Add tun support

app/tun/packet_conn.go

@@ -0,0 +1,42 @@
+package tun
+
+import (
+	sing_common "github.com/sagernet/sing/common"
+	sing_buf "github.com/sagernet/sing/common/buf"
+	N "github.com/sagernet/sing/common/network"
+	"github.com/xtls/xray-core/common/buf"
+	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/common/singbridge"
+)
+
+type PacketConn struct {
+	N.PacketConn
+}
+
+func (p *PacketConn) ReadMultiBuffer() (buf.MultiBuffer, error) {
+	packet := buf.New()
+	packet.Extend(buf.Size)
+	sPacket := sing_buf.With(packet.Bytes())
+	destination, err := p.ReadPacket(sPacket)
+	if err != nil {
+		packet.Release()
+		return nil, err
+	}
+	packet.Clear()
+	packet.Resize(int32(sPacket.Start()), int32(sPacket.Start()+sPacket.Len()))
+	destinationX := singbridge.ToDestination(destination, net.Network_UDP)
+	packet.UDP = &destinationX
+	return buf.MultiBuffer{packet}, nil
+}
+
+func (p *PacketConn) WriteMultiBuffer(mb buf.MultiBuffer) error {
+	defer buf.ReleaseMulti(mb)
+	for _, buffer := range mb {
+		destination := sing_common.PtrValueOrDefault(buffer.UDP)
+		err := p.PacketConn.WritePacket(sing_buf.As(buffer.Bytes()), singbridge.ToSocksaddr(destination))
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}