src/basic/replace-var.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <errno.h>
   4 #include <stddef.h>
   5 #include <stdlib.h>
   6
   7 #include "alloc-util.h"
   8 #include "macro.h"
   9 #include "replace-var.h"
  10 #include "string-util.h"
  11
  12 /*
  13  * Generic infrastructure for replacing @FOO@ style variables in
  14  * strings. Will call a callback for each replacement.
  15  */
  16
  17 static int get_variable(const char *b, char **r) {
  18         size_t k;
  19         char *t;
  20
  21         assert(b);
  22         assert(r);
  23
  24         if (*b != '@')
  25                 return 0;
  26
  27         k = strspn(b + 1, UPPERCASE_LETTERS "_");
  28         if (k <= 0 || b[k+1] != '@')
  29                 return 0;
  30
  31         t = strndup(b + 1, k);
  32         if (!t)
  33                 return -ENOMEM;
  34
  35         *r = t;
  36         return 1;
  37 }
  38
  39 char *replace_var(const char *text, char *(*lookup)(const char *variable, void *userdata), void *userdata) {
  40         char *r, *t;
  41         const char *f;
  42         size_t l;
  43
  44         assert(text);
  45         assert(lookup);
  46
  47         l = strlen(text);
  48         r = new(char, l+1);
  49         if (!r)
  50                 return NULL;
  51
  52         f = text;
  53         t = r;
  54         while (*f) {
  55                 _cleanup_free_ char *v = NULL, *n = NULL;
  56                 char *a;
  57                 int k;
  58                 size_t skip, d, nl;
  59
  60                 k = get_variable(f, &v);
  61                 if (k < 0)
  62                         goto oom;
  63                 if (k == 0) {
  64                         *(t++) = *(f++);
  65                         continue;
  66                 }
  67
  68                 n = lookup(v, userdata);
  69                 if (!n)
  70                         goto oom;
  71
  72                 skip = strlen(v) + 2;
  73
  74                 d = t - r;
  75                 nl = l - skip + strlen(n);
  76                 a = realloc(r, nl + 1);
  77                 if (!a)
  78                         goto oom;
  79
  80                 l = nl;
  81                 r = a;
  82                 t = r + d;
  83
  84                 t = stpcpy(t, n);
  85                 f += skip;
  86         }
  87
  88         *t = 0;
  89         return r;
  90
  91 oom:
  92         return mfree(r);
  93 }