1/* $xMach: strnsubst.c,v 1.3 2002/02/23 02:10:24 jmallett Exp $ */
2
3/*
4 * Copyright (c) 2002 J. Mallett.  All rights reserved.
5 * You may do whatever you want with this file as long as
6 * the above copyright and this notice remain intact, along
7 * with the following statement:
8 * 	For the man who taught me vi, and who got too old, too young.
9 */
10
11#include <sys/cdefs.h>
12__FBSDID("$FreeBSD$");
13
14#include <err.h>
15#include <stdlib.h>
16#include <string.h>
17#include <unistd.h>
18
19void	strnsubst(char **, const char *, const char *, size_t);
20
21/*
22 * Replaces str with a string consisting of str with match replaced with
23 * replstr as many times as can be done before the constructed string is
24 * maxsize bytes large.  It does not free the string pointed to by str, it
25 * is up to the calling program to be sure that the original contents of
26 * str as well as the new contents are handled in an appropriate manner.
27 * If replstr is NULL, then that internally is changed to a nil-string, so
28 * that we can still pretend to do somewhat meaningful substitution.
29 * No value is returned.
30 */
31void
32strnsubst(char **str, const char *match, const char *replstr, size_t maxsize)
33{
34	char *s1, *s2, *this;
35
36	s1 = *str;
37	if (s1 == NULL)
38		return;
39	/*
40	 * If maxsize is 0 then set it to to the length of s1, because we have
41	 * to duplicate s1.  XXX we maybe should double-check whether the match
42	 * appears in s1.  If it doesn't, then we also have to set the length
43	 * to the length of s1, to avoid modifying the argument.  It may make
44	 * sense to check if maxsize is <= strlen(s1), because in that case we
45	 * want to return the unmodified string, too.
46	 */
47	if (maxsize == 0) {
48		match = NULL;
49		maxsize = strlen(s1) + 1;
50	}
51	s2 = calloc(maxsize, 1);
52	if (s2 == NULL)
53		err(1, "calloc");
54
55	if (replstr == NULL)
56		replstr = "";
57
58	if (match == NULL || replstr == NULL || maxsize == strlen(s1)) {
59		strlcpy(s2, s1, maxsize);
60		goto done;
61	}
62
63	for (;;) {
64		this = strstr(s1, match);
65		if (this == NULL)
66			break;
67		if ((strlen(s2) + strlen(s1) + strlen(replstr) -
68		    strlen(match) + 1) > maxsize) {
69			strlcat(s2, s1, maxsize);
70			goto done;
71		}
72		strncat(s2, s1, (uintptr_t)this - (uintptr_t)s1);
73		strcat(s2, replstr);
74		s1 = this + strlen(match);
75	}
76	strcat(s2, s1);
77done:
78	*str = s2;
79	return;
80}
81
82#ifdef TEST
83#include <stdio.h>
84
85int
86main(void)
87{
88	char *x, *y, *z, *za;
89
90	x = "{}%$";
91	strnsubst(&x, "%$", "{} enpury!", 255);
92	y = x;
93	strnsubst(&y, "}{}", "ybir", 255);
94	z = y;
95	strnsubst(&z, "{", "v ", 255);
96	za = z;
97	strnsubst(&z, NULL, za, 255);
98	if (strcmp(z, "v ybir enpury!") == 0)
99		printf("strnsubst() seems to work!\n");
100	else
101		printf("strnsubst() is broken.\n");
102	printf("%s\n", z);
103	free(x);
104	free(y);
105	free(z);
106	free(za);
107	return 0;
108}
109#endif
110