/*      $OpenBSD: __mktemp4.c,v 1.1 2024/01/19 19:45:02 millert Exp $ */
/*
 * Copyright (c) 1996-1998, 2008 Theo de Raadt
 * Copyright (c) 1997, 2008-2009, 2024 Todd C. Miller
 *
 * 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 <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>

#define TEMPCHARS       "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
#define NUM_CHARS       (sizeof(TEMPCHARS) - 1)
#define MIN_X           6

#ifndef nitems
#define nitems(_a)      (sizeof((_a)) / sizeof((_a)[0]))
#endif

/*
 * Internal driver for the mktemp(3) family of functions.
 * The supplied callback does the actual work of testing or
 * creating the file/directory.
 */
int
__mktemp4(char *path, int slen, int flags, int (*cb)(const char *, int))
{
        char *start, *cp, *ep;
        const char tempchars[] = TEMPCHARS;
        unsigned int tries;
        size_t len;
        int ret;

        len = strlen(path);
        if (len < MIN_X || slen < 0 || (size_t)slen > len - MIN_X) {
                errno = EINVAL;
                return -1;
        }
        ep = path + len - slen;

        for (start = ep; start > path && start[-1] == 'X'; start--)
                ;
        if (ep - start < MIN_X) {
                errno = EINVAL;
                return -1;
        }

        tries = INT_MAX;
        do {
                cp = start;
                do {
                        unsigned short rbuf[16];
                        unsigned int i;

                        /*
                         * Avoid lots of arc4random() calls by using
                         * a buffer sized for up to 16 Xs at a time.
                         */
                        arc4random_buf(rbuf, sizeof(rbuf));
                        for (i = 0; i < nitems(rbuf) && cp != ep; i++)
                                *cp++ = tempchars[rbuf[i] % NUM_CHARS];
                } while (cp != ep);

                ret = cb(path, flags);
                if (ret != -1 || errno != EEXIST)
                        return ret;
        } while (--tries);

        errno = EEXIST;
        return -1;
}