Name: WebSocket in Django
Rating: 4.8 (460 reviews)
Author: foxy4096

What are WebSocket?

Well, they are computer communication protocol which is used to communicate bidirectionally.
It can be used by server to send data to the client.

In short, they are used for real-time communication.
Example: Chat applications, real-time data sync in games, SSE etc.

Thought WebSocket seems cool they could get too overpacked for simple apps like a weather app which polls data between few intervals.

How can you implement them in Django?

Well, that's easy we can use a python package called channels.
They are built by the same developers who have made Django.

Just open up a terminal and type the following to install the channels

python -m pip install -U channels["daphne"]

It will install channels and a special ASGI web server called daphne which is used to handle the ws:// protocol.

We will also be needing [django](https://pypi.org/project/Django/) of course, just enter the following command to install it

pip install django

We also might need to get redis and channel_redis

pip install redis channel_redis

And also don't forget the real redis itself from Redis

If you are on windows, you can use memurai

Now in this post, we will be making an Online User Presence Indicator. This app will tell the client the number of users connected to the server.

Also we will not be using the channel_layer to broadcast the message, as it will over complicate the things.

Create a django application

django-admin startproject django_websocket

Go to the django_websocket folder and type this command to create a new django app.

cd django_websocket
python manage.py startapp presence

In settings.py add the daphne server and our presence app.

Add daphne to the top.

# django_websocket/settings.py

INSTALLED_APPS = [
    'daphne' # ⬅ ASGI Webserver
    'presence', # ⬅ Our Custom App
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
]

Add the following lines in the settings.py to allow the django to also handle ASGI and also handle the login and logout redirect.

# django_websocket/settings.py
# Daphne Conf
ASGI_APPLICATION = "django_websocket.asgi.application"

LOGIN_REDIRECT_URL = "index"
LOGOUT_REDIRECT_URL = "index"

Now let's add some code in asgi.py and replace the code with this:

import os

from django.core.asgi import get_asgi_application
from channels.routing import ProtocolTypeRouter # <- Add this
from channels.auth import AuthMiddlewareStack # <- Add this
from presence.consumers import PresenceConsumer # <- Add this

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'django_websockets.settings')

application = ProtocolTypeRouter(
    {
        "http": get_asgi_application(),
        "websocket": AuthMiddlewareStack(
            PresenceConsumer.as_asgi()
        ),
    }
)

Let's break it down:

From line 1 to 6 we are importing all the required modules
- os: For setting some required environment variables
- get_asgi_application: Just handles the http side of our application.
- ProtocolTypeRouter: Allow us to handle different type of protocol interfaces, like for http we will just do the http things but for WebSocket protocol connections we will let our application handle with the websockets part.
- AuthMiddlewareStack: Supports standard Django authentication, where the user details are stored in the session. It allows read-only access to a user object in the scope. In short it allows us to get the current request.user
- PresenceConsumer: It our custom made ASGI consumer which will handle the websockets. We will be making this next
- Line 8 is where we are adding the file is adding the project settings.py in an env named DJANGO_SETTINGS_MODULE. We don't have to worry about it.
- From line 10 to 17 is where we are declaring the application It is the same "django_websocket.asgi.application.
The application is equal to the ProtocolTypeRouter which takes a dictionary of protocols such as http and websocket
The WebSocket is taking a function called AuthMiddlewareStack which takes our Consumers

Now we get to the interesting part which is making the WebSocket consumers itself.

firstly, create a file name consumers.py in presence folder, and write this code in it.

import json

from channels.generic.websocket import WebsocketConsumer


class PresenceConsumer(WebsocketConsumer):

    connections = []

    def connect(self):
        self.accept()
        self.user = self.scope["user"]
        self.connections.append(self)
        self.update_indicator(msg="Connected")

    def disconnect(self, code):
        self.update_indicator(msg="Disconnected")
        self.connections.remove(self)
        return super().disconnect(code)

    def update_indicator(self, msg):
        for connection in self.connections:
            connection.send(
                text_data=json.dumps(
                    {
                        "msg": f"{self.user} {msg}",
                        "online": f"{len(self.connections)}",
                        "users": [f"{user.scope['user']}" for user in self.connections],                        
                    }
                )
            )

Now this code may look intimidating, but actually it's pretty simple once you understand the basic concept of Consumers.

Let's break it down.

From line 1 to 3, we are importing some important modules such as json and WebsocketConsumer.
From line 6 we are creating a class named PresenceConsumer which is extended from WebsocketConsumer
- The WebsocketConsumer gives us some of the methods for the WebSocket like
  - connect method is called when client connects to the WebSocket. If we are overriding this method, then we have to add self.accept().
  - disconnect method is called when client disconnects to the WebSocket.
  - receive method is called when the client sends request to the to the WebSocket
The method named update_indicator is a custom method which we have created.
The connections is an empty list which will store the connected users.

