Delete current state when server leaves a room (#6792)

Otherwise its just stale data, which may get deleted later anyway so
can't be relied on. It's also a bit of a shotgun if we're trying to get
the current state of a room we're not in.

3 files changed, 198 insertions, 75 deletions

diff --git a/changelog.d/6792.misc b/changelog.d/6792.misc
new file mode 100644
index 0000000000..fa31d509b3
--- /dev/null
+++ b/changelog.d/6792.misc
@@ -0,0 +1 @@
+Delete current state from the database when server leaves a room.
diff --git a/synapse/storage/data_stores/main/events.py b/synapse/storage/data_stores/main/events.py
index ce553566a5..c9d0d68c3a 100644
--- a/synapse/storage/data_stores/main/events.py
+++ b/synapse/storage/data_stores/main/events.py
@@ -32,6 +32,7 @@ from twisted.internet import defer
 import synapse.metrics
 from synapse.api.constants import EventContentFields, EventTypes
 from synapse.api.errors import SynapseError
+from synapse.api.room_versions import RoomVersions
 from synapse.events import EventBase  # noqa: F401
 from synapse.events.snapshot import EventContext  # noqa: F401
 from synapse.events.utils import prune_event_dict
@@ -468,84 +469,93 @@ class EventsStore(
             to_delete = delta_state.to_delete
             to_insert = delta_state.to_insert
 
-            # First we add entries to the current_state_delta_stream. We
-            # do this before updating the current_state_events table so
-            # that we can use it to calculate the `prev_event_id`. (This
-            # allows us to not have to pull out the existing state
-            # unnecessarily).
-            #
-            # The stream_id for the update is chosen to be the minimum of the stream_ids
-            # for the batch of the events that we are persisting; that means we do not
-            # end up in a situation where workers see events before the
-            # current_state_delta updates.
-            #
-            sql = """
-                INSERT INTO current_state_delta_stream
-                (stream_id, room_id, type, state_key, event_id, prev_event_id)
-                SELECT ?, ?, ?, ?, ?, (
-                    SELECT event_id FROM current_state_events
-                    WHERE room_id = ? AND type = ? AND state_key = ?
+            if delta_state.no_longer_in_room:
+                # Server is no longer in the room so we delete the room from
+                # current_state_events, being careful we've already updated the
+                # rooms.room_version column (which gets populated in a
+                # background task).
+                self._upsert_room_version_txn(txn, room_id)
+
+                # Before deleting we populate the current_state_delta_stream
+                # so that async background tasks get told what happened.
+                sql = """
+                    INSERT INTO current_state_delta_stream
+                        (stream_id, room_id, type, state_key, event_id, prev_event_id)
+                    SELECT ?, room_id, type, state_key, null, event_id
+                        FROM current_state_events
+                        WHERE room_id = ?
+                """
+                txn.execute(sql, (stream_id, room_id))
+
+                self.db.simple_delete_txn(
+                    txn, table="current_state_events", keyvalues={"room_id": room_id},
                 )
-            """
-            txn.executemany(
-                sql,
-                (
-                    (
-                        stream_id,
-                        room_id,
-                        etype,
-                        state_key,
-                        None,
-                        room_id,
-                        etype,
-                        state_key,
+            else:
+                # We're still in the room, so we update the current state as normal.
+
+                # First we add entries to the current_state_delta_stream. We
+                # do this before updating the current_state_events table so
+                # that we can use it to calculate the `prev_event_id`. (This
+                # allows us to not have to pull out the existing state
+                # unnecessarily).
+                #
+                # The stream_id for the update is chosen to be the minimum of the stream_ids
+                # for the batch of the events that we are persisting; that means we do not
+                # end up in a situation where workers see events before the
+                # current_state_delta updates.
+                #
+                sql = """
+                    INSERT INTO current_state_delta_stream
+                    (stream_id, room_id, type, state_key, event_id, prev_event_id)
+                    SELECT ?, ?, ?, ?, ?, (
+                        SELECT event_id FROM current_state_events
+                        WHERE room_id = ? AND type = ? AND state_key = ?
                     )
-                    for etype, state_key in to_delete
-                    # We sanity check that we're deleting rather than updating
-                    if (etype, state_key) not in to_insert
-                ),
-            )
-            txn.executemany(
-                sql,
-                (
+                """
+                txn.executemany(
+                    sql,
                     (
-                        stream_id,
-                        room_id,
-                        etype,
-                        state_key,
-                        ev_id,
-                        room_id,
-                        etype,
-                        state_key,
-                    )
-                    for (etype, state_key), ev_id in iteritems(to_insert)
-                ),
-            )
+                        (
+                            stream_id,
+                            room_id,
+                            etype,
+                            state_key,
+                            to_insert.get((etype, state_key)),
+                            room_id,
+                            etype,
+                            state_key,
+                        )
+                        for etype, state_key in itertools.chain(to_delete, to_insert)
+                    ),
+                )
+                # Now we actually update the current_state_events table
 
