stdlib/canonicalize.c

   1 /* Return the canonical absolute name of a given file.
   2    Copyright (C) 1996, 1997 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Library General Public License as
   7    published by the Free Software Foundation; either version 2 of the
   8    License, or (at your option) any later version.
   9
  10    The GNU C Library 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 GNU
  13    Library General Public License for more details.
  14
  15    You should have received a copy of the GNU Library General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.  */
  19
  20 #include <assert.h>
  21 #include <stdlib.h>
  22 #include <string.h>
  23 #include <unistd.h>
  24 #include <limits.h>
  25 #include <sys/param.h>
  26 #include <sys/stat.h>
  27 #include <errno.h>
  28
  29 /* Return the canonical absolute name of file NAME.  A canonical name
  30    does not contain any `.', `..' components nor any repeated path
  31    separators ('/') or symlinks.  All path components must exist.  If
  32    RESOLVED is null, the result is malloc'd; otherwise, if the
  33    canonical name is PATH_MAX chars or more, returns null with `errno'
  34    set to ENAMETOOLONG; if the name fits in fewer than PATH_MAX chars,
  35    returns the name in RESOLVED.  If the name cannot be resolved and
  36    RESOLVED is non-NULL, it contains the path of the first component
  37    that cannot be resolved.  If the path can be resolved, RESOLVED
  38    holds the same value as the value returned.  */
  39
  40 static char *
  41 canonicalize (const char *name, char *resolved)
  42 {
  43   char *rpath, *dest, *extra_buf = NULL;
  44   const char *start, *end, *rpath_limit;
  45   long int path_max;
  46   int num_links = 0;
  47
  48   if (name == NULL || resolved == NULL)
  49     {
  50       /* As per Single Unix Specification V2 we must return an error if
  51          either parameter is a null pointer.  */
  52       __set_errno (EINVAL);
  53       return NULL;
  54     }
  55
  56   if (name[0] == '\0')
  57     {
  58       /* As per Single Unix Specification V2 we must return an error if
  59          the name argument points to an empty string.  */
  60       __set_errno (ENOENT);
  61       return NULL;
  62     }
  63
  64 #ifdef PATH_MAX
  65   path_max = PATH_MAX;
  66 #else
  67   path_max = pathconf (name, _PC_PATH_MAX);
  68   if (path_max <= 0)
  69     path_max = 1024;
  70 #endif
  71
  72   rpath = resolved ? __alloca (path_max) : malloc (path_max);
  73   rpath_limit = rpath + path_max;
  74
  75   if (name[0] != '/')
  76     {
  77       if (!getcwd (rpath, path_max))
  78         goto error;
  79       dest = strchr (rpath, '\0');
  80     }
  81   else
  82     {
  83       rpath[0] = '/';
  84       dest = rpath + 1;
  85     }
  86
  87   for (start = end = name; *start; start = end)
  88     {
  89       struct stat st;
  90       int n;
  91
  92       /* Skip sequence of multiple path-separators.  */
  93       while (*start == '/') ++start;
  94
  95       /* Find end of path component.  */
  96       for (end = start; *end && *end != '/'; ++end);
  97
  98       if (end - start == 0)
  99         break;
 100       else if (strncmp (start, ".", end - start) == 0)
 101         /* nothing */;
 102       else if (strncmp (start, "..", end - start) == 0)
 103         {
 104           /* Back up to previous component, ignore if at root already.  */
 105           if (dest > rpath + 1)
 106             while ((--dest)[-1] != '/');
 107         }
 108       else
 109         {
 110           size_t new_size;
 111
 112           if (dest[-1] != '/')
 113             *dest++ = '/';
 114
 115           if (dest + (end - start) >= rpath_limit)
 116             {
 117               if (resolved)
 118                 {
 119                   __set_errno (ENAMETOOLONG);
 120                   goto error;
 121                 }
 122               new_size = rpath_limit - rpath;
 123               if (end - start + 1 > path_max)
 124                 new_size += end - start + 1;
 125               else
 126                 new_size += path_max;
 127               rpath = realloc (rpath, new_size);
 128               rpath_limit = rpath + new_size;
 129               if (!rpath)
 130                 return NULL;
 131             }
 132
 133           dest = __mempcpy (dest, start, end - start);
 134           *dest = '\0';
 135
 136           if (__lstat (rpath, &st) < 0)
 137             goto error;
 138
 139           if (S_ISLNK (st.st_mode))
 140             {
 141               char *buf = __alloca (path_max);
 142               size_t len;
 143
 144               if (++num_links > MAXSYMLINKS)
 145                 {
 146                   __set_errno (ELOOP);
 147                   goto error;
 148                 }
 149
 150               n = readlink (rpath, buf, path_max);
 151               if (n < 0)
 152                 goto error;
 153               buf[n] = '\0';
 154
 155               if (!extra_buf)
 156                 extra_buf = __alloca (path_max);
 157
 158               len = strlen (end);
 159               if ((long int) (n + len) >= path_max)
 160                 {
 161                   __set_errno (ENAMETOOLONG);
 162                   goto error;
 163                 }
 164
 165               /* Careful here, end may be a pointer into extra_buf... */
 166               memmove (&extra_buf[n], end, len + 1);
 167               memcpy (extra_buf, buf, n);
 168               name = end = extra_buf;
 169
 170               if (buf[0] == '/')
 171                 dest = rpath + 1;       /* It's an absolute symlink */
 172               else
 173                 /* Back up to previous component, ignore if at root already: */
 174                 if (dest > rpath + 1)
 175                   while ((--dest)[-1] != '/');
 176             }
 177           else
 178             num_links = 0;
 179         }
 180     }
 181   if (dest > rpath + 1 && dest[-1] == '/')
 182     --dest;
 183   *dest = '\0';
 184
 185   return resolved ? strcpy (resolved, rpath) : rpath;
 186
 187 error:
 188   if (resolved)
 189     strcpy (resolved, rpath);
 190   else
 191     free (rpath);
 192   return NULL;
 193 }
 194 weak_alias (canonicalize, realpath)
 195
 196
 197 char *
 198 canonicalize_file_name (const char *name)
 199 {
 200   return canonicalize (name, NULL);
 201 }