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.

       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 _ALTSVC&section=3">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 7.77.0                 November 4, 2020        CURLOPT_HTTP_VERSION(3)