In the connect method, we are overriding the methods so that when a new user connects to the WebSocket, we are getting the user from the session with this code self.user = self.scope["user"], as we have wrapped our PrescenceConsumer in AuthMiddlewareStack, we can get the current user from the session and save it in the self.user. After we got the user, we are going to append the current user connection to the connection and then calling the self.update_indicator and passing the msg as connected.

Now if we look in the update_indicator we can see that we are looping through the connection list and sending the all the client a json data.

Example:
If a user named Sid connects to the WebSocket with 3 users connected all the clients connected to the WebSocket including Sid will get the following json

{
    "msg": "Sid Connected",
    "online": 4,
    "users" [
                "user1",
                "user2",
                "user3",
                "Sid"
            ]
}

Now we will handle some of our views for displaying the index page and login page. Just add this 4 lines of code and you are done

from django.shortcuts import render

def index(request):
    return render(request, "index.html")

Yup that's it.

Now we will handle the routing of the WebSocket.

This is just like url mapping your views in a typical django app.

Now mostly in a very large scale applications we should just seperate the views routing and ws routing, but here to save time we are just going to write it in the urls.py

Firstly create a urls.py file in the presence app and add the following code.

from django.urls import path

from . import consumers
from . import views
from django.contrib.auth.views import LoginView, LogoutView


urlpatterns = [
    path('', views.index, name="index"),
    path('login/', LoginView.as_view(template_name='login.html'), name='login'),
    path('logout/', LogoutView.as_view(), name='logout'),
    path("ws/presence", consumers.PresenceConsumer.as_asgi()),
]

Here we are creating an URL mapping for our views and WebSocket.
As you can see, we are also using the django authentication views to get login and logout functionality in our app.

To add the WS Consumer we just need to map it in the urlpatterns just like any other class based views, just instead of .as_view(), here we write .as_asgi().

Phew! That was the backend part, now we need to setup our frontend part.

Now Let's Get to the frontend part

Create a template directory in the presence app and create two files named index.html and login.html

In the index.html write the following code.

<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8" />
  <title>Online Presence Indicator</title>
  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bulma@0.9.4/css/bulma.min.css">
</head>

<body>
  <div class="container">
    <section class="section">
      <div class="columns">
        <div class="column">

          {% if user.is_authenticated %}
          Hello <strong>{{ user }}</strong>
          <br>
          <a href="{% url 'logout' %}">Logout</a>
          {% else %}
          <a href="{% url 'login' %}">Login</a>
          {% endif %}
          <h1 class="title">Online Presence Indicator</h1>
          <div id="presence"><span class="tag is-success" id="pre_cnt">0</span> users online</div>
          <ul id="messages"></ul>
        </div>
        <div class="column">
          <div class="box">
            <h1 class="title">Online Users</h1>
            <div id="online-users"></div>
          </div>
        </div>
      </div>
    </section>
  </div>

  <script>
    const ws = new WebSocket('ws://localhost:8000/ws/presence/');
    const presenceEl = document.getElementById('pre_cnt');
    const messagesEl = document.getElementById('messages');
    const onlineUsers = document.querySelector("#online-users");

    ws.onmessage = (event) => {
      onlineUsers.innerHTML = "";
      let data = JSON.parse(event.data)
      presenceEl.innerHTML = data.online;
      const li1 = document.createElement('li');
      li1.innerHTML = data.msg;
      messagesEl.appendChild(li1);
      data.users.forEach(user => {
        const li2 = document.createElement("li");
        li2.classList.add("on-us")
        li2.innerHTML = user;
        onlineUsers.appendChild(li2);
      });

    };
  </script>
</body>

</html>

Here we are using Bulma to style our page, you can use your own stylesheet if you want.

The main thing we have to look here is the javascript.

Firstly we are creating a WebSocket object and passing the WebSocket url.
Next we are storing the html elements by using getElementById.
Then we are WebSocket.onmessage event handle to real-time messages from the server. The event contains a data attribute, to which we will use JSON.parse to convert the coming JSON to object
When the WebSocket receives the message from the serve we will show that the user is connected in the #messages div and append the user in #online-users div.

Now let's just quickly create our login page.
Open login.html and write this html.

<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8" />
  <title>Online Presence Indicator</title>
  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bulma@0.9.4/css/bulma.min.css">
</head>

<body>
  <div class="container">
    <section class="section">
        <h1 class="title">Login</h1>
      <form action="." method="post">
        {{form.as_p}}
        {% csrf_token %}
        <br>
        <button class="button">Login</button>
      </form>
    </section>
  </div>
</body>

</html>

Just that's it and now our application is complete.

Let's setup the database by running the migrations

python manage.py migrate

Let's now test it by running the server

python manage.py runserver

You should see the following stream.

Watching for file changes with StatReloader
Performing system checks...

System check identified no issues (0 silenced).
May 23, 2023 - 22:54:21
Django version 4.2.1, using settings 'myproject.settings'
Starting ASGI/Daphne version 4.0.0 development server at http://127.0.0.1:8000/
Quit the server with CTRL-BREAK.