Return membership on each event returned to the client

17 files changed, 221 insertions, 38 deletions

diff --git a/synapse/api/constants.py b/synapse/api/constants.py
index 98884b4967..0a9123c56b 100644
--- a/synapse/api/constants.py
+++ b/synapse/api/constants.py
@@ -234,6 +234,13 @@ class EventContentFields:
     TO_DEVICE_MSGID: Final = "org.matrix.msgid"
 
 
+class EventUnsignedContentFields:
+    """Fields found inside the 'unsigned' data on events"""
+
+    # Requesting user's membership, per MSC4115
+    MSC4115_MEMBERSHIP: Final = "io.element.msc4115.membership"
+
+
 class RoomTypes:
     """Understood values of the room_type field of m.room.create events."""
 
diff --git a/synapse/config/experimental.py b/synapse/config/experimental.py
index 353ae23f91..23f9e77aa8 100644
--- a/synapse/config/experimental.py
+++ b/synapse/config/experimental.py
@@ -422,3 +422,7 @@ class ExperimentalConfig(Config):
                 "MSC4108 requires MSC3861 to be enabled",
                 ("experimental", "msc4108_delegation_endpoint"),
             )
+
+        self.msc4115_membership_on_events = experimental.get(
+            "msc4115_membership_on_events", False
+        )
diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index e0613d0dbc..8b7c5885db 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -49,7 +49,7 @@ from synapse.api.errors import Codes, SynapseError
 from synapse.api.room_versions import RoomVersion
 from synapse.types import JsonDict, Requester
 
-from . import EventBase
+from . import EventBase, make_event_from_dict
 
 if TYPE_CHECKING:
     from synapse.handlers.relations import BundledAggregations
@@ -82,8 +82,6 @@ def prune_event(event: EventBase) -> EventBase:
     """
     pruned_event_dict = prune_event_dict(event.room_version, event.get_dict())
 
-    from . import make_event_from_dict
-
     pruned_event = make_event_from_dict(
         pruned_event_dict, event.room_version, event.internal_metadata.get_dict()
     )
@@ -101,6 +99,25 @@ def prune_event(event: EventBase) -> EventBase:
     return pruned_event
 
 
+def clone_event(event: EventBase) -> EventBase:
+    """Take a copy of the event.
+
+    This is mostly useful because it does a *shallow* copy of the `unsigned` data,
+    which means it can then be updated without corrupting the in-memory cache.
+    """
+    new_event = make_event_from_dict(
+        event.get_dict(), event.room_version, event.internal_metadata.get_dict()
+    )
+
+    # copy the internal fields
+    new_event.internal_metadata.stream_ordering = (
+        event.internal_metadata.stream_ordering
+    )
+    new_event.internal_metadata.outlier = event.internal_metadata.outlier
+
+    return new_event
+
+
 def prune_event_dict(room_version: RoomVersion, event_dict: JsonDict) -> JsonDict:
     """Redacts the event_dict in the same way as `prune_event`, except it
     operates on dicts rather than event objects
diff --git a/synapse/handlers/admin.py b/synapse/handlers/admin.py
index 360614e25b..702d40332c 100644
--- a/synapse/handlers/admin.py
+++ b/synapse/handlers/admin.py
@@ -42,6 +42,7 @@ class AdminHandler:
         self._device_handler = hs.get_device_handler()
         self._storage_controllers = hs.get_storage_controllers()
         self._state_storage_controller = self._storage_controllers.state
+        self._hs_config = hs.config
         self._msc3866_enabled = hs.config.experimental.msc3866.enabled
 
     async def get_whois(self, user: UserID) -> JsonMapping:
@@ -217,7 +218,10 @@ class AdminHandler:
                 )
 
                 events = await filter_events_for_client(
-                    self._storage_controllers, user_id, events
+                    self._storage_controllers,
+                    user_id,
+                    events,
+                    msc4115_membership_on_events=self._hs_config.experimental.msc4115_membership_on_events,
                 )
 
                 writer.write_events(room_id, events)
diff --git a/synapse/handlers/events.py b/synapse/handlers/events.py
index c3fee74a98..09d553cff1 100644
--- a/synapse/handlers/events.py
+++ b/synapse/handlers/events.py
@@ -148,6 +148,7 @@ class EventHandler:
     def __init__(self, hs: "HomeServer"):
         self.store = hs.get_datastores().main
         self._storage_controllers = hs.get_storage_controllers()
+        self._config = hs.config
 
     async def get_event(
         self,
@@ -189,7 +190,11 @@ class EventHandler:
         is_peeking = not is_user_in_room
 
