First Commmit

common/redir/redir_linux.go

@@ -0,0 +1,40 @@
+package redir
+
+import (
+	"encoding/binary"
+	"net"
+	"net/netip"
+	"os"
+	"syscall"
+
+	"github.com/sagernet/sing/common"
+	"github.com/sagernet/sing/common/control"
+	M "github.com/sagernet/sing/common/metadata"
+)
+
+func GetOriginalDestination(conn net.Conn) (destination netip.AddrPort, err error) {
+	syscallConn, ok := common.Cast[syscall.Conn](conn)
+	if !ok {
+		return netip.AddrPort{}, os.ErrInvalid
+	}
+	err = control.Conn(syscallConn, func(fd uintptr) error {
+		const SO_ORIGINAL_DST = 80
+		if conn.RemoteAddr().(*net.TCPAddr).IP.To4() != nil {
+			raw, err := syscall.GetsockoptIPv6Mreq(int(fd), syscall.IPPROTO_IP, SO_ORIGINAL_DST)
+			if err != nil {
+				return err
+			}
+			destination = netip.AddrPortFrom(M.AddrFromIP(raw.Multiaddr[4:8]), uint16(raw.Multiaddr[2])<<8+uint16(raw.Multiaddr[3]))
+		} else {
+			raw, err := syscall.GetsockoptIPv6MTUInfo(int(fd), syscall.IPPROTO_IPV6, SO_ORIGINAL_DST)
+			if err != nil {
+				return err
+			}
+			var port [2]byte
+			binary.BigEndian.PutUint16(port[:], raw.Addr.Port)
+			destination = netip.AddrPortFrom(M.AddrFromIP(raw.Addr.Addr[:]), binary.LittleEndian.Uint16(port[:]))
+		}
+		return nil
+	})
+	return
+}