lib/filenamecat-lgpl.c

   1 /* Concatenate two arbitrary file names.
   2
   3    Copyright (C) 1996-2007, 2009-2020 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* Written by Jim Meyering.  */
  19
  20 #include <config.h>
  21
  22 /* Specification.  */
  23 #include "filenamecat.h"
  24
  25 #include <stdlib.h>
  26 #include <string.h>
  27
  28 #include "basename-lgpl.h"
  29 #include "filename.h"
  30
  31 #if ! HAVE_MEMPCPY && ! defined mempcpy
  32 # define mempcpy(D, S, N) ((void *) ((char *) memcpy (D, S, N) + (N)))
  33 #endif
  34
  35 /* Concatenate two file name components, DIR and BASE, in
  36    newly-allocated storage and return the result.
  37    The resulting file name F is such that the commands "ls F" and "(cd
  38    DIR; ls ./BASE)" refer to the same file.  If necessary, put
  39    a separator between DIR and BASE in the result.  Typically this
  40    separator is "/", but in rare cases it might be ".".
  41    In any case, if BASE_IN_RESULT is non-NULL, set
  42    *BASE_IN_RESULT to point to the copy of BASE at the end of the
  43    returned concatenation.
  44
  45    If malloc fails, return NULL with errno set.  */
  46
  47 char *
  48 mfile_name_concat (char const *dir, char const *base, char **base_in_result)
  49 {
  50   char const *dirbase = last_component (dir);
  51   size_t dirbaselen = base_len (dirbase);
  52   size_t dirlen = dirbase - dir + dirbaselen;
  53   size_t baselen = strlen (base);
  54   char sep = '\0';
  55   if (dirbaselen)
  56     {
  57       /* DIR is not a file system root, so separate with / if needed.  */
  58       if (! ISSLASH (dir[dirlen - 1]) && ! ISSLASH (*base))
  59         sep = '/';
  60     }
  61   else if (ISSLASH (*base))
  62     {
  63       /* DIR is a file system root and BASE begins with a slash, so
  64          separate with ".".  For example, if DIR is "/" and BASE is
  65          "/foo" then return "/./foo", as "//foo" would be wrong on
  66          some POSIX systems.  A fancier algorithm could omit "." in
  67          some cases but is not worth the trouble.  */
  68       sep = '.';
  69     }
  70
  71   char *p_concat = malloc (dirlen + (sep != '\0')  + baselen + 1);
  72   if (p_concat == NULL)
  73     return NULL;
  74
  75   {
  76     char *p;
  77
  78     p = mempcpy (p_concat, dir, dirlen);
  79     *p = sep;
  80     p += sep != '\0';
  81
  82     if (base_in_result)
  83       *base_in_result = p;
  84
  85     p = mempcpy (p, base, baselen);
  86     *p = '\0';
  87   }
  88
  89   return p_concat;
  90 }