.\" **************************************************************************
.\" *                                  _   _ ____  _
.\" *  Project                     ___| | | |  _ \| |
.\" *                             / __| | | | |_) | |
.\" *                            | (__| |_| |  _ <| |___
.\" *                             \___|\___/|_| \_\_____|
.\" *
.\" * Copyright (C) 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.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.
.\" *
.\" * SPDX-License-Identifier: curl
.\" *
.\" **************************************************************************
.\"
.TH CURLOPT_HSTS 3 "December 04, 2023" "ibcurl 8.5.0" libcurl

.SH NAME
CURLOPT_HSTS \- HSTS cache file name
.SH SYNOPSIS
.nf
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HSTS, char *filename);
.fi
.SH DESCRIPTION
Make the \fIfilename\fP point to a file name to load an existing HSTS cache
from, and to store the cache in when the easy handle is closed. Setting a file
name with this option also enables HSTS for this handle (the equivalent of
setting \fICURLHSTS_ENABLE\fP with \fICURLOPT_HSTS_CTRL(3)\fP).

If the given file does not exist or contains no HSTS entries at startup, the
HSTS cache simply starts empty. Setting the file name to NULL or "" only
enables HSTS without reading from or writing to any file.

If this option is set multiple times, libcurl loads cache entries from each
given file but only stores the last used name for later writing.
.SH "FILE FORMAT"
The HSTS cache is saved to and loaded from a text file with one entry per
physical line. Each line in the file has the following format:

[host] [stamp]

[host] is the domain name for the entry and the name is dot-prefixed if it is
an entry valid for all subdomains to the name as well or only for the exact
name.

[stamp] is the time (in UTC) when the entry expires and it uses the format
\&"YYYYMMDD HH:MM:SS".

Lines starting with "#" are treated as comments and are ignored. There is
currently no length or size limit.
.SH DEFAULT
NULL, no file name
.SH PROTOCOLS
HTTPS and HTTP
.SH EXAMPLE
.nf
int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_HSTS, "/home/user/.hsts-cache");
    curl_easy_perform(curl);
  }
}
.fi
.SH AVAILABILITY
Added in 7.74.0
.SH RETURN VALUE
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
.SH "SEE ALSO"
.BR CURLOPT_ALTSVC (3),
.BR CURLOPT_HSTS_CTRL (3),
.BR CURLOPT_RESOLVE (3)