+    }
+
+    /// Sets the max size of received header frames.
+    ///
+    /// Default is currently ~16MB, but may change.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_header_list_size(&mut self, max: u32) -> &mut Self {
+        self.h2_builder.max_header_list_size = max;
+        self
+    }
+
+    /// Set the maximum buffer size for the connection.
+    ///
+    /// Default is ~400kb.
+    ///
+    /// # Panics
+    ///
+    /// The minimum value allowed is 8192. This method panics if the passed `max` is less than the minimum.
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn max_buf_size(&mut self, max: usize) -> &mut Self {
+        assert!(
+            max >= proto::h1::MINIMUM_MAX_BUFFER_SIZE,
+            "the max_buf_size cannot be smaller than the minimum that h1 specifies."
+        );
+        self.max_buf_size = Some(max);
+        self
+    }
+
+    /// Aggregates flushes to better support pipelined responses.
+    ///
+    /// Experimental, may have bugs.
+    ///
+    /// Default is false.
+    pub fn pipeline_flush(&mut self, enabled: bool) -> &mut Self {
+        self.pipeline_flush = enabled;
+        self
+    }
+
+    /// Set the executor used to spawn background tasks.
+    ///
+    /// Default uses implicit default (like `tokio::spawn`).
+    pub fn with_executor<E2>(self, exec: E2) -> Http<E2> {
+        Http {
+            exec,
+            h1_half_close: self.h1_half_close,
+            h1_keep_alive: self.h1_keep_alive,
+            h1_title_case_headers: self.h1_title_case_headers,
+            h1_preserve_header_case: self.h1_preserve_header_case,
+            #[cfg(all(feature = "http1", feature = "runtime"))]
+            h1_header_read_timeout: self.h1_header_read_timeout,
+            h1_writev: self.h1_writev,
+            #[cfg(feature = "http2")]
+            h2_builder: self.h2_builder,
+            mode: self.mode,
+            max_buf_size: self.max_buf_size,
+            pipeline_flush: self.pipeline_flush,
+        }
+    }
+
+    /// Bind a connection together with a [`Service`](crate::service::Service).
+    ///
+    /// This returns a Future that must be polled in order for HTTP to be
+    /// driven on the connection.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use hyper::{Body, Request, Response};
+    /// # use hyper::service::Service;
+    /// # use hyper::server::conn::Http;
+    /// # use tokio::io::{AsyncRead, AsyncWrite};
+    /// # async fn run<I, S>(some_io: I, some_service: S)
+    /// # where
+    /// #     I: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    /// #     S: Service<hyper::Request<Body>, Response=hyper::Response<Body>> + Send + 'static,
+    /// #     S::Error: Into<Box<dyn std::error::Error + Send + Sync>>,
+    /// #     S::Future: Send,
+    /// # {
+    /// let http = Http::new();
+    /// let conn = http.serve_connection(some_io, some_service);
+    ///
+    /// if let Err(e) = conn.await {
+    ///     eprintln!("server connection error: {}", e);
+    /// }
+    /// # }
+    /// # fn main() {}
+    /// ```
+    pub fn serve_connection<S, I, Bd>(&self, io: I, service: S) -> Connection<I, S, E>
+    where
+        S: HttpService<Body, ResBody = Bd>,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        Bd: HttpBody + 'static,
+        Bd::Error: Into<Box<dyn StdError + Send + Sync>>,
+        I: AsyncRead + AsyncWrite + Unpin,
+        E: ConnStreamExec<S::Future, Bd>,
+    {
+        #[cfg(feature = "http1")]
+        macro_rules! h1 {
+            () => {{
+                let mut conn = proto::Conn::new(io);
+                if !self.h1_keep_alive {
+                    conn.disable_keep_alive();
+                }
+                if self.h1_half_close {
+                    conn.set_allow_half_close();
+                }
+                if self.h1_title_case_headers {
+                    conn.set_title_case_headers();
+                }
+                if self.h1_preserve_header_case {
+                    conn.set_preserve_header_case();
+                }
+                #[cfg(all(feature = "http1", feature = "runtime"))]
+                if let Some(header_read_timeout) = self.h1_header_read_timeout {
+                    conn.set_http1_header_read_timeout(header_read_timeout);
+                }
+                if let Some(writev) = self.h1_writev {
+                    if writev {
+                        conn.set_write_strategy_queue();
+                    } else {
+                        conn.set_write_strategy_flatten();
+                    }
+                }
+                conn.set_flush_pipeline(self.pipeline_flush);
+                if let Some(max) = self.max_buf_size {
+                    conn.set_max_buf_size(max);
+                }
+                let sd = proto::h1::dispatch::Server::new(service);
+                ProtoServer::H1 {
+                    h1: proto::h1::Dispatcher::new(sd, conn),
+                }
+            }};
+        }
+
+        let proto = match self.mode {
+            #[cfg(feature = "http1")]
+            #[cfg(not(feature = "http2"))]
+            ConnectionMode::H1Only => h1!(),
+            #[cfg(feature = "http2")]
+            #[cfg(feature = "http1")]
+            ConnectionMode::H1Only | ConnectionMode::Fallback => h1!(),
+            #[cfg(feature = "http2")]
+            ConnectionMode::H2Only => {
+                let rewind_io = Rewind::new(io);
+                let h2 =
+                    proto::h2::Server::new(rewind_io, service, &self.h2_builder, self.exec.clone());
+                ProtoServer::H2 { h2 }
+            }
+        };
+
+        Connection {
+            conn: Some(proto),
+            #[cfg(all(feature = "http1", feature = "http2"))]
+            fallback: if self.mode == ConnectionMode::Fallback {
+                Fallback::ToHttp2(self.h2_builder.clone(), self.exec.clone())
+            } else {
+                Fallback::Http1Only
+            },
+            #[cfg(not(all(feature = "http1", feature = "http2")))]
+            fallback: PhantomData,
+        }
+    }
+}
+
+// ===== impl Connection =====
+
+#[cfg(any(feature = "http1", feature = "http2"))]
+impl<I, B, S, E> Connection<I, S, E>
+where
+    S: HttpService<Body, ResBody = B>,
+    S::Error: Into<Box<dyn StdError + Send + Sync>>,
+    I: AsyncRead + AsyncWrite + Unpin,
+    B: HttpBody + 'static,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    E: ConnStreamExec<S::Future, B>,
+{
+    /// Start a graceful shutdown process for this connection.
+    ///
+    /// This `Connection` should continue to be polled until shutdown
+    /// can finish.
+    ///
+    /// # Note
+    ///
+    /// This should only be called while the `Connection` future is still
+    /// pending. If called after `Connection::poll` has resolved, this does
+    /// nothing.
+    pub fn graceful_shutdown(mut self: Pin<&mut Self>) {
+        match self.conn {
+            #[cfg(feature = "http1")]
+            Some(ProtoServer::H1 { ref mut h1, .. }) => {
+                h1.disable_keep_alive();
+            }
+            #[cfg(feature = "http2")]
+            Some(ProtoServer::H2 { ref mut h2 }) => {
+                h2.graceful_shutdown();
+            }
+            None => (),
+
+            #[cfg(not(feature = "http1"))]
+            Some(ProtoServer::H1 { ref mut h1, .. }) => match h1.0 {},
+            #[cfg(not(feature = "http2"))]
+            Some(ProtoServer::H2 { ref mut h2 }) => match h2.0 {},
+        }
+    }
+
+    /// Return the inner IO object, and additional information.
+    ///
+    /// If the IO object has been "rewound" the io will not contain those bytes rewound.
+    /// This should only be called after `poll_without_shutdown` signals
+    /// that the connection is "done". Otherwise, it may not have finished
+    /// flushing all necessary HTTP bytes.
+    ///
+    /// # Panics
+    /// This method will panic if this connection is using an h2 protocol.
+    #[cfg_attr(feature = "deprecated", allow(deprecated))]
+    pub fn into_parts(self) -> Parts<I, S> {
+        self.try_into_parts()
+            .unwrap_or_else(|| panic!("h2 cannot into_inner"))
+    }
+
+    /// Return the inner IO object, and additional information, if available.
+    ///
+    /// This method will return a `None` if this connection is using an h2 protocol.
+    #[cfg_attr(feature = "deprecated", allow(deprecated))]
+    pub fn try_into_parts(self) -> Option<Parts<I, S>> {
+        match self.conn.unwrap() {
+            #[cfg(feature = "http1")]
+            ProtoServer::H1 { h1, .. } => {
+                let (io, read_buf, dispatch) = h1.into_inner();
+                Some(Parts {
+                    io,
+                    read_buf,
+                    service: dispatch.into_service(),
+                    _inner: (),
+                })
+            }
+            ProtoServer::H2 { .. } => None,
+
+            #[cfg(not(feature = "http1"))]
+            ProtoServer::H1 { h1, .. } => match h1.0 {},
+        }
+    }
+
+    /// Poll the connection for completion, but without calling `shutdown`
+    /// on the underlying IO.
+    ///
+    /// This is useful to allow running a connection while doing an HTTP
+    /// upgrade. Once the upgrade is completed, the connection would be "done",
+    /// but it is not desired to actually shutdown the IO object. Instead you
+    /// would take it back using `into_parts`.
+    pub fn poll_without_shutdown(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>> {
+        loop {
+            match *self.conn.as_mut().unwrap() {
+                #[cfg(feature = "http1")]
+                ProtoServer::H1 { ref mut h1, .. } => match ready!(h1.poll_without_shutdown(cx)) {
+                    Ok(()) => return Poll::Ready(Ok(())),
+                    Err(e) => {
+                        #[cfg(feature = "http2")]
+                        match *e.kind() {
+                            Kind::Parse(Parse::VersionH2) if self.fallback.to_h2() => {
+                                self.upgrade_h2();
+                                continue;
+                            }
+                            _ => (),
+                        }
+
+                        return Poll::Ready(Err(e));
+                    }
+                },
+                #[cfg(feature = "http2")]
+                ProtoServer::H2 { ref mut h2 } => return Pin::new(h2).poll(cx).map_ok(|_| ()),
+
+                #[cfg(not(feature = "http1"))]
+                ProtoServer::H1 { ref mut h1, .. } => match h1.0 {},
+                #[cfg(not(feature = "http2"))]
+                ProtoServer::H2 { ref mut h2 } => match h2.0 {},
+            };
+        }
+    }
+
+    /// Prevent shutdown of the underlying IO object at the end of service the request,
+    /// instead run `into_parts`. This is a convenience wrapper over `poll_without_shutdown`.
+    ///
+    /// # Error
+    ///
+    /// This errors if the underlying connection protocol is not HTTP/1.
+    #[cfg_attr(feature = "deprecated", allow(deprecated))]
+    pub fn without_shutdown(self) -> impl Future<Output = crate::Result<Parts<I, S>>> {
+        let mut conn = Some(self);
+        futures_util::future::poll_fn(move |cx| {
+            ready!(conn.as_mut().unwrap().poll_without_shutdown(cx))?;
+            Poll::Ready(
+                conn.take()
+                    .unwrap()
+                    .try_into_parts()
+                    .ok_or_else(crate::Error::new_without_shutdown_not_h1),
+            )
+        })
+    }
+
+    #[cfg(all(feature = "http1", feature = "http2"))]
+    fn upgrade_h2(&mut self) {
+        trace!("Trying to upgrade connection to h2");
+        let conn = self.conn.take();
+
+        let (io, read_buf, dispatch) = match conn.unwrap() {
+            ProtoServer::H1 { h1, .. } => h1.into_inner(),
+            ProtoServer::H2 { .. } => {
+                panic!("h2 cannot into_inner");
+            }
+        };
+        let mut rewind_io = Rewind::new(io);
+        rewind_io.rewind(read_buf);
+        let (builder, exec) = match self.fallback {
+            Fallback::ToHttp2(ref builder, ref exec) => (builder, exec),
+            Fallback::Http1Only => unreachable!("upgrade_h2 with Fallback::Http1Only"),
+        };
+        let h2 = proto::h2::Server::new(rewind_io, dispatch.into_service(), builder, exec.clone());
+
+        debug_assert!(self.conn.is_none());
+        self.conn = Some(ProtoServer::H2 { h2 });
+    }
+
+    /// Enable this connection to support higher-level HTTP upgrades.
+    ///
+    /// See [the `upgrade` module](crate::upgrade) for more.
+    pub fn with_upgrades(self) -> UpgradeableConnection<I, S, E>
+    where
+        I: Send,
+    {
+        UpgradeableConnection { inner: self }
+    }
+}
+
+#[cfg(any(feature = "http1", feature = "http2"))]
+impl<I, B, S, E> Future for Connection<I, S, E>
+where
+    S: HttpService<Body, ResBody = B>,
+    S::Error: Into<Box<dyn StdError + Send + Sync>>,
+    I: AsyncRead + AsyncWrite + Unpin,
+    B: HttpBody + 'static,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    E: ConnStreamExec<S::Future, B>,
+{
+    type Output = crate::Result<()>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        loop {
+            match ready!(Pin::new(self.conn.as_mut().unwrap()).poll(cx)) {
+                Ok(done) => {
+                    match done {
+                        proto::Dispatched::Shutdown => {}
+                        #[cfg(feature = "http1")]
+                        proto::Dispatched::Upgrade(pending) => {
+                            // With no `Send` bound on `I`, we can't try to do
+                            // upgrades here. In case a user was trying to use
+                            // `Body::on_upgrade` with this API, send a special
+                            // error letting them know about that.
+                            pending.manual();
+                        }
+                    };
+                    return Poll::Ready(Ok(()));
+                }
+                Err(e) => {
+                    #[cfg(feature = "http1")]
+                    #[cfg(feature = "http2")]
+                    match *e.kind() {
+                        Kind::Parse(Parse::VersionH2) if self.fallback.to_h2() => {
+                            self.upgrade_h2();
+                            continue;
+                        }
+                        _ => (),
+                    }
+
+                    return Poll::Ready(Err(e));
+                }
+            }
+        }
+    }
+}
+
+#[cfg(any(feature = "http1", feature = "http2"))]
+impl<I, S> fmt::Debug for Connection<I, S>
+where
+    S: HttpService<Body>,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Connection").finish()
+    }
+}
+
+// ===== impl ConnectionMode =====
+
+#[cfg(any(feature = "http1", feature = "http2"))]
+impl Default for ConnectionMode {
+    #[cfg(all(feature = "http1", feature = "http2"))]
+    fn default() -> ConnectionMode {
+        ConnectionMode::Fallback
+    }
+
+    #[cfg(all(feature = "http1", not(feature = "http2")))]
+    fn default() -> ConnectionMode {
+        ConnectionMode::H1Only
+    }
+
+    #[cfg(all(not(feature = "http1"), feature = "http2"))]
+    fn default() -> ConnectionMode {
+        ConnectionMode::H2Only
+    }
+}
+
+// ===== impl ProtoServer =====
+
+#[cfg(any(feature = "http1", feature = "http2"))]
+impl<T, B, S, E> Future for ProtoServer<T, B, S, E>
+where
+    T: AsyncRead + AsyncWrite + Unpin,
+    S: HttpService<Body, ResBody = B>,
+    S::Error: Into<Box<dyn StdError + Send + Sync>>,
+    B: HttpBody + 'static,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    E: ConnStreamExec<S::Future, B>,
+{
+    type Output = crate::Result<proto::Dispatched>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match self.project() {
+            #[cfg(feature = "http1")]
+            ProtoServerProj::H1 { h1, .. } => h1.poll(cx),
+            #[cfg(feature = "http2")]
+            ProtoServerProj::H2 { h2 } => h2.poll(cx),
+
+            #[cfg(not(feature = "http1"))]
+            ProtoServerProj::H1 { h1, .. } => match h1.0 {},
+            #[cfg(not(feature = "http2"))]
+            ProtoServerProj::H2 { h2 } => match h2.0 {},
+        }
+    }
+}
+
+#[cfg(any(feature = "http1", feature = "http2"))]
+mod upgrades {
+    use super::*;
+
+    // A future binding a connection with a Service with Upgrade support.
