/*      $OpenBSD: users.c,v 1.16 2022/12/04 23:50:48 cheloha Exp $      */
/*      $NetBSD: users.c,v 1.5 1994/12/20 15:58:19 jtc Exp $    */

/*
 * Copyright (c) 1980, 1987, 1993
 *      The Regents of the University of California.  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.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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 <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <utmp.h>

typedef char    namebuf[UT_NAMESIZE];

int scmp(const void *, const void *);

int
main(int argc, char *argv[])
{
        namebuf *names = NULL;
        int ncnt = 0;
        int nmax = 0;
        int cnt;
        struct utmp utmp;
        int ch;

        if (unveil(_PATH_UTMP, "r") == -1)
                err(1, "unveil %s", _PATH_UTMP);
        if (pledge("stdio rpath", NULL) == -1)
                err(1, "pledge");

        while ((ch = getopt(argc, argv, "")) != -1)
                switch(ch) {
                default:
                        (void)fprintf(stderr, "usage: users\n");
                        exit(1);
                }
        argc -= optind;
        argv += optind;

        if (!freopen(_PATH_UTMP, "r", stdin)) {
                err(1, "can't open %s", _PATH_UTMP);
                /* NOTREACHED */
        }

        while (fread((char *)&utmp, sizeof(utmp), 1, stdin) == 1) {
                if (*utmp.ut_name) {
                        if (ncnt >= nmax) {
                                size_t newmax = nmax + 32;
                                namebuf *newnames;

                                newnames = reallocarray(names, newmax,
                                    sizeof(*names));

                                if (newnames == NULL) {
                                        err(1, NULL);
                                        /* NOTREACHED */
                                }
                                names = newnames;
                                nmax = newmax;
                        }

                        (void)strncpy(names[ncnt], utmp.ut_name, UT_NAMESIZE);
                        ++ncnt;
                }
        }

        if (ncnt) {
                qsort(names, ncnt, UT_NAMESIZE, scmp);
                (void)printf("%.*s", UT_NAMESIZE, names[0]);
                for (cnt = 1; cnt < ncnt; ++cnt)
                        if (strncmp(names[cnt], names[cnt - 1], UT_NAMESIZE))
                                (void)printf(" %.*s", UT_NAMESIZE, names[cnt]);
                (void)printf("\n");
        }
        exit(0);
}

int
scmp(const void *p, const void *q)
{
        return(strncmp((char *) p, (char *) q, UT_NAMESIZE));
}