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- Modify realpath() not to alter process wide state current working
  directory.  Strategy from FreeBSD.  Addess PR#28986.
- Make realpath() to return an error when null string is passed or
  the last component is symlink to null string.  The kernel lookup
  routine returns an error if such path are passed.

/*	$NetBSD: getcwd.c,v 1.36 2005/01/30 22:37:32 enami Exp $	*/

/*
 * Copyright (c) 1989, 1991, 1993, 1995
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Jan-Simon Pendry.
 *
 * 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.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 */

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
#if 0
static char sccsid[] = "@(#)getcwd.c	8.5 (Berkeley) 2/7/95";
#else
__RCSID("$NetBSD: getcwd.c,v 1.36 2005/01/30 22:37:32 enami Exp $");
#endif
#endif /* LIBC_SCCS and not lint */

#include "namespace.h"
#include <sys/param.h>
#include <sys/stat.h>

#include <assert.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "extern.h"

#ifdef __weak_alias
__weak_alias(getcwd,_getcwd)
__weak_alias(realpath,_realpath)
#endif

/*
 * char *realpath(const char *path, char resolved[MAXPATHLEN]);
 *
 * Find the real name of path, by removing all ".", ".." and symlink
 * components.  Returns (resolved) on success, or (NULL) on failure,
 * in which case the path which caused trouble is left in (resolved).
 */
char *
realpath(const char *path, char *resolved)
{
	struct stat sb;
	int idx = 0, n, nlnk = 0, serrno = errno;
	const char *q;
	char *p, wbuf[2][MAXPATHLEN];
	size_t len;

	_DIAGASSERT(path != NULL);
	_DIAGASSERT(resolved != NULL);

	/*
	 * Build real path one by one with paying an attention to .,
	 * .. and symbolic link.
	 */

	/*
	 * `p' is where we'll put a new component with prepending
	 * a delimiter.
	 */
	p = resolved;

	if (*path == 0) {
		*p = 0;
		errno = ENOENT;
		return (NULL);
	}

	/* If relative path, start from current working directory. */
	if (*path != '/') {
		if (getcwd(resolved, MAXPATHLEN) == NULL) {
			p[0] = '.';
			p[1] = 0;
			return (NULL);
		}
		len = strlen(resolved);
		if (len > 1)
			p += len;
	}

loop:
	/* Skip any slash. */
	while (*path == '/')
		path++;

	if (*path == 0) {
		if (p == resolved)
			*p++ = '/';
		*p = 0;
		return (resolved);
	}

	/* Find the end of this component. */
	q = path;
	do
		q++;
	while (*q != '/' && *q != 0);

	/* Test . or .. */
	if (path[0] == '.') {
		if (q - path == 1) {
			path = q;
			goto loop;
		}
		if (path[1] == '.' && q - path == 2) {
			/* Trim the last component. */
			if (p != resolved)
				while (*--p != '/')
					;
			path = q;
			goto loop;
		}
	}

	/* Append this component. */
	if (p - resolved + 1 + q - path + 1 > MAXPATHLEN) {
		errno = ENAMETOOLONG;
		if (p == resolved)
			*p++ = '/';
		*p = 0;
		return (NULL);
	}
	p[0] = '/';
	memcpy(&p[1], path,
	    /* LINTED We know q > path. */
	    q - path);
	p[1 + q - path] = 0;

	/*
	 * If this component is a symlink, toss it and prepend link
	 * target to unresolved path.
	 */
	if (lstat(resolved, &sb) == -1) {
		/* Allow nonexistent component if this is the last one. */
		if (*q == 0 && errno == ENOENT) {
			errno = serrno;
			return (resolved);
		}
		return (NULL);
	}
	if (S_ISLNK(sb.st_mode)) {
		if (nlnk++ >= MAXSYMLINKS) {
			errno = ELOOP;
			return (NULL);
		}
		n = readlink(resolved, wbuf[idx], sizeof(wbuf[0]) - 1);
		if (n < 0)
			return (NULL);
		if (n == 0) {
			errno = ENOENT;
			return (NULL);
		}

		/* Append unresolved path to link target and switch to it. */
		if (n + (len = strlen(q)) + 1 > sizeof(wbuf[0])) {
			errno = ENAMETOOLONG;
			return (NULL);
		}
		memcpy(&wbuf[idx][n], q, len + 1);
		path = wbuf[idx];
		idx ^= 1;

		/* If absolute symlink, start from root. */
		if (*path == '/')
			p = resolved;
		goto loop;
	}

	/* Advance both resolved and unresolved path. */
	p += 1 + q - path;
	path = q;
	goto loop;
}

char *
getcwd(char *pt, size_t size)
{
	char *npt;

	/*
	 * If a buffer is specified, the size has to be non-zero.
	 */
	if (pt != NULL) {
		if (size == 0) {
			/* __getcwd(pt, 0) results ERANGE. */
			errno = EINVAL;
			return (NULL);
		}
		if (__getcwd(pt, size) >= 0)
			return (pt);
		return (NULL);
	}

	/*
	 * If no buffer specified by the user, allocate one as necessary.
	 */
	size = 1024 >> 1;
	do {
		if ((npt = realloc(pt, size <<= 1)) == NULL)
			break;
		pt = npt;
		if (__getcwd(pt, size) >= 0)
			return (pt);
	} while (size <= MAXPATHLEN * 4 && errno == ERANGE);

	free(pt);
	return (NULL);
}