src/basic/replace-var.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /***
   3   This file is part of systemd.
   4
   5   Copyright 2012 Lennart Poettering
   6
   7   systemd is free software; you can redistribute it and/or modify it
   8   under the terms of the GNU Lesser General Public License as published by
   9   the Free Software Foundation; either version 2.1 of the License, or
  10   (at your option) any later version.
  11
  12   systemd is distributed in the hope that it will be useful, but
  13   WITHOUT ANY WARRANTY; without even the implied warranty of
  14   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  15   Lesser General Public License for more details.
  16
  17   You should have received a copy of the GNU Lesser General Public License
  18   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  19 ***/
  20
  21 #include <errno.h>
  22 #include <stddef.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25
  26 #include "alloc-util.h"
  27 #include "macro.h"
  28 #include "replace-var.h"
  29 #include "string-util.h"
  30
  31 /*
  32  * Generic infrastructure for replacing @FOO@ style variables in
  33  * strings. Will call a callback for each replacement.
  34  */
  35
  36 static int get_variable(const char *b, char **r) {
  37         size_t k;
  38         char *t;
  39
  40         assert(b);
  41         assert(r);
  42
  43         if (*b != '@')
  44                 return 0;
  45
  46         k = strspn(b + 1, UPPERCASE_LETTERS "_");
  47         if (k <= 0 || b[k+1] != '@')
  48                 return 0;
  49
  50         t = strndup(b + 1, k);
  51         if (!t)
  52                 return -ENOMEM;
  53
  54         *r = t;
  55         return 1;
  56 }
  57
  58 char *replace_var(const char *text, char *(*lookup)(const char *variable, void *userdata), void *userdata) {
  59         char *r, *t;
  60         const char *f;
  61         size_t l;
  62
  63         assert(text);
  64         assert(lookup);
  65
  66         l = strlen(text);
  67         r = new(char, l+1);
  68         if (!r)
  69                 return NULL;
  70
  71         f = text;
  72         t = r;
  73         while (*f) {
  74                 _cleanup_free_ char *v = NULL, *n = NULL;
  75                 char *a;
  76                 int k;
  77                 size_t skip, d, nl;
  78
  79                 k = get_variable(f, &v);
  80                 if (k < 0)
  81                         goto oom;
  82                 if (k == 0) {
  83                         *(t++) = *(f++);
  84                         continue;
  85                 }
  86
  87                 n = lookup(v, userdata);
  88                 if (!n)
  89                         goto oom;
  90
  91                 skip = strlen(v) + 2;
  92
  93                 d = t - r;
  94                 nl = l - skip + strlen(n);
  95                 a = realloc(r, nl + 1);
  96                 if (!a)
  97                         goto oom;
  98
  99                 l = nl;
 100                 r = a;
 101                 t = r + d;
 102
 103                 t = stpcpy(t, n);
 104                 f += skip;
 105         }
 106
 107         *t = 0;
 108         return r;
 109
 110 oom:
 111         return mfree(r);
 112 }