Improve: UDP relay refactor (#441)

Co-authored-by: Dreamacro <Dreamacro@vip.qq.com>

adapters/inbound/packet.go

@@ -0,0 +1,33 @@
+package inbound
+
+import (
+	"github.com/Dreamacro/clash/component/socks5"
+	C "github.com/Dreamacro/clash/constant"
+)
+
+// PacketAdapter is a UDP Packet adapter for socks/redir/tun
+type PacketAdapter struct {
+	C.UDPPacket
+	metadata *C.Metadata
+}
+
+// Metadata returns destination metadata
+func (s *PacketAdapter) Metadata() *C.Metadata {
+	return s.metadata
+}
+
+// NewPacket is PacketAdapter generator
+func NewPacket(target socks5.Addr, packet C.UDPPacket, source C.Type, netType C.NetWork) *PacketAdapter {
+	metadata := parseSocksAddr(target)
+	metadata.NetWork = netType
+	metadata.Type = source
+	if ip, port, err := parseAddr(packet.LocalAddr().String()); err == nil {
+		metadata.SrcIP = ip
+		metadata.SrcPort = port
+	}
+
+	return &PacketAdapter{
+		UDPPacket: packet,
+		metadata:  metadata,
+	}
+}

adapters/outbound/shadowsocks.go

@@ -201,8 +201,13 @@ func (uc *ssUDPConn) WriteTo(b []byte, addr net.Addr) (n int, err error) {
 }
 
 func (uc *ssUDPConn) ReadFrom(b []byte) (int, net.Addr, error) {
-	n, a, e := uc.PacketConn.ReadFrom(b)
+	n, _, e := uc.PacketConn.ReadFrom(b)
 	addr := socks5.SplitAddr(b[:n])
+	var from net.Addr
+	if e == nil {
+		// Get the source IP/Port of packet.
+		from = addr.UDPAddr()
+	}
 	copy(b, b[len(addr):])
-	return n - len(addr), a, e
+	return n - len(addr), from, e
 }