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CURLMOPT_SOCKETFUNCTION(3)          libcurl         CURLMOPT_SOCKETFUNCTION(3)


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 will be 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 will be aborted and fail.

       clientp is set with CURLMOPT_SOCKETDATA(3).

       socketp is set with curl_multi_assign(3) or will be 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

       All


EXAMPLE

       static int sock_cb(CURL *e, curl_socket_t s, int what, void *cbp, void *sockp)
       {
         GlobalInfo *g = cbp;
         SockInfo *fdp = sockp;

         if(what == CURL_POLL_REMOVE) {
           remsock(fdp);
         }
         else {
           if(!fdp) {
             addsock(s, e, what, g);
           }
           else {
             setsock(fdp, s, e, what, g);
           }
         }
         return 0;
       }

       main()
       {
         GlobalInfo setup;
         /* ... use socket callback and custom pointer */
         curl_multi_setopt(multi, CURLMOPT_SOCKETFUNCTION, sock_cb);
         curl_multi_setopt(multi, CURLMOPT_SOCKETDATA, &setup);
       }


AVAILABILITY

       Added in 7.15.4


RETURN VALUE

       Returns CURLM_OK.


SEE ALSO

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

ibcurl 8.1.2                    April 26, 2023      CURLMOPT_SOCKETFUNCTION(3)

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