Feature: add UDP TPROXY support on Linux (#562)

proxy/redir/utils.go

@@ -0,0 +1,41 @@
+package redir
+
+import (
+	"net"
+
+	"github.com/Dreamacro/clash/common/pool"
+)
+
+type fakeConn struct {
+	net.PacketConn
+	origDst net.Addr
+	rAddr   net.Addr
+	buf     []byte
+}
+
+func (c *fakeConn) Data() []byte {
+	return c.buf
+}
+
+// WriteBack opens a new socket binding `origDst` to wirte UDP packet back
+func (c *fakeConn) WriteBack(b []byte, addr net.Addr) (n int, err error) {
+	tc, err := dialUDP("udp", c.origDst.(*net.UDPAddr), c.rAddr.(*net.UDPAddr))
+	if err != nil {
+		n = 0
+		return
+	}
+	n, err = tc.Write(b)
+	tc.Close()
+	return
+}
+
+// LocalAddr returns the source IP/Port of UDP Packet
+func (c *fakeConn) LocalAddr() net.Addr {
+	return c.rAddr
+}
+
+func (c *fakeConn) Close() error {
+	err := c.PacketConn.Close()
+	pool.BufPool.Put(c.buf[:cap(c.buf)])
+	return err
+}