Print IP address and headers in Cloud Functions

print_ip_and_headers.js

const functions = require('firebase-functions');
const util = require('util');

exports.helloWorld = functions.https.onRequest((req, res) => {
  // For Firebase Hosting URIs, use req.headers['fastly-client-ip']
  // For callable functions, use rawRequest
  // Some users have better success with req.headers['x-appengine-user-ip']
  const ipAddress = req.headers['x-forwarded-for'] || req.connection.remoteAddress;
  const headers = JSON.stringify(req.headers, null, 2);
  const message = util.format("<pre>Hello world!\n\nYour IP address: %s\n\nRequest headers: %s</pre>", ipAddress, headers);
  res.send(message);
});

I don't know why I have to use res.rawRequest.headers['x-forwarded-for']

2022 and Google still not published any documentation about how to get the client IP.
Increible.