Building an HTTP Server

Node.js was built for networking. Let's create an HTTP server from scratch - no frameworks needed.

Your First Server

// server.js
const http = require('http');

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

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

Run it:

node server.js

Output:

Server running at http://localhost:3000/

Open http://localhost:3000 in your browser - you'll see "Hello, World!"

Press Ctrl+C to stop the server.

Understanding Request and Response

const http = require('http');

const server = http.createServer((req, res) => {
  // req = incoming request
  console.log('Method:', req.method);    // GET, POST, etc.
  console.log('URL:', req.url);          // /path/to/resource
  console.log('Headers:', req.headers);  // Object with all headers

  // res = our response
  res.statusCode = 200;                  // HTTP status
  res.setHeader('Content-Type', 'text/plain');
  res.write('Hello ');                   // Write partial response
  res.end('World!');                     // Complete the response
});

server.listen(3000);

Basic Routing

Route different URLs to different responses:

// router.js
const http = require('http');

const server = http.createServer((req, res) => {
  // Set default headers
  res.setHeader('Content-Type', 'text/plain');

  // Route based on URL
  if (req.url === '/') {
    res.statusCode = 200;
    res.end('Welcome to the homepage!');
  } else if (req.url === '/about') {
    res.statusCode = 200;
    res.end('About us page');
  } else if (req.url === '/contact') {
    res.statusCode = 200;
    res.end('Contact us at hello@example.com');
  } else {
    res.statusCode = 404;
    res.end('Page not found');
  }
});

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

Test it:

curl http://localhost:3000/
curl http://localhost:3000/about
curl http://localhost:3000/unknown

Output:

Welcome to the homepage!
About us page
Page not found

Returning JSON

APIs return JSON. Here's how:

// api.js
const http = require('http');

const users = [
  { id: 1, name: 'Alice', email: 'alice@example.com' },
  { id: 2, name: 'Bob', email: 'bob@example.com' },
  { id: 3, name: 'Charlie', email: 'charlie@example.com' }
];

const server = http.createServer((req, res) => {
  // CORS headers (allow browser requests from any origin)
  res.setHeader('Access-Control-Allow-Origin', '*');

  if (req.url === '/api/users' && req.method === 'GET') {
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify(users));
  } else if (req.url.startsWith('/api/users/') && req.method === 'GET') {
    const id = parseInt(req.url.split('/')[3]);
    const user = users.find(u => u.id === id);

    if (user) {
      res.writeHead(200, { 'Content-Type': 'application/json' });
      res.end(JSON.stringify(user));
    } else {
      res.writeHead(404, { 'Content-Type': 'application/json' });
      res.end(JSON.stringify({ error: 'User not found' }));
    }
  } else {
    res.writeHead(404, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({ error: 'Not found' }));
  }
});

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

Test it:

curl http://localhost:3000/api/users
curl http://localhost:3000/api/users/1
curl http://localhost:3000/api/users/99

Output:

[{"id":1,"name":"Alice","email":"alice@example.com"},...]
{"id":1,"name":"Alice","email":"alice@example.com"}
{"error":"User not found"}

Handling POST Requests

POST requests have a body. You need to collect it:

// post-server.js
const http = require('http');

const users = [];

const server = http.createServer((req, res) => {
  res.setHeader('Content-Type', 'application/json');

  if (req.url === '/api/users' && req.method === 'GET') {
    res.end(JSON.stringify(users));
  } else if (req.url === '/api/users' && req.method === 'POST') {
    // Collect the request body
    let body = '';

    req.on('data', chunk => {
      body += chunk.toString();
    });

    req.on('end', () => {
      try {
        const newUser = JSON.parse(body);
        newUser.id = users.length + 1;
        users.push(newUser);

        res.statusCode = 201;
        res.end(JSON.stringify(newUser));
      } catch (err) {
        res.statusCode = 400;
        res.end(JSON.stringify({ error: 'Invalid JSON' }));
      }
    });
  } else {
    res.statusCode = 404;
    res.end(JSON.stringify({ error: 'Not found' }));
  }
});

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

Test it:

# Create a user
curl -X POST http://localhost:3000/api/users \
  -H "Content-Type: application/json" \
  -d '{"name":"Alice","email":"alice@example.com"}'

# Get all users
curl http://localhost:3000/api/users

Output:

{"name":"Alice","email":"alice@example.com","id":1}
[{"name":"Alice","email":"alice@example.com","id":1}]

Serving HTML Files

// html-server.js
const http = require('http');
const fs = require('fs');
const path = require('path');

const server = http.createServer((req, res) => {
  // Default to index.html
  let filePath = req.url === '/' ? '/index.html' : req.url;
  filePath = path.join(__dirname, 'public', filePath);

