CURLOPT_HTTP_VERSION

SYNOPSIS

#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. This is not sensible to do unless you have a good reason. You have to set this option if you want to use libcurl's HTTP/2 support.

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)