Middleware ka Funda

💻 Middleware Code ke Examples

// 🚀 Express.js Middleware Basics
const express = require('express');
const app = express();
// Middleware 1: Request Logger (Watchman)
app.use((req, res, next) => {
  console.log(`${new Date().toISOString()} - ${req.method} ${req.url}`);
  console.log('👮 Watchman: Kahan ja rahe ho?', req.url);
  next(); // Aage bhejo
});
// Middleware 2: Authentication (Security Guard)
app.use((req, res, next) => {
  const token = req.headers.authorization;
  if (!token) {
    console.log('🔍 Security Guard: ID card dikhao!');
    return res.status(401).json({ error: 'Token chahiye' });
  }
  console.log('🔍 Security Guard: ID check ho gaya, jao!');
  next();
});

// Main API Route (Aakhri Manzil)
app.get('/user/profile', (req, res) => {
  console.log('🚪 API Handler: Request apni manzil tak pohunch gaya!');
  res.json({
    message: 'Welcome Babita Ji!',
    user: { name: 'Babita', role: 'user' }
  });
});
app.listen(3000, () => {
  console.log('🏢 Society server port 3000 pe chal raha hai');
});

Express middleware test karne ke liye click karo...

// 🔧 Custom Middleware Functions
// 👮 Watchman Middleware
function requestLogger(req, res, next) {
  const timestamp = new Date().toISOString();
  console.log(`[${timestamp}] ${req.method} ${req.url}`);
  req.requestTime = timestamp; // Request mein data daal do
  next(); // Aage bhejo
}
// 🔍 Security Guard Middleware
function authenticateToken(req, res, next) {
  const authHeader = req.headers['authorization'];
  const token = authHeader && authHeader.split(' ')[1];
  if (!token) {
    return res.status(401).json({
      error: 'Access band hai. Token chahiye.',
      message: '🚫 Security Guard: ID card nahi dikhaya!'
    });
  }
  // Token check karo (simple version)
  if (token === 'valid-token') {
    req.user = { id: 1, name: 'Babita', role: 'user' };
    next();
  } else {
    return res.status(403).json({
      error: 'Token galat hai',
      message: '🚫 Security Guard: Nakli ID card!'
    });
  }
}

// 📝 Log Book Middleware
function logEntry(req, res, next) {
  const entry = {
    user: req.user?.name || 'Pata nahi',
    action: `${req.method} ${req.url}`,
    timestamp: req.requestTime,
    ip: req.ip
  };
  console.log('📝 Log Book Entry:', entry);
  // Database mein save karna padega
  // await logToDatabase(entry);
  next();
}
// Usage: Middleware chain
app.use(requestLogger);
app.use(authenticateToken);
app.use(logEntry);

Custom middleware test karne ke liye click karo...

// ⚠️ Error Handling Middleware
// Global Error Handler (Aakhir mein)
function errorHandler(err, req, res, next) {
  console.error('🚨 Error aaya:', err.message);
  // Error ke type ke hisaab se response
  if (err.name === 'ValidationError') {
    return res.status(400).json({
      error: 'Validation fail hua',
      message: '📝 Log Book: Galat information di hai!'
    });
  }
  if (err.name === 'UnauthorizedError') {
    return res.status(401).json({
      error: 'Permission nahi hai',
      message: '🔍 Security Guard: Ijaazat nahi hai!'
    });
  }
  // General server error
  res.status(500).json({
    error: 'Server mein kharabi',
    message: '🏢 Society mein koi problem hai!'
  });
}

// Async Error Wrapper
function asyncHandler(fn) {
  return (req, res, next) => {
    Promise.resolve(fn(req, res, next)).catch(next);
  };
}
// Routes mein use
app.get('/user/profile', asyncHandler(async (req, res) => {
  // Ye async function hai, errors apne aap handle honge
  const user = await getUserFromDatabase(req.user.id);
  if (!user) {
    throw new Error('User nahi mila'); // Apne aap pakda jayega
  }
  res.json(user);
}));
// Error handler ko aakhir mein register karo
app.use(errorHandler);

Error handling test karne ke liye click karo...

// 🔗 Poora Middleware Chain Setup
const express = require('express');
const app = express();
// 1️⃣ Global Middlewares (Sab routes ke liye)
app.use(express.json()); // JSON parser
app.use(requestLogger); // Har request log karo
app.use(corsHandler); // CORS headers daalo
// 2️⃣ Public Routes (Koi authentication nahi)
app.get('/public/news', (req, res) => {
  res.json({ news: 'Gokuldham Society mein nayi khabrein!' });
});
// 3️⃣ Protected Routes (Authentication chahiye)
app.use('/user', authenticateToken); // Sab /user routes protected
app.get('/user/profile', logEntry, (req, res) => {
  res.json({ user: req.user });
});
// 4️⃣ Admin Routes (Role-based access)
app.use('/admin', authenticateToken, requireAdmin);
app.get('/admin/dashboard', logEntry, (req, res) => {
  res.json({ message: 'Admin dashboard ka data' });
});

// 5️⃣ Route-specific Middleware
function requireAdmin(req, res, next) {
  if (req.user.role !== 'admin') {
    return res.status(403).json({
      message: '🚫 Sirf Secretary ko ijaazat hai!'
    });
  }
  next();
}
// 6️⃣ Rate Limiting Middleware
function rateLimiter(maxRequests = 100) {
  const requests = new Map();
  return (req, res, next) => {
    const clientIP = req.ip;
    const now = Date.now();
    const windowStart = now - (60 * 1000); // 1 minute ka window
    if (!requests.has(clientIP)) {
      requests.set(clientIP, []);
    }
    const userRequests = requests.get(clientIP);
    const recentRequests = userRequests.filter(time => time > windowStart);
    if (recentRequests.length >= maxRequests) {
      return res.status(429).json({
        message: '🚫 Bahut zyada requests! Thodi der wait karo!'
      });
    }
    recentRequests.push(now);
    requests.set(clientIP, recentRequests);
    next();
  };
}

Middleware chain test karne ke liye click karo...

Scenario	Zaroori Middleware	Kaise Lagaya	Faayde
🛒 E-commerce API	Auth, Rate limiting, Logging, Validation	JWT check, Request/min limits	Surakshit shopping, misuse se bachao
📱 Social Media App	Auth, Image processing, Content moderation	Token check, Multer, AI filtering	User safety, content quality
🏦 Banking System	Strong auth, Encryption, Audit logs	2FA, SSL/TLS, Poora logging	Security rules follow, fraud detection
📰 News Website	Caching, Compression, Analytics	Redis cache, Gzip, User tracking	Tez loading, user insights
🎮 Gaming API	Real-time auth, Rate limiting, Analytics	WebSocket auth, Game-specific limits	Fair khel, performance dekho

🚪 Middleware Kya Hai?

🏢 Society Gate Checkpoint System

🌐 Live API Request Flow

🔄 Middleware Pipeline:

🎬 Real-time Middleware Execution

Execution Log:

💻 Middleware Code ke Examples

🌍 Real-world Middleware Scenarios