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+.\" **************************************************************************
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+.\" *  Project                     ___| | | |  _ \| |
+.\" *                             / __| | | | |_) | |
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+.\" *                             \___|\___/|_| \_\_____|
+.\" *
+.\" * Copyright (C) 1998 - 2019, Daniel Stenberg, <[email protected]>, et al.
+.\" *
+.\" * This software is licensed as described in the file COPYING, which
+.\" * you should have received as part of this distribution. The terms
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+.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+.\" * copies of the Software, and permit persons to whom the Software is
+.\" * furnished to do so, under the terms of the COPYING file.
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+.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+.\" * KIND, either express or implied.
+.\" *
+.\" **************************************************************************
+.\"
+.TH CURLOPT_HTTP_VERSION 3 "November 04, 2020" "libcurl 7.75.0" "curl_easy_setopt options"
+
+.SH NAME
+CURLOPT_HTTP_VERSION \- specify HTTP protocol version to use
+.SH SYNOPSIS
+#include <curl/curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTP_VERSION, long version);
+.SH DESCRIPTION
+Pass \fIversion\fP 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 will still prioritize to
+re-use an existing connection so it might then re-use a connection using a
+HTTP version you haven't asked for.
+
+.IP CURL_HTTP_VERSION_NONE
+We don't care about what version the library uses. libcurl will use whatever
+it thinks fit.
+.IP CURL_HTTP_VERSION_1_0
+Enforce HTTP 1.0 requests.
+.IP CURL_HTTP_VERSION_1_1
+Enforce HTTP 1.1 requests.
+.IP CURL_HTTP_VERSION_2_0
+Attempt HTTP 2 requests. libcurl will fall back to HTTP 1.1 if HTTP 2 can't be
+negotiated with the server. (Added in 7.33.0)
+
+The alias \fICURL_HTTP_VERSION_2\fP was added in 7.43.0 to better reflect the
+actual protocol name.
+.IP CURL_HTTP_VERSION_2TLS
+Attempt HTTP 2 over TLS (HTTPS) only. libcurl will fall back to HTTP 1.1 if
+HTTP 2 can't be negotiated with the HTTPS server. For clear text HTTP servers,
+libcurl will use 1.1. (Added in 7.47.0)
+.IP 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
+will still do HTTP/2 the standard way with negotiated protocol version in the
+TLS handshake. (Added in 7.49.0)
+.IP CURL_HTTP_VERSION_3
+(Added in 7.66.0) Setting this value will make libcurl attempt to use HTTP/3
+directly to server given in the URL. Note that this cannot gracefully
+downgrade to earlier HTTP version if the server doesn't support HTTP/3.
+
+For more reliably upgrading to HTTP/3, set the preferred version to something
+lower and let the server announce its HTTP/3 support via Alt-Svc:. See
+\fICURLOPT_ALTSVC(3)\fP.
+.SH DEFAULT
+Since curl 7.62.0: CURL_HTTP_VERSION_2TLS
+
+Before that: CURL_HTTP_VERSION_1_1
+.SH PROTOCOLS
+HTTP
+.SH EXAMPLE
+.nf
+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, CURL_HTTP_VERSION_2TLS);
+  ret = curl_easy_perform(curl);
+  if(ret == CURLE_HTTP_RETURNED_ERROR) {
+    /* an HTTP response error problem */
+  }
+}
+.fi
+.SH AVAILABILITY
+Along with HTTP
+.SH RETURN VALUE
+Returns CURLE_OK if HTTP is supported, and CURLE_UNKNOWN_OPTION if not.
+.SH "SEE ALSO"
+.BR CURLOPT_SSLVERSION "(3), " CURLOPT_HTTP200ALIASES "(3), "
+.BR CURLOPT_HTTP09_ALLOWED "(3), " CURLOPT_ALTSVC "(3) "