From c027bc0e4b071d3d40c7b0c1e7011ad5c8c3d0a0 Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Date: Fri, 21 Jan 2022 09:10:01 +0000
Subject: [PATCH] Add `FrozenEvent.get_state_key` and use it in a couple of
 places (#11793)

This is more efficient, since we only have to look up `state_key` in the event
dict once, rather than three (!) times.
---
 changelog.d/11793.misc     |  1 +
 synapse/events/__init__.py | 13 +++++++++----
 synapse/events/snapshot.py |  2 +-
 3 files changed, 11 insertions(+), 5 deletions(-)
 create mode 100644 changelog.d/11793.misc

diff --git a/changelog.d/11793.misc b/changelog.d/11793.misc
new file mode 100644
index 000000000000..fc0530bf2cb6
--- /dev/null
+++ b/changelog.d/11793.misc
@@ -0,0 +1 @@
+Add `FrozenEvent.get_state_key` and use it in a couple of places.
diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index 38f3cf4d330d..9acb3c0cc454 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -315,10 +315,11 @@ def __init__(
     redacts: DefaultDictProperty[Optional[str]] = DefaultDictProperty("redacts", None)
     room_id: DictProperty[str] = DictProperty("room_id")
     sender: DictProperty[str] = DictProperty("sender")
-    # TODO state_key should be Optional[str], this is generally asserted in Synapse
-    # by calling is_state() first (which ensures this), but it is hard (not possible?)
+    # TODO state_key should be Optional[str]. This is generally asserted in Synapse
+    # by calling is_state() first (which ensures it is not None), but it is hard (not possible?)
     # to properly annotate that calling is_state() asserts that state_key exists
-    # and is non-None.
+    # and is non-None. It would be better to replace such direct references with
+    # get_state_key() (and a check for None).
     state_key: DictProperty[str] = DictProperty("state_key")
     type: DictProperty[str] = DictProperty("type")
     user_id: DictProperty[str] = DictProperty("sender")
@@ -332,7 +333,11 @@ def membership(self) -> str:
         return self.content["membership"]
 
     def is_state(self) -> bool:
-        return hasattr(self, "state_key") and self.state_key is not None
+        return self.get_state_key() is not None
+
+    def get_state_key(self) -> Optional[str]:
+        """Get the state key of this event, or None if it's not a state event"""
+        return self._dict.get("state_key")
 
     def get_dict(self) -> JsonDict:
         d = dict(self._dict)
diff --git a/synapse/events/snapshot.py b/synapse/events/snapshot.py
index 0eab1aefd637..5833fee25fce 100644
--- a/synapse/events/snapshot.py
+++ b/synapse/events/snapshot.py
@@ -163,7 +163,7 @@ async def serialize(self, event: EventBase, store: "DataStore") -> JsonDict:
         return {
             "prev_state_id": prev_state_id,
             "event_type": event.type,
-            "event_state_key": event.state_key if event.is_state() else None,
+            "event_state_key": event.get_state_key(),
             "state_group": self._state_group,
             "state_group_before_event": self.state_group_before_event,
             "rejected": self.rejected,