Why middleware processes requests globally in FastAPI - See It in Action

Understanding Global Request Processing with FastAPI Middleware

📖 Scenario: You are building a simple web API using FastAPI. You want to understand how middleware works by processing every request globally before it reaches any specific route.

🎯 Goal: Create a FastAPI app with middleware that logs every incoming request globally, showing how middleware processes requests for all routes.

📋 What You'll Learn

Create a FastAPI app instance called app

Add a middleware function that logs the path of every incoming request

Use the @app.middleware("http") decorator to define the middleware

Create at least one route /hello that returns a greeting message

💡 Why This Matters

🌍 Real World

Middleware is used in real web apps to handle tasks like logging, authentication, and modifying requests or responses globally.

💼 Career

Understanding middleware is essential for backend developers working with FastAPI or similar frameworks to build scalable and maintainable APIs.

1

Create the FastAPI app instance

Create a FastAPI app instance called app by importing FastAPI and initializing it.

FastAPI

from fastapi import FastAPI

# Create the FastAPI app instance called app
# Your code here

Need a hint?

Import FastAPI and then create an instance named app.

2

Add a middleware function to log requests

Add a middleware function using @app.middleware("http") that logs the request path for every incoming request. The function should accept request and call_next parameters and return the response from call_next(request).

FastAPI

from fastapi import FastAPI

app = FastAPI()

# Add middleware to log request paths
# Your code here

Need a hint?

Use @app.middleware("http") decorator and define an async function with request and call_next parameters.

3

Create a route to test the middleware

Create a GET route /hello using @app.get("/hello") that returns a JSON message {"message": "Hello, world!"}.

FastAPI

from fastapi import FastAPI, Request

app = FastAPI()

@app.middleware("http")
async def log_request_path(request: Request, call_next):
    print(f"Request path: {request.url.path}")
    response = await call_next(request)
    return response

# Create a GET route /hello that returns a greeting message
# Your code here

Need a hint?

Use @app.get("/hello") decorator and return the JSON message inside an async function.

4

Complete the app with middleware processing globally

Ensure the middleware processes requests globally by keeping the middleware function and the route in the same app instance app. This setup shows middleware runs for all requests before route handlers.

FastAPI

from fastapi import FastAPI, Request

app = FastAPI()

@app.middleware("http")
async def log_request_path(request: Request, call_next):
    print(f"Request path: {request.url.path}")
    response = await call_next(request)
    return response

@app.get("/hello")
async def hello():
    return {"message": "Hello, world!"}

# Confirm middleware processes all requests globally
# Your code here

Need a hint?

Keep the middleware and route in the same app instance to ensure global processing.