stdlib/canonicalize.c

   1 /* Return the canonical absolute name of a given file.
   2 Copyright (C) 1996 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
  17 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  18 Cambridge, MA 02139, USA.  */
  19
  20 #include <stdlib.h>
  21 #include <string.h>
  22 #include <unistd.h>
  23 #include <limits.h>
  24 #include <sys/stat.h>
  25 #include <errno.h>
  26
  27 /* Return the canonical absolute name of file NAME.  The last file name
  28    component need not exist, and may be a symlink to a nonexistent file.
  29    If RESOLVED is null, the result is malloc'd; otherwise, if the canonical
  30    name is PATH_MAX chars or more, returns null with `errno' set to
  31    ENAMETOOLONG; if the name fits in fewer than PATH_MAX chars, returns the
  32    name in RESOLVED.  */
  33
  34 static char *
  35 canonicalize (const char *name, char *resolved)
  36 {
  37   struct stat st;
  38   const char *p;
  39   long int path_max;
  40   char *result, *dir, *end;
  41   size_t namelen;
  42
  43   if (! resolved)
  44     path_max = 0;
  45   else
  46     {
  47 #ifdef PATH_MAX
  48       path_max = PATH_MAX;
  49 #else
  50       path_max = sysconf (_SC_PATH_MAX);
  51       if (path_max <= 0)
  52         path_max = 1024;
  53 #endif
  54     }
  55
  56   p = strrchr (name, '/');
  57   if (!p)
  58     {
  59       dir = (char *) ".";
  60       p = name;
  61     }
  62   else
  63     {
  64       if (p++ == name)
  65         dir = (char *) "/";
  66       else
  67         {
  68           dir = __alloca (p - name);
  69           memcpy (dir, name, p - name - 1);
  70           dir[p - name] = '\0';
  71         }
  72     }
  73
  74   result = __canonicalize_directory_name_internal (dir, resolved, path_max);
  75   if (!result)
  76     return NULL;
  77
  78   /* Reconstruct the file name in the canonicalized directory.  */
  79   namelen = strlen (name);
  80   end = strchr (result, '\0');
  81   if (resolved)
  82     {
  83       /* Make sure the name is not too long.  */
  84       if (end - result + namelen > path_max)
  85         {
  86           errno = ENAMETOOLONG;
  87           return NULL;
  88         }
  89     }
  90   else
  91     {
  92       /* The name is dynamically allocated.  Extend it.  */
  93       char *new = realloc (result, end - result + namelen + 1);
  94       if (! new)
  95         {
  96           free (result);
  97           return NULL;
  98         }
  99       end = new + (end - result);
 100       result = new;
 101     }
 102   memcpy (end, name, namelen + 1);
 103
 104   while (__lstat (result, &st) == 0 && S_ISLNK (st.st_mode))
 105     {
 106       /* The file is a symlink.  Read its contents.  */
 107       ssize_t n;
 108     read_link_contents:
 109       n = readlink (result, end,
 110                     resolved ? result + path_max - end : namelen + 1);
 111       if (n < 0)
 112         /* Error reading the link contents.  */
 113         return NULL;
 114
 115       if (end[0] == '/')
 116         {
 117           /* Absolute symlink.  */
 118           if (resolved ? (end + n < result + path_max) : (n < namelen + 1))
 119             {
 120               /* It fit in our buffer, so we have the whole thing.  */
 121               memcpy (result, end, n);
 122               result[n] = '\0';
 123             }
 124           else if (resolved)
 125             {
 126               /* It didn't fit in the remainder of the buffer.  Either it
 127                  fits in the entire buffer, or it doesn't.  Copy back the
 128                  unresolved name onto the canonical directory and try once
 129                  more.  */
 130               memcpy (end, name, namelen + 1);
 131               n = readlink (result, result, path_max);
 132               if (n < 0)
 133                 return NULL;
 134               if (n == path_max)
 135                 {
 136                   errno = ENAMETOOLONG;
 137                   return NULL;
 138                 }
 139               result[n] = '\0';
 140             }
 141           else
 142             /* Try again with a bigger buffer.  */
 143             goto extend_buffer;
 144
 145           /* Check the resolved name for being a symlink too.  */
 146           continue;
 147         }
 148
 149       if (resolved)
 150         {
 151           if (end + n == result + path_max)
 152             {
 153               /* The link contents we read fill the buffer completely.
 154                  There may be even more to read, and there is certainly no
 155                  space for the null terminator.  */
 156               errno = ENAMETOOLONG;
 157               return NULL;
 158             }
 159         }
 160       else if (n == namelen + 1)
 161       extend_buffer:
 162         {
 163           /* The name buffer is dynamically allocated.  Extend it.  */
 164           char *new;
 165
 166           /* Copy back the unresolved name onto the canonical directory.  */
 167           memcpy (end, name, namelen + 1);
 168
 169           /* Make more space for readlink.  */
 170           namelen *= 2;
 171           new = realloc (result, end - result + namelen + 1);
 172           if (! new)
 173             {
 174               free (result);
 175               return NULL;
 176             }
 177           end = new + (end - result);
 178           result = new;
 179
 180           goto read_link_contents;
 181         }
 182
 183       /* Terminate the string; readlink does not.  */
 184       end[n] = '\0';
 185     }
 186
 187   return result;
 188 }
 189
 190 weak_alias (canonicalize, realpath)
 191
 192 char *
 193 canonicalize_file_name (const char *name)
 194 {
 195   return canonicalize (name, NULL);
 196 }