Populate `rooms.creator` field for easy lookup (#10697)

Part of https://github.com/matrix-org/synapse/pull/10566

 - Fill in creator whenever we insert into the rooms table
 - Add background update to backfill any missing creator values

6 files changed, 213 insertions, 4 deletions

diff --git a/changelog.d/10697.misc b/changelog.d/10697.misc
new file mode 100644
index 0000000000..a9ad17faf2
--- /dev/null
+++ b/changelog.d/10697.misc
@@ -0,0 +1 @@
+Ensure `rooms.creator` field is always populated for easy lookup in [MSC2716](https://github.com/matrix-org/matrix-doc/pull/2716) usage later.
diff --git a/synapse/api/constants.py b/synapse/api/constants.py
index 829061c870..5e34eb7e13 100644
--- a/synapse/api/constants.py
+++ b/synapse/api/constants.py
@@ -198,6 +198,9 @@ class EventContentFields:
     # cf https://github.com/matrix-org/matrix-doc/pull/1772
     ROOM_TYPE = "type"
 
+    # The creator of the room, as used in `m.room.create` events.
+    ROOM_CREATOR = "creator"
+
     # Used on normal messages to indicate they were historically imported after the fact
     MSC2716_HISTORICAL = "org.matrix.msc2716.historical"
     # For "insertion" events to indicate what the next chunk ID should be in
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index daf1d3bfb3..77df9185f6 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -507,6 +507,7 @@ class FederationHandler(BaseHandler):
             await self.store.upsert_room_on_join(
                 room_id=room_id,
                 room_version=room_version_obj,
+                auth_events=auth_chain,
             )
 
             max_stream_id = await self._persist_auth_tree(
diff --git a/synapse/storage/databases/main/room.py b/synapse/storage/databases/main/room.py
index f98b892598..6e7312266d 100644
--- a/synapse/storage/databases/main/room.py
+++ b/synapse/storage/databases/main/room.py
@@ -19,9 +19,10 @@ from abc import abstractmethod
 from enum import Enum
 from typing import Any, Dict, List, Optional, Tuple
 
-from synapse.api.constants import EventTypes, JoinRules
+from synapse.api.constants import EventContentFields, EventTypes, JoinRules
 from synapse.api.errors import StoreError
 from synapse.api.room_versions import RoomVersion, RoomVersions
+from synapse.events import EventBase
 from synapse.storage._base import SQLBaseStore, db_to_json
 from synapse.storage.database import DatabasePool, LoggingTransaction
 from synapse.storage.databases.main.search import SearchStore
@@ -1013,6 +1014,7 @@ class _BackgroundUpdates:
     ADD_ROOMS_ROOM_VERSION_COLUMN = "add_rooms_room_version_column"
     POPULATE_ROOM_DEPTH_MIN_DEPTH2 = "populate_room_depth_min_depth2"
     REPLACE_ROOM_DEPTH_MIN_DEPTH = "replace_room_depth_min_depth"
+    POPULATE_ROOMS_CREATOR_COLUMN = "populate_rooms_creator_column"
 
 
 _REPLACE_ROOM_DEPTH_SQL_COMMANDS = (
@@ -1054,6 +1056,11 @@ class RoomBackgroundUpdateStore(SQLBaseStore):
             self._background_replace_room_depth_min_depth,
         )
 
+        self.db_pool.updates.register_background_update_handler(
+            _BackgroundUpdates.POPULATE_ROOMS_CREATOR_COLUMN,
+            self._background_populate_rooms_creator_column,
+        )
+
     async def _background_insert_retention(self, progress, batch_size):
         """Retrieves a list of all rooms within a range and inserts an entry for each of
         them into the room_retention table.
@@ -1273,7 +1280,7 @@ class RoomBackgroundUpdateStore(SQLBaseStore):
             keyvalues={"room_id": room_id},
             retcol="MAX(stream_ordering)",
             allow_none=True,
-            desc="upsert_room_on_join",
+            desc="has_auth_chain_index_fallback",
         )
 
