/*-
 * Copyright (c) 2017 Taylor R. Campbell
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
 */

#define	_POSIX_C_SOURCE	200809L

#include "strlcat.h"

#include <stddef.h>
#include <string.h>

#include "strlcpy.h"

/*
 * strlcat(dst, src, n)
 *
 *	Copy the NUL-terminated string at src to position of the first
 *	NUL byte in the n-byte buffer dst, guaranteeing NUL-termination
 *	of dst as long as n > 0, and return the length of the
 *	concatenation of what was already at dst with str.
 */
size_t
strlcat(char *dst, const char *src, size_t n)
{
	const char *const dstart = dst;

	/* If no space for a NUL terminator, just return strlen(src).  */
	if (n == 0)
		return strlen(src);

	/* Find the NUL terminator or the end of the buffer.  */
	while (*dst++ != '\0' && --n > 0)
		continue;

	/* Check whether we hit the end of the buffer.  */
	if (n == 0) {
		/* Truncated.  NUL-terminate and count the length.  */
		*--dst = '\0';
		return (size_t)(dst - dstart) + strlen(src);
	}

	/*
	 * All set.  Back up over the NUL-terminator, count the number
	 * of non-NUL bytes read, and strlcpy.
	 */
	--dst;
	return (size_t)(dst - dstart) + strlcpy(dst, src, n);
}