/*      $OpenBSD: srcaddr.c,v 1.1 2020/04/13 03:09:29 pamela Exp $      */

/*
 * Copyright (c) 2020 Pamela Mosiejczuk <pamela@openbsd.org>
 * Copyright (c) 2020 Florian Obser <florian@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

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

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

__dead void     usage(void);

/* given an IPv6 destination address, return the source address selected */
int
main(int argc, char *argv[])
{
        struct addrinfo          hints, *res;
        struct sockaddr_storage  ss;
        socklen_t                len;
        int                      ch, error, s;
        char                    *target, src[NI_MAXHOST];

        while ((ch = getopt(argc, argv, "")) != -1) {
                switch (ch) {
                default:
                        usage();
                }
        }
        argc -= optind;
        argv += optind;

        if (argc != 1)
                usage();

        target = *argv;

        memset(&hints, 0, sizeof(hints));
        hints.ai_flags = AI_NUMERICHOST | AI_NUMERICSERV;
        hints.ai_family = AF_INET6;
        hints.ai_socktype = SOCK_DGRAM;

        if ((error = getaddrinfo(target, "8888", &hints, &res)))
                errx(1, "%s", gai_strerror(error));

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

        if (connect(s, res->ai_addr, res->ai_addrlen) == -1)
                err(1, "connect");
        freeaddrinfo(res);

        len = sizeof(ss);
        if (getsockname(s, (struct sockaddr *)&ss, &len) == -1)
                err(1, "getsockname");

        if ((error = getnameinfo((struct sockaddr *)&ss, ss.ss_len, src,
            sizeof(src), NULL, 0, NI_NUMERICHOST | NI_NUMERICSERV)))
                errx(1, "%s", gai_strerror(error));

        printf("%s\n", src);

        return (0);
}

__dead void
usage(void)
{
        fprintf(stderr, "usage: srcaddr destination\n");
        exit (1);
}