+    //
+    // This type is unnameable outside the crate, and so basically just an
+    // `impl Future`, without requiring Rust 1.26.
+    #[must_use = "futures do nothing unless polled"]
+    #[allow(missing_debug_implementations)]
+    pub struct UpgradeableConnection<T, S, E>
+    where
+        S: HttpService<Body>,
+    {
+        pub(super) inner: Connection<T, S, E>,
+    }
+
+    impl<I, B, S, E> UpgradeableConnection<I, S, E>
+    where
+        S: HttpService<Body, ResBody = B>,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        I: AsyncRead + AsyncWrite + Unpin,
+        B: HttpBody + 'static,
+        B::Error: Into<Box<dyn StdError + Send + Sync>>,
+        E: ConnStreamExec<S::Future, B>,
+    {
+        /// Start a graceful shutdown process for this connection.
+        ///
+        /// This `Connection` should continue to be polled until shutdown
+        /// can finish.
+        pub fn graceful_shutdown(mut self: Pin<&mut Self>) {
+            Pin::new(&mut self.inner).graceful_shutdown()
+        }
+    }
+
+    impl<I, B, S, E> Future for UpgradeableConnection<I, S, E>
+    where
+        S: HttpService<Body, ResBody = B>,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        I: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+        B: HttpBody + 'static,
+        B::Error: Into<Box<dyn StdError + Send + Sync>>,
+        E: ConnStreamExec<S::Future, B>,
+    {
+        type Output = crate::Result<()>;
+
+        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+            loop {
+                match ready!(Pin::new(self.inner.conn.as_mut().unwrap()).poll(cx)) {
+                    Ok(proto::Dispatched::Shutdown) => return Poll::Ready(Ok(())),
+                    #[cfg(feature = "http1")]
+                    Ok(proto::Dispatched::Upgrade(pending)) => {
+                        match self.inner.conn.take() {
+                            Some(ProtoServer::H1 { h1, .. }) => {
+                                let (io, buf, _) = h1.into_inner();
+                                pending.fulfill(Upgraded::new(io, buf));
+                                return Poll::Ready(Ok(()));
+                            }
+                            _ => {
+                                drop(pending);
+                                unreachable!("Upgrade expects h1")
+                            }
+                        };
+                    }
+                    Err(e) => {
+                        #[cfg(feature = "http1")]
+                        #[cfg(feature = "http2")]
+                        match *e.kind() {
+                            Kind::Parse(Parse::VersionH2) if self.inner.fallback.to_h2() => {
+                                self.inner.upgrade_h2();
+                                continue;
+                            }
+                            _ => (),
+                        }
+
+                        return Poll::Ready(Err(e));
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/src/server/conn/http1.rs b/src/server/conn/http1.rs
new file mode 100644
index 0000000..ab833b9
--- /dev/null
+++ b/src/server/conn/http1.rs
@@ -0,0 +1,449 @@
+//! HTTP/1 Server Connections
+
+use std::error::Error as StdError;
+use std::fmt;
+use std::future::Future;
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::time::Duration;
+
+use bytes::Bytes;
+use tokio::io::{AsyncRead, AsyncWrite};
+
+use crate::body::{Body as IncomingBody, HttpBody as Body};
+use crate::proto;
+use crate::service::HttpService;
+
+type Http1Dispatcher<T, B, S> = proto::h1::Dispatcher<
+    proto::h1::dispatch::Server<S, IncomingBody>,
+    B,
+    T,
+    proto::ServerTransaction,
+>;
+
+pin_project_lite::pin_project! {
+    /// A future binding an http1 connection with a Service.
+    ///
+    /// Polling this future will drive HTTP forward.
+    #[must_use = "futures do nothing unless polled"]
+    pub struct Connection<T, S>
+    where
+        S: HttpService<IncomingBody>,
+    {
+        conn: Http1Dispatcher<T, S::ResBody, S>,
+    }
+}
+
+/// A configuration builder for HTTP/1 server connections.
+#[derive(Clone, Debug)]
+pub struct Builder {
+    h1_half_close: bool,
+    h1_keep_alive: bool,
+    h1_title_case_headers: bool,
+    h1_preserve_header_case: bool,
+    h1_header_read_timeout: Option<Duration>,
+    h1_writev: Option<bool>,
+    max_buf_size: Option<usize>,
+    pipeline_flush: bool,
+}
+
+/// Deconstructed parts of a `Connection`.
+///
+/// This allows taking apart a `Connection` at a later time, in order to
+/// reclaim the IO object, and additional related pieces.
+#[derive(Debug)]
+pub struct Parts<T, S> {
+    /// The original IO object used in the handshake.
+    pub io: T,
+    /// A buffer of bytes that have been read but not processed as HTTP.
+    ///
+    /// If the client sent additional bytes after its last request, and
+    /// this connection "ended" with an upgrade, the read buffer will contain
+    /// those bytes.
+    ///
+    /// You will want to check for any existing bytes if you plan to continue
+    /// communicating on the IO object.
+    pub read_buf: Bytes,
+    /// The `Service` used to serve this connection.
+    pub service: S,
+    _inner: (),
+}
+
+// ===== impl Connection =====
+
+impl<I, S> fmt::Debug for Connection<I, S>
+where
+    S: HttpService<IncomingBody>,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Connection").finish()
+    }
+}
+
+impl<I, B, S> Connection<I, S>
+where
+    S: HttpService<IncomingBody, ResBody = B>,
+    S::Error: Into<Box<dyn StdError + Send + Sync>>,
+    I: AsyncRead + AsyncWrite + Unpin,
+    B: Body + 'static,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    /// Start a graceful shutdown process for this connection.
+    ///
+    /// This `Connection` should continue to be polled until shutdown
+    /// can finish.
+    ///
+    /// # Note
+    ///
+    /// This should only be called while the `Connection` future is still
+    /// pending. If called after `Connection::poll` has resolved, this does
+    /// nothing.
+    pub fn graceful_shutdown(mut self: Pin<&mut Self>) {
+        self.conn.disable_keep_alive();
+    }
+
+    /// Return the inner IO object, and additional information.
+    ///
+    /// If the IO object has been "rewound" the io will not contain those bytes rewound.
+    /// This should only be called after `poll_without_shutdown` signals
+    /// that the connection is "done". Otherwise, it may not have finished
+    /// flushing all necessary HTTP bytes.
+    ///
+    /// # Panics
+    /// This method will panic if this connection is using an h2 protocol.
+    pub fn into_parts(self) -> Parts<I, S> {
+        let (io, read_buf, dispatch) = self.conn.into_inner();
+        Parts {
+            io,
+            read_buf,
+            service: dispatch.into_service(),
+            _inner: (),
+        }
+    }
+
+    /// Poll the connection for completion, but without calling `shutdown`
+    /// on the underlying IO.
+    ///
+    /// This is useful to allow running a connection while doing an HTTP
+    /// upgrade. Once the upgrade is completed, the connection would be "done",
+    /// but it is not desired to actually shutdown the IO object. Instead you
+    /// would take it back using `into_parts`.
+    pub fn poll_without_shutdown(&mut self, cx: &mut Context<'_>) -> Poll<crate::Result<()>>
+    where
+        S: Unpin,
+        S::Future: Unpin,
+        B: Unpin,
+    {
+        self.conn.poll_without_shutdown(cx)
+    }
+
+    /// Prevent shutdown of the underlying IO object at the end of service the request,
+    /// instead run `into_parts`. This is a convenience wrapper over `poll_without_shutdown`.
+    ///
+    /// # Error
+    ///
+    /// This errors if the underlying connection protocol is not HTTP/1.
+    pub fn without_shutdown(self) -> impl Future<Output = crate::Result<Parts<I, S>>>
+    where
+        S: Unpin,
+        S::Future: Unpin,
+        B: Unpin,
+    {
+        let mut zelf = Some(self);
+        futures_util::future::poll_fn(move |cx| {
+            ready!(zelf.as_mut().unwrap().conn.poll_without_shutdown(cx))?;
+            Poll::Ready(Ok(zelf.take().unwrap().into_parts()))
+        })
+    }
+
+    /// Enable this connection to support higher-level HTTP upgrades.
+    ///
+    /// See [the `upgrade` module](crate::upgrade) for more.
+    pub fn with_upgrades(self) -> upgrades::UpgradeableConnection<I, S>
+    where
+        I: Send,
+    {
+        upgrades::UpgradeableConnection { inner: Some(self) }
+    }
+}
+
+impl<I, B, S> Future for Connection<I, S>
+where
+    S: HttpService<IncomingBody, ResBody = B>,
+    S::Error: Into<Box<dyn StdError + Send + Sync>>,
+    I: AsyncRead + AsyncWrite + Unpin + 'static,
+    B: Body + 'static,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type Output = crate::Result<()>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match ready!(Pin::new(&mut self.conn).poll(cx)) {
+            Ok(done) => {
+                match done {
+                    proto::Dispatched::Shutdown => {}
+                    proto::Dispatched::Upgrade(pending) => {
+                        // With no `Send` bound on `I`, we can't try to do
+                        // upgrades here. In case a user was trying to use
+                        // `Body::on_upgrade` with this API, send a special
+                        // error letting them know about that.
+                        pending.manual();
+                    }
+                };
+                return Poll::Ready(Ok(()));
+            }
+            Err(e) => Poll::Ready(Err(e)),
+        }
+    }
+}
+
+// ===== impl Builder =====
+
+impl Builder {
+    /// Create a new connection builder.
+    pub fn new() -> Self {
+        Self {
+            h1_half_close: false,
+            h1_keep_alive: true,
+            h1_title_case_headers: false,
+            h1_preserve_header_case: false,
+            h1_header_read_timeout: None,
+            h1_writev: None,
+            max_buf_size: None,
+            pipeline_flush: false,
+        }
+    }
+    /// Set whether HTTP/1 connections should support half-closures.
+    ///
+    /// Clients can chose to shutdown their write-side while waiting
+    /// for the server to respond. Setting this to `true` will
+    /// prevent closing the connection immediately if `read`
+    /// detects an EOF in the middle of a request.
+    ///
+    /// Default is `false`.
+    pub fn half_close(&mut self, val: bool) -> &mut Self {
+        self.h1_half_close = val;
+        self
+    }
+
+    /// Enables or disables HTTP/1 keep-alive.
+    ///
+    /// Default is true.
+    pub fn keep_alive(&mut self, val: bool) -> &mut Self {
+        self.h1_keep_alive = val;
+        self
+    }
+
+    /// Set whether HTTP/1 connections will write header names as title case at
+    /// the socket level.
+    ///
+    /// Default is false.
+    pub fn title_case_headers(&mut self, enabled: bool) -> &mut Self {
+        self.h1_title_case_headers = enabled;
+        self
+    }
+
+    /// Set whether to support preserving original header cases.
+    ///
+    /// Currently, this will record the original cases received, and store them
+    /// in a private extension on the `Request`. It will also look for and use
+    /// such an extension in any provided `Response`.
+    ///
+    /// Since the relevant extension is still private, there is no way to
+    /// interact with the original cases. The only effect this can have now is
+    /// to forward the cases in a proxy-like fashion.
+    ///
+    /// Default is false.
+    pub fn preserve_header_case(&mut self, enabled: bool) -> &mut Self {
+        self.h1_preserve_header_case = enabled;
+        self
+    }
+
+    /// Set a timeout for reading client request headers. If a client does not
+    /// transmit the entire header within this time, the connection is closed.
+    ///
+    /// Default is None.
+    pub fn header_read_timeout(&mut self, read_timeout: Duration) -> &mut Self {
+        self.h1_header_read_timeout = Some(read_timeout);
+        self
+    }
+
+    /// Set whether HTTP/1 connections should try to use vectored writes,
+    /// or always flatten into a single buffer.
+    ///
+    /// Note that setting this to false may mean more copies of body data,
+    /// but may also improve performance when an IO transport doesn't
+    /// support vectored writes well, such as most TLS implementations.
+    ///
+    /// Setting this to true will force hyper to use queued strategy
+    /// which may eliminate unnecessary cloning on some TLS backends
+    ///
+    /// Default is `auto`. In this mode hyper will try to guess which
+    /// mode to use
+    pub fn writev(&mut self, val: bool) -> &mut Self {
+        self.h1_writev = Some(val);
+        self
+    }
+
+    /// Set the maximum buffer size for the connection.
+    ///
+    /// Default is ~400kb.
+    ///
+    /// # Panics
+    ///
+    /// The minimum value allowed is 8192. This method panics if the passed `max` is less than the minimum.
+    pub fn max_buf_size(&mut self, max: usize) -> &mut Self {
+        assert!(
+            max >= proto::h1::MINIMUM_MAX_BUFFER_SIZE,
+            "the max_buf_size cannot be smaller than the minimum that h1 specifies."
+        );
+        self.max_buf_size = Some(max);
+        self
+    }
+
+    /// Aggregates flushes to better support pipelined responses.
+    ///
+    /// Experimental, may have bugs.
+    ///
+    /// Default is false.
+    pub fn pipeline_flush(&mut self, enabled: bool) -> &mut Self {
+        self.pipeline_flush = enabled;
+        self
+    }
+
+    // /// Set the timer used in background tasks.
+    // pub fn timer<M>(&mut self, timer: M) -> &mut Self
+    // where
+    //     M: Timer + Send + Sync + 'static,
+    // {
+    //     self.timer = Time::Timer(Arc::new(timer));
+    //     self
+    // }
+
+    /// Bind a connection together with a [`Service`](crate::service::Service).
+    ///
+    /// This returns a Future that must be polled in order for HTTP to be
+    /// driven on the connection.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use hyper::{Body as Incoming, Request, Response};
+    /// # use hyper::service::Service;
+    /// # use hyper::server::conn::http1::Builder;
+    /// # use tokio::io::{AsyncRead, AsyncWrite};
+    /// # async fn run<I, S>(some_io: I, some_service: S)
+    /// # where
+    /// #     I: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    /// #     S: Service<hyper::Request<Incoming>, Response=hyper::Response<Incoming>> + Send + 'static,
+    /// #     S::Error: Into<Box<dyn std::error::Error + Send + Sync>>,
+    /// #     S::Future: Send,
+    /// # {
+    /// let http = Builder::new();
+    /// let conn = http.serve_connection(some_io, some_service);
+    ///
+    /// if let Err(e) = conn.await {
+    ///     eprintln!("server connection error: {}", e);
+    /// }
+    /// # }
+    /// # fn main() {}
+    /// ```
+    pub fn serve_connection<I, S>(&self, io: I, service: S) -> Connection<I, S>
+    where
+        S: HttpService<IncomingBody>,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        S::ResBody: 'static,
+        <S::ResBody as Body>::Error: Into<Box<dyn StdError + Send + Sync>>,
+        I: AsyncRead + AsyncWrite + Unpin,
+    {
+        let mut conn = proto::Conn::new(io);
+        if !self.h1_keep_alive {
+            conn.disable_keep_alive();
+        }
+        if self.h1_half_close {
+            conn.set_allow_half_close();
+        }
+        if self.h1_title_case_headers {
+            conn.set_title_case_headers();
+        }
+        if self.h1_preserve_header_case {
+            conn.set_preserve_header_case();
+        }
+        if let Some(header_read_timeout) = self.h1_header_read_timeout {
+            conn.set_http1_header_read_timeout(header_read_timeout);
+        }
+        if let Some(writev) = self.h1_writev {
+            if writev {
+                conn.set_write_strategy_queue();
+            } else {
+                conn.set_write_strategy_flatten();
+            }
+        }
+        conn.set_flush_pipeline(self.pipeline_flush);
+        if let Some(max) = self.max_buf_size {
+            conn.set_max_buf_size(max);
+        }
+        let sd = proto::h1::dispatch::Server::new(service);
+        let proto = proto::h1::Dispatcher::new(sd, conn);
+        Connection { conn: proto }
+    }
+}
+
+mod upgrades {
+    use crate::upgrade::Upgraded;
+
+    use super::*;
+
+    // A future binding a connection with a Service with Upgrade support.
