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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 a request. libcurl still prioritizes to reuse existing connections so it might then reuse a connection using an HTTP ver- sion 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 negoti- ated protocol version in the TLS handshake. Since 8.10.0 if this option is set for an HTTPS request then the ap- plication 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 ear- lier 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 This functionality affects http only EXAMPLE 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 ver- sion a long cast was necessary when passed to curl_easy_setopt(3). 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 2026-06-11 CURLOPT_HTTP_VERSION(3)
NAME | SYNOPSIS | DESCRIPTION | DEFAULT | PROTOCOLS | EXAMPLE | HISTORY | AVAILABILITY | RETURN VALUE | SEE ALSO
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