Fix Socks UDP implementation

proxy/socks/protocol/udp.go

@@ -22,6 +22,28 @@ func (request *Socks5UDPRequest) Destination() v2net.Destination {
 	return v2net.NewUDPDestination(request.Address)
 }
 
+func (request *Socks5UDPRequest) Bytes(buffer []byte) []byte {
+  if buffer == nil {
+    buffer = make([]byte, 0, 2*1024)
+  }
+  buffer = append(buffer, 0, 0, request.Fragment)
+  switch {
+    case request.Address.IsIPv4():
+    buffer = append(buffer, AddrTypeIPv4)
+    buffer = append(buffer, request.Address.IP()...)
+    case request.Address.IsIPv6():
+    buffer = append(buffer, AddrTypeIPv6)
+    buffer = append(buffer, request.Address.IP()...)
+    case request.Address.IsDomain():
+    buffer = append(buffer, AddrTypeDomain)
+    buffer = append(buffer, byte(len(request.Address.Domain())))
+    buffer = append(buffer, []byte(request.Address.Domain())...)
+  }
+  buffer = append(buffer, request.Address.PortBytes()...)
+  buffer = append(buffer, request.Data...)
+  return buffer
+}
+
 func ReadUDPRequest(packet []byte) (request Socks5UDPRequest, err error) {
 	// packet[0] and packet[1] are reserved
 	request.Fragment = packet[2]

proxy/socks/udp.go

@@ -54,15 +54,17 @@ func (server *SocksServer) AcceptPackets(conn *net.UDPConn) error {
 		}
 
 		udpPacket := v2net.NewPacket(request.Destination(), request.Data, false)
-		go server.handlePacket(conn, udpPacket, addr)
+		go server.handlePacket(conn, udpPacket, addr, request)
 	}
 }
 
-func (server *SocksServer) handlePacket(conn *net.UDPConn, packet v2net.Packet, clientAddr *net.UDPAddr) {
+func (server *SocksServer) handlePacket(conn *net.UDPConn, packet v2net.Packet, clientAddr *net.UDPAddr, request protocol.Socks5UDPRequest) {
 	ray := server.vPoint.DispatchToOutbound(packet)
 	close(ray.InboundInput())
 
 	if data, ok := <-ray.InboundOutput(); ok {
-		conn.WriteToUDP(data, clientAddr)
+    request.Data = data
+    udpMessage := request.Bytes(nil)
+		nBytes, err := conn.WriteToUDP(udpMessage, clientAddr)
 	}
 }