Port `EventInternalMetadata` class to Rust (#16782)

There are a couple of things we need to be careful of here:

1. The current python code does no validation when loading from the DB,
so we need to be careful to ignore such errors (at least on jki.re there
are some old events with internal metadata fields of the wrong type).
2. We want to be memory efficient, as we often have many hundreds of
thousands of events in the cache at a time.

---------

Co-authored-by: Quentin Gliech <quenting@element.io>

3 files changed, 7 insertions, 5 deletions

diff --git a/tests/storage/databases/main/test_events_worker.py b/tests/storage/databases/main/test_events_worker.py
index ed747a8b3c..caa5752032 100644
--- a/tests/storage/databases/main/test_events_worker.py
+++ b/tests/storage/databases/main/test_events_worker.py
@@ -324,7 +324,7 @@ class DatabaseOutageTestCase(unittest.HomeserverTestCase):
         )
 
         self.event_ids: List[str] = []
-        for idx in range(20):
+        for idx in range(1, 21):  # Stream ordering starts at 1.
             event_json = {
                 "type": f"test {idx}",
                 "room_id": self.room_id,
diff --git a/tests/storage/test_event_federation.py b/tests/storage/test_event_federation.py
index b3e0bc47ec..0a6253e22c 100644
--- a/tests/storage/test_event_federation.py
+++ b/tests/storage/test_event_federation.py
@@ -44,12 +44,13 @@ from synapse.api.room_versions import (
     EventFormatVersions,
     RoomVersion,
 )
-from synapse.events import EventBase, _EventInternalMetadata
+from synapse.events import EventBase
 from synapse.rest import admin
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
 from synapse.storage.database import LoggingTransaction
 from synapse.storage.types import Cursor
+from synapse.synapse_rust.events import EventInternalMetadata
 from synapse.types import JsonDict
 from synapse.util import Clock, json_encoder
 
@@ -1209,7 +1210,7 @@ class FakeEvent:
     type = "foo"
     state_key = "foo"
 
-    internal_metadata = _EventInternalMetadata({})
+    internal_metadata = EventInternalMetadata({})
 
     def auth_event_ids(self) -> List[str]:
         return self.auth_events
diff --git a/tests/storage/test_redaction.py b/tests/storage/test_redaction.py
index c88ec69c94..cb459d6b03 100644
--- a/tests/storage/test_redaction.py
+++ b/tests/storage/test_redaction.py
@@ -25,9 +25,10 @@ from twisted.test.proto_helpers import MemoryReactor
 
 from synapse.api.constants import EventTypes, Membership
 from synapse.api.room_versions import RoomVersions
-from synapse.events import EventBase, _EventInternalMetadata
+from synapse.events import EventBase
 from synapse.events.builder import EventBuilder
 from synapse.server import HomeServer
+from synapse.synapse_rust.events import EventInternalMetadata
 from synapse.types import JsonDict, RoomID, UserID
 from synapse.util import Clock
 
@@ -268,7 +269,7 @@ class RedactionTestCase(unittest.HomeserverTestCase):
                 return self._base_builder.type
 
             @property
-            def internal_metadata(self) -> _EventInternalMetadata:
+            def internal_metadata(self) -> EventInternalMetadata:
                 return self._base_builder.internal_metadata
 
         event_1, unpersisted_context_1 = self.get_success(