func NewPeripheral(u UUID) Peripheral { return &peripheral{id: xpc.UUID(u.b)} }
// process device events and asynchronous errors
// (implements XpcEventHandler)
func (d *device) HandleXpcEvent(event xpc.Dict, err error) {
	if err != nil {
		log.Println("error:", err)
		return
	}

	id := event.MustGetInt("kCBMsgId")
	args := event.MustGetDict("kCBMsgArgs")
	//log.Printf(">> %d, %v", id, args)

	switch id {
	case // device event
		6,  // StateChanged
		16, // AdvertisingStarted
		17, // AdvertisingStopped
		18: // ServiceAdded
		d.rspc <- message{id: id, args: args}

	case
		19, // ReadRequest
		20, // WriteRequest
		21, // Subscribe
		22, // Unubscribe
		23: // Confirmation
		d.respondToRequest(id, args)

	case peripheralDiscovered:
		xa := args.MustGetDict("kCBMsgArgAdvertisementData")
		if len(xa) == 0 {
			return
		}
		u := UUID{args.MustGetUUID("kCBMsgArgDeviceUUID")}
		a := &Advertisement{
			LocalName:        xa.GetString("kCBAdvDataLocalName", args.GetString("kCBMsgArgName", "")),
			TxPowerLevel:     xa.GetInt("kCBAdvDataTxPowerLevel", 0),
			ManufacturerData: xa.GetBytes("kCBAdvDataManufacturerData", nil),
		}

		rssi := args.MustGetInt("kCBMsgArgRssi")

		if xu, ok := xa["kCBAdvDataServiceUUIDs"]; ok {
			for _, xs := range xu.(xpc.Array) {
				s := UUID{reverse(xs.([]byte))}
				a.Services = append(a.Services, s)
			}
		}
		if xsds, ok := xa["kCBAdvDataServiceData"]; ok {
			xsd := xsds.(xpc.Array)
			for i := 0; i < len(xsd); i += 2 {
				sd := ServiceData{
					UUID: UUID{xsd[i].([]byte)},
					Data: xsd[i+1].([]byte),
				}
				a.ServiceData = append(a.ServiceData, sd)
			}
		}
		if d.peripheralDiscovered != nil {
			go d.peripheralDiscovered(&peripheral{id: xpc.UUID(u.b), d: d}, a, rssi)
		}

	case peripheralConnected:
		u := UUID{args.MustGetUUID("kCBMsgArgDeviceUUID")}
		p := &peripheral{
			id:    xpc.UUID(u.b),
			d:     d,
			reqc:  make(chan message),
			rspc:  make(chan message),
			quitc: make(chan struct{}),
			sub:   newSubscriber(),
		}
		d.plistmu.Lock()
		d.plist[u.String()] = p
		d.plistmu.Unlock()
		go p.loop()

		if d.peripheralConnected != nil {
			go d.peripheralConnected(p, nil)
		}

	case peripheralDisconnected:
		u := UUID{args.MustGetUUID("kCBMsgArgDeviceUUID")}
		d.plistmu.Lock()
		p := d.plist[u.String()]
		delete(d.plist, u.String())
		d.plistmu.Unlock()
		if d.peripheralDisconnected != nil {
			d.peripheralDisconnected(p, nil) // TODO: Get Result as error?
		}
		close(p.quitc)

	case // Peripheral events
		rssiRead,
		serviceDiscovered,
		includedServicesDiscovered,
		characteristicsDiscovered,
		characteristicRead,
		characteristicWritten,
		notificationValueSet,
		descriptorsDiscovered,
		descriptorRead,
		descriptorWritten:

		u := UUID{args.MustGetUUID("kCBMsgArgDeviceUUID")}
		d.plistmu.Lock()
		p := d.plist[u.String()]
		d.plistmu.Unlock()
		p.rspc <- message{id: id, args: args}

	default:
		log.Printf("Unhandled event: %#v", event)
	}
}