Tribblix: manual page: CURLOPT_HTTP

CURLOPT_HTTP_VERSION(3) Introduction to Library Functions

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)

Since 8.10.0 if this option is set for an HTTPS request then
the application layer protocol version (ALPN) offered to the
server is only HTTP/2. Prior to that both HTTP/1.1 and HTTP/2
were offered.

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

curl_easy_setopt(3) returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK, non-zero means an error
occurred, see libcurl-errors(3).