From bce96c2ff9d0f5fbf13f1d1c56399d8ec066bd20 Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Fri, 23 Apr 2021 10:22:51 -0400
Subject: [PATCH 01/17] Allow a user who could join a restricted room to see it
 in spaces summary.

Allows discovery of restricted rooms via the intersection of MSC2946 and MSC3083.
---
 changelog.d/9922.feature          |  1 +
 synapse/handlers/space_summary.py | 37 ++++++++++++++++++++++---------
 2 files changed, 27 insertions(+), 11 deletions(-)
 create mode 100644 changelog.d/9922.feature

diff --git a/changelog.d/9922.feature b/changelog.d/9922.feature
new file mode 100644
index 000000000000..2c655350c04f
--- /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/handlers/space_summary.py b/synapse/handlers/space_summary.py
index eb80a5ad67db..fb422a9d399c 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -20,8 +20,12 @@
 
 import attr
 
-from synapse.api.constants import EventContentFields, EventTypes, HistoryVisibility
-from synapse.api.errors import AuthError
+from synapse.api.constants import (
+    EventContentFields,
+    EventTypes,
+    HistoryVisibility,
+    Membership,
+)
 from synapse.events import EventBase
 from synapse.events.utils import format_event_for_client_v2
 from synapse.types import JsonDict
@@ -47,6 +51,7 @@ def __init__(self, hs: "HomeServer"):
         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
@@ -339,6 +344,7 @@ async def _is_room_accessible(self, room_id: str, requester: Optional[str]) -> b
         It should be included if:
 
         * The requester is joined or invited to the room.
+        * The requester can join without an invite (per MSC3083).
         * The history visibility is set to world readable.
 
         Args:
@@ -350,27 +356,36 @@ async def _is_room_accessible(self, room_id: str, requester: Optional[str]) -> b
         Returns:
              True if the room should be included in the spaces summary.
         """
+        state_ids = await self._store.get_current_state_ids(room_id)
 
         # if we have an authenticated requesting user, first check if they are able to view
         # stripped state in the room.
         if requester:
-            try:
-                await self._auth.check_user_in_room(room_id, requester)
+            member_event_id = state_ids.get((EventTypes.Member, requester), None)
+
+            # If they're in the room they can see info on it.
+            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, if they should be allowed access via membership in a space.
+            room_version = await self._store.get_room_version(room_id)
+            if await self._event_auth_handler.can_join_without_invite(
+                state_ids, room_version, requester
+            ):
                 return True
-            except AuthError:
-                pass
 
         # 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,
         )

From 0a881ac8ea8362576a0129dae04a3adbe9bde644 Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Wed, 28 Apr 2021 09:30:30 -0400
Subject: [PATCH 02/17] Check if the origin server can access a room when
 queried over federation.

---
 synapse/federation/transport/server.py |  2 +-
 synapse/handlers/space_summary.py      | 25 +++++++++++++++++++++----
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index e1b746247469..c17a085a4f93 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -1428,7 +1428,7 @@ async def on_POST(
             )
 
         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/space_summary.py b/synapse/handlers/space_summary.py
index fb422a9d399c..0aa611f38565 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -117,7 +117,7 @@ async def get_space_summary(
 
             if is_in_room:
                 rooms, events = await self._summarize_local_room(
-                    requester, room_id, suggested_only, max_children
+                    requester, None, room_id, suggested_only, max_children
                 )
             else:
                 rooms, events = await self._summarize_remote_room(
@@ -167,6 +167,7 @@ async def get_space_summary(
 
     async def federation_space_summary(
         self,
+        origin: str,
         room_id: str,
         suggested_only: bool,
         max_rooms_per_space: Optional[int],
@@ -176,6 +177,8 @@ async def federation_space_summary(
         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"
@@ -211,7 +214,7 @@ async def federation_space_summary(
             logger.debug("Processing room %s", room_id)
 
             rooms, events = await self._summarize_local_room(
-                None, room_id, suggested_only, max_rooms_per_space
+                None, origin, room_id, suggested_only, max_rooms_per_space
             )
 
             processed_rooms.add(room_id)
@@ -227,6 +230,7 @@ async def federation_space_summary(
     async def _summarize_local_room(
         self,
         requester: Optional[str],
+        origin: Optional[str],
         room_id: str,
         suggested_only: bool,
         max_children: Optional[int],
@@ -238,6 +242,9 @@ async def _summarize_local_room(
             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.
@@ -252,7 +259,7 @@ async def _summarize_local_room(
                 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):
+        if not await self._is_room_accessible(room_id, requester, origin):
             return (), ()
 
         room_entry = await self._build_room_entry(room_id)
@@ -337,7 +344,9 @@ async def _summarize_remote_room(
             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.
 
