/*	$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;
}