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.

       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)

       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 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)