/*

 * CDDL HEADER START

 *

 * The contents of this file are subject to the terms of the

 * Common Development and Distribution License (the "License").

 * You may not use this file except in compliance with the License.

 *

 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE

 * or http://www.opensolaris.org/os/licensing.

 * See the License for the specific language governing permissions

 * and limitations under the License.

 *

 * When distributing Covered Code, include this CDDL HEADER in each

 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.

 * If applicable, add the following below this CDDL HEADER, with the

 * fields enclosed by brackets "[]" replaced with your own identifying

 * information: Portions Copyright [yyyy] [name of copyright owner]

 *

 * CDDL HEADER END

 */

/*

 * Copyright (c) 1988, 2010, Oracle and/or its affiliates. All rights reserved.

 */

/*	Copyright (c) 1988 AT&T	*/

/*	  All Rights Reserved  	*/

/*

 *	mktemp() expects a string with up to six trailing 'X's.

 *	These will be overlaid with letters, digits and symbols from

 *	the portable filename character set.  If every combination thus

 *	inserted leads to an existing file name, the string is shortened

 *	to length zero and a pointer to a null string is returned.

 *

 *	The guarantee made by mktime() to the caller is that the

 *	generated file name string will not match the string

 *	produced by any other concurrent process using mktemp().

 *	To guarantee uniqueness across the process-id space,

 *	the process-id of the caller is encoded into the string.

 *	To allow repeated calls within the same process to generate

 *	different strings on each call, a sequence number is encoded

 *	into the string along with process-id.

 *

 *	The encoding is performed using radix-64 (6 bits per character),

 *	with 64 characters taken from the portable file name character set.

 *	This allows the six X's to be a representation of a 36-bit integer

 *	composed of bit fields:

 *		( pid | seq )

 *	where the process-id occupies the high-order bits and the sequence

 *	number occupies the low-order bits.  The size of the pid field is

 *	not fixed at the traditional 15 bits (MAXPID = 30000); the system

 *	now allows a larger process-id space and MAXPID is obtained from

 *	the system with a call to sysconf(_SC_MAXPID).

 *

 *	mktime() should fail if fewer than six X's are presented to it.

 *	However, this has been traditionally accepted and is preserved

 *	in the present code.  The consequence is that the 36-bit integer

 *	is reduced to a (6*N)-bit integer, where N is the number of X's.

 *	mktime() fails immediately if the resulting integer is not large

 *	enough to contain MAXPID.

 *

 *	In an attempt to confuse and thwart hackers, the starting

 *	sequence number is randomized using the current time.

 */

#pragma weak _mktemp = mktemp

#define	XCNT  6

#include "lint.h"

#include "mtlib.h"

#include <sys/types.h>

#include <string.h>

#include <unistd.h>

#include <thread.h>

#include <synch.h>

#include <sys/stat.h>

#include <errno.h>

#include <sys/time.h>

#include <stdlib.h>

#include <stdio.h>

#include <sys/param.h>

/*

 * 64-bit digits, must be from the POSIX "portable file name character set".

 */

static char

chars[64] = {

	'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',

	'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',

	'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',

	'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',

	'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.', '_',

};

char *

libc_mktemps(char *as, int slen)

{

	/* statics are protected by this static mutex */

	static mutex_t	mktemp_lock = DEFAULTMUTEX;

	static int	pidshift = 0;

	static int	previous_try = 0;

	static pid_t	previous_pid = 0;

	static int	previous_xcnt = XCNT;

	pid_t		pid;

	int		try;

	int		tryshift;

	int		max_try;

	char		*s;

	char		*first_x;

	int		len;

	uint_t		xcnt;

	struct stat64	buf;

	if (as == NULL || *as == '\0')	/* If the string passed is null then */

		return (as);	/* a pointer to a null string is returned. */

	lmutex_lock(&mktemp_lock);

	pid = getpid();

	if (pid != previous_pid) {	/* first time or first after fork() */

		/*

		 * Randomize the starting sequence number in

		 * an attempt to confuse and thwart hackers.

		 * Use the low 12 bits of the time in milliseconds.

		 */

		struct timeval tm;

		(void) gettimeofday(&tm, NULL);

		previous_try = (tm.tv_sec * 1000 + tm.tv_usec / 1000) & 0xfff;

		previous_pid = pid;

		previous_xcnt = XCNT;

	}

	/* for all possible values of pid, 0 <= pid < (1 << pidshift) */

	if (pidshift == 0)	/* one-time initialization */

		pidshift = fls((uint_t)MAXPID);		/* high bit number */

	/* count the X's */

	xcnt = 0;

	len = (int)strlen(as);

	if (slen >= len || slen < 0)

		goto fail;

	len -= slen;

	s = as + (len - 1);

	while ((len != 0) && (xcnt < XCNT) && (*s == 'X')) {

		xcnt++;

		len--;

		--s;

	}

	first_x = s + 1;	/* Remember pointer to the first X */

	/* fail if we don't have enough X's to represent MAXPID */

	if ((tryshift = xcnt * 6 - pidshift) < 0) {

		/*

		 * Some broken programs call mktemp() repeatedly,

		 * passing the same string without reinserting the X's.

		 * Check to see if this is such a call by testing

		 * the trailing characters of the string for a

		 * match with the process-id.

		 */

		uint64_t xpid = 0;		/* reconstructed pid */

		s = as + len;

		for (xcnt = previous_xcnt; xcnt && s > as; xcnt--) {

			int c;

			int i;

			c = *--s;

			for (i = 0; i < 64; i++)

				if (c == chars[i])

					break;

			if (i == 64)

				goto fail;

			xpid = xpid * 64 + i;

		}

		xpid >>= (previous_xcnt * 6 - pidshift);

		xpid &= ((1 << pidshift) - 1);

		if (xpid == pid &&

		    lstat64(as, &buf) == -1 && errno == ENOENT) {

			lmutex_unlock(&mktemp_lock);

			return (as);

		}

		goto fail;

	}

	/* we can try sequence numbers in the range 0 <= try < max_try */

	max_try = 1 << tryshift;

	if (previous_try >= max_try)

		previous_try = 0;

	try = previous_try;

	for (;;) {

		/* num is up to a 36-bit integer ... */

		uint64_t num = ((uint64_t)pid << tryshift) + (uint64_t)try;

		int i;

		/* ... which we represent backwards in base 64 */

		for (i = 0, s = first_x; i < xcnt; i++) {

			*s++ = chars[num & 077];

			num >>= 6;

		}

		if (lstat64(as, &buf) == -1) {

			if (errno != ENOENT)

				break;		/* unrecoverable error */

			/* remember where we left off for the next call */

			previous_try = try + 1;

			previous_xcnt = xcnt;

			lmutex_unlock(&mktemp_lock);

			return (as);

		}

		if (++try == max_try)

			try = 0;

		if (try == previous_try)

			break;

	}

fail:

	lmutex_unlock(&mktemp_lock);

	*as = '\0';

	return (as);

}

char *

mktemp(char *template)

{

	return (libc_mktemps(template, 0));

}