@@ -345,6 +354,7 @@ async def _is_room_accessible(self, room_id: str, requester: Optional[str]) -> b
 
         * 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:
@@ -352,6 +362,9 @@ async def _is_room_accessible(self, room_id: str, requester: Optional[str]) -> b
             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.
@@ -376,6 +389,10 @@ async def _is_room_accessible(self, room_id: str, requester: Optional[str]) -> b
             ):
                 return True
 
+        # If this is a request over federation, check if the host is in the room.
+        elif origin and await self._auth.check_host_in_room(room_id, origin):
+            return True
+
         # otherwise, check if the room is peekable
         hist_vis_event_id = state_ids.get((EventTypes.RoomHistoryVisibility, ""), None)
         if hist_vis_event_id:

From 45ad823d637688c847a94f71ae8ac87f154401be Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Wed, 28 Apr 2021 09:32:01 -0400
Subject: [PATCH 03/17] Check if an origin server has access to any spaces for
 a restricted room when queried over federation.

---
 synapse/handlers/event_auth.py    | 67 ++++++++++++++++++++++---------
 synapse/handlers/space_summary.py | 44 +++++++++++++++++---
 2 files changed, 88 insertions(+), 23 deletions(-)

diff --git a/synapse/handlers/event_auth.py b/synapse/handlers/event_auth.py
index eff639f40760..ad9099c9de76 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
+from typing import TYPE_CHECKING, Collection, Tuple
 
 from synapse.api.constants import EventTypes, JoinRules
 from synapse.api.room_versions import RoomVersion
@@ -29,46 +29,42 @@ class EventAuthHandler:
     def __init__(self, hs: "HomeServer"):
         self._store = hs.get_datastore()
 
-    async def can_join_without_invite(
-        self, state_ids: StateMap[str], room_version: RoomVersion, user_id: str
-    ) -> bool:
+    async def get_allowed_spaces(
+        self, state_ids: StateMap[str], room_version: RoomVersion
+    ) -> Tuple[bool, Collection[str]]:
         """
-        Check whether a user can join a room without an invite.
-
-        When joining a room with restricted joined rules (as defined in MSC3083),
-        the membership of spaces must be checked during join.
+        Generate a list of spaces allow access to a room.
 
         Args:
             state_ids: The state of the room as it currently is.
             room_version: The room version of the room being joined.
-            user_id: The user joining the room.
 
         Returns:
-            True if the user can join the room, false otherwise.
+            A tuple:
+                True if spaces give access to the room.
+                A collection of spaces (if any) which provide membership to the room.
         """
         # This only applies to room versions which support the new join rule.
         if not room_version.msc3083_join_rules:
-            return True
+            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 True
+            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)
         if join_rules_event.content.get("join_rule") != JoinRules.MSC3083_RESTRICTED:
-            return True
+            return False, ()
 
         # 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):
-            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)
+            return True, ()
 
-        # Pull out the other room IDs, invalid data gets filtered.
+        # Pull out the room IDs, invalid data gets filtered.
+        result = []
         for space in allowed_spaces:
             if not isinstance(space, dict):
                 continue
@@ -79,6 +75,41 @@ async def can_join_without_invite(
 
