Handling Requests and Responses

Now that you can create a basic server, let's dive deeper into handling incoming requests and crafting appropriate responses. You'll learn to extract data from requests and send proper HTTP responses.

---

Parsing the Request URL

The req.url property contains the path and query string:

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

const server = http.createServer((req, res) => {
  // req.url example: "/users?page=1&limit=10"

  // Parse the URL
  const parsedUrl = new URL(req.url, `http://${req.headers.host}`);

  console.log('Pathname:', parsedUrl.pathname);  // "/users"
  console.log('Search:', parsedUrl.search);      // "?page=1&limit=10"

  // Get query parameters
  const page = parsedUrl.searchParams.get('page');    // "1"
  const limit = parsedUrl.searchParams.get('limit'); // "10"

  res.end(`Page: ${page}, Limit: ${limit}`);
});

---

HTTP Methods

Different methods indicate different operations:

Method	Purpose	Has Body
GET	Retrieve data	No
POST	Create data	Yes
PUT	Update data (replace)	Yes
PATCH	Update data (partial)	Yes
DELETE	Delete data	Usually no
HEAD	Get headers only	No
OPTIONS	Get allowed methods	No

const server = http.createServer((req, res) => {
  console.log('Method:', req.method);

  switch (req.method) {
    case 'GET':
      // Return data
      res.end('Here is your data');
      break;
    case 'POST':
      // Handle creation
      res.end('Data created');
      break;
    case 'DELETE':
      // Handle deletion
      res.end('Data deleted');
      break;
    default:
      res.statusCode = 405;
      res.end('Method Not Allowed');
  }
});

---

Reading Request Headers

const server = http.createServer((req, res) => {
  // All headers (lowercase keys)
  console.log(req.headers);

  // Common headers
  const contentType = req.headers['content-type'];
  const userAgent = req.headers['user-agent'];
  const authorization = req.headers['authorization'];
  const accept = req.headers['accept'];

  res.end('Headers received');
});

---

Reading Request Body

For POST/PUT requests, you need to collect the body data:

const http = require('http');

const server = http.createServer((req, res) => {
  if (req.method === 'POST') {
    let body = '';

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

    // All data received
    req.on('end', () => {
      console.log('Body:', body);

      // Parse JSON body
      try {
        const data = JSON.parse(body);
        console.log('Parsed:', data);
        res.end('Data received');
      } catch (err) {
        res.statusCode = 400;
        res.end('Invalid JSON');
      }
    });
  } else {
    res.end('Send a POST request');
  }
});

---

Helper Function for Body Parsing

Create a reusable body parser:

function getBody(req) {
  return new Promise((resolve, reject) => {
    let body = '';

    req.on('data', chunk => {
      body += chunk.toString();
      // Prevent too-large bodies
      if (body.length > 1e6) {
        req.destroy();
        reject(new Error('Body too large'));
      }
    });

    req.on('end', () => resolve(body));
    req.on('error', reject);
  });
}

// Usage
const server = http.createServer(async (req, res) => {
  if (req.method === 'POST') {
    try {
      const body = await getBody(req);
      const data = JSON.parse(body);
      res.end(JSON.stringify({ received: data }));
    } catch (err) {
      res.statusCode = 400;
      res.end(JSON.stringify({ error: err.message }));
    }
  }
});

---

Setting Response Headers

const server = http.createServer((req, res) => {
  // Set individual headers
  res.setHeader('Content-Type', 'application/json');
  res.setHeader('X-Powered-By', 'Node.js');
  res.setHeader('Cache-Control', 'no-cache');

  // Or use writeHead for status + headers together
  res.writeHead(200, {
    'Content-Type': 'application/json',
    'X-Request-Id': '12345'
  });

  res.end(JSON.stringify({ status: 'ok' }));
});

Common Response Headers

Header	Purpose	Example
Content-Type	Body format	application/json
Content-Length	Body size	1234
Cache-Control	Caching rules	max-age=3600
Location	Redirect URL	https://example.com
Set-Cookie	Set cookie	session=abc; HttpOnly
Access-Control-Allow-Origin	CORS	*

---

Sending Different Response Types

---

Redirects

const server = http.createServer((req, res) => {
  if (req.url === '/old-page') {
    // Permanent redirect (301)
    res.writeHead(301, { 'Location': '/new-page' });
    res.end();
    return;
  }

  if (req.url === '/temporary') {
    // Temporary redirect (302)
    res.writeHead(302, { 'Location': '/somewhere-else' });
    res.end();
    return;
  }

  res.end('Normal page');
});

---

Error Responses

function sendError(res, statusCode, message) {
  res.statusCode = statusCode;
  res.setHeader('Content-Type', 'application/json');
  res.end(JSON.stringify({
    error: true,
    message: message,
    statusCode: statusCode
  }));
}

const server = http.createServer((req, res) => {
  if (req.url === '/protected' && !req.headers.authorization) {
    sendError(res, 401, 'Authentication required');
    return;
  }

  if (req.url === '/admin' && !isAdmin(req)) {
    sendError(res, 403, 'Access forbidden');
    return;
  }

  res.end('OK');
});

---

CORS Headers

Enable cross-origin requests:

const server = http.createServer((req, res) => {
  // CORS headers
  res.setHeader('Access-Control-Allow-Origin', '*');
  res.setHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE');
  res.setHeader('Access-Control-Allow-Headers', 'Content-Type, Authorization');

  // Handle preflight
  if (req.method === 'OPTIONS') {
    res.writeHead(204);
    res.end();
    return;
  }

  // Normal request handling
  res.end('CORS enabled');
});

---

Complete Request/Response Example

const http = require('http');

const server = http.createServer(async (req, res) => {
  // Parse URL
  const url = new URL(req.url, `http://${req.headers.host}`);

  // Log request
  console.log(`${req.method} ${url.pathname}`);

  // Set CORS
  res.setHeader('Access-Control-Allow-Origin', '*');

  // Handle preflight
  if (req.method === 'OPTIONS') {
    res.writeHead(204);
    res.end();
    return;
  }

  // Route handling
  if (req.method === 'GET' && url.pathname === '/api/health') {
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({ status: 'healthy' }));
    return;
  }

  if (req.method === 'POST' && url.pathname === '/api/echo') {
    let body = '';
    for await (const chunk of req) {
      body += chunk;
    }
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(body);
    return;
  }

  // 404 for unknown routes
  res.writeHead(404, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify({ error: 'Not found' }));
});

server.listen(3000);

---

Key Takeaways

• Use new URL(req.url, base) to parse URLs and query parameters
• Check req.method to handle different HTTP methods
• Access headers via req.headers (lowercase keys)
• Collect body data using req.on('data') and req.on('end')
• Use res.writeHead() or res.setHeader() for response headers
• Always set appropriate Content-Type header
• Return proper status codes (200, 400, 401, 404, 500, etc.)

---

Summary

You now know how to fully process incoming HTTP requests—parsing URLs, reading headers and body data, and responding appropriately. You can handle different content types, implement redirects, and return proper error responses. These skills form the foundation for building APIs and web applications.

Next, you'll learn about routing—directing different requests to different handlers based on URL patterns.