when someone follows the bot, but they're ineligible, reject their fo…

…llow

for #758 (comment)

https://www.w3.org/TR/activitypub/#reject-activity-inbox

protocol.py

@@ -1072,7 +1072,14 @@ def receive(from_cls, obj, authed_as=None, internal=False, received_at=None):
             if proto := Protocol.for_bridgy_subdomain(inner_obj_id):
                 # follow of one of our protocol bot users; enable that protocol.
                 # fall through so that we send an accept.
-                from_user.enable_protocol(proto)
+                try:
+                    from_user.enable_protocol(proto)
+                except ErrorButDoNotRetryTask:
+                    from web import Web
+                    bot = Web.get_by_id(proto.bot_user_id())
+                    from_cls.respond_to_follow('reject', follower=from_user,
+                                               followee=bot, follow=obj)
+                    raise
                 proto.bot_follow(from_user)
 
             from_cls.handle_follow(obj)
@@ -1167,34 +1174,37 @@ def handle_follow(from_cls, obj):
             follower_obj = Follower.get_or_create(to=to_user, from_=from_user,
                                                   follow=obj.key, status='active')
             obj.add('notify', to_key)
-            from_cls.maybe_accept_follow(follower=from_user, followee=to_user,
-                                         follow=obj)
+            from_cls.respond_to_follow('accept', follower=from_user,
+                                       followee=to_user, follow=obj)
 
     @classmethod
-    def maybe_accept_follow(_, follower, followee, follow):
-        """Sends an accept activity for a follow.
+    def respond_to_follow(_, verb, follower, followee, follow):
+        """Sends an accept or reject activity for a follow.
 
-        ...if the follower protocol handles accepts. Otherwise, does nothing.
+        ...if the follower's protocol supports accepts/rejects. Otherwise, does
+        nothing.
 
         Args:
-          follower: :class:`models.User`
-          followee: :class:`models.User`
-          follow: :class:`models.Object`
+          verb (str): ``accept`` or  ``reject``
+          follower (models.User)
+          followee (models.User)
+          follow (models.Object)
         """
-        if 'accept' not in follower.SUPPORTED_AS1_TYPES:
+        assert verb in ('accept', 'reject')
+        if verb not in follower.SUPPORTED_AS1_TYPES:
             return
 
         target = follower.target_for(follower.obj)
         if not target:
             error(f"Couldn't find delivery target for follower {follower.key.id()}")
 
-        # send accept. note that this is one accept for the whole
-        # follow, even if it has multiple followees!
-        id = f'{followee.key.id()}/followers#accept-{follow.key.id()}'
+        # send. note that this is one response for the whole follow, even if it
+        # has multiple followees!
+        id = f'{followee.key.id()}/followers#{verb}-{follow.key.id()}'
         accept = {
             'id': id,
             'objectType': 'activity',
-            'verb': 'accept',
+            'verb': verb,
             'actor': followee.key.id(),
             'object': follow.as1,
         }

tests/test_dms.py

@@ -64,12 +64,12 @@ def assert_replied(self, *args, **kwargs):
         kwargs.setdefault('in_reply_to', 'efake:dm')
         self.assert_sent(*args, **kwargs)
 
-    def assert_sent(self, from_cls, tos, type, text, in_reply_to=None):
+    def assert_sent(self, from_cls, tos, type, text, in_reply_to=None, strict=True):
         if not isinstance(tos, list):
             tos = [tos]
 
         from_id = f'{from_cls.ABBREV}.brid.gy'
-        for expected, (target, activity) in zip(tos, tos[-1].sent, strict=True):
+        for expected, (target, activity) in zip(tos, tos[-1].sent, strict=strict):
             id = expected.key.id()
             self.assertEqual(f'{id}:target', target)
             content = activity['object'].pop('content')

tests/test_protocol.py

@@ -3002,21 +3002,38 @@ def test_follow_bot_user_spam_filter_doesnt_enable(self):
         user = self.make_user('efake:user', cls=ExplicitFake)
         ExplicitFake.fetchable = {'efake:user': {'id': 'efake:user'}}
 
