/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2023 Klara, Inc.
 *
 * 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 AUTHOR 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 AUTHOR 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/cdefs.h>

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

static int
exec_shortargs(char *argv[])
{
        char *flag_arg = argv[2];
        char *sentinel = argv[3];
        char * nargv[] = { argv[0], __DECONST(char *, "--spin"), flag_arg,
            sentinel, NULL };
        char * const nenvp[] = { NULL };

        execve(argv[0], nargv, nenvp);
        err(1, "execve");
}

static int
exec_largeargs(char *argv[])
{
        char *flag_arg = argv[2];
        char *sentinel = argv[3];
        /*
         * Account for each argument and their NUL terminator, as well as an
         * extra NUL terminator.
         */
        size_t bufsz = ARG_MAX -
            ((strlen(argv[0]) + 1) + sizeof("--spin") + (strlen(flag_arg) + 1) +
            (strlen(sentinel) + 1) + 1);
        char *s = NULL;
        char * nargv[] = { argv[0], __DECONST(char *, "--spin"), flag_arg, NULL,
            sentinel, NULL };
        char * const nenvp[] = { NULL };

        /*
         * Our heuristic may or may not be accurate, we'll keep trying with
         * smaller argument sizes as needed until we stop getting E2BIG.
         */
        do {
                if (s == NULL)
                        s = malloc(bufsz + 1);
                else
                        s = realloc(s, bufsz + 1);
                if (s == NULL)
                        abort();
                memset(s, 'x', bufsz);
                s[bufsz] = '\0';
                nargv[3] = s;

                execve(argv[0], nargv, nenvp);
                bufsz--;
        } while (errno == E2BIG);
        err(1, "execve");
}

int
main(int argc, char *argv[])
{

        if (argc > 1 && strcmp(argv[1], "--spin") == 0) {
                int fd;

                if (argc < 4) {
                        fprintf(stderr, "usage: %s --spin flagfile ...\n", argv[0]);
                        return (1);
                }

                fd = open(argv[2], O_RDWR | O_CREAT, 0755);
                if (fd < 0)
                        err(1, "%s", argv[2]);
                close(fd);

                for (;;) {
                        sleep(1);
                }

                return (1);
        }

        if (argc != 4) {
                fprintf(stderr, "usage: %s [--short | --long] flagfile sentinel\n",
                    argv[0]);
                return (1);
        }

        if (strcmp(argv[1], "--short") == 0)
                exec_shortargs(argv);
        else
                exec_largeargs(argv);
}