lib/path_searcher.c

   1 /*
   2     libpsh/path_searcher.c - path searcher
   3     Copyright 2020 Zhang Maiyun.
   4
   5     This file is part of Psh, P shell.
   6
   7     Psh is free software: you can redistribute it and/or modify
   8     it under the terms of the GNU General Public License as published by
   9     the Free Software Foundation, either version 3 of the License, or
  10     (at your option) any later version.
  11
  12     Psh is distributed in the hope that it will be useful,
  13     but WITHOUT ANY WARRANTY; without even the implied warranty of
  14     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15     GNU General Public License for more details.
  16
  17     You should have received a copy of the GNU General Public License
  18     along with this program.  If not, see <https://www.gnu.org/licenses/>.
  19  */
  20
  21 #include <stddef.h>
  22 #include <string.h>
  23
  24 #include "libpsh/xmalloc.h"
  25
  26 /* Call CHK_FUNC on each (substr + TARGET) concatenated string in PATH
  27  * separated by SEPARATOR.
  28  * Returns the first concatenated string for which CHK_FUNC returns non-zero;
  29  * or NULL if none succeeded. Result should be free()d */
  30 char *psh_search_path(const char *path, int separator, const char *target,
  31                       int (*chk_func)(const char *))
  32 {
  33     /* +1 for '\0' */
  34     size_t len_substr, len_target = strlen(target) + 1,
  35                        size_allocated = 2 * len_target;
  36     char *concatenated = xmalloc(size_allocated), *occur = (char *)1;
  37
  38     while (occur)
  39     {
  40         occur = strchr(path, separator);
  41         len_substr = occur ? (size_t)(occur - path) : strlen(path);
  42
  43         /* Realloc concatenated if it's too small */
  44         if (len_substr + len_target > size_allocated)
  45         {
  46             size_allocated = len_target + len_substr;
  47             concatenated = xrealloc(concatenated, size_allocated);
  48         }
  49
  50         /* Copy substr */
  51         memcpy(concatenated, path, len_substr);
  52         /* Copy target str */
  53         memcpy(concatenated + len_substr, target, len_target);
  54         /* End string */
  55         *(concatenated + len_target + len_substr - 1) = 0;
  56         if (chk_func(concatenated))
  57             return concatenated;
  58         /* Jump over the substr */
  59         path += len_substr + 1; /* +1 for separator */
  60     }
  61     xfree(concatenated);
  62     return NULL;
  63 }