-            # Now we actually update the current_state_events table
+                txn.executemany(
+                    "DELETE FROM current_state_events"
+                    " WHERE room_id = ? AND type = ? AND state_key = ?",
+                    (
+                        (room_id, etype, state_key)
+                        for etype, state_key in itertools.chain(to_delete, to_insert)
+                    ),
+                )
 
-            txn.executemany(
-                "DELETE FROM current_state_events"
-                " WHERE room_id = ? AND type = ? AND state_key = ?",
-                (
-                    (room_id, etype, state_key)
-                    for etype, state_key in itertools.chain(to_delete, to_insert)
-                ),
-            )
+                # We include the membership in the current state table, hence we do
+                # a lookup when we insert. This assumes that all events have already
+                # been inserted into room_memberships.
+                txn.executemany(
+                    """INSERT INTO current_state_events
+                        (room_id, type, state_key, event_id, membership)
+                    VALUES (?, ?, ?, ?, (SELECT membership FROM room_memberships WHERE event_id = ?))
+                    """,
+                    [
+                        (room_id, key[0], key[1], ev_id, ev_id)
+                        for key, ev_id in iteritems(to_insert)
+                    ],
+                )
 
-            # We include the membership in the current state table, hence we do
-            # a lookup when we insert. This assumes that all events have already
-            # been inserted into room_memberships.
-            txn.executemany(
-                """INSERT INTO current_state_events
-                    (room_id, type, state_key, event_id, membership)
-                VALUES (?, ?, ?, ?, (SELECT membership FROM room_memberships WHERE event_id = ?))
-                """,
-                [
-                    (room_id, key[0], key[1], ev_id, ev_id)
-                    for key, ev_id in iteritems(to_insert)
-                ],
-            )
+            # We now update `local_current_membership`. We do this regardless
+            # of whether we're still in the room or not to handle the case where
+            # e.g. we just got banned (where we need to record that fact here).
 
             # Note: Do we really want to delete rows here (that we do not
             # subsequently reinsert below)? While technically correct it means
@@ -601,6 +611,35 @@ class EventsStore(
 
             self._invalidate_state_caches_and_stream(txn, room_id, members_changed)
 
+    def _upsert_room_version_txn(self, txn: LoggingTransaction, room_id: str):
+        """Update the room version in the database based off current state
+        events.
+
+        This is used when we're about to delete current state and we want to
+        ensure that the `rooms.room_version` column is up to date.
+        """
+
+        sql = """
+            SELECT json FROM event_json
+            INNER JOIN current_state_events USING (room_id, event_id)
+            WHERE room_id = ? AND type = ? AND state_key = ?
+        """
+        txn.execute(sql, (room_id, EventTypes.Create, ""))
+        row = txn.fetchone()
+        if row:
+            event_json = json.loads(row[0])
+            content = event_json.get("content", {})
+            creator = content.get("creator")
+            room_version_id = content.get("room_version", RoomVersions.V1.identifier)
+
+            self.db.simple_upsert_txn(
+                txn,
+                table="rooms",
+                keyvalues={"room_id": room_id},
+                values={"room_version": room_version_id},
+                insertion_values={"is_public": False, "creator": creator},
+            )
+
     def _update_forward_extremities_txn(
         self, txn, new_forward_extremities, max_stream_order
     ):
diff --git a/synapse/storage/persist_events.py b/synapse/storage/persist_events.py
index 368c457321..d060c8b992 100644
--- a/synapse/storage/persist_events.py
+++ b/synapse/storage/persist_events.py
@@ -15,6 +15,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import itertools
 import logging
 from collections import deque, namedtuple
 from typing import Iterable, List, Optional, Tuple
@@ -27,7 +28,7 @@ from prometheus_client import Counter, Histogram
 
 from twisted.internet import defer
 
-from synapse.api.constants import EventTypes
+from synapse.api.constants import EventTypes, Membership
 from synapse.events import FrozenEvent
 from synapse.events.snapshot import EventContext
 from synapse.logging.context import PreserveLoggingContext, make_deferred_yieldable
@@ -72,17 +73,20 @@ stale_forward_extremities_counter = Histogram(
 )
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True)
 class DeltaState:
     """Deltas to use to update the `current_state_events` table.
 
