Fix overwriting profile when making room public (#11003)

This splits apart `handle_new_user` into a function which adds an entry to the `user_directory` and a function which updates the room sharing tables. I plan to continue doing more of this kind of refactoring to clarify the implementation.

changelog.d/11003.bugfix

+Fix a long-standing bug where a user's per-room nickname/avatar would overwrite their profile in the user directory when a room was made public.
\ No newline at end of file

synapse/handlers/user_directory.py

@@ -242,18 +242,15 @@ class UserDirectoryHandler(StateDeltasHandler):
                         continue
 
                     if change is MatchChange.now_true:  # The user joined
-                        event = await self.store.get_event(event_id, allow_none=True)
-                        # It isn't expected for this event to not exist, but we
-                        # don't want the entire background process to break.
-                        if event is None:
-                            continue
-
-                        profile = ProfileInfo(
-                            avatar_url=event.content.get("avatar_url"),
-                            display_name=event.content.get("displayname"),
-                        )
-
-                        await self._handle_new_user(room_id, state_key, profile)
+                        # This may be the first time we've seen a remote user. If
+                        # so, ensure we have a directory entry for them. (We don't
+                        # need to do this for local users: their directory entry
+                        # is created at the point of registration.
+                        if is_remote:
+                            await self._upsert_directory_entry_for_remote_user(
+                                state_key, event_id
+                            )
+                        await self._track_user_joined_room(room_id, state_key)
                     else:  # The user left
                         await self._handle_remove_user(room_id, state_key)
             else:
@@ -303,7 +300,7 @@ class UserDirectoryHandler(StateDeltasHandler):
             room_id
         )
 
-        logger.debug("Change: %r, publicness: %r", publicness, is_public)
+        logger.debug("Publicness change: %r, is_public: %r", publicness, is_public)
 
         if publicness is MatchChange.now_true and not is_public:
             # If we became world readable but room isn't currently public then
@@ -314,42 +311,50 @@ class UserDirectoryHandler(StateDeltasHandler):
             # ignore the change
             return
 
-        other_users_in_room_with_profiles = (
-            await self.store.get_users_in_room_with_profiles(room_id)
-        )
+        users_in_room = await self.store.get_users_in_room(room_id)
 
         # Remove every user from the sharing tables for that room.
-        for user_id in other_users_in_room_with_profiles.keys():
+        for user_id in users_in_room:
             await self.store.remove_user_who_share_room(user_id, room_id)
 
         # Then, re-add them to the tables.
-        # NOTE: this is not the most efficient method, as handle_new_user sets
+        # NOTE: this is not the most efficient method, as _track_user_joined_room sets
         # up local_user -> other_user and other_user_whos_local -> local_user,
         # which when ran over an entire room, will result in the same values
         # being added multiple times. The batching upserts shouldn't make this
         # too bad, though.
-        for user_id, profile in other_users_in_room_with_profiles.items():
-            await self._handle_new_user(room_id, user_id, profile)
+        for user_id in users_in_room:
+            await self._track_user_joined_room(room_id, user_id)
 
-    async def _handle_new_user(
-        self, room_id: str, user_id: str, profile: ProfileInfo
+    async def _upsert_directory_entry_for_remote_user(
+        self, user_id: str, event_id: str
     ) -> None:
-        """Called when we might need to add user to directory
-
-        Args:
-            room_id: The room ID that user joined or started being public
-            user_id
+        """A remote user has just joined a room. Ensure they have an entry in
+        the user directory. The caller is responsible for making sure they're
+        remote.
         """
+        event = await self.store.get_event(event_id, allow_none=True)
+        # It isn't expected for this event to not exist, but we
+        # don't want the entire background process to break.
+        if event is None:
+            return
+
         logger.debug("Adding new user to dir, %r", user_id)
 
         await self.store.update_profile_in_user_dir(
-            user_id, profile.display_name, profile.avatar_url
+            user_id, event.content.get("displayname"), event.content.get("avatar_url")
         )
 