         filtered = await filter_events_for_client(
-            self._storage_controllers, user.to_string(), [event], is_peeking=is_peeking
+            self._storage_controllers,
+            user.to_string(),
+            [event],
+            is_peeking=is_peeking,
+            msc4115_membership_on_events=self._config.experimental.msc4115_membership_on_events,
         )
 
         if not filtered:
diff --git a/synapse/handlers/initial_sync.py b/synapse/handlers/initial_sync.py
index bcc5b285ac..d99fc4bec0 100644
--- a/synapse/handlers/initial_sync.py
+++ b/synapse/handlers/initial_sync.py
@@ -221,7 +221,10 @@ class InitialSyncHandler:
                 ).addErrback(unwrapFirstError)
 
                 messages = await filter_events_for_client(
-                    self._storage_controllers, user_id, messages
+                    self._storage_controllers,
+                    user_id,
+                    messages,
+                    msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
                 )
 
                 start_token = now_token.copy_and_replace(StreamKeyType.ROOM, token)
@@ -380,6 +383,7 @@ class InitialSyncHandler:
             requester.user.to_string(),
             messages,
             is_peeking=is_peeking,
+            msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
         )
 
         start_token = StreamToken.START.copy_and_replace(StreamKeyType.ROOM, token)
@@ -494,6 +498,7 @@ class InitialSyncHandler:
             requester.user.to_string(),
             messages,
             is_peeking=is_peeking,
+            msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
         )
 
         start_token = now_token.copy_and_replace(StreamKeyType.ROOM, token)
diff --git a/synapse/handlers/pagination.py b/synapse/handlers/pagination.py
index cd3a9088cd..6617105cdb 100644
--- a/synapse/handlers/pagination.py
+++ b/synapse/handlers/pagination.py
@@ -623,6 +623,7 @@ class PaginationHandler:
                 user_id,
                 events,
                 is_peeking=(member_event_id is None),
+                msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
             )
 
         # if after the filter applied there are no more events
diff --git a/synapse/handlers/relations.py b/synapse/handlers/relations.py
index 931ac0c813..c5cee8860b 100644
--- a/synapse/handlers/relations.py
+++ b/synapse/handlers/relations.py
@@ -95,6 +95,7 @@ class RelationsHandler:
         self._event_handler = hs.get_event_handler()
         self._event_serializer = hs.get_event_client_serializer()
         self._event_creation_handler = hs.get_event_creation_handler()
+        self._config = hs.config
 
     async def get_relations(
         self,
@@ -163,6 +164,7 @@ class RelationsHandler:
             user_id,
             events,
             is_peeking=(member_event_id is None),
+            msc4115_membership_on_events=self._config.experimental.msc4115_membership_on_events,
         )
 
         # The relations returned for the requested event do include their
@@ -608,6 +610,7 @@ class RelationsHandler:
             user_id,
             events,
             is_peeking=(member_event_id is None),
+            msc4115_membership_on_events=self._config.experimental.msc4115_membership_on_events,
         )
 
         aggregations = await self.get_bundled_aggregations(
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 5e81a51638..51739a2653 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -1476,6 +1476,7 @@ class RoomContextHandler:
                 user.to_string(),
                 events,
                 is_peeking=is_peeking,
+                msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
             )
 
         event = await self.store.get_event(
diff --git a/synapse/handlers/search.py b/synapse/handlers/search.py
index 19c5a2f257..fdbe98de3b 100644
--- a/synapse/handlers/search.py
+++ b/synapse/handlers/search.py
@@ -480,7 +480,10 @@ class SearchHandler:
         filtered_events = await search_filter.filter([r["event"] for r in results])
 
         events = await filter_events_for_client(
-            self._storage_controllers, user.to_string(), filtered_events
+            self._storage_controllers,
+            user.to_string(),
+            filtered_events,
+            msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
         )
 
         events.sort(key=lambda e: -rank_map[e.event_id])
@@ -579,7 +582,10 @@ class SearchHandler:
             filtered_events = await search_filter.filter([r["event"] for r in results])
 
             events = await filter_events_for_client(
-                self._storage_controllers, user.to_string(), filtered_events
+                self._storage_controllers,
+                user.to_string(),
+                filtered_events,
+                msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
             )
 
             room_events.extend(events)
@@ -664,11 +670,17 @@ class SearchHandler:
             )
 
             events_before = await filter_events_for_client(
-                self._storage_controllers, user.to_string(), res.events_before
+                self._storage_controllers,
+                user.to_string(),
+                res.events_before,
+                msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
             )
 
