---
name: "CURLOPT_HSTSREADDATA"
section: "3"
platform: "linux"
package: "curl"
version: "8.23.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLOPT_HSTSREADDATA"
---

# CURLOPT\_HSTSREADDATA(3)

pointer passed to the HSTS read callback

## NAME

CURLOPT\_HSTSREADDATA - pointer passed to the HSTS read callback

## SYNOPSIS

```
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HSTSREADDATA, void *pointer);
```

## DESCRIPTION

Data *pointer* to pass to the HSTS read function. If you use the *[CURLOPT\_HSTSREADFUNCTION(3)](/CURLOPT_HSTSREADFUNCTION/3.md)* option, this is the pointer you get as input in the 3rd argument to the callback.

This option does not enable HSTS, you need to use *[CURLOPT\_HSTS\_CTRL(3)](/CURLOPT_HSTS_CTRL/3.md)* to do that.

## DEFAULT

NULL

## PROTOCOLS

This functionality affects http only

## EXAMPLE

```
struct MyData {
  void *custom;
};
static CURLSTScode hsts_cb(CURL *easy, struct curl_hstsentry *sts,
                           void *clientp)
{
  /* populate the struct as documented */
  return CURLSTS_OK;
}
int main(void)
{
  CURL *curl = curl_easy_init();
  struct MyData my_data;
  if(curl) {
    CURLcode result;
    curl_easy_setopt(curl, CURLOPT_URL, "http://example.com");
    /* pass pointer that gets passed in to the
       CURLOPT_HSTSREADFUNCTION callback */
    curl_easy_setopt(curl, CURLOPT_HSTSREADDATA, &my_data);
    /* set HSTS read callback */
    curl_easy_setopt(curl, CURLOPT_HSTSREADFUNCTION, hsts_cb);
    result = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}
```

## AVAILABILITY

Added in curl 7.74.0

## RETURN VALUE

This returns CURLE\_OK.

## SEE ALSO

[**CURLOPT\_HSTS**(3)](/CURLOPT_HSTS/3.md), [**CURLOPT\_HSTSREADFUNCTION**(3)](/CURLOPT_HSTSREADFUNCTION/3.md), [**CURLOPT\_HSTSWRITEDATA**(3)](/CURLOPT_HSTSWRITEDATA/3.md), [**CURLOPT\_HSTSWRITEFUNCTION**(3)](/CURLOPT_HSTSWRITEFUNCTION/3.md)