Using Websocket in Django View Not Working - django

Question

Problem Summary
I am sending data to a front-end (React component) using Django and web-sockets. When I run the app and send the data from my console everything works. When I use a button on the front-end to trigger a Django view that runs the same function, it does not work and generates a confusing error message.
I want to be able to click a front-end button which begins sending the data to the websocket.
I am new to Django, websockets and React and so respectfully ask you to be patient.
Overview
Django back-end and React front-end connected using Django Channels (web-sockets).
User clicks button on front-end, which does fetch() on Django REST API end-point.
[NOT WORKING] The above endpoint's view begins sending data through the web-socket.
Front-end is updated with this value.
Short Error Description
The error Traceback is long, so it is included at the end of this post. It begins with:
Internal Server Error: /api/run-create
And ends with:
ConnectionResetError: [WinError 10054] An existing connection was forcibly closed by the remote host
What I've Tried
Sending Data Outside The Django View
The function below sends data to the web-socket.
Works perfectly when I run it in my console - front-end updates as expected.
Note: the same function causes the attached error when run from inside the Django view.
import json
import time
import numpy as np
import websocket
def gen_fake_path(num_cities):
path = list(np.random.choice(num_cities, num_cities, replace=False))
path = [int(num) for num in path]
return json.dumps({"path": path})
def fake_run(num_cities, limit=1000):
ws = websocket.WebSocket()
ws.connect("ws://localhost:8000/ws/canvas_data")
while limit:
path_json = gen_fake_path(num_cities)
print(f"Sending {path_json} (limit: {limit})")
ws.send(path_json)
time.sleep(3)
limit -= 1
print("Sending complete!")
ws.close()
return
Additional Detail
Relevant Files and Configuration
consumer.py
class AsyncCanvasConsumer(AsyncWebsocketConsumer):
async def connect(self):
self.group_name = "dashboard"
await self.channel_layer.group_add(self.group_name, self.channel_name)
await self.accept()
async def disconnect(self, close_code):
await self.channel_layer.group_discard(self.group_name, self.channel_name)
async def receive(self, text_data=None, bytes_data=None):
print(f"Received: {text_data}")
data = json.loads(text_data)
to_send = {"type": "prep", "path": data["path"]}
await self.channel_layer.group_send(self.group_name, to_send)
async def prep(self, event):
send_json = json.dumps({"path": event["path"]})
await self.send(text_data=send_json)
Relevant views.py
#api_view(["POST", "GET"])
def run_create(request):
serializer = RunSerializer(data=request.data)
if not serializer.is_valid():
return Response({"Bad Request": "Invalid data..."}, status=status.HTTP_400_BAD_REQUEST)
# TODO: Do run here.
serializer.save()
fake_run(num_cities, limit=1000)
return Response(serializer.data, status=status.HTTP_200_OK)
Relevant settings.py
WSGI_APPLICATION = 'evolving_salesman.wsgi.application'
ASGI_APPLICATION = 'evolving_salesman.asgi.application'
CHANNEL_LAYERS = {
"default": {
"BACKEND": "channels.layers.InMemoryChannelLayer"
}
}
Relevant routing.py
websocket_url_pattern = [
path("ws/canvas_data", AsyncCanvasConsumer.as_asgi()),
]
Full Error
https://pastebin.com/rnGhrgUw
EDIT: SOLUTION
The suggestion by Kunal Solanke solved the issue. Instead of using fake_run() I used the following:
layer = get_channel_layer()
for i in range(10):
path = list(np.random.choice(4, 4, replace=False))
path = [int(num) for num in path]
async_to_sync(layer.group_send)("dashboard", {"type": "prep", "path": path})
time.sleep(3)

Answer 1

Rather than creating a new connection from same server to itself , I'd suggest you to use the get_channel_layer utitlity .Because you are in the end increasing the server load by opening so many connections .
Once you get the channel layer , you can simply do group send as we normally do to send evnets .
You can read more about here
from channels.layers import get_channel_layer
from asgiref.sync import async_to_sync
def media_image(request,chat_id) :
if request.method == "POST" :
data = {}
if request.FILES["media_image"] is not None :
item = Image.objects.create(owner = request.user,file=request.FILES["media_image"])
message=Message.objects.create(item =item,user=request.user )
chat = Chat.objects.get(id=chat_id)
chat.messages.add(message)
layer = get_channel_layer()
item = {
"media_type": "image",
"url" : item.file.url,
"user" : request.user.username,
'caption':item.title
}
async_to_sync(layer.group_send)(
'chat_%s'%str(chat_id),
#this is the channel group name,which is defined inside your consumer"
{
"type":"send_media",
"item" : item
}
)
return HttpResponse("media sent")
In the error log, I can see that the handshake succeded for the first iteration and failed for 2nd . You can check that by printing something in the for loop . If that's the case the handshake most probably failed due to mulitple connections . I don't know how many connections the Inmemrorycache supports from same origin,but that can be reason that the 2nd connection is getting diconnected . You can get some idea in channel docs.Try using redis if you don't want to change your code,its pretty easy if you are using linux .