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package main
import "encoding/binary"
type DNSHeader struct {
ID uint16
QR uint8
OPCODE uint8
AA uint8
TC uint8
RD uint8
RA uint8
Z uint8
RCODE uint8
QDCOUNT uint16
ANCOUNT uint16
NSCOUNT uint16
ARCOUNT uint16
}
type DNSMessage struct {
Header DNSHeader
Question []byte
Answer DNSAnswer
}
type DNSAnswer struct {
Name []byte
Type uint16
Class uint16
TTL uint32
RDLength uint16
RData []byte
}
func (m *DNSHeader) Bytes() []byte {
bytes := make([]byte, 12)
binary.BigEndian.PutUint16(bytes[0:], m.ID)
binary.BigEndian.PutUint16(bytes[2:4], m.combineFlags())
binary.BigEndian.PutUint16(bytes[4:6], m.QDCOUNT)
binary.BigEndian.PutUint16(bytes[6:8], m.ANCOUNT)
binary.BigEndian.PutUint16(bytes[8:10], m.NSCOUNT)
binary.BigEndian.PutUint16(bytes[10:12], m.ARCOUNT)
return bytes
}
func (m *DNSHeader) combineFlags() uint16 {
return uint16(m.QR)<<15 | uint16(m.OPCODE)<<11 | uint16(m.AA)<<10 |
uint16(m.TC)<<9 | uint16(m.RD)<<8 | uint16(m.RA)<<7 | uint16(m.Z)<<4 |
uint16(m.RCODE)
}
func (m *DNSMessage) AddQuestion(q []byte) {
m.Question = q
m.Question = binary.BigEndian.AppendUint16(m.Question, 1)
m.Question = binary.BigEndian.AppendUint16(m.Question, 1)
}
func (m *DNSMessage) Bytes() []byte {
headerBytes := m.Header.Bytes()
answerBytes := m.Answer.Bytes()
bytes := []byte{}
bytes = append(bytes, headerBytes...)
bytes = append(bytes, m.Question...)
bytes = append(bytes, answerBytes...)
return bytes
}
func (a *DNSAnswer) Bytes() []byte {
bytes := []byte{}
bytes = append(bytes, a.Name...)
bytes = binary.BigEndian.AppendUint16(bytes, a.Type)
bytes = binary.BigEndian.AppendUint16(bytes, a.Class)
bytes = binary.BigEndian.AppendUint32(bytes, a.TTL)
bytes = binary.BigEndian.AppendUint16(bytes, a.RDLength)
bytes = binary.BigEndian.AppendUint32(bytes, binary.BigEndian.Uint32(a.RData))
return bytes
}
func MakeMessage(header DNSHeader) DNSMessage {
return DNSMessage{Header: header, Question: []byte{}, Answer: DNSAnswer{}}
}
func (m *DNSMessage) AddAnswer(a DNSAnswer) {
m.Answer = a
m.Header.ANCOUNT = 1
}
func MakeAnswer(name []byte, rdata []byte) DNSAnswer {
return DNSAnswer{Name: name, Type: 1, Class: 1, TTL: 60, RDLength: uint16(len(rdata)), RData: rdata}
}
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