What is Middleware in FastAPI and why is it needed?

Middleware in FastAPI is a component that intercepts HTTP requests and responses at the application level, allowing for additional processing before and after calling endpoints.

Why is Middleware needed:

• Logging requests and responses
• Error and exception handling
• Managing CORS
• Authentication and authorization
• Modifying or adding headers

Example of simple middleware that outputs the request processing time:

from fastapi import FastAPI, Request
import time

app = FastAPI()

@app.middleware("http")
async def add_process_time_header(request: Request, call_next):
    start_time = time.time()
    response = await call_next(request)
    process_time = time.time() - start_time
    response.headers["X-Process-Time"] = str(process_time)
    return response