NAME

       CURLOPT_SOCKOPTFUNCTION - callback for setting socket options

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;

       #define CURL_SOCKOPT_OK 0
       #define CURL_SOCKOPT_ERROR 1 /* causes libcurl to abort and return
                                       CURLE_ABORTED_BY_CALLBACK */
       #define CURL_SOCKOPT_ALREADY_CONNECTED 2

       int sockopt_callback(void *clientp,
                            curl_socket_t curlfd,
                            curlsocktype purpose);

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SOCKOPTFUNCTION, sockopt_callback);

DESCRIPTION

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

       When  set, this callback function gets called by libcurl when the socket has been created,
       but before the connect call to allow applications to change specific socket  options.  The
       callback's purpose argument identifies the exact purpose for this particular socket:

       CURLSOCKTYPE_IPCXN  for  actively  created connections or since 7.28.0 CURLSOCKTYPE_ACCEPT
       for FTP when the connection was setup with PORT/EPSV (in earlier  versions  these  sockets
       were not passed to this callback).

       Future  versions  of  libcurl  may support more purposes. libcurl passes the newly created
       socket descriptor to the callback in the curlfd parameter so additional setsockopt() calls
       can be done at the user's discretion.

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

       Return CURL_SOCKOPT_OK from the callback on success. Return  CURL_SOCKOPT_ERROR  from  the
       callback function to signal an unrecoverable error to the library and it closes the socket
       and  returns  CURLE_COULDNT_CONNECT.  Alternatively,  the  callback  function  can  return
       CURL_SOCKOPT_ALREADY_CONNECTED,  to  tell libcurl that the socket is already connected and
       then libcurl does no attempt to connect. This allows an application to pass in an  already
       connected  socket  with  CURLOPT_OPENSOCKETFUNCTION(3)  and  then  have this function make
       libcurl not attempt to connect (again).

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

       int main(void)
       {
         CURL *curl = curl_easy_init();
         if(curl) {
           CURLcode res;
           int sockfd; /* our custom file descriptor */
           /* 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);

           res = curl_easy_perform(curl);

           curl_easy_cleanup(curl);
         }
       }

AVAILABILITY

       Added in curl 7.16.0

RETURN VALUE

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

SEE ALSO

       CURLOPT_OPENSOCKETFUNCTION(3), CURLOPT_SEEKFUNCTION(3), CURLOPT_SOCKOPTDATA(3)