**************************************************************************
* _ _ ____ _
* Project ___| | | | _ \| |
* / __| | | | |_) | |
* | (__| |_| | _ <| |___
* \___|\___/|_| \_\_____|
*
* Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
*
* This software is licensed as described in the file COPYING, which
* you should have received as part of this distribution. The terms
* are also available at https://curl.haxx.se/docs/copyright.html.
*
* You may opt to use, copy, modify, merge, publish, distribute and/or sell
* copies of the Software, and permit persons to whom the Software is
* furnished to do so, under the terms of the COPYING file.
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
**************************************************************************

CURLOPT_OPENSOCKETDATA - custom pointer passed to open socket callback #include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_OPENSOCKETDATA, void *pointer); Pass a pointer that will be untouched by libcurl and passed as the first argument in the opensocket callback set with CURLOPT_OPENSOCKETFUNCTION(3). The default value of this parameter is NULL. All

/* 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)
{
 /* This return code was added in libcurl 7.21.5 */
 return CURL_SOCKOPT_ALREADY_CONNECTED;
}

curl = curl_easy_init();
if(curl) {
 /* libcurl will internally think 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);

 res = curl_easy_perform(curl);

 curl_easy_cleanup(curl);
}

Added in 7.17.1 Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not. CURLOPT_OPENSOCKETFUNCTION "(3), " CURLOPT_SOCKOPTFUNCTION "(3), "