don't automatically accept follows from protocols that support them natively

for #710. adds per-protocol `HAS_FOLLOW_ACCEPTS` constant

activitypub.py

@@ -63,6 +63,7 @@ class ActivityPub(User, Protocol):
     ABBREV = 'ap'
     LOGO_HTML = '<img src="/static/fediverse_logo.svg">'
     CONTENT_TYPE = as2.CONTENT_TYPE
+    HAS_FOLLOW_ACCEPTS = True
 
     def _pre_put_hook(self):
         """Validate id, require URL, don't allow Bridgy Fed domains.

protocol.py

@@ -60,11 +60,14 @@ class Protocol:
       LOGO_HTML (str): logo emoji or ``<img>`` tag
       CONTENT_TYPE (str): MIME type of this protocol's native data format,
         appropriate for the ``Content-Type`` HTTP header.
+      HAS_FOLLOW_ACCEPTS (bool): whether this protocol supports explicit
+        accept/reject activities in response to follows, eg ActivityPub
     """
     ABBREV = None
     OTHER_LABELS = ()
     LOGO_HTML = ''
     CONTENT_TYPE = None
+    HAS_FOLLOW_ACCEPTS = False
 
     def __init__(self):
         assert False
@@ -798,24 +801,25 @@ class Protocol:
                                                   follow=obj.key, status='active')
             obj.add('notify', to_key)
 
-            # send accept. note that this is one accept for the whole follow, even
-            # if it has multiple followees!
-            id = to_user.ap_actor(f'followers#accept-{obj.key.id()}')
-            accept = Object.get_or_create(id, our_as1={
-                'id': id,
-                'objectType': 'activity',
-                'verb': 'accept',
-                'actor': to_id,
-                'object': obj.as1,
-            })
+            if not to_user.HAS_FOLLOW_ACCEPTS:
+                # send accept. note that this is one accept for the whole
+                # follow, even if it has multiple followees!
+                id = to_user.ap_actor(f'followers#accept-{obj.key.id()}')
+                accept = Object.get_or_create(id, our_as1={
+                    'id': id,
+                    'objectType': 'activity',
+                    'verb': 'accept',
+                    'actor': to_id,
+                    'object': obj.as1,
+                })
 
-            sent = from_cls.send(accept, from_target, from_user=to_user)
-            if sent:
-                accept.populate(
-                    delivered=[Target(protocol=from_cls.LABEL, uri=from_target)],
-                    status='complete',
-                )
-                accept.put()
+                sent = from_cls.send(accept, from_target, from_user=to_user)
+                if sent:
+                    accept.populate(
+                        delivered=[Target(protocol=from_cls.LABEL, uri=from_target)],
+                        status='complete',
+                    )
+                    accept.put()
 
     @classmethod
     def handle_bare_object(cls, obj):

tests/test_protocol.py

@@ -1317,6 +1317,33 @@ class ProtocolReceiveTest(TestCase):
             ignore=['created', 'updated'],
         )
 
+    def test_follow_with_accepts_protocol(self, **extra):
+        OtherFake.fetchable['other:user'] = {}
+
+        follow_as1 = {
+            'id': 'fake:follow',
+            'objectType': 'activity',
+            'verb': 'follow',
+            'actor': 'fake:alice',
+            'object': 'other:user',
+        }
+        self.assertEqual(('OK', 202), Fake.receive_as1(follow_as1))
+
+        other = OtherFake.get_by_id('other:user')
+        follow_obj = self.assert_object('fake:follow',
+                                        our_as1=follow_as1,
+                                        status='complete',
+                                        users=[self.alice.key],
+                                        notify=[other.key],
+                                        delivered=['other:user:target'],
+                                        delivered_protocol='other',
+                                        )
+
+        self.assertIsNone(Object.get_by_id(
+            'https://fa.brid.gy/ap/other:user/followers#accept-fake:follow'))
+        self.assertEqual(0, Object.query(Object.type == 'accept').count())
+        self.assertEqual([], Fake.sent)
+
     def test_follow_no_actor(self):
         with self.assertRaises(BadRequest):
             Fake.receive_as1({

tests/testutil.py

@@ -150,6 +150,7 @@ class OtherFake(Fake):
     """Different class because the same-protocol check special cases Fake."""
     LABEL = ABBREV = 'other'
     CONTENT_TYPE = 'ot/her'
+    HAS_FOLLOW_ACCEPTS = True
 
     fetchable = {}
     sent = []