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

       curl_easy_setopt(3) returns a CURLcode indicating success or error.

       CURLE_OK (0) means everything was OK, non-zero means an error occurred, see libcurl-errors(3).

SEE ALSO

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

libcurl                                            2025-03-05                            CURLOPT_HTTP_VERSION(3)