CURLOPT_HTTP_VERSION

Section: curl_easy_setopt options (3)
Updated: November 04, 2020
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NAME

CURLOPT_HTTP_VERSION - specify HTTP protocol version to use

SYNOPSIS

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 will still prioritize to re-use an existing connection so it might then re-use a connection using a HTTP version you haven't asked for.

CURL_HTTP_VERSION_NONE: We don't care about what version the library uses. libcurl will use 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 will fall back to HTTP 1.1 if HTTP 2 can't be negotiated with the server. (Added in 7.33.0)
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 will fall back to HTTP 1.1 if HTTP 2 can't be negotiated with the HTTPS server. For clear text HTTP servers, libcurl will use 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 will 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) Setting this value will make libcurl attempt to use HTTP/3 directly to server given in the URL. Note that this cannot gracefully downgrade to earlier HTTP version if the server doesn't support HTTP/3.
For more reliably upgrading to HTTP/3, set the preferred version to something lower and let the server announce its HTTP/3 support via Alt-Svc:. See CURLOPT_ALTSVC(3).

DEFAULT

Since curl 7.62.0: CURL_HTTP_VERSION_2TLS

Before that: CURL_HTTP_VERSION_1_1

PROTOCOLS

HTTP

EXAMPLE

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, 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.