CURLOPT_HTTP_VERSION(3)    Library Functions Manual    CURLOPT_HTTP_VERSION(3)

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
       HTTP

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
       Along with HTTP

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)

libcurl                          April 02 2024         CURLOPT_HTTP_VERSION(3)