Django Channels - Introduction and Basic Setup

Django is a powerful Python framework for web development. It is fast, secure, and reliable. Channels allow Django projects to handle HTTP along with asynchronous protocols like WebSockets, MQTT, chatbots, and more.

Channels:

Channels preserve the synchronous behavior of Django and add a layer of asynchronous protocols allowing users to write the views that are entirely synchronous, asynchronous, or a mixture of both. Channels basically allow the application to support "long-running connections". It replaces Django's default WSGI with its ASGI .

Django Channels allow for handling WebSockets, and understanding this can elevate your web development skills. The Complete Django Web Development Course - Basics to Advance provides a deeper exploration of Django Channels and other advanced topics."

ASGI:

ASGI (Asynchronous Server Gateway Interface) provides an interface between async Python web servers and applications while it supports all the features provided by WSGI.

Consumers:

A consumer is a basic unit of Channels. It is an event-driven class that supports both async and sync applications. Consumers can run longer and hence they support web sockets that need persistent connection.

In this post, we will set up a basic example of channels. We will build a calculator app that will allow the user to send multiple expressions to the server and receive the result through a single persistent connection.

Environment Setup:

• It is always a good idea to create a virtual environment for the python apps in order to avoid version conflicts. Run the following commands in the terminal to get started

easy-install pip
python3 -m pip install virtualenv
virtualenv venv
source venv/bin/activate

• Now install Django and Channels :

pip install django
pip install channels
# On windows, try an unofficial wheel of 'Twisted' in case of dependency errors

LiveCalculator App:

Now start a Django project and create an app named 'liveCalculator'

django-admin startproject sampleProject
cd sampleProject
python3 manage.py startapp liveCalculator

In sampleProject/settings.py , register channels and liveCalculator .

settings.py:

INSTALLED_APPS = [
 'channels',
 'liveCalculator',
 'django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
]

In sampleProject/asgi.py, add the http protocol.

asgi.py:

Now we need to register this asgi into our application. Add this line in sampleProject/settings.py :

ASGI_APPLICATION = "sampleProject.asgi.application"

Create a new folder liveCalculator/templates/liveCalculator and create a new file index.html inside it. It will be the starting page of our app. Add the following code in index.html:

index.html:

The above code will render a text area and an input box where the user can enter the expression. It will create a socket connection that we will make later and append the received result in the text area. When the user inputs the expression, it will send the expression through a socket connection.

Now create a view to render this page in liveCalculator/views.py :

liveCalculator/views.py:

Next, we need to create a route for this view. Add a new file urls.py in liveCalculator directory and add the following code:

liveCalculator/urls.py:

Register this route in sampleProject/urls.py :

sampleProject/urls.py:

Now we need to create the consumer for our web socket connection. We will use the generic WebsocketConsumer class to implement its event-driven methods. Create a new file consumers.py in liveCalculator folder and add the following code:

consumers.py:

The WebsocketConsumer class supports these user-defined methods:

• connect() : We can write the business logic of what should happen when the client sends a connection request.
• disconnect() : We can write the business logic of what should happen when the client sends a disconnection request.
• receive(): We can write the business logic of what should happen when the client sends a message.

It also supports these built-in methods:

• accept(): It will accept the incoming connection.
• close(): It will close the current connection.
• send(): It will send the specified message to the client.

We have simply used the above methods in our Calculator class to accept the connection, evaluate the expression when a message a received, and send it to the client.

Next, we also need to define the routing method for this consumer. Create a new file routing.py in the same folder and add the following code to it:

routing.py:

Note that we have used as_asgi() method on our Calculator class to use it for our application. This will enable the socket on ws://<IP:Port>/ws/livec . Now register routing.py into asgi.py by declaring the WebSocket protocol.

asgi.py:

We are almost done with our first Channels application. Save all the files and run the following commands in the terminal:

python3 manage.py makemigrations
python3 manage.py migrate
python3 manage.py runserver

Now open http://localhost:8000 on your browser, and you should see the output like this:

See the log of the server. Note that we have created the connection only once, and we can send the message multiple times without creating a new connection.