func (d *Discoverer) recvAnnouncements(b beacon.Interface) {
	for {
		buf, addr := b.Recv()

		var pkt Announce
		err := pkt.UnmarshalXDR(buf)
		if err != nil && err != io.EOF {
			if debug {
				l.Debugf("discover: Failed to unmarshal local announcement from %s:\n%s", addr, hex.Dump(buf))
			}
			continue
		}

		if debug {
			l.Debugf("discover: Received local announcement from %s for %s", addr, protocol.DeviceIDFromBytes(pkt.This.ID))
		}

		var newDevice bool
		if bytes.Compare(pkt.This.ID, d.myID[:]) != 0 {
			newDevice = d.registerDevice(addr, pkt.This)
		}

		if newDevice {
			select {
			case d.forcedBcastTick <- time.Now():
			}
		}
	}
}

func (c *localClient) recvAnnouncements(b beacon.Interface) {
	for {
		buf, addr := b.Recv()

		var pkt Announce
		err := pkt.UnmarshalXDR(buf)
		if err != nil && err != io.EOF {
			l.Debugf("discover: Failed to unmarshal local announcement from %s:\n%s", addr, hex.Dump(buf))
			continue
		}

		if pkt.Magic != AnnouncementMagic {
			l.Debugf("discover: Incorrect magic from %s: %s != %s", addr, pkt.Magic, AnnouncementMagic)
			continue
		}

		l.Debugf("discover: Received local announcement from %s for %s", addr, protocol.DeviceIDFromBytes(pkt.This.ID))

		var newDevice bool
		if !bytes.Equal(pkt.This.ID, c.myID[:]) {
			newDevice = c.registerDevice(addr, pkt.This)
		}

		if newDevice {
			// Force a transmit to announce ourselves, if we are ready to do
			// so right away.
			select {
			case c.forcedBcastTick <- time.Now():
			default:
			}
		}
	}
}

// receives and prints discovery announcements
func recv(bc beacon.Interface) {
	seen := make(map[string]bool)
	for {
		data, src := bc.Recv()
		var ann discover.Announce
		ann.UnmarshalXDR(data)

		if bytes.Equal(ann.This.ID, myID) {
			// This is one of our own fake packets, don't print it.
			continue
		}

		// Print announcement details for the first packet from a given
		// device ID and source address, or if -all was given.
		key := string(ann.This.ID) + src.String()
		if all || !seen[key] {
			log.Printf("Announcement from %v\n", src)
			log.Printf(" %v at %s\n", protocol.DeviceIDFromBytes(ann.This.ID), strings.Join(addrStrs(ann.This), ", "))

			for _, dev := range ann.Extra {
				log.Printf(" %v at %s\n", protocol.DeviceIDFromBytes(dev.ID), strings.Join(addrStrs(dev), ", "))
			}
			seen[key] = true
		}
	}
}

func runbeacon(bc beacon.Interface, fake bool) {
	go bc.Serve()
	go recv(bc)
	if fake {
		go send(bc)
	}
}

// receives and prints discovery announcements
func recv(bc beacon.Interface) {
	seen := make(map[string]bool)
	for {
		data, src := bc.Recv()
		if m := binary.BigEndian.Uint32(data); m != discover.Magic {
			log.Printf("Incorrect magic %x in announcement from %v", m, src)
			continue
		}

		var ann discover.Announce
		ann.Unmarshal(data[4:])

		if ann.ID == myID {
			// This is one of our own fake packets, don't print it.
			continue
		}

		// Print announcement details for the first packet from a given
		// device ID and source address, or if -all was given.
		key := ann.ID.String() + src.String()
		if all || !seen[key] {
			log.Printf("Announcement from %v\n", src)
			log.Printf(" %v at %s\n", ann.ID, strings.Join(ann.Addresses, ", "))
			seen[key] = true
		}
	}
}

// sends fake discovery announcements once every second
func send(bc beacon.Interface) {
	ann := discover.Announce{
		ID:        myID,
		Addresses: []string{"tcp://fake.example.com:12345"},
	}
	bs, _ := ann.Marshal()

	for {
		bc.Send(bs)
		time.Sleep(time.Second)
	}
}

func (c *localClient) recvAnnouncements(b beacon.Interface) {
	warnedAbout := make(map[string]bool)
	for {
		buf, addr := b.Recv()
		if len(buf) < 4 {
			l.Debugf("discover: short packet from %s")
			continue
		}

		magic := binary.BigEndian.Uint32(buf)
		switch magic {
		case Magic:
			// All good

		case v13Magic:
			// Old version
			if !warnedAbout[addr.String()] {
				l.Warnf("Incompatible (v0.13) local discovery packet from %v - upgrade that device to connect", addr)
				warnedAbout[addr.String()] = true
			}
			continue

		default:
			l.Debugf("discover: Incorrect magic %x from %s", magic, addr)
			continue
		}

		var pkt Announce
		err := pkt.Unmarshal(buf[4:])
		if err != nil && err != io.EOF {
			l.Debugf("discover: Failed to unmarshal local announcement from %s:\n%s", addr, hex.Dump(buf))
			continue
		}

		l.Debugf("discover: Received local announcement from %s for %s", addr, pkt.ID)

		var newDevice bool
		if pkt.ID != c.myID {
			newDevice = c.registerDevice(addr, pkt)
		}

		if newDevice {
			// Force a transmit to announce ourselves, if we are ready to do
			// so right away.
			select {
			case c.forcedBcastTick <- time.Now():
			default:
			}
		}
	}
}

// sends fake discovery announcements once every second
func send(bc beacon.Interface) {
	ann := discover.Announce{
		Magic: discover.AnnouncementMagic,
		This: discover.Device{
			ID: myID,
			Addresses: []discover.Address{
				{URL: "tcp://fake.example.com:12345"},
			},
		},
	}
	bs, _ := ann.MarshalXDR()

	for {
		bc.Send(bs)
		time.Sleep(time.Second)
	}
}