do not close a socket that is already closed

See miguelgrinberg/Flask-SocketIO#312

engineio/socket.py

@@ -98,12 +98,13 @@ def handle_post_request(self, environ):
 
     def close(self, wait=True, abort=False):
         """Close the socket connection."""
-        self.server._trigger_event('disconnect', self.sid, async=False)
-        if not abort:
-            self.send(packet.Packet(packet.CLOSE))
-        self.closed = True
-        if wait:
-            self.queue.join()
+        if not self.closed:
+            self.server._trigger_event('disconnect', self.sid, async=False)
+            if not abort:
+                self.send(packet.Packet(packet.CLOSE))
+            self.closed = True
+            if wait:
+                self.queue.join()
 
     def _upgrade_websocket(self, environ, start_response):
         """Upgrade the connection from polling to websocket."""

tests/test_socket.py

@@ -356,6 +356,17 @@ def test_send_after_close(self):
         s.close(wait=False)
         self.assertRaises(IOError, s.send, packet.Packet(packet.NOOP))
 
+    def test_close_after_close(self):
+        mock_server = self._get_mock_server()
+        s = socket.Socket(mock_server, 'sid')
+        s.close(wait=False)
+        self.assertTrue(s.closed)
+        self.assertEqual(mock_server._trigger_event.call_count, 1)
+        mock_server._trigger_event.assert_called_once_with('disconnect', 'sid',
+                                                           async=False)
+        s.close()
+        self.assertEqual(mock_server._trigger_event.call_count, 1)
+
     def test_close_and_wait(self):
         mock_server = self._get_mock_server()
         s = socket.Socket(mock_server, 'sid')