+    //
+    // This type is unnameable outside the crate.
+    #[must_use = "futures do nothing unless polled"]
+    #[allow(missing_debug_implementations)]
+    pub struct UpgradeableConnection<T, S>
+    where
+        S: HttpService<IncomingBody>,
+    {
+        pub(super) inner: Option<Connection<T, S>>,
+    }
+
+    impl<I, B, S> UpgradeableConnection<I, S>
+    where
+        S: HttpService<IncomingBody, ResBody = B>,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        I: AsyncRead + AsyncWrite + Unpin,
+        B: Body + 'static,
+        B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    {
+        /// Start a graceful shutdown process for this connection.
+        ///
+        /// This `Connection` should continue to be polled until shutdown
+        /// can finish.
+        pub fn graceful_shutdown(mut self: Pin<&mut Self>) {
+            Pin::new(self.inner.as_mut().unwrap()).graceful_shutdown()
+        }
+    }
+
+    impl<I, B, S> Future for UpgradeableConnection<I, S>
+    where
+        S: HttpService<IncomingBody, ResBody = B>,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        I: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+        B: Body + 'static,
+        B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    {
+        type Output = crate::Result<()>;
+
+        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+            match ready!(Pin::new(&mut self.inner.as_mut().unwrap().conn).poll(cx)) {
+                Ok(proto::Dispatched::Shutdown) => Poll::Ready(Ok(())),
+                Ok(proto::Dispatched::Upgrade(pending)) => {
+                    let (io, buf, _) = self.inner.take().unwrap().conn.into_inner();
+                    pending.fulfill(Upgraded::new(io, buf));
+                    Poll::Ready(Ok(()))
+                }
+                Err(e) => Poll::Ready(Err(e)),
+            }
+        }
+    }
+}
diff --git a/src/server/conn/http2.rs b/src/server/conn/http2.rs
new file mode 100644
index 0000000..4f7df82
--- /dev/null
+++ b/src/server/conn/http2.rs
@@ -0,0 +1,260 @@
+//! HTTP/2 Server Connections
+
+use std::error::Error as StdError;
+use std::fmt;
+use std::future::Future;
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::time::Duration;
+
+use pin_project_lite::pin_project;
+use tokio::io::{AsyncRead, AsyncWrite};
+
+use crate::body::{Body as IncomingBody, HttpBody as Body};
+use crate::common::exec::ConnStreamExec;
+use crate::proto;
+use crate::service::HttpService;
+
+pin_project! {
+    /// A future binding an HTTP/2 connection with a Service.
+    ///
+    /// Polling this future will drive HTTP forward.
+    #[must_use = "futures do nothing unless polled"]
+    pub struct Connection<T, S, E>
+    where
+        S: HttpService<IncomingBody>,
+    {
+        conn: proto::h2::Server<T, S, S::ResBody, E>,
+    }
+}
+
+/// A configuration builder for HTTP/2 server connections.
+#[derive(Clone, Debug)]
+pub struct Builder<E> {
+    exec: E,
+    h2_builder: proto::h2::server::Config,
+}
+
+// ===== impl Connection =====
+
+impl<I, S, E> fmt::Debug for Connection<I, S, E>
+where
+    S: HttpService<IncomingBody>,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Connection").finish()
+    }
+}
+
+impl<I, B, S, E> Connection<I, S, E>
+where
+    S: HttpService<IncomingBody, ResBody = B>,
+    S::Error: Into<Box<dyn StdError + Send + Sync>>,
+    I: AsyncRead + AsyncWrite + Unpin,
+    B: Body + 'static,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    E: ConnStreamExec<S::Future, B>,
+{
+    /// Start a graceful shutdown process for this connection.
+    ///
+    /// This `Connection` should continue to be polled until shutdown
+    /// can finish.
+    ///
+    /// # Note
+    ///
+    /// This should only be called while the `Connection` future is still
+    /// pending. If called after `Connection::poll` has resolved, this does
+    /// nothing.
+    pub fn graceful_shutdown(mut self: Pin<&mut Self>) {
+        self.conn.graceful_shutdown();
+    }
+}
+
+impl<I, B, S, E> Future for Connection<I, S, E>
+where
+    S: HttpService<IncomingBody, ResBody = B>,
+    S::Error: Into<Box<dyn StdError + Send + Sync>>,
+    I: AsyncRead + AsyncWrite + Unpin + 'static,
+    B: Body + 'static,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    E: ConnStreamExec<S::Future, B>,
+{
+    type Output = crate::Result<()>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match ready!(Pin::new(&mut self.conn).poll(cx)) {
+            Ok(_done) => {
+                //TODO: the proto::h2::Server no longer needs to return
+                //the Dispatched enum
+                Poll::Ready(Ok(()))
+            }
+            Err(e) => Poll::Ready(Err(e)),
+        }
+    }
+}
+
+// ===== impl Builder =====
+
+impl<E> Builder<E> {
+    /// Create a new connection builder.
+    ///
+    /// This starts with the default options, and an executor.
+    pub fn new(exec: E) -> Self {
+        Self {
+            exec: exec,
+            h2_builder: Default::default(),
+        }
+    }
+
+    /// Sets the [`SETTINGS_INITIAL_WINDOW_SIZE`][spec] option for HTTP2
+    /// stream-level flow control.
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    ///
+    /// [spec]: https://http2.github.io/http2-spec/#SETTINGS_INITIAL_WINDOW_SIZE
+    pub fn initial_stream_window_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
+        if let Some(sz) = sz.into() {
+            self.h2_builder.adaptive_window = false;
+            self.h2_builder.initial_stream_window_size = sz;
+        }
+        self
+    }
+
+    /// Sets the max connection-level flow control for HTTP2.
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    pub fn initial_connection_window_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
+        if let Some(sz) = sz.into() {
+            self.h2_builder.adaptive_window = false;
+            self.h2_builder.initial_conn_window_size = sz;
+        }
+        self
+    }
+
+    /// Sets whether to use an adaptive flow control.
+    ///
+    /// Enabling this will override the limits set in
+    /// `initial_stream_window_size` and
+    /// `initial_connection_window_size`.
+    pub fn adaptive_window(&mut self, enabled: bool) -> &mut Self {
+        use proto::h2::SPEC_WINDOW_SIZE;
+
+        self.h2_builder.adaptive_window = enabled;
+        if enabled {
+            self.h2_builder.initial_conn_window_size = SPEC_WINDOW_SIZE;
+            self.h2_builder.initial_stream_window_size = SPEC_WINDOW_SIZE;
+        }
+        self
+    }
+
+    /// Sets the maximum frame size to use for HTTP2.
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    pub fn max_frame_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
+        if let Some(sz) = sz.into() {
+            self.h2_builder.max_frame_size = sz;
+        }
+        self
+    }
+
+    /// Sets the [`SETTINGS_MAX_CONCURRENT_STREAMS`][spec] option for HTTP2
+    /// connections.
+    ///
+    /// Default is no limit (`std::u32::MAX`). Passing `None` will do nothing.
+    ///
+    /// [spec]: https://http2.github.io/http2-spec/#SETTINGS_MAX_CONCURRENT_STREAMS
+    pub fn max_concurrent_streams(&mut self, max: impl Into<Option<u32>>) -> &mut Self {
+        self.h2_builder.max_concurrent_streams = max.into();
+        self
+    }
+
+    /// Sets an interval for HTTP2 Ping frames should be sent to keep a
+    /// connection alive.
+    ///
+    /// Pass `None` to disable HTTP2 keep-alive.
+    ///
+    /// Default is currently disabled.
+    ///
+    /// # Cargo Feature
+    ///
+    pub fn keep_alive_interval(&mut self, interval: impl Into<Option<Duration>>) -> &mut Self {
+        self.h2_builder.keep_alive_interval = interval.into();
+        self
+    }
+
+    /// Sets a timeout for receiving an acknowledgement of the keep-alive ping.
+    ///
+    /// If the ping is not acknowledged within the timeout, the connection will
+    /// be closed. Does nothing if `keep_alive_interval` is disabled.
+    ///
+    /// Default is 20 seconds.
+    ///
+    /// # Cargo Feature
+    ///
+    pub fn keep_alive_timeout(&mut self, timeout: Duration) -> &mut Self {
+        self.h2_builder.keep_alive_timeout = timeout;
+        self
+    }
+
+    /// Set the maximum write buffer size for each HTTP/2 stream.
+    ///
+    /// Default is currently ~400KB, but may change.
+    ///
+    /// # Panics
+    ///
+    /// The value must be no larger than `u32::MAX`.
+    pub fn max_send_buf_size(&mut self, max: usize) -> &mut Self {
+        assert!(max <= std::u32::MAX as usize);
+        self.h2_builder.max_send_buffer_size = max;
+        self
+    }
+
+    /// Enables the [extended CONNECT protocol].
+    ///
+    /// [extended CONNECT protocol]: https://datatracker.ietf.org/doc/html/rfc8441#section-4
+    pub fn enable_connect_protocol(&mut self) -> &mut Self {
+        self.h2_builder.enable_connect_protocol = true;
+        self
+    }
+
+    /// Sets the max size of received header frames.
+    ///
+    /// Default is currently ~16MB, but may change.
+    pub fn max_header_list_size(&mut self, max: u32) -> &mut Self {
+        self.h2_builder.max_header_list_size = max;
+        self
+    }
+
+    // /// Set the timer used in background tasks.
+    // pub fn timer<M>(&mut self, timer: M) -> &mut Self
+    // where
+    //     M: Timer + Send + Sync + 'static,
+    // {
+    //     self.timer = Time::Timer(Arc::new(timer));
+    //     self
+    // }
+
+    /// Bind a connection together with a [`Service`](crate::service::Service).
+    ///
+    /// This returns a Future that must be polled in order for HTTP to be
+    /// driven on the connection.
+    pub fn serve_connection<S, I, Bd>(&self, io: I, service: S) -> Connection<I, S, E>
+    where
+        S: HttpService<IncomingBody, ResBody = Bd>,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        Bd: Body + 'static,
+        Bd::Error: Into<Box<dyn StdError + Send + Sync>>,
+        I: AsyncRead + AsyncWrite + Unpin,
+        E: ConnStreamExec<S::Future, Bd>,
+    {
+        let proto = proto::h2::Server::new(io, service, &self.h2_builder, self.exec.clone());
+        Connection { conn: proto }
+    }
+}
diff --git a/src/server/mod.rs b/src/server/mod.rs
new file mode 100644
index 0000000..65eb706
--- /dev/null
+++ b/src/server/mod.rs
@@ -0,0 +1,173 @@
+//! HTTP Server
+//!
+//! A `Server` is created to listen on a port, parse HTTP requests, and hand
+//! them off to a `Service`.
+//!
+//! There are two levels of APIs provide for constructing HTTP servers:
+//!
+//! - The higher-level [`Server`](Server) type.
+//! - The lower-level [`conn`](conn) module.
+//!
+//! # Server
+//!
+//! The [`Server`](Server) is main way to start listening for HTTP requests.
+//! It wraps a listener with a [`MakeService`](crate::service), and then should
+//! be executed to start serving requests.
+//!
+//! [`Server`](Server) accepts connections in both HTTP1 and HTTP2 by default.
+//!
+//! ## Examples
+//!
+//! ```no_run
+//! use std::convert::Infallible;
+//! use std::net::SocketAddr;
+//! use hyper::{Body, Request, Response, Server};
+//! use hyper::service::{make_service_fn, service_fn};
+//!
+//! async fn handle(_req: Request<Body>) -> Result<Response<Body>, Infallible> {
+//!     Ok(Response::new(Body::from("Hello World")))
+//! }
+//!
+//! # #[cfg(feature = "runtime")]
+//! #[tokio::main]
+//! async fn main() {
+//!     // Construct our SocketAddr to listen on...
+//!     let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
+//!
+//!     // And a MakeService to handle each connection...
+//!     let make_service = make_service_fn(|_conn| async {
+//!         Ok::<_, Infallible>(service_fn(handle))
+//!     });
+//!
+//!     // Then bind and serve...
+//!     let server = Server::bind(&addr).serve(make_service);
+//!
+//!     // And run forever...
+//!     if let Err(e) = server.await {
+//!         eprintln!("server error: {}", e);
+//!     }
+//! }
+//! # #[cfg(not(feature = "runtime"))]
+//! # fn main() {}
+//! ```
+//!
+//! If you don't need the connection and your service implements `Clone` you can use
+//! [`tower::make::Shared`] instead of `make_service_fn` which is a bit simpler:
+//!
+//! ```no_run
+//! # use std::convert::Infallible;
+//! # use std::net::SocketAddr;
+//! # use hyper::{Body, Request, Response, Server};
+//! # use hyper::service::{make_service_fn, service_fn};
+//! # use tower::make::Shared;
+//! # async fn handle(_req: Request<Body>) -> Result<Response<Body>, Infallible> {
+//! #     Ok(Response::new(Body::from("Hello World")))
+//! # }
+//! # #[cfg(feature = "runtime")]
+//! #[tokio::main]
+//! async fn main() {
+//!     // Construct our SocketAddr to listen on...
+//!     let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
+//!
+//!     // Shared is a MakeService that produces services by cloning an inner service...
+//!     let make_service = Shared::new(service_fn(handle));
+//!
+//!     // Then bind and serve...
+//!     let server = Server::bind(&addr).serve(make_service);
+//!
+//!     // And run forever...
+//!     if let Err(e) = server.await {
+//!         eprintln!("server error: {}", e);
+//!     }
+//! }
+//! # #[cfg(not(feature = "runtime"))]
+//! # fn main() {}
+//! ```
+//!
+//! Passing data to your request handler can be done like so:
+//!
+//! ```no_run
+//! use std::convert::Infallible;
+//! use std::net::SocketAddr;
+//! use hyper::{Body, Request, Response, Server};
+//! use hyper::service::{make_service_fn, service_fn};
+//! # #[cfg(feature = "runtime")]
+//! use hyper::server::conn::AddrStream;
+//!
+//! #[derive(Clone)]
+//! struct AppContext {
+//!     // Whatever data your application needs can go here
+//! }
+//!
+//! async fn handle(
+//!     context: AppContext,
+//!     addr: SocketAddr,
+//!     req: Request<Body>
+//! ) -> Result<Response<Body>, Infallible> {
+//!     Ok(Response::new(Body::from("Hello World")))
+//! }
+//!
+//! # #[cfg(feature = "runtime")]
+//! #[tokio::main]
+//! async fn main() {
+//!     let context = AppContext {
+//!         // ...
