1/* Concatenate two arbitrary file names.
2
3   Copyright (C) 1996-2007, 2009-2022 Free Software Foundation, Inc.
4
5   This file is free software: you can redistribute it and/or modify
6   it under the terms of the GNU Lesser General Public License as
7   published by the Free Software Foundation; either version 2.1 of the
8   License, or (at your option) any later version.
9
10   This file 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 Lesser General Public License for more details.
14
15   You should have received a copy of the GNU Lesser 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
47char *
48mfile_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}
91