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.TH CURLMOPT_SOCKETFUNCTION 3 "3 Nov 2016" "libcurl 7.39.0" "curl_multi_setopt options"
.SH NAME
CURLMOPT_SOCKETFUNCTION \- callback informed about what to wait for
.SH SYNOPSIS
.nf
#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);
.SH DESCRIPTION
Pass a pointer to your callback function, which should match the prototype
shown above.

When the \fIcurl_multi_socket_action(3)\fP function is called, it informs the
application about updates in the socket (file descriptor) status by doing
none, one, or multiple calls to the \fBsocket_callback\fP. 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.
.SH "CALLBACK ARGUMENTS"
\fIeasy\fP identifies the specific transfer for which this update is related.

\fIs\fP is the specific socket this function invocation concerns. If the
\fBwhat\fP 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 \fBwhat\fP bits
for a socket that is already monitored.

\fBuserp\fP is set with \fICURLMOPT_SOCKETDATA(3)\fP.

\fBsocketp\fP is set with \fIcurl_multi_assign(3)\fP or will be NULL.

The \fBwhat\fP parameter informs the callback on the status of the given
socket. It can hold one of these values:
.IP CURL_POLL_IN
Wait for incoming data. For the socket to become readable.
.IP CURL_POLL_OUT
Wait for outgoing data. For the socket to become writable.
.IP CURL_POLL_INOUT
Wait for incoming and outgoing data. For the socket to become readable or
writable.
.IP CURL_POLL_REMOVE
The specified socket/file descriptor is no longer used by libcurl.
.SH DEFAULT
NULL (no callback)
.SH PROTOCOLS
All
.SH EXAMPLE
.nf
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);
}
.fi
.SH AVAILABILITY
Added in 7.15.4
.SH RETURN VALUE
Returns CURLM_OK.
.SH "SEE ALSO"
.BR CURLMOPT_SOCKETDATA "(3), " curl_multi_socket_action "(3), "
.BR CURLMOPT_TIMERFUNCTION "(3) "