+//!     };
+//!
+//!     // A `MakeService` that produces a `Service` to handle each connection.
+//!     let make_service = make_service_fn(move |conn: &AddrStream| {
+//!         // We have to clone the context to share it with each invocation of
+//!         // `make_service`. If your data doesn't implement `Clone` consider using
+//!         // an `std::sync::Arc`.
+//!         let context = context.clone();
+//!
+//!         // You can grab the address of the incoming connection like so.
+//!         let addr = conn.remote_addr();
+//!
+//!         // Create a `Service` for responding to the request.
+//!         let service = service_fn(move |req| {
+//!             handle(context.clone(), addr, req)
+//!         });
+//!
+//!         // Return the service to hyper.
+//!         async move { Ok::<_, Infallible>(service) }
+//!     });
+//!
+//!     // Run the server like above...
+//!     let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
+//!
+//!     let server = Server::bind(&addr).serve(make_service);
+//!
+//!     if let Err(e) = server.await {
+//!         eprintln!("server error: {}", e);
+//!     }
+//! }
+//! # #[cfg(not(feature = "runtime"))]
+//! # fn main() {}
+//! ```
+//!
+//! [`tower::make::Shared`]: https://docs.rs/tower/latest/tower/make/struct.Shared.html
+
+pub mod accept;
+pub mod conn;
+#[cfg(feature = "tcp")]
+mod tcp;
+
+pub use self::server::Server;
+
+cfg_feature! {
+    #![any(feature = "http1", feature = "http2")]
+
+    #[cfg_attr(feature = "deprecated", allow(deprecated))]
+    pub(crate) mod server;
+    pub use self::server::Builder;
+
+    mod shutdown;
+}
+
+cfg_feature! {
+    #![not(any(feature = "http1", feature = "http2"))]
+
+    mod server_stub;
+    use server_stub as server;
+}
diff --git a/src/server/server.rs b/src/server/server.rs
new file mode 100644
index 0000000..6d7d69e
--- /dev/null
+++ b/src/server/server.rs
@@ -0,0 +1,825 @@
+use std::error::Error as StdError;
+use std::fmt;
+use std::future::Future;
+use std::marker::Unpin;
+#[cfg(feature = "tcp")]
+use std::net::{SocketAddr, TcpListener as StdTcpListener};
+use std::pin::Pin;
+use std::task::{Context, Poll};
+#[cfg(feature = "tcp")]
+use std::time::Duration;
+
+use pin_project_lite::pin_project;
+
+use tokio::io::{AsyncRead, AsyncWrite};
+use tracing::trace;
+
+use super::accept::Accept;
+#[cfg(all(feature = "tcp"))]
+use super::tcp::AddrIncoming;
+use crate::body::{Body, HttpBody};
+use crate::common::exec::Exec;
+use crate::common::exec::{ConnStreamExec, NewSvcExec};
+// Renamed `Http` as `Http_` for now so that people upgrading don't see an
+// error that `hyper::server::Http` is private...
+use super::conn::{Connection, Http as Http_, UpgradeableConnection};
+use super::shutdown::{Graceful, GracefulWatcher};
+use crate::service::{HttpService, MakeServiceRef};
+
+use self::new_svc::NewSvcTask;
+
+pin_project! {
+    /// A listening HTTP server that accepts connections in both HTTP1 and HTTP2 by default.
+    ///
+    /// `Server` is a `Future` mapping a bound listener with a set of service
+    /// handlers. It is built using the [`Builder`](Builder), and the future
+    /// completes when the server has been shutdown. It should be run by an
+    /// `Executor`.
+    pub struct Server<I, S, E = Exec> {
+        #[pin]
+        incoming: I,
+        make_service: S,
+        protocol: Http_<E>,
+    }
+}
+
+/// A builder for a [`Server`](Server).
+#[derive(Debug)]
+#[cfg_attr(docsrs, doc(cfg(any(feature = "http1", feature = "http2"))))]
+pub struct Builder<I, E = Exec> {
+    incoming: I,
+    protocol: Http_<E>,
+}
+
+// ===== impl Server =====
+
+#[cfg_attr(docsrs, doc(cfg(any(feature = "http1", feature = "http2"))))]
+impl<I> Server<I, ()> {
+    /// Starts a [`Builder`](Builder) with the provided incoming stream.
+    pub fn builder(incoming: I) -> Builder<I> {
+        Builder {
+            incoming,
+            protocol: Http_::new(),
+        }
+    }
+}
+
+#[cfg(feature = "tcp")]
+#[cfg_attr(
+    docsrs,
+    doc(cfg(all(feature = "tcp", any(feature = "http1", feature = "http2"))))
+)]
+impl Server<AddrIncoming, ()> {
+    /// Binds to the provided address, and returns a [`Builder`](Builder).
+    ///
+    /// # Panics
+    ///
+    /// This method will panic if binding to the address fails. For a method
+    /// to bind to an address and return a `Result`, see `Server::try_bind`.
+    pub fn bind(addr: &SocketAddr) -> Builder<AddrIncoming> {
+        let incoming = AddrIncoming::new(addr).unwrap_or_else(|e| {
+            panic!("error binding to {}: {}", addr, e);
+        });
+        Server::builder(incoming)
+    }
+
+    /// Tries to bind to the provided address, and returns a [`Builder`](Builder).
+    pub fn try_bind(addr: &SocketAddr) -> crate::Result<Builder<AddrIncoming>> {
+        AddrIncoming::new(addr).map(Server::builder)
+    }
+
+    /// Create a new instance from a `std::net::TcpListener` instance.
+    pub fn from_tcp(listener: StdTcpListener) -> Result<Builder<AddrIncoming>, crate::Error> {
+        AddrIncoming::from_std(listener).map(Server::builder)
+    }
+}
+
+#[cfg(feature = "tcp")]
+#[cfg_attr(
+    docsrs,
+    doc(cfg(all(feature = "tcp", any(feature = "http1", feature = "http2"))))
+)]
+impl<S, E> Server<AddrIncoming, S, E> {
+    /// Returns the local address that this server is bound to.
+    pub fn local_addr(&self) -> SocketAddr {
+        self.incoming.local_addr()
+    }
+}
+
+#[cfg_attr(docsrs, doc(cfg(any(feature = "http1", feature = "http2"))))]
+impl<I, IO, IE, S, E, B> Server<I, S, E>
+where
+    I: Accept<Conn = IO, Error = IE>,
+    IE: Into<Box<dyn StdError + Send + Sync>>,
+    IO: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    S: MakeServiceRef<IO, Body, ResBody = B>,
+    S::Error: Into<Box<dyn StdError + Send + Sync>>,
+    B: HttpBody + 'static,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    E: ConnStreamExec<<S::Service as HttpService<Body>>::Future, B>,
+{
+    /// Prepares a server to handle graceful shutdown when the provided future
+    /// completes.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # fn main() {}
+    /// # #[cfg(feature = "tcp")]
+    /// # async fn run() {
+    /// # use hyper::{Body, Response, Server, Error};
+    /// # use hyper::service::{make_service_fn, service_fn};
+    /// # let make_service = make_service_fn(|_| async {
+    /// #     Ok::<_, Error>(service_fn(|_req| async {
+    /// #         Ok::<_, Error>(Response::new(Body::from("Hello World")))
+    /// #     }))
+    /// # });
+    /// // Make a server from the previous examples...
+    /// let server = Server::bind(&([127, 0, 0, 1], 3000).into())
+    ///     .serve(make_service);
+    ///
+    /// // Prepare some signal for when the server should start shutting down...
+    /// let (tx, rx) = tokio::sync::oneshot::channel::<()>();
+    /// let graceful = server
+    ///     .with_graceful_shutdown(async {
+    ///         rx.await.ok();
+    ///     });
+    ///
+    /// // Await the `server` receiving the signal...
+    /// if let Err(e) = graceful.await {
+    ///     eprintln!("server error: {}", e);
+    /// }
+    ///
+    /// // And later, trigger the signal by calling `tx.send(())`.
+    /// let _ = tx.send(());
+    /// # }
+    /// ```
+    pub fn with_graceful_shutdown<F>(self, signal: F) -> Graceful<I, S, F, E>
+    where
+        F: Future<Output = ()>,
+        E: NewSvcExec<IO, S::Future, S::Service, E, GracefulWatcher>,
+    {
+        Graceful::new(self, signal)
+    }
+
+    fn poll_next_(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<crate::Result<Connecting<IO, S::Future, E>>>> {
+        let me = self.project();
+        match ready!(me.make_service.poll_ready_ref(cx)) {
+            Ok(()) => (),
+            Err(e) => {
+                trace!("make_service closed");
+                return Poll::Ready(Some(Err(crate::Error::new_user_make_service(e))));
+            }
+        }
+
+        if let Some(item) = ready!(me.incoming.poll_accept(cx)) {
+            let io = item.map_err(crate::Error::new_accept)?;
+            let new_fut = me.make_service.make_service_ref(&io);
+            Poll::Ready(Some(Ok(Connecting {
+                future: new_fut,
+                io: Some(io),
+                protocol: me.protocol.clone(),
+            })))
+        } else {
+            Poll::Ready(None)
+        }
+    }
+
+    pub(super) fn poll_watch<W>(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        watcher: &W,
+    ) -> Poll<crate::Result<()>>
+    where
+        E: NewSvcExec<IO, S::Future, S::Service, E, W>,
+        W: Watcher<IO, S::Service, E>,
+    {
+        loop {
+            if let Some(connecting) = ready!(self.as_mut().poll_next_(cx)?) {
+                let fut = NewSvcTask::new(connecting, watcher.clone());
+                self.as_mut().project().protocol.exec.execute_new_svc(fut);
+            } else {
+                return Poll::Ready(Ok(()));
+            }
+        }
+    }
+}
+
+#[cfg_attr(docsrs, doc(cfg(any(feature = "http1", feature = "http2"))))]
+impl<I, IO, IE, S, B, E> Future for Server<I, S, E>
+where
+    I: Accept<Conn = IO, Error = IE>,
+    IE: Into<Box<dyn StdError + Send + Sync>>,
+    IO: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    S: MakeServiceRef<IO, Body, ResBody = B>,
+    S::Error: Into<Box<dyn StdError + Send + Sync>>,
+    B: HttpBody + 'static,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    E: ConnStreamExec<<S::Service as HttpService<Body>>::Future, B>,
+    E: NewSvcExec<IO, S::Future, S::Service, E, NoopWatcher>,
+{
+    type Output = crate::Result<()>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.poll_watch(cx, &NoopWatcher)
+    }
+}
+
+impl<I: fmt::Debug, S: fmt::Debug> fmt::Debug for Server<I, S> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut st = f.debug_struct("Server");
+        st.field("listener", &self.incoming);
+        st.finish()
+    }
+}
+
+// ===== impl Builder =====
+
+#[cfg_attr(docsrs, doc(cfg(any(feature = "http1", feature = "http2"))))]
+impl<I, E> Builder<I, E> {
+    /// Start a new builder, wrapping an incoming stream and low-level options.
+    ///
+    /// For a more convenient constructor, see [`Server::bind`](Server::bind).
+    pub fn new(incoming: I, protocol: Http_<E>) -> Self {
+        Builder { incoming, protocol }
+    }
+
+    /// Sets whether to use keep-alive for HTTP/1 connections.
+    ///
+    /// Default is `true`.
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn http1_keepalive(mut self, val: bool) -> Self {
+        self.protocol.http1_keep_alive(val);
+        self
+    }
+
+    /// Set whether HTTP/1 connections should support half-closures.
+    ///
+    /// Clients can chose to shutdown their write-side while waiting
+    /// for the server to respond. Setting this to `true` will
+    /// prevent closing the connection immediately if `read`
+    /// detects an EOF in the middle of a request.
+    ///
+    /// Default is `false`.
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn http1_half_close(mut self, val: bool) -> Self {
+        self.protocol.http1_half_close(val);
+        self
+    }
+
+    /// Set the maximum buffer size.
+    ///
+    /// Default is ~ 400kb.
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn http1_max_buf_size(mut self, val: usize) -> Self {
+        self.protocol.max_buf_size(val);
+        self
+    }
+
+    // Sets whether to bunch up HTTP/1 writes until the read buffer is empty.
+    //
+    // This isn't really desirable in most cases, only really being useful in
+    // silly pipeline benchmarks.
+    #[doc(hidden)]
+    #[cfg(feature = "http1")]
+    pub fn http1_pipeline_flush(mut self, val: bool) -> Self {
+        self.protocol.pipeline_flush(val);
+        self
+    }
+
+    /// Set whether HTTP/1 connections should try to use vectored writes,
+    /// or always flatten into a single buffer.
+    ///
+    /// Note that setting this to false may mean more copies of body data,
+    /// but may also improve performance when an IO transport doesn't
+    /// support vectored writes well, such as most TLS implementations.
+    ///
+    /// Setting this to true will force hyper to use queued strategy
+    /// which may eliminate unnecessary cloning on some TLS backends
+    ///
+    /// Default is `auto`. In this mode hyper will try to guess which
+    /// mode to use
+    #[cfg(feature = "http1")]
+    pub fn http1_writev(mut self, enabled: bool) -> Self {
+        self.protocol.http1_writev(enabled);
+        self
+    }
+
+    /// Set whether HTTP/1 connections will write header names as title case at
+    /// the socket level.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn http1_title_case_headers(mut self, val: bool) -> Self {
+        self.protocol.http1_title_case_headers(val);
+        self
+    }
+
+    /// Set whether to support preserving original header cases.
+    ///
+    /// Currently, this will record the original cases received, and store them
+    /// in a private extension on the `Request`. It will also look for and use
+    /// such an extension in any provided `Response`.
+    ///
+    /// Since the relevant extension is still private, there is no way to
+    /// interact with the original cases. The only effect this can have now is
+    /// to forward the cases in a proxy-like fashion.
+    ///
+    /// Note that this setting does not affect HTTP/2.
+    ///
+    /// Default is false.
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn http1_preserve_header_case(mut self, val: bool) -> Self {
+        self.protocol.http1_preserve_header_case(val);
+        self
+    }
+
+    /// Set a timeout for reading client request headers. If a client does not
+    /// transmit the entire header within this time, the connection is closed.
+    ///
+    /// Default is None.
+    #[cfg(all(feature = "http1", feature = "runtime"))]
+    #[cfg_attr(docsrs, doc(cfg(all(feature = "http1", feature = "runtime"))))]
+    pub fn http1_header_read_timeout(mut self, read_timeout: Duration) -> Self {
+        self.protocol.http1_header_read_timeout(read_timeout);
+        self
+    }
+
+    /// Sets whether HTTP/1 is required.
+    ///
+    /// Default is `false`.
+    #[cfg(feature = "http1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http1")))]
+    pub fn http1_only(mut self, val: bool) -> Self {
+        self.protocol.http1_only(val);
+        self
+    }
+
+    /// Sets whether HTTP/2 is required.
+    ///
+    /// Default is `false`.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_only(mut self, val: bool) -> Self {
+        self.protocol.http2_only(val);
+        self
+    }
+
+    /// Configures the maximum number of pending reset streams allowed before a GOAWAY will be sent.
+    ///
+    /// This will default to whatever the default in h2 is. As of v0.3.17, it is 20.
+    ///
+    /// See <https://github.com/hyperium/hyper/issues/2877> for more information.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_pending_accept_reset_streams(mut self, max: impl Into<Option<usize>>) -> Self {
+        self.protocol.http2_max_pending_accept_reset_streams(max);
+        self
+    }
+
+    /// Sets the [`SETTINGS_INITIAL_WINDOW_SIZE`][spec] option for HTTP2
+    /// stream-level flow control.
