Request/response middleware flow in Django

Introduction

Middleware lets you run code before and after Django handles a web request. It helps you change requests or responses easily.

You want to check or change user login status before views run.

You need to add headers or cookies to every response.

You want to log details about each request and response.

You want to block certain IP addresses from accessing your site.

You want to handle errors globally and show custom error pages.

Syntax

Django

class MyMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        # Code before view
        response = self.get_response(request)
        # Code after view
        return response

The __init__ method runs once when Django starts.

The __call__ method runs for each request, before and after the view.

Examples

This middleware prints messages before and after the view runs.

Django

class SimpleMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        print('Before view')
        response = self.get_response(request)
        print('After view')
        return response

This middleware adds a custom header to every response.

Django

class AddHeaderMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        response = self.get_response(request)
        response['X-Custom-Header'] = 'Hello'
        return response

Sample Program

This middleware logs the URL path of each request and the status code of the response.

Django

class LogMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        print(f'Request path: {request.path}')
        response = self.get_response(request)
        print(f'Response status: {response.status_code}')
        return response

Important Notes

Middleware order matters: Django runs them in the order listed in MIDDLEWARE settings.

Middleware can modify both request and response objects.

Use middleware for cross-cutting concerns like logging, security, and headers.

Summary

Middleware runs code before and after views to handle requests and responses.

Define middleware as a class with __init__ and __call__ methods.

Middleware helps add features like logging, headers, and security checks easily.