             # The user was joined to one of the spaces specified, they can join
             # this room!
+            result.append(space_id)
+
+        return True, result
+
+    async def can_join_without_invite(
+        self, state_ids: StateMap[str], room_version: RoomVersion, user_id: str
+    ) -> bool:
+        """
+        Check whether a user can join a room without an invite.
+
+        When joining a room with restricted joined rules (as defined in MSC3083),
+        the membership of spaces must be checked during join.
+
+        Args:
+            state_ids: The state of the room as it currently is.
+            room_version: The room version of the room being joined.
+            user_id: The user joining the room.
+
+        Returns:
+            True if the user can join the room, false otherwise.
+        """
+        # Get whether spaces allow access to the room and the allowed spaces.
+        allow_via_spaces, allowed_spaces = await self.get_allowed_spaces(
+            state_ids, room_version
+        )
+        # Access via spaces doesn't apply to this room.
+        if not allow_via_spaces:
+            return True
+
+        # Get the list of joined rooms and see if there's an overlap.
+        joined_rooms = await self._store.get_rooms_for_user(user_id)
+
+        # If the user was joined to one of the spaces specified, they can join
+        # this room!
+        for space_id in allowed_spaces:
             if space_id in joined_rooms:
                 return True
 
diff --git a/synapse/handlers/space_summary.py b/synapse/handlers/space_summary.py
index 0aa611f38565..680466e92bd5 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -120,13 +120,31 @@ async def get_space_summary(
                     requester, None, room_id, suggested_only, max_children
                 )
             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,
                 )
 
+                # 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. Handle that filtering.
+                room_ids = set()
+                rooms = []
+                events = []
+                for room in fed_rooms:
+                    fed_room_id = room.get("room_id")
+                    if fed_room_id and await self._is_room_accessible(
+                        fed_room_id, requester, None
+                    ):
+                        rooms.append(room)
+                        room_ids.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",
                 queue_entry.room_id,
@@ -370,6 +388,7 @@ async def _is_room_accessible(
              True if the room should be included in the spaces summary.
         """
         state_ids = await self._store.get_current_state_ids(room_id)
+        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.
@@ -383,15 +402,30 @@ async def _is_room_accessible(
                     return True
 
             # Otherwise, if they should be allowed access via membership in a space.
-            room_version = await self._store.get_room_version(room_id)
             if await self._event_auth_handler.can_join_without_invite(
                 state_ids, room_version, requester
             ):
                 return True
 
-        # If this is a request over federation, check if the host is in the room.
-        elif origin and await self._auth.check_host_in_room(room_id, origin):
-            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).
+            (
+                allow_via_spaces,
+                allowed_spaces,
+            ) = await self._event_auth_handler.get_allowed_spaces(
+                state_ids, room_version
+            )
+            if allow_via_spaces:
+                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_event_id = state_ids.get((EventTypes.RoomHistoryVisibility, ""), None)

From 5225ef125a2b8de06ce732a5b08173195fa3f55c Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Wed, 28 Apr 2021 09:59:48 -0400
Subject: [PATCH 04/17] Do not revisit any of the rooms received over
 federation.

---
 synapse/handlers/space_summary.py | 49 ++++++++++++++++++-------------
 1 file changed, 29 insertions(+), 20 deletions(-)

diff --git a/synapse/handlers/space_summary.py b/synapse/handlers/space_summary.py
index 680466e92bd5..aff39c7a888f 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -116,9 +116,18 @@ async def get_space_summary(
             max_children = max_rooms_per_space if processed_rooms else None
 
             if is_in_room:
-                rooms, events = await self._summarize_local_room(
+                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:
                 fed_rooms, fed_events = await self._summarize_remote_room(
                     queue_entry,
@@ -131,31 +140,30 @@ async def get_space_summary(
                 # as the requesting server, are allowed to see, but the requesting
                 # user is not permitted see. Handle that filtering.
                 room_ids = set()
-                rooms = []
+                rooms = []  # type: List[JsonDict]
                 events = []
                 for room in fed_rooms:
                     fed_room_id = room.get("room_id")
                     if fed_room_id and await self._is_room_accessible(
                         fed_room_id, requester, None
                     ):
-                        rooms.append(room)
+                        rooms_result.append(room)
                         room_ids.add(fed_room_id)
 
+                    # any rooms returned don't need visiting again (even if the user
+                    # didn't have access to them).
+                    processed_rooms.add(cast(str, 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",
-                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)
+                logger.debug(
+                    "Query of %s returned rooms %s, events %s",
+                    room_id,
+                    [room.get("room_id") for room in rooms],
+                    ["%s->%s" % (ev["room_id"], ev["state_key"]) for ev in events],
+                )
 
             # the room we queried may or may not have been returned, but don't process
             # it again, anyway.
@@ -231,14 +239,15 @@ async def federation_space_summary(
 
             logger.debug("Processing room %s", room_id)
 
-            rooms, events = await self._summarize_local_room(
+            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)
@@ -252,7 +261,7 @@ async def _summarize_local_room(
         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.
 
