Refactor: optimize UDP module

Symmetric NAT support for now.

core/adapter.go

@@ -2,33 +2,15 @@ package core
 
 import (
 	"net"
-
-	"gvisor.dev/gvisor/pkg/tcpip/stack"
 )
 
+// TCPConn implements the net.Conn interface.
 type TCPConn interface {
 	net.Conn
-	ID() *stack.TransportEndpointID
 }
 
-type UDPPacket interface {
-	// Data get the payload of UDP Packet.
-	Data() []byte
-
-	// Drop call after packet is used, could release resources in this function.
-	Drop()
-
-	// ID returns the transport endpoint id of packet.
-	ID() *stack.TransportEndpointID
-
-	// LocalAddr returns the source IP/Port of packet.
-	LocalAddr() net.Addr
-
-	// RemoteAddr returns the destination IP/Port of packet.
-	RemoteAddr() net.Addr
-
-	// WriteBack writes the payload with source IP/Port equals addr
-	// - variable source IP/Port is important to STUN
-	// - if addr is not provided, WriteBack will write out UDP packet with SourceIP/Port equals to original Target.
-	WriteBack([]byte, net.Addr) (int, error)
+// UDPConn implements net.Conn and net.PacketConn.
+type UDPConn interface {
+	net.Conn
+	net.PacketConn
 }