python - Send message using Django Channels from outside Consumer class

Question

I am building an online game, which uses Django channels 2.1.5 for websockets.

I am able to build the connection between the client and the server, and also able to send data between them only inside the consumer class:

from channels.generic.websocket import WebsocketConsumer
import json
from . import controller

class GameConsumer(WebsocketConsumer):
    def connect(self):
        self.accept()
        print("Wohooo .. Connected to client!")
        self.render()
        controller.startTurn()

    def render(self, type="render", message=None):
        self.send(controller.renderMap(type, message))

    def disconnect(self, close_code):
        print("WebSocket connection is lost...")

    def receive(self, text_data):
        text_data_json = json.loads(text_data)
        controller.handleRecieved(text_data)
...

Now, What I wish to do, is to call the function render, -which is inside the consumer class-, from another module

I tried this:

from .. import consumer

def sendDeployments(owner, armies):
    type = "renderDeployments"
    message = owner + " has " + str(armies) + " to deploy"
    dummyConsumer = consumer.GameConsumer()
    consumer.GameConsumer.render(type, message)

But failed because I can't use the "self" parameter from outside the class.

Can anybody think of a way to achieve my goal?

Ps: I don't care about synchronization at this occasion.

Answer 1

Firstly you need your consumer instance to subscribe to a group.

from asgiref.sync import async_to_sync

class GameConsumer(WebsocketConsumer):
    def connect(self):
        self.accept()
        self.render()
        async_to_sync(self.add_group)('render_updates_group') 
        controller.startTurn()
...

Then if you are outside of your consumer you will need to send a message to that group so that all the consumers that have registered onto the group get the message.

from channels.layers import get_channel_layer
from asgiref.sync import async_to_sync

def sendDeployments(owner, armies):
    type = "renderDeployments"
    message = owner + " has " + str(armies) + " to deploy"
    channel_layer = get_channel_layer()
    async_to_sync(channel_layer.group_send)(
        'render_updates_group',
        {'type': 'render', 'message': message}
    )

However, you also need to remember to remove your consumer from the group when it disconnects.

class GameConsumer(WebsocketConsumer):
    ....

    def disconnect(self, close_code):
         async_to_sync(self.group_name)('render_updates_group')

If you want to limit which open connections get this render message you need to build your group name accordingly.

eg if you are thinking about some online game then maybe you include a MATCH-ID in the group name that is shared by all connections for the same match.

A good reference for this is the channels Layers documentation but do remember when running this in production you will need a messaging layer (normally Redis) set up.