@@ -278,7 +287,7 @@ async def _summarize_local_room(
                 to a maximum size or may include all children.
         """
         if not await self._is_room_accessible(room_id, requester, origin):
-            return (), ()
+            return None, ()
 
         room_entry = await self._build_room_entry(room_id)
 
@@ -302,7 +311,7 @@ async def _summarize_local_room(
                     event_format=format_event_for_client_v2,
                 )
             )
-        return (room_entry,), events_result
+        return room_entry, events_result
 
     async def _summarize_remote_room(
         self,

From 31bb2ad69cc252fc8faa7104104f72be01766f35 Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Mon, 3 May 2021 12:09:22 -0400
Subject: [PATCH 05/17] Fix filtering for world readable rooms.

---
 synapse/handlers/space_summary.py | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/synapse/handlers/space_summary.py b/synapse/handlers/space_summary.py
index aff39c7a888f..eab72a0780aa 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -138,15 +138,25 @@ async def get_space_summary(
 
                 # 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. Handle that filtering.
+                # user is not permitted see.
+                #
+                # A room may be visible if it is world readable, or if it is accessible
+                # to the specific user.
                 room_ids = set()
                 rooms = []  # type: List[JsonDict]
                 events = []
                 for room in fed_rooms:
+                    # Pull whether it is world readable from the returned information
+                    # since we may not have the state of this room.
+                    include_room = room.get("world_readable") is True
                     fed_room_id = room.get("room_id")
-                    if fed_room_id and await self._is_room_accessible(
-                        fed_room_id, requester, None
-                    ):
+
+                    if not include_room and fed_room_id:
+                        include_room = await self._is_room_accessible(
+                            fed_room_id, requester, None
+                        )
+
+                    if include_room:
                         rooms_result.append(room)
                         room_ids.add(fed_room_id)
 
@@ -397,6 +407,12 @@ async def _is_room_accessible(
              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

From 417aa6cddb853d172c92bd1404b24a7df74e8e0d Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Wed, 12 May 2021 15:34:26 -0400
Subject: [PATCH 06/17] Abstract out a helper for checking if a space is in a
 list.

---
 synapse/handlers/event_auth.py | 37 +++++++++++++++++++++++++---------
 1 file changed, 27 insertions(+), 10 deletions(-)

diff --git a/synapse/handlers/event_auth.py b/synapse/handlers/event_auth.py
index ad9099c9de76..f01bb6bd7ebe 100644
--- a/synapse/handlers/event_auth.py
+++ b/synapse/handlers/event_auth.py
@@ -37,7 +37,7 @@ async def get_allowed_spaces(
 
         Args:
             state_ids: The state of the room as it currently is.
-            room_version: The room version of the room being joined.
+            room_version: The room version of the room to query.
 
         Returns:
             A tuple:
@@ -79,6 +79,31 @@ async def get_allowed_spaces(
 
         return True, result
 
+    async def 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
+
     async def can_join_without_invite(
         self, state_ids: StateMap[str], room_version: RoomVersion, user_id: str
     ) -> bool:
@@ -104,14 +129,6 @@ async def can_join_without_invite(
         if not allow_via_spaces:
             return True
 
-        # Get the list of joined rooms and see if there's an overlap.
-        joined_rooms = await self._store.get_rooms_for_user(user_id)
-
         # If the user was joined to one of the spaces specified, they can join
         # this room!
-        for space_id in allowed_spaces:
-            if space_id in joined_rooms:
-                return True
-
-        # The user was not in any of the required spaces.
-        return False
+        return await self.user_in_rooms(allowed_spaces, user_id)

From 36d3932d16ebbde7eb25cc5d8a92e91106e9d246 Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Wed, 12 May 2021 15:34:34 -0400
Subject: [PATCH 07/17] Return the allowed spaces over federation and filter on
 it.

