stdlib/canonicalize.c

   1 /* Return the canonical absolute name of a given file.
   2    Copyright (C) 1996, 1997, 1998, 1999 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 <stdlib.h>
  21 #include <string.h>
  22 #include <unistd.h>
  23 #include <limits.h>
  24 #include <sys/param.h>
  25 #include <sys/stat.h>
  26 #include <errno.h>
  27
  28 /* Return the canonical absolute name of file NAME.  A canonical name
  29    does not contain any `.', `..' components nor any repeated path
  30    separators ('/') or symlinks.  All path components must exist.  If
  31    RESOLVED is null, the result is malloc'd; otherwise, if the
  32    canonical name is PATH_MAX chars or more, returns null with `errno'
  33    set to ENAMETOOLONG; if the name fits in fewer than PATH_MAX chars,
  34    returns the name in RESOLVED.  If the name cannot be resolved and
  35    RESOLVED is non-NULL, it contains the path of the first component
  36    that cannot be resolved.  If the path can be resolved, RESOLVED
  37    holds the same value as the value returned.  */
  38
  39 static char *
  40 canonicalize (const char *name, char *resolved)
  41 {
  42   char *rpath, *dest, *extra_buf = NULL;
  43   const char *start, *end, *rpath_limit;
  44   long int path_max;
  45   int num_links = 0;
  46
  47   if (name == NULL)
  48     {
  49       /* As per Single Unix Specification V2 we must return an error if
  50          either parameter is a null pointer.  We extend this to allow
  51          the RESOLVED parameter be NULL in case the we are expected to
  52          allocate the room for the return value.  */
  53       __set_errno (EINVAL);
  54       return NULL;
  55     }
  56
  57   if (name[0] == '\0')
  58     {
  59       /* As per Single Unix Specification V2 we must return an error if
  60          the name argument points to an empty string.  */
  61       __set_errno (ENOENT);
  62       return NULL;
  63     }
  64
  65 #ifdef PATH_MAX
  66   path_max = PATH_MAX;
  67 #else
  68   path_max = pathconf (name, _PC_PATH_MAX);
  69   if (path_max <= 0)
  70     path_max = 1024;
  71 #endif
  72
  73   rpath = resolved ? __alloca (path_max) : malloc (path_max);
  74   rpath_limit = rpath + path_max;
  75
  76   if (name[0] != '/')
  77     {
  78       if (!__getcwd (rpath, path_max))
  79         goto error;
  80       dest = strchr (rpath, '\0');
  81     }
  82   else
  83     {
  84       rpath[0] = '/';
  85       dest = rpath + 1;
  86     }
  87
  88   for (start = end = name; *start; start = end)
  89     {
  90       struct stat st;
  91       int n;
  92
  93       /* Skip sequence of multiple path-separators.  */
  94       while (*start == '/')
  95         ++start;
  96
  97       /* Find end of path component.  */
  98       for (end = start; *end && *end != '/'; ++end)
  99         /* Nothing.  */;
 100
 101       if (end - start == 0)
 102         break;
 103       else if (end - start == 1 && start[0] == '.')
 104         /* nothing */;
 105       else if (end - start == 2 && start[0] == '.' && start[1] == '.')
 106         {
 107           /* Back up to previous component, ignore if at root already.  */
 108           if (dest > rpath + 1)
 109             while ((--dest)[-1] != '/');
 110         }
 111       else
 112         {
 113           size_t new_size;
 114
 115           if (dest[-1] != '/')
 116             *dest++ = '/';
 117
 118           if (dest + (end - start) >= rpath_limit)
 119             {
 120               ptrdiff_t dest_offset = dest - rpath;
 121
 122               if (resolved)
 123                 {
 124                   __set_errno (ENAMETOOLONG);
 125                   goto error;
 126                 }
 127               new_size = rpath_limit - rpath;
 128               if (end - start + 1 > path_max)
 129                 new_size += end - start + 1;
 130               else
 131                 new_size += path_max;
 132               rpath = realloc (rpath, new_size);
 133               rpath_limit = rpath + new_size;
 134               if (rpath == NULL)
 135                 return NULL;
 136
 137               dest = rpath + dest_offset;
 138             }
 139
 140           dest = __mempcpy (dest, start, end - start);
 141           *dest = '\0';
 142
 143           if (__lxstat (_STAT_VER, rpath, &st) < 0)
 144             goto error;
 145
 146           if (S_ISLNK (st.st_mode))
 147             {
 148               char *buf = __alloca (path_max);
 149               size_t len;
 150
 151               if (++num_links > MAXSYMLINKS)
 152                 {
 153                   __set_errno (ELOOP);
 154                   goto error;
 155                 }
 156
 157               n = __readlink (rpath, buf, path_max);
 158               if (n < 0)
 159                 goto error;
 160               buf[n] = '\0';
 161
 162               if (!extra_buf)
 163                 extra_buf = __alloca (path_max);
 164
 165               len = strlen (end);
 166               if ((long int) (n + len) >= path_max)
 167                 {
 168                   __set_errno (ENAMETOOLONG);
 169                   goto error;
 170                 }
 171
 172               /* Careful here, end may be a pointer into extra_buf... */
 173               memmove (&extra_buf[n], end, len + 1);
 174               name = end = memcpy (extra_buf, buf, n);
 175
 176               if (buf[0] == '/')
 177                 dest = rpath + 1;       /* It's an absolute symlink */
 178               else
 179                 /* Back up to previous component, ignore if at root already: */
 180                 if (dest > rpath + 1)
 181                   while ((--dest)[-1] != '/');
 182             }
 183         }
 184     }
 185   if (dest > rpath + 1 && dest[-1] == '/')
 186     --dest;
 187   *dest = '\0';
 188
 189   return resolved ? memcpy (resolved, rpath, dest - rpath + 1) : rpath;
 190
 191 error:
 192   if (resolved)
 193     strcpy (resolved, rpath);
 194   else
 195     free (rpath);
 196   return NULL;
 197 }
 198
 199
 200 char *
 201 __realpath (const char *name, char *resolved)
 202 {
 203   if (resolved == NULL)
 204     {
 205       __set_errno (EINVAL);
 206       return NULL;
 207     }
 208
 209   return canonicalize (name, resolved);
 210 }
 211 weak_alias (__realpath, realpath)
 212
 213
 214 char *
 215 __canonicalize_file_name (const char *name)
 216 {
 217   return canonicalize (name, NULL);
 218 }
 219 weak_alias (__canonicalize_file_name, canonicalize_file_name)