Request timing middleware in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of request timing middleware in FastAPI?

Request timing middleware measures how long each HTTP request takes to process. It helps developers understand performance and find slow parts in their app.

beginner

How do you add middleware in FastAPI?

You use the @app.middleware decorator with 'http' as the first argument. Then define an async function that takes request and call_next parameters.

intermediate

In request timing middleware, what does the call_next(request) function do?

call_next(request) passes the request to the next step in the app (like route handlers) and returns the response. It lets middleware run code before and after the request.

intermediate

Why use time.monotonic() instead of time.time() for measuring request duration?

time.monotonic() always moves forward and is not affected by system clock changes, making it reliable for measuring elapsed time.

intermediate

How can you add the request duration to the HTTP response headers in FastAPI middleware?

After getting the response from call_next, add a header like response.headers['X-Process-Time'] = str(duration). This sends timing info back to the client.

What is the correct way to define a request timing middleware in FastAPI?

A Use @app.middleware('http') and an async function with request and call_next parameters

B Use @app.route and a sync function with request only

C Use @app.middleware('ws') and an async function with websocket parameter

D Use @app.event and a function with no parameters

FastAPI middleware for HTTP requests uses @app.middleware('http') with an async function that takes request and call_next.

Which Python function is best for measuring elapsed time in request timing middleware?

A time.monotonic()

B time.sleep()

C time.time()

D time.clock()

time.monotonic() is best because it is steady and not affected by system clock changes.

What does call_next(request) return in FastAPI middleware?

A A boolean value

B The request object

C The middleware function

D The HTTP response object

call_next(request) processes the request and returns the response object.

Where can you add the request duration information so the client can see it?

A In the request body

B In the response headers

C In the URL path

D In the server logs only

Adding timing info to response headers lets clients see how long the request took.

Why is middleware useful for timing requests?

A It replaces route handlers

B It only runs once when the app starts

C It runs code before and after every request automatically

D It blocks requests from reaching routes

Middleware wraps requests so you can measure time before and after processing.

Explain how to create a request timing middleware in FastAPI and how it measures request duration.

Think about how middleware wraps the request and response process.

Why is it important to use middleware for timing requests instead of adding timing code in each route?

Consider the benefits of code reuse and consistency.