node-gamedig/protocols/minecraft.js

const Core = require('./core'),
    Varint = require('varint');

class Minecraft extends Core {
    constructor() {
        super();
        this.srvRecord = "_minecraft._tcp";
    }
    async run(state) {
        const portBuf = Buffer.alloc(2);
        portBuf.writeUInt16BE(this.options.port,0);

        const addressBuf = Buffer.from(this.options.host,'utf8');

        const bufs = [
            this.varIntBuffer(4),
            this.varIntBuffer(addressBuf.length),
            addressBuf,
            portBuf,
            this.varIntBuffer(1)
        ];

        const outBuffer = Buffer.concat([
            this.buildPacket(0,Buffer.concat(bufs)),
            this.buildPacket(0)
        ]);

        const data = await this.withTcp(async socket => {
            return await this.tcpSend(socket, outBuffer, data => {
                if(data.length < 10) return;
                const reader = this.reader(data);
                const length = reader.varint();
                if(data.length < length) return;
                return reader.rest();
            });
        });

        const reader = this.reader(data);

        const packetId = reader.varint();
        this.debugLog("Packet ID: "+packetId);

        const strLen = reader.varint();
        this.debugLog("String Length: "+strLen);

        const str = reader.rest().toString('utf8');
        this.debugLog(str);

        const json = JSON.parse(str);
        delete json.favicon;

        state.raw = json;
        state.maxplayers = json.players.max;
        if(json.players.sample) {
            for(const player of json.players.sample) {
                state.players.push({
                    id: player.id,
                    name: player.name
                });
            }
        }
        while(state.players.length < json.players.online) {
            state.players.push({});
        }
    }

    varIntBuffer(num) {
        return Buffer.from(Varint.encode(num));
    }
    buildPacket(id,data) {
        if(!data) data = Buffer.from([]);
        const idBuffer = this.varIntBuffer(id);
        return Buffer.concat([
            this.varIntBuffer(data.length+idBuffer.length),
            idBuffer,
            data
        ]);
    }
}

module.exports = Minecraft;