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WebSocket Broadcaster Service - Phase 5
Subscribes to Kafka task-updates topic and broadcasts to WebSocket clients
"""
import json
import asyncio
from typing import Optional
from dapr.clients import DaprClient
from sqlalchemy.orm import Session
from src.db.session import get_db
from src.models.task import Task
from src.services.websocket_manager import get_websocket_manager
from src.utils.logger import get_logger
logger = get_logger(__name__)
class WebSocketBroadcaster:
"""
Background service that subscribes to Kafka task-updates topic
and broadcasts updates to connected WebSocket clients.
This enables real-time multi-client synchronization.
"""
def __init__(self, check_interval_seconds: int = 1):
"""
Initialize the WebSocket broadcaster.
Args:
check_interval_seconds: How often to poll for new messages (default: 1s)
"""
self.dapr = DaprClient()
self.pubsub_name = "kafka-pubsub"
self.topic_name = "task-updates"
self.check_interval = check_interval_seconds
self._running = False
self._task: Optional[asyncio.Task] = None
self.websocket_manager = get_websocket_manager()
async def start(self):
"""Start the background broadcaster."""
if self._running:
logger.warning("WebSocket broadcaster already running")
return
logger.info("Starting WebSocket broadcaster", topic=self.topic_name)
self._running = True
self._task = asyncio.create_task(self._poll_messages())
async def stop(self):
"""Stop the background broadcaster."""
if not self._running:
return
logger.info("Stopping WebSocket broadcaster")
self._running = False
if self._task:
self._task.cancel()
try:
await self._task
except asyncio.CancelledError:
pass
async def _poll_messages(self):
"""
Main polling loop - continuously checks for new Kafka messages.
Dapr doesn't support async subscribe, so we poll in a loop.
"""
while self._running:
try:
# Use Dapr's subscribe method in a thread pool
# to avoid blocking the event loop
loop = asyncio.get_event_loop()
await loop.run_in_executor(None, self._subscribe_sync)
except Exception as e:
logger.error(
"Error in broadcaster loop",
error=str(e),
exc_info=True
)
# Small delay between polls
await asyncio.sleep(self.check_interval)
def _subscribe_sync(self):
"""
Synchronous Dapr subscription.
This runs in a thread pool to avoid blocking the async event loop.
Dapr client doesn't support async, so we use this approach.
"""
try:
# Subscribe to Kafka topic via Dapr
with self.dapr.subscribe(
pubsub_name=self.pubsub_name,
topic=self.topic_name,
disable_beta_message_headers=True
) as subscription:
for msg in subscription:
try:
# Parse message data
data = json.loads(msg.data())
# Handle the update
asyncio.create_task(self._handle_task_update(data))
except Exception as e:
logger.error(
"Error processing Kafka message",
error=str(e),
exc_info=True
)
except Exception as e:
logger.error("Dapr subscribe error", error=str(e), exc_info=True)
async def _handle_task_update(self, event_data: dict):
"""
Handle a task update event from Kafka.
Args:
event_data: The event payload from Kafka
"""
try:
event_type = event_data.get("event_type", "")
payload = event_data.get("payload", {})
user_id = payload.get("user_id")
task_id = payload.get("task_id")
if not user_id or not task_id:
logger.warning("Missing user_id or task_id in event", event_data=event_data)
return
# Determine update type
update_type = event_type.replace("task.", "")
# Fetch full task data from database
db: Session = next(get_db())
try:
task = db.query(Task).filter(Task.id == task_id).first()
if not task:
logger.debug("Task not found, may have been deleted", task_id=task_id)
task_data = payload # Use event data if task not found
else:
task_data = task.to_dict()
# Broadcast to user's WebSocket connections
await self.websocket_manager.broadcast_task_update(
user_id=user_id,
update_type=update_type,
task_data=task_data
)
logger.info(
"Task update broadcast to WebSocket",
user_id=user_id,
task_id=task_id,
update_type=update_type
)
finally:
db.close()
except Exception as e:
logger.error(
"Failed to handle task update",
error=str(e),
exc_info=True
)
async def broadcast_direct(
self,
user_id: str,
update_type: str,
task_data: dict
):
"""
Direct broadcast method (for testing or manual triggering).
Args:
user_id: ID of the user
update_type: Type of update (created, updated, completed, deleted)
task_data: Task data to broadcast
"""
await self.websocket_manager.broadcast_task_update(
user_id=user_id,
update_type=update_type,
task_data=task_data
)
# Global broadcaster instance
_broadcaster: Optional[WebSocketBroadcaster] = None
def get_websocket_broadcaster() -> WebSocketBroadcaster:
"""Get the global WebSocket broadcaster instance."""
global _broadcaster
if _broadcaster is None:
_broadcaster = WebSocketBroadcaster()
return _broadcaster
async def start_broadcaster():
"""Start the global WebSocket broadcaster."""
broadcaster = get_websocket_broadcaster()
await broadcaster.start()
logger.info("WebSocket broadcaster started")
async def stop_broadcaster():
"""Stop the global WebSocket broadcaster."""
global _broadcaster
if _broadcaster:
await _broadcaster.stop()
logger.info("WebSocket broadcaster stopped")
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