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).

4 files changed, 254 insertions, 54 deletions

diff --git a/changelog.d/9922.feature b/changelog.d/9922.feature
new file mode 100644
index 0000000000..2c655350c0
--- /dev/null
+++ b/changelog.d/9922.feature
@@ -0,0 +1 @@
+Experimental support to allow a user who could join a restricted room to view it in the spaces summary.
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index e1b7462474..c17a085a4f 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -1428,7 +1428,7 @@ class FederationSpaceSummaryServlet(BaseFederationServlet):
             )
 
         return 200, await self.handler.federation_space_summary(
-            room_id, suggested_only, max_rooms_per_space, exclude_rooms
+            origin, room_id, suggested_only, max_rooms_per_space, exclude_rooms
         )
 
 
diff --git a/synapse/handlers/event_auth.py b/synapse/handlers/event_auth.py
index 5b2fe103e7..a0df16a32f 100644
--- a/synapse/handlers/event_auth.py
+++ b/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)
+
+        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 required spaces.
-        raise AuthError(
-            403,
-            "You do not belong to any of the required spaces to join this room.",
-        )
+        # The user was not in any of the rooms.
+        return False
diff --git a/synapse/handlers/space_summary.py b/synapse/handlers/space_summary.py
index eb80a5ad67..8d49ba8164 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -16,11 +16,16 @@ import itertools
 import logging
 import re
 from collections import deque
-from typing import TYPE_CHECKING, Iterable, List, Optional, Sequence, Set, Tuple, cast
+from typing import TYPE_CHECKING, Iterable, List, Optional, Sequence, Set, Tuple
 
 import attr
 
-from synapse.api.constants import EventContentFields, EventTypes, HistoryVisibility
+from synapse.api.constants import (
+    EventContentFields,
+    EventTypes,
+    HistoryVisibility,
+    Membership,
+)
 from synapse.api.errors import AuthError
 from synapse.events import EventBase
 from synapse.events.utils import format_event_for_client_v2
@@ -47,6 +52,7 @@ class SpaceSummaryHandler:
         self._auth = hs.get_auth()
         self._room_list_handler = hs.get_room_list_handler()
         self._state_handler = hs.get_state_handler()
+        self._event_auth_handler = hs.get_event_auth_handler()
         self._store = hs.get_datastore()
         self._event_serializer = hs.get_event_client_serializer()
         self._server_name = hs.hostname
@@ -111,28 +117,88 @@ class SpaceSummaryHandler:
             max_children = max_rooms_per_space if processed_rooms else None
 
             if is_in_room:
-                rooms, events = await self._summarize_local_room(
-                    requester, room_id, suggested_only, max_children
+                room, events = await self._summarize_local_room(
+                    requester, None, room_id, suggested_only, max_children
                 )
+
+                logger.debug(
+                    "Query of local room %s returned events %s",
+                    room_id,
+                    ["%s->%s" % (ev["room_id"], ev["state_key"]) for ev in events],
+                )
+
+                if room:
+                    rooms_result.append(room)
             else:
-                rooms, events = await self._summarize_remote_room(
+                fed_rooms, fed_events = await self._summarize_remote_room(
                     queue_entry,
                     suggested_only,
                     max_children,
                     exclude_rooms=processed_rooms,
                 )
 
