CURLOPT_HSTSWRITEFUNCTION - Man Page

#include <curl/curl.h>

struct curl_hstsentry {
  char *name;
  size_t namelen;
  unsigned int includeSubDomains:1;
  char expire[18]; /* YYYYMMDD HH:MM:SS [null-terminated] */
};

struct curl_index {
  size_t index; /* the provided entry's "index" or count */
  size_t total; /* total number of entries to save */
};

CURLSTScode hstswrite(CURL *easy, struct curl_hstsentry *sts,
                      struct curl_index *count, void *clientp);

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HSTSWRITEFUNCTION, hstswrite);

Pass a pointer to your callback function, as the prototype shows above.

This callback function gets called by libcurl repeatedly to allow the application to store the in-memory HSTS cache when libcurl is about to discard it.

Set the clientp argument with the CURLOPT_HSTSWRITEDATA(3) option or it is NULL. When the callback is invoked, the sts pointer points to a populated struct: Read the hostname to 'name' (it is namelen bytes long and null terminated. The includeSubDomains field is non-zero if the entry matches subdomains. The expire string is a date stamp null-terminated string using the syntax YYYYMMDD HH:MM:SS.

The callback should return CURLSTS_OK if it succeeded and is prepared to be called again (for another host) or CURLSTS_DONE if there is nothing more to do. It can also return CURLSTS_FAIL to signal error.

This option does not enable HSTS, you need to use CURLOPT_HSTS_CTRL(3) to do that.

NULL - no callback.

This functionality affects http only

struct priv {
  void *custom;
};

static CURLSTScode hswr_cb(CURL *easy, struct curl_hstsentry *sts,
                           struct curl_index *count, void *clientp)
{
  /* save the passed in HSTS data somewhere */
  return CURLSTS_OK;
}

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    struct priv my_stuff;
    CURLcode res;

    /* set HSTS read callback */
    curl_easy_setopt(curl, CURLOPT_HSTSWRITEFUNCTION, hswr_cb);

    /* pass in suitable argument to the callback */
    curl_easy_setopt(curl, CURLOPT_HSTSWRITEDATA, &my_stuff);

    res = curl_easy_perform(curl);
  }
}

Added in curl 7.74.0

This returns CURLE_OK.

CURLOPT_HSTS(3), CURLOPT_HSTSWRITEDATA(3), CURLOPT_HSTSWRITEFUNCTION(3), CURLOPT_HSTS_CTRL(3)

curl_easy_setopt(3), CURLOPT_HSTSREADDATA(3), CURLOPT_HSTSREADFUNCTION(3), CURLOPT_HSTSWRITEDATA(3), libcurl-symbols(3).