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HTTP Module

The http module allows Node.js to transfer data over the Hyper Text Transfer Protocol (HTTP). It is the foundation for web servers in Node.js. 
const http = require('http');

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Creating a Server

The http.createServer() method includes a request listener function which is automatically added to the 'request' event. 
const server = http.createServer((req, res) => {
  res.write('Hello World');
  res.end();
});

server.listen(5000, () => {
  console.log('Server running on port 5000...');
});
Run this script and navigate to http://localhost:5000 in your browser.

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The Request and Response Objects

The callback function receives two arguments:
  1. req (Request): Contains information about the incoming request (URL, method, headers, etc.).
  2. res (Response): Used to send a response back to the client.

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Inspecting the Request

const server = http.createServer((req, res) => {
  console.log(req.url, req.method);
  // ...
});

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Setting Headers and Status Code

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World');
});

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Basic Routing

You can use req.url to handle different routes. 
const server = http.createServer((req, res) => {
  if (req.url === '/') {
    res.write('Welcome to the Home Page');
    res.end();
  } else if (req.url === '/about') {
    res.write('Welcome to the About Page');
    res.end();
  } else {
    res.statusCode = 404;
    res.write('Page Not Found');
    res.end();
  }
});

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Serving JSON

To serve an API, you typically return JSON data. 
const server = http.createServer((req, res) => {
  if (req.url === '/api/users') {
    const users = [
      { name: 'Alice', age: 25 },
      { name: 'Bob', age: 30 }
    ];
    
    res.setHeader('Content-Type', 'application/json');
    res.end(JSON.stringify(users));
  }
});

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Serving HTML Files

To serve actual HTML files, we combine the http module with the fs module. 
const http = require('http');
const fs = require('fs');
const path = require('path');

const server = http.createServer((req, res) => {
  if (req.url === '/') {
    fs.readFile(path.join(__dirname, 'index.html'), (err, content) => {
      if (err) throw err;
      res.writeHead(200, { 'Content-Type': 'text/html' });
      res.end(content);
    });
  }
});

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Handling POST Requests

Unlike GET requests, POST data comes in chunks and must be collected: 
const server = http.createServer((req, res) => {
  if (req.method === 'POST' && req.url === '/api/users') {
    let body = '';
    
    // Collect data chunks
    req.on('data', chunk => {
      body += chunk.toString();
    });
    
    // All data received
    req.on('end', () => {
      try {
        const user = JSON.parse(body);
        console.log('Received user:', user);
        
        res.writeHead(201, { 'Content-Type': 'application/json' });
        res.end(JSON.stringify({ message: 'User created', user }));
      } catch (error) {
        res.writeHead(400, { 'Content-Type': 'application/json' });
        res.end(JSON.stringify({ error: 'Invalid JSON' }));
      }
    });
  }
});

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Query Parameters

const http = require('http');
const url = require('url');

const server = http.createServer((req, res) => {
  const parsedUrl = new URL(req.url, `http://${req.headers.host}`);
  const pathname = parsedUrl.pathname;
  const query = parsedUrl.searchParams;
  
  // GET /search?q=nodejs&limit=10
  if (pathname === '/search') {
    const searchTerm = query.get('q');
    const limit = parseInt(query.get('limit')) || 10;
    
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({
      search: searchTerm,
      limit: limit,
      results: []
    }));
  }
});

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Headers Deep Dive

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Request Headers

const server = http.createServer((req, res) => {
  console.log('User-Agent:', req.headers['user-agent']);
  console.log('Content-Type:', req.headers['content-type']);
  console.log('Authorization:', req.headers['authorization']);
  console.log('Accept-Language:', req.headers['accept-language']);
  console.log('All headers:', req.headers);
  
  // Check for JSON content
  const isJson = req.headers['content-type'] === 'application/json';
});

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Response Headers

res.setHeader('Content-Type', 'application/json');
res.setHeader('X-Powered-By', 'Node.js');
res.setHeader('Cache-Control', 'no-cache');
res.setHeader('Access-Control-Allow-Origin', '*');

// Set multiple headers at once
res.writeHead(200, {
  'Content-Type': 'text/html',
  'Set-Cookie': 'session=abc123; HttpOnly',
  'X-Request-Id': '12345'
});

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Building a Simple Router

const http = require('http');

class Router {
  constructor() {
    this.routes = {
      GET: {},
      POST: {},
      PUT: {},
      DELETE: {}
    };
  }

  get(path, handler) {
    this.routes.GET[path] = handler;
  }

  post(path, handler) {
    this.routes.POST[path] = handler;
  }

  put(path, handler) {
    this.routes.PUT[path] = handler;
  }

  delete(path, handler) {
    this.routes.DELETE[path] = handler;
  }

  async handle(req, res) {
    const handler = this.routes[req.method]?.[req.url];
    
    if (handler) {
      await handler(req, res);
    } else {
      res.writeHead(404, { 'Content-Type': 'application/json' });
      res.end(JSON.stringify({ error: 'Not Found' }));
    }
  }
}

// Usage
const router = new Router();

router.get('/', (req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('Home Page');
});

router.get('/api/users', (req, res) => {
  res.writeHead(200, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify([{ id: 1, name: 'John' }]));
});

const server = http.createServer((req, res) => router.handle(req, res));
server.listen(3000);

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HTTPS Server

For production, you need HTTPS: 
const https = require('https');
const fs = require('fs');

const options = {
  key: fs.readFileSync('server.key'),
  cert: fs.readFileSync('server.cert')
};

const server = https.createServer(options, (req, res) => {
  res.writeHead(200);
  res.end('Secure Hello World!');
});

server.listen(443, () => {
  console.log('HTTPS server running on port 443');
});

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Summary

  • The http module creates web servers without external dependencies
  • Use req.url and req.method for routing
  • POST data arrives in chunks via 'data' and 'end' events
  • Parse query strings with the URL class
  • Set appropriate Content-Type headers for responses
  • Build custom routers for organized code
  • Use https module with SSL certificates for production
  • Frameworks like Express.js abstract this complexity