client.js

// builtin
var net = require('net');
var url = require('url');
var request = require('request');
var EventEmitter = require('events').EventEmitter;

// request upstream url and connection info
var request_url = function(params, cb) {
    request(params, function(err, res, body) {
        if (err) {
            cb(err);
        }

        cb(null, body);
    });
};

var connect = function(opt) {
    var ev = new EventEmitter();

    // local port
    var local_port = opt.port;

    var base_uri = opt.host + '/';

    // optionally override the upstream server
    var upstream = url.parse(opt.host);

    // no subdomain at first, maybe use requested domain
    var assigned_domain = opt.subdomain;

    // connect to upstream given connection parameters
    var tunnel = function (remote_host, remote_port) {

        var remote_opt = {
            host: remote_host,
            port: remote_port
        };

        var local_opt = {
            host: 'localhost',
            port: local_port
        };

        var remote_attempts = 0;

        (function conn(conn_had_error) {
            if (conn_had_error) {
                return;
            }

            if (++remote_attempts >= 3) {
                console.error('localtunnel server offline - try again');
                process.exit(-1);
            }

            // connection to localtunnel server
            var remote = net.connect(remote_opt);

            remote.once('error', function(err) {
                if (err.code !== 'ECONNREFUSED') {
                    local.emit('error', err);
                }

                // retrying connection to local server
                setTimeout(conn, 1000);
            });

            function recon_local() {
                remote.pause();
                remote_attempts = 0;

                // connection to local http server
                var local = net.connect(local_opt);

                local.once('error', function(err) {
                    if (err.code !== 'ECONNREFUSED') {
                        local.emit('error', err);
                    }

                    // retrying connection to local server
                    setTimeout(recon_local, 1000);
                });

                local.once('connect', function() {
                    remote.resume();
                    remote.pipe(local).pipe(remote, {end: false});
                });

                local.once('close', function(had_error) {
                    if (had_error) {
                        return;
                    }
                    recon_local();
                });
            }

            remote.once('close', conn);
            remote.once('connect', recon_local);
        })();
    };

    var params = {
        path: '/',
        json: true
    };

    // where to quest
    params.uri = base_uri + ((assigned_domain) ? assigned_domain : '?new');

    // get an id from lt server and setup forwarding tcp connections
    request_url(params, function(err, body) {

        if (err) {
            ev.emit('error', new Error('tunnel server not available: %s, retry 1s', err.message));

            // retry interval for id request
            return setTimeout(function() {
                connect_proxy(opt);
            }, 1000);
        }

        // our assigned hostname and tcp port
        var port = body.port;
        var host = upstream.hostname;

        // store the id so we can try to get the same one
        assigned_domain = body.id;

        var max_conn = body.max_conn_count || 1;
        for (var count = 0 ; count < max_conn ; ++count) {
            tunnel(host, port);
        }

        ev.emit('url', body.url);
    });

    return ev;
};

module.exports.connect = connect;