HTTP/HTTPS & Web Communication

1// ============================================
2// HTTP Communication — Essential Patterns
3// ============================================
4
5// ---------- HTTP Methods & Idempotency ----------
6
7// ❌ BAD: Using POST for everything (not idempotent, can't cache)
8app.post('/get-users', (req, res) => { /* wrong method for reads */ });
9app.post('/delete-user', (req, res) => { /* should use DELETE */ });
10
11// ✅ GOOD: RESTful HTTP methods
12app.get('/api/users', async (req, res) => {
13  // GET is idempotent and cacheable
14  const users = await db.query('SELECT * FROM users LIMIT 100');
15  res.set('Cache-Control', 'public, max-age=60');  // Cache for 60 seconds
16  res.json({ users });
17});
18
19app.post('/api/users', async (req, res) => {
20  // POST creates a new resource — NOT idempotent
21  const user = await db.query(
22    'INSERT INTO users (name, email) VALUES (?, ?)',
23    [req.body.name, req.body.email]
24  );
25  res.status(201).json({ user });  // 201 = Created
26});
27
28app.put('/api/users/:id', async (req, res) => {
29  // PUT replaces the entire resource — IS idempotent
30  // Calling PUT twice with the same data = same result
31  await db.query(
32    'UPDATE users SET name = ?, email = ? WHERE id = ?',
33    [req.body.name, req.body.email, req.params.id]
34  );
35  res.json({ updated: true });
36});
37
38app.delete('/api/users/:id', async (req, res) => {
39  // DELETE is idempotent — deleting twice = same state (resource gone)
40  await db.query('DELETE FROM users WHERE id = ?', [req.params.id]);
41  res.status(204).end();  // 204 = No Content
42});
43
44// ---------- HTTP Status Codes in Practice ----------
45
46// Rate limiting with 429
47const rateLimit = new Map();
48
49function rateLimitMiddleware(req, res, next) {
50  const clientIP = req.ip;
51  const now = Date.now();
52
53  if (!rateLimit.has(clientIP)) {
54    rateLimit.set(clientIP, { count: 1, windowStart: now });
55    return next();
56  }
57
58  const entry = rateLimit.get(clientIP);
59  const windowMs = 60000; // 1-minute window
60  const maxRequests = 100;
61
62  if (now - entry.windowStart > windowMs) {
63    // Window expired, reset
64    rateLimit.set(clientIP, { count: 1, windowStart: now });
65    return next();
66  }
67
68  if (entry.count >= maxRequests) {
69    // ✅ Use 429 with Retry-After header
70    const retryAfter = Math.ceil((entry.windowStart + windowMs - now) / 1000);
71    res.set('Retry-After', retryAfter.toString());
72    res.set('X-RateLimit-Limit', maxRequests.toString());
73    res.set('X-RateLimit-Remaining', '0');
74    return res.status(429).json({
75      error: 'Too Many Requests',
76      retryAfter,
77    });
78  }
79
80  entry.count++;
81  next();
82}
83
84// ---------- HTTP/2 Multiplexing Concept ----------
85
86// HTTP/1.1: Browser opens 6 parallel connections to same domain
87// Each connection handles ONE request at a time
88// └── Connection 1: GET /style.css ──────────────> response
89// └── Connection 2: GET /app.js ────────────────> response
90// └── Connection 3: GET /image1.jpg ────────────> response
91// └── Connection 4: GET /image2.jpg ────────────> response
92// └── Connection 5: waiting... (only 6 allowed!)
93// └── Connection 6: waiting...
94
95// HTTP/2: Browser opens ONE connection
96// Multiple requests/responses interleaved on the same connection
97// └── Single Connection:
98//     Stream 1: GET /style.css ──> response (interleaved)
99//     Stream 2: GET /app.js ────> response (interleaved)
100//     Stream 3: GET /image1.jpg > response (interleaved)
101//     Stream 4: GET /image2.jpg > response (interleaved)
102//     Stream 5: GET /api/data ──> response (interleaved)
103//     ... unlimited streams!
104
105// ---------- Caching Headers ----------
106
107function serveCacheableResource(req, res) {
108  // ✅ Proper cache headers for static assets
109  res.set({
110    'Cache-Control': 'public, max-age=31536000, immutable', // 1 year
111    'ETag': 'W/"abc123"',                                    // Weak ETag
112    'Last-Modified': 'Tue, 15 Jan 2024 10:30:00 GMT',
113    'Vary': 'Accept-Encoding',                               // Cache varies by compression
114  });
115  res.sendFile('/static/bundle.hash123.js');
116}
117
118function serveAPIResponse(req, res) {
119  // ✅ API responses: short cache, must revalidate
120  res.set({
121    'Cache-Control': 'private, max-age=0, must-revalidate',
122    'ETag': `W/"\${computeHash(data)}"`,
123  });
124  res.json(data);
125}
126
127console.log("HTTP examples configured correctly!");