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    ///
+    /// [spec]: https://http2.github.io/http2-spec/#SETTINGS_INITIAL_WINDOW_SIZE
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_initial_stream_window_size(mut self, sz: impl Into<Option<u32>>) -> Self {
+        self.protocol.http2_initial_stream_window_size(sz.into());
+        self
+    }
+
+    /// Sets the max connection-level flow control for HTTP2
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_initial_connection_window_size(mut self, sz: impl Into<Option<u32>>) -> Self {
+        self.protocol
+            .http2_initial_connection_window_size(sz.into());
+        self
+    }
+
+    /// Sets whether to use an adaptive flow control.
+    ///
+    /// Enabling this will override the limits set in
+    /// `http2_initial_stream_window_size` and
+    /// `http2_initial_connection_window_size`.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_adaptive_window(mut self, enabled: bool) -> Self {
+        self.protocol.http2_adaptive_window(enabled);
+        self
+    }
+
+    /// Sets the maximum frame size to use for HTTP2.
+    ///
+    /// Passing `None` will do nothing.
+    ///
+    /// If not set, hyper will use a default.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_frame_size(mut self, sz: impl Into<Option<u32>>) -> Self {
+        self.protocol.http2_max_frame_size(sz);
+        self
+    }
+
+    /// Sets the max size of received header frames.
+    ///
+    /// Default is currently ~16MB, but may change.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_header_list_size(mut self, max: u32) -> Self {
+        self.protocol.http2_max_header_list_size(max);
+        self
+    }
+
+    /// Sets the [`SETTINGS_MAX_CONCURRENT_STREAMS`][spec] option for HTTP2
+    /// connections.
+    ///
+    /// Default is no limit (`std::u32::MAX`). Passing `None` will do nothing.
+    ///
+    /// [spec]: https://http2.github.io/http2-spec/#SETTINGS_MAX_CONCURRENT_STREAMS
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_concurrent_streams(mut self, max: impl Into<Option<u32>>) -> Self {
+        self.protocol.http2_max_concurrent_streams(max.into());
+        self
+    }
+
+    /// Sets an interval for HTTP2 Ping frames should be sent to keep a
+    /// connection alive.
+    ///
+    /// Pass `None` to disable HTTP2 keep-alive.
+    ///
+    /// Default is currently disabled.
+    ///
+    /// # Cargo Feature
+    ///
+    /// Requires the `runtime` cargo feature to be enabled.
+    #[cfg(all(feature = "runtime", feature = "http2"))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_keep_alive_interval(mut self, interval: impl Into<Option<Duration>>) -> Self {
+        self.protocol.http2_keep_alive_interval(interval);
+        self
+    }
+
+    /// Sets a timeout for receiving an acknowledgement of the keep-alive ping.
+    ///
+    /// If the ping is not acknowledged within the timeout, the connection will
+    /// be closed. Does nothing if `http2_keep_alive_interval` is disabled.
+    ///
+    /// Default is 20 seconds.
+    ///
+    /// # Cargo Feature
+    ///
+    /// Requires the `runtime` cargo feature to be enabled.
+    #[cfg(all(feature = "runtime", feature = "http2"))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_keep_alive_timeout(mut self, timeout: Duration) -> Self {
+        self.protocol.http2_keep_alive_timeout(timeout);
+        self
+    }
+
+    /// Set the maximum write buffer size for each HTTP/2 stream.
+    ///
+    /// Default is currently ~400KB, but may change.
+    ///
+    /// # Panics
+    ///
+    /// The value must be no larger than `u32::MAX`.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_send_buf_size(mut self, max: usize) -> Self {
+        self.protocol.http2_max_send_buf_size(max);
+        self
+    }
+
+    /// Enables the [extended CONNECT protocol].
+    ///
+    /// [extended CONNECT protocol]: https://datatracker.ietf.org/doc/html/rfc8441#section-4
+    #[cfg(feature = "http2")]
+    pub fn http2_enable_connect_protocol(mut self) -> Self {
+        self.protocol.http2_enable_connect_protocol();
+        self
+    }
+
+    /// Sets the `Executor` to deal with connection tasks.
+    ///
+    /// Default is `tokio::spawn`.
+    pub fn executor<E2>(self, executor: E2) -> Builder<I, E2> {
+        Builder {
+            incoming: self.incoming,
+            protocol: self.protocol.with_executor(executor),
+        }
+    }
+
+    /// Consume this `Builder`, creating a [`Server`](Server).
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # #[cfg(feature = "tcp")]
+    /// # async fn run() {
+    /// use hyper::{Body, Error, Response, Server};
+    /// use hyper::service::{make_service_fn, service_fn};
+    ///
+    /// // Construct our SocketAddr to listen on...
+    /// let addr = ([127, 0, 0, 1], 3000).into();
+    ///
+    /// // And a MakeService to handle each connection...
+    /// let make_svc = make_service_fn(|_| async {
+    ///     Ok::<_, Error>(service_fn(|_req| async {
+    ///         Ok::<_, Error>(Response::new(Body::from("Hello World")))
+    ///     }))
+    /// });
+    ///
+    /// // Then bind and serve...
+    /// let server = Server::bind(&addr)
+    ///     .serve(make_svc);
+    ///
+    /// // Run forever-ish...
+    /// if let Err(err) = server.await {
+    ///     eprintln!("server error: {}", err);
+    /// }
+    /// # }
+    /// ```
+    pub fn serve<S, B>(self, make_service: S) -> Server<I, S, E>
+    where
+        I: Accept,
+        I::Error: Into<Box<dyn StdError + Send + Sync>>,
+        I::Conn: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+        S: MakeServiceRef<I::Conn, Body, ResBody = B>,
+        S::Error: Into<Box<dyn StdError + Send + Sync>>,
+        B: HttpBody + 'static,
+        B::Error: Into<Box<dyn StdError + Send + Sync>>,
+        E: NewSvcExec<I::Conn, S::Future, S::Service, E, NoopWatcher>,
+        E: ConnStreamExec<<S::Service as HttpService<Body>>::Future, B>,
+    {
+        Server {
+            incoming: self.incoming,
+            make_service,
+            protocol: self.protocol.clone(),
+        }
+    }
+}
+
+#[cfg(feature = "tcp")]
+#[cfg_attr(
+    docsrs,
+    doc(cfg(all(feature = "tcp", any(feature = "http1", feature = "http2"))))
+)]
+impl<E> Builder<AddrIncoming, E> {
+    /// Set the duration to remain idle before sending TCP keepalive probes.
+    ///
+    /// If `None` is specified, keepalive is disabled.
+    pub fn tcp_keepalive(mut self, keepalive: Option<Duration>) -> Self {
+        self.incoming.set_keepalive(keepalive);
+        self
+    }
+
+    /// Set the duration between two successive TCP keepalive retransmissions,
+    /// if acknowledgement to the previous keepalive transmission is not received.
+    pub fn tcp_keepalive_interval(mut self, interval: Option<Duration>) -> Self {
+        self.incoming.set_keepalive_interval(interval);
+        self
+    }
+
+    /// Set the number of retransmissions to be carried out before declaring that remote end is not available.
+    pub fn tcp_keepalive_retries(mut self, retries: Option<u32>) -> Self {
+        self.incoming.set_keepalive_retries(retries);
+        self
+    }
+
+    /// Set the value of `TCP_NODELAY` option for accepted connections.
+    pub fn tcp_nodelay(mut self, enabled: bool) -> Self {
+        self.incoming.set_nodelay(enabled);
+        self
+    }
+
+    /// Set whether to sleep on accept errors.
+    ///
+    /// A possible scenario is that the process has hit the max open files
+    /// allowed, and so trying to accept a new connection will fail with
+    /// EMFILE. In some cases, it's preferable to just wait for some time, if
+    /// the application will likely close some files (or connections), and try
+    /// to accept the connection again. If this option is true, the error will
+    /// be logged at the error level, since it is still a big deal, and then
+    /// the listener will sleep for 1 second.
+    ///
+    /// In other cases, hitting the max open files should be treat similarly
+    /// to being out-of-memory, and simply error (and shutdown). Setting this
+    /// option to false will allow that.
+    ///
+    /// For more details see [`AddrIncoming::set_sleep_on_errors`]
+    pub fn tcp_sleep_on_accept_errors(mut self, val: bool) -> Self {
+        self.incoming.set_sleep_on_errors(val);
+        self
+    }
+
+    /// Returns the local address that the server will be bound to.
+    ///
+    /// This might be useful when knowing the address is required before calling `Builder::serve`,
+    /// but the address is not otherwise available (for e.g. when binding to port 0).
+    pub fn local_addr(&self) -> SocketAddr {
+        self.incoming.local_addr()
+    }
+}
+
+// Used by `Server` to optionally watch a `Connection` future.
+//
+// The regular `hyper::Server` just uses a `NoopWatcher`, which does
+// not need to watch anything, and so returns the `Connection` untouched.
+//
+// The `Server::with_graceful_shutdown` needs to keep track of all active
+// connections, and signal that they start to shutdown when prompted, so
+// it has a `GracefulWatcher` implementation to do that.
+pub trait Watcher<I, S: HttpService<Body>, E>: Clone {
+    type Future: Future<Output = crate::Result<()>>;
+
+    fn watch(&self, conn: UpgradeableConnection<I, S, E>) -> Self::Future;
+}
+
+#[allow(missing_debug_implementations)]
+#[derive(Copy, Clone)]
+pub struct NoopWatcher;
+
+impl<I, S, E> Watcher<I, S, E> for NoopWatcher
+where
+    I: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    S: HttpService<Body>,
+    E: ConnStreamExec<S::Future, S::ResBody>,
+    S::ResBody: 'static,
+    <S::ResBody as HttpBody>::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type Future = UpgradeableConnection<I, S, E>;
+
+    fn watch(&self, conn: UpgradeableConnection<I, S, E>) -> Self::Future {
+        conn
+    }
+}
+
+// used by exec.rs
+pub(crate) mod new_svc {
+    use std::error::Error as StdError;
+    use std::future::Future;
+    use std::marker::Unpin;
+    use std::pin::Pin;
+    use std::task::{Context, Poll};
+
+    use tokio::io::{AsyncRead, AsyncWrite};
+    use tracing::debug;
+
+    use super::{Connecting, Watcher};
+    use crate::body::{Body, HttpBody};
+    use crate::common::exec::ConnStreamExec;
+    use crate::service::HttpService;
+    use pin_project_lite::pin_project;
+
+    // This is a `Future<Item=(), Error=()>` spawned to an `Executor` inside
+    // the `Server`. By being a nameable type, we can be generic over the
+    // user's `Service::Future`, and thus an `Executor` can execute it.
+    //
+    // Doing this allows for the server to conditionally require `Send` futures,
+    // depending on the `Executor` configured.
+    //
+    // Users cannot import this type, nor the associated `NewSvcExec`. Instead,
+    // a blanket implementation for `Executor<impl Future>` is sufficient.
+
+    pin_project! {
+        #[allow(missing_debug_implementations)]
+        pub struct NewSvcTask<I, N, S: HttpService<Body>, E, W: Watcher<I, S, E>> {
+            #[pin]
+            state: State<I, N, S, E, W>,
+        }
+    }
+
+    pin_project! {
+        #[project = StateProj]
+        pub(super) enum State<I, N, S: HttpService<Body>, E, W: Watcher<I, S, E>> {
+            Connecting {
+                #[pin]
+                connecting: Connecting<I, N, E>,
+                watcher: W,
+            },
+            Connected {
+                #[pin]
+                future: W::Future,
+            },
+        }
+    }
+
+    impl<I, N, S: HttpService<Body>, E, W: Watcher<I, S, E>> NewSvcTask<I, N, S, E, W> {
+        pub(super) fn new(connecting: Connecting<I, N, E>, watcher: W) -> Self {
+            NewSvcTask {
+                state: State::Connecting {
+                    connecting,
+                    watcher,
+                },
+            }
+        }
+    }
+
+    impl<I, N, S, NE, B, E, W> Future for NewSvcTask<I, N, S, E, W>
+    where
+        I: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+        N: Future<Output = Result<S, NE>>,
+        NE: Into<Box<dyn StdError + Send + Sync>>,
+        S: HttpService<Body, ResBody = B>,
+        B: HttpBody + 'static,
+        B::Error: Into<Box<dyn StdError + Send + Sync>>,
+        E: ConnStreamExec<S::Future, B>,
+        W: Watcher<I, S, E>,
+    {
+        type Output = ();
+
+        fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+            // If it weren't for needing to name this type so the `Send` bounds
+            // could be projected to the `Serve` executor, this could just be
+            // an `async fn`, and much safer. Woe is me.
+
+            let mut me = self.project();
+            loop {
+                let next = {
+                    match me.state.as_mut().project() {
+                        StateProj::Connecting {
+                            connecting,
+                            watcher,
+                        } => {
+                            let res = ready!(connecting.poll(cx));
+                            let conn = match res {
+                                Ok(conn) => conn,
+                                Err(err) => {
+                                    let err = crate::Error::new_user_make_service(err);
+                                    debug!("connecting error: {}", err);
+                                    return Poll::Ready(());
+                                }
+                            };
+                            let future = watcher.watch(conn.with_upgrades());
+                            State::Connected { future }
+                        }
+                        StateProj::Connected { future } => {
+                            return future.poll(cx).map(|res| {
+                                if let Err(err) = res {
+                                    debug!("connection error: {}", err);
+                                }
+                            });
+                        }
+                    }
+                };
+
+                me.state.set(next);
+            }
+        }
+    }
+}
+
+pin_project! {
+    /// A future building a new `Service` to a `Connection`.
+    ///
+    /// Wraps the future returned from `MakeService` into one that returns
+    /// a `Connection`.
+    #[must_use = "futures do nothing unless polled"]
+    #[derive(Debug)]
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "http1", feature = "http2"))))]
+    pub struct Connecting<I, F, E = Exec> {
+        #[pin]
+        future: F,
+        io: Option<I>,
+        protocol: Http_<E>,
+    }
+}
+
+impl<I, F, S, FE, E, B> Future for Connecting<I, F, E>
+where
+    I: AsyncRead + AsyncWrite + Unpin,
+    F: Future<Output = Result<S, FE>>,
+    S: HttpService<Body, ResBody = B>,
+    B: HttpBody + 'static,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    E: ConnStreamExec<S::Future, B>,
+{
+    type Output = Result<Connection<I, S, E>, FE>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut me = self.project();
+        let service = ready!(me.future.poll(cx))?;
+        let io = Option::take(&mut me.io).expect("polled after complete");
+        Poll::Ready(Ok(me.protocol.serve_connection(io, service)))
+    }
+}
diff --git a/src/server/server_stub.rs b/src/server/server_stub.rs
new file mode 100644
index 0000000..87b1f51
--- /dev/null
+++ b/src/server/server_stub.rs
@@ -0,0 +1,16 @@
+use std::fmt;
+
+use crate::common::exec::Exec;
+
+/// A listening HTTP server that accepts connections in both HTTP1 and HTTP2 by default.
+///
+/// Needs at least one of the `http1` and `http2` features to be activated to actually be useful.