---
 synapse/handlers/space_summary.py | 34 +++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/synapse/handlers/space_summary.py b/synapse/handlers/space_summary.py
index eab72a0780aa..9bd579ef5f4d 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -146,12 +146,24 @@ async def get_space_summary(
                 rooms = []  # type: List[JsonDict]
                 events = []
                 for room in fed_rooms:
-                    # Pull whether it is world readable from the returned information
-                    # since we may not have the state of this room.
-                    include_room = room.get("world_readable") is True
                     fed_room_id = room.get("room_id")
+                    if not fed_room_id:
+                        continue
+
+                    # Check whether the room is world readable from the response.
+                    include_room = room.get("world_readable") is True
+
+                    # If the room is not world-readable, get the allowed spaces from
+                    # the response.
+                    allowed_spaces = room.get("allowed_spaces")
+                    if not include_room and allowed_spaces:
+                        include_room = await self._event_auth_handler.user_in_rooms(
+                            allowed_spaces, requester
+                        )
 
-                    if not include_room and fed_room_id:
+                    # Finally, check ourselves if we can access the room (this will
+                    # fail if we don't have any state for this room).
+                    if not include_room:
                         include_room = await self._is_room_accessible(
                             fed_room_id, requester, None
                         )
@@ -199,6 +211,11 @@ async def get_space_summary(
                 )
                 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(
@@ -486,6 +503,14 @@ async def _build_room_entry(self, room_id: str) -> JsonDict:
         if not room_type:
             room_type = create_event.content.get(EventContentFields.MSC1772_ROOM_TYPE)
 
+        room_version = await self._store.get_room_version(room_id)
+        (
+            allow_via_spaces,
+            allowed_spaces,
+        ) = await self._event_auth_handler.get_allowed_spaces(
+            current_state_ids, room_version
+        )
+
         entry = {
             "room_id": stats["room_id"],
             "name": stats["name"],
@@ -499,6 +524,7 @@ async def _build_room_entry(self, room_id: str) -> JsonDict:
             "guest_can_join": stats["guest_access"] == "can_join",
             "creation_ts": create_event.origin_server_ts,
             "room_type": room_type,
+            "allowed_spaces": allowed_spaces if allow_via_spaces else None,
         }
 
         # Filter out Nones – rather omit the field altogether

From 9157200a76b1ae14268b6b4d295acb9bf0bf1d53 Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Mon, 17 May 2021 13:24:49 -0400
Subject: [PATCH 08/17] Remove unused variable.

---
 synapse/handlers/space_summary.py | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/synapse/handlers/space_summary.py b/synapse/handlers/space_summary.py
index 9bd579ef5f4d..8bc8ccb6e5cc 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -143,7 +143,6 @@ async def get_space_summary(
                 # A room may be visible if it is world readable, or if it is accessible
                 # to the specific user.
                 room_ids = set()
-                rooms = []  # type: List[JsonDict]
                 events = []
                 for room in fed_rooms:
                     fed_room_id = room.get("room_id")
@@ -183,8 +182,8 @@ async def get_space_summary(
                 logger.debug(
                     "Query of %s returned rooms %s, events %s",
                     room_id,
-                    [room.get("room_id") for room in rooms],
-                    ["%s->%s" % (ev["room_id"], ev["state_key"]) for ev in events],
+                    [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

From c97917b0cee1db80ee5adc69a7413f3057ae8e32 Mon Sep 17 00:00:00 2001
From: Patrick Cloke <clokep@users.noreply.github.com>
Date: Mon, 17 May 2021 14:08:01 -0400
Subject: [PATCH 09/17] Fix typo.

Co-authored-by: Sumner Evans <me@sumnerevans.com>
---
 synapse/handlers/event_auth.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/synapse/handlers/event_auth.py b/synapse/handlers/event_auth.py
index f01bb6bd7ebe..f07c5e7d08d0 100644
--- a/synapse/handlers/event_auth.py
+++ b/synapse/handlers/event_auth.py
@@ -33,7 +33,7 @@ async def get_allowed_spaces(
         self, state_ids: StateMap[str], room_version: RoomVersion
     ) -> Tuple[bool, Collection[str]]:
         """
-        Generate a list of spaces allow access to a room.
+        Generate a list of spaces which allow access to a room.
 
