fix(backend): listen connections reconnect after a dropped connection or a postgres restart and catch up on what they missed

backend/src/api/realtime.py

@@ -5,8 +5,8 @@ from typing import Any
 
 import asyncpg
 
-from utils.env import env
 from utils.events import BG_EVENTS_CHANNEL
+from utils.listen import Listener
 from utils.read import chats as chats_read
 from utils.read import presence as presence_read
 
@@ -26,7 +26,7 @@ class EventHub:
     def __init__(self) -> None:
         self._subscribers: set[Subscriber] = set()
         self._pool: asyncpg.Pool | None = None
-        self._conn: asyncpg.Connection | None = None
+        self._listener = Listener("realtime", {BG_EVENTS_CHANNEL: self._on_notify})
         self._tasks: set[asyncio.Task] = set()
 
     def subscribe(self, account_id: int, chat_id: int | None) -> Subscriber:
@@ -39,21 +39,14 @@ class EventHub:
 
     async def start(self, pool: asyncpg.Pool) -> None:
         self._pool = pool
-        conn = await asyncpg.connect(dsn=env.db.connection_url)
-        await conn.add_listener(BG_EVENTS_CHANNEL, self._on_notify)
-        self._conn = conn
-        logger.info("Realtime hub listening on %s", BG_EVENTS_CHANNEL)
+        await self._listener.start()
 
     async def stop(self) -> None:
         for task in self._tasks:
             task.cancel()
-        if self._conn is not None:
-            await self._conn.close()
-            self._conn = None
+        await self._listener.stop()
 
-    def _on_notify(
-        self, _conn: asyncpg.Connection, _pid: int, _channel: str, payload: str
-    ) -> None:
+    def _on_notify(self, payload: str) -> None:
         task = asyncio.create_task(self._dispatch(payload))
         self._tasks.add(task)
         task.add_done_callback(self._tasks.discard)