             events_after = await filter_events_for_client(
-                self._storage_controllers, user.to_string(), res.events_after
+                self._storage_controllers,
+                user.to_string(),
+                res.events_after,
+                msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
             )
 
             context: JsonDict = {
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index a6d54ee4b8..8ff45a3353 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -596,6 +596,7 @@ class SyncHandler:
                     sync_config.user.to_string(),
                     recents,
                     always_include_ids=current_state_ids,
+                    msc4115_membership_on_events=self.hs_config.experimental.msc4115_membership_on_events,
                 )
                 log_kv({"recents_after_visibility_filtering": len(recents)})
             else:
@@ -681,6 +682,7 @@ class SyncHandler:
                     sync_config.user.to_string(),
                     loaded_recents,
                     always_include_ids=current_state_ids,
+                    msc4115_membership_on_events=self.hs_config.experimental.msc4115_membership_on_events,
                 )
 
                 loaded_recents = []
diff --git a/synapse/notifier.py b/synapse/notifier.py
index e87333a80a..7c1cd3b5f2 100644
--- a/synapse/notifier.py
+++ b/synapse/notifier.py
@@ -721,6 +721,7 @@ class Notifier:
                         user.to_string(),
                         new_events,
                         is_peeking=is_peeking,
+                        msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
                     )
                 elif keyname == StreamKeyType.PRESENCE:
                     now = self.clock.time_msec()
diff --git a/synapse/push/mailer.py b/synapse/push/mailer.py
index f1ffc8115f..d5079652e4 100644
--- a/synapse/push/mailer.py
+++ b/synapse/push/mailer.py
@@ -513,7 +513,10 @@ class Mailer:
         }
 
         the_events = await filter_events_for_client(
-            self._storage_controllers, user_id, results.events_before
+            self._storage_controllers,
+            user_id,
+            results.events_before,
+            msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
         )
         the_events.append(notif_event)
 
diff --git a/synapse/visibility.py b/synapse/visibility.py
index 4be4ac81e7..17ec15f42c 100644
--- a/synapse/visibility.py
+++ b/synapse/visibility.py
@@ -36,10 +36,15 @@ from typing import (
 
 import attr
 
-from synapse.api.constants import EventTypes, HistoryVisibility, Membership
+from synapse.api.constants import (
+    EventTypes,
+    EventUnsignedContentFields,
+    HistoryVisibility,
+    Membership,
+)
 from synapse.events import EventBase
 from synapse.events.snapshot import EventContext
-from synapse.events.utils import prune_event
+from synapse.events.utils import clone_event, prune_event
 from synapse.logging.opentracing import trace
 from synapse.storage.controllers import StorageControllers
 from synapse.storage.databases.main import DataStore
@@ -77,6 +82,7 @@ async def filter_events_for_client(
     is_peeking: bool = False,
     always_include_ids: FrozenSet[str] = frozenset(),
     filter_send_to_client: bool = True,
+    msc4115_membership_on_events: bool = False,
 ) -> List[EventBase]:
     """
     Check which events a user is allowed to see. If the user can see the event but its
@@ -95,9 +101,12 @@ async def filter_events_for_client(
         filter_send_to_client: Whether we're checking an event that's going to be
             sent to a client. This might not always be the case since this function can
             also be called to check whether a user can see the state at a given point.
+        msc4115_membership_on_events: Whether to include the requesting user's
+            membership in the "unsigned" data, per MSC4115.
 
     Returns:
-        The filtered events.
+        The filtered events. If `msc4115_membership_on_events` is true, the `unsigned`
+        data is annotated with the membership state of `user_id` at each event.
     """
     # Filter out events that have been soft failed so that we don't relay them
     # to clients.
@@ -134,7 +143,8 @@ async def filter_events_for_client(
             )
 
     def allowed(event: EventBase) -> Optional[EventBase]:
-        return _check_client_allowed_to_see_event(
+        state_after_event = event_id_to_state.get(event.event_id)
+        filtered = _check_client_allowed_to_see_event(
             user_id=user_id,
             event=event,
             clock=storage.main.clock,
@@ -142,13 +152,45 @@ async def filter_events_for_client(
             sender_ignored=event.sender in ignore_list,
             always_include_ids=always_include_ids,
             retention_policy=retention_policies[room_id],
-            state=event_id_to_state.get(event.event_id),
+            state=state_after_event,
             is_peeking=is_peeking,
             sender_erased=erased_senders.get(event.sender, False),
         )
+        if filtered is None:
+            return None
+
+        if not msc4115_membership_on_events:
+            return filtered
+
+        # Annotate the event with the user's membership after the event.
+        #
+        # Normally we just look in `state_after_event`, but if the event is an outlier
+        # we won't have such a state. The only outliers that are returned here are the
+        # user's own membership event, so we can just inspect that.
+
+        user_membership_event: Optional[EventBase]
+        if event.type == EventTypes.Member and event.state_key == user_id:
+            user_membership_event = event
+        elif state_after_event is not None:
+            user_membership_event = state_after_event.get((EventTypes.Member, user_id))
+        else:
+            # unreachable!
+            raise Exception("Missing state for event that is not user's own membership")
+
+        user_membership = (
+            user_membership_event.membership
+            if user_membership_event
+            else Membership.LEAVE
+        )
 