+pub struct Server<I, S, E = Exec> {
+    _marker: std::marker::PhantomData<(I, S, E)>,
+}
+
+impl<I: fmt::Debug, S: fmt::Debug> fmt::Debug for Server<I, S> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Server").finish()
+    }
+}
diff --git a/src/server/shutdown.rs b/src/server/shutdown.rs
new file mode 100644
index 0000000..be85848
--- /dev/null
+++ b/src/server/shutdown.rs
@@ -0,0 +1,131 @@
+use std::error::Error as StdError;
+use std::future::Future;
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use pin_project_lite::pin_project;
+use tokio::io::{AsyncRead, AsyncWrite};
+use tracing::debug;
+
+use super::accept::Accept;
+use super::conn::UpgradeableConnection;
+use super::server::{Server, Watcher};
+use crate::body::{Body, HttpBody};
+use crate::common::drain::{self, Draining, Signal, Watch, Watching};
+use crate::common::exec::{ConnStreamExec, NewSvcExec};
+use crate::service::{HttpService, MakeServiceRef};
+
+pin_project! {
+    #[allow(missing_debug_implementations)]
+    pub struct Graceful<I, S, F, E> {
+        #[pin]
+        state: State<I, S, F, E>,
+    }
+}
+
+pin_project! {
+    #[project = StateProj]
+    pub(super) enum State<I, S, F, E> {
+        Running {
+            drain: Option<(Signal, Watch)>,
+            #[pin]
+            server: Server<I, S, E>,
+            #[pin]
+            signal: F,
+        },
+        Draining { draining: Draining },
+    }
+}
+
+impl<I, S, F, E> Graceful<I, S, F, E> {
+    pub(super) fn new(server: Server<I, S, E>, signal: F) -> Self {
+        let drain = Some(drain::channel());
+        Graceful {
+            state: State::Running {
+                drain,
+                server,
+                signal,
+            },
+        }
+    }
+}
+
+impl<I, IO, IE, S, B, F, E> Future for Graceful<I, S, F, E>
+where
+    I: Accept<Conn = IO, Error = IE>,
+    IE: Into<Box<dyn StdError + Send + Sync>>,
+    IO: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    S: MakeServiceRef<IO, Body, ResBody = B>,
+    S::Error: Into<Box<dyn StdError + Send + Sync>>,
+    B: HttpBody + 'static,
+    B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    F: Future<Output = ()>,
+    E: ConnStreamExec<<S::Service as HttpService<Body>>::Future, B>,
+    E: NewSvcExec<IO, S::Future, S::Service, E, GracefulWatcher>,
+{
+    type Output = crate::Result<()>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut me = self.project();
+        loop {
+            let next = {
+                match me.state.as_mut().project() {
+                    StateProj::Running {
+                        drain,
+                        server,
+                        signal,
+                    } => match signal.poll(cx) {
+                        Poll::Ready(()) => {
+                            debug!("signal received, starting graceful shutdown");
+                            let sig = drain.take().expect("drain channel").0;
+                            State::Draining {
+                                draining: sig.drain(),
+                            }
+                        }
+                        Poll::Pending => {
+                            let watch = drain.as_ref().expect("drain channel").1.clone();
+                            return server.poll_watch(cx, &GracefulWatcher(watch));
+                        }
+                    },
+                    StateProj::Draining { ref mut draining } => {
+                        return Pin::new(draining).poll(cx).map(Ok);
+                    }
+                }
+            };
+            me.state.set(next);
+        }
+    }
+}
+
+#[allow(missing_debug_implementations)]
+#[derive(Clone)]
+pub struct GracefulWatcher(Watch);
+
+impl<I, S, E> Watcher<I, S, E> for GracefulWatcher
+where
+    I: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    S: HttpService<Body>,
+    E: ConnStreamExec<S::Future, S::ResBody>,
+    S::ResBody: 'static,
+    <S::ResBody as HttpBody>::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type Future =
+        Watching<UpgradeableConnection<I, S, E>, fn(Pin<&mut UpgradeableConnection<I, S, E>>)>;
+
+    fn watch(&self, conn: UpgradeableConnection<I, S, E>) -> Self::Future {
+        self.0.clone().watch(conn, on_drain)
+    }
+}
+
+fn on_drain<I, S, E>(conn: Pin<&mut UpgradeableConnection<I, S, E>>)
+where
+    S: HttpService<Body>,
+    S::Error: Into<Box<dyn StdError + Send + Sync>>,
+    I: AsyncRead + AsyncWrite + Unpin,
+    S::ResBody: HttpBody + 'static,
+    <S::ResBody as HttpBody>::Error: Into<Box<dyn StdError + Send + Sync>>,
+    E: ConnStreamExec<S::Future, S::ResBody>,
+{
+    conn.graceful_shutdown()
+}
diff --git a/src/server/tcp.rs b/src/server/tcp.rs
new file mode 100644
index 0000000..edbddcd
--- /dev/null
+++ b/src/server/tcp.rs
@@ -0,0 +1,485 @@
+use socket2::TcpKeepalive;
+use std::fmt;
+use std::future::Future;
+use std::io;
+use std::net::{SocketAddr, TcpListener as StdTcpListener};
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::time::Duration;
+
+use tokio::net::TcpListener;
+use tokio::time::Sleep;
+use tracing::{debug, error, trace};
+
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::addr_stream::AddrStream;
+use super::accept::Accept;
+
+#[derive(Default, Debug, Clone, Copy)]
+struct TcpKeepaliveConfig {
+    time: Option<Duration>,
+    interval: Option<Duration>,
+    retries: Option<u32>,
+}
+
+impl TcpKeepaliveConfig {
+    /// Converts into a `socket2::TcpKeealive` if there is any keep alive configuration.
+    fn into_socket2(self) -> Option<TcpKeepalive> {
+        let mut dirty = false;
+        let mut ka = TcpKeepalive::new();
+        if let Some(time) = self.time {
+            ka = ka.with_time(time);
+            dirty = true
+        }
+        if let Some(interval) = self.interval {
+            ka = Self::ka_with_interval(ka, interval, &mut dirty)
+        };
+        if let Some(retries) = self.retries {
+            ka = Self::ka_with_retries(ka, retries, &mut dirty)
+        };
+        if dirty {
+            Some(ka)
+        } else {
+            None
+        }
+    }
+
+    #[cfg(any(
+        target_os = "android",
+        target_os = "dragonfly",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "linux",
+        target_os = "netbsd",
+        target_vendor = "apple",
+        windows,
+    ))]
+    fn ka_with_interval(ka: TcpKeepalive, interval: Duration, dirty: &mut bool) -> TcpKeepalive {
+        *dirty = true;
+        ka.with_interval(interval)
+    }
+
+    #[cfg(not(any(
+        target_os = "android",
+        target_os = "dragonfly",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "linux",
+        target_os = "netbsd",
+        target_vendor = "apple",
+        windows,
+    )))]
+    fn ka_with_interval(ka: TcpKeepalive, _: Duration, _: &mut bool) -> TcpKeepalive {
+        ka // no-op as keepalive interval is not supported on this platform
+    }
+
+    #[cfg(any(
+        target_os = "android",
+        target_os = "dragonfly",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "linux",
+        target_os = "netbsd",
+        target_vendor = "apple",
+    ))]
+    fn ka_with_retries(ka: TcpKeepalive, retries: u32, dirty: &mut bool) -> TcpKeepalive {
+        *dirty = true;
+        ka.with_retries(retries)
+    }
+
+    #[cfg(not(any(
+        target_os = "android",
+        target_os = "dragonfly",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "linux",
+        target_os = "netbsd",
+        target_vendor = "apple",
+    )))]
+    fn ka_with_retries(ka: TcpKeepalive, _: u32, _: &mut bool) -> TcpKeepalive {
+        ka // no-op as keepalive retries is not supported on this platform
+    }
+}
+
+/// A stream of connections from binding to an address.
+#[must_use = "streams do nothing unless polled"]
+pub struct AddrIncoming {
+    addr: SocketAddr,
+    listener: TcpListener,
+    sleep_on_errors: bool,
+    tcp_keepalive_config: TcpKeepaliveConfig,
+    tcp_nodelay: bool,
+    timeout: Option<Pin<Box<Sleep>>>,
+}
+
+impl AddrIncoming {
+    pub(super) fn new(addr: &SocketAddr) -> crate::Result<Self> {
+        let std_listener = StdTcpListener::bind(addr).map_err(crate::Error::new_listen)?;
+
+        AddrIncoming::from_std(std_listener)
+    }
+
+    pub(super) fn from_std(std_listener: StdTcpListener) -> crate::Result<Self> {
+        // TcpListener::from_std doesn't set O_NONBLOCK
+        std_listener
+            .set_nonblocking(true)
+            .map_err(crate::Error::new_listen)?;
+        let listener = TcpListener::from_std(std_listener).map_err(crate::Error::new_listen)?;
+        AddrIncoming::from_listener(listener)
+    }
+
+    /// Creates a new `AddrIncoming` binding to provided socket address.
+    pub fn bind(addr: &SocketAddr) -> crate::Result<Self> {
+        AddrIncoming::new(addr)
+    }
+
+    /// Creates a new `AddrIncoming` from an existing `tokio::net::TcpListener`.
+    pub fn from_listener(listener: TcpListener) -> crate::Result<Self> {
+        let addr = listener.local_addr().map_err(crate::Error::new_listen)?;
+        Ok(AddrIncoming {
+            listener,
+            addr,
+            sleep_on_errors: true,
+            tcp_keepalive_config: TcpKeepaliveConfig::default(),
+            tcp_nodelay: false,
+            timeout: None,
+        })
+    }
+
+    /// Get the local address bound to this listener.
+    pub fn local_addr(&self) -> SocketAddr {
+        self.addr
+    }
+
+    /// Set the duration to remain idle before sending TCP keepalive probes.
+    ///
+    /// If `None` is specified, keepalive is disabled.
+    pub fn set_keepalive(&mut self, time: Option<Duration>) -> &mut Self {
+        self.tcp_keepalive_config.time = time;
+        self
+    }
+
+    /// Set the duration between two successive TCP keepalive retransmissions,
+    /// if acknowledgement to the previous keepalive transmission is not received.
+    pub fn set_keepalive_interval(&mut self, interval: Option<Duration>) -> &mut Self {
+        self.tcp_keepalive_config.interval = interval;
+        self
+    }
+
+    /// Set the number of retransmissions to be carried out before declaring that remote end is not available.
+    pub fn set_keepalive_retries(&mut self, retries: Option<u32>) -> &mut Self {
+        self.tcp_keepalive_config.retries = retries;
+        self
+    }
+
+    /// Set the value of `TCP_NODELAY` option for accepted connections.
+    pub fn set_nodelay(&mut self, enabled: bool) -> &mut Self {
+        self.tcp_nodelay = enabled;
+        self
+    }
+
+    /// Set whether to sleep on accept errors.
+    ///
+    /// A possible scenario is that the process has hit the max open files
+    /// allowed, and so trying to accept a new connection will fail with
+    /// `EMFILE`. In some cases, it's preferable to just wait for some time, if
+    /// the application will likely close some files (or connections), and try
+    /// to accept the connection again. If this option is `true`, the error
+    /// will be logged at the `error` level, since it is still a big deal,
+    /// and then the listener will sleep for 1 second.
+    ///
+    /// In other cases, hitting the max open files should be treat similarly
+    /// to being out-of-memory, and simply error (and shutdown). Setting
+    /// this option to `false` will allow that.
+    ///
+    /// Default is `true`.
+    pub fn set_sleep_on_errors(&mut self, val: bool) {
+        self.sleep_on_errors = val;
+    }
+
+    fn poll_next_(&mut self, cx: &mut Context<'_>) -> Poll<io::Result<AddrStream>> {
+        // Check if a previous timeout is active that was set by IO errors.
+        if let Some(ref mut to) = self.timeout {
+            ready!(Pin::new(to).poll(cx));
+        }
+        self.timeout = None;
+
+        loop {
+            match ready!(self.listener.poll_accept(cx)) {
+                Ok((socket, remote_addr)) => {
+                    if let Some(tcp_keepalive) = &self.tcp_keepalive_config.into_socket2() {
+                        let sock_ref = socket2::SockRef::from(&socket);
+                        if let Err(e) = sock_ref.set_tcp_keepalive(tcp_keepalive) {
+                            trace!("error trying to set TCP keepalive: {}", e);
+                        }
+                    }
+                    if let Err(e) = socket.set_nodelay(self.tcp_nodelay) {
+                        trace!("error trying to set TCP nodelay: {}", e);
+                    }
+                    let local_addr = socket.local_addr()?;
+                    return Poll::Ready(Ok(AddrStream::new(socket, remote_addr, local_addr)));
+                }
+                Err(e) => {
+                    // Connection errors can be ignored directly, continue by
+                    // accepting the next request.
+                    if is_connection_error(&e) {
+                        debug!("accepted connection already errored: {}", e);
+                        continue;
+                    }
+
+                    if self.sleep_on_errors {
+                        error!("accept error: {}", e);
+
+                        // Sleep 1s.
+                        let mut timeout = Box::pin(tokio::time::sleep(Duration::from_secs(1)));
+
+                        match timeout.as_mut().poll(cx) {
+                            Poll::Ready(()) => {
+                                // Wow, it's been a second already? Ok then...
+                                continue;
+                            }
+                            Poll::Pending => {
+                                self.timeout = Some(timeout);
+                                return Poll::Pending;
+                            }
+                        }
+                    } else {
+                        return Poll::Ready(Err(e));
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl Accept for AddrIncoming {
+    type Conn = AddrStream;
+    type Error = io::Error;
+
+    fn poll_accept(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<Self::Conn, Self::Error>>> {
+        let result = ready!(self.poll_next_(cx));
+        Poll::Ready(Some(result))
+    }
+}
+
+/// This function defines errors that are per-connection. Which basically
+/// means that if we get this error from `accept()` system call it means
+/// next connection might be ready to be accepted.
+///
+/// All other errors will incur a timeout before next `accept()` is performed.
+/// The timeout is useful to handle resource exhaustion errors like ENFILE
+/// and EMFILE. Otherwise, could enter into tight loop.
+fn is_connection_error(e: &io::Error) -> bool {
+    matches!(
+        e.kind(),
+        io::ErrorKind::ConnectionRefused
+            | io::ErrorKind::ConnectionAborted
+            | io::ErrorKind::ConnectionReset
+    )
+}
+
+impl fmt::Debug for AddrIncoming {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("AddrIncoming")
+            .field("addr", &self.addr)
+            .field("sleep_on_errors", &self.sleep_on_errors)
+            .field("tcp_keepalive_config", &self.tcp_keepalive_config)
+            .field("tcp_nodelay", &self.tcp_nodelay)
+            .finish()
+    }
+}
+
+mod addr_stream {
+    use std::io;
+    use std::net::SocketAddr;
+    #[cfg(unix)]
+    use std::os::unix::io::{AsRawFd, RawFd};
+    use std::pin::Pin;
+    use std::task::{Context, Poll};
+    use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
+    use tokio::net::TcpStream;
+
+    pin_project_lite::pin_project! {
+        /// A transport returned yieled by `AddrIncoming`.
+        #[derive(Debug)]
+        pub struct AddrStream {
+            #[pin]
+            inner: TcpStream,
+            pub(super) remote_addr: SocketAddr,
+            pub(super) local_addr: SocketAddr
+        }
+    }
+
+    impl AddrStream {
+        pub(super) fn new(
+            tcp: TcpStream,
+            remote_addr: SocketAddr,
+            local_addr: SocketAddr,
+        ) -> AddrStream {
+            AddrStream {
+                inner: tcp,
+                remote_addr,
+                local_addr,
+            }
+        }
+
+        /// Returns the remote (peer) address of this connection.
