Interview question

What is middleware and how do you use it? Middleware क्या है और कैसे use करते हैं?

Answer

# Flask middleware
from flask import Flask, request, g
import time

app = Flask(__name__)

# Request/response hook
@app.before_request
def before_request():
    g.start_time = time.time()
    print(f'Request: {request.method} {request.path}')

@app.after_request
def after_request(response):
    duration = time.time() - g.start_time
    print(f'Response: {response.status_code} ({duration:.2f}s)')
    return response

# Custom middleware
class TimingMiddleware:
    def __init__(self, app):
        self.app = app
    
    def __call__(self, environ, start_response):
        start = time.time()
        result = self.app(environ, start_response)
        duration = time.time() - start
        print(f'Request took {duration:.2f}s')
        return result

app.wsgi_app = TimingMiddleware(app.wsgi_app)

# Django middleware
class CustomMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response
    
    def __call__(self, request):
        print(f'Processing request: {request.path}')
        response = self.get_response(request)
        print(f'Generating response with status {response.status_code}')
        return response

# In settings.py
MIDDLEWARE = [
    'django.middleware.security.SecurityMiddleware',
    'myapp.middleware.CustomMiddleware',
]

# FastAPI middleware
from fastapi import FastAPI
from starlette.middleware.base import BaseHTTPMiddleware
import time

app = FastAPI()

class TimingMiddleware(BaseHTTPMiddleware):
    async def dispatch(self, request, call_next):
        start = time.time()
        response = await call_next(request)
        duration = time.time() - start
        response.headers['X-Process-Time'] = str(duration)
        return response

app.add_middleware(TimingMiddleware)

# CORS middleware
from fastapi.middleware.cors import CORSMiddleware

app.add_middleware(
    CORSMiddleware,
    allow_origins=['http://localhost:3000'],
    allow_credentials=True,
    allow_methods=['*'],
    allow_headers=['*'],
)

Flask:
@app.before_request
@app.after_request
Custom WSGI middleware

Django:
Middleware class
__init__ and __call__ methods
Add to MIDDLEWARE setting

FastAPI:
BaseHTTPMiddleware
app.add_middleware()
CORSMiddleware for CORS

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