-            logger.debug(
-                "Query of %s returned rooms %s, events %s",
-                queue_entry.room_id,
-                [room.get("room_id") for room in rooms],
-                ["%s->%s" % (ev["room_id"], ev["state_key"]) for ev in events],
-            )
-
-            rooms_result.extend(rooms)
-
-            # any rooms returned don't need visiting again
-            processed_rooms.update(cast(str, room.get("room_id")) for room in rooms)
+                # The results over federation might include rooms that the we,
+                # as the requesting server, are allowed to see, but the requesting
+                # user is not permitted see.
+                #
+                # Filter the returned results to only what is accessible to the user.
+                room_ids = set()
+                events = []
+                for room in fed_rooms:
+                    fed_room_id = room.get("room_id")
+                    if not fed_room_id or not isinstance(fed_room_id, str):
+                        continue
+
+                    # The room should only be included in the summary if:
+                    #     a. the user is in the room;
+                    #     b. the room is world readable; or
+                    #     c. the user is in a space that has been granted access to
+                    #        the room.
+                    #
+                    # Note that we know the user is not in the root room (which is
+                    # why the remote call was made in the first place), but the user
+                    # could be in one of the children rooms and we just didn't know
+                    # about the link.
+                    include_room = room.get("world_readable") is True
+
+                    # Check if the user is a member of any of the allowed spaces
+                    # from the response.
+                    allowed_spaces = room.get("allowed_spaces")
+                    if (
+                        not include_room
+                        and allowed_spaces
+                        and isinstance(allowed_spaces, list)
+                    ):
+                        include_room = await self._event_auth_handler.is_user_in_rooms(
+                            allowed_spaces, requester
+                        )
+
+                    # Finally, if this isn't the requested room, check ourselves
+                    # if we can access the room.
+                    if not include_room and fed_room_id != queue_entry.room_id:
+                        include_room = await self._is_room_accessible(
+                            fed_room_id, requester, None
+                        )
+
+                    # The user can see the room, include it!
+                    if include_room:
+                        rooms_result.append(room)
+                        room_ids.add(fed_room_id)
+
+                    # All rooms returned don't need visiting again (even if the user
+                    # didn't have access to them).
+                    processed_rooms.add(fed_room_id)
+
+                for event in fed_events:
+                    if event.get("room_id") in room_ids:
+                        events.append(event)
+
+                logger.debug(
+                    "Query of %s returned rooms %s, events %s",
+                    room_id,
+                    [room.get("room_id") for room in fed_rooms],
+                    ["%s->%s" % (ev["room_id"], ev["state_key"]) for ev in fed_events],
+                )
 
             # the room we queried may or may not have been returned, but don't process
             # it again, anyway.
@@ -158,10 +224,16 @@ class SpaceSummaryHandler:
                 )
                 processed_events.add(ev_key)
 
+        # Before returning to the client, remove the allowed_spaces key for any
+        # rooms.
+        for room in rooms_result:
+            room.pop("allowed_spaces", None)
+
         return {"rooms": rooms_result, "events": events_result}
 
     async def federation_space_summary(
         self,
+        origin: str,
         room_id: str,
         suggested_only: bool,
         max_rooms_per_space: Optional[int],
@@ -171,6 +243,8 @@ class SpaceSummaryHandler:
         Implementation of the space summary Federation API
 
         Args:
+            origin: The server requesting the spaces summary.
+
             room_id: room id to start the summary at
 
             suggested_only: whether we should only return children with the "suggested"
@@ -205,14 +279,15 @@ class SpaceSummaryHandler:
 
             logger.debug("Processing room %s", room_id)
 
-            rooms, events = await self._summarize_local_room(
-                None, room_id, suggested_only, max_rooms_per_space
+            room, events = await self._summarize_local_room(
+                None, origin, room_id, suggested_only, max_rooms_per_space
             )
 
             processed_rooms.add(room_id)
 
-            rooms_result.extend(rooms)
-            events_result.extend(events)
+            if room:
+                rooms_result.append(room)
+                events_result.extend(events)
 
             # add any children to the queue
             room_queue.extend(edge_event["state_key"] for edge_event in events)
@@ -222,10 +297,11 @@ class SpaceSummaryHandler:
     async def _summarize_local_room(
         self,
         requester: Optional[str],
+        origin: Optional[str],
         room_id: str,
         suggested_only: bool,
         max_children: Optional[int],
-    ) -> Tuple[Sequence[JsonDict], Sequence[JsonDict]]:
+    ) -> Tuple[Optional[JsonDict], Sequence[JsonDict]]:
         """
         Generate a room entry and a list of event entries for a given room.
 
@@ -233,6 +309,9 @@ class SpaceSummaryHandler:
             requester:
                 The user requesting the summary, if it is a local request. None
                 if this is a federation request.
+            origin:
+                The server requesting the summary, if it is a federation request.
+                None if this is a local request.
             room_id: The room ID to summarize.
             suggested_only: True if only suggested children should be returned.
                 Otherwise, all children are returned.
@@ -247,8 +326,8 @@ class SpaceSummaryHandler:
                 An iterable of the sorted children events. This may be limited
                 to a maximum size or may include all children.
         """
-        if not await self._is_room_accessible(room_id, requester):
-            return (), ()
+        if not await self._is_room_accessible(room_id, requester, origin):
+            return None, ()
 
         room_entry = await self._build_room_entry(room_id)
 
@@ -272,7 +351,7 @@ class SpaceSummaryHandler:
                     event_format=format_event_for_client_v2,
                 )
             )
-        return (room_entry,), events_result
+        return room_entry, events_result
 
     async def _summarize_remote_room(
         self,
@@ -332,13 +411,17 @@ class SpaceSummaryHandler:
             or ev.event_type == EventTypes.SpaceChild
         )
 
-    async def _is_room_accessible(self, room_id: str, requester: Optional[str]) -> bool:
+    async def _is_room_accessible(
+        self, room_id: str, requester: Optional[str], origin: Optional[str]
+    ) -> bool:
         """
         Calculate whether the room should be shown in the spaces summary.
 