+    async def _track_user_joined_room(self, room_id: str, user_id: str) -> None:
+        """Someone's just joined a room. Update `users_in_public_rooms` or
+        `users_who_share_private_rooms` as appropriate.
+
+        The caller is responsible for ensuring that the given user is not excluded
+        from the user directory.
+        """
         is_public = await self.store.is_room_world_readable_or_publicly_joinable(
             room_id
         )
-        # Now we update users who share rooms with users.
         other_users_in_room = await self.store.get_users_in_room(room_id)
 
         if is_public:

tests/handlers/test_user_directory.py

@@ -372,8 +372,6 @@ class UserDirectoryTestCase(unittest.HomeserverTestCase):
         # Alice makes two rooms. Bob joins one of them.
         room1 = self.helper.create_room_as(alice, tok=alice_token)
         room2 = self.helper.create_room_as(alice, tok=alice_token)
-        print("room1=", room1)
-        print("room2=", room2)
         self.helper.join(room1, bob, tok=bob_token)
 
         # The user sharing tables should have been updated.
@@ -436,6 +434,75 @@ class UserDirectoryTestCase(unittest.HomeserverTestCase):
             0,
         )
 
+    def test_making_room_public_doesnt_alter_directory_entry(self) -> None:
+        """Per-room names shouldn't go to the directory when the room becomes public.
+
+        This isn't about preventing a leak (the room is now public, so the nickname
+        is too). It's about preserving the invariant that we only show a user's public
+        profile in the user directory results.
+
+        I made this a Synapse test case rather than a Complement one because
+        I think this is (strictly speaking) an implementation choice. Synapse
+        has chosen to only ever use the public profile when responding to a user
+        directory search. There's no privacy leak here, because making the room
+        public discloses the per-room name.
+
+        The spec doesn't mandate anything about _how_ a user
+        should appear in a /user_directory/search result. Hypothetical example:
+        suppose Bob searches for Alice. When representing Alice in a search
+        result, it's reasonable to use any of Alice's nicknames that Bob is
+        aware of. Heck, maybe we even want to use lots of them in a combined
+        displayname like `Alice (aka "ali", "ally", "41iC3")`.
+        """
+
+        # TODO the same should apply when Alice is a remote user.
+        alice = self.register_user("alice", "pass")
+        alice_token = self.login(alice, "pass")
+        bob = self.register_user("bob", "pass")
+        bob_token = self.login(bob, "pass")
+
+        # Alice and Bob are in a private room.
+        room = self.helper.create_room_as(alice, is_public=False, tok=alice_token)
+        self.helper.invite(room, src=alice, targ=bob, tok=alice_token)
+        self.helper.join(room, user=bob, tok=bob_token)
+
+        # Alice has a nickname unique to that room.
+
+        self.helper.send_state(
+            room,
+            "m.room.member",
+            {
+                "displayname": "Freddy Mercury",
+                "membership": "join",
+            },
+            alice_token,
+            state_key=alice,
+        )
+
+        # Check Alice isn't recorded as being in a public room.
+        public = self.get_success(self.user_dir_helper.get_users_in_public_rooms())
+        self.assertNotIn((alice, room), public)
+
+        # One of them makes the room public.
+        self.helper.send_state(
+            room,
+            "m.room.join_rules",
+            {"join_rule": "public"},
+            alice_token,
+        )
+
+        # Check that Alice is now recorded as being in a public room
+        public = self.get_success(self.user_dir_helper.get_users_in_public_rooms())
+        self.assertIn((alice, room), public)
+
+        # Alice's display name remains the same in the user directory.
+        search_result = self.get_success(self.handler.search_users(bob, alice, 10))
+        self.assertEqual(
+            search_result["results"],
+            [{"display_name": "alice", "avatar_url": None, "user_id": alice}],
+            0,
+        )
+
     def test_private_room(self) -> None:
         """
         A user can be searched for only by people that are either in a public