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 still prioritizes to reuse  existing
       connections  so  it might then reuse a connection using an HTTP version you have not asked
       for.

       CURL_HTTP_VERSION_NONE
              We do not care about what version the library uses. libcurl uses 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  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 CURLOPT_SSLVERSION(3).

              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 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)

       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)

              Since 8.10.0 if this option is set for an HTTPS request then the application  layer
              protocol  version  (ALPN)  offered to the server is only HTTP/2. Prior to that both
              HTTP/1.1 and HTTP/2 were offered.

       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.

       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.

DEFAULT

       Since curl 7.62.0: CURL_HTTP_VERSION_2TLS

       Before that: CURL_HTTP_VERSION_1_1

PROTOCOLS

       This functionality affects http only

EXAMPLE

       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 */
           }
         }
       }

AVAILABILITY

       Added in curl 7.9.1

RETURN VALUE

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

SEE ALSO

       CURLOPT_ALTSVC(3),          CURLOPT_HTTP09_ALLOWED(3),          CURLOPT_HTTP200ALIASES(3),
       CURLOPT_SSLVERSION(3)