Write Custom Django Middleware

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Hello Techies,

In this blog, we will discuss the use of Django middleware with a practical example.

Middleware is a regular class of Python that hooks into Django’s request / response life cycle.

There are 2 types of Django middleware :

Built-in middleware
Custom middleware

Table of Contents

Built-in middleware

Django provides built-in middleware classes.

MIDDLEWARE = [
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
]

Each middleware component is responsible for performing certain tasks.

During the request cycle, middleware classes run top-down, first Security middleware, then SessionMiddleware until XframeOptions middleware.

During the response cycle, the middleware classes run bottom-up, meaning they will run up to XframeOptionMidalware, then MessageMidalware, Security Middleware.

So this is some basic information about the Built-in middleware.

How Django Middleware Works:

Let’s look at an example, when a user sends a request to the server, that request goes through the middleware between the user and the server. The same process is performed when a response is sent to a user. This situation may change in some cases, such as middleware may also response to the user.

Check the below images with different scenarios:

How requests and responses work between user and server.

How to activate Django Middleware:

To activate any middleware, add it to the MIDDLEWARE_CLASS list in your Django settings.
In the MIDDLEWARE class, each middleware component is represented with a full Python path to the middleware function name or class.
The middleware order is matters because a middleware can depend on other middleware.

Function-Based Django Middleware

A middleware factory is a callable one that takes the called get_response and returns a middleware.
Just like a view, the middleware takes a request and returns the response.

Syntax:

def my_middleware(get_response):
    # one-time configuration and initialization.
    def my_function(request):
        # Code executed for each request before view
. 
        response = get_response(request)
        # Code executed for each request/response after view.
        return response
    return my_function

get_response():

This might be the actual view or it might be the next middleware in the chain.
Current middleware doesn’t need to know or care exactly what it is, it just represents what comes next.

Let’s check one function based middleware example.

Create a middleware file where we will add our all middleware function.

def middleware_name(get_response):
    print("One Time initialization")
    # write your code as per your requirement
    def middleware_func(request):
        print("Before View")
        # this code will work before view
        # write your code as per your requirement
        response = get_response(request)
        print("After view")
        # this code will work after view
        # write your code as per your requirement
        return response
    return middleware_func

You can add multiple middleware as per your requirements and then add it to MIDDLEWARE_CLASS in setting.py file.

Add the file path to the middleware class in the setting.py file.

# settings.py

MIDDLEWARE = [
'django.middleware.security.SecurityMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'django.middleware.common.CommonMiddleware',
'django.middleware.csrf.CsrfViewMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',
'django.contrib.messages.middleware.MessageMiddleware',
'django.middleware.clickjacking.XFrameOptionsMiddleware',
'app.middlewares.middleware_name'
]

That’s it now you can check how this middleware will work.

Class-Based Django Middleware

Syntax:

class Middleware:
    def __init__(self, get_response):
        self.get_response = get_response
        # one time configuration and initialization.
    def __call__(self, request):
        # Code executed for each request before view
.
        response = self.get_response(request)
        # Code executed for each request/response after view.
        return response

__init__(get_response):

__init__(get_response) – Middleware factories must accept a get_response arguments.
Django initializes middleware with only the get_response argument.

Let’s check one Class-based middleware example.