src/basic/replace-var.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <errno.h>
   4 #include <stddef.h>
   5 #include <stdlib.h>
   6 #include <string.h>
   7
   8 #include "alloc-util.h"
   9 #include "macro.h"
  10 #include "replace-var.h"
  11 #include "string-util.h"
  12
  13 /*
  14  * Generic infrastructure for replacing @FOO@ style variables in
  15  * strings. Will call a callback for each replacement.
  16  */
  17
  18 static int get_variable(const char *b, char **r) {
  19         size_t k;
  20         char *t;
  21
  22         assert(b);
  23         assert(r);
  24
  25         if (*b != '@')
  26                 return 0;
  27
  28         k = strspn(b + 1, UPPERCASE_LETTERS "_");
  29         if (k <= 0 || b[k+1] != '@')
  30                 return 0;
  31
  32         t = strndup(b + 1, k);
  33         if (!t)
  34                 return -ENOMEM;
  35
  36         *r = t;
  37         return 1;
  38 }
  39
  40 char *replace_var(const char *text, char *(*lookup)(const char *variable, void *userdata), void *userdata) {
  41         char *r, *t;
  42         const char *f;
  43         size_t l;
  44
  45         assert(text);
  46         assert(lookup);
  47
  48         l = strlen(text);
  49         r = new(char, l+1);
  50         if (!r)
  51                 return NULL;
  52
  53         f = text;
  54         t = r;
  55         while (*f) {
  56                 _cleanup_free_ char *v = NULL, *n = NULL;
  57                 char *a;
  58                 int k;
  59                 size_t skip, d, nl;
  60
  61                 k = get_variable(f, &v);
  62                 if (k < 0)
  63                         goto oom;
  64                 if (k == 0) {
  65                         *(t++) = *(f++);
  66                         continue;
  67                 }
  68
  69                 n = lookup(v, userdata);
  70                 if (!n)
  71                         goto oom;
  72
  73                 skip = strlen(v) + 2;
  74
  75                 d = t - r;
  76                 nl = l - skip + strlen(n);
  77                 a = realloc(r, nl + 1);
  78                 if (!a)
  79                         goto oom;
  80
  81                 l = nl;
  82                 r = a;
  83                 t = r + d;
  84
  85                 t = stpcpy(t, n);
  86                 f += skip;
  87         }
  88
  89         *t = 0;
  90         return r;
  91
  92 oom:
  93         return mfree(r);
  94 }