interpolate.c

   1 /*
   2  * Copyright 2006 Jon Loeliger
   3  */
   4
   5 #include <string.h>
   6
   7 #include "interpolate.h"
   8
   9
  10 /*
  11  * Convert a NUL-terminated string in buffer orig
  12  * into the supplied buffer, result, whose length is reslen,
  13  * performing substitutions on %-named sub-strings from
  14  * the table, interps, with ninterps entries.
  15  *
  16  * Example interps:
  17  *    {
  18  *        { "%H", "example.org"},
  19  *        { "%port", "123"},
  20  *        { "%%", "%"},
  21  *    }
  22  *
  23  * Returns 1 on a successful substitution pass that fits in result,
  24  * Returns 0 on a failed or overflowing substitution pass.
  25  */
  26
  27 int interpolate(char *result, int reslen,
  28                 const char *orig,
  29                 const struct interp *interps, int ninterps)
  30 {
  31         const char *src = orig;
  32         char *dest = result;
  33         int newlen = 0;
  34         char *name, *value;
  35         int namelen, valuelen;
  36         int i;
  37         char c;
  38
  39         memset(result, 0, reslen);
  40
  41         while ((c = *src) && newlen < reslen - 1) {
  42                 if (c == '%') {
  43                         /* Try to match an interpolation string. */
  44                         for (i = 0; i < ninterps; i++) {
  45                                 name = interps[i].name;
  46                                 namelen = strlen(name);
  47                                 if (strncmp(src, name, namelen) == 0) {
  48                                         break;
  49                                 }
  50                         }
  51
  52                         /* Check for valid interpolation. */
  53                         if (i < ninterps) {
  54                                 value = interps[i].value;
  55                                 valuelen = strlen(value);
  56
  57                                 if (newlen + valuelen < reslen - 1) {
  58                                         /* Substitute. */
  59                                         strncpy(dest, value, valuelen);
  60                                         newlen += valuelen;
  61                                         dest += valuelen;
  62                                         src += namelen;
  63                                 } else {
  64                                         /* Something's not fitting. */
  65                                         return 0;
  66                                 }
  67
  68                         } else {
  69                                 /* Skip bogus interpolation. */
  70                                 *dest++ = *src++;
  71                                 newlen++;
  72                         }
  73
  74                 } else {
  75                         /* Straight copy one non-interpolation character. */
  76                         *dest++ = *src++;
  77                         newlen++;
  78                 }
  79         }
  80
  81         return newlen < reslen - 1;
  82 }