--- c: Copyright (C) Daniel Stenberg, , 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) --- # NAME CURLOPT_HTTP_VERSION - HTTP protocol version to use # SYNOPSIS ~~~c #include 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) ## 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 # EXAMPLE ~~~c 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 Along with HTTP # RETURN VALUE Returns CURLE_OK if HTTP is supported, and CURLE_UNKNOWN_OPTION if not.