CURLOPT_HTTP_VERSION - Man Page

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTP_VERSION, long version);

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.

Since curl 7.62.0: CURL_HTTP_VERSION_2TLS

Before that: CURL_HTTP_VERSION_1_1

This functionality affects http only

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 */
    }
  }
}

Added in curl 7.9.1

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

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

curl_easy_setopt(3), CURLOPT_CUSTOMREQUEST(3), CURLOPT_HTTP09_ALLOWED(3), CURLOPT_HTTP200ALIASES(3), CURLOPT_IGNORE_CONTENT_LENGTH(3), CURLOPT_IPRESOLVE(3), CURLOPT_PROXY_SSLVERSION(3), CURLOPT_PROXYTYPE(3), CURLOPT_SSLVERSION(3), CURLOPT_STREAM_DEPENDS(3), CURLOPT_STREAM_DEPENDS_E(3), libcurl-symbols(3), nbdkit-curl-plugin(1).