Add redir tproxy and dns inbound

common/redir/redir_linux.go

@@ -0,0 +1,37 @@
+package redir
+
+import (
+	"net"
+	"net/netip"
+	"syscall"
+
+	M "github.com/sagernet/sing/common/metadata"
+)
+
+func GetOriginalDestination(conn net.Conn) (destination netip.AddrPort, err error) {
+	rawConn, err := conn.(syscall.Conn).SyscallConn()
+	if err != nil {
+		return
+	}
+	var rawFd uintptr
+	err = rawConn.Control(func(fd uintptr) {
+		rawFd = fd
+	})
+	if err != nil {
+		return
+	}
+	const SO_ORIGINAL_DST = 80
+	if conn.RemoteAddr().(*net.TCPAddr).IP.To4() != nil {
+		raw, err := syscall.GetsockoptIPv6Mreq(int(rawFd), syscall.IPPROTO_IP, SO_ORIGINAL_DST)
+		if err != nil {
+			return netip.AddrPort{}, err
+		}
+		return netip.AddrPortFrom(M.AddrFromIP(raw.Multiaddr[4:8]), uint16(raw.Multiaddr[2])<<8+uint16(raw.Multiaddr[3])), nil
+	} else {
+		raw, err := syscall.GetsockoptIPv6MTUInfo(int(rawFd), syscall.IPPROTO_IPV6, SO_ORIGINAL_DST)
+		if err != nil {
+			return netip.AddrPort{}, err
+		}
+		return netip.AddrPortFrom(M.AddrFromIP(raw.Addr.Addr[:]), raw.Addr.Port), nil
+	}
+}