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)

       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)