         Args:
             state_ids: The state of the room as it currently is.

From ce8efa95892c5d615f55080d013d2d4e358830f0 Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Tue, 18 May 2021 11:12:53 -0400
Subject: [PATCH 10/17] Split the method in two.

---
 synapse/handlers/event_auth.py | 68 ++++++++++++++++++++++++----------
 1 file changed, 48 insertions(+), 20 deletions(-)

diff --git a/synapse/handlers/event_auth.py b/synapse/handlers/event_auth.py
index 5b2fe103e742..eea6f13b1d0e 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 +59,67 @@ async def check_restricted_join_rules(
         ):
             return
 
+        # Get the spaces which allow access to this room, if applicable.
+        allowed_spaces = await self.get_spaces_that_allow_join(state_ids, room_version)
+        if allowed_spaces is None:
+            return
+
+        # 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 = ()
+
+        # Pull out the other room IDs, invalid data gets filtered.
+        for space_id in allowed_spaces:
+            # The user was joined to one of the spaces specified, they can join
+            # this room!
+            if space_id in joined_rooms:
+                return
+
+        # 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.",
+        )
+
+    async def get_spaces_that_allow_join(
+        self, state_ids: StateMap[str], room_version: RoomVersion
+    ) -> Optional[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.
+            room_version: The room version of the room to query.
+
+        Returns:
+            None if room access via spaces doesn't apply for this room.
+
+            Otherwise, a collection of spaces (if any) which provide membership
+            to the room.
+        """
         # This only applies to room versions which support the new join rule.
         if not room_version.msc3083_join_rules:
-            return
+            return None
 
         # 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 None
 
         # 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
+            return None
 
         # 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 +128,6 @@ async def check_restricted_join_rules(
             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

From 83974e8a4878d092c40cd86568ae49a63ad5037a Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Tue, 18 May 2021 11:18:19 -0400
Subject: [PATCH 11/17] Further split the methods.

---
 synapse/handlers/event_auth.py | 47 ++++++++++++++++++++++------------
 1 file changed, 30 insertions(+), 17 deletions(-)

diff --git a/synapse/handlers/event_auth.py b/synapse/handlers/event_auth.py
index eea6f13b1d0e..484eb3834740 100644
--- a/synapse/handlers/event_auth.py
+++ b/synapse/handlers/event_auth.py
@@ -64,24 +64,12 @@ async def check_restricted_join_rules(
         if allowed_spaces is None:
             return
 
-        # 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 = ()
-
-        # Pull out the other room IDs, invalid data gets filtered.
-        for space_id in allowed_spaces:
-            # The user was joined to one of the spaces specified, they can join
-            # this room!
-            if space_id in joined_rooms:
-                return
-
         # 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.",
-        )
+        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 get_spaces_that_allow_join(
         self, state_ids: StateMap[str], room_version: RoomVersion
@@ -131,3 +119,28 @@ async def get_spaces_that_allow_join(
             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 rooms.
+        return False

From 225e06d2774877ee47606c435be328c445e85ba4 Mon Sep 17 00:00:00 2001
From: Patrick Cloke <clokep@users.noreply.github.com>
Date: Wed, 19 May 2021 09:36:16 -0400
Subject: [PATCH 12/17] Clarify comment.

Co-authored-by: Erik Johnston <erik@matrix.org>
---
 synapse/handlers/event_auth.py | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/synapse/handlers/event_auth.py b/synapse/handlers/event_auth.py
index 484eb3834740..107ffe7bab09 100644
--- a/synapse/handlers/event_auth.py
+++ b/synapse/handlers/event_auth.py
@@ -62,6 +62,11 @@ async def check_restricted_join_rules(
         # Get the spaces which allow access to this room, if applicable.
         allowed_spaces = await self.get_spaces_that_allow_join(state_ids, room_version)
         if allowed_spaces is None:
+            # 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.
             return
 
         # The user was not in any of the required spaces.

From 7c28513101e879b82df7f7fa6f509c152bc6860f Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Wed, 19 May 2021 10:24:15 -0400
Subject: [PATCH 13/17] Clarify comments about when a room can be included.

