Test to ensure we share the same `state_group` across the whole historical batch (MSC2716) (#11487)

Part of MSC2716: https://github.com/matrix-org/matrix-doc/pull/2716

We did some work on making sure the `state_groups` were shared in
https://github.com/matrix-org/synapse/pull/10975

changelog.d/11487.misc

@@ -0,0 +1 @@
+Add test to ensure we share the same `state_group` across the whole historical batch when using the [MSC2716](https://github.com/matrix-org/matrix-doc/pull/2716) `/batch_send` endpoint.

tests/rest/client/test_room_batch.py

@@ -0,0 +1,180 @@
+import logging
+from typing import List, Tuple
+from unittest.mock import Mock, patch
+
+from twisted.test.proto_helpers import MemoryReactor
+
+from synapse.api.constants import EventContentFields, EventTypes
+from synapse.appservice import ApplicationService
+from synapse.rest import admin
+from synapse.rest.client import login, register, room, room_batch
+from synapse.server import HomeServer
+from synapse.types import JsonDict
+from synapse.util import Clock
+
+from tests import unittest
+
+logger = logging.getLogger(__name__)
+
+
+def _create_join_state_events_for_batch_send_request(
+    virtual_user_ids: List[str],
+    insert_time: int,
+) -> List[JsonDict]:
+    return [
+        {
+            "type": EventTypes.Member,
+            "sender": virtual_user_id,
+            "origin_server_ts": insert_time,
+            "content": {
+                "membership": "join",
+                "displayname": "display-name-for-%s" % (virtual_user_id,),
+            },
+            "state_key": virtual_user_id,
+        }
+        for virtual_user_id in virtual_user_ids
+    ]
+
+
+def _create_message_events_for_batch_send_request(
+    virtual_user_id: str, insert_time: int, count: int
+) -> List[JsonDict]:
+    return [
+        {
+            "type": EventTypes.Message,
+            "sender": virtual_user_id,
+            "origin_server_ts": insert_time,
+            "content": {
+                "msgtype": "m.text",
+                "body": "Historical %d" % (i),
+                EventContentFields.MSC2716_HISTORICAL: True,
+            },
+        }
+        for i in range(count)
+    ]
+
+
+class RoomBatchTestCase(unittest.HomeserverTestCase):
+    """Test importing batches of historical messages."""
+
+    servlets = [
+        admin.register_servlets_for_client_rest_resource,
+        room_batch.register_servlets,
+        room.register_servlets,
+        register.register_servlets,
+        login.register_servlets,
+    ]
+
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
+        config = self.default_config()
+
+        self.appservice = ApplicationService(
+            token="i_am_an_app_service",
+            hostname="test",
+            id="1234",
+            namespaces={"users": [{"regex": r"@as_user.*", "exclusive": True}]},
+            # Note: this user does not have to match the regex above
+            sender="@as_main:test",
+        )
+
+        mock_load_appservices = Mock(return_value=[self.appservice])
+        with patch(
+            "synapse.storage.databases.main.appservice.load_appservices",
+            mock_load_appservices,
+        ):
+            hs = self.setup_test_homeserver(config=config)
+        return hs
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.clock = clock
+        self.storage = hs.get_storage()
+
+        self.virtual_user_id = self.register_appservice_user(
+            "as_user_potato", self.appservice.token
+        )
+
+    def _create_test_room(self) -> Tuple[str, str, str, str]:
+        room_id = self.helper.create_room_as(
+            self.appservice.sender, tok=self.appservice.token
+        )
+
+        res_a = self.helper.send_event(
+            room_id=room_id,
+            type=EventTypes.Message,
+            content={
+                "msgtype": "m.text",
+                "body": "A",
+            },
+            tok=self.appservice.token,
+        )
+        event_id_a = res_a["event_id"]
+
+        res_b = self.helper.send_event(
+            room_id=room_id,
+            type=EventTypes.Message,
+            content={
+                "msgtype": "m.text",
+                "body": "B",
+            },
+            tok=self.appservice.token,
+        )
+        event_id_b = res_b["event_id"]
+
+        res_c = self.helper.send_event(
+            room_id=room_id,
+            type=EventTypes.Message,
+            content={
+                "msgtype": "m.text",
+                "body": "C",
+            },
+            tok=self.appservice.token,
+        )
+        event_id_c = res_c["event_id"]
+
+        return room_id, event_id_a, event_id_b, event_id_c
+
+    @unittest.override_config({"experimental_features": {"msc2716_enabled": True}})
+    def test_same_state_groups_for_whole_historical_batch(self):
+        """Make sure that when using the `/batch_send` endpoint to import a
+        bunch of historical messages, it re-uses the same `state_group` across
+        the whole batch. This is an easy optimization to make sure we're getting
+        right because the state for the whole batch is contained in
+        `state_events_at_start` and can be shared across everything.
+        """
+
+        time_before_room = int(self.clock.time_msec())
+        room_id, event_id_a, _, _ = self._create_test_room()
+
+        channel = self.make_request(
+            "POST",
+            "/_matrix/client/unstable/org.matrix.msc2716/rooms/%s/batch_send?prev_event_id=%s"
+            % (room_id, event_id_a),
+            content={
+                "events": _create_message_events_for_batch_send_request(
+                    self.virtual_user_id, time_before_room, 3
+                ),
+                "state_events_at_start": _create_join_state_events_for_batch_send_request(
+                    [self.virtual_user_id], time_before_room
+                ),
+            },
+            access_token=self.appservice.token,
+        )
+        self.assertEqual(channel.code, 200, channel.result)
+
+        # Get the historical event IDs that we just imported
+        historical_event_ids = channel.json_body["event_ids"]
+        self.assertEqual(len(historical_event_ids), 3)
+
+        # Fetch the state_groups
+        state_group_map = self.get_success(
+            self.storage.state.get_state_groups_ids(room_id, historical_event_ids)
+        )
+
+        # We expect all of the historical events to be using the same state_group
+        # so there should only be a single state_group here!
+        self.assertEqual(
+            len(state_group_map.keys()),
+            1,
+            "Expected a single state_group to be returned by saw state_groups=%s"
+            % (state_group_map.keys(),),
+        )