73 lines
2.1 KiB
Go
73 lines
2.1 KiB
Go
package main
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import (
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"bytes"
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"encoding/binary"
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_ "fmt"
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"net"
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"strings"
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"time"
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"github.com/google/gopacket"
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"github.com/google/gopacket/layers"
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)
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func serveDNS(u *net.UDPConn, clientaddr net.Addr, request *layers.DNS) {
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replyMess := request
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var dnsAnswer layers.DNSResourceRecord
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if request == nil || request.Questions == nil || len(request.Questions) == 0 {
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return
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} else {
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dnsAnswer.Name = []byte(request.Questions[0].Name)
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}
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//fmt.Println(clientaddr.String())
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replyMess.QR = true
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replyMess.ANCount = 1
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replyMess.OpCode = layers.DNSOpCodeQuery
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replyMess.AA = true
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if request.Questions[0].Type == layers.DNSTypeA {
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dnsAnswer.Type = layers.DNSTypeA
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dnsAnswer.Class = layers.DNSClassIN
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dnsAnswer.IP = net.ParseIP(strings.Split(clientaddr.String(), ":")[0])
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dnsAnswer.TTL = 1000
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} else if request.Questions[0].Type == layers.DNSTypeAAAA {
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dnsAnswer.Type = layers.DNSTypeAAAA
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dnsAnswer.Class = layers.DNSClassIN
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t := time.Now().UnixMicro()
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rdns_ipv4 := net.ParseIP(strings.Split(clientaddr.String(), ":")[0]).To4()
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bytebuf := bytes.NewBuffer([]byte{})
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binary.Write(bytebuf, binary.BigEndian, t)
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binary.Write(bytebuf, binary.BigEndian, rdns_ipv4)
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binary.Write(bytebuf, binary.BigEndian, []byte{0, 0, 0, 0})
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dnsAnswer.IP = net.IP(bytebuf.Bytes())
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dnsAnswer.TTL = 1000
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}
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replyMess.Answers = append(replyMess.Answers, dnsAnswer)
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replyMess.ResponseCode = layers.DNSResponseCodeNoErr
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buf := gopacket.NewSerializeBuffer()
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opts := gopacket.SerializeOptions{}
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err := replyMess.SerializeTo(buf, opts)
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if err != nil {
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panic(err)
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}
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u.WriteTo(buf.Bytes(), clientaddr)
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}
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func main() {
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addr := net.UDPAddr{
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Port: 53,
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IP: net.ParseIP("localhost.localdomain"), //localhost
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}
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u, _ := net.ListenUDP("udp", &addr)
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for {
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tmp := make([]byte, 1024)
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_, addr, _ := u.ReadFrom(tmp)
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clientaddr := addr
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packet := gopacket.NewPacket(tmp, layers.LayerTypeDNS, gopacket.Default)
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dnsPacket := packet.Layer(layers.LayerTypeDNS)
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tcp, _ := dnsPacket.(*layers.DNS)
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serveDNS(u, clientaddr, tcp)
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}
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}
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