/*      $NetBSD: natt_terminator.c,v 1.2 2018/11/22 04:51:41 knakahara Exp $    */

/*-
* Copyright (c) 2017 Internet Initiative Japan Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in the
*    documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <sys/time.h>

#include <netinet/in.h>
#include <netinet/udp.h>

#include <stdio.h>
#include <err.h>
#include <netdb.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>

static void
usage(void)
{
       const char *prog = "natt_terminator";

       fprintf(stderr, "Usage: %s [-46] <addr> <port>\n", prog);
}

int
main(int argc, char **argv)
{
       struct addrinfo hints;
       struct addrinfo *res;
       int s, e;
       const char *addr, *port;
       int option;
       int c, family = AF_INET;

       while ((c = getopt(argc, argv, "46")) != -1) {
               switch (c) {
               case '4':
                       family = AF_INET;
                       break;
               case '6':
                       family = AF_INET6;
                       break;
               default:
                       usage();
                       return 1;
               }
       }
       argc -= optind;
       argv += optind;

       if (argc != 2) {
               usage();
               return 1;
       }

       addr = argv[0];
       port = argv[1];

       memset(&hints, 0, sizeof(hints));
       hints.ai_family = family;
       hints.ai_socktype = SOCK_DGRAM;
       hints.ai_protocol = IPPROTO_UDP;
       hints.ai_flags = 0;

       e = getaddrinfo(addr, port, &hints, &res);
       if (e != 0)
               errx(EXIT_FAILURE, "getaddrinfo failed: %s", gai_strerror(e));

       s = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
       if (s == -1)
               err(EXIT_FAILURE, "socket");

       /*
        * Set the option to tell the kernel that the socket can handle
        * UDP-encapsulated ESP packets for NAT-T.
        */
       option = UDP_ENCAP_ESPINUDP;
       e = setsockopt(s, IPPROTO_UDP, UDP_ENCAP, &option, sizeof(option));
       if (e == -1)
               err(EXIT_FAILURE, "setsockopt(UDP_ENCAP)");

       e = bind(s, res->ai_addr, res->ai_addrlen);
       if (e == -1)
               err(EXIT_FAILURE, "bind");

       /* Receiving a packet make the NAPT create a mapping. */
       {
               char buf[64];
               struct sockaddr_storage z;
               socklen_t len = sizeof(z);

               e = recvfrom(s, buf, 64, MSG_PEEK,
                   (struct sockaddr *)&z, &len);
               if (e == -1)
                       err(EXIT_FAILURE, "recvfrom");
       }

       /*
        * Keep the socket in the kernel to handle UDP-encapsulated ESP packets.
        */
       pause();

       close(s);

       return 0;
}