cosmopolitan/libc/str/strlcat.c

/*-*- mode:c;indent-tabs-mode:t;c-basic-offset:8;tab-width:8;coding:utf-8   -*-│
│ vi: set noet ft=c ts=8 sw=8 fenc=utf-8                                   :vi │
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright (c) 1998, 2015 Todd C. Miller <millert@openbsd.org>                │
│                                                                              │
│ Permission to use, copy, modify, and/or 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 "libc/str/str.h"
// clang-format off
// $OpenBSD: strlcat.c,v 1.19 2019/01/25 00:19:25 millert Exp $
__static_yoink("openbsd_strings_notice");

/**
 * Appends string, the BSD way.
 * 
 * Appends `src` to string `dst` of size `dsize` (unlike strncat,
 * `dsize` is the full size of `dst`, not space left). At most `dsize-1`
 * characters will be copied. Always NUL terminates (unless `dsize <=
 * strlen(dst)`). Returns `strlen(src) + MIN(dsize, strlen(initial
 * dst))`. If `retval >= dsize`, truncation occurred.
 *
 * @asyncsignalsafe
 * @vforksafe
 */
size_t
strlcat(char *dst, const char *src, size_t dsize)
{
	const char *odst = dst;
	const char *osrc = src;
	size_t n = dsize;
	size_t dlen;

	/* Find the end of dst and adjust bytes left but don't go past end. */
	while (n-- != 0 && *dst != '\0')
		dst++;
	dlen = dst - odst;
	n = dsize - dlen;

	if (n-- == 0)
		return(dlen + strlen(src));
	while (*src != '\0') {
		if (n != 0) {
			*dst++ = *src;
			n--;
		}
		src++;
	}
	*dst = '\0';

	return(dlen + (src - osrc));	/* count does not include NUL */
}