Refactor: autonomize core package

core/adapter.go

@@ -0,0 +1,34 @@
+package core
+
+import (
+	"net"
+
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
+)
+
+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)
+}