+        #[inline]
+        pub fn remote_addr(&self) -> SocketAddr {
+            self.remote_addr
+        }
+
+        /// Returns the local address of this connection.
+        #[inline]
+        pub fn local_addr(&self) -> SocketAddr {
+            self.local_addr
+        }
+
+        /// Consumes the AddrStream and returns the underlying IO object
+        #[inline]
+        pub fn into_inner(self) -> TcpStream {
+            self.inner
+        }
+
+        /// Attempt to receive data on the socket, without removing that data
+        /// from the queue, registering the current task for wakeup if data is
+        /// not yet available.
+        pub fn poll_peek(
+            &mut self,
+            cx: &mut Context<'_>,
+            buf: &mut tokio::io::ReadBuf<'_>,
+        ) -> Poll<io::Result<usize>> {
+            self.inner.poll_peek(cx, buf)
+        }
+    }
+
+    impl AsyncRead for AddrStream {
+        #[inline]
+        fn poll_read(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            buf: &mut ReadBuf<'_>,
+        ) -> Poll<io::Result<()>> {
+            self.project().inner.poll_read(cx, buf)
+        }
+    }
+
+    impl AsyncWrite for AddrStream {
+        #[inline]
+        fn poll_write(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            buf: &[u8],
+        ) -> Poll<io::Result<usize>> {
+            self.project().inner.poll_write(cx, buf)
+        }
+
+        #[inline]
+        fn poll_write_vectored(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            bufs: &[io::IoSlice<'_>],
+        ) -> Poll<io::Result<usize>> {
+            self.project().inner.poll_write_vectored(cx, bufs)
+        }
+
+        #[inline]
+        fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            // TCP flush is a noop
+            Poll::Ready(Ok(()))
+        }
+
+        #[inline]
+        fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            self.project().inner.poll_shutdown(cx)
+        }
+
+        #[inline]
+        fn is_write_vectored(&self) -> bool {
+            // Note that since `self.inner` is a `TcpStream`, this could
+            // *probably* be hard-coded to return `true`...but it seems more
+            // correct to ask it anyway (maybe we're on some platform without
+            // scatter-gather IO?)
+            self.inner.is_write_vectored()
+        }
+    }
+
+    #[cfg(unix)]
+    impl AsRawFd for AddrStream {
+        fn as_raw_fd(&self) -> RawFd {
+            self.inner.as_raw_fd()
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::server::tcp::TcpKeepaliveConfig;
+    use std::time::Duration;
+
+    #[test]
+    fn no_tcp_keepalive_config() {
+        assert!(TcpKeepaliveConfig::default().into_socket2().is_none());
+    }
+
+    #[test]
+    fn tcp_keepalive_time_config() {
+        let mut kac = TcpKeepaliveConfig::default();
+        kac.time = Some(Duration::from_secs(60));
+        if let Some(tcp_keepalive) = kac.into_socket2() {
+            assert!(format!("{tcp_keepalive:?}").contains("time: Some(60s)"));
+        } else {
+            panic!("test failed");
+        }
+    }
+
+    #[cfg(any(
+        target_os = "android",
+        target_os = "dragonfly",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "linux",
+        target_os = "netbsd",
+        target_vendor = "apple",
+        windows,
+    ))]
+    #[test]
+    fn tcp_keepalive_interval_config() {
+        let mut kac = TcpKeepaliveConfig::default();
+        kac.interval = Some(Duration::from_secs(1));
+        if let Some(tcp_keepalive) = kac.into_socket2() {
+            assert!(format!("{tcp_keepalive:?}").contains("interval: Some(1s)"));
+        } else {
+            panic!("test failed");
+        }
+    }
+
+    #[cfg(any(
+        target_os = "android",
+        target_os = "dragonfly",
+        target_os = "freebsd",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "linux",
+        target_os = "netbsd",
+        target_vendor = "apple",
+    ))]
+    #[test]
+    fn tcp_keepalive_retries_config() {
+        let mut kac = TcpKeepaliveConfig::default();
+        kac.retries = Some(3);
+        if let Some(tcp_keepalive) = kac.into_socket2() {
+            assert!(format!("{tcp_keepalive:?}").contains("retries: Some(3)"));
+        } else {
+            panic!("test failed");
+        }
+    }
+}
diff --git a/src/service/http.rs b/src/service/http.rs
new file mode 100644
index 0000000..d0586d8
--- /dev/null
+++ b/src/service/http.rs
@@ -0,0 +1,59 @@
+use std::error::Error as StdError;
+use std::future::Future;
+use std::task::{Context, Poll};
+
+use crate::body::HttpBody;
+use crate::{Request, Response};
+
+/// An asynchronous function from `Request` to `Response`.
+pub trait HttpService<ReqBody>: sealed::Sealed<ReqBody> {
+    /// The `HttpBody` body of the `http::Response`.
+    type ResBody: HttpBody;
+
+    /// The error type that can occur within this `Service`.
+    ///
+    /// Note: Returning an `Error` to a hyper server will cause the connection
+    /// to be abruptly aborted. In most cases, it is better to return a `Response`
+    /// with a 4xx or 5xx status code.
+    type Error: Into<Box<dyn StdError + Send + Sync>>;
+
+    /// The `Future` returned by this `Service`.
+    type Future: Future<Output = Result<Response<Self::ResBody>, Self::Error>>;
+
+    #[doc(hidden)]
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>;
+
+    #[doc(hidden)]
+    fn call(&mut self, req: Request<ReqBody>) -> Self::Future;
+}
+
+impl<T, B1, B2> HttpService<B1> for T
+where
+    T: tower_service::Service<Request<B1>, Response = Response<B2>>,
+    B2: HttpBody,
+    T::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type ResBody = B2;
+
+    type Error = T::Error;
+    type Future = T::Future;
+
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        tower_service::Service::poll_ready(self, cx)
+    }
+
+    fn call(&mut self, req: Request<B1>) -> Self::Future {
+        tower_service::Service::call(self, req)
+    }
+}
+
+impl<T, B1, B2> sealed::Sealed<B1> for T
+where
+    T: tower_service::Service<Request<B1>, Response = Response<B2>>,
+    B2: HttpBody,
+{
+}
+
+mod sealed {
+    pub trait Sealed<T> {}
+}
diff --git a/src/service/make.rs b/src/service/make.rs
new file mode 100644
index 0000000..188e4f4
--- /dev/null
+++ b/src/service/make.rs
@@ -0,0 +1,188 @@
+use std::error::Error as StdError;
+use std::fmt;
+use std::future::Future;
+use std::task::{Context, Poll};
+
+use tokio::io::{AsyncRead, AsyncWrite};
+
+use super::{HttpService, Service};
+use crate::body::HttpBody;
+
+// The same "trait alias" as tower::MakeConnection, but inlined to reduce
+// dependencies.
+pub trait MakeConnection<Target>: self::sealed::Sealed<(Target,)> {
+    type Connection: AsyncRead + AsyncWrite;
+    type Error;
+    type Future: Future<Output = Result<Self::Connection, Self::Error>>;
+
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>;
+    fn make_connection(&mut self, target: Target) -> Self::Future;
+}
+
+impl<S, Target> self::sealed::Sealed<(Target,)> for S where S: Service<Target> {}
+
+impl<S, Target> MakeConnection<Target> for S
+where
+    S: Service<Target>,
+    S::Response: AsyncRead + AsyncWrite,
+{
+    type Connection = S::Response;
+    type Error = S::Error;
+    type Future = S::Future;
+
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Service::poll_ready(self, cx)
+    }
+
+    fn make_connection(&mut self, target: Target) -> Self::Future {
+        Service::call(self, target)
+    }
+}
+
+// Just a sort-of "trait alias" of `MakeService`, not to be implemented
+// by anyone, only used as bounds.
+pub trait MakeServiceRef<Target, ReqBody>: self::sealed::Sealed<(Target, ReqBody)> {
+    type ResBody: HttpBody;
+    type Error: Into<Box<dyn StdError + Send + Sync>>;
+    type Service: HttpService<ReqBody, ResBody = Self::ResBody, Error = Self::Error>;
+    type MakeError: Into<Box<dyn StdError + Send + Sync>>;
+    type Future: Future<Output = Result<Self::Service, Self::MakeError>>;
+
+    // Acting like a #[non_exhaustive] for associated types of this trait.
+    //
+    // Basically, no one outside of hyper should be able to set this type
+    // or declare bounds on it, so it should prevent people from creating
+    // trait objects or otherwise writing code that requires using *all*
+    // of the associated types.
+    //
+    // Why? So we can add new associated types to this alias in the future,
+    // if necessary.
+    type __DontNameMe: self::sealed::CantImpl;
+
+    fn poll_ready_ref(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::MakeError>>;
+
+    fn make_service_ref(&mut self, target: &Target) -> Self::Future;
+}
+
+impl<T, Target, E, ME, S, F, IB, OB> MakeServiceRef<Target, IB> for T
+where
+    T: for<'a> Service<&'a Target, Error = ME, Response = S, Future = F>,
+    E: Into<Box<dyn StdError + Send + Sync>>,
+    ME: Into<Box<dyn StdError + Send + Sync>>,
+    S: HttpService<IB, ResBody = OB, Error = E>,
+    F: Future<Output = Result<S, ME>>,
+    IB: HttpBody,
+    OB: HttpBody,
+{
+    type Error = E;
+    type Service = S;
+    type ResBody = OB;
+    type MakeError = ME;
+    type Future = F;
+
+    type __DontNameMe = self::sealed::CantName;
+
+    fn poll_ready_ref(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::MakeError>> {
+        self.poll_ready(cx)
+    }
+
+    fn make_service_ref(&mut self, target: &Target) -> Self::Future {
+        self.call(target)
+    }
+}
+
+impl<T, Target, S, B1, B2> self::sealed::Sealed<(Target, B1)> for T
+where
+    T: for<'a> Service<&'a Target, Response = S>,
+    S: HttpService<B1, ResBody = B2>,
+    B1: HttpBody,
+    B2: HttpBody,
+{
+}
+
+/// Create a `MakeService` from a function.
+///
+/// # Example
+///
+/// ```
+/// # #[cfg(feature = "runtime")]
+/// # async fn run() {
+/// use std::convert::Infallible;
+/// use hyper::{Body, Request, Response, Server};
+/// use hyper::server::conn::AddrStream;
+/// use hyper::service::{make_service_fn, service_fn};
+///
+/// let addr = ([127, 0, 0, 1], 3000).into();
+///
+/// let make_svc = make_service_fn(|socket: &AddrStream| {
+///     let remote_addr = socket.remote_addr();
+///     async move {
+///         Ok::<_, Infallible>(service_fn(move |_: Request<Body>| async move {
+///             Ok::<_, Infallible>(
+///                 Response::new(Body::from(format!("Hello, {}!", remote_addr)))
+///             )
+///         }))
+///     }
+/// });
+///
+/// // Then bind and serve...
+/// let server = Server::bind(&addr)
+///     .serve(make_svc);
+///
+/// // Finally, spawn `server` onto an Executor...
+/// if let Err(e) = server.await {
+///     eprintln!("server error: {}", e);
+/// }
+/// # }
+/// # fn main() {}
+/// ```
+pub fn make_service_fn<F, Target, Ret>(f: F) -> MakeServiceFn<F>
+where
+    F: FnMut(&Target) -> Ret,
+    Ret: Future,
+{
+    MakeServiceFn { f }
+}
+
+/// `MakeService` returned from [`make_service_fn`]
+#[derive(Clone, Copy)]
+pub struct MakeServiceFn<F> {
+    f: F,
+}
+
+impl<'t, F, Ret, Target, Svc, MkErr> Service<&'t Target> for MakeServiceFn<F>
+where
+    F: FnMut(&Target) -> Ret,
+    Ret: Future<Output = Result<Svc, MkErr>>,
+    MkErr: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type Error = MkErr;
+    type Response = Svc;
+    type Future = Ret;
+
+    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, target: &'t Target) -> Self::Future {
+        (self.f)(target)
+    }
+}
+
+impl<F> fmt::Debug for MakeServiceFn<F> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("MakeServiceFn").finish()
+    }
+}
+
+mod sealed {
+    pub trait Sealed<X> {}
+
+    #[allow(unreachable_pub)] // This is intentional.
+    pub trait CantImpl {}
+
+    #[allow(missing_debug_implementations)]
+    pub enum CantName {}
+
+    impl CantImpl for CantName {}
+}
diff --git a/src/service/mod.rs b/src/service/mod.rs
new file mode 100644
index 0000000..22f850c
--- /dev/null
+++ b/src/service/mod.rs
@@ -0,0 +1,55 @@
+//! Asynchronous Services
+//!
+//! A [`Service`](Service) is a trait representing an asynchronous
+//! function of a request to a response. It's similar to
+//! `async fn(Request) -> Result<Response, Error>`.
+//!
+//! The argument and return value isn't strictly required to be for HTTP.
+//! Therefore, hyper uses several "trait aliases" to reduce clutter around
+//! bounds. These are:
+//!
+//! - `HttpService`: This is blanketly implemented for all types that
+//!   implement `Service<http::Request<B1>, Response = http::Response<B2>>`.
+//! - `MakeService`: When a `Service` returns a new `Service` as its "response",
+//!   we consider it a `MakeService`. Again, blanketly implemented in those cases.
+//! - `MakeConnection`: A `Service` that returns a "connection", a type that
+//!   implements `AsyncRead` and `AsyncWrite`.
+//!
+//! # HttpService
+//!
+//! In hyper, especially in the server setting, a `Service` is usually bound
+//! to a single connection. It defines how to respond to **all** requests that
+//! connection will receive.
+//!
+//! The helper [`service_fn`](service_fn) should be sufficient for most cases, but
+//! if you need to implement `Service` for a type manually, you can follow the example
+//! in `service_struct_impl.rs`.
+//!
+//! # MakeService
+//!
+//! Since a `Service` is bound to a single connection, a [`Server`](crate::Server)
+//! needs a way to make them as it accepts connections. This is what a
+//! `MakeService` does.
+//!
+//! Resources that need to be shared by all `Service`s can be put into a
+//! `MakeService`, and then passed to individual `Service`s when `call`
+//! is called.
+
+pub use tower_service::Service;
+
+mod http;
+mod make;
+#[cfg(all(any(feature = "http1", feature = "http2"), feature = "client"))]
+mod oneshot;
+mod util;
+
+pub(super) use self::http::HttpService;
+#[cfg(all(any(feature = "http1", feature = "http2"), feature = "client"))]
+pub(super) use self::make::MakeConnection;
+#[cfg(all(any(feature = "http1", feature = "http2"), feature = "server"))]
+pub(super) use self::make::MakeServiceRef;
+#[cfg(all(any(feature = "http1", feature = "http2"), feature = "client"))]
+pub(super) use self::oneshot::{oneshot, Oneshot};
+
+pub use self::make::make_service_fn;
+pub use self::util::service_fn;
diff --git a/src/service/oneshot.rs b/src/service/oneshot.rs
new file mode 100644
index 0000000..5e2ca47
--- /dev/null
+++ b/src/service/oneshot.rs
@@ -0,0 +1,75 @@
+// TODO: Eventually to be replaced with tower_util::Oneshot.
+
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use pin_project_lite::pin_project;
+use tower_service::Service;
+
+pub(crate) fn oneshot<S, Req>(svc: S, req: Req) -> Oneshot<S, Req>
+where
+    S: Service<Req>,
+{
+    Oneshot {
+        state: State::NotReady { svc, req },
+    }
+}
+
+pin_project! {
+    // A `Future` consuming a `Service` and request, waiting until the `Service`
+    // is ready, and then calling `Service::call` with the request, and
+    // waiting for that `Future`.
