Get client IP address and user agent in Node.js

To get the client IP address and user agent in a Node.js application, you can use the http or express package.

1) Using Express

If you’re using Express, it’s straightforward:

const express = require('express');
const app = express();

app.get('/', (req, res) => {
    // Get the client's IP address
    const ip = req.headers['x-forwarded-for'] || req.connection.remoteAddress;

    // Get the client's User-Agent
    const userAgent = req.headers['user-agent'];

    res.send(`IP Address: ${ip}, User-Agent: ${userAgent}`);
});

app.listen(3000, () => {
    console.log('Server is running on port 3000');
});

2) Using the HTTP Module

If you’re using the built-in http module:

const http = require('http');

const server = http.createServer((req, res) => {
    // Get the client's IP address
    const ip = req.headers['x-forwarded-for'] || req.connection.remoteAddress;

    // Get the client's User-Agent
    const userAgent = req.headers['user-agent'];

    res.writeHead(200, {'Content-Type': 'text/plain'});
    res.end(`IP Address: ${ip}, User-Agent: ${userAgent}`);
});

server.listen(3000, () => {
    console.log('Server is running on port 3000');
});

Notes

• req.headers['x-forwarded-for'] is often used to get the real IP address of the client, especially when behind a proxy or load balancer.
• req.connection.remoteAddress will give you the direct IP address from the connection.
• The User-Agent is available in req.headers['user-agent'].

Make sure to handle the case where x-forwarded-for might contain a list of IPs (comma-separated), with the client’s IP being the first one in the list.