Send a message from a celery background task to the browser with Django Channels

Question

I have a long running task running on Celery. When it is done, I want to send a message to the browser that will simply instruct it to refresh the page. To do that, I want to use channels V2.

It's not clear from the docs how to achieve that.

This is what I have in my background task, but I'm not sure how to set up the Consumer

@shared_task
def my_task():
    time.sleep(5)
    Channel('my-background-task').send({"refresh": True})

Answer 1

class ReloadConsumer(WebsocketConsumer):
    def connect(self):
        self.group_name = self.scope['user']
        print(self.group_name)  # use this for debugging not sure what the scope returns

        # Join group
        async_to_sync(self.channel_layer.group_add)(
            self.group_name,
            self.channel_name
        )
        self.accept()

    def disconnect(self, close_code):
        # Leave group
        async_to_sync(self.channel_layer.group_discard)(
            self.group_name,
            self.channel_name
        )

    def reload_page(self, event):
        # Send message to WebSocket
        self.send(text_data=json.dumps({
            'reload': True
        }))
        self.disconnect()

Then when your celery task is completed you send a reload_page message to the relevant group.

@shared_task
def my_task():
    ... do your task ...
    group_name = get_user_name()  # Find out way to get same as what is printed on connect()

    channel_layer = get_channel_layer()
    # Trigger reload message sent to group
    async_to_sync(channel_layer.group_send)(
        group_name,
        {'type': 'reload_page'}
    )

Once you can successfully create a group for the user when they start the celery task, then send a message to the user's group on completion it's as simple as adding this script:

webSocket.onmessage = function() {
    window.location.reload();
}