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Fast, safe, compile error. Pick two.
Zerocopy makes zero-cost memory manipulation effortless. We write unsafe
so you don't have to.
Zerocopy provides four core marker traits, each of which can be derived (e.g., #[derive(FromZeroes)]
):
FromZeroes
indicates that a sequence of zero bytes represents a valid instance of a typeFromBytes
indicates that a type may safely be converted from an arbitrary byte sequenceAsBytes
indicates that a type may safely be converted to a byte sequenceUnaligned
indicates that a type's alignment requirement is 1Types which implement a subset of these traits can then be converted to/from byte sequences with little to no runtime overhead.
Zerocopy also provides byte-order aware integer types that support these conversions; see the byteorder
module. These types are especially useful for network parsing.
alloc
By default, zerocopy
is no_std
. When the alloc
feature is enabled, the alloc
crate is added as a dependency, and some allocation-related functionality is added.
byteorder
(enabled by default) Adds the byteorder
module and a dependency on the byteorder
crate. The byteorder
module provides byte order-aware equivalents of the multi-byte primitive numerical types. Unlike their primitive equivalents, the types in this module have no alignment requirement and support byte order conversions. This can be useful in handling file formats, network packet layouts, etc which don't provide alignment guarantees and which may use a byte order different from that of the execution platform.
derive
Provides derives for the core marker traits via the zerocopy-derive
crate. These derives are re-exported from zerocopy
, so it is not necessary to depend on zerocopy-derive
directly.
However, you may experience better compile times if you instead directly depend on both zerocopy
and zerocopy-derive
in your Cargo.toml
, since doing so will allow Rust to compile these crates in parallel. To do so, do not enable the derive
feature, and list both dependencies in your Cargo.toml
with the same leading non-zero version number; e.g:
[dependencies] zerocopy = "0.X" zerocopy-derive = "0.X"
simd
When the simd
feature is enabled, FromZeroes
, FromBytes
, and AsBytes
impls are emitted for all stable SIMD types which exist on the target platform. Note that the layout of SIMD types is not yet stabilized, so these impls may be removed in the future if layout changes make them invalid. For more information, see the Unsafe Code Guidelines Reference page on the layout of packed SIMD vectors.
simd-nightly
Enables the simd
feature and adds support for SIMD types which are only available on nightly. Since these types are unstable, support for any type may be removed at any point in the future.
Zerocopy is expressly designed for use in security-critical contexts. We strive to ensure that that zerocopy code is sound under Rust's current memory model, and any future memory model. We ensure this by:
unsafe
code with a precise rationale for its soundness that cites a relevant section of Rust‘s official documentation. When Rust’s documented semantics are unclear, we work with the Rust Operational Semantics Team to clarify Rust's documentation.For more information, see our full soundness policy.
Project Safe Transmute is an official initiative of the Rust Project to develop language-level support for safer transmutation. The Project consults with crates like zerocopy to identify aspects of safer transmutation that would benefit from compiler support, and has developed an experimental, compiler-supported analysis which determines whether, for a given type, any value of that type may be soundly transmuted into another type. Once this functionality is sufficiently mature, zerocopy intends to replace its internal transmutability analysis (implemented by our custom derives) with the compiler-supported one. This change will likely be an implementation detail that is invisible to zerocopy's users.
Project Safe Transmute will not replace the need for most of zerocopy's higher-level abstractions. The experimental compiler analysis is a tool for checking the soundness of unsafe
code, not a tool to avoid writing unsafe
code altogether. For the foreseeable future, crates like zerocopy will still be required in order to provide higher-level abstractions on top of the building block provided by Project Safe Transmute.
See our MSRV policy.
Zerocopy uses GitHub Releases.
Disclaimer: Zerocopy is not an officially supported Google product.