---
name: "CURLOPT_HSTS"
section: "3"
platform: "macos"
package: "curl"
version: "166.0.0.0.1"
release: "macOS 26.5"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLOPT_HSTS"
---

# CURLOPT\_HSTS(3)

HSTS cache file name

## NAME

CURLOPT\_HSTS - HSTS cache file name

## SYNOPSIS

```
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HSTS, char *filename);
```

## DESCRIPTION

Make the *filename* point to a filename to load an existing HSTS cache from, and to store the cache in when the easy handle is closed. Setting a file name with this option also enables HSTS for this handle (the equivalent of setting *CURLHSTS\_ENABLE* with *[CURLOPT\_HSTS\_CTRL(3)](/CURLOPT_HSTS_CTRL/3.md)*).

If the given file does not exist or contains no HSTS entries at startup, the HSTS cache simply starts empty. Setting the filename to NULL or "" only enables HSTS without reading from or writing to any file.

If this option is set multiple times, libcurl loads cache entries from each given file but only stores the last used name for later writing.

## FILE FORMAT

The HSTS cache is saved to and loaded from a text file with one entry per physical line. Each line in the file has the following format:

\[host\] \[stamp\]

\[host\] is the domain name for the entry and the name is dot-prefixed if it is an entry valid for all subdomains to the name as well or only for the exact name.

\[stamp\] is the time (in UTC) when the entry expires and it uses the format "YYYYMMDD HH:MM:SS".

Lines starting with "#" are treated as comments and are ignored. There is currently no length or size limit.

## DEFAULT

NULL, no file name

## PROTOCOLS

HTTPS and HTTP

## EXAMPLE

```
int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_HSTS, "/home/user/.hsts-cache");
    curl_easy_perform(curl);
  }
}
```

## AVAILABILITY

Added in 7.74.0

## RETURN VALUE

Returns CURLE\_OK if the option is supported, and CURLE\_UNKNOWN\_OPTION if not.

## SEE ALSO

[**CURLOPT\_ALTSVC**(3)](/CURLOPT_ALTSVC/3.md), [**CURLOPT\_HSTS\_CTRL**(3)](/CURLOPT_HSTS_CTRL/3.md), [**CURLOPT\_RESOLVE**(3)](/CURLOPT_RESOLVE/3.md)