docs/libcurl/opts/CURLOPT_HTTP_VERSION.3

.\" **************************************************************************
.\" *                                  _   _ ____  _
.\" *  Project                     ___| | | |  _ \| |
.\" *                             / __| | | | |_) | |
.\" *                            | (__| |_| |  _ <| |___
.\" *                             \___|\___/|_| \_\_____|
.\" *
.\" * Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
.\" *
.\" * This software is licensed as described in the file COPYING, which
.\" * you should have received as part of this distribution. The terms
.\" * are also available at https://curl.se/docs/copyright.html.
.\" *
.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
.\" * copies of the Software, and permit persons to whom the Software is
.\" * furnished to do so, under the terms of the COPYING file.
.\" *
.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
.\" * KIND, either express or implied.
.\" *
.\" **************************************************************************
.\"
.TH CURLOPT_HTTP_VERSION 3 "November 04, 2020" "libcurl 7.78.0" "curl_easy_setopt options"

.SH NAME
CURLOPT_HTTP_VERSION \- specify HTTP protocol version to use
.SH SYNOPSIS
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTP_VERSION, long version);
.SH DESCRIPTION
Pass \fIversion\fP a long, set to one of the values described below. They ask
libcurl to use the specific HTTP versions.

Note that the HTTP version is just a request. libcurl will still prioritize to
re-use an existing connection so it might then re-use a connection using a
HTTP version you haven't asked for.

.IP CURL_HTTP_VERSION_NONE
We don't care about what version the library uses. libcurl will use whatever
it thinks fit.
.IP CURL_HTTP_VERSION_1_0
Enforce HTTP 1.0 requests.
.IP CURL_HTTP_VERSION_1_1
Enforce HTTP 1.1 requests.
.IP CURL_HTTP_VERSION_2_0
Attempt HTTP 2 requests. libcurl will fall back to HTTP 1.1 if HTTP 2 can't be
negotiated with the server. (Added in 7.33.0)

The alias \fICURL_HTTP_VERSION_2\fP was added in 7.43.0 to better reflect the
actual protocol name.
.IP CURL_HTTP_VERSION_2TLS
Attempt HTTP 2 over TLS (HTTPS) only. libcurl will fall back to HTTP 1.1 if
HTTP 2 can't be negotiated with the HTTPS server. For clear text HTTP servers,
libcurl will use 1.1. (Added in 7.47.0)
.IP CURL_HTTP_VERSION_2_PRIOR_KNOWLEDGE
Issue non-TLS HTTP requests using HTTP/2 without HTTP/1.1 Upgrade. It requires
prior knowledge that the server supports HTTP/2 straight away. HTTPS requests
will still do HTTP/2 the standard way with negotiated protocol version in the
TLS handshake. (Added in 7.49.0)
.IP CURL_HTTP_VERSION_3
(Added in 7.66.0) Setting this value will make libcurl attempt to use HTTP/3
directly to server given in the URL. Note that this cannot gracefully
downgrade to earlier HTTP version if the server doesn't support HTTP/3.

For more reliably upgrading to HTTP/3, set the preferred version to something
lower and let the server announce its HTTP/3 support via Alt-Svc:. See
\fICURLOPT_ALTSVC(3)\fP.
.SH DEFAULT
Since curl 7.62.0: CURL_HTTP_VERSION_2TLS

Before that: CURL_HTTP_VERSION_1_1
.SH PROTOCOLS
HTTP
.SH EXAMPLE
.nf
CURL *curl = curl_easy_init();
if(curl) {
  CURLcode ret;
  curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
  curl_easy_setopt(curl, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2TLS);
  ret = curl_easy_perform(curl);
  if(ret == CURLE_HTTP_RETURNED_ERROR) {
    /* an HTTP response error problem */
  }
}
.fi
.SH AVAILABILITY
Along with HTTP
.SH RETURN VALUE
Returns CURLE_OK if HTTP is supported, and CURLE_UNKNOWN_OPTION if not.
.SH "SEE ALSO"
.BR CURLOPT_SSLVERSION "(3), " CURLOPT_HTTP200ALIASES "(3), "
.BR CURLOPT_HTTP09_ALLOWED "(3), " CURLOPT_ALTSVC "(3) "