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CURLMOPT_SOCKETFUNCTION

Section: curl_multi_setopt options (3)
Updated: May 31, 2017
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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 curl_multi_socket_action(3) function runs, 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 gets status updates with changes since the previous time the callback was called. If the given callback pointer is NULL, no callback will be called. Set the callback's userp argument with CURLMOPT_SOCKETDATA(3). See curl_multi_socket_action(3) for more details on how the callback is used and should work.

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.