NAME

       CURLOPT_HTTP_VERSION - 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.

       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 have not asked for.

       CURL_HTTP_VERSION_NONE
              We do not 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 cannot 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  cannot  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)

       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
              does not 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 CURLOPT_ALTSVC(3).

DEFAULT

       Since curl 7.62.0: CURL_HTTP_VERSION_2TLS

       Before that: CURL_HTTP_VERSION_1_1

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) {
           /* an 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), CURLOPT_HTTP09_ALLOWED(3), CURLOPT_ALTSVC(3)

libcurl 7.81.0                                  November 26, 2021                        CURLOPT_HTTP_VERSION(3)