Beeper previews: omit key if we don't populate preview

Author: Fizzadar

synapse/handlers/sync.py

@@ -2467,7 +2467,7 @@ async def _generate_room_entry(
                     unread_thread_notifications={},
                     summary=summary,
                     unread_count=0,
-                    preview={},
+                    preview=None,
                 )
 
                 # Only generate previews if we have new events that would change it

synapse/rest/client/sync.py

@@ -536,13 +536,14 @@ async def encode_room(
             if self._msc2654_enabled:
                 result["org.matrix.msc2654.unread_count"] = room.unread_count
 
-            if room.preview and "event" in room.preview:
-                room.preview["event"] = self._event_serializer.serialize_events(
-                    [room.preview["event"]],
-                    time_now,
-                    config=serialize_options,
-                )[0]
-            result["com.beeper.inbox.preview"] = room.preview
+            if room.preview:
+                if "event" in room.preview:
+                    room.preview["event"] = self._event_serializer.serialize_events(
+                        [room.preview["event"]],
+                        time_now,
+                        config=serialize_options,
+                    )[0]
+                result["com.beeper.inbox.preview"] = room.preview
 
         return result
 

tests/rest/client/test_sync.py

@@ -873,15 +873,16 @@ def _check_preview_event_ids(self, auth_token: str, expected: dict) -> None:
                 channel.json_body.get("rooms", {}).get("join", {}).get(room_id, {})
             )
 
-            preview_id = room_entry.get("com.beeper.inbox.preview", {}).get(
-                "event_id", {}
-            )
-
-            self.assertEqual(
-                preview_id,
-                expected_entry,
-                room_entry,
-            )
+            preview = room_entry.get("com.beeper.inbox.preview")
+            if preview:
+                preview_id = preview.get("event_id")
+                self.assertEqual(
+                    preview_id,
+                    expected_entry,
+                    room_entry,
+                )
+            else:
+                self.assertIsNone(expected_entry, room_entry)
 
         # Store the next batch for the next request.
         self.next_batches[auth_token] = channel.json_body["next_batch"]
@@ -1114,6 +1115,34 @@ def test_room_preview_edits(self) -> None:
             auth_token=self.tok, expected={self.room_id: send_5_body["event_id"]}
         )
 
+    def test_room_preview_no_change(self) -> None:
+        """Tests that /sync only includes previews when we have new events."""
+
+        self.helper.join(room=self.room_id, user=self.user_id, tok=self.tok)
+
+        send_body = self.helper.send(self.room_id, "hello", tok=self.tok)
+
+        # Should have preview on first sync
+        self._check_preview_event_ids(
+            auth_token=self.tok,
+            expected={self.room_id: send_body["event_id"]},
+        )
+
+        # Should have no preview on second sync (no timeline changes)
+        self._check_preview_event_ids(
+            auth_token=self.tok,
+            expected={self.room_id: None},
+        )
+
+        # Send a join event, this isn't previewed but will be in the timeline
+        self.helper.join(room=self.room_id, user=self.user2, tok=self.tok2)
+
+        # Should have preview because we have timeline, but preview is unchanged
+        self._check_preview_event_ids(
+            auth_token=self.tok,
+            expected={self.room_id: send_body["event_id"]},
+        )
+
 
 class SyncCacheTestCase(unittest.HomeserverTestCase):
     servlets = [