-    # Check each event: gives an iterable of None or (a potentially modified)
-    # EventBase.
+        # Copy the event before updating the unsigned data: this shouldn't be persisted
+        # to the cache!
+        cloned = clone_event(filtered)
+        cloned.unsigned[EventUnsignedContentFields.MSC4115_MEMBERSHIP] = user_membership
+
+        return cloned
+
+    # Check each event: gives an iterable of None or (a modified) EventBase.
     filtered_events = map(allowed, events)
 
     # Turn it into a list and remove None entries before returning.
@@ -412,8 +454,7 @@ def _check_membership(
     state: StateMap[EventBase],
     is_peeking: bool,
 ) -> _CheckMembershipReturn:
-    """Check whether the user can see the event due to their membership
-    """
+    """Check whether the user can see the event due to their membership"""
     # If the event is the user's own membership event, use the 'most joined'
     # membership
     membership = None
diff --git a/tests/events/test_utils.py b/tests/events/test_utils.py
index cf81bcf52c..975c285ec7 100644
--- a/tests/events/test_utils.py
+++ b/tests/events/test_utils.py
@@ -32,6 +32,7 @@ from synapse.events.utils import (
     PowerLevelsContent,
     SerializeEventConfig,
     _split_field,
+    clone_event,
     copy_and_fixup_power_levels_contents,
     maybe_upsert_event_field,
     prune_event,
@@ -611,6 +612,18 @@ class PruneEventTestCase(stdlib_unittest.TestCase):
         )
 
 
+class CloneEventTestCase(stdlib_unittest.TestCase):
+    def test_unsigned_is_copied(self) -> None:
+        original = make_event_from_dict(
+            {"type": "A", "event_id": "$test:domain", "unsigned": {"a": 1, "b": 2}}
+        )
+        cloned = clone_event(original)
+        cloned.unsigned["b"] = 3
+
+        self.assertEqual(original.unsigned, {"a": 1, "b": 2})
+        self.assertEqual(cloned.unsigned, {"a": 1, "b": 3})
+
+
 class SerializeEventTestCase(stdlib_unittest.TestCase):
     def serialize(self, ev: EventBase, fields: Optional[List[str]]) -> JsonDict:
         return serialize_event(
diff --git a/tests/rest/client/test_retention.py b/tests/rest/client/test_retention.py
index 09a5d64349..ceae40498e 100644
--- a/tests/rest/client/test_retention.py
+++ b/tests/rest/client/test_retention.py
@@ -163,7 +163,12 @@ class RetentionTestCase(unittest.HomeserverTestCase):
         )
         self.assertEqual(2, len(events), "events retrieved from database")
         filtered_events = self.get_success(
-            filter_events_for_client(storage_controllers, self.user_id, events)
+            filter_events_for_client(
+                storage_controllers,
+                self.user_id,
+                events,
+                msc4115_membership_on_events=True,
+            )
         )
 
         # We should only get one event back.
diff --git a/tests/test_visibility.py b/tests/test_visibility.py
index c67a169ebd..1f7bc81ef6 100644
--- a/tests/test_visibility.py
+++ b/tests/test_visibility.py
@@ -21,6 +21,7 @@ import logging
 from typing import Optional
 from unittest.mock import patch
 