     Attributes:
         to_delete: List of type/state_keys to delete from current state
         to_insert: Map of state to upsert into current state
+        no_longer_in_room: The server is not longer in the room, so the room
+            should e.g. be removed from `current_state_events` table.
     """
 
     to_delete = attr.ib(type=List[Tuple[str, str]])
     to_insert = attr.ib(type=StateMap[str])
+    no_longer_in_room = attr.ib(type=bool, default=False)
 
 
 class _EventPeristenceQueue(object):
@@ -396,11 +400,12 @@ class EventsPersistenceStorage(object):
                         # If either are not None then there has been a change,
                         # and we need to work out the delta (or use that
                         # given)
+                        delta = None
                         if delta_ids is not None:
                             # If there is a delta we know that we've
                             # only added or replaced state, never
                             # removed keys entirely.
-                            state_delta_for_room[room_id] = DeltaState([], delta_ids)
+                            delta = DeltaState([], delta_ids)
                         elif current_state is not None:
                             with Measure(
                                 self._clock, "persist_events.calculate_state_delta"
@@ -408,6 +413,22 @@ class EventsPersistenceStorage(object):
                                 delta = await self._calculate_state_delta(
                                     room_id, current_state
                                 )
+
+                        if delta:
+                            # If we have a change of state then lets check
+                            # whether we're actually still a member of the room,
+                            # or if our last user left. If we're no longer in
+                            # the room then we delete the current state and
+                            # extremities.
+                            is_still_joined = await self._is_server_still_joined(
+                                room_id, ev_ctx_rm, delta, current_state
+                            )
+                            if not is_still_joined:
+                                logger.info("Server no longer in room %s", room_id)
+                                latest_event_ids = []
+                                current_state = {}
+                                delta.no_longer_in_room = True
+
                             state_delta_for_room[room_id] = delta
 
                         # If we have the current_state then lets prefill
@@ -660,3 +681,65 @@ class EventsPersistenceStorage(object):
         }
 
         return DeltaState(to_delete=to_delete, to_insert=to_insert)
+
+    async def _is_server_still_joined(
+        self,
+        room_id: str,
+        ev_ctx_rm: List[Tuple[FrozenEvent, EventContext]],
+        delta: DeltaState,
+        current_state: Optional[StateMap[str]],
+    ) -> bool:
+        """Check if the server will still be joined after the given events have
+        been persised.
+
+        Args:
+            room_id
+            ev_ctx_rm
+            delta: The delta of current state between what is in the database
+                and what the new current state will be.
+            current_state: The new current state if it already been calculated,
+                otherwise None.
+        """
+
+        if not any(
+            self.is_mine_id(state_key)
+            for typ, state_key in itertools.chain(delta.to_delete, delta.to_insert)
+            if typ == EventTypes.Member
+        ):
+            # There have been no changes to membership of our users, so nothing
+            # has changed and we assume we're still in the room.
+            return True
+
+        # Check if any of the given events are a local join that appear in the
+        # current state
+        for (typ, state_key), event_id in delta.to_insert.items():
+            if typ != EventTypes.Member or not self.is_mine_id(state_key):
+                continue
+
+            for event, _ in ev_ctx_rm:
+                if event_id == event.event_id:
+                    if event.membership == Membership.JOIN:
+                        return True
+
+        # There's been a change of membership but we don't have a local join
+        # event in the new events, so we need to check the full state.
+        if current_state is None:
+            current_state = await self.main_store.get_current_state_ids(room_id)
+            current_state = dict(current_state)
+            for key in delta.to_delete:
+                current_state.pop(key, None)
+
+            current_state.update(delta.to_insert)
+
+        event_ids = [
+            event_id
+            for (typ, state_key,), event_id in current_state.items()
+            if typ == EventTypes.Member and self.is_mine_id(state_key)
+        ]
+
+        rows = await self.main_store.get_membership_from_event_ids(event_ids)
+        is_still_joined = any(row["membership"] == Membership.JOIN for row in rows)
+        if is_still_joined:
+            return True
+        else:
+            return False