---
 synapse/handlers/space_summary.py | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/synapse/handlers/space_summary.py b/synapse/handlers/space_summary.py
index c6e0e52009e3..bbf0a899f1f7 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -140,8 +140,7 @@ async def get_space_summary(
                 # as the requesting server, are allowed to see, but the requesting
                 # user is not permitted see.
                 #
-                # A room may be visible if it is world readable, or if it is accessible
-                # to the specific user.
+                # Filter the returned results to only what is accessible o the user.
                 room_ids = set()
                 events = []
                 for room in fed_rooms:
@@ -149,29 +148,39 @@ async def get_space_summary(
                     if not fed_room_id:
                         continue
 
-                    # Check whether the room is world readable from the response.
+                    # 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
 
-                    # If the room is not world-readable, get the allowed spaces from
-                    # the response.
+                    # 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:
                         include_room = await self._event_auth_handler.is_user_in_rooms(
                             allowed_spaces, requester
                         )
 
-                    # Finally, check ourselves if we can access the room (this will
-                    # fail if we don't have any state for this room).
-                    if not include_room:
+                    # 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)
 
-                    # any rooms returned don't need visiting again (even if the user
+                    # All rooms returned don't need visiting again (even if the user
                     # didn't have access to them).
                     processed_rooms.add(cast(str, room_id))
 

From 7c0ec1ad3a014ab7e69cefbb378c73752eb69894 Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Wed, 19 May 2021 10:24:33 -0400
Subject: [PATCH 14/17] Fix-up some type hints (and fix a bug about processed
 rooms).

---
 synapse/handlers/space_summary.py | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/synapse/handlers/space_summary.py b/synapse/handlers/space_summary.py
index bbf0a899f1f7..35ec992f77e9 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -16,7 +16,7 @@
 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
 
@@ -145,7 +145,7 @@ async def get_space_summary(
                 events = []
                 for room in fed_rooms:
                     fed_room_id = room.get("room_id")
-                    if not fed_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:
@@ -163,7 +163,11 @@ async def get_space_summary(
                     # 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:
+                    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
                         )
@@ -182,7 +186,7 @@ async def get_space_summary(
 
                     # All rooms returned don't need visiting again (even if the user
                     # didn't have access to them).
-                    processed_rooms.add(cast(str, room_id))
+                    processed_rooms.add(fed_room_id)
 
                 for event in fed_events:
                     if event.get("room_id") in room_ids:

From 4888f02ab51b38fb93d8bc861f44fc053b8e9650 Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Wed, 19 May 2021 11:06:02 -0400
Subject: [PATCH 15/17] Further split the join rules checks.

---
 synapse/handlers/event_auth.py    | 56 ++++++++++++++++++++-----------
 synapse/handlers/space_summary.py | 31 +++++++++++------
 2 files changed, 56 insertions(+), 31 deletions(-)

diff --git a/synapse/handlers/event_auth.py b/synapse/handlers/event_auth.py
index 107ffe7bab09..a0df16a32f68 100644
--- a/synapse/handlers/event_auth.py
+++ b/synapse/handlers/event_auth.py
@@ -59,52 +59,68 @@ async def check_restricted_join_rules(
         ):
             return
 
-        # Get the spaces which allow access to this room, if applicable.
-        allowed_spaces = await self.get_spaces_that_allow_join(state_ids, room_version)
-        if allowed_spaces is None:
-            # 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.
+        # 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
 
-        # The user was not in any of the required spaces.
+        # 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 get_spaces_that_allow_join(
+    async def has_restricted_join_rules(
         self, state_ids: StateMap[str], room_version: RoomVersion
-    ) -> Optional[Collection[str]]:
+    ) -> bool:
         """
-        Generate a list of spaces which allow access to a room.
+        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:
-            None if room access via spaces doesn't apply for this room.
-
-            Otherwise, a collection of spaces (if any) which provide membership
-            to the room.
+            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 None
+            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 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 None
+            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 None
 
