stdlib/canonicalize.c

   1 /* Return the canonical absolute name of a given file.
   2    Copyright (C) 1996, 1997, 1998 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)
  49     {
  50       /* As per Single Unix Specification V2 we must return an error if
  51          either parameter is a null pointer.  We extend this to allow
  52          the RESOLVED parameter be NULL in case the we are expected to
  53          allocate the room for the return value.  */
  54       __set_errno (EINVAL);
  55       return NULL;
  56     }
  57
  58   if (name[0] == '\0')
  59     {
  60       /* As per Single Unix Specification V2 we must return an error if
  61          the name argument points to an empty string.  */
  62       __set_errno (ENOENT);
  63       return NULL;
  64     }
  65
  66 #ifdef PATH_MAX
  67   path_max = PATH_MAX;
  68 #else
  69   path_max = pathconf (name, _PC_PATH_MAX);
  70   if (path_max <= 0)
  71     path_max = 1024;
  72 #endif
  73
  74   rpath = resolved ? __alloca (path_max) : malloc (path_max);
  75   rpath_limit = rpath + path_max;
  76
  77   if (name[0] != '/')
  78     {
  79       if (!__getcwd (rpath, path_max))
  80         goto error;
  81       dest = strchr (rpath, '\0');
  82     }
  83   else
  84     {
  85       rpath[0] = '/';
  86       dest = rpath + 1;
  87     }
  88
  89   for (start = end = name; *start; start = end)
  90     {
  91       struct stat st;
  92       int n;
  93
  94       /* Skip sequence of multiple path-separators.  */
  95       while (*start == '/') ++start;
  96
  97       /* Find end of path component.  */
  98       for (end = start; *end && *end != '/'; ++end);
  99
 100       if (end - start == 0)
 101         break;
 102       else if (strncmp (start, ".", end - start) == 0)
 103         /* nothing */;
 104       else if (strncmp (start, "..", end - start) == 0)
 105         {
 106           /* Back up to previous component, ignore if at root already.  */
 107           if (dest > rpath + 1)
 108             while ((--dest)[-1] != '/');
 109         }
 110       else
 111         {
 112           size_t new_size;
 113
 114           if (dest[-1] != '/')
 115             *dest++ = '/';
 116
 117           if (dest + (end - start) >= rpath_limit)
 118             {
 119               if (resolved)
 120                 {
 121                   __set_errno (ENAMETOOLONG);
 122                   goto error;
 123                 }
 124               new_size = rpath_limit - rpath;
 125               if (end - start + 1 > path_max)
 126                 new_size += end - start + 1;
 127               else
 128                 new_size += path_max;
 129               rpath = realloc (rpath, new_size);
 130               rpath_limit = rpath + new_size;
 131               if (!rpath)
 132                 return NULL;
 133             }
 134
 135           dest = __mempcpy (dest, start, end - start);
 136           *dest = '\0';
 137
 138           if (__lxstat (_STAT_VER, rpath, &st) < 0)
 139             goto error;
 140
 141           if (S_ISLNK (st.st_mode))
 142             {
 143               char *buf = __alloca (path_max);
 144               size_t len;
 145
 146               if (++num_links > MAXSYMLINKS)
 147                 {
 148                   __set_errno (ELOOP);
 149                   goto error;
 150                 }
 151
 152               n = __readlink (rpath, buf, path_max);
 153               if (n < 0)
 154                 goto error;
 155               buf[n] = '\0';
 156
 157               if (!extra_buf)
 158                 extra_buf = __alloca (path_max);
 159
 160               len = strlen (end);
 161               if ((long int) (n + len) >= path_max)
 162                 {
 163                   __set_errno (ENAMETOOLONG);
 164                   goto error;
 165                 }
 166
 167               /* Careful here, end may be a pointer into extra_buf... */
 168               memmove (&extra_buf[n], end, len + 1);
 169               memcpy (extra_buf, buf, n);
 170               name = end = extra_buf;
 171
 172               if (buf[0] == '/')
 173                 dest = rpath + 1;       /* It's an absolute symlink */
 174               else
 175                 /* Back up to previous component, ignore if at root already: */
 176                 if (dest > rpath + 1)
 177                   while ((--dest)[-1] != '/');
 178             }
 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
 195
 196 char *
 197 __realpath (const char *name, char *resolved)
 198 {
 199   if (resolved == NULL)
 200     {
 201       __set_errno (EINVAL);
 202       return NULL;
 203     }
 204
 205   return canonicalize (name, resolved);
 206 }
 207 weak_alias (__realpath, realpath)
 208
 209
 210 char *
 211 __canonicalize_file_name (const char *name)
 212 {
 213   return canonicalize (name, NULL);
 214 }
 215 weak_alias (__canonicalize_file_name, canonicalize_file_name)