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package arping
import (
"bytes"
"encoding/binary"
"net"
)
const (
requestOper = 1
responseOper = 2
)
type arpDatagram struct {
htype uint16 // Hardware Type
ptype uint16 // Protocol Type
hlen uint8 // Hardware address Length
plen uint8 // Protocol address length
oper uint16 // Operation 1->request, 2->response
sha []byte // Sender hardware address, length from Hlen
spa []byte // Sender protocol address, length from Plen
tha []byte // Target hardware address, length from Hlen
tpa []byte // Target protocol address, length from Plen
}
func newArpRequest(
srcMac net.HardwareAddr,
srcIP net.IP,
dstMac net.HardwareAddr,
dstIP net.IP) arpDatagram {
return arpDatagram{
htype: uint16(1),
ptype: uint16(0x0800),
hlen: uint8(6),
plen: uint8(4),
oper: uint16(requestOper),
sha: srcMac,
spa: srcIP.To4(),
tha: dstMac,
tpa: dstIP.To4()}
}
func (datagram arpDatagram) Marshal() []byte {
buf := new(bytes.Buffer)
binary.Write(buf, binary.BigEndian, datagram.htype)
binary.Write(buf, binary.BigEndian, datagram.ptype)
binary.Write(buf, binary.BigEndian, datagram.hlen)
binary.Write(buf, binary.BigEndian, datagram.plen)
binary.Write(buf, binary.BigEndian, datagram.oper)
buf.Write(datagram.sha)
buf.Write(datagram.spa)
buf.Write(datagram.tha)
buf.Write(datagram.tpa)
return buf.Bytes()
}
func (datagram arpDatagram) MarshalWithEthernetHeader() []byte {
// ethernet frame header
var ethernetHeader []byte
ethernetHeader = append(ethernetHeader, datagram.tha...)
ethernetHeader = append(ethernetHeader, datagram.sha...)
ethernetHeader = append(ethernetHeader, []byte{0x08, 0x06}...) // arp
return append(ethernetHeader, datagram.Marshal()...)
}
func (datagram arpDatagram) SenderIP() net.IP {
return net.IP(datagram.spa)
}
func (datagram arpDatagram) SenderMac() net.HardwareAddr {
return net.HardwareAddr(datagram.sha)
}
func (datagram arpDatagram) IsResponseOf(request arpDatagram) bool {
return datagram.oper == responseOper && bytes.Compare(request.spa, datagram.tpa) == 0
}
func parseArpDatagram(buffer []byte) arpDatagram {
var datagram arpDatagram
b := bytes.NewBuffer(buffer)
binary.Read(b, binary.BigEndian, &datagram.htype)
binary.Read(b, binary.BigEndian, &datagram.ptype)
binary.Read(b, binary.BigEndian, &datagram.hlen)
binary.Read(b, binary.BigEndian, &datagram.plen)
binary.Read(b, binary.BigEndian, &datagram.oper)
haLen := int(datagram.hlen)
paLen := int(datagram.plen)
datagram.sha = b.Next(haLen)
datagram.spa = b.Next(paLen)
datagram.tha = b.Next(haLen)
datagram.tpa = b.Next(paLen)
return datagram
}
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