overleaf/services/real-time/app/coffee/SessionSockets.js

/*
 * decaffeinate suggestions:
 * DS102: Remove unnecessary code created because of implicit returns
 * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
 */
const {EventEmitter} = require('events');

module.exports = function(io, sessionStore, cookieParser, cookieName) {
	const missingSessionError = new Error('could not look up session by key');

	const sessionSockets = new EventEmitter();
	const next = (error, socket, session) => sessionSockets.emit('connection', error, socket, session);

	io.on('connection', function(socket) {
		const req = socket.handshake;
		return cookieParser(req, {}, function() {
			const sessionId = req.signedCookies && req.signedCookies[cookieName];
			if (!sessionId) {
				return next(missingSessionError, socket);
			}
			return sessionStore.get(sessionId, function(error, session) {
				if (error) {
					return next(error, socket);
				}
				if (!session) {
					return next(missingSessionError, socket);
				}
				return next(null, socket, session);
			});
		});
	});

	return sessionSockets;
};