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CURLOPT_OPENSOCKETDATA(3)   Library Functions Manual   CURLOPT_OPENSOCKETDATA(3)

NAME
     CURLOPT_OPENSOCKETDATA - pointer passed to open socket callback

SYNOPSIS
     #include <curl/curl.h>

     CURLcode curl_easy_setopt(CURL *handle, CURLOPT_OPENSOCKETDATA, void *pointer);

DESCRIPTION
     Pass  a  pointer that is untouched by libcurl and passed as the first argu-
     ment in the open socket callback set with CURLOPT_OPENSOCKETFUNCTION(3).

DEFAULT
     NULL

PROTOCOLS
     This functionality affects all supported protocols

EXAMPLE
     /* make libcurl use the already established socket 'sockfd' */

     static curl_socket_t opensocket(void *clientp,
				     curlsocktype purpose,
				     struct curl_sockaddr *address)
     {
       curl_socket_t sockfd;
       sockfd = *(curl_socket_t *)clientp;
       /* the actual externally set socket is passed in via the OPENSOCKETDATA
	  option */
       return sockfd;
     }

     static int sockopt_callback(void *clientp, curl_socket_t curlfd,
				 curlsocktype purpose)
     {
       return CURL_SOCKOPT_ALREADY_CONNECTED;
     }

     int main(void)
     {
       CURL *curl = curl_easy_init();
       if(curl) {
	 CURLcode result;
	 extern int sockfd; /* the already connected one */

	 /* libcurl thinks that you connect to the host
	  * and port that you specify in the URL option. */
	 curl_easy_setopt(curl, CURLOPT_URL, "http://99.99.99.99:9999");
	 /* call this function to get a socket */
	 curl_easy_setopt(curl, CURLOPT_OPENSOCKETFUNCTION, opensocket);
	 curl_easy_setopt(curl, CURLOPT_OPENSOCKETDATA, &sockfd);

	 /* call this function to set options for the socket */
	 curl_easy_setopt(curl, CURLOPT_SOCKOPTFUNCTION, sockopt_callback);

	 result = curl_easy_perform(curl);

	 curl_easy_cleanup(curl);
       }
     }

AVAILABILITY
     Added in curl 7.17.1

RETURN VALUE
     curl_easy_setopt(3) returns a CURLcode indicating success or error.

     CURLE_OK (0) means everything was OK, non-zero means an error occurred, see
     libcurl-errors(3).

SEE ALSO
     CURLOPT_CLOSESOCKETFUNCTION(3),	 CURLOPT_OPENSOCKETFUNCTION(3),     CUR-
     LOPT_SOCKOPTFUNCTION(3)

libcurl 			   2026-06-11	       CURLOPT_OPENSOCKETDATA(3)

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