+        follow_as1 = {
+            'objectType': 'activity',
+            'verb': 'follow',
+            'id': 'efake:follow',
+            'actor': 'efake:user',
+            'object': 'efake:bot',
+        }
         with self.assertRaises(ErrorButDoNotRetryTask):
-            _, code = ExplicitFake.receive_as1({
-                'objectType': 'activity',
-                'verb': 'follow',
-                'id': 'efake:follow',
-                'actor': 'efake:user',
-                'object': 'efake:bot',
-            })
+            _, code = ExplicitFake.receive_as1(follow_as1)
 
         user = user.key.get()
         self.assertEqual('requires-name', user.status)
         self.assertFalse(user.is_enabled(Fake))
         self.assertEqual(['efake:user'], ExplicitFake.fetched)
 
-        test_dms.DmsTest().assert_sent(Fake, user, 'requires-name', "Hi! Your account isn't eligible for bridging yet because you haven't set a profile name that's different from your username.")
+        self.assertEqual(2, len(ExplicitFake.sent))
+        test_dms.DmsTest().assert_sent(
+            Fake, user, 'requires-name',
+            "Hi! Your account isn't eligible for bridging yet because you haven't set a profile name that's different from your username.",
+            strict=False)
+        self.assertEqual(('efake:user:target', {
+            'objectType': 'activity',
+            'verb': 'reject',
+            'id': 'fa.brid.gy/followers#reject-efake:follow',
+            'actor': 'fa.brid.gy',
+            'object': {
+                **follow_as1,
+                'actor': {'id': 'efake:user'},
+                'object': 'fa.brid.gy',
+            },
+        }), ExplicitFake.sent[1])
+
 
     @patch.object(Fake, 'owns_handle', return_value=False)
     @patch.object(ExplicitFake, 'owns_handle', return_value=True)
@@ -3027,18 +3044,35 @@ def test_follow_bot_user_unsupported_handle(self, _, __):
         user = self.make_user('efake:user-nope', cls=ExplicitFake)
         ExplicitFake.fetchable = {'efake:user-nope': {'id': 'efake:user-nope'}}
 
+        follow_as1 = {
+            'objectType': 'activity',
+            'verb': 'follow',
+            'id': 'efake:follow',
+            'actor': 'efake:user-nope',
+            'object': 'efake:bot',
+        }
         with self.assertRaises(ErrorButDoNotRetryTask):
-            _, code = ExplicitFake.receive_as1({
-                'objectType': 'activity',
-                'verb': 'follow',
-                'id': 'efake:follow',
-                'actor': 'efake:user-nope',
-                'object': 'efake:bot',
-            })
+            _, code = ExplicitFake.receive_as1(follow_as1)
 
         user = user.key.get()
         self.assertFalse(user.is_enabled(Fake))
-        test_dms.DmsTest().assert_sent(Fake, user, 'unsupported-handle-fa', "Hi! Your account isn't eligible for bridging yet because efake:handle:user-nope translated to fake-phrase is fake:handle:efake:handle:user-nope, which isn't supported there.")
+
+        self.assertEqual(2, len(ExplicitFake.sent))
+        test_dms.DmsTest().assert_sent(
+            Fake, user, 'unsupported-handle-fa',
+            "Hi! Your account isn't eligible for bridging yet because efake:handle:user-nope translated to fake-phrase is fake:handle:efake:handle:user-nope, which isn't supported there.",
+            strict=False)
+        self.assertEqual(('efake:user-nope:target', {
+            'objectType': 'activity',
+            'verb': 'reject',
+            'id': 'fa.brid.gy/followers#reject-efake:follow',
+            'actor': 'fa.brid.gy',
+            'object': {
+                **follow_as1,
+                'actor': {'id': 'efake:user-nope'},
+                'object': 'fa.brid.gy',
+            },
+        }), ExplicitFake.sent[1])
 
     def test_block_then_follow_protocol_user_recreates_copy(self):
         # bot user