/*      $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;
}