SimpleDiscord.js

/**
  Simple(ish) example of discord gateway
  This code will get to ready, and then remain connected with heartbeats
  see https://discordapi.com/topics/gateway for more info
  zlib compression is implemented as it will be required in gateway v7 (so get used to it now)
*/

const WebSocket = require('ws'); // npmjs.org/ws
const zlib = require('zlib-sync'); // npmjs.org/zlib-sync
const erlpack = require('erlpack'); // github.com/discordapp/erlpack
const os = require('os') // from node "standard library"

// https://discordapi.com/topics/gateway#gateway-opcodespayloads
const OPCodes = {
  HEARTBEAT: 1,
  IDENTIFY: 2,
  HELLO: 10,
  HEARTBEAT_ACK: 11,
};

// zlib inflate context for zlib-stream
const inflate = new zlib.Inflate({
  chunkSize: 65535,
  flush: zlib.Z_SYNC_FLUSH,
});

// create websocket (technically you should perform a GET to /api/gateway and use the response)
const ws = new WebSocket('wss://gateway.discord.gg/?v=6&encoding=etf&compress=zlib-stream');

// sequence used for sessions and heartbeats
let sequence = 0;

function send(op, d) {
  ws.send(erlpack.pack({ op, d }));
}

ws.onmessage = ({ data }) => {
  const l = data.length;
  // if data.length >= 4 and data ends with Z_SYNC_FLUSH constant
  const flush = l >= 4 &&
    data[l - 4] === 0x00 &&
    data[l - 3] === 0x00 &&
    data[l - 2] === 0xFF &&
    data[l - 1] === 0xFF;

  inflate.push(data, flush && zlib.Z_SYNC_FLUSH);

  if (!flush) return;

  // parse packet with erlpack after its inflated
  const packet = erlpack.unpack(inflate.result);

  // keep track of sequence for heartbeats
  if (packet.s) sequence = packet.s;

  // handle gateway ops
  switch (packet.op) {
    case OPCodes.HELLO:
      console.log('Got op 10 HELLO');
      // set heartbeat interval
      setInterval(() => send(OPCodes.HEARTBEAT, sequence), packet.d.heartbeat_interval);
      // https://discordapi.com/topics/gateway#gateway-identify
      send(OPCodes.IDENTIFY, {
        // you should put your token here _without_ the "Bot" prefix
        token: '',
        properties: {
          $os: process.platform,
          $browser: 'node.js',
          $device: os.type(),
        },
        compress: false,
      });
  }

  // handle gateway packet types
  if (!packet.t) return;
  switch (packet.t) {
    // we should get this after we send identify
    case 'READY':
      console.log('ready as', packet.d.user);
      break;
  }
};

ws.onopen = () => console.log('websocket opened!');
ws.onclose = ws.onerror = (e) => {
  console.log(e);
};