179 lines
4.2 KiB
Go
179 lines
4.2 KiB
Go
package dnsProxy
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import (
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"encoding/binary"
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"errors"
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"fmt"
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)
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var (
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ErrInvalidDNSMessageHeader = errors.New("invalid DNS message header")
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ErrInvalidDNSResourceRecordHeader = errors.New("invalid DNS resource record header")
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ErrInvalidDNSResourceRecordData = errors.New("invalid DNS resource record data")
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ErrInvalidDNSAddressResourceData = errors.New("invalid DNS address resource data")
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)
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func parseName(response []byte, pos int) (Name, int) {
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var nameParts []string
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var jumped bool
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var outPos int
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responseLen := len(response)
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for {
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length := int(response[pos])
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pos++
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if length == 0 {
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break
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}
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if length&0xC0 == 0xC0 {
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if !jumped {
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outPos = pos + 1
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}
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pos = int(binary.BigEndian.Uint16(response[pos-1:pos+1]) & 0x3FFF)
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jumped = true
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continue
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}
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if pos+length > responseLen {
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break
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}
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nameParts = append(nameParts, string(response[pos:pos+length]))
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pos += length
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}
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if !jumped {
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outPos = pos
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}
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return Name{Parts: nameParts}, outPos
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}
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func parseResourceRecord(response []byte, pos int) (ResourceRecord, int, error) {
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responseLen := len(response)
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var rhname Name
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rhname, pos = parseName(response, pos)
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if responseLen < pos+10 {
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return nil, pos, ErrInvalidDNSResourceRecordHeader
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}
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rh := ResourceRecordHeader{
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Name: rhname,
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Type: binary.BigEndian.Uint16(response[pos+0 : pos+2]),
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Class: binary.BigEndian.Uint16(response[pos+2 : pos+4]),
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TTL: binary.BigEndian.Uint32(response[pos+4 : pos+8]),
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}
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rdlength := int(binary.BigEndian.Uint16(response[pos+8 : pos+10]))
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pos += 10
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if pos+rdlength > responseLen {
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return nil, pos, ErrInvalidDNSResourceRecordData
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}
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switch rh.Type {
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case 1:
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if rdlength == 4 {
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return Address{
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ResourceRecordHeader: rh,
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Address: response[pos+0 : pos+4],
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}, pos + 4, nil
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} else {
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return nil, pos, ErrInvalidDNSAddressResourceData
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}
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case 2:
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var ns Name
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ns, pos = parseName(response, pos)
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return NameServer{
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ResourceRecordHeader: rh,
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NSDName: ns,
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}, pos, nil
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case 5:
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var cname Name
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cname, pos = parseName(response, pos)
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return CName{
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ResourceRecordHeader: rh,
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CName: cname,
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}, pos, nil
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}
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return Unknown{
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ResourceRecordHeader: rh,
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Data: response[pos+0 : pos+rdlength],
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}, pos + rdlength, nil
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}
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func ParseResponse(response []byte) (*Message, error) {
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var err error
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responseLen := len(response)
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if responseLen < 12 {
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return nil, ErrInvalidDNSMessageHeader
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}
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msg := new(Message)
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msg.ID = binary.BigEndian.Uint16(response[0:2])
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flagsRAW := binary.BigEndian.Uint16(response[2:4])
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msg.Flags = Flags{
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QR: uint8(flagsRAW >> 15 & 0x1),
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Opcode: uint8(flagsRAW >> 11 & 0xF),
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AA: uint8(flagsRAW >> 10 & 0x1),
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TC: uint8(flagsRAW >> 9 & 0x1),
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RD: uint8(flagsRAW >> 8 & 0x1),
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RA: uint8(flagsRAW >> 7 & 0x1),
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Z1: uint8(flagsRAW >> 6 & 0x1),
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Z2: uint8(flagsRAW >> 5 & 0x1),
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Z3: uint8(flagsRAW >> 4 & 0x1),
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RCode: uint8(flagsRAW >> 0 & 0xF),
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}
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qdCount := int(binary.BigEndian.Uint16(response[4:6]))
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anCount := int(binary.BigEndian.Uint16(response[6:8]))
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nsCount := int(binary.BigEndian.Uint16(response[8:10]))
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arCount := int(binary.BigEndian.Uint16(response[10:12]))
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pos := 12
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msg.QD = make([]Question, qdCount)
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for i := 0; i < qdCount; i++ {
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var name Name
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name, pos = parseName(response, pos)
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msg.QD[i] = Question{
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QName: name,
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QType: binary.BigEndian.Uint16(response[pos+0 : pos+2]),
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QClass: binary.BigEndian.Uint16(response[pos+2 : pos+4]),
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}
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pos += 4
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}
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msg.AN = make([]ResourceRecord, anCount)
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for i := 0; i < anCount; i++ {
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msg.AN[i], pos, err = parseResourceRecord(response, pos)
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if err != nil {
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return nil, fmt.Errorf("error while parsing AN record: %w", err)
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}
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}
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msg.NS = make([]ResourceRecord, nsCount)
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for i := 0; i < nsCount; i++ {
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msg.NS[i], pos, err = parseResourceRecord(response, pos)
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if err != nil {
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return nil, fmt.Errorf("error while parsing NS record: %w", err)
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}
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}
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msg.AR = make([]ResourceRecord, arCount)
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for i := 0; i < arCount; i++ {
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msg.AR[i], pos, err = parseResourceRecord(response, pos)
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if err != nil {
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return nil, fmt.Errorf("error while parsing AR record: %w", err)
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}
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}
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return msg, nil
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}
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