Rocket.Chat/apps/meteor/server/routes/timesync.ts

import { WebApp } from 'meteor/webapp';
// Use rawConnectHandlers so we get a response as quickly as possible
// https://github.com/meteor/meteor/blob/devel/packages/webapp/webapp_server.js

const syncUrl = `${(global as any)?.ROOT_URL_PATH_PREFIX || ''}/_timesync`;

WebApp.rawConnectHandlers.use(syncUrl, function (_req, res) {
	// Never ever cache this, otherwise weird times are shown on reload
	// http://stackoverflow.com/q/18811286/586086
	res.setHeader('Cache-Control', 'no-cache, no-store, must-revalidate');
	res.setHeader('Pragma', 'no-cache');
	res.setHeader('Expires', 0);

	// Avoid MIME type warnings in browsers
	res.setHeader('Content-Type', 'text/plain');

	res.end(Date.now().toString());
});