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
   8 #include <errno.h>
   9 #include <stddef.h>
  10 #include <stdlib.h>
  11 #include <string.h>
  12
  13 #include "alloc-util.h"
  14 #include "macro.h"
  15 #include "replace-var.h"
  16 #include "string-util.h"
  17
  18 /*
  19  * Generic infrastructure for replacing @FOO@ style variables in
  20  * strings. Will call a callback for each replacement.
  21  */
  22
  23 static int get_variable(const char *b, char **r) {
  24         size_t k;
  25         char *t;
  26
  27         assert(b);
  28         assert(r);
  29
  30         if (*b != '@')
  31                 return 0;
  32
  33         k = strspn(b + 1, UPPERCASE_LETTERS "_");
  34         if (k <= 0 || b[k+1] != '@')
  35                 return 0;
  36
  37         t = strndup(b + 1, k);
  38         if (!t)
  39                 return -ENOMEM;
  40
  41         *r = t;
  42         return 1;
  43 }
  44
  45 char *replace_var(const char *text, char *(*lookup)(const char *variable, void *userdata), void *userdata) {
  46         char *r, *t;
  47         const char *f;
  48         size_t l;
  49
  50         assert(text);
  51         assert(lookup);
  52
  53         l = strlen(text);
  54         r = new(char, l+1);
  55         if (!r)
  56                 return NULL;
  57
  58         f = text;
  59         t = r;
  60         while (*f) {
  61                 _cleanup_free_ char *v = NULL, *n = NULL;
  62                 char *a;
  63                 int k;
  64                 size_t skip, d, nl;
  65
  66                 k = get_variable(f, &v);
  67                 if (k < 0)
  68                         goto oom;
  69                 if (k == 0) {
  70                         *(t++) = *(f++);
  71                         continue;
  72                 }
  73
  74                 n = lookup(v, userdata);
  75                 if (!n)
  76                         goto oom;
  77
  78                 skip = strlen(v) + 2;
  79
  80                 d = t - r;
  81                 nl = l - skip + strlen(n);
  82                 a = realloc(r, nl + 1);
  83                 if (!a)
  84                         goto oom;
  85
  86                 l = nl;
  87                 r = a;
  88                 t = r + d;
  89
  90                 t = stpcpy(t, n);
  91                 f += skip;
  92         }
  93
  94         *t = 0;
  95         return r;
  96
  97 oom:
  98         return mfree(r);
  99 }