add getOriginDst of cgo

the cgo version support both ipv4 and ipv6

redir_iptables.go

@@ -1,4 +1,4 @@
-// +build linux
+// +build linux,!cgo
 
 package obfssh
 

redir_iptables_2.go

@@ -0,0 +1,108 @@
+// +build linux,cgo
+
+package obfssh
+
+/*
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <linux/if.h>
+#include <netinet/ip.h>
+#include <netinet/ip6.h>
+#include <linux/netfilter_ipv4.h>
+#include <linux/netfilter_ipv6/ip6_tables.h>
+
+int get_original_dst4(int fd, void *addr);
+int get_original_dst6(int fd, void *addr);
+
+unsigned short _ntohs(unsigned short a);
+
+int get_original_dst4(int fd, void *addr){
+	int ret;
+	int l = sizeof(struct sockaddr_in);
+	ret = getsockopt(fd, SOL_IP, SO_ORIGINAL_DST,
+		(struct sockaddr_in *)addr, &l);
+	return ret;
+}
+
+int get_original_dst6(int fd, void *addr){
+	int ret;
+	int l = sizeof(struct sockaddr_in6);
+	ret = getsockopt(fd, SOL_IPV6, IP6T_SO_ORIGINAL_DST,
+		(struct sockaddr_in6 *)addr, &l);
+	return ret;
+}
+
+unsigned short _ntohs(unsigned short a) {
+	return ntohs(a);
+}
+
+*/
+import "C"
+
+import (
+	"fmt"
+	//"log"
+	"net"
+	"syscall"
+	"unsafe"
+)
+
+func getOriginDst(c net.Conn) (net.Addr, error) {
+	var addr net.Addr
+	var err error
+
+	if _, ok := c.(*net.TCPConn); !ok {
+		return nil, fmt.Errorf("only tcp socket supported")
+	}
+
+	ip := c.LocalAddr().(*net.TCPAddr).IP
+
+	if ip.To4() != nil { // ipv4
+		addr, err = getOriginDst4(c)
+	} else {
+		addr, err = getOriginDst6(c)
+	}
+	return addr, err
+}
+
+func getOriginDst4(c net.Conn) (net.Addr, error) {
+
+	c1 := c.(*net.TCPConn)
+
+	f, _ := c1.File()
+
+	defer f.Close()
+
+	var addr4 syscall.RawSockaddrInet4
+
+	ret := C.get_original_dst4(C.int(f.Fd()), unsafe.Pointer(&addr4))
+	if int(ret) != 0 {
+		return nil, fmt.Errorf("ipv4 getsockopt SO_ORIGINAL_DST return %v", int(ret))
+	}
+
+	port := int(C._ntohs(C.ushort(addr4.Port)))
+	ip := net.IP(addr4.Addr[0:])
+
+	return &net.TCPAddr{IP: ip, Port: port}, nil
+}
+
+func getOriginDst6(c net.Conn) (net.Addr, error) {
+
+	c1 := c.(*net.TCPConn)
+
+	f, _ := c1.File()
+
+	defer f.Close()
+
+	var addr6 syscall.RawSockaddrInet6
+
+	ret := C.get_original_dst6(C.int(f.Fd()), unsafe.Pointer(&addr6))
+	if int(ret) != 0 {
+		return nil, fmt.Errorf("ipv6 getsockopt IP6T_ORIGINAL_DST return %v", int(ret))
+	}
+
+	port := int(C._ntohs(C.ushort(addr6.Port)))
+	ip := net.IP(addr6.Addr[0:])
+
+	return &net.TCPAddr{IP: ip, Port: port}, nil
+}