Hand-crafted CNAME query

dns.go

package main

import (
	"net"

	"github.com/google/gopacket"
	"github.com/google/gopacket/layers"
	"github.com/google/gopacket/pcap"
)

func main() {
    // Select the interace to use
	handle, err := pcap.OpenLive("lo", 1500, false, pcap.BlockForever)
	if err != nil {
		panic(err)
	}

	// Create ethernet layer
	eth := layers.Ethernet{
		SrcMAC:       net.HardwareAddr{0x00, 0x00, 0x00, 0x00, 0x00, 0x00},
		DstMAC:       net.HardwareAddr{0x00, 0x00, 0x00, 0x00, 0x00, 0x00},
		EthernetType: layers.EthernetTypeIPv4,
	}

	// Create ip layer
	ip := layers.IPv4{
		Version:  4,
		TTL:      64,
		SrcIP:    net.IP{1, 3, 3, 7},
		DstIP:    net.IP{127, 0, 0, 1},
		Protocol: layers.IPProtocolUDP,
	}

	// Create udp layer
	udp := layers.UDP{
		SrcPort: 62003,
		DstPort: 53,
	}
	udp.SetNetworkLayerForChecksum(&ip)

    // Create the DNS question
	qst := layers.DNSQuestion{
		Name:  []byte{'w', 'w', 'w', '.', 'g', 'o', 'o', 'g', 'l', 'e', '.', 'c', 'o', 'm', '.'},
		Type:  layers.DNSTypeCNAME,
		Class: layers.DNSClassIN,
	}

    // Create the DNS layer
	dns := layers.DNS{
		BaseLayer:    layers.BaseLayer{},
		ID:           0,
		QR:           true,
		OpCode:       0,
		AA:           false,
		TC:           false,
		RD:           true,
		RA:           true,
		Z:            0,
		ResponseCode: 0,
		QDCount:      1,
		ANCount:      0,
		NSCount:      0,
		ARCount:      0,
		Questions:    []layers.DNSQuestion{qst},
	}

    // Create the data buffer and its options
	buffer := gopacket.NewSerializeBuffer()
	options := gopacket.SerializeOptions{
		ComputeChecksums: true,
		FixLengths:       true,
	}

    // Assemble the layers to create a packet
	if err = gopacket.SerializeLayers(buffer, options,
		&eth,
		&ip,
		&udp,
		&dns,
	); err != nil {
		panic(err)
	}
	outgoingPacket := buffer.Bytes()

    // Send the packet
	if err = handle.WritePacketData(outgoingPacket); err != nil {
		panic(err)
	}
}