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