gc.js

const { createSocket } = require('dgram'),
  { EventEmitter } = require('events'),
  regex = /^AMXB<-UUID=GlobalCache_([\dA-F]{12})>/,
  MULTICAST_ADDRESS = '239.255.250.250';

class GlobalCacheDiscovery extends EventEmitter {
  /**
   * Discover Global Cache devices.
   * @param {string} identifier - An optional Global Cache identifier to limit multicast results to.
   */
  discover(identifier) {
    const socket = createSocket('udp4'),
      timeout = global.setTimeout(() => this.stop(), 60500),
      devices = {};
    socket
      .on('error', error => {
        this.emit('error', error);
        global.clearTimeout(timeout);
        this.stop();
      })
      .on('close', () => {
        socket.removeAllListeners();
        global.clearTimeout(timeout);
        this.socket = undefined;
        this.emit('end');
      })
      .on('message', (msg, rinfo) => {
        const matches = regex.exec(msg);
        if (!matches) {
          return;
        }
        const [, id] = matches, { address } = rinfo;
        if (devices[id] !== address) {
          devices[id] = address;
          if (!identifier || id === identifier) {
            this.emit('device', id, devices);
          }
        }
        if (identifier && !id.localeCompare(identifier, undefined, { sensitivity: 'accent' })) {
          global.clearTimeout(timeout);
          this.stop();
        }
      });

    socket.bind(9131, undefined, () => (this.socket = socket).addMembership(MULTICAST_ADDRESS));
  }

  stop() {
    const { socket } = this;
    if (socket) {
      socket.dropMembership(MULTICAST_ADDRESS);
      socket.close();
    }
  }
}

// DEMO

const finder = new GlobalCacheDiscovery();
finder.on('device', (addedIdentifier, devices) => {
  // Obviously you'll be interacting with the GC device by IP address.
  // That said, a user may have multiple GC devices in their home, and the IP address may be assigned by DHCP.
  // Find it again, by looking for a specific identifier (which can also be passed as a parameter to the `discover` method).
  console.log(addedIdentifier, devices[addedIdentifier]);
  finder.stop();
});
finder.on('end', () => finder.removeAllListeners());
finder.discover();