Server-list-ping feature of Minecraft Forge servers.

forge.js

var net = require("net");

function makeBuf(server, port) {
    var bufSize = 7 + server.length;
    var buffer = new Buffer(bufSize);

    buffer.writeUInt8(bufSize - 1, 0);
    buffer.writeUInt8(0, 1);
    buffer.writeUInt8(5, 2);
    buffer.writeUInt8(server.length, 3);
    for (var i = 0; i < server.length; i++) {
        buffer.write(server[i], 4 + i);
    }
    buffer.writeUInt16BE(25565, server.length + 4);
    buffer.writeUInt8(1, server.length + 6);

    return buffer;
}

var ping = function (server, port, callback, timeout) {
    var MC_DEFAULT_PORT = 25565;
    var started = false;
    var response = "";
    var buf = new Buffer("227d5d7d7d", "hex");
    if (typeof port == "function") {
        callback = port;
        port = MC_DEFAULT_PORT;
    }

    if (typeof port !== "number") {
        port = MC_DEFAULT_PORT;
    }

    if (typeof timeout == "undefined") {
        timeout = 3000;
    }
    var socket = net.connect({
        port: port,
        host: server
    }, function () {
        socket.write(makeBuf(server, port), function () {
            socket.write(new Buffer("0100", "hex"));
        });
    });

    socket.setTimeout(timeout, function () {
        if (callback != undefined) {
            callback(new Error("Socket timed out when connecting to " + server + ":" + port), null);
        }
        socket.end();
    });

    socket.on("data", function (data) {
        if (!started) {
            response += data.slice(5);
            started = true;
        } else {
            response += data;
        }

        if (data.slice(data.length - 5).compare(buf) == 0) {
            if (callback !== undefined) {
                callback(null, response);
            }
        }
        socket.end();
    });

    socket.once('error', function (e) {
        if (callback !== undefined) {
            callback(e, null);
        }
    });
};

ping("ftb.oblivion-networks.com", 25565, function (error, data) {
    if (error) {
        return console.log(error);
    }

    console.log(data);

    var data = JSON.parse(data);
    console.log(data.description)
    console.log(data.players.online);
    var players;
    if (data.players.online > 0 && data.players.hasOwnProperty("sample")) {
        if (data.players.sample.length > 0) {
            var players = "Players:\n";
            for (var i = 0; i < data.players.sample.length; i++) {
                players += data.players.sample[i].name + "\n";
            }
        }
        console.log(players);
    }
    
    var mods = data.modinfo.modList;
    console.log(mods);
});