Provided by: libcurl4-doc_7.88.1-8ubuntu1_all bug


       CURLOPT_OPENSOCKETFUNCTION - callback for opening socket


       #include <curl/curl.h>

       typedef enum  {
         CURLSOCKTYPE_IPCXN,  /* socket created for a specific IP connection */
       } curlsocktype;

       struct curl_sockaddr {
         int family;
         int socktype;
         int protocol;
         unsigned int addrlen;
         struct sockaddr addr;

       curl_socket_t opensocket_callback(void *clientp,
                                         curlsocktype purpose,
                                         struct curl_sockaddr *address);

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_OPENSOCKETFUNCTION, opensocket_callback);


       Pass a pointer to your callback function, which should match the prototype shown above.

       This  callback  function  gets  called  by  libcurl  instead  of  the  socket(2) call. The
       callback's purpose argument identifies the  exact  purpose  for  this  particular  socket.
       CURLSOCKTYPE_IPCXN  is  for IP based connections and is the only purpose currently used in
       libcurl. Future versions of libcurl may support more purposes.

       The   clientp   pointer   contains   whatever   user-defined   value   set    using    the
       CURLOPT_OPENSOCKETDATA(3) function.

       The  callback  gets  the  resolved  peer address as the address argument and is allowed to
       modify the address or refuse to connect completely. The callback  function  should  return
       the  newly created socket or CURL_SOCKET_BAD in case no connection could be established or
       another error was detected. Any additional setsockopt(2) calls can of course  be  done  on
       the  socket  at  the  user's discretion.  A CURL_SOCKET_BAD return value from the callback
       function  will  signal  an  unrecoverable  error   to   libcurl   and   it   will   return
       CURLE_COULDNT_CONNECT  from  the  function that triggered this callback.  This return code
       can be used for IP address block listing.

       If you want to pass in a socket with an already established connection,  pass  the  socket
       back  with this callback and then use CURLOPT_SOCKOPTFUNCTION(3) to signal that it already
       is connected.


       The default behavior is the equivalent of this:
          return socket(addr->family, addr->socktype, addr->protocol);




       /* 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 */

       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, "");
         /* 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);



       Added in 7.17.1.


       Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.