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
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)