  // Get file extension for content type
  const ext = path.extname(filePath);
  const contentTypes = {
    '.html': 'text/html',
    '.css': 'text/css',
    '.js': 'text/javascript',
    '.json': 'application/json',
    '.png': 'image/png',
    '.jpg': 'image/jpeg'
  };

  const contentType = contentTypes[ext] || 'text/plain';

  // Read and serve the file
  fs.readFile(filePath, (err, content) => {
    if (err) {
      if (err.code === 'ENOENT') {
        res.writeHead(404, { 'Content-Type': 'text/html' });
        res.end('<h1>404 - File Not Found</h1>');
      } else {
        res.writeHead(500);
        res.end('Server Error');
      }
    } else {
      res.writeHead(200, { 'Content-Type': contentType });
      res.end(content);
    }
  });
});

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

Create public/index.html:

<!DOCTYPE html>
<html>
<head>
  <title>My Node.js Server</title>
</head>
<body>
  <h1>Hello from Node.js!</h1>
  <p>This HTML file is served by our custom server.</p>
</body>
</html>

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Try It Yourself

Build a simple todo API:

// todo-api.js
const http = require('http');

let todos = [
  { id: 1, text: 'Learn Node.js', done: false },
  { id: 2, text: 'Build an API', done: false }
];

function sendJSON(res, statusCode, data) {
  res.writeHead(statusCode, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify(data));
}

function parseBody(req) {
  return new Promise((resolve, reject) => {
    let body = '';
    req.on('data', chunk => body += chunk);
    req.on('end', () => {
      try {
        resolve(body ? JSON.parse(body) : {});
      } catch (e) {
        reject(e);
      }
    });
  });
}

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

  // GET /todos - List all todos
  if (url === '/todos' && method === 'GET') {
    sendJSON(res, 200, todos);
  }
  // POST /todos - Create a todo
  else if (url === '/todos' && method === 'POST') {
    const body = await parseBody(req);
    const todo = {
      id: todos.length + 1,
      text: body.text,
      done: false
    };
    todos.push(todo);
    sendJSON(res, 201, todo);
  }
  // PATCH /todos/:id - Toggle done status
  else if (url.match(/^\/todos\/\d+$/) && method === 'PATCH') {
    const id = parseInt(url.split('/')[2]);
    const todo = todos.find(t => t.id === id);
    if (todo) {
      todo.done = !todo.done;
      sendJSON(res, 200, todo);
    } else {
      sendJSON(res, 404, { error: 'Todo not found' });
    }
  }
  // DELETE /todos/:id - Delete a todo
  else if (url.match(/^\/todos\/\d+$/) && method === 'DELETE') {
    const id = parseInt(url.split('/')[2]);
    const index = todos.findIndex(t => t.id === id);
    if (index !== -1) {
      todos.splice(index, 1);
      sendJSON(res, 200, { message: 'Deleted' });
    } else {
      sendJSON(res, 404, { error: 'Todo not found' });
    }
  }
  // 404 for everything else
  else {
    sendJSON(res, 404, { error: 'Not found' });
  }
});

server.listen(3000, () => {
  console.log('Todo API at http://localhost:3000/');
  console.log('Try: curl http://localhost:3000/todos');
});

Test it:

# List todos
curl http://localhost:3000/todos

# Create a todo
curl -X POST http://localhost:3000/todos \
  -H "Content-Type: application/json" \
  -d '{"text":"Read documentation"}'

# Toggle done
curl -X PATCH http://localhost:3000/todos/1

# Delete
curl -X DELETE http://localhost:3000/todos/2

Key Takeaways

http.createServer creates a server with a request handler
req contains method, url, headers, and body (as stream)
res is used to send status, headers, and body back
JSON.stringify converts objects to JSON strings
Routing is matching req.url and req.method to handlers
POST bodies must be collected from the stream

This manual routing works, but gets tedious. Next, let's see how Express makes this much easier!

Building an HTTP Server

Your First Server

Understanding Request and Response

Basic Routing

Returning JSON

Handling POST Requests

Serving HTML Files

Deploy Your Server

Try It Yourself

Key Takeaways

🧠 Quick Quiz

What does req.url contain?

What does res.end() do?

How do you return JSON from an HTTP server?

Launch Offer

Building an HTTP Server

Your First Server

Understanding Request and Response

Basic Routing

Returning JSON

Handling POST Requests

Serving HTML Files

Deploy Your Server

Try It Yourself

Key Takeaways

🧠 Quick Quiz

What does req.url contain?

What does res.end() do?

How do you return JSON from an HTTP server?

Lesson Complete!

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