         It should be included if:
 
         * The requester is joined or invited to the room.
+        * The requester can join without an invite (per MSC3083).
+        * The origin server has any user that is joined or invited to the room.
         * The history visibility is set to world readable.
 
         Args:
@@ -346,31 +429,75 @@ class SpaceSummaryHandler:
             requester:
                 The user requesting the summary, if it is a local request. None
                 if this is a federation request.
+            origin:
+                The server requesting the summary, if it is a federation request.
+                None if this is a local request.
 
         Returns:
              True if the room should be included in the spaces summary.
         """
+        state_ids = await self._store.get_current_state_ids(room_id)
+
+        # If there's no state for the room, it isn't known.
+        if not state_ids:
+            logger.info("room %s is unknown, omitting from summary", room_id)
+            return False
+
+        room_version = await self._store.get_room_version(room_id)
 
         # if we have an authenticated requesting user, first check if they are able to view
         # stripped state in the room.
         if requester:
+            member_event_id = state_ids.get((EventTypes.Member, requester), None)
+
+            # If they're in the room they can see info on it.
+            member_event = None
+            if member_event_id:
+                member_event = await self._store.get_event(member_event_id)
+                if member_event.membership in (Membership.JOIN, Membership.INVITE):
+                    return True
+
+            # Otherwise, check if they should be allowed access via membership in a space.
             try:
-                await self._auth.check_user_in_room(room_id, requester)
-                return True
+                await self._event_auth_handler.check_restricted_join_rules(
+                    state_ids, room_version, requester, member_event
+                )
             except AuthError:
+                # The user doesn't have access due to spaces, but might have access
+                # another way. Keep trying.
                 pass
+            else:
+                return True
+
+        # If this is a request over federation, check if the host is in the room or
+        # is in one of the spaces specified via the join rules.
+        elif origin:
+            if await self._auth.check_host_in_room(room_id, origin):
+                return True
+
+            # Alternately, if the host has a user in any of the spaces specified
+            # for access, then the host can see this room (and should do filtering
+            # if the requester cannot see it).
+            if await self._event_auth_handler.has_restricted_join_rules(
+                state_ids, room_version
+            ):
+                allowed_spaces = (
+                    await self._event_auth_handler.get_spaces_that_allow_join(state_ids)
+                )
+                for space_id in allowed_spaces:
+                    if await self._auth.check_host_in_room(space_id, origin):
+                        return True
 
         # otherwise, check if the room is peekable
-        hist_vis_ev = await self._state_handler.get_current_state(
-            room_id, EventTypes.RoomHistoryVisibility, ""
-        )
-        if hist_vis_ev:
+        hist_vis_event_id = state_ids.get((EventTypes.RoomHistoryVisibility, ""), None)
+        if hist_vis_event_id:
+            hist_vis_ev = await self._store.get_event(hist_vis_event_id)
             hist_vis = hist_vis_ev.content.get("history_visibility")
             if hist_vis == HistoryVisibility.WORLD_READABLE:
                 return True
 
         logger.info(
-            "room %s is unpeekable and user %s is not a member, omitting from summary",
+            "room %s is unpeekable and user %s is not a member / not allowed to join, omitting from summary",
             room_id,
             requester,
         )
@@ -395,6 +522,15 @@ class SpaceSummaryHandler:
         if not room_type:
             room_type = create_event.content.get(EventContentFields.MSC1772_ROOM_TYPE)
 
+        room_version = await self._store.get_room_version(room_id)
+        allowed_spaces = None
+        if await self._event_auth_handler.has_restricted_join_rules(
+            current_state_ids, room_version
+        ):
+            allowed_spaces = await self._event_auth_handler.get_spaces_that_allow_join(
+                current_state_ids
+            )
+
         entry = {
             "room_id": stats["room_id"],
             "name": stats["name"],
@@ -408,6 +544,7 @@ class SpaceSummaryHandler:
             "guest_can_join": stats["guest_access"] == "can_join",
             "creation_ts": create_event.origin_server_ts,
             "room_type": room_type,
+            "allowed_spaces": allowed_spaces,
         }
 
         # Filter out Nones – rather omit the field altogether