Xray-core/transport/internet/headers/dns/dns.go

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package dns
import (
"context"
"encoding/binary"
"errors"
"github.com/xtls/xray-core/common"
"github.com/xtls/xray-core/common/dice"
)
type DNS struct {
header []byte
}
func (d DNS) Size() int32 {
return int32(len(d.header))
}
// Serialize implements PacketHeader.
func (d DNS) Serialize(b []byte) {
copy(b, d.header)
binary.BigEndian.PutUint16(b[0:], dice.RollUint16()) // random transaction ID
}
// NewDNS returns a new DNS instance based on given config.
func NewDNS(ctx context.Context, config interface{}) (interface{}, error) {
var header []byte
header = binary.BigEndian.AppendUint16(header, 0x0000) // Transaction ID
header = binary.BigEndian.AppendUint16(header, 0x0100) // Flags: Standard query
header = binary.BigEndian.AppendUint16(header, 0x0001) // Questions
header = binary.BigEndian.AppendUint16(header, 0x0000) // Answer RRs
header = binary.BigEndian.AppendUint16(header, 0x0000) // Authority RRs
header = binary.BigEndian.AppendUint16(header, 0x0000) // Additional RRs
buf := make([]byte, 0x100)
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off1, err := packDomainName(config.(*Config).Domain+".", buf)
if err != nil {
return nil, err
}
header = append(header, buf[:off1]...)
header = binary.BigEndian.AppendUint16(header, 0x0001) // Type: A
header = binary.BigEndian.AppendUint16(header, 0x0001) // Class: IN
return DNS{
header: header,
}, nil
}
// copied from github.com/miekg/dns
func packDomainName(s string, msg []byte) (off1 int, err error) {
off := 0
ls := len(s)
// Each dot ends a segment of the name.
// We trade each dot byte for a length byte.
// Except for escaped dots (\.), which are normal dots.
// There is also a trailing zero.
// Emit sequence of counted strings, chopping at dots.
var (
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begin int
bs []byte
)
for i := 0; i < ls; i++ {
var c byte
if bs == nil {
c = s[i]
} else {
c = bs[i]
}
switch c {
case '\\':
if off+1 > len(msg) {
return len(msg), errors.New("buffer size too small")
}
if bs == nil {
bs = []byte(s)
}
copy(bs[i:ls-1], bs[i+1:])
ls--
case '.':
labelLen := i - begin
if labelLen >= 1<<6 { // top two bits of length must be clear
return len(msg), errors.New("bad rdata")
}
// off can already (we're in a loop) be bigger than len(msg)
// this happens when a name isn't fully qualified
if off+1+labelLen > len(msg) {
return len(msg), errors.New("buffer size too small")
}
// The following is covered by the length check above.
msg[off] = byte(labelLen)
if bs == nil {
copy(msg[off+1:], s[begin:i])
} else {
copy(msg[off+1:], bs[begin:i])
}
off += 1 + labelLen
begin = i + 1
default:
}
}
if off < len(msg) {
msg[off] = 0
}
return off + 1, nil
}
func init() {
common.Must(common.RegisterConfig((*Config)(nil), NewDNS))
}