Improvements to Kafka backend (#125)

Author: alex-oleshkevich

broadcaster/_backends/kafka.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import asyncio
 import typing
 from urllib.parse import urlparse
 
@@ -10,9 +11,11 @@
 
 
 class KafkaBackend(BroadcastBackend):
-    def __init__(self, url: str):
-        self._servers = [urlparse(url).netloc]
+    def __init__(self, urls: str | list[str]) -> None:
+        urls = [urls] if isinstance(urls, str) else urls
+        self._servers = [urlparse(url).netloc for url in urls]
         self._consumer_channels: set[str] = set()
+        self._ready = asyncio.Event()
 
     async def connect(self) -> None:
         self._producer = AIOKafkaProducer(bootstrap_servers=self._servers)
@@ -27,6 +30,7 @@ async def disconnect(self) -> None:
     async def subscribe(self, channel: str) -> None:
         self._consumer_channels.add(channel)
         self._consumer.subscribe(topics=self._consumer_channels)
+        await self._wait_for_assignment()
 
     async def unsubscribe(self, channel: str) -> None:
         self._consumer.unsubscribe()
@@ -35,5 +39,13 @@ async def publish(self, channel: str, message: typing.Any) -> None:
         await self._producer.send_and_wait(channel, message.encode("utf8"))
 
     async def next_published(self) -> Event:
+        await self._ready.wait()
         message = await self._consumer.getone()
         return Event(channel=message.topic, message=message.value.decode("utf8"))
+
+    async def _wait_for_assignment(self) -> None:
+        """Wait for the consumer to be assigned to the partition."""
+        while not self._consumer.assignment():
+            await asyncio.sleep(0.001)
+
+        self._ready.set()

tests/test_broadcast.py

@@ -6,6 +6,7 @@
 import pytest
 
 from broadcaster import Broadcast, BroadcastBackend, Event
+from broadcaster._backends.kafka import KafkaBackend
 
 
 class CustomBackend(BroadcastBackend):
@@ -80,7 +81,6 @@ async def test_postgres():
             assert event.message == "hello"
 
 
-@pytest.mark.skip("Deadlock on `next_published`")
 @pytest.mark.asyncio
 async def test_kafka():
     async with Broadcast("kafka://localhost:9092") as broadcast:
@@ -91,6 +91,16 @@ async def test_kafka():
             assert event.message == "hello"
 
 
+@pytest.mark.asyncio
+async def test_kafka_multiple_urls():
+    async with Broadcast(backend=KafkaBackend(urls=["kafka://localhost:9092", "kafka://localhost:9092"])) as broadcast:
+        async with broadcast.subscribe("chatroom") as subscriber:
+            await broadcast.publish("chatroom", "hello")
+            event = await subscriber.get()
+            assert event.channel == "chatroom"
+            assert event.message == "hello"
+
+
 @pytest.mark.asyncio
 async def test_custom():
     backend = CustomBackend("")