send follow accepts to protocols that support them

for #710

protocol.py

@@ -641,8 +641,13 @@ class Protocol:
         actor_id = actor.get('id')
 
         # handle activity!
-        if obj.type == 'accept':  # eg in response to a Follow
-            return 'OK'  # noop
+
+        # accept, eg in response to a follow. only send if the destination
+        # supports accepts.
+        if obj.type == 'accept':
+            to_cls = Protocol.for_id(inner_obj_id)
+            if not to_cls or not to_cls.HAS_FOLLOW_ACCEPTS:
+                return 'OK'  # noop
 
         elif obj.type == 'stop-following':
             # TODO: unify with handle_follow?

tests/test_protocol.py

@@ -1381,6 +1381,35 @@ class ProtocolReceiveTest(TestCase):
         self.assertEqual([], Follower.query().fetch())
         self.assertEqual([], Fake.sent)
 
+    def test_accept_noop(self, **extra):
+        eve = self.make_user('other:eve', cls=OtherFake)
+        accept_as1 = {
+            'id': 'other:accept',
+            'objectType': 'activity',
+            'verb': 'accept',
+            'actor': 'other:eve',
+            'object': 'fake:follow'
+        }
+
+        self.assertEqual('OK', OtherFake.receive_as1(accept_as1))
+        self.assertEqual([], Fake.sent)
+        self.assertEqual([], OtherFake.sent)
+
+    def test_accept_with_has_accepts_protocol(self, **extra):
+        OtherFake.fetchable['other:follow'] = {'id': 'other:follow'}
+        accept_as1 = {
+            'id': 'fake:accept',
+            'objectType': 'activity',
+            'verb': 'accept',
+            'actor': 'fake:alice',
+            'object': 'other:follow'
+        }
+
+        self.assertEqual(('OK', 202), Fake.receive_as1(accept_as1))
+        self.assertEqual([
+            ('fake:accept', 'other:follow:target'),
+        ], OtherFake.sent)
+
     def test_stop_following(self):
         follower = Follower.get_or_create(to=self.user, from_=self.alice)