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remove dnsfallback

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Jason
2019-08-12 18:48:22 +08:00
parent 4c289ed8b3
commit c07c92cbe3
1 changed files with 0 additions and 66 deletions
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66
proxy/dnsfallback/udp.go
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@@ -1,66 +0,0 @@
package dnsfallback
import (
"encoding/binary"
"errors"
"net"
"github.com/xjasonlyu/tun2socks/common/dns"
"github.com/xjasonlyu/tun2socks/core"
)
// UDP handler that intercepts DNS queries and replies with a truncated response (TC bit)
// in order for the client to retry over TCP. This DNS/TCP fallback mechanism is
// useful for proxy servers that do not support UDP.
// Note that non-DNS UDP traffic is dropped.
type udpHandler struct{}
const (
dnsHeaderLength = 12
dnsMaskQr = uint8(0x80)
dnsMaskTc = uint8(0x02)
dnsMaskRcode = uint8(0x0F)
)
func NewUDPHandler() core.UDPConnHandler {
return &udpHandler{}
}
func (h *udpHandler) Connect(conn core.UDPConn, udpAddr *net.UDPAddr) error {
if udpAddr.Port != dns.CommonDnsPort {
return errors.New("cannot handle non-DNS packet")
}
return nil
}
func (h *udpHandler) ReceiveTo(conn core.UDPConn, data []byte, addr *net.UDPAddr) error {
if len(data) < dnsHeaderLength {
return errors.New("received malformed DNS query")
}
// DNS Header
// 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// | ID |
// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// |QR| Opcode |AA|TC|RD|RA| Z | RCODE |
// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// | QDCOUNT |
// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// | ANCOUNT |
// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// | NSCOUNT |
// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// | ARCOUNT |
// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// Set response and truncated bits
data[2] |= dnsMaskQr | dnsMaskTc
// Set response code to 'no error'.
data[3] &= ^dnsMaskRcode
// Set ANCOUNT to QDCOUNT. This is technically incorrect, since the response does not
// include an answer. However, without it some DNS clients (i.e. Windows 7) do not retry
// over TCP.
var qdcount = binary.BigEndian.Uint16(data[4:6])
binary.BigEndian.PutUint16(data[6:], qdcount)
_, err := conn.WriteFrom(data, addr)
return err
}