From 4fb1c5a66a7cf6cd85d71bc0d39cb3653eb7724e Mon Sep 17 00:00:00 2001
From: Olivier 'reivilibre <oliverw@matrix.org>
Date: Fri, 19 Dec 2025 17:40:40 +0000
Subject: [PATCH] Don't duplicate clamping logic

---
 synapse/events/__init__.py                    |  7 ++++++
 .../storage/databases/main/sticky_events.py   | 23 ++++++++-----------
 2 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index d723fa0847..83916211af 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -324,6 +324,13 @@ class EventBase(metaclass=abc.ABCMeta):
         self._dict = freeze(self._dict)
 
     def sticky_duration(self) -> int | None:
+        """
+        Returns the effective sticky duration of this event, or None
+        if the event does not have a sticky duration.
+        (Sticky Events are a MSC4354 feature.)
+
+        Clamps the sticky duration to the maximum allowed duration.
+        """
         sticky_obj = self.get_dict().get(StickyEvent.FIELD_NAME, None)
         if type(sticky_obj) is not dict:
             return None
diff --git a/synapse/storage/databases/main/sticky_events.py b/synapse/storage/databases/main/sticky_events.py
index 092b897f8b..03c79f544b 100644
--- a/synapse/storage/databases/main/sticky_events.py
+++ b/synapse/storage/databases/main/sticky_events.py
@@ -21,7 +21,7 @@ from typing import (
 from twisted.internet.defer import Deferred
 
 from synapse import event_auth
-from synapse.api.constants import EventTypes, StickyEvent
+from synapse.api.constants import EventTypes
 from synapse.api.errors import AuthError
 from synapse.events import EventBase
 from synapse.events.snapshot import EventPersistencePair
@@ -315,21 +315,16 @@ class StickyEventsWorkerStore(StateGroupWorkerStore, CacheInvalidationWorkerStor
             # We can't persist outlier sticky events as we don't know the room state at that event
             if ev.internal_metadata.is_outlier():
                 continue
-            # MSC: The presence of sticky.duration_ms with a valid value makes the event “sticky”
             sticky_duration = ev.sticky_duration()
-            if sticky_duration:
-                # MSC: The start time is min(now, origin_server_ts).
-                # This ensures that malicious origin timestamps cannot specify start times in the future.
-                # Calculate the end time as start_time + min(sticky.duration_ms, MAX_DURATION_MS).
-                expires_at = min(ev.origin_server_ts, now_ms) + min(
-                    ev.get_dict()[StickyEvent.FIELD_NAME]["duration_ms"],
-                    StickyEvent.MAX_DURATION_MS,
+            if sticky_duration is None:
+                continue
+            # Calculate the end time as start_time + effecitve sticky duration
+            expires_at = min(ev.origin_server_ts, now_ms) + sticky_duration
+            # Filter out already expired sticky events
+            if expires_at > now_ms:
+                sticky_events.append(
+                    (ev, expires_at, self._sticky_events_id_gen.get_next_txn(txn))
                 )
-                # filter out already expired sticky events
-                if expires_at > now_ms:
-                    sticky_events.append(
-                        (ev, expires_at, self._sticky_events_id_gen.get_next_txn(txn))
-                    )
         if len(sticky_events) == 0:
             return
         logger.info(