.\" generated by cd2nroff 0.1 from CURLOPT_HTTP_VERSION.md
.TH CURLOPT_HTTP_VERSION 3 "2024-04-19" libcurl
.SH NAME
CURLOPT_HTTP_VERSION \- HTTP protocol version to use
.SH SYNOPSIS
.nf
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTP_VERSION, long version);
.fi
.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 still prioritizes to
reuse existing connections so it might then reuse a connection using an HTTP
version you have not asked for.
.IP CURL_HTTP_VERSION_NONE
We do not care about what version the library uses. libcurl uses 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 falls back to HTTP 1.1 if HTTP 2 cannot be
negotiated with the server. (Added in 7.33.0)

When libcurl uses HTTP/2 over HTTPS, it does not itself insist on TLS 1.2 or
higher even though that is required by the specification. A user can add this
version requirement with \fICURLOPT_SSLVERSION(3)\fP.

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 falls back to HTTP 1.1 if HTTP 2
cannot be negotiated with the HTTPS server. For clear text HTTP servers,
libcurl uses 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
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) This option makes libcurl attempt to use HTTP/3 to the host
given in the URL, with fallback to earlier HTTP versions if needed.
.IP CURL_HTTP_VERSION_3ONLY
(Added in 7.88.0) Setting this makes libcurl attempt to use HTTP/3 directly to
server given in the URL and does not downgrade to earlier HTTP version if the
server does not support HTTP/3.
.SH DEFAULT
Since curl 7.62.0: CURL_HTTP_VERSION_2TLS

Before that: CURL_HTTP_VERSION_1_1
.SH PROTOCOLS
HTTP
.SH EXAMPLE
.nf
int main(void)
{
  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,
                     (long)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_ALTSVC (3),
.BR CURLOPT_HTTP09_ALLOWED (3),
.BR CURLOPT_HTTP200ALIASES (3),
.BR CURLOPT_SSLVERSION (3)