+    #[allow(missing_debug_implementations)]
+    pub struct Oneshot<S: Service<Req>, Req> {
+        #[pin]
+        state: State<S, Req>,
+    }
+}
+
+pin_project! {
+    #[project = StateProj]
+    #[project_replace = StateProjOwn]
+    enum State<S: Service<Req>, Req> {
+        NotReady {
+            svc: S,
+            req: Req,
+        },
+        Called {
+            #[pin]
+            fut: S::Future,
+        },
+        Tmp,
+    }
+}
+
+impl<S, Req> Future for Oneshot<S, Req>
+where
+    S: Service<Req>,
+{
+    type Output = Result<S::Response, S::Error>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut me = self.project();
+
+        loop {
+            match me.state.as_mut().project() {
+                StateProj::NotReady { ref mut svc, .. } => {
+                    ready!(svc.poll_ready(cx))?;
+                    // fallthrough out of the match's borrow
+                }
+                StateProj::Called { fut } => {
+                    return fut.poll(cx);
+                }
+                StateProj::Tmp => unreachable!(),
+            }
+
+            match me.state.as_mut().project_replace(State::Tmp) {
+                StateProjOwn::NotReady { mut svc, req } => {
+                    me.state.set(State::Called { fut: svc.call(req) });
+                }
+                _ => unreachable!(),
+            }
+        }
+    }
+}
diff --git a/src/service/util.rs b/src/service/util.rs
new file mode 100644
index 0000000..59760a6
--- /dev/null
+++ b/src/service/util.rs
@@ -0,0 +1,85 @@
+use std::error::Error as StdError;
+use std::fmt;
+use std::future::Future;
+use std::marker::PhantomData;
+use std::task::{Context, Poll};
+
+use crate::body::HttpBody;
+use crate::{Request, Response};
+
+/// Create a `Service` from a function.
+///
+/// # Example
+///
+/// ```
+/// use hyper::{Body, Request, Response, Version};
+/// use hyper::service::service_fn;
+///
+/// let service = service_fn(|req: Request<Body>| async move {
+///     if req.version() == Version::HTTP_11 {
+///         Ok(Response::new(Body::from("Hello World")))
+///     } else {
+///         // Note: it's usually better to return a Response
+///         // with an appropriate StatusCode instead of an Err.
+///         Err("not HTTP/1.1, abort connection")
+///     }
+/// });
+/// ```
+pub fn service_fn<F, R, S>(f: F) -> ServiceFn<F, R>
+where
+    F: FnMut(Request<R>) -> S,
+    S: Future,
+{
+    ServiceFn {
+        f,
+        _req: PhantomData,
+    }
+}
+
+/// Service returned by [`service_fn`]
+pub struct ServiceFn<F, R> {
+    f: F,
+    _req: PhantomData<fn(R)>,
+}
+
+impl<F, ReqBody, Ret, ResBody, E> tower_service::Service<crate::Request<ReqBody>>
+    for ServiceFn<F, ReqBody>
+where
+    F: FnMut(Request<ReqBody>) -> Ret,
+    ReqBody: HttpBody,
+    Ret: Future<Output = Result<Response<ResBody>, E>>,
+    E: Into<Box<dyn StdError + Send + Sync>>,
+    ResBody: HttpBody,
+{
+    type Response = crate::Response<ResBody>;
+    type Error = E;
+    type Future = Ret;
+
+    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: Request<ReqBody>) -> Self::Future {
+        (self.f)(req)
+    }
+}
+
+impl<F, R> fmt::Debug for ServiceFn<F, R> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("impl Service").finish()
+    }
+}
+
+impl<F, R> Clone for ServiceFn<F, R>
+where
+    F: Clone,
+{
+    fn clone(&self) -> Self {
+        ServiceFn {
+            f: self.f.clone(),
+            _req: PhantomData,
+        }
+    }
+}
+
+impl<F, R> Copy for ServiceFn<F, R> where F: Copy {}
diff --git a/src/upgrade.rs b/src/upgrade.rs
new file mode 100644
index 0000000..a46a8d2
--- /dev/null
+++ b/src/upgrade.rs
@@ -0,0 +1,381 @@
+//! HTTP Upgrades
+//!
+//! This module deals with managing [HTTP Upgrades][mdn] in hyper. Since
+//! several concepts in HTTP allow for first talking HTTP, and then converting
+//! to a different protocol, this module conflates them into a single API.
+//! Those include:
+//!
+//! - HTTP/1.1 Upgrades
+//! - HTTP `CONNECT`
+//!
+//! You are responsible for any other pre-requisites to establish an upgrade,
+//! such as sending the appropriate headers, methods, and status codes. You can
+//! then use [`on`][] to grab a `Future` which will resolve to the upgraded
+//! connection object, or an error if the upgrade fails.
+//!
+//! [mdn]: https://developer.mozilla.org/en-US/docs/Web/HTTP/Protocol_upgrade_mechanism
+//!
+//! # Client
+//!
+//! Sending an HTTP upgrade from the [`client`](super::client) involves setting
+//! either the appropriate method, if wanting to `CONNECT`, or headers such as
+//! `Upgrade` and `Connection`, on the `http::Request`. Once receiving the
+//! `http::Response` back, you must check for the specific information that the
+//! upgrade is agreed upon by the server (such as a `101` status code), and then
+//! get the `Future` from the `Response`.
+//!
+//! # Server
+//!
+//! Receiving upgrade requests in a server requires you to check the relevant
+//! headers in a `Request`, and if an upgrade should be done, you then send the
+//! corresponding headers in a response. To then wait for hyper to finish the
+//! upgrade, you call `on()` with the `Request`, and then can spawn a task
+//! awaiting it.
+//!
+//! # Example
+//!
+//! See [this example][example] showing how upgrades work with both
+//! Clients and Servers.
+//!
+//! [example]: https://github.com/hyperium/hyper/blob/master/examples/upgrades.rs
+
+use std::any::TypeId;
+use std::error::Error as StdError;
+use std::fmt;
+use std::future::Future;
+use std::io;
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use bytes::Bytes;
+use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
+use tokio::sync::oneshot;
+#[cfg(any(feature = "http1", feature = "http2"))]
+use tracing::trace;
+
+use crate::common::io::Rewind;
+
+/// An upgraded HTTP connection.
+///
+/// This type holds a trait object internally of the original IO that
+/// was used to speak HTTP before the upgrade. It can be used directly
+/// as a `Read` or `Write` for convenience.
+///
+/// Alternatively, if the exact type is known, this can be deconstructed
+/// into its parts.
+pub struct Upgraded {
+    io: Rewind<Box<dyn Io + Send>>,
+}
+
+/// A future for a possible HTTP upgrade.
+///
+/// If no upgrade was available, or it doesn't succeed, yields an `Error`.
+pub struct OnUpgrade {
+    rx: Option<oneshot::Receiver<crate::Result<Upgraded>>>,
+}
+
+/// The deconstructed parts of an [`Upgraded`](Upgraded) type.
+///
+/// Includes the original IO type, and a read buffer of bytes that the
+/// HTTP state machine may have already read before completing an upgrade.
+#[derive(Debug)]
+pub struct Parts<T> {
+    /// The original IO object used before the upgrade.
+    pub io: T,
+    /// A buffer of bytes that have been read but not processed as HTTP.
+    ///
+    /// For instance, if the `Connection` is used for an HTTP upgrade request,
+    /// it is possible the server sent back the first bytes of the new protocol
+    /// along with the response upgrade.
+    ///
+    /// You will want to check for any existing bytes if you plan to continue
+    /// communicating on the IO object.
+    pub read_buf: Bytes,
+    _inner: (),
+}
+
+/// Gets a pending HTTP upgrade from this message.
+///
+/// This can be called on the following types:
+///
+/// - `http::Request<B>`
+/// - `http::Response<B>`
+/// - `&mut http::Request<B>`
+/// - `&mut http::Response<B>`
+pub fn on<T: sealed::CanUpgrade>(msg: T) -> OnUpgrade {
+    msg.on_upgrade()
+}
+
+#[cfg(any(feature = "http1", feature = "http2"))]
+pub(super) struct Pending {
+    tx: oneshot::Sender<crate::Result<Upgraded>>,
+}
+
+#[cfg(any(feature = "http1", feature = "http2"))]
+pub(super) fn pending() -> (Pending, OnUpgrade) {
+    let (tx, rx) = oneshot::channel();
+    (Pending { tx }, OnUpgrade { rx: Some(rx) })
+}
+
+// ===== impl Upgraded =====
+
+impl Upgraded {
+    #[cfg(any(feature = "http1", feature = "http2", test))]
+    pub(super) fn new<T>(io: T, read_buf: Bytes) -> Self
+    where
+        T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    {
+        Upgraded {
+            io: Rewind::new_buffered(Box::new(io), read_buf),
+        }
+    }
+
+    /// Tries to downcast the internal trait object to the type passed.
+    ///
+    /// On success, returns the downcasted parts. On error, returns the
+    /// `Upgraded` back.
+    pub fn downcast<T: AsyncRead + AsyncWrite + Unpin + 'static>(self) -> Result<Parts<T>, Self> {
+        let (io, buf) = self.io.into_inner();
+        match io.__hyper_downcast() {
+            Ok(t) => Ok(Parts {
+                io: *t,
+                read_buf: buf,
+                _inner: (),
+            }),
+            Err(io) => Err(Upgraded {
+                io: Rewind::new_buffered(io, buf),
+            }),
+        }
+    }
+}
+
+impl AsyncRead for Upgraded {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.io).poll_read(cx, buf)
+    }
+}
+
+impl AsyncWrite for Upgraded {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        Pin::new(&mut self.io).poll_write(cx, buf)
+    }
+
+    fn poll_write_vectored(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        Pin::new(&mut self.io).poll_write_vectored(cx, bufs)
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.io).poll_flush(cx)
+    }
+
+    fn poll_shutdown(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.io).poll_shutdown(cx)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        self.io.is_write_vectored()
+    }
+}
+
+impl fmt::Debug for Upgraded {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Upgraded").finish()
+    }
+}
+
+// ===== impl OnUpgrade =====
+
+impl OnUpgrade {
+    pub(super) fn none() -> Self {
+        OnUpgrade { rx: None }
+    }
+
+    #[cfg(feature = "http1")]
+    pub(super) fn is_none(&self) -> bool {
+        self.rx.is_none()
+    }
+}
+
+impl Future for OnUpgrade {
+    type Output = Result<Upgraded, crate::Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match self.rx {
+            Some(ref mut rx) => Pin::new(rx).poll(cx).map(|res| match res {
+                Ok(Ok(upgraded)) => Ok(upgraded),
+                Ok(Err(err)) => Err(err),
+                Err(_oneshot_canceled) => Err(crate::Error::new_canceled().with(UpgradeExpected)),
+            }),
+            None => Poll::Ready(Err(crate::Error::new_user_no_upgrade())),
+        }
+    }
+}
+
+impl fmt::Debug for OnUpgrade {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("OnUpgrade").finish()
+    }
+}
+
+// ===== impl Pending =====
+
+#[cfg(any(feature = "http1", feature = "http2"))]
+impl Pending {
+    pub(super) fn fulfill(self, upgraded: Upgraded) {
+        trace!("pending upgrade fulfill");
+        let _ = self.tx.send(Ok(upgraded));
+    }
+
+    #[cfg(feature = "http1")]
+    /// Don't fulfill the pending Upgrade, but instead signal that
+    /// upgrades are handled manually.
+    pub(super) fn manual(self) {
+        trace!("pending upgrade handled manually");
+        let _ = self.tx.send(Err(crate::Error::new_user_manual_upgrade()));
+    }
+}
+
+// ===== impl UpgradeExpected =====
+
+/// Error cause returned when an upgrade was expected but canceled
+/// for whatever reason.
+///
+/// This likely means the actual `Conn` future wasn't polled and upgraded.
+#[derive(Debug)]
+struct UpgradeExpected;
+
+impl fmt::Display for UpgradeExpected {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("upgrade expected but not completed")
+    }
+}
+
+impl StdError for UpgradeExpected {}
+
+// ===== impl Io =====
+
+pub(super) trait Io: AsyncRead + AsyncWrite + Unpin + 'static {
+    fn __hyper_type_id(&self) -> TypeId {
+        TypeId::of::<Self>()
+    }
+}
+
+impl<T: AsyncRead + AsyncWrite + Unpin + 'static> Io for T {}
+
+impl dyn Io + Send {
+    fn __hyper_is<T: Io>(&self) -> bool {
+        let t = TypeId::of::<T>();
+        self.__hyper_type_id() == t
+    }
+
+    fn __hyper_downcast<T: Io>(self: Box<Self>) -> Result<Box<T>, Box<Self>> {
+        if self.__hyper_is::<T>() {
+            // Taken from `std::error::Error::downcast()`.
+            unsafe {
+                let raw: *mut dyn Io = Box::into_raw(self);
+                Ok(Box::from_raw(raw as *mut T))
+            }
+        } else {
+            Err(self)
+        }
+    }
+}
+
+mod sealed {
+    use super::OnUpgrade;
+
+    pub trait CanUpgrade {
+        fn on_upgrade(self) -> OnUpgrade;
+    }
+
+    impl<B> CanUpgrade for http::Request<B> {
+        fn on_upgrade(mut self) -> OnUpgrade {
+            self.extensions_mut()
+                .remove::<OnUpgrade>()
+                .unwrap_or_else(OnUpgrade::none)
+        }
+    }
+
+    impl<B> CanUpgrade for &'_ mut http::Request<B> {
+        fn on_upgrade(self) -> OnUpgrade {
+            self.extensions_mut()
+                .remove::<OnUpgrade>()
+                .unwrap_or_else(OnUpgrade::none)
+        }
+    }
+
+    impl<B> CanUpgrade for http::Response<B> {
+        fn on_upgrade(mut self) -> OnUpgrade {
+            self.extensions_mut()
+                .remove::<OnUpgrade>()
+                .unwrap_or_else(OnUpgrade::none)
+        }
+    }
+
+    impl<B> CanUpgrade for &'_ mut http::Response<B> {
+        fn on_upgrade(self) -> OnUpgrade {
+            self.extensions_mut()
+                .remove::<OnUpgrade>()
+                .unwrap_or_else(OnUpgrade::none)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn upgraded_downcast() {
+        let upgraded = Upgraded::new(Mock, Bytes::new());
+
+        let upgraded = upgraded.downcast::<std::io::Cursor<Vec<u8>>>().unwrap_err();
+
+        upgraded.downcast::<Mock>().unwrap();
+    }
+
+    // TODO: replace with tokio_test::io when it can test write_buf
+    struct Mock;
+
+    impl AsyncRead for Mock {
+        fn poll_read(
+            self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+            _buf: &mut ReadBuf<'_>,
+        ) -> Poll<io::Result<()>> {
+            unreachable!("Mock::poll_read")
+        }
+    }
+
+    impl AsyncWrite for Mock {
+        fn poll_write(
+            self: Pin<&mut Self>,
+            _: &mut Context<'_>,
+            buf: &[u8],
+        ) -> Poll<io::Result<usize>> {
+            // panic!("poll_write shouldn't be called");
+            Poll::Ready(Ok(buf.len()))
+        }
+
+        fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            unreachable!("Mock::poll_flush")
+        }
+
+        fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            unreachable!("Mock::poll_shutdown")
+        }
+    }
+}