remove dnsfallback

proxy/dnsfallback/udp.go

@@ -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
-}