From 3070af4809016f547adf55fb02dbe9e569590f7e Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Date: Mon, 21 Feb 2022 19:27:35 +0000
Subject: [PATCH] remote join processing: get create event from state, not
 auth_chain (#12039)

A follow-up to #12005, in which I apparently missed that there are a bunch of other places that assume the create event is in the auth chain.
---
 changelog.d/12039.misc                  | 1 +
 synapse/federation/federation_client.py | 6 ++++--
 synapse/handlers/federation.py          | 2 +-
 synapse/storage/databases/main/room.py  | 4 ++--
 4 files changed, 8 insertions(+), 5 deletions(-)
 create mode 100644 changelog.d/12039.misc

diff --git a/changelog.d/12039.misc b/changelog.d/12039.misc
new file mode 100644
index 0000000000..45e21dbe59
--- /dev/null
+++ b/changelog.d/12039.misc
@@ -0,0 +1 @@
+Preparation for faster-room-join work: when parsing the `send_join` response, get the `m.room.create` event from `state`, not `auth_chain`.
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index 9f56f97d99..48c90bf0bb 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -870,13 +870,15 @@ class FederationClient(FederationBase):
             for s in signed_state:
                 s.internal_metadata = copy.deepcopy(s.internal_metadata)
 
-            # double-check that the same create event has ended up in the auth chain
+            # double-check that the auth chain doesn't include a different create event
             auth_chain_create_events = [
                 e.event_id
                 for e in signed_auth
                 if (e.type, e.state_key) == (EventTypes.Create, "")
             ]
-            if auth_chain_create_events != [create_event.event_id]:
+            if auth_chain_create_events and auth_chain_create_events != [
+                create_event.event_id
+            ]:
                 raise InvalidResponseError(
                     "Unexpected create event(s) in auth chain: %s"
                     % (auth_chain_create_events,)
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index c0f642005f..c8356f233d 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -516,7 +516,7 @@ class FederationHandler:
             await self.store.upsert_room_on_join(
                 room_id=room_id,
                 room_version=room_version_obj,
-                auth_events=auth_chain,
+                state_events=state,
             )
 
             max_stream_id = await self._federation_event_handler.process_remote_join(
diff --git a/synapse/storage/databases/main/room.py b/synapse/storage/databases/main/room.py
index 95167116c9..0416df64ce 100644
--- a/synapse/storage/databases/main/room.py
+++ b/synapse/storage/databases/main/room.py
@@ -1498,7 +1498,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
         self._event_reports_id_gen = IdGenerator(db_conn, "event_reports", "id")
 
     async def upsert_room_on_join(
-        self, room_id: str, room_version: RoomVersion, auth_events: List[EventBase]
+        self, room_id: str, room_version: RoomVersion, state_events: List[EventBase]
     ) -> None:
         """Ensure that the room is stored in the table
 
@@ -1511,7 +1511,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
         has_auth_chain_index = await self.has_auth_chain_index(room_id)
 
         create_event = None
-        for e in auth_events:
+        for e in state_events:
             if (e.type, e.state_key) == (EventTypes.Create, ""):
                 create_event = e
                 break