Add a `make_event_from_dict` method (#6858)

... and use it in places where it's trivial to do so.

This will make it easier to pass room versions into the FrozenEvent
constructors.

2 files changed, 17 insertions, 9 deletions

diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index 89d41d82b6..a842661a90 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -16,12 +16,13 @@
 
 import os
 from distutils.util import strtobool
+from typing import Optional, Type
 
 import six
 
 from unpaddedbase64 import encode_base64
 
-from synapse.api.room_versions import EventFormatVersions
+from synapse.api.room_versions import EventFormatVersions, RoomVersion, RoomVersions
 from synapse.types import JsonDict
 from synapse.util.caches import intern_dict
 from synapse.util.frozenutils import freeze
@@ -407,7 +408,7 @@ class FrozenEventV3(FrozenEventV2):
         return self._event_id
 
 
-def event_type_from_format_version(format_version):
+def event_type_from_format_version(format_version: int) -> Type[EventBase]:
     """Returns the python type to use to construct an Event object for the
     given event format version.
 
@@ -427,3 +428,14 @@ def event_type_from_format_version(format_version):
         return FrozenEventV3
     else:
         raise Exception("No event format %r" % (format_version,))
+
+
+def make_event_from_dict(
+    event_dict: JsonDict,
+    room_version: RoomVersion = RoomVersions.V1,
+    internal_metadata_dict: JsonDict = {},
+    rejected_reason: Optional[str] = None,
+) -> EventBase:
+    """Construct an EventBase from the given event dict"""
+    event_type = event_type_from_format_version(room_version.event_format)
+    return event_type(event_dict, internal_metadata_dict, rejected_reason)
diff --git a/synapse/events/builder.py b/synapse/events/builder.py
index 8d63ad6dc3..a0c4a40c27 100644
--- a/synapse/events/builder.py
+++ b/synapse/events/builder.py
@@ -28,11 +28,7 @@ from synapse.api.room_versions import (
     RoomVersion,
 )
 from synapse.crypto.event_signing import add_hashes_and_signatures
-from synapse.events import (
-    EventBase,
-    _EventInternalMetadata,
-    event_type_from_format_version,
-)
+from synapse.events import EventBase, _EventInternalMetadata, make_event_from_dict
 from synapse.types import EventID, JsonDict
 from synapse.util import Clock
 from synapse.util.stringutils import random_string
@@ -256,8 +252,8 @@ def create_local_event_from_event_dict(
     event_dict.setdefault("signatures", {})
 
     add_hashes_and_signatures(room_version, event_dict, hostname, signing_key)
-    return event_type_from_format_version(format_version)(
-        event_dict, internal_metadata_dict=internal_metadata_dict
+    return make_event_from_dict(
+        event_dict, room_version, internal_metadata_dict=internal_metadata_dict
     )