cgit.sxemacs.org Git - sxemacs/blob - src/realpath.c

   1 /*
   2  * realpath.c -- canonicalize pathname by removing symlinks
   3  * Copyright (C) 1993 Rick Sladkey <jrs@world.std.com>
   4  *
   5
   6 This file is part of SXEmacs
   7
   8 SXEmacs is free software: you can redistribute it and/or modify
   9 it under the terms of the GNU General Public License as published by
  10 the Free Software Foundation, either version 3 of the License, or
  11 (at your option) any later version.
  12
  13 SXEmacs is distributed in the hope that it will be useful,
  14 but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 GNU General Public License for more details.
  17
  18 You should have received a copy of the GNU General Public License
  19 along with this program.  If not, see <http://www.gnu.org/licenses/>. */
  20
  21
  22 /* Synched up with: Not in FSF. */
  23
  24 #include <config.h>
  25 #include "lisp.h"
  26 #include <errno.h>
  27
  28 #ifdef HAVE_UNISTD_H
  29 #include <unistd.h>
  30 #endif
  31
  32 #if defined (HAVE_SYS_PARAM_H)
  33 #include <sys/param.h>
  34 #endif
  35
  36 #include <sys/stat.h>           /* for S_IFLNK */
  37
  38 /* First char after start of absolute filename. */
  39 #define ABS_START(name) (name + ABS_LENGTH (name))
  40
  41 #define ABS_LENGTH(name) (IS_DIRECTORY_SEP (*name) ? 1 : 0)
  42 #define system_readlink readlink
  43
  44
  45 #if !defined (HAVE_GETCWD) && defined (HAVE_GETWD)
  46 #undef getcwd
  47 #define getcwd(buffer, len) getwd (buffer)
  48 #endif
  49
  50 #ifndef PATH_MAX
  51 # if defined (_POSIX_PATH_MAX)
  52 #  define PATH_MAX _POSIX_PATH_MAX
  53 # elif defined (MAXPATHLEN)
  54 #  define PATH_MAX MAXPATHLEN
  55 # else
  56 #  define PATH_MAX 1024
  57 # endif
  58 #endif
  59
  60 #define MAX_READLINKS 32
  61
  62 char *xrealpath(const char *path, char *restrict resolved_path);
  63 char *xrealpath(const char *path, char *restrict resolved_path)
  64 {
  65         char copy_path[PATH_MAX];
  66         char *new_path = resolved_path;
  67         char *max_path;
  68 #if defined (S_IFLNK)
  69         int readlinks = 0;
  70         char link_path[PATH_MAX];
  71         int n;
  72         int abslen = ABS_LENGTH(path);
  73 #endif
  74
  75         /* Make a copy of the source path since we may need to modify it. */
  76         strncpy(copy_path, path, sizeof(copy_path)-1);
  77         copy_path[sizeof(copy_path)-1]='\0';
  78         path = copy_path;
  79         max_path = copy_path + PATH_MAX - 2;
  80
  81         /* If it's a relative pathname use getcwd for starters. */
  82         if (abslen == 0) {
  83                 getcwd(new_path, PATH_MAX - 1);
  84                 new_path += strlen(new_path);
  85                 if (!IS_DIRECTORY_SEP(new_path[-1]))
  86                         *new_path++ = DIRECTORY_SEP;
  87         } else {
  88                 /* Copy first directory sep. */
  89                 strncpy(new_path, path, abslen);
  90                 new_path += abslen;
  91                 path += abslen;
  92         }
  93
  94         /* Expand each slash-separated pathname component. */
  95         while (*path != '\0') {
  96                 /* Ignore stray "/". */
  97                 if (IS_DIRECTORY_SEP(*path)) {
  98                         path++;
  99                         continue;
 100                 }
 101
 102                 if (*path == '.') {
 103                         /* Ignore ".". */
 104                         if (path[1] == '\0' || IS_DIRECTORY_SEP(path[1])) {
 105                                 path++;
 106                                 continue;
 107                         }
 108
 109                         /* Handle ".." */
 110                         if (path[1] == '.' &&
 111                             (path[2] == '\0' || IS_DIRECTORY_SEP(path[2]))) {
 112                                 path += 2;
 113
 114                                 /* Ignore ".." at root. */
 115                                 if (new_path == ABS_START(resolved_path))
 116                                         continue;
 117
 118                                 /* Handle ".." by backing up. */
 119                                 --new_path;
 120                                 while (!IS_DIRECTORY_SEP(new_path[-1]))
 121                                         --new_path;
 122                                 continue;
 123                         }
 124                 }
 125
 126                 /* Safely copy the next pathname component. */
 127                 while (*path != '\0' && !IS_DIRECTORY_SEP(*path)) {
 128                         if (path > max_path) {
 129                                 errno = ENAMETOOLONG;
 130                                 return NULL;
 131                         }
 132                         *new_path++ = *path++;
 133                 }
 134
 135 #if defined (S_IFLNK)
 136                 /* See if latest pathname component is a symlink. */
 137                 *new_path = '\0';
 138                 n = system_readlink(resolved_path, link_path, PATH_MAX - 1);
 139
 140                 if (n < 0) {
 141                         /* EINVAL means the file exists but isn't a symlink. */
 142                         if (errno != EINVAL)
 143                                 return NULL;
 144                 } else {
 145                         /* Protect against infinite loops. */
 146                         if (readlinks++ > MAX_READLINKS) {
 147                                 errno = ELOOP;
 148                                 return NULL;
 149                         }
 150
 151                         /* Note: readlink doesn't add the null byte. */
 152                         link_path[n] = '\0';
 153
 154                         if (ABS_LENGTH(link_path) > 0)
 155                                 /* Start over for an absolute symlink. */
 156                                 new_path =
 157                                     resolved_path + ABS_LENGTH(link_path) - 1;
 158                         else
 159                                 /* Otherwise back up over this component. */
 160                                 for (--new_path; !IS_DIRECTORY_SEP(*new_path);
 161                                      --new_path)
 162                                         assert(new_path > resolved_path);
 163
 164                         /* Safe sex check. */
 165                         if (strlen(path) + n >= PATH_MAX) {
 166                                 errno = ENAMETOOLONG;
 167                                 return NULL;
 168                         }
 169
 170                         /* Insert symlink contents into path. */
 171                         strcat(link_path, path);
 172                         strcpy(copy_path, link_path);
 173                         path = copy_path;
 174                 }
 175 #endif                          /* S_IFLNK */
 176                 *new_path++ = DIRECTORY_SEP;
 177         }
 178
 179         /* Delete trailing slash but don't whomp a lone slash. */
 180         if (new_path != ABS_START(resolved_path)
 181             && IS_DIRECTORY_SEP(new_path[-1]))
 182                 new_path--;
 183
 184         /* Make sure it's null terminated. */
 185         *new_path = '\0';
 186
 187         return resolved_path;
 188 }