This is xnu-8019. See this file in:
/*
 * Copyright (c) 1999-2010 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * Mach Operating System
 * Copyright (c) 1991,1990,1989 Carnegie Mellon University
 * All Rights Reserved.
 *
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie Mellon
 * the rights to redistribute these changes.
 */
/*
 * mig_strncpy.c - by Joshua Block
 *
 * mig_strncpy -- Bounded string copy.  Does what the library routine strncpy
 * OUGHT to do:  Copies the (null terminated) string in src into dest, a
 * buffer of length len.  Assures that the copy is still null terminated
 * and doesn't overflow the buffer, truncating the copy if necessary.
 *
 * Parameters:
 *
 *     dest - Pointer to destination buffer.
 *
 *     src - Pointer to source string.
 *
 *     len - Length of destination buffer.
 *
 * Result:
 *	length of string copied, INCLUDING the trailing 0.
 */
#include <mach/mig_errors.h>

int
mig_strncpy(
	char *dest,
	const char *src,
	int len)
{
	int i;

	if (len <= 0) {
		return 0;
	}

	for (i = 1; i < len; i++) {
		if (!(*dest++ = *src++)) {
			return i;
		}
	}

	*dest = '\0';
	return i;
}

/*
 * mig_strncpy_zerofill -- Bounded string copy.  Does what the
 * library routine strncpy OUGHT to do:  Copies the (null terminated)
 * string in src into dest, a buffer of length len.  Assures that
 * the copy is still null terminated and doesn't overflow the buffer,
 * truncating the copy if necessary. If the string in src is smaller
 * than given length len, it will zero fill the remaining bytes in dest.
 *
 * Parameters:
 *
 *     dest - Pointer to destination buffer.
 *
 *     src - Pointer to source string.
 *
 *     len - Length of destination buffer.
 *
 * Result:
 *	length of string copied, INCLUDING the trailing 0.
 */
int
mig_strncpy_zerofill(
	char *dest,
	const char *src,
	int len)
{
	int i;
	boolean_t terminated = FALSE;
	int retval = 0;

	if (len <= 0 || dest == 0) {
		return 0;
	}

	if (src == 0) {
		terminated = TRUE;
	}

	for (i = 1; i < len; i++) {
		if (!terminated) {
			if (!(*dest++ = *src++)) {
				retval = i;
				terminated = TRUE;
			}
		} else {
			*dest++ = '\0';
		}
	}

	*dest = '\0';
	if (!terminated) {
		retval = i;
	}

	return retval;
}