CURLOPT_HSTS_CTRL(3) Library Functions Manual CURLOPT_HSTS_CTRL(3)
NAME
CURLOPT_HSTS_CTRL - control HSTS behavior
SYNOPSIS
#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);
DESCRIPTION
HSTS (HTTP Strict Transport Security) means that an HTTPS server can in-
struct 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
This functionality affects http only
EXAMPLE
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_HSTS_CTRL, (long)CURLHSTS_ENABLE);
curl_easy_perform(curl);
}
}
AVAILABILITY
Added in curl 7.74.0
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).
SEE ALSO
CURLOPT_ALTSVC(3), CURLOPT_CONNECT_TO(3), CURLOPT_HSTS(3), CURLOPT_RE-
SOLVE(3)
libcurl 2026-07-12 CURLOPT_HSTS_CTRL(3)
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