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|
package main
import (
"encoding/binary"
"strings"
)
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
}
type DNSQuestion struct {
Name []byte
Type uint16
Class uint16
}
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 DNSQuestion) {
m.Question = q.Bytes()
}
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 (m *DNSMessage) AddAnswer(a DNSAnswer) {
m.Answer = a
m.Header.ANCOUNT = 1
}
func (q *DNSQuestion) Bytes() []byte {
bytes := []byte{}
bytes = append(bytes, q.Name...)
bytes = binary.BigEndian.AppendUint16(bytes, q.Type)
bytes = binary.BigEndian.AppendUint16(bytes, q.Class)
return bytes
}
func MakeMessage(header DNSHeader) DNSMessage {
return DNSMessage{Header: header, Question: []byte{}, Answer: DNSAnswer{}}
}
func MakeAnswer(name []byte, rdata []byte) DNSAnswer {
return DNSAnswer{Name: name, Type: 1, Class: 1, TTL: 60, RDLength: uint16(len(rdata)), RData: rdata}
}
func ParseHeader(buf []byte) DNSHeader {
return DNSHeader{
ID: binary.BigEndian.Uint16(buf[0:2]),
QR: uint8(buf[2] >> 7),
OPCODE: uint8(buf[2] >> 3 & 0x0f),
AA: uint8(buf[2] >> 2 & 0x01),
TC: uint8(buf[2] >> 1 & 0x01),
RD: uint8(buf[2] & 0x01),
RA: uint8(buf[3] >> 7),
Z: uint8(buf[3] >> 4 & 0x07),
RCODE: uint8(buf[3] & 0x0f),
QDCOUNT: binary.BigEndian.Uint16(buf[4:6]),
ANCOUNT: binary.BigEndian.Uint16(buf[6:8]),
NSCOUNT: binary.BigEndian.Uint16(buf[8:10]),
ARCOUNT: binary.BigEndian.Uint16(buf[10:12]),
}
}
func MakeQuestion(name []byte) DNSQuestion {
return DNSQuestion{Name: name, Type: 1, Class: 1}
}
func ParseQuestion(buf []byte) DNSQuestion {
return MakeQuestion(ParseDomain(buf))
}
func ParseDomain(data []byte) []byte {
domainByte := data[12:]
domain := decodeDNSPacket(domainByte)
segments := strings.Split(domain, ".")
var encodedDomain []byte
for _, segment := range segments {
encodedDomain = append(encodedDomain, byte(len(segment)))
encodedDomain = append(encodedDomain, []byte(segment)...)
}
encodedDomain = append(encodedDomain, 0x00)
return encodedDomain
}
func decodeDNSPacket(packet []byte) string {
var domain string
i := 0
for i < len(packet) && packet[i] != 0 {
labelLength := int(packet[i])
i++
if i+labelLength > len(packet) {
break
}
domain += string(packet[i : i+labelLength])
i += labelLength
if i < len(packet) && packet[i] != 0 {
domain += "."
}
}
return domain
}
|
