usr.bin/xargs/strnsubst.c

   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  * $FreeBSD: head/usr.bin/xargs/strnsubst.c 327230 2017-12-27 03:23:01Z eadler $
  11  */
  12
  13 #include <err.h>
  14 #include <stdbool.h>
  15 #include <stdint.h>
  16 #include <stdlib.h>
  17 #include <string.h>
  18 #include <unistd.h>
  19
  20 bool   strnsubst(char **, const char *, const char *, size_t);
  21
  22 /*
  23  * Replaces str with a string consisting of str with match replaced with
  24  * replstr as many times as can be done before the constructed string is
  25  * maxsize bytes large.  It does not free the string pointed to by str, it
  26  * is up to the calling program to be sure that the original contents of
  27  * str as well as the new contents are handled in an appropriate manner.
  28  * If replstr is NULL, then that internally is changed to a nil-string, so
  29  * that we can still pretend to do somewhat meaningful substitution.
  30  * Returns true if truncation was needed to do the replacement, false if
  31  * truncation was not required.
  32  */
  33 bool
  34 strnsubst(char **str, const char *match, const char *replstr, size_t maxsize)
  35 {
  36         char *s1, *s2, *this;
  37         bool error = false;
  38
  39         s1 = *str;
  40         if (s1 == NULL)
  41                 return false;
  42         /*
  43          * If maxsize is 0 then set it to the length of s1, because we have
  44          * to duplicate s1.  XXX we maybe should double-check whether the match
  45          * appears in s1.  If it doesn't, then we also have to set the length
  46          * to the length of s1, to avoid modifying the argument.  It may make
  47          * sense to check if maxsize is <= strlen(s1), because in that case we
  48          * want to return the unmodified string, too.
  49          */
  50         if (maxsize == 0) {
  51                 match = NULL;
  52                 maxsize = strlen(s1) + 1;
  53         }
  54         s2 = calloc(1, maxsize);
  55         if (s2 == NULL)
  56                 err(1, "calloc");
  57
  58         if (replstr == NULL)
  59                 replstr = "";
  60
  61         if (match == NULL || replstr == NULL || maxsize == strlen(s1)) {
  62                 strlcpy(s2, s1, maxsize);
  63                 goto done;
  64         }
  65
  66         for (;;) {
  67                 this = strstr(s1, match);
  68                 if (this == NULL)
  69                         break;
  70                 if ((strlen(s2) + strlen(s1) + strlen(replstr) -
  71                     strlen(match) + 1) > maxsize) {
  72                         strlcat(s2, s1, maxsize);
  73                         error = true;
  74                         goto done;
  75                 }
  76                 strncat(s2, s1, (uintptr_t)this - (uintptr_t)s1);
  77                 strcat(s2, replstr);
  78                 s1 = this + strlen(match);
  79         }
  80         strcat(s2, s1);
  81 done:
  82         *str = s2;
  83         return error;
  84 }
  85
  86 #ifdef TEST
  87 #include <stdio.h>
  88
  89 int
  90 main(void)
  91 {
  92         char *x, *y, *z, *za;
  93
  94         x = "{}%$";
  95         strnsubst(&x, "%$", "{} enpury!", 255);
  96         y = x;
  97         strnsubst(&y, "}{}", "ybir", 255);
  98         z = y;
  99         strnsubst(&z, "{", "v ", 255);
 100         za = z;
 101         strnsubst(&z, NULL, za, 255);
 102         if (strcmp(z, "v ybir enpury!") == 0)
 103                 printf("strnsubst() seems to work!\n");
 104         else
 105                 printf("strnsubst() is broken.\n");
 106         printf("%s\n", z);
 107         free(x);
 108         free(y);
 109         free(z);
 110         free(za);
 111         return 0;
 112 }
 113 #endif