.\" **************************************************************************
.\" *                                  _   _ ____  _
.\" *  Project                     ___| | | |  _ \| |
.\" *                             / __| | | | |_) | |
.\" *                            | (__| |_| |  _ <| |___
.\" *                             \___|\___/|_| \_\_____|
.\" *
.\" * Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
.\" *
.\" * This software is licensed as described in the file COPYING, which
.\" * you should have received as part of this distribution. The terms
.\" * are also available at https://curl.haxx.se/docs/copyright.html.
.\" *
.\" * 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.
.\" *
.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
.\" * KIND, either express or implied.
.\" *
.\" **************************************************************************
.\"
.TH GNURLOPT_ALTSVC_CTRL 3 "5 Feb 2019" "libcurl 7.64.1" "curl_easy_setopt options"
.SH NAME
CURLOPT_ALTSVC_CTRL \- control alt-svc behavior
.SH SYNOPSIS
.nf
#include <gnurl/curl.h>

#define CURLALTSVC_IMMEDIATELY  (1<<0)
#define CURLALTSVC_ALTUSED      (1<<1)
#define CURLALTSVC_READONLYFILE (1<<2)
#define CURLALTSVC_H1           (1<<3)
#define CURLALTSVC_H2           (1<<4)
#define CURLALTSVC_H3           (1<<5)

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ALTSVC_CTRL, long bitmask);
.fi
.SH EXPERIMENTAL
Warning: this feature is early code and is marked as experimental. It can only
be enabled by explicitly telling configure with \fB--enable-alt-svc\fP. You are
advised to not ship this in production before the experimental label is
removed.
.SH DESCRIPTION
Populate the long \fIbitmask\fP with the correct set of features to instruct
libcurl how to handle Alt-Svc for the transfers using this handle.

libcurl will only accept Alt-Svc headers over a secure transport, meaning
HTTPS. It will also only complete a request to an alternative origin if that
origin is properly hosted over HTTPS. These requirements are there to make
sure both the source and the destination are legitimate.

Setting any bit will enable the alt-svc engine.
.IP "CURLALTSVC_IMMEDIATELY"
If an Alt-Svc: header is received, this instructs libcurl to switch to one of
those alternatives asap rather than to save it and use for the next request.
.IP "CURLALTSVC_ALTUSED"
Issue the Alt-Used: header in all requests that have been redirected by
alt-svc.
.IP "CURLALTSVC_READONLYFILE"
Do not write the alt-svc cache back to the file specified with
\fICURLOPT_ALTSVC(3)\fP even if it gets updated. By default a file specified
with that option will be read and written to as deemed necessary.
.IP "CURLALTSVC_H1"
Accept alternative services offered over HTTP/1.1.
.IP "CURLALTSVC_H2"
Accept alternative services offered over HTTP/2. This will only be used if
libcurl was also built to actually support HTTP/2, otherwise this bit will be
ignored.
.IP "CURLALTSVC_H3"
Accept alternative services offered over HTTP/3. This will only be used if
libcurl was also built to actually support HTTP/3, otherwise this bit will be
ignored.
.SH DEFAULT
0. No Alt-Svc treatment.
.SH PROTOCOLS
HTTPS
.SH EXAMPLE
.nf
CURL *curl = curl_easy_init();
if(curl) {
  curl_easy_setopt(curl, CURLOPT_ALTSVC_CTRL, CURLALTSVC_H1);
  curl_easy_setopt(curl, CURLOPT_ALTSVC, "altsvc-cache.txt");
  curl_easy_perform(curl);
}
.fi
.SH AVAILABILITY
Added in 7.64.1
.SH RETURN VALUE
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
.SH "SEE ALSO"
.BR CURLOPT_ALTSVC "(3), " CURLOPT_CONNECT_TO "(3), " CURLOPT_RESOLVE "(3), "