CURLOPT_HSTS_CTRL(3) Library Functions Manual CURLOPT_HSTS_CTRL(3)

CURLOPT_HSTS_CTRL - control HSTS behavior

#include <curl/curl.h>
#define CURLHSTS_ENABLE       (1<<0)
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HSTS_CTRL, long bitmask);

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.

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

0. HSTS is disabled by default.


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

Added in 7.74.0

Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.


2024-05-22 libcurl