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#include <errno.h>
27#include <stdlib.h>
28#include <string.h>
29#include "pathconv.h" /* prototypes */
30/*
31 * abs2rel: convert an absolute path name into relative.
32 *
33 *	i)	path	absolute path
34 *	i)	base	base directory (must be absolute path)
35 *	o)	result	result buffer
36 *	i)	size	size of result buffer
37 *	r)		!= NULL: relative path
38 *			== NULL: error
39 */
40char *
41abs2rel(const char *path, const char *base, char *result, const size_t size)
42{
43	const char *pp, *bp, *branch;
44	/*
45	 * endp points the last position which is safe in the result buffer.
46	 */
47	const char *endp = result + size - 1;
48	char *rp;
49
50	if (*path != '/') {
51		if (strlen(path) >= size)
52			goto erange;
53		strcpy(result, path);
54		goto finish;
55	} else if (*base != '/' || !size) {
56		errno = EINVAL;
57		return (NULL);
58	} else if (size == 1)
59		goto erange;
60	/*
61	 * seek to branched point.
62	 */
63	branch = path;
64	for (pp = path, bp = base; *pp && *bp && *pp == *bp; pp++, bp++)
65		if (*pp == '/')
66			branch = pp;
67	if ((*pp == 0 || (*pp == '/' && *(pp + 1) == 0)) &&
68	    (*bp == 0 || (*bp == '/' && *(bp + 1) == 0))) {
69		rp = result;
70		*rp++ = '.';
71		if (*pp == '/' || *(pp - 1) == '/')
72			*rp++ = '/';
73		if (rp > endp)
74			goto erange;
75		*rp = 0;
76		goto finish;
77	}
78	if ((*pp == 0 && *bp == '/') || (*pp == '/' && *bp == 0))
79		branch = pp;
80	/*
81	 * up to root.
82	 */
83	rp = result;
84	for (bp = base + (branch - path); *bp; bp++)
85		if (*bp == '/' && *(bp + 1) != 0) {
86			if (rp + 3 > endp)
87				goto erange;
88			*rp++ = '.';
89			*rp++ = '.';
90			*rp++ = '/';
91		}
92	if (rp > endp)
93		goto erange;
94	*rp = 0;
95	/*
96	 * down to leaf.
97	 */
98	if (*branch) {
99		if (rp + strlen(branch + 1) > endp)
100			goto erange;
101		strcpy(rp, branch + 1);
102	} else
103		*--rp = 0;
104finish:
105	return result;
106erange:
107	errno = ERANGE;
108	return (NULL);
109}
110