RabbitMQ Pika and Django Channels websocket - django

Question

I am using Django Channels and RabbitMQ pika, for the first time. I am trying to consume from RabbitMQ queue. I am using Django Channels AsyncConsumer to group send it to everyone connected in the websocket.
User type 1 : Can create a task
User type 2 : Can accept the task.
Use case : When user type 1 creates the task it is published in the rabbitmq. When it is consumed from the queue, it has to be group-sent to frontend. And when the user type 2 accepts the task other instances of user type 2 cannot accept the same and we consume from the queue again and send the next task in the queue to everyone.
I have created the connection in a different thread using sync_to_async I am appending it to an in-memory list from the callback function.
And whenever someone accepts I just pop it out of the list and acknowledge the queue.
class AcceptTaskConsumer(AsyncConsumer):
body = [] #IN MEMORY LIST
delivery = {} #To store ack delivery_tag
async def websocket_connect(self, event):
print("AcceptTaskConsumer connected", event)
AcceptTaskConsumer.get_task() #STARTS Queue listener in new thread
self.room_group_name = "user_type_2"
await self.channel_layer.group_add(
self.room_group_name,
self.channel_name
)
await self.send({
"type": "websocket.accept"
})
async def websocket_receive(self, event):
if event["text"] == "Hi": #If connecting first time
if AcceptTaskConsumer.body:
await self.channel_layer.group_send(
self.room_group_name,
{
"type": "message",
"text": AcceptTaskConsumer.body[0]["body"]
}
)
else:
await self.channel_layer.group_send(
self.room_group_name,
{
"type": "message",
"text": "No New Tasks"
}
)
else: #When someone accepts a task-> ack and send next task in queue
print(json.loads(event["text"])["id"])
AcceptTaskConsumer.channel.basic_ack(delivery_tag=AcceptTaskConsumer.delivery[json.loads(event["text"])["id"]])
AcceptTaskConsumer.delivery.pop(json.loads(event["text"])["id"])
AcceptTaskConsumer.body.pop(0)
await self.channel_layer.group_send(
self.room_group_name,
{
"type": "message",
"text": "No New Tasks"
}
)
if AcceptTaskConsumer.body:
await self.channel_layer.group_send(
self.room_group_name,
{
"type": "message",
"text": AcceptTaskConsumer.body[0]["body"]
}
)
async def message(self, event):
await self.send({
"type": "websocket.send",
"text": event["text"]
})
#classmethod
#sync_to_async
def get_task(cls): #pika consumer
cls.connection = pika.BlockingConnection(
pika.ConnectionParameters(host='localhost'))
cls.channel = cls.connection.channel()
cls.channel.queue_declare(queue='task_', arguments={"x-max-priority": 3})
cls.channel.basic_consume(
queue='task_', on_message_callback=AcceptTaskConsumer.callback, auto_ack=False)
cls.channel.start_consuming()
#classmethod
def callback(cls, ch, method, properties, body):
task_obj = {"body": json.dumps(body.decode("utf-8")),
"delivery_tag": method.delivery_tag}
AcceptTaskConsumer.body.append(task_obj)
AcceptTaskConsumer.delivery[json.loads(json.loads(task_obj["body"]))["id"]] = method.delivery_tag
cls.channel.stop_consuming()
async def websocket_disconnect(self, event):
print(event)
await self.send({
"type": "websocket.close"
})
await self.channel_layer.group_discard(
self.room_group_name,
self.channel_name
)
I am pretty sure this is not the right way to do it, because it's not working as expected
I run into frequent errors like.
39 of 169 channels over capacity in group delivery
pika.exceptions.StreamLostError: Stream connection lost: BrokenPipeError(32, 'Broken pipe')
I tried running the queue listener like this answer as well. Nothing working.
Any one experienced has any thoughts about this? Is there a better way to approach this problem.?

Answer 1

you should move the rabitMQ cosumering logic out of the websocket consumer.
Just have a django command that runs the Rabbit Consumer, that consumer can take messages from RabbitMQ and then use send_group to send them over groups to channels.
if your django command you will need to call send_group see https://channels.readthedocs.io/en/latest/topics/channel_layers.html#using-outside-of-consumers
from channels.layers import get_channel_layer
channel_layer = get_channel_layer()
async_to_sync(
channel_layer.group_send
)(
"user_type_2",
{"type": "message", "msg": 123}
)
Then in the websocket consumer you should subscribe to the groups that the user wants/has permition to get.