Styjun

Django 2.1.1,
Django Channels 2.1.3,
Celery 4.2.1

I've set up a task in Celery and at the end of the task, I need to send a websocket message to the client(s). However, the websocket message is never sent. There are no errors thrown, it just simply doesn't send.

I've set up a channel layer using Redis as the backend. Doing this from a normal Django view works fine. But when run in a Celery task, it sends the message to Channels and I can see that Channels does indeed run the code shown in my consumers.py code below, but the client never receives the websocket message.

tasks.py

def import_job(self):
 # (do task calculations, store in data dict)
 message = 'type': 'send_my_data',
 'data': json.dumps(thecalcs) 
 channel_layer = get_channel_layer()
 async_to_sync(channel_layer.group_send)('core-data', message)

consumers.py

class AsyncDataConsumer(AsyncWebsocketConsumer):
 async def connect(self):
 self.channel_group_name = 'core-data'

 # Join the group
 await self.channel_layer.group_add(
 self.channel_group_name,
 self.channel_name
 )
 await self.accept()

 async def disconnect(self, close_code):
 # Leave the group
 await self.channel_layer.group_discard(
 self.channel_group_name,
 self.channel_name
 )

 # Receive message from WebSocket
 async def receive(self, text_data=None, bytes_data=None):
 pass

 # Receive message from the group
 async def send_my_data(self, event):
 text = event['data']
 # Send message to WebSocket
 await self.send(text_data=text)

settings.py

CHANNEL_LAYERS = 
 'default': 
 'BACKEND': 'channels_redis.core.RedisChannelLayer',
 'CONFIG': 
 "hosts": [('127.0.0.1', 6379)],
 ,
 ,

Since there is no exception/error, I am completely at a loss as to which part of this process is failing.

1. Celery triggers the task? Yes


2. The task runs and sends a message to the channel layer? Yes


3. The consumer receives the message from the group and executes the send()? Yes


4. Client receives the a websocket message? NO

Is this a problem between Channels and Redis? Is it a problem between Channels and the client?

It turns out Celery was swallowing an exception in my code during the task. I need to implement more thorough logging to catch these exceptions.