.\" **************************************************************************
.\" *                                  _   _ ____  _
.\" *  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_CTRL 3 "January 02, 2023" "libcurl 7.88.1" "curl_easy_setopt options"

.SH NAME
CURLOPT_HSTS_CTRL \- control HSTS behavior
.SH SYNOPSIS
.nf
#include <curl/curl.h>

#define CURLHSTS_ENABLE       (1<<0)
#define CURLHSTS_READONLYFILE (1<<1)

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HSTS_CTRL, long bitmask);
.fi
.SH DESCRIPTION
HSTS (HTTP Strict Transport Security) means that an HTTPS server can instruct
the client to not contact it again over clear-text HTTP for a certain period
into the future. libcurl will then automatically redirect HTTP attempts to
such hosts to instead use HTTPS. This is done by libcurl retaining this
knowledge in an in-memory cache.

Populate the long \fIbitmask\fP with the correct set of features to instruct
libcurl how to handle HSTS for the transfers using this handle.
.SH BITS
.IP "CURLHSTS_ENABLE"
Enable the in-memory HSTS cache for this handle.
.IP "CURLHSTS_READONLYFILE"
Make the HSTS file (if specified) read-only - makes libcurl not save the cache
to the file when closing the handle.
.SH DEFAULT
0. HSTS is disabled by default.
.SH PROTOCOLS
HTTPS and HTTP
.SH EXAMPLE
.nf
CURL *curl = curl_easy_init();
if(curl) {
  curl_easy_setopt(curl, CURLOPT_HSTS_CTRL, (long)CURLHSTS_ENABLE);
  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_HSTS "(3), " CURLOPT_CONNECT_TO "(3), " CURLOPT_RESOLVE "(3), "
.BR CURLOPT_ALTSVC "(3), "