1/*
2 * Copyright (c) 1997 Shigio Yamaguchi. All rights reserved.
3 * Copyright (c) 1999 Tama Communications Corporation. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 *
26 * $FreeBSD$
27 */
28#include <errno.h>
29#include <stdlib.h>
30#include <string.h>
31#include "pathconv.h" /* prototypes */
32/*
33 * abs2rel: convert an absolute path name into relative.
34 *
35 *	i)	path	absolute path
36 *	i)	base	base directory (must be absolute path)
37 *	o)	result	result buffer
38 *	i)	size	size of result buffer
39 *	r)		!= NULL: relative path
40 *			== NULL: error
41 */
42char *
43abs2rel(const char *path, const char *base, char *result, const size_t size)
44{
45	const char *pp, *bp, *branch;
46	/*
47	 * endp points the last position which is safe in the result buffer.
48	 */
49	const char *endp = result + size - 1;
50	char *rp;
51
52	if (*path != '/') {
53		if (strlen(path) >= size)
54			goto erange;
55		strcpy(result, path);
56		goto finish;
57	} else if (*base != '/' || !size) {
58		errno = EINVAL;
59		return (NULL);
60	} else if (size == 1)
61		goto erange;
62	/*
63	 * seek to branched point.
64	 */
65	branch = path;
66	for (pp = path, bp = base; *pp && *bp && *pp == *bp; pp++, bp++)
67		if (*pp == '/')
68			branch = pp;
69	if ((*pp == 0 || (*pp == '/' && *(pp + 1) == 0)) &&
70	    (*bp == 0 || (*bp == '/' && *(bp + 1) == 0))) {
71		rp = result;
72		*rp++ = '.';
73		if (*pp == '/' || *(pp - 1) == '/')
74			*rp++ = '/';
75		if (rp > endp)
76			goto erange;
77		*rp = 0;
78		goto finish;
79	}
80	if ((*pp == 0 && *bp == '/') || (*pp == '/' && *bp == 0))
81		branch = pp;
82	/*
83	 * up to root.
84	 */
85	rp = result;
86	for (bp = base + (branch - path); *bp; bp++)
87		if (*bp == '/' && *(bp + 1) != 0) {
88			if (rp + 3 > endp)
89				goto erange;
90			*rp++ = '.';
91			*rp++ = '.';
92			*rp++ = '/';
93		}
94	if (rp > endp)
95		goto erange;
96	*rp = 0;
97	/*
98	 * down to leaf.
99	 */
100	if (*branch) {
101		if (rp + strlen(branch + 1) > endp)
102			goto erange;
103		strcpy(rp, branch + 1);
104	} else
105		*--rp = 0;
106finish:
107	return result;
108erange:
109	errno = ERANGE;
110	return (NULL);
111}
112