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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

#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

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_HSTS_CTRL, CURLHSTS_ENABLE);
    curl_easy_perform(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).