         return max_ordering is None
@@ -1343,6 +1350,65 @@ class RoomBackgroundUpdateStore(SQLBaseStore):
 
         return 0
 
+    async def _background_populate_rooms_creator_column(
+        self, progress: dict, batch_size: int
+    ):
+        """Background update to go and add creator information to `rooms`
+        table from `current_state_events` table.
+        """
+
+        last_room_id = progress.get("room_id", "")
+
+        def _background_populate_rooms_creator_column_txn(txn: LoggingTransaction):
+            sql = """
+                SELECT room_id, json FROM event_json
+                INNER JOIN rooms AS room USING (room_id)
+                INNER JOIN current_state_events AS state_event USING (room_id, event_id)
+                WHERE room_id > ? AND (room.creator IS NULL OR room.creator = '') AND state_event.type = 'm.room.create' AND state_event.state_key = ''
+                ORDER BY room_id
+                LIMIT ?
+            """
+
+            txn.execute(sql, (last_room_id, batch_size))
+            room_id_to_create_event_results = txn.fetchall()
+
+            new_last_room_id = ""
+            for room_id, event_json in room_id_to_create_event_results:
+                event_dict = db_to_json(event_json)
+
+                creator = event_dict.get("content").get(EventContentFields.ROOM_CREATOR)
+
+                self.db_pool.simple_update_txn(
+                    txn,
+                    table="rooms",
+                    keyvalues={"room_id": room_id},
+                    updatevalues={"creator": creator},
+                )
+                new_last_room_id = room_id
+
+            if new_last_room_id == "":
+                return True
+
+            self.db_pool.updates._background_update_progress_txn(
+                txn,
+                _BackgroundUpdates.POPULATE_ROOMS_CREATOR_COLUMN,
+                {"room_id": new_last_room_id},
+            )
+
+            return False
+
+        end = await self.db_pool.runInteraction(
+            "_background_populate_rooms_creator_column",
+            _background_populate_rooms_creator_column_txn,
+        )
+
+        if end:
+            await self.db_pool.updates._end_background_update(
+                _BackgroundUpdates.POPULATE_ROOMS_CREATOR_COLUMN
+            )
+
+        return batch_size
+
 
 class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore, SearchStore):
     def __init__(self, database: DatabasePool, db_conn, hs):
@@ -1350,7 +1416,9 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore, SearchStore):
 
         self.config = hs.config
 
-    async def upsert_room_on_join(self, room_id: str, room_version: RoomVersion):
+    async def upsert_room_on_join(
+        self, room_id: str, room_version: RoomVersion, auth_events: List[EventBase]
+    ):
         """Ensure that the room is stored in the table
 
         Called when we join a room over federation, and overwrites any room version
@@ -1361,6 +1429,24 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore, SearchStore):
         # mark the room as having an auth chain cover index.
         has_auth_chain_index = await self.has_auth_chain_index(room_id)
 
