/*      $OpenBSD: getusershell.c,v 1.18 2019/12/10 02:35:16 millert Exp $ */
/*
 * Copyright (c) 1985, 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 <paths.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

/*
 * Local shells should NOT be added here.  They should be added in
 * /etc/shells.
 */

static char *okshells[] = { _PATH_BSHELL, _PATH_CSHELL, _PATH_KSHELL, NULL };
static char **curshell, **shells;
static char **initshells(void);

/*
 * Get a list of shells from _PATH_SHELLS, if it exists.
 */
char *
getusershell(void)
{
        char *ret;

        if (curshell == NULL)
                curshell = initshells();
        ret = *curshell;
        if (ret != NULL)
                curshell++;
        return (ret);
}

void
endusershell(void)
{
        char **s;

        if ((s = shells))
                while (*s)
                        free(*s++);
        free(shells);
        shells = NULL;

        curshell = NULL;
}

void
setusershell(void)
{

        curshell = initshells();
}

static char **
initshells(void)
{
        size_t nshells, nalloc, linesize;
        char *line;
        FILE *fp;

        free(shells);
        shells = NULL;

        if ((fp = fopen(_PATH_SHELLS, "re")) == NULL)
                return (okshells);

        line = NULL;
        nalloc = 10; // just an initial guess
        nshells = 0;
        shells = reallocarray(NULL, nalloc, sizeof (char *));
        if (shells == NULL)
                goto fail;
        linesize = 0;
        while (getline(&line, &linesize, fp) != -1) {
                if (*line != '/')
                        continue;
                line[strcspn(line, "#\n")] = '\0';
                if (!(shells[nshells] = strdup(line)))
                        goto fail;

                if (nshells + 1 == nalloc) {
                        char **new = reallocarray(shells, nalloc * 2, sizeof(char *));
                        if (!new)
                                goto fail;
                        shells = new;
                        nalloc *= 2;
                }
                nshells++;
        }
        free(line);
        shells[nshells] = NULL;
        (void)fclose(fp);
        return (shells);

fail:
        free(line);
        while (nshells)
                free(shells[nshells--]);
        free(shells);
        shells = NULL;
        (void)fclose(fp);
        return (okshells);
}