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CURLOPT_HSTSREADFUNCTION(3) Library Functions Manual CURLOPT_HSTSREADFUNCTION(3)

NAME
     CURLOPT_HSTSREADFUNCTION - read callback for HSTS hosts

SYNOPSIS
     #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] */
     };

     CURLSTScode hstsread(CURL *easy, struct curl_hstsentry *sts, void *clientp);

     CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HSTSREADFUNCTION, hstsread);

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

     This  callback function gets called by libcurl repeatedly when it populates
     the in-memory HSTS cache.

     Set the clientp argument with the CURLOPT_HSTSREADDATA(3) option or  it  is
     NULL.

     When  this  callback  is  invoked,  the  sts  pointer points to a populated
     struct: Copy the hostname to name (no longer than namelen bytes).	Make  it
     null-terminated.  Set  includeSubDomains  to TRUE or FALSE. Set expire to a
     date stamp or a zero length string for forever  (wrong  date  stamp  format
     might cause the name to not get accepted)

     The  callback should return CURLSTS_OK if it returns a name and is prepared
     to be called again (for another host) or CURLSTS_DONE if it has no entry to
     return. It can also return CURLSTS_FAIL to signal	error.	Returning  CURL-
     STS_FAIL	 stops	  the	transfer   from   being   performed   and   make
     CURLE_ABORTED_BY_CALLBACK get returned.

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

     The hostname provided to libcurl should not have a trailing dot nor leading
     dot.

DEFAULT
     NULL - no callback.

PROTOCOLS
     This functionality affects http only

EXAMPLE
     struct priv {
       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();
       if(curl) {
	 struct priv my_stuff;
	 CURLcode result;

	 curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

	 /* set HSTS read callback */
	 curl_easy_setopt(curl, CURLOPT_HSTSREADFUNCTION, hsts_cb);

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

	 result = curl_easy_perform(curl);
       }
     }

AVAILABILITY
     Added in curl 7.74.0

RETURN VALUE
     This returns CURLE_OK.

SEE ALSO
     CURLOPT_HSTS(3),	CURLOPT_HSTSREADDATA(3),   CURLOPT_HSTSWRITEFUNCTION(3),
     CURLOPT_HSTS_CTRL(3)

libcurl 			   2026-06-11	     CURLOPT_HSTSREADFUNCTION(3)

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