+        create_event = None
+        for e in auth_events:
+            if (e.type, e.state_key) == (EventTypes.Create, ""):
+                create_event = e
+                break
+
+        if create_event is None:
+            # If the state doesn't have a create event then the room is
+            # invalid, and it would fail auth checks anyway.
+            raise StoreError(400, "No create event in state")
+
+        room_creator = create_event.content.get(EventContentFields.ROOM_CREATOR)
+
+        if not isinstance(room_creator, str):
+            # If the create event does not have a creator then the room is
+            # invalid, and it would fail auth checks anyway.
+            raise StoreError(400, "No creator defined on the create event")
+
         await self.db_pool.simple_upsert(
             desc="upsert_room_on_join",
             table="rooms",
@@ -1368,7 +1454,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore, SearchStore):
             values={"room_version": room_version.identifier},
             insertion_values={
                 "is_public": False,
-                "creator": "",
+                "creator": room_creator,
                 "has_auth_chain_index": has_auth_chain_index,
             },
             # rooms has a unique constraint on room_id, so no need to lock when doing an
@@ -1396,6 +1482,9 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore, SearchStore):
             insertion_values={
                 "room_version": room_version.identifier,
                 "is_public": False,
+                # We don't worry about setting the `creator` here because
+                # we don't process any messages in a room while a user is
+                # invited (only after the join).
                 "creator": "",
                 "has_auth_chain_index": has_auth_chain_index,
             },
diff --git a/synapse/storage/schema/main/delta/63/02populate-rooms-creator.sql b/synapse/storage/schema/main/delta/63/02populate-rooms-creator.sql
new file mode 100644
index 0000000000..f7c0b31261
--- /dev/null
+++ b/synapse/storage/schema/main/delta/63/02populate-rooms-creator.sql
@@ -0,0 +1,17 @@
+/* Copyright 2021 The Matrix.org Foundation C.I.C
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * 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.
+ */
+
+INSERT INTO background_updates (ordering, update_name, progress_json)
+    VALUES (6302, 'populate_rooms_creator_column', '{}');
diff --git a/tests/storage/databases/main/test_room.py b/tests/storage/databases/main/test_room.py
new file mode 100644
index 0000000000..ffee707153
--- /dev/null
+++ b/tests/storage/databases/main/test_room.py
@@ -0,0 +1,98 @@
+# Copyright 2021 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the 'License');
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an 'AS IS' BASIS,
+# 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 synapse.rest import admin
+from synapse.rest.client import login, room
+from synapse.storage.databases.main.room import _BackgroundUpdates
+
+from tests.unittest import HomeserverTestCase
+
+
+class RoomBackgroundUpdateStoreTestCase(HomeserverTestCase):
+
+    servlets = [
+        admin.register_servlets,
+        room.register_servlets,
+        login.register_servlets,
+    ]
+
+    def prepare(self, reactor, clock, hs):
+        self.store = hs.get_datastore()
+        self.user_id = self.register_user("foo", "pass")
+        self.token = self.login("foo", "pass")
+
+    def _generate_room(self) -> str:
+        room_id = self.helper.create_room_as(self.user_id, tok=self.token)
+
+        return room_id
+
+    def test_background_populate_rooms_creator_column(self):
+        """Test that the background update to populate the rooms creator column
+        works properly.
+        """
+
+        # Insert a room without the creator
+        room_id = self._generate_room()
+        self.get_success(
+            self.store.db_pool.simple_update(
+                table="rooms",
+                keyvalues={"room_id": room_id},
+                updatevalues={"creator": None},
+                desc="test",
+            )
+        )
+
+        # Make sure the test is starting out with a room without a creator
+        room_creator_before = self.get_success(
+            self.store.db_pool.simple_select_one_onecol(
+                table="rooms",
+                keyvalues={"room_id": room_id},
+                retcol="creator",
+                allow_none=True,
+            )
+        )
+        self.assertEqual(room_creator_before, None)
+
+        # Insert and run the background update.
+        self.get_success(
+            self.store.db_pool.simple_insert(
+                "background_updates",
+                {
+                    "update_name": _BackgroundUpdates.POPULATE_ROOMS_CREATOR_COLUMN,
+                    "progress_json": "{}",
+                },
+            )
+        )
+
+        # ... and tell the DataStore that it hasn't finished all updates yet
+        self.store.db_pool.updates._all_done = False
+
+        # Now let's actually drive the updates to completion
+        while not self.get_success(
+            self.store.db_pool.updates.has_completed_background_updates()
+        ):
+            self.get_success(
+                self.store.db_pool.updates.do_next_background_update(100), by=0.1
+            )
+
+        # Make sure the background update filled in the room creator
+        room_creator_after = self.get_success(
+            self.store.db_pool.simple_select_one_onecol(
+                table="rooms",
+                keyvalues={"room_id": room_id},
+                retcol="creator",
+                allow_none=True,
+            )
+        )
+        self.assertEqual(room_creator_after, self.user_id)