Man pages sections > man3 > CURLOPT_HTTP_VERSION

CURLOPT_HTTP_VERSION - specify HTTP protocol version to use

CURLOPT_HTTP_VERSION(3) curl_easy_setopt options CURLOPT_HTTP_VERSION(3)

NAME

CURLOPT_HTTP_VERSION - specify HTTP protocol version to use

SYNOPSIS

#include <curl/curl.h>
 
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTP_VERSION, long version);

DESCRIPTION

Pass version a long, set to one of the values described below. They ask libcurl to use the specific HTTP versions. This is not sensible to do unless you have a good reason. You have to set this option if you want to use libcurl's HTTP/2 support.
 
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.
 
CURL_HTTP_VERSION_NONE
We don't care about what version the library uses. libcurl will use whatever it thinks fit.
CURL_HTTP_VERSION_1_0
Enforce HTTP 1.0 requests.
CURL_HTTP_VERSION_1_1
Enforce HTTP 1.1 requests.
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 CURL_HTTP_VERSION_2 was added in 7.43.0 to better reflect the actual protocol name.
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)
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)

DEFAULT

CURL_HTTP_VERSION_NONE

PROTOCOLS

HTTP

EXAMPLE

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) {
    /* a HTTP response error problem */
  }
}

AVAILABILITY

Along with HTTP

RETURN VALUE

Returns CURLE_OK if HTTP is supported, and CURLE_UNKNOWN_OPTION if not.

SEE ALSO

CURLOPT_SSLVERSION(3), CURLOPT_HTTP200ALIASES(3),
May 30, 2017 libcurl 7.55.1