+from synapse.api.constants import EventUnsignedContentFields
 from synapse.api.room_versions import RoomVersions
 from synapse.events import EventBase, make_event_from_dict
 from synapse.events.snapshot import EventContext
@@ -29,6 +30,7 @@ from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.types import create_requester
 from synapse.visibility import filter_events_for_client, filter_events_for_server
+
 from tests import unittest
 from tests.test_utils.event_injection import inject_event, inject_member_event
 from tests.unittest import HomeserverTestCase
@@ -286,22 +288,22 @@ class FilterEventsForClientTestCase(HomeserverTestCase):
         room_id = self.helper.create_room_as("resident", tok=resident_token)
 
         self.get_success(
-            inject_visibility_event(self.hs, room_id, "@resident:hs", "joined")
+            inject_visibility_event(self.hs, room_id, "@resident:test", "joined")
         )
         before_event = self.get_success(
-            inject_message_event(self.hs, room_id, "@resident:hs", body="before")
+            inject_message_event(self.hs, room_id, "@resident:test", body="before")
         )
         join_event = self.get_success(
-            inject_member_event(self.hs, room_id, "@joiner:hs", "join")
+            inject_member_event(self.hs, room_id, "@joiner:test", "join")
         )
         during_event = self.get_success(
-            inject_message_event(self.hs, room_id, "@resident:hs", body="during")
+            inject_message_event(self.hs, room_id, "@resident:test", body="during")
         )
         leave_event = self.get_success(
-            inject_member_event(self.hs, room_id, "@joiner:hs", "leave")
+            inject_member_event(self.hs, room_id, "@joiner:test", "leave")
         )
         after_event = self.get_success(
-            inject_message_event(self.hs, room_id, "@resident:hs", body="after")
+            inject_message_event(self.hs, room_id, "@resident:test", body="after")
         )
 
         # We have to reload the events from the db, to ensure that prev_content is
@@ -322,17 +324,64 @@ class FilterEventsForClientTestCase(HomeserverTestCase):
             ]
         ]
 
-        filtered_events = self.get_success(
+        # Now run the events through the filter, and check that we can see the events
+        # we expect, and that the membership prop is as expected.
+        #
+        # We deliberately do the queries for both users upfront; this simulates
+        # concurrent queries on the server, and helps ensure that we aren't
+        # accidentally serving the same event object (with the same unsigned.membership
+        # property) to both users.
+        joiner_filtered_events = self.get_success(
+            filter_events_for_client(
+                self.hs.get_storage_controllers(),
+                "@joiner:test",
+                events_to_filter,
+                msc4115_membership_on_events=True,
+            )
+        )
+        resident_filtered_events = self.get_success(
             filter_events_for_client(
                 self.hs.get_storage_controllers(),
-                "@joiner:hs",
+                "@resident:test",
                 events_to_filter,
+                msc4115_membership_on_events=True,
             )
         )
 
+        # The joiner should be able to seem the join and leave,
+        # and messages sent between the two, but not before or after.
         self.assertEqual(
             [e.event_id for e in [join_event, during_event, leave_event]],
-            [e.event_id for e in filtered_events],
+            [e.event_id for e in joiner_filtered_events],
+        )
+        self.assertEqual(
+            ["join", "join", "leave"],
+            [
+                e.unsigned[EventUnsignedContentFields.MSC4115_MEMBERSHIP]
+                for e in joiner_filtered_events
+            ],
+        )
+
+        # The resident user should see all the events.
+        self.assertEqual(
+            [
+                e.event_id
+                for e in [
+                    before_event,
+                    join_event,
+                    during_event,
+                    leave_event,
+                    after_event,
+                ]
+            ],
+            [e.event_id for e in resident_filtered_events],
+        )
+        self.assertEqual(
+            ["join", "join", "join", "join", "join"],
+            [
+                e.unsigned[EventUnsignedContentFields.MSC4115_MEMBERSHIP]
+                for e in resident_filtered_events
+            ],
         )
 
 
@@ -387,15 +436,24 @@ class FilterEventsOutOfBandEventsForClientTestCase(
         )
 
         # the invited user should be able to see both the invite and the rejection
+        filtered_events = self.get_success(
+            filter_events_for_client(
+                self.hs.get_storage_controllers(),
+                "@user:test",
+                [invite_event, reject_event],
+                msc4115_membership_on_events=True,
+            )
+        )
         self.assertEqual(
-            self.get_success(
-                filter_events_for_client(
-                    self.hs.get_storage_controllers(),
-                    "@user:test",
-                    [invite_event, reject_event],
-                )
-            ),
-            [invite_event, reject_event],
+            [e.event_id for e in filtered_events],
+            [e.event_id for e in [invite_event, reject_event]],
+        )
+        self.assertEqual(
+            ["invite", "leave"],
+            [
+                e.unsigned[EventUnsignedContentFields.MSC4115_MEMBERSHIP]
+                for e in filtered_events
+            ],
         )
 
         # other users should see neither
@@ -405,6 +463,7 @@ class FilterEventsOutOfBandEventsForClientTestCase(
                     self.hs.get_storage_controllers(),
                     "@other:test",
                     [invite_event, reject_event],
+                    msc4115_membership_on_events=True,
                 )
             ),
             [],