1 files changed, 131 insertions, 0 deletions
diff --git a/pkg/server/socket/sys.go b/pkg/server/socket/sys.go
new file mode 100644
index 0000000..d09df12
--- /dev/null
+++ b/pkg/server/socket/sys.go
@@ -0,0 +1,131 @@
+package socket
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"golang.org/x/sys/unix"
+	"net"
+	"strconv"
+	"syscall"
+	"unsafe"
+)
+
+func be16toh(n uint16) uint16 {
+	b := (*[2]byte)(unsafe.Pointer(&n))
+	return binary.BigEndian.Uint16(b[:])
+}
+
+func getsockopt(s int, level, name int, ptr unsafe.Pointer, size int) error {
+	tmpsize := uint32(size)
+
+	_, _, errno := unix.Syscall6(unix.SYS_GETSOCKOPT,
+		uintptr(s),
+		uintptr(level),
+		uintptr(name),
+		uintptr(ptr),
+		uintptr(unsafe.Pointer(&tmpsize)),
+		0)
+
+	if errno != 0 {
+		return fmt.Errorf("getsockopt: %w", errno)
+	}
+
+	return nil
+}
+
+func ioctl(fd int, req int, ptr unsafe.Pointer) error {
+	_, _, errno := unix.Syscall(unix.SYS_IOCTL,
+		uintptr(fd),
+		uintptr(req),
+		uintptr(ptr))
+
+	if errno != 0 {
+		return fmt.Errorf("ioctl: %w", errno)
+	}
+
+	return nil
+}
+
+func getRawConn(conn net.Conn) (syscall.RawConn, error) {
+	switch c := conn.(type) {
+	case *net.TCPConn:
+		return c.SyscallConn()
+	default:
+		return nil, errors.New("unknown connection type")
+	}
+}
+
+func withConnControl(conn net.Conn, f func(fd int) error) (err error) {
+	var c syscall.RawConn
+	var ferr error
+
+	c, err = getRawConn(conn)
+	if err != nil {
+		return
+	}
+
+	err = c.Control(func(fd uintptr) {
+		ferr = f(int(fd))
+	})
+	if ferr != nil {
+		err = ferr
+	}
+
+	return
+}
+
+func getSocketOriginalDst(fd int, sa *unix.RawSockaddrAny) error {
+	const SO_ORIGINAL_DST = 80
+
+	p, n := unsafe.Pointer(sa), int(unsafe.Sizeof(*sa))
+
+	family, err := unix.GetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_DOMAIN)
+	if err != nil {
+		return err
+	}
+
+	switch family {
+	case unix.AF_INET6:
+		err := getsockopt(fd, unix.SOL_IPV6, SO_ORIGINAL_DST, p, n)
+		if !errors.Is(err, unix.ENOENT) {
+			return err
+		}
+		// skipped check for ipv4 encoded as ipv6 address
+		fallthrough
+	case unix.AF_INET:
+		return getsockopt(fd, unix.SOL_IP, SO_ORIGINAL_DST, p, n)
+	default:
+		return errors.New("unknown address family")
+	}
+}
+
+func getConnOriginalAddr(conn net.Conn, addr *string) error {
+	var sa unix.RawSockaddrAny
+
+	f := func(fd int) error {
+		return getSocketOriginalDst(fd, &sa)
+	}
+
+	if err := withConnControl(conn, f); err != nil {
+		return fmt.Errorf("get-original-addr: %w", err)
+	}
+
+	var host net.IP
+	var port uint16
+
+	switch sa.Addr.Family {
+	case unix.AF_INET:
+		sin := (*unix.RawSockaddrInet4)(unsafe.Pointer(&sa))
+		host, port = sin.Addr[:], sin.Port
+	case unix.AF_INET6:
+		sin := (*unix.RawSockaddrInet6)(unsafe.Pointer(&sa))
+		host, port = sin.Addr[:], sin.Port
+	default:
+		return errors.New("get-original-addr: unknown address family")
+	}
+
+	*addr = net.JoinHostPort(host.String(), strconv.Itoa(int(be16toh(port))))
+
+	return nil
+}