do not allow callbacks outside of a server context

socketio/pubsub_manager.py

@@ -46,6 +46,9 @@ class PubSubManager(BaseManager):
         """
         namespace = namespace or '/'
         if callback is not None:
+            if self.server is None:
+                raise RuntimeError('Callbacks can only be issued from the '
+                                   'context of a server.')
             if room is None:
                 raise ValueError('Cannot use callback without a room set.')
             id = self._generate_ack_id(room, namespace, callback)

tests/test_pubsub_manager.py

@@ -66,6 +66,11 @@ class TestBaseManager(unittest.TestCase):
                  'namespace': '/', 'room': 'baz', 'skip_sid': None,
                  'callback': ('baz', '/', '123')})
 
+    def test_emit_with_callback_without_server(self):
+        standalone_pm = pubsub_manager.PubSubManager()
+        self.assertRaises(RuntimeError, standalone_pm.emit, 'foo', 'bar',
+                          callback='cb')
+
     def test_emit_with_callback_missing_room(self):
         with mock.patch.object(self.pm, '_generate_ack_id',
                                return_value='123'):