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Middleware FastAPI

5 min read Quiz at the end

Add CORS, Gzip, request logging, and timing headers via FastAPI middleware.

Middleware

from fastapi import FastAPI, Request
from fastapi.middleware.cors import CORSMiddleware
from fastapi.middleware.gzip import GZipMiddleware
import time

app = FastAPI()

# CORS
app.add_middleware(
    CORSMiddleware,
    allow_origins   = ["https://myapp.com", "https://www.myapp.com"],
    allow_methods   = ["*"],
    allow_headers   = ["*"],
    allow_credentials = True,
)

# Gzip compression
app.add_middleware(GZipMiddleware, minimum_size=1000)

# Custom middleware
@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

@app.middleware("http")
async def log_requests(request: Request, call_next):
    print(str(request.method) + " " + str(request.url))
    response = await call_next(request)
    print("Status: " + str(response.status_code))
    return response

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Topic Quiz · 2 questions

Test your understanding before moving on

1. What does CORSMiddleware do?

💡 CORS middleware adds Access-Control-Allow headers to permit cross-origin requests.

2. How do you add a custom middleware in FastAPI?

💡 Both @app.middleware() async function and app.add_middleware(Class) work.

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Middleware FastAPI

Middleware

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