Allow a user who could join a restricted room to see it in spaces summary. (#9922)

This finishes up the experimental implementation of MSC3083 by showing
the restricted rooms in the spaces summary (from MSC2946).

synapse/handlers/event_auth.py

@@ -11,7 +11,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-from typing import TYPE_CHECKING, Optional
+from typing import TYPE_CHECKING, Collection, Optional
 
 from synapse.api.constants import EventTypes, JoinRules, Membership
 from synapse.api.errors import AuthError
@@ -59,32 +59,76 @@ class EventAuthHandler:
         ):
             return
 
+        # This is not a room with a restricted join rule, so we don't need to do the
+        # restricted room specific checks.
+        #
+        # Note: We'll be applying the standard join rule checks later, which will
+        # catch the cases of e.g. trying to join private rooms without an invite.
+        if not await self.has_restricted_join_rules(state_ids, room_version):
+            return
+
+        # Get the spaces which allow access to this room and check if the user is
+        # in any of them.
+        allowed_spaces = await self.get_spaces_that_allow_join(state_ids)
+        if not await self.is_user_in_rooms(allowed_spaces, user_id):
+            raise AuthError(
+                403,
+                "You do not belong to any of the required spaces to join this room.",
+            )
+
+    async def has_restricted_join_rules(
+        self, state_ids: StateMap[str], room_version: RoomVersion
+    ) -> bool:
+        """
+        Return if the room has the proper join rules set for access via spaces.
+
+        Args:
+            state_ids: The state of the room as it currently is.
+            room_version: The room version of the room to query.
+
+        Returns:
+            True if the proper room version and join rules are set for restricted access.
+        """
         # This only applies to room versions which support the new join rule.
         if not room_version.msc3083_join_rules:
-            return
+            return False
 
         # If there's no join rule, then it defaults to invite (so this doesn't apply).
         join_rules_event_id = state_ids.get((EventTypes.JoinRules, ""), None)
         if not join_rules_event_id:
-            return
+            return False
+
+        # If the join rule is not restricted, this doesn't apply.
+        join_rules_event = await self._store.get_event(join_rules_event_id)
+        return join_rules_event.content.get("join_rule") == JoinRules.MSC3083_RESTRICTED
+
+    async def get_spaces_that_allow_join(
+        self, state_ids: StateMap[str]
+    ) -> Collection[str]:
+        """
+        Generate a list of spaces which allow access to a room.
+
+        Args:
+            state_ids: The state of the room as it currently is.
+
+        Returns:
+            A collection of spaces which provide membership to the room.
+        """
+        # If there's no join rule, then it defaults to invite (so this doesn't apply).
+        join_rules_event_id = state_ids.get((EventTypes.JoinRules, ""), None)
+        if not join_rules_event_id:
+            return ()
 
         # If the join rule is not restricted, this doesn't apply.
         join_rules_event = await self._store.get_event(join_rules_event_id)
-        if join_rules_event.content.get("join_rule") != JoinRules.MSC3083_RESTRICTED:
-            return
 
         # If allowed is of the wrong form, then only allow invited users.
         allowed_spaces = join_rules_event.content.get("allow", [])
         if not isinstance(allowed_spaces, list):
-            allowed_spaces = ()
-
-        # Get the list of joined rooms and see if there's an overlap.
-        if allowed_spaces:
-            joined_rooms = await self._store.get_rooms_for_user(user_id)
-        else:
-            joined_rooms = ()
+            return ()
 
         # Pull out the other room IDs, invalid data gets filtered.
+        result = []
         for space in allowed_spaces:
             if not isinstance(space, dict):
                 continue
@@ -93,13 +137,31 @@ class EventAuthHandler:
             if not isinstance(space_id, str):
                 continue
 
-            # The user was joined to one of the spaces specified, they can join
-            # this room!
-            if space_id in joined_rooms:
-                return
+            result.append(space_id)
 
-        # The user was not in any of the required spaces.
-        raise AuthError(
-            403,
-            "You do not belong to any of the required spaces to join this room.",
-        )
+        return result
+
+    async def is_user_in_rooms(self, room_ids: Collection[str], user_id: str) -> bool:
+        """
+        Check whether a user is a member of any of the provided rooms.
+
+        Args:
+            room_ids: The rooms to check for membership.
+            user_id: The user to check.
+
+        Returns:
+            True if the user is in any of the rooms, false otherwise.
+        """
+        if not room_ids:
+            return False
+
+        # Get the list of joined rooms and see if there's an overlap.
+        joined_rooms = await self._store.get_rooms_for_user(user_id)
+
+        # Check each room and see if the user is in it.
+        for room_id in room_ids:
+            if room_id in joined_rooms:
+                return True
+
+        # The user was not in any of the rooms.
+        return False