Fix notify_decorator errors

* getattr is built-in function, so should not be used as attribute.
* When ctxt is None, rpc.get_notifier('api').info(ctxt, name, body)
  leads NoneType exception at context.to_dict(). So we need guarantee
  one valid context here.

Closes-Bug: #1476931

Change-Id: I25953467aca641448d25b2d63352f756ec3655aa

nova/notifications.py

@@ -80,14 +80,16 @@ def notify_decorator(name, fn):
         for key in kwarg:
             body['kwarg'][key] = kwarg[key]
 
-        ctxt = common_context.get_context_from_function_and_args(
-            fn, args, kwarg)
+        ctxt = (common_context.get_context_from_function_and_args(
+                    fn, args, kwarg) or
+                common_context.get_current() or
+                nova.context.RequestContext())
 
         notifier = rpc.get_notifier('api',
                                     publisher_id=(CONF.default_publisher_id
                                                   or CONF.host))
-        method = notifier.getattr(CONF.default_notification_level.lower(),
-                                  'info')
+        method = getattr(notifier, CONF.default_notification_level.lower(),
+                         'info')
         method(ctxt, name, body)
 
         return fn(*args, **kwarg)

nova/tests/unit/test_notifications.py

@@ -70,6 +70,8 @@ class NotificationsTestCase(test.TestCase):
 
         self.instance = self._wrapped_create()
 
+        self.decorated_function_called = False
+
     def _wrapped_create(self, params=None):
         instance_type = flavors.get_flavor_by_name('m1.tiny')
         inst = objects.Instance(image_ref=1,
@@ -462,6 +464,28 @@ class NotificationsTestCase(test.TestCase):
         self.assertEqual(0, len(fake_notifier.NOTIFICATIONS))
         self.assertEqual(0, mock_log_exception.call_count)
 
+    def _decorated_function(self, arg1, arg2):
+        self.decorated_function_called = True
+
+    def test_notify_decorator(self):
+        func_name = self._decorated_function.__name__
+
+        # Decorated with notify_decorator like monkey_patch
+        self._decorated_function = notifications.notify_decorator(
+            func_name,
+            self._decorated_function)
+
+        ctxt = o_context.RequestContext()
+
+        self._decorated_function(1, ctxt)
+
+        self.assertEqual(1, len(fake_notifier.NOTIFICATIONS))
+        n = fake_notifier.NOTIFICATIONS[0]
+        self.assertEqual(n.priority, 'INFO')
+        self.assertEqual(n.event_type, func_name)
+        self.assertEqual(n.context, ctxt)
+        self.assertTrue(self.decorated_function_called)
+
 
 class NotificationsFormatTestCase(test.NoDBTestCase):