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refactor dns record parser

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This commit is contained in:
Vladimir Avtsenov 2024-08-25 00:50:34 +03:00
parent 11ddf5aedb
commit 0f716a3c49
1 changed files with 55 additions and 38 deletions
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87
dns-proxy/parser.go
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@ -4,22 +4,23 @@ import (
"encoding/binary"
"errors"
"fmt"
"io"
)
var (
ErrInvalidDNSMessageHeader = errors.New("invalid DNS message header")
ErrInvalidDNSResourceRecordHeader = errors.New("invalid DNS resource record header")
ErrInvalidDNSResourceRecordData = errors.New("invalid DNS resource record data")
ErrInvalidDNSAddressResourceData = errors.New("invalid DNS address resource data")
)
func parseName(response []byte, pos int) (Name, int) {
func parseName(response []byte, pos int) (*Name, int, error) {
var nameParts []string
var jumped bool
var outPos int
responseLen := len(response)
for {
if responseLen < pos+1 {
return nil, pos, io.EOF
}
length := int(response[pos])
pos++
if length == 0 {
@ -27,6 +28,9 @@ func parseName(response []byte, pos int) (Name, int) {
}
if length&0xC0 == 0xC0 {
if responseLen < pos+1 {
return nil, pos, io.EOF
}
if !jumped {
outPos = pos + 1
}
@ -35,8 +39,8 @@ func parseName(response []byte, pos int) (Name, int) {
continue
}
if pos+length > responseLen {
break
if responseLen < pos+length {
return nil, pos, io.EOF
}
nameParts = append(nameParts, string(response[pos:pos+length]))
@ -46,75 +50,82 @@ func parseName(response []byte, pos int) (Name, int) {
if !jumped {
outPos = pos
}
return Name{Parts: nameParts}, outPos
return &Name{Parts: nameParts}, outPos, nil
}
func parseResourceRecord(response []byte, pos int) (ResourceRecord, int, error) {
responseLen := len(response)
var rhname Name
rhname, pos = parseName(response, pos)
rhName, pos, err := parseName(response, pos)
if err != nil {
return nil, pos, fmt.Errorf("error while parsing DNS name: %w", err)
}
if responseLen < pos+10 {
return nil, pos, ErrInvalidDNSResourceRecordHeader
return nil, pos, io.EOF
}
rh := ResourceRecordHeader{
Name: rhname,
Name: *rhName,
Type: binary.BigEndian.Uint16(response[pos+0 : pos+2]),
Class: binary.BigEndian.Uint16(response[pos+2 : pos+4]),
TTL: binary.BigEndian.Uint32(response[pos+4 : pos+8]),
}
rdlength := int(binary.BigEndian.Uint16(response[pos+8 : pos+10]))
rdLen := int(binary.BigEndian.Uint16(response[pos+8 : pos+10]))
pos += 10
if pos+rdlength > responseLen {
return nil, pos, ErrInvalidDNSResourceRecordData
if responseLen < pos+rdLen {
return nil, pos, io.EOF
}
switch rh.Type {
case 1:
if rdlength == 4 {
if rdLen != 4 {
return nil, pos, ErrInvalidDNSAddressResourceData
}
return Address{
ResourceRecordHeader: rh,
Address: response[pos+0 : pos+4],
}, pos + 4, nil
} else {
return nil, pos, ErrInvalidDNSAddressResourceData
}
case 2:
var ns Name
ns, pos = parseName(response, pos)
var ns *Name
ns, pos, err = parseName(response, pos)
if err != nil {
return nil, pos, fmt.Errorf("error while parsing DNS resource record: %w", err)
}
return NameServer{
ResourceRecordHeader: rh,
NSDName: ns,
NSDName: *ns,
}, pos, nil
case 5:
var cname Name
cname, pos = parseName(response, pos)
var cname *Name
cname, pos, err = parseName(response, pos)
if err != nil {
return nil, pos, fmt.Errorf("error while parsing DNS resource record: %w", err)
}
return CName{
ResourceRecordHeader: rh,
CName: cname,
CName: *cname,
}, pos, nil
}
return Unknown{
ResourceRecordHeader: rh,
Data: response[pos+0 : pos+rdlength],
}, pos + rdlength, nil
Data: response[pos+0 : pos+rdLen],
}, pos + rdLen, nil
}
func ParseResponse(response []byte) (*Message, error) {
var err error
msg := new(Message)
responseLen := len(response)
if responseLen < 12 {
return nil, ErrInvalidDNSMessageHeader
return msg, io.EOF
}
msg := new(Message)
msg.ID = binary.BigEndian.Uint16(response[0:2])
flagsRAW := binary.BigEndian.Uint16(response[2:4])
@ -140,10 +151,16 @@ func ParseResponse(response []byte) (*Message, error) {
msg.QD = make([]Question, qdCount)
for i := 0; i < qdCount; i++ {
var name Name
name, pos = parseName(response, pos)
var name *Name
name, pos, err = parseName(response, pos)
if err != nil {
return msg, fmt.Errorf("error while parsing DNS name: %w", err)
}
if responseLen < pos+4 {
return msg, io.EOF
}
msg.QD[i] = Question{
QName: name,
QName: *name,
QType: binary.BigEndian.Uint16(response[pos+0 : pos+2]),
QClass: binary.BigEndian.Uint16(response[pos+2 : pos+4]),
}
@ -154,7 +171,7 @@ func ParseResponse(response []byte) (*Message, error) {
for i := 0; i < anCount; i++ {
msg.AN[i], pos, err = parseResourceRecord(response, pos)
if err != nil {
return nil, fmt.Errorf("error while parsing AN record: %w", err)
return msg, fmt.Errorf("error while parsing AN record: %w", err)
}
}
@ -162,7 +179,7 @@ func ParseResponse(response []byte) (*Message, error) {
for i := 0; i < nsCount; i++ {
msg.NS[i], pos, err = parseResourceRecord(response, pos)
if err != nil {
return nil, fmt.Errorf("error while parsing NS record: %w", err)
return msg, fmt.Errorf("error while parsing NS record: %w", err)
}
}
@ -170,7 +187,7 @@ func ParseResponse(response []byte) (*Message, error) {
for i := 0; i < arCount; i++ {
msg.AR[i], pos, err = parseResourceRecord(response, pos)
if err != nil {
return nil, fmt.Errorf("error while parsing AR record: %w", err)
return msg, fmt.Errorf("error while parsing AR record: %w", err)
}
}