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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
}
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()
bytes := make([]byte, len(headerBytes)+len(m.Question))
copy(bytes, headerBytes)
copy(bytes[len(headerBytes):], m.Question)
return bytes
}
func MakeMessage(header DNSHeader) DNSMessage {
return DNSMessage{Header: header, Question: []byte{}}
}
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