---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_HSTS_CTRL
Section: 3
Source: libcurl
Protocol:
  - HTTP
See-also:
  - CURLOPT_ALTSVC (3)
  - CURLOPT_CONNECT_TO (3)
  - CURLOPT_HSTS (3)
  - CURLOPT_RESOLVE (3)
Added-in: 7.74.0
---

# NAME

CURLOPT_HSTS_CTRL - control HSTS behavior

# SYNOPSIS

~~~c
#include <curl/curl.h>

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

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HSTS_CTRL, long bitmask);
~~~

# 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 then automatically redirects 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 *bitmask* with the correct set of features to instruct
libcurl how to handle HSTS for the transfers using this handle.

# BITS

## CURLHSTS_ENABLE

Enable the in-memory HSTS cache for this handle.

## CURLHSTS_READONLYFILE

Make the HSTS file (if specified) read-only - makes libcurl not save the cache
to the file when closing the handle.

# DEFAULT

0

# %PROTOCOLS%

# EXAMPLE

~~~c
int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode result;
    /* enable HSTS */
    curl_easy_setopt(curl, CURLOPT_HSTS_CTRL, CURLHSTS_ENABLE);
    /* specify where to store the HSTS cache */
    curl_easy_setopt(curl, CURLOPT_HSTS, "/home/user/.hsts-cache");
    result = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}
~~~

# %AVAILABILITY%

# 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).
