Addition Django Channels to DRF

Question

I'm tryna add channel to my project to send download state percent. I have a method download_file() which downloads file to server from several endpoints.

I got to add channels to project, but it's an API without front-end.

asgi.py

import os
import django

from django.core.asgi import get_asgi_application

from src.apps import api
from channels.routing import ProtocolTypeRouter, URLRouter

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'src.settings')
django.setup()


application = ProtocolTypeRouter({
    'http': get_asgi_application(),
    'websocket': URLRouter(api.routing.websocket_urlpatterns),
})

settings.py

THIRD_PARTY_APPS = (
    '...' ,
    'channels',
)

# ...

# channels
ASGI_APPLICATION = 'src.asgi.application'

CHANNEL_LAYERS = {
    "default": {
        "BACKEND": "channels_rabbitmq.core.RabbitmqChannelLayer",
    },
}

routing.py

from django.urls import path

from src.apps.api.consumers import DownloadStateConsumer

websocket_urlpatterns = [
    path('download_state/', DownloadStateConsumer.as_asgi()),
]

consumers.py

from channels.generic.websocket import AsyncWebsocketConsumer

class DownloadStateConsumer(AsyncJsonWebsocketConsumer):
    async def connect(self):
        await self.accept()

    async def receive(self, text_data=None, bytes_data=None, **kwargs):
        await self.send_json({'message': text_data})

file_download.py

def download_file():
    # ...
    response = requests.get(link.link, stream=True)
    total_length = response.headers.get('content-length')
    size = 0
    with response as r:
        r.raise_for_status()
        with open(filename, 'wb') as f:
            state = -1
            for chunk in r.iter_content(chunk_size=8192):
                size += len(chunk)
                f.write(chunk)
                done = int(100 * size / int(total_length))
                sys.stdout.write("\r%s%s" % (str(done), "%"))
                if done != state:         
                    async_to_sync(
                        get_channel_layer().group_send(
                            'download_state', {
                                'type': 'send.percent',
                                'message': done,
                            }
                        )
                    )
                    state = done
                sys.stdout.flush()
# ...

I understand that on the client the script should be sort of this

const webSocket = new WebSocket(
    'ws://'
    + window.location.host
    + '/download_state/'
);

webSocket.onmessage = function(e) {
    const data = JSON.parse(e.data);
    document.querySelector('#download-state').value = data.message;
};

webSocket.onclose = function(e) {
    console.error('Chat socket closed unexpectedly');
};

The question is how send to client download state from download_file() method? Current way doesn't work - the client don't receive messages. Thanks!

Answer 1

Eventually I changed to channels_redis instead channels_rabbitmq:

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

I ran redis image into Docker on specified port and now it works.