The network sniffing functionality for the Amazon Dash Button hack.

dashbutton_sniff.go

func SnifferStart() {
	// Get a list of all interfaces.
	ifaces, err := net.Interfaces()
	if err != nil {
		panic(err)
	}

	var wg sync.WaitGroup
	for _, iface := range ifaces {
		wg.Add(1)
		// Start up a scan on each interface.
		go func(iface net.Interface) {
			defer wg.Done()
			if err := scan(&iface); err != nil {
				log.Printf("interface %v: %v", iface.Name, err)
			}
		}(iface)
	}

	wg.Wait()
}

func scan(iface *net.Interface) error {
	// We just look for IPv4 addresses, so try to find if the interface has one.
	var addr *net.IPNet
	if addrs, err := iface.Addrs(); err != nil {
		return err
	} else {
		for _, a := range addrs {
			if ipnet, ok := a.(*net.IPNet); ok {
				if ip4 := ipnet.IP.To4(); ip4 != nil {
					addr = &net.IPNet{
						IP:   ip4,
						Mask: ipnet.Mask[len(ipnet.Mask)-4:],
					}
					break
				}
			}
		}
	}

	// Sanity-check that the interface has a good address.
	if addr == nil {
		return fmt.Errorf("no good IP network found")
	} else if addr.IP[0] == 127 {
		return fmt.Errorf("skipping localhost")
	} else if addr.Mask[0] != 0xff || addr.Mask[1] != 0xff {
		return fmt.Errorf("mask means network is too large")
	}
	log.Printf("Using network range %v for interface %v", addr, iface.Name)

	// Open up a pcap handle for packet reads/writes.
	handle, err := pcap.OpenLive(iface.Name, 65536, true, pcap.BlockForever)
	if err != nil {
		return err
	}
	defer handle.Close()

	stop := make(chan struct{})
	readARP(handle, iface, stop)
	defer close(stop)

	return err
}

func readARP(handle *pcap.Handle, iface *net.Interface, stop chan struct{}) {
	src := gopacket.NewPacketSource(handle, layers.LayerTypeEthernet)
	in := src.Packets()
	for {
		var packet gopacket.Packet
		select {
		case <-stop:
			return
		case packet = <-in:
			arpLayer := packet.Layer(layers.LayerTypeARP)
			if arpLayer == nil {
				continue
			}

			arp := arpLayer.(*layers.ARP)

			if !net.IP(arp.SourceProtAddress).Equal(net.ParseIP("0.0.0.0")) {
				continue
			}

			found := false

			for mac, fn := range DashMacs {
				if net.HardwareAddr(arp.SourceHwAddress).String() == mac {
					log.Printf("Click sniffed for %v", mac)
					fn()

					found = true
				}
			}

			if !found {
				log.Printf("FOUND UNKNOWN MAC: %v", net.HardwareAddr(arp.SourceHwAddress))
			}
		}
	}
}