Verify the value of the "void *s" passed to the monitor function.

This formerly unused parameter actually represents the socket
on which the event was received. As such, we should check that
its value makes sense: it must be either "rep" or "req", and in
the case of some kinds of events, it must be specifically one
or the other.

After this change, "s" is no longer unused.

tests/test_monitor.cpp

@@ -28,29 +28,38 @@
 
 static int events;
 
-void socket_monitor (void *s, int event_, zmq_event_data_t *data_)
+typedef void *ZmqSocket;
+ZmqSocket rep, req;
+
+void socket_monitor (ZmqSocket s, int event_, zmq_event_data_t *data_)
 {
+    assert(s == rep || s == req);
+
     const char *addr = "tcp://127.0.0.1:5560";
     // Only some of the exceptional events could fire
     switch (event_) {
     // listener specific
     case ZMQ_EVENT_LISTENING:
+        assert (s == rep);
         assert (data_->listening.fd > 0);
         assert (!strcmp (data_->listening.addr, addr));
         events |= ZMQ_EVENT_LISTENING;
         break;
     case ZMQ_EVENT_ACCEPTED:
+        assert (s == rep);
         assert (data_->accepted.fd > 0);
         assert (!strcmp (data_->accepted.addr, addr));
         events |= ZMQ_EVENT_ACCEPTED;
         break;
     // connecter specific
     case ZMQ_EVENT_CONNECTED:
+        assert (s == req);
         assert (data_->connected.fd > 0);
         assert (!strcmp (data_->connected.addr, addr));
         events |= ZMQ_EVENT_CONNECTED;
         break;
     case ZMQ_EVENT_CONNECT_DELAYED:
+        assert (s == req);
         assert (data_->connect_delayed.err != 0);
         assert (!strcmp (data_->connect_delayed.addr, addr));
         events |= ZMQ_EVENT_CONNECT_DELAYED;
@@ -77,7 +86,7 @@ void socket_monitor (void *s, int event_, zmq_event_data_t *data_)
     }
 }
 
-int main (int argc, char *argv [])
+int main (void)
 {
     int rc;
 
@@ -87,13 +96,13 @@ int main (int argc, char *argv [])
     // set socket monitor
     rc = zmq_ctx_set_monitor (ctx, socket_monitor);
     assert (rc == 0);
-    void *rep = zmq_socket (ctx, ZMQ_REP);
+    rep = zmq_socket (ctx, ZMQ_REP);
     assert (rep);
 
     rc = zmq_bind (rep, "tcp://127.0.0.1:5560");
     assert (rc == 0);
 
-    void *req = zmq_socket (ctx, ZMQ_REQ);
+    req = zmq_socket (ctx, ZMQ_REQ);
     assert (req);
 
     rc = zmq_connect (req, "tcp://127.0.0.1:5560");