How does HTTP redirect work?

Redirect in HTTP is a mechanism that redirects the client (browser) from one URL to another.

It works as follows:

1. The client sends an HTTP request to the original URL.
2. The server receives the request and instead of sending a page for the original URL, sends an HTTP response with a redirect status code (e.g., 301 - permanent, 302 - temporary).
3. The server also includes a Location header with the new URL to redirect to.
4. The browser, upon receiving the redirect status code and Location header, automatically sends a new HTTP request to the URL specified in Location.

Examples of redirect status codes:

Status code	Description
301	Moved Permanently
302	Found
303	See Other
307	Temporary Redirect
308	Permanent Redirect

Example of an HTTP redirect response:

HTTP/1.1 301 Moved Permanently
Location: https://new-example.com/new/path/
Content-Length: 0

In Node.js, redirect is usually implemented by setting the appropriate status code and Location header in the response object.

Example in Express.js:

// In route handler
app.get('/old-path', (req, res) => {
  res.redirect(301, '/new-path'); // Redirect with 301 to /new-path
});

Example in plain Node.js:

// In http server
const http = require('http');

const server = http.createServer((req, res) => {
  if (req.url === '/old-path') {
    res.writeHead(302, { 'Location': '/new-path' }); // Temporary redirect
    res.end();
  } else {
    // Handle other requests
    res.writeHead(200, { 'Content-Type': 'text/plain' });
    res.end('Hello World!');
  }
});

server.listen(3000);

This mechanism is essential for guiding clients to the correct resource, handling URL changes, or implementing load balancing and other server-side logic.