---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_HTTP_VERSION
Section: 3
Source: libcurl
Protocol:
  - HTTP
See-also:
  - CURLOPT_ALTSVC (3)
  - CURLOPT_HTTP09_ALLOWED (3)
  - CURLOPT_HTTP200ALIASES (3)
  - CURLOPT_SSLVERSION (3)
Added-in: 7.9.1
---

# NAME

CURLOPT_HTTP_VERSION - HTTP protocol version to use

# SYNOPSIS

~~~c
#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 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.

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 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.

## 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.

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 8.13.0: CURL_HTTP_VERSION_NONE

Since curl 7.62.0: CURL_HTTP_VERSION_2TLS

Before that: CURL_HTTP_VERSION_1_1

# %PROTOCOLS%

# EXAMPLE

~~~c
int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode result;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
    curl_easy_setopt(curl, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2TLS);
    result = curl_easy_perform(curl);
    if(result == CURLE_HTTP_RETURNED_ERROR) {
      /* an HTTP response error problem */
    }
  }
}
~~~

# HISTORY

**CURL_HTTP_VERSION_*** enums became `long` types in 8.13.0, prior to this
version a `long` cast was necessary when passed to curl_easy_setopt(3).

# %AVAILABILITY%

# 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).
