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#include <err.h>
13#include <stdbool.h>
14#include <stdlib.h>
15#include <string.h>
16#include <unistd.h>
17
18bool	strnsubst(char **, const char *, const char *, size_t);
19
20/*
21 * Replaces str with a string consisting of str with match replaced with
22 * replstr as many times as can be done before the constructed string is
23 * maxsize bytes large.  It does not free the string pointed to by str, it
24 * is up to the calling program to be sure that the original contents of
25 * str as well as the new contents are handled in an appropriate manner.
26 * If replstr is NULL, then that internally is changed to a nil-string, so
27 * that we can still pretend to do somewhat meaningful substitution.
28 *
29 * Returns true if truncation was needed to do the replacement, false if
30 * truncation was not required.
31 */
32bool
33strnsubst(char **str, const char *match, const char *replstr, size_t maxsize)
34{
35	char *s1, *s2, *this;
36	bool error = false;
37
38	s1 = *str;
39	if (s1 == NULL)
40		return false;
41	/*
42	 * If maxsize is 0 then set it to the length of s1, because we have
43	 * to duplicate s1.  XXX we maybe should double-check whether the match
44	 * appears in s1.  If it doesn't, then we also have to set the length
45	 * to the length of s1, to avoid modifying the argument.  It may make
46	 * sense to check if maxsize is <= strlen(s1), because in that case we
47	 * want to return the unmodified string, too.
48	 */
49	if (maxsize == 0) {
50		match = NULL;
51		maxsize = strlen(s1) + 1;
52	}
53	s2 = calloc(1, maxsize);
54	if (s2 == NULL)
55		err(1, "calloc");
56
57	if (replstr == NULL)
58		replstr = "";
59
60	if (match == NULL || replstr == NULL || maxsize == strlen(s1)) {
61		strlcpy(s2, s1, maxsize);
62		goto done;
63	}
64
65	for (;;) {
66		this = strstr(s1, match);
67		if (this == NULL)
68			break;
69		if ((strlen(s2) + strlen(s1) + strlen(replstr) -
70		    strlen(match) + 1) > maxsize) {
71			strlcat(s2, s1, maxsize);
72			error = true;
73			goto done;
74		}
75		strncat(s2, s1, (uintptr_t)this - (uintptr_t)s1);
76		strcat(s2, replstr);
77		s1 = this + strlen(match);
78	}
79	strcat(s2, s1);
80done:
81	*str = s2;
82	return error;
83}
84
85#ifdef TEST
86#include <stdio.h>
87
88int
89main(void)
90{
91	char *x, *y, *z, *za;
92
93	x = "{}%$";
94	strnsubst(&x, "%$", "{} enpury!", 255);
95	y = x;
96	strnsubst(&y, "}{}", "ybir", 255);
97	z = y;
98	strnsubst(&z, "{", "v ", 255);
99	za = z;
100	strnsubst(&z, NULL, za, 255);
101	if (strcmp(z, "v ybir enpury!") == 0)
102		printf("strnsubst() seems to work!\n");
103	else
104		printf("strnsubst() is broken.\n");
105	printf("%s\n", z);
106	free(x);
107	free(y);
108	free(z);
109	free(za);
110	return 0;
111}
112#endif
113