CURLOPT\_HSTSREADDATA(3) Library Functions Manual CURLOPT\_HSTSREADDATA(3)

# [NAME](#NAME)

CURLOPT\_HSTSREADDATA - pointer passed to the HSTS read callback

# [SYNOPSIS](#SYNOPSIS)

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

# [DESCRIPTION](#DESCRIPTION)

Data *pointer* to pass to the HSTS read function. If you use the [*CURLOPT\_HSTSREADFUNCTION(3)*](/man/os/curl/CURLOPT_HSTSREADFUNCTION.3) 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)*](/man/os/curl/CURLOPT_HSTS_CTRL.3) to do that.

# [DEFAULT](#DEFAULT)

NULL

# [PROTOCOLS](#PROTOCOLS)

This functionality affects http only

# [EXAMPLE](#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](#AVAILABILITY)

Added in curl 7.74.0

# [RETURN VALUE](#RETURN_VALUE)

This returns CURLE\_OK.

# [SEE ALSO](#SEE_ALSO)

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

2026-10-31 libcurl

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Document: CURLOPT_HSTSREADDATA(3) from curl 8.23.0-r3 (Chainguard OS)
Source: https://github.com/curl/curl.git