Complete Node.js HTTP Module Tutorial

1. What is HTTP?

The Theory

HTTP (Hypertext Transfer Protocol) is the foundation of web communication. It defines how clients and servers exchange data.

You (Client)                    Waiter (HTTP)                    Kitchen (Server)
    │                                │                                 │
    │  "I want a pizza"              │                                 │
    │ ──────────────────────────────>│                                 │
    │                                │  "Get pizza from kitchen"       │
    │                                │ ───────────────────────────────>│
    │                                │                                 │
    │                                │  "Here's your pizza"            │
    │                                │ <───────────────────────────────│
    │  "Here's your pizza"           │                                 │
    │ <──────────────────────────────│                                 │

Key Concepts

2. Understanding the HTTP Module

The built-in http module helps you create servers and make outgoing HTTP requests.

const http = require('http'); // built-in, no installation needed

const server = http.createServer((request, response) => {
    response.writeHead(200, { 'Content-Type': 'text/plain' });
    response.end('Hello, World!\n');
});

server.listen(3000, () => {
    console.log('Server running at http://localhost:3000/');
});

3. Creating an HTTP Server

Route-based example

const http = require('http');

const server = http.createServer((req, res) => {
    const path = req.url;

    if (path === '/') {
        res.writeHead(200, { 'Content-Type': 'text/html' });
        res.end('<h1>Home Page</h1>');
    } else if (path === '/about') {
        res.writeHead(200, { 'Content-Type': 'text/html' });
        res.end('<h1>About Us</h1>');
    } else if (path === '/api/time') {
        res.writeHead(200, { 'Content-Type': 'application/json' });
        res.end(JSON.stringify({ time: new Date().toISOString() }));
    } else {
        res.writeHead(404, { 'Content-Type': 'text/html' });
        res.end('<h1>404 - Not Found</h1>');
    }
});

server.listen(3000);

Request-response lifecycle

const server2 = http.createServer((req, res) => {
    console.log(req.method, req.url, req.headers);
    res.statusCode = 200;
    res.setHeader('Content-Type', 'text/plain');
    res.end('Hello from lifecycle example');
});

4. Working with Requests

URL and query parsing

const url = require('url');

const server = http.createServer((req, res) => {
    const parsedUrl = url.parse(req.url, true);
    const path = parsedUrl.pathname;
    const queryParams = parsedUrl.query;
    res.end(`Path: ${path} Query: ${JSON.stringify(queryParams)}`);
});

Headers and body

if (req.method === 'POST') {
    let body = '';
    req.on('data', chunk => body += chunk.toString());
    req.on('end', () => {
        console.log('Body:', body);
        res.end('Received');
    });
}

5. Sending Responses

HTML, JSON, redirects, errors

if (req.url === '/json') {
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({ ok: true }));
} else if (req.url === '/redirect') {
    res.writeHead(301, { 'Location': '/' });
    res.end();
} else if (req.url === '/error') {
    res.writeHead(500, { 'Content-Type': 'text/plain' });
    res.end('Server error');
}

res.statusCode = 200;
res.setHeader('Content-Type', 'text/html');
res.write('<h1>Part 1</h1>');
res.end('<p>Final Part</p>');

6. HTTP Methods Explained

// Minimal CRUD pattern uses method + route matching
// GET /todos
// GET /todos/:id
// POST /todos
// PUT /todos/:id
// DELETE /todos/:id

7. Status Codes & Headers

Status ranges

2xx: Success
3xx: Redirect
4xx: Client Error
5xx: Server Error

Common content types

// HTML
res.writeHead(200, { 'Content-Type': 'text/html' });

// JSON
res.writeHead(200, { 'Content-Type': 'application/json' });

// Text
res.writeHead(200, { 'Content-Type': 'text/plain' });

// XML
res.writeHead(200, { 'Content-Type': 'application/xml' });

// Other useful headers
res.setHeader('Cache-Control', 'max-age=3600');
res.setHeader('X-Custom-Header', 'MyValue');
res.setHeader('Location', '/new-path');

8. Making HTTP Requests (Client)

GET request

const http = require('http');

http.get('http://jsonplaceholder.typicode.com/posts/1', (res) => {
    let data = '';
    res.on('data', chunk => data += chunk);
    res.on('end', () => console.log(JSON.parse(data)));
}).on('error', (err) => console.error(err.message));

POST request

const postData = JSON.stringify({ title: 'My New Post', body: 'Content', userId: 1 });
const options = {
    hostname: 'jsonplaceholder.typicode.com',
    port: 80,
    path: '/posts',
    method: 'POST',
    headers: {
        'Content-Type': 'application/json',
        'Content-Length': Buffer.byteLength(postData)
    }
};

const req = http.request(options, (res) => {
    let data = '';
    res.on('data', chunk => data += chunk);
    res.on('end', () => console.log(JSON.parse(data)));
});
req.on('error', err => console.error(err.message));
req.write(postData);
req.end();

// Promise helper
const https = require('https');
function fetchJSON(url) {
    return new Promise((resolve, reject) => {
        https.get(url, (res) => {
            let data = '';
            res.on('data', chunk => data += chunk);
            res.on('end', () => {
                try { resolve(JSON.parse(data)); } catch (e) { reject(e); }
            });
        }).on('error', reject);
    });
}

9. Best Practices

Error handling

server.on('error', (error) => {
    if (error.code === 'EADDRINUSE') console.error('Port already in use');
    else console.error(error);
});

Security headers

res.setHeader('X-Content-Type-Options', 'nosniff');
res.setHeader('X-Frame-Options', 'DENY');
res.setHeader('X-XSS-Protection', '1; mode=block');

Timeout + body limits + logging + graceful shutdown

// Timeout
req.setTimeout(30000, () => {
    res.writeHead(408);
    res.end('Request Timeout');
    req.destroy();
});

// Body size limit
const MAX_SIZE = 1024 * 1024;

// Request logging
res.on('finish', () => console.log(`${req.method} ${req.url} - ${res.statusCode}`));

// Graceful shutdown
process.on('SIGTERM', () => {
    server.close(() => process.exit(0));
});

Quick Reference

// Server
const http = require('http');
const server = http.createServer((req, res) => {});
server.listen(3000);

// Request
req.method; req.url; req.headers;

// Response
res.statusCode = 200;
res.setHeader('Content-Type', 'application/json');
res.end(JSON.stringify({ ok: true }));

// Client
http.get('http://example.com', (res) => {});
const req = http.request(options, (res) => {});
req.write(data);
req.end();

10 Interview Questions + 10 MCQs

Contextual Learning Links

• Node.js Events - HTTP server lifecycle is event-driven
• Node.js Buffers & Streams - request/response body streaming and backpressure
• Node.js Timers & Process - timeouts and process-level server control
• Building REST APIs - practical API design on top of HTTP module basics
• JavaScript Async - callbacks/promises used in request handling