/*      $OpenBSD: nonxt-reflect.c,v 1.2 2018/05/21 01:19:21 bluhm Exp $ */
/*
 * Copyright (c) Alexander Bluhm <bluhm@genua.de>
 *
 * 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 <netdb.h>

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

void __dead usage(void);

void
usage(void)
{
        fprintf(stderr, "usage: nonxt-reflect localaddr\n"
            "Daemonize, wait for protocol 59 packets, and answer them.\n");
        exit(1);
}

int
main(int argc, char *argv[])
{
        struct addrinfo hints, *res, *res0;
        const char *cause = NULL, *local;
        int error;
        int save_errno;
        int s;
        char buf[1024];

        switch (argc) {
        case 2:
                local = argv[1];
                break;
        default:
                usage();
        }

        if (pledge("stdio inet dns proc", NULL) == -1)
                err(1, "pledge");

        /* Create socket and bind it to local address. */
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = AF_UNSPEC;
        hints.ai_socktype = SOCK_RAW;
        hints.ai_protocol = IPPROTO_NONE;
        hints.ai_flags = AI_PASSIVE;
        error = getaddrinfo(local, NULL, &hints, &res0);
        if (error)
                errx(1, "getaddrinfo local: %s", gai_strerror(error));
        for (res = res0; res; res = res->ai_next) {
                s = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
                if (s == -1) {
                        cause = "socket";
                        continue;
                }
                if (bind(s, res->ai_addr, res->ai_addrlen) == -1) {
                        cause = "bind";
                        save_errno = errno;
                        close(s);
                        errno = save_errno;
                        continue;
                }
                break;
        }
        if (res == NULL)
                err(1, "%s", cause);
        freeaddrinfo(res0);

        /* Socket is ready to receive, parent process may proceed. */
        daemon(1, 1);
        if (pledge("stdio inet", NULL) == -1)
                err(1, "pledge");

        for (;;) {
                struct sockaddr_storage ss;
                socklen_t slen;

                /* Receive a protocol 59 packet. */
                slen = sizeof(ss);
                if (recvfrom(s, buf, sizeof(buf), 0, (struct sockaddr *)&ss,
                    &slen) == -1)
                        err(1, "recv");
                /* Send back a reply packet. */
                if (sendto(s, buf, 0, 0, (struct sockaddr *)&ss, slen) == -1)
                        err(1, "send");
        }

        /* NOTREACHED */
        return 0;
}