NAME

       CURLMOPT_SOCKETFUNCTION - callback informed about what to wait for

SYNOPSIS

       #include <curl/curl.h>

       int socket_callback(CURL *easy,      /* easy handle */
                           curl_socket_t s, /* socket */
                           int what,        /* describes the socket */
                           void *clientp,   /* private callback pointer */
                           void *socketp);  /* private socket pointer */

       CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_SOCKETFUNCTION, socket_callback);

DESCRIPTION

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

       When  the  curl_multi_socket_action(3) function is called, it uses this callback to inform
       the application about updates in the socket (file descriptor) status by doing  none,  one,
       or  multiple  calls to the socket_callback. The callback function gets status updates with
       changes since the previous time the callback was called. If the given callback pointer  is
       set to NULL, no callback is called.

       libcurl  then  expects  the application to monitor the sockets for the specific activities
       and tell libcurl again when something happens on one of  them.  Tell  libcurl  by  calling
       curl_multi_socket_action(3).

CALLBACK ARGUMENTS

       easy  identifies  the  specific  transfer  for  which  this update is related.  Since this
       callback manages a whole multi handle, an application should not  make  assumptions  about
       which particular handle that is passed here. It might even be an internal easy handle that
       the application did not add itself.

       s is the specific socket this function invocation concerns. If the what  argument  is  not
       CURL_POLL_REMOVE  then  it  holds  information  about  what  activity  on  this socket the
       application is supposed to monitor. Subsequent calls to this  callback  might  update  the
       what bits for a socket that is already monitored.

       The  socket callback should return 0 on success, and -1 on error. If this callback returns
       error, all transfers currently in progress in this multi handle are aborted  and  made  to
       fail.

       clientp is set with CURLMOPT_SOCKETDATA(3).

       socketp is set with curl_multi_assign(3) or NULL.

       The what parameter informs the callback on the status of the given socket. It can hold one
       of these values:

       CURL_POLL_IN
              Wait for incoming data. For the socket to become readable.

       CURL_POLL_OUT
              Wait for outgoing data. For the socket to become writable.

       CURL_POLL_INOUT
              Wait for incoming and outgoing data. For the socket to become readable or writable.

       CURL_POLL_REMOVE
              The specified socket/file descriptor is no longer used by libcurl  for  any  active
              transfer. It might soon be added again.

DEFAULT

       NULL (no callback)

PROTOCOLS

       This functionality affects all supported protocols

EXAMPLE

       struct priv {
         void *ours;
       };

       static int sock_cb(CURL *e, curl_socket_t s, int what, void *cbp, void *sockp)
       {
         struct priv *p = sockp;
         printf("our ptr: %p\n", p->ours);

         if(what == CURL_POLL_REMOVE) {
           /* remove the socket from our collection */
         }
         if(what & CURL_POLL_IN) {
           /* wait for read on this socket */
         }
         if(what & CURL_POLL_OUT) {
           /* wait for write on this socket */
         }

         return 0;
       }

       int main(void)
       {
         struct priv setup;
         CURLM *multi = curl_multi_init();
         /* ... use socket callback and custom pointer */
         curl_multi_setopt(multi, CURLMOPT_SOCKETFUNCTION, sock_cb);
         curl_multi_setopt(multi, CURLMOPT_SOCKETDATA, &setup);
       }

AVAILABILITY

       Added in curl 7.15.4

RETURN VALUE

       Returns CURLM_OK.

SEE ALSO

       CURLMOPT_SOCKETDATA(3), CURLMOPT_TIMERFUNCTION(3), curl_multi_socket_action(3)