CURLMOPT_SOCKETFUNCTION(3)                           curl_multi_setopt options

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 *userp,     /* 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 _multi_socket_action&section=3">curl_multi_socket_action(3) function is called, it informs 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.

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.

       userp is set with _SOCKETDATA&section=3">CURLMOPT_SOCKETDATA(3).

       socketp is set with _multi_assign&section=3">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.

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 = (GlobalInfo*) cbp;
         SockInfo *fdp = (SockInfo*) 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)

libcurl 7.77.0                 November 4, 2020     CURLMOPT_SOCKETFUNCTION(3)