WSGI middleware concept in Flask - Mini Project: Build & Apply

WSGI Middleware Concept with Flask

📖 Scenario: You are building a simple Flask web app that shows a greeting message. You want to add a WSGI middleware that logs each request path before the app handles it.

🎯 Goal: Create a Flask app and a WSGI middleware that logs the request path. The middleware should wrap the Flask app and print the path of every incoming request.

📋 What You'll Learn

Create a Flask app with one route '/' that returns 'Hello, World!'

Create a WSGI middleware class called LogMiddleware

The middleware should print the request path from the environ dictionary

Wrap the Flask app with the LogMiddleware before running

💡 Why This Matters

🌍 Real World

WSGI middleware is used in real web apps to add features like logging, authentication, or response modification without changing the main app code.

💼 Career

Understanding WSGI middleware helps backend developers customize and extend Python web apps efficiently, a valuable skill in web development jobs.

1

Create a basic Flask app

Create a Flask app called app with one route '/' that returns the string 'Hello, World!'.

Flask

# Create a Flask app called app with one route '/' that returns 'Hello, World!'
# Your code here

Need a hint?

Use Flask(__name__) to create the app and @app.route('/') to define the route.

2

Create the WSGI middleware class

Create a WSGI middleware class called LogMiddleware with an __init__ method that takes app and stores it. Add a __call__ method that takes environ and start_response parameters.

Flask

from flask import Flask

app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello, World!'

# Create LogMiddleware class with __init__ and __call__ methods
# Your code here

Need a hint?

The middleware class needs to store the app and define a callable method.

3

Add logging of request path in middleware

Inside the __call__ method of LogMiddleware, print the request path from environ['PATH_INFO']. Then call the wrapped app with self.app(environ, start_response) and return its result.

Flask

from flask import Flask

app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello, World!'

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

    def __call__(self, environ, start_response):
        # Print the request path
        # Call the wrapped app and return its response
        # Your code here

Need a hint?

Use environ['PATH_INFO'] to get the path and print it before calling the app.

4

Wrap the Flask app with the middleware

Wrap the Flask app app with the LogMiddleware by assigning app = LogMiddleware(app) before running the app.

Flask

from flask import Flask

app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello, World!'

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

    def __call__(self, environ, start_response):
        print(f"Request path: {environ['PATH_INFO']}")
        return self.app(environ, start_response)

# Wrap the app with LogMiddleware
# Your code here

Need a hint?

Assign app = LogMiddleware(app) to wrap the Flask app.