         # If allowed is of the wrong form, then only allow invited users.
         allowed_spaces = join_rules_event.content.get("allow", [])
diff --git a/synapse/handlers/space_summary.py b/synapse/handlers/space_summary.py
index 35ec992f77e9..b14e39b8b97a 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -457,13 +457,16 @@ async def _is_room_accessible(
 
             # Otherwise, if they should be allowed access via membership in a space.
             # Get the spaces which allow access to this room, if applicable.
-            allowed_spaces = await self._event_auth_handler.get_spaces_that_allow_join(
+            if await self._event_auth_handler.has_restricted_join_rules(
                 state_ids, room_version
-            )
-            if allowed_spaces and await self._event_auth_handler.is_user_in_rooms(
-                allowed_spaces, requester
             ):
-                return True
+                allowed_spaces = (
+                    await self._event_auth_handler.get_spaces_that_allow_join(state_ids)
+                )
+                if await self._event_auth_handler.is_user_in_rooms(
+                    allowed_spaces, requester
+                ):
+                    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.
@@ -474,10 +477,12 @@ async def _is_room_accessible(
             # 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).
-            allowed_spaces = await self._event_auth_handler.get_spaces_that_allow_join(
+            if await self._event_auth_handler.has_restricted_join_rules(
                 state_ids, room_version
-            )
-            if allowed_spaces:
+            ):
+                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
@@ -517,9 +522,13 @@ async def _build_room_entry(self, room_id: str) -> JsonDict:
             room_type = create_event.content.get(EventContentFields.MSC1772_ROOM_TYPE)
 
         room_version = await self._store.get_room_version(room_id)
-        allowed_spaces = await self._event_auth_handler.get_spaces_that_allow_join(
+        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"],
@@ -534,7 +543,7 @@ async def _build_room_entry(self, room_id: str) -> JsonDict:
             "guest_can_join": stats["guest_access"] == "can_join",
             "creation_ts": create_event.origin_server_ts,
             "room_type": room_type,
-            "allowed_spaces": allowed_spaces if allowed_spaces else None,
+            "allowed_spaces": allowed_spaces,
         }
 
         # Filter out Nones – rather omit the field altogether

From 9ba347bebfb1132253965a7bd3d7ba03b91c5a7a Mon Sep 17 00:00:00 2001
From: Patrick Cloke <clokep@users.noreply.github.com>
Date: Wed, 19 May 2021 12:38:14 -0400
Subject: [PATCH 16/17] Fix typo.

Co-authored-by: Erik Johnston <erik@matrix.org>
---
 synapse/handlers/space_summary.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/synapse/handlers/space_summary.py b/synapse/handlers/space_summary.py
index b14e39b8b97a..4c63e192f0c3 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -140,7 +140,7 @@ async def get_space_summary(
                 # 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 o the user.
+                # Filter the returned results to only what is accessible to the user.
                 room_ids = set()
                 events = []
                 for room in fed_rooms:

From fe1eb1809e85904117b98ffd7fd0fe690c77346a Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Wed, 19 May 2021 13:54:41 -0400
Subject: [PATCH 17/17] Remove some duplicated code.

---
 synapse/handlers/space_summary.py | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/synapse/handlers/space_summary.py b/synapse/handlers/space_summary.py
index 4c63e192f0c3..8d49ba81646e 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -26,6 +26,7 @@
     HistoryVisibility,
     Membership,
 )
+from synapse.api.errors import AuthError
 from synapse.events import EventBase
 from synapse.events.utils import format_event_for_client_v2
 from synapse.types import JsonDict
@@ -450,23 +451,23 @@ async def _is_room_accessible(
             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, if they should be allowed access via membership in a space.
-            # Get the spaces which allow access to this room, if applicable.
-            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)
+            # Otherwise, check if they should be allowed access via membership in a space.
+            try:
+                await self._event_auth_handler.check_restricted_join_rules(
+                    state_ids, room_version, requester, member_event
                 )
-                if await self._event_auth_handler.is_user_in_rooms(
-                    allowed_spaces, requester
-                ):
-                    return True
+            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.