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CURLOPT_OPENSOCKETFUNCTION(3)       libcurl      CURLOPT_OPENSOCKETFUNCTION(3)

NAME
       CURLOPT_OPENSOCKETFUNCTION - callback for opening socket

SYNOPSIS
       #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);

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 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.

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),

ibcurl 8.1.2                    April 26, 2023   CURLOPT_OPENSOCKETFUNCTION(3)