NAME

       CURLOPT_OPENSOCKETFUNCTION - set callback for opening sockets

SYNOPSIS

       #include <curl/curl.h>

       typedef enum  {
         CURLSOCKTYPE_IPCXN,  /* socket created for a specific IP connection */
         CURLSOCKTYPE_ACCEPT, /* socket created by accept() call */
         CURLSOCKTYPE_LAST    /* never use */
       } 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);

DESCRIPTION

       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 CURLSOCKTYPE_ACCEPT is for sockets
       created after accept() - such as when doing active FTP. 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 blacklisting.

       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.

DEFAULT

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

PROTOCOLS

       All

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)
       {
         /* 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);
       }

AVAILABILITY

       Added in 7.17.1.

RETURN VALUE

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

SEE ALSO

       CURLOPT_OPENSOCKETDATA(3), CURLOPT_SOCKOPTFUNCTION(3), CURLOPT_CLOSESOCKETFUNCTION(3),