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.

       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)