CURLOPT_HTTP_VERSION(3) Library Functions Manual 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 specifica-
tion. A user can add this version requirement with CURLOPT_SS-
LVERSION(3).
The alias CURL_HTTP_VERSION_2 was added in 7.43.0 to better re-
flect 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 Up-
grade. 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 of-
fered.
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 ver-
sions 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).
SEE ALSO
CURLOPT_ALTSVC(3), CURLOPT_HTTP09_ALLOWED(3), CURLOPT_HTTP200ALIASES(3),
CURLOPT_SSLVERSION(3)
libcurl 2026-07-12 CURLOPT_HTTP_VERSION(3)
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