dns.go

package packemon

import (
	"bytes"
	"encoding/binary"
	"strings"
)

const PORT_DNS = 0x0035 // 53

// https://datatracker.ietf.org/doc/html/rfc1035#section-4.1.1 の「QR」
// 関連: https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml#dns-parameters-5 の「Opcode」の逆引きは廃止（IQuery (Inverse Query, OBSOLETE)）
const (
	DNS_QR_REQUEST  = 0 << 15 // 0
	DNS_QR_RESPONSE = 1 << 15 // 1000 0000 0000 0000
)

func IsDNSRequest(flags uint16) bool {
	return !IsDNSResponse(flags)
}

func IsDNSResponse(flags uint16) bool {
	return flags&DNS_QR_RESPONSE == DNS_QR_RESPONSE
}

const (
	DNS_QUERY_TYPE_A    = 0x0001
	DNS_QUERY_TYPE_AAAA = 0x001c
)

const (
	DNS_QUERY_CLASS_IN = 0x0001
)

// https://atmarkit.itmedia.co.jp/ait/articles/1601/29/news014.html
// 上記とパケットキャプチャ見てイメージがつく、domain
type DNS struct {
	TransactionID uint16
	Flags         uint16 // TODO: ここにビット単位で意味があるから、structにして管理したい
	Questions     uint16
	AnswerRRs     uint16
	AuthorityRRs  uint16
	AdditionalRRs uint16
	Queries       *Queries
	Answers       []*Answer
}

// TODO: 個別にQueryで定義してスライスで持つようにする
type Queries struct {
	Domain     []uint8
	Typ        uint16
	Class      uint16
	Ttl        uint32
	DataLength uint16
}

type Answer struct {
	Name       uint16
	Typ        uint16
	Class      uint16
	Ttl        uint32
	DataLength uint16
	Address    uint32
}

func ParsedDNSRequest(payload []byte) *DNS {
	flags := binary.BigEndian.Uint16(payload[2:4])
	qCnt := binary.BigEndian.Uint16(payload[4:6])
	anCnt := binary.BigEndian.Uint16(payload[6:8])
	auCnt := binary.BigEndian.Uint16(payload[8:10])
	adCnt := binary.BigEndian.Uint16(payload[10:12])
	// 一旦Questionsは1固定で進める
	// また、domainは、0x00 までとなる。そういう判定処理
	offset := bytes.IndexByte(payload[12:], 0x00) + 12 + 1
	q := &Queries{
		Domain: payload[12:offset],
		Typ:    binary.BigEndian.Uint16(payload[offset : offset+2]),
		Class:  binary.BigEndian.Uint16(payload[offset+2 : offset+4]),
	}

	return &DNS{
		TransactionID: binary.BigEndian.Uint16(payload[0:2]),
		Flags:         flags,
		Questions:     qCnt,
		AnswerRRs:     anCnt,
		AuthorityRRs:  auCnt,
		AdditionalRRs: adCnt,
		Queries:       q,
	}
}

func ParsedDNSResponse(payload []byte) *DNS {
	flags := binary.BigEndian.Uint16(payload[2:4])
	qCnt := binary.BigEndian.Uint16(payload[4:6])
	anCnt := binary.BigEndian.Uint16(payload[6:8])
	auCnt := binary.BigEndian.Uint16(payload[8:10])
	adCnt := binary.BigEndian.Uint16(payload[10:12])

	// 一旦Questionsは1固定として進める
	// また、domainは、0x00 までとなる。そういう判定処理
	offset := bytes.IndexByte(payload[12:], 0x00) + 12 + 1
	q := &Queries{
		Domain: payload[12:offset],
		Typ:    binary.BigEndian.Uint16(payload[offset : offset+2]),
		Class:  binary.BigEndian.Uint16(payload[offset+2 : offset+4]),
	}

	answers := []*Answer{}
	for i := 0; i < int(anCnt); i++ {
		offsetOfAns := offset + 4 + (16 * i)
		a := &Answer{
			Name:       binary.BigEndian.Uint16(payload[offsetOfAns : offsetOfAns+2]),
			Typ:        binary.BigEndian.Uint16(payload[offsetOfAns+2 : offsetOfAns+4]),
			Class:      binary.BigEndian.Uint16(payload[offsetOfAns+4 : offsetOfAns+6]),
			Ttl:        binary.BigEndian.Uint32(payload[offsetOfAns+6 : offsetOfAns+10]),
			DataLength: binary.BigEndian.Uint16(payload[offsetOfAns+10 : offsetOfAns+12]),
			Address:    binary.BigEndian.Uint32(payload[offsetOfAns+12 : offsetOfAns+16]),
		}
		answers = append(answers, a)
	}

	return &DNS{
		TransactionID: binary.BigEndian.Uint16(payload[0:2]),
		Flags:         flags,
		Questions:     qCnt,
		AnswerRRs:     anCnt,
		AuthorityRRs:  auCnt,
		AdditionalRRs: adCnt,
		Queries:       q, // TODO: スライスで持つ
		Answers:       answers,
	}
}

func (d *DNS) Domain(domain string) {
	splited := strings.Split(domain, ".")
	buf := make([]uint8, len(domain)+2)

	cnt := 0
	for _, s := range splited {
		buf[cnt] = uint8(len(s))
		cnt++
		for _, c := range s {
			buf[cnt] = uint8(rune(c)) // ドメインに絵文字とか使えた気が。そうするとバグるはず
			cnt++
		}
	}

	buf[len(domain)+1] = 0x00
	d.Queries.Domain = buf
}

func (d *DNS) Bytes() []byte {
	buf := &bytes.Buffer{}
	WriteUint16(buf, d.TransactionID)
	WriteUint16(buf, d.Flags)
	WriteUint16(buf, d.Questions)
	WriteUint16(buf, d.AnswerRRs)
	WriteUint16(buf, d.AuthorityRRs)
	WriteUint16(buf, d.AdditionalRRs)
	buf.Write(d.Queries.Domain)
	WriteUint16(buf, d.Queries.Typ)
	WriteUint16(buf, d.Queries.Class)
	for i := range d.Answers {
		WriteUint16(buf, d.Answers[i].Name)
		WriteUint16(buf, d.Answers[i].Typ)
		WriteUint16(buf, d.Answers[i].Class)
		WriteUint32(buf, d.Answers[i].Ttl)
		WriteUint16(buf, d.Answers[i].DataLength)
		WriteUint32(buf, d.Answers[i].Address)
	}
	return buf.Bytes()
}