AP: strip Link attachments since fedi instances generate their own link previews

hopefully fixes #958

activitypub.py

@@ -664,12 +664,18 @@ def postprocess_as2(activity, orig_obj=None, wrap=True):
     # https://chrisbeckstrom.com/2018/12/27/32551/
     # assert activity.get('id') or (isinstance(obj, dict) and obj.get('id'))
 
+    # drop Link attachments since fediverse instances generate their own link previews
+    # https://github.com/snarfed/bridgy-fed/issues/958
+    obj_or_activity = obj if obj.keys() > set(['id']) else activity
+    obj_or_activity['attachment'] = [
+        a for a in as1.get_objects(obj_or_activity, 'attachment')
+        if a.get('type') != 'Link']
+
     # copy image(s) into attachment(s). may be Mastodon-specific.
     # https://github.com/snarfed/bridgy-fed/issues/33#issuecomment-440965618
-    obj_or_activity = obj if obj.keys() > set(['id']) else activity
     imgs = util.get_list(obj_or_activity, 'image')
-    atts = obj_or_activity.setdefault('attachment', [])
     if imgs:
+        atts = obj_or_activity['attachment']
         atts.extend(img for img in imgs if img not in atts)
 
     # cc target's author(s), recipients, mentions

tests/test_activitypub.py

@@ -1960,6 +1960,15 @@ class ActivityPubUtilsTest(TestCase):
             ],
         }))
 
+    def test_postprocess_as2_strips_link_attachment(self):
+        self.assertNotIn('attachment', postprocess_as2({
+            'type': 'Note',
+            'attachment': [{
+                'type': 'Link',
+                'url': 'http://a/link',
+            }],
+        }))
+
     def test_postprocess_as2_actor_url_attachments(self):
         got = postprocess_as2_actor(as2.from_as1({
             'objectType': 'person',
@@ -2279,13 +2288,6 @@ class ActivityPubUtilsTest(TestCase):
             'object': ACTOR,
         }, ActivityPub.convert(obj))
 
-    # TODO: remove
-    @skip
-    def test_convert_protocols_not_enabled(self):
-        obj = Object(our_as1={'foo': 'bar'}, source_protocol='atproto')
-        with self.assertRaises(BadRequest):
-            ActivityPub.convert(obj)
-
     def test_postprocess_as2_idempotent(self):
         for obj in (ACTOR, REPLY_OBJECT, REPLY_OBJECT_WRAPPED, REPLY,
                     NOTE_OBJECT, NOTE, MENTION_OBJECT, MENTION, LIKE,