From de3e9b49ecc09e9f31ea80cc3cd4292762838d33 Mon Sep 17 00:00:00 2001
From: Kegan Dougal <7190048+kegsay@users.noreply.github.com>
Date: Mon, 29 Sep 2025 16:26:32 +0100
Subject: [PATCH] Add msc4354_sticky_duration_ttl_ms support

---
 synapse/api/constants.py                      |  3 +++
 synapse/events/__init__.py                    | 21 ++++++++++++++++++-
 .../storage/databases/main/sticky_events.py   | 17 ++++-----------
 synapse/visibility.py                         |  9 ++++++++
 4 files changed, 36 insertions(+), 14 deletions(-)

diff --git a/synapse/api/constants.py b/synapse/api/constants.py
index 5f2b1a4b5a..105a3fe7c7 100644
--- a/synapse/api/constants.py
+++ b/synapse/api/constants.py
@@ -279,6 +279,8 @@ class EventUnsignedContentFields:
     # Requesting user's membership, per MSC4115
     MEMBERSHIP: Final = "membership"
 
+    STICKY_TTL: Final = "msc4354_sticky_duration_ttl_ms"
+
 
 class MTextFields:
     """Fields found inside m.text content blocks."""
@@ -369,3 +371,4 @@ class StickyEventField(TypedDict):
 class StickyEvent:
     QUERY_PARAM_NAME: Final = "msc4354_stick_duration_ms"
     FIELD_NAME: Final = "msc4354_sticky"
+    MAX_DURATION_MS: Final = 3600000  # 1 hour
diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index db38754280..82f8940dc9 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -41,7 +41,12 @@ from typing import (
 import attr
 from unpaddedbase64 import encode_base64
 
-from synapse.api.constants import EventContentFields, EventTypes, RelationTypes
+from synapse.api.constants import (
+    EventContentFields,
+    EventTypes,
+    RelationTypes,
+    StickyEvent,
+)
 from synapse.api.room_versions import EventFormatVersions, RoomVersion, RoomVersions
 from synapse.synapse_rust.events import EventInternalMetadata
 from synapse.types import (
@@ -323,6 +328,20 @@ class EventBase(metaclass=abc.ABCMeta):
         # this will be a no-op if the event dict is already frozen.
         self._dict = freeze(self._dict)
 
+    def sticky_duration(self) -> Optional[int]:
+        sticky_obj = self.get_dict().get(StickyEvent.FIELD_NAME, None)
+        if type(sticky_obj) is not dict:
+            return None
+        sticky_duration_ms = sticky_obj.get("duration_ms", None)
+        # MSC: Valid values are the integer range 0-MAX_DURATION_MS
+        if (
+            type(sticky_duration_ms) is int
+            and sticky_duration_ms >= 0
+            and sticky_duration_ms <= StickyEvent.MAX_DURATION_MS
+        ):
+            return sticky_duration_ms
+        return None
+
     def __str__(self) -> str:
         return self.__repr__()
 
diff --git a/synapse/storage/databases/main/sticky_events.py b/synapse/storage/databases/main/sticky_events.py
index db7b8c641e..5672a9b79f 100644
--- a/synapse/storage/databases/main/sticky_events.py
+++ b/synapse/storage/databases/main/sticky_events.py
@@ -57,7 +57,6 @@ logger = logging.getLogger(__name__)
 # Consumers call 'get_sticky_events_in_rooms' which has `WHERE expires_at > ?`
 # to filter out expired sticky events that have yet to be deleted.
 DELETE_EXPIRED_STICKY_EVENTS_MS = 60 * 1000 * 60  # 1 hour
-MAX_STICKY_DURATION_MS = 3600000  # 1 hour
 
 
 class StickyEventsWorkerStore(StateGroupWorkerStore, CacheInvalidationWorkerStore):
@@ -297,22 +296,14 @@ class StickyEventsWorkerStore(StateGroupWorkerStore, CacheInvalidationWorkerStor
             if ev.rejected_reason is not None:
                 continue
             # MSC: The presence of sticky.duration_ms with a valid value makes the event “sticky”
-            sticky_obj = ev.get_dict().get(StickyEvent.FIELD_NAME, None)
-            if type(sticky_obj) is not dict:
-                continue
-            sticky_duration_ms = sticky_obj.get("duration_ms", None)
-            # MSC: Valid values are the integer range 0-MAX_STICKY_DURATION_MS
-            if (
-                type(sticky_duration_ms) is int
-                and sticky_duration_ms >= 0
-                and sticky_duration_ms <= MAX_STICKY_DURATION_MS
-            ):
+            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_STICKY_DURATION_MS).
+                # 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"],
-                    MAX_STICKY_DURATION_MS,
+                    StickyEvent.MAX_DURATION_MS,
                 )
                 # filter out already expired sticky events
                 if expires_at > now_ms:
diff --git a/synapse/visibility.py b/synapse/visibility.py
index d460d8f4c2..d0d23c54a4 100644
--- a/synapse/visibility.py
+++ b/synapse/visibility.py
@@ -209,6 +209,15 @@ async def filter_events_for_client(
         # to the cache!
         cloned = clone_event(filtered)
         cloned.unsigned[EventUnsignedContentFields.MEMBERSHIP] = user_membership
+        if storage.main.config.experimental.msc4354_enabled:
+            sticky_duration = cloned.sticky_duration()
+            if sticky_duration:
+                now = storage.main.clock.time_msec()
+                expires_at = min(cloned.origin_server_ts, now) + sticky_duration
+                if sticky_duration and expires_at > now:
+                    cloned.unsigned[EventUnsignedContentFields.STICKY_TTL] = (
+                        expires_at - now
+                    )
 
         return cloned