realpath.c revision 236769 
1/* $Id: realpath.c,v 1.2 2010/04/21 17:47:49 sjg Exp $ */
2/* from: $NetBSD: getcwd.c,v 1.45 2007/10/26 19:48:14 christos Exp $	*/
3
4/*
5 * Copyright (c) 1989, 1991, 1993, 1995
6 *	The Regents of the University of California.  All rights reserved.
7 *
8 * This code is derived from software contributed to Berkeley by
9 * Jan-Simon Pendry.
10 *
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
13 * are met:
14 * 1. Redistributions of source code must retain the above copyright
15 *    notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 *    notice, this list of conditions and the following disclaimer in the
18 *    documentation and/or other materials provided with the distribution.
19 * 3. Neither the name of the University nor the names of its contributors
20 *    may be used to endorse or promote products derived from this software
21 *    without specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * SUCH DAMAGE.
34 */
35#ifdef HAVE_CONFIG_H
36# include <config.h>
37#endif
38#ifndef HAVE_REALPATH
39
40#include <sys/cdefs.h>
41#include <sys/param.h>
42#include <sys/stat.h>
43
44#include <errno.h>
45#ifdef HAVE_STDLIB_H
46# include <stdlib.h>
47#endif
48#ifdef HAVE_STRING_H
49# include <string.h>
50#endif
51#ifdef HAVE_UNISTD_H
52# include <unistd.h>
53#endif
54
55/*
56 * char *realpath(const char *path, char resolved[MAXPATHLEN]);
57 *
58 * Find the real name of path, by removing all ".", ".." and symlink
59 * components.  Returns (resolved) on success, or (NULL) on failure,
60 * in which case the path which caused trouble is left in (resolved).
61 */
62char *
63realpath(const char *path, char *resolved)
64{
65	struct stat sb;
66	int idx = 0, n, nlnk = 0;
67	const char *q;
68	char *p, wbuf[2][MAXPATHLEN];
69	size_t len;
70
71	if (!path || !resolved || path == resolved)
72		return (NULL);
73
74	/*
75	 * Build real path one by one with paying an attention to .,
76	 * .. and symbolic link.
77	 */
78
79	/*
80	 * `p' is where we'll put a new component with prepending
81	 * a delimiter.
82	 */
83	p = resolved;
84
85	if (*path == 0) {
86		*p = 0;
87		errno = ENOENT;
88		return (NULL);
89	}
90
91	/* If relative path, start from current working directory. */
92	if (*path != '/') {
93		/* check for resolved pointer to appease coverity */
94		if (resolved && getcwd(resolved, MAXPATHLEN) == NULL) {
95			p[0] = '.';
96			p[1] = 0;
97			return (NULL);
98		}
99		len = strlen(resolved);
100		if (len > 1)
101			p += len;
102	}
103
104loop:
105	/* Skip any slash. */
106	while (*path == '/')
107		path++;
108
109	if (*path == 0) {
110		if (p == resolved)
111			*p++ = '/';
112		*p = 0;
113		return (resolved);
114	}
115
116	/* Find the end of this component. */
117	q = path;
118	do
119		q++;
120	while (*q != '/' && *q != 0);
121
122	/* Test . or .. */
123	if (path[0] == '.') {
124		if (q - path == 1) {
125			path = q;
126			goto loop;
127		}
128		if (path[1] == '.' && q - path == 2) {
129			/* Trim the last component. */
130			if (p != resolved)
131				while (*--p != '/')
132					;
133			path = q;
134			goto loop;
135		}
136	}
137
138	/* Append this component. */
139	if (p - resolved + 1 + q - path + 1 > MAXPATHLEN) {
140		errno = ENAMETOOLONG;
141		if (p == resolved)
142			*p++ = '/';
143		*p = 0;
144		return (NULL);
145	}
146	p[0] = '/';
147	memcpy(&p[1], path,
148	    /* LINTED We know q > path. */
149	    q - path);
150	p[1 + q - path] = 0;
151
152	/*
153	 * If this component is a symlink, toss it and prepend link
154	 * target to unresolved path.
155	 */
156	if (lstat(resolved, &sb) == -1) {
157		return (NULL);
158	}
159	if (S_ISLNK(sb.st_mode)) {
160		if (nlnk++ >= MAXSYMLINKS) {
161			errno = ELOOP;
162			return (NULL);
163		}
164		n = readlink(resolved, wbuf[idx], sizeof(wbuf[0]) - 1);
165		if (n < 0)
166			return (NULL);
167		if (n == 0) {
168			errno = ENOENT;
169			return (NULL);
170		}
171
172		/* Append unresolved path to link target and switch to it. */
173		if (n + (len = strlen(q)) + 1 > sizeof(wbuf[0])) {
174			errno = ENAMETOOLONG;
175			return (NULL);
176		}
177		memcpy(&wbuf[idx][n], q, len + 1);
178		path = wbuf[idx];
179		idx ^= 1;
180
181		/* If absolute symlink, start from root. */
182		if (*path == '/')
183			p = resolved;
184		goto loop;
185	}
186	if (*q == '/' && !S_ISDIR(sb.st_mode)) {
187		errno = ENOTDIR;
188		return (NULL);
189	}
190
191	/* Advance both resolved and unresolved path. */
192	p += 1 + q - path;
193	path = q;
194	goto loop;
195}
196#endif
197