Protocol.receive: following protocol user enables that protocol

for #880

protocol.py

@@ -800,13 +800,12 @@ def receive(from_cls, obj, authed_as=None, internal=False):
                 return 'OK', 200
 
             @ndb.transactional()
-            def block():
-                nonlocal from_user
-                from_user = from_user.key.get()
-                remove(from_user.enabled_protocols, proto.LABEL)
-                from_user.put()
+            def disable_protocol():
+                user = from_user.key.get()
+                remove(user.enabled_protocols, proto.LABEL)
+                user.put()
 
-            block()
+            disable_protocol()
             return 'OK', 200
 
         # fetch actor if necessary
@@ -832,6 +831,18 @@ def block():
                 }
 
         if obj.type == 'follow':
+            proto = Protocol.for_bridgy_subdomain(inner_obj_id)
+            if proto:
+                # follow of one of our protocol users; enable that protocol
+                @ndb.transactional()
+                def enable_protocol():
+                    user = from_user.key.get()
+                    add(user.enabled_protocols, proto.LABEL)
+                    user.put()
+
+                enable_protocol()
+                return 'OK', 200
+
             from_cls.handle_follow(obj)
 
         # deliver to targets

tests/test_activitypub.py

@@ -1200,9 +1200,9 @@ def test_inbox_unsupported_type(self, mock_head, mock_get, mock_post):
         got = self.post('/user.com/inbox', json={
             '@context': ['https://www.w3.org/ns/activitystreams'],
             'id': 'https://xoxo.zone/users/aaronpk#follows/40',
-            'type': 'Block',
+            'type': 'Arrive',
             'actor': 'https://xoxo.zone/users/aaronpk',
-            'object': 'http://snarfed.org/',
+            'object': 'http://a/place',
         })
         self.assertEqual(501, got.status_code)
 

tests/test_protocol.py

@@ -1779,7 +1779,14 @@ def test_resolve_ids_reply(self):
             }],
         }, obj.key.get().our_as1)
 
-    def test_block_protocol_user_removes_from_enabled_protocols(self):
+    def test_follow_and_block_protocol_user_adds_and_removes_enabled_protocols(self):
+        follow = {
+            'objectType': 'activity',
+            'verb': 'follow',
+            'id': 'eefake:follow',
+            'actor': 'eefake:user',
+            'object': 'fa.brid.gy',
+        }
         block = {
             'objectType': 'activity',
             'verb': 'block',
@@ -1791,16 +1798,24 @@ def test_block_protocol_user_removes_from_enabled_protocols(self):
         user = self.make_user('eefake:user', cls=ExplicitEnableFake)
         self.assertFalse(ExplicitEnableFake.is_enabled_to(Fake, user))
 
-        # protocol isn't enabled yet, block is a noop
+        # protocol isn't enabled yet, block should be a noop
         self.assertEqual(('OK', 200), ExplicitEnableFake.receive_as1(block))
         user = user.key.get()
         self.assertEqual([], user.enabled_protocols)
 
-        # enable protocol, now block should remove it
-        user.enabled_protocols = ['fake']
-        user.put()
+        # follow should add to enabled_protocols
+        self.assertEqual(('OK', 200), ExplicitEnableFake.receive_as1(follow))
+        user = user.key.get()
+        self.assertEqual(['fake'], user.enabled_protocols)
         self.assertTrue(ExplicitEnableFake.is_enabled_to(Fake, user))
 
+        # another follow should be a noop
+        follow['id'] += '2'
+        self.assertEqual(('OK', 200), ExplicitEnableFake.receive_as1(follow))
+        user = user.key.get()
+        self.assertEqual(['fake'], user.enabled_protocols)
+
+        # block should remove from enabled_protocols
         block['id'] += '2'
         self.assertEqual(('OK', 200), ExplicitEnableFake.receive_as1(block))
         user = user.key.get()