Catching ARP packet in Go

arp-packet-scanner.go

package main

import (
  "fmt"
  "github.com/google/gopacket"
  "github.com/google/gopacket/layers"
  "github.com/google/gopacket/pcap"
  "log"
  "net"
)

func printDevices() {
  // find all devices
  devices, err := pcap.FindAllDevs()
  if err != nil {
    log.Fatal(err)
  }

  // print device information
  for _, device := range devices {
    fmt.Println("Interface: ", device.Name)
    for _, address := range device.Addresses {
      var ipType string
      if ipType = "IPv4"; len(address.IP) == 4 {
        ipType = "IPv6"
      }
      fmt.Println("- IP address: ", address.IP, " ", ipType)
      fmt.Println("- Subnet mask: ", address.Netmask)
    }
  }
}

func listenToDevice(device string) error {
  fmt.Println("Listening on device ", device)
  // Open a pcap handler to read packets
  handle, err := pcap.OpenLive(device, 65536, true,
                               pcap.BlockForever)
  if err != nil {
    return err
  }
  // Create a new PacketDataSource
  src := gopacket.NewPacketSource(handle, layers.LayerTypeEthernet)
  // Packets returns a channel of packets
  in := src.Packets()
  for {
    var packet gopacket.Packet
    select {
      //case <-stop:
      //  break
      case packet = <-in:
        arpLayer := packet.Layer(layers.LayerTypeARP)
        if arpLayer == nil {
          continue
        }
        arp := arpLayer.(*layers.ARP)
        log.Println("Source hardware address ",
                    net.HardwareAddr(arp.SourceHwAddress).String(),
                    "\nDestination hardware address ",
                    net.HardwareAddr(arp.DstHwAddress).String(),
                    "\nOperation ",
                    arp.Operation)
    }
  }
  defer handle.Close()
  return nil
}

func main() {
  if err := listenToDevice("wlan0"); err != nil {
    log.Fatal(err)
  }
}