src/basic/replace-var.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /***
   3   Copyright 2012 Lennart Poettering
   4 ***/
   5
   6 #include <errno.h>
   7 #include <stddef.h>
   8 #include <stdlib.h>
   9 #include <string.h>
  10
  11 #include "alloc-util.h"
  12 #include "macro.h"
  13 #include "replace-var.h"
  14 #include "string-util.h"
  15
  16 /*
  17  * Generic infrastructure for replacing @FOO@ style variables in
  18  * strings. Will call a callback for each replacement.
  19  */
  20
  21 static int get_variable(const char *b, char **r) {
  22         size_t k;
  23         char *t;
  24
  25         assert(b);
  26         assert(r);
  27
  28         if (*b != '@')
  29                 return 0;
  30
  31         k = strspn(b + 1, UPPERCASE_LETTERS "_");
  32         if (k <= 0 || b[k+1] != '@')
  33                 return 0;
  34
  35         t = strndup(b + 1, k);
  36         if (!t)
  37                 return -ENOMEM;
  38
  39         *r = t;
  40         return 1;
  41 }
  42
  43 char *replace_var(const char *text, char *(*lookup)(const char *variable, void *userdata), void *userdata) {
  44         char *r, *t;
  45         const char *f;
  46         size_t l;
  47
  48         assert(text);
  49         assert(lookup);
  50
  51         l = strlen(text);
  52         r = new(char, l+1);
  53         if (!r)
  54                 return NULL;
  55
  56         f = text;
  57         t = r;
  58         while (*f) {
  59                 _cleanup_free_ char *v = NULL, *n = NULL;
  60                 char *a;
  61                 int k;
  62                 size_t skip, d, nl;
  63
  64                 k = get_variable(f, &v);
  65                 if (k < 0)
  66                         goto oom;
  67                 if (k == 0) {
  68                         *(t++) = *(f++);
  69                         continue;
  70                 }
  71
  72                 n = lookup(v, userdata);
  73                 if (!n)
  74                         goto oom;
  75
  76                 skip = strlen(v) + 2;
  77
  78                 d = t - r;
  79                 nl = l - skip + strlen(n);
  80                 a = realloc(r, nl + 1);
  81                 if (!a)
  82                         goto oom;
  83
  84                 l = nl;
  85                 r = a;
  86                 t = r + d;
  87
  88                 t = stpcpy(t, n);
  89                 f += skip;
  90         }
  91
  92         *t = 0;
  93         return r;
  94
  95 oom:
  96         return mfree(r);
  97 }