Linux Cubed Series 2: Applications/Linux Cubed Series 2 - Applications.iso/editors/emacs/xemacs/xemacs-1.004/xemacs-1/xemacs-19.13/src/realpath.c

C/C++ Source or Header | 1995-03-11 | 4.2 KB | 200 lines

/*
 * realpath.c -- canonicalize pathname by removing symlinks
 * Copyright (C) 1993 Rick Sladkey <[e-mail]>
 *

This file is part of XEmacs.

XEmacs is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2, or (at your option) any
later version.

XEmacs is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with XEmacs; see the file COPYING.  If not, write to the Free
Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */

/* Synched up with: Not in FSF. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <sys/types.h>
#if defined(HAVE_UNISTD_H) || defined(STDC_HEADERS)
#include <unistd.h>
#endif
#include <stdio.h>
#include <string.h>
#ifdef _POSIX_VERSION
#include <limits.h>            /* for PATH_MAX */
#else
#include <sys/param.h>            /* for MAXPATHLEN */
#endif
#include <errno.h>
#ifndef STDC_HEADERS
extern int errno;
#endif

#include <sys/stat.h>            /* for S_IFLNK */

#ifndef PATH_MAX
#ifdef _POSIX_VERSION
#define PATH_MAX _POSIX_PATH_MAX
#else
#ifdef MAXPATHLEN
#define PATH_MAX MAXPATHLEN
#else
#define PATH_MAX 1024
#endif
#endif
#endif

#define MAX_READLINKS 32

#ifdef __STDC__
char *realpath(const char *path, char resolved_path [])
#else
char *realpath(path, resolved_path)
const char *path;
char resolved_path [];
#endif
{
  char copy_path[PATH_MAX];
  char link_path[PATH_MAX];
  char *new_path = resolved_path;
  char *max_path;
  int readlinks = 0;
  int n;

  /* Make a copy of the source path since we may need to modify it. */
  strcpy(copy_path, path);
  path = copy_path;
  max_path = copy_path + PATH_MAX - 2;
  /* If it's a relative pathname use getwd for starters. */
  if (*path != '/')
    {
#ifdef HAVE_GETCWD
      getcwd(new_path, PATH_MAX - 1);
#else
      getwd(new_path);
#endif
      new_path += strlen(new_path);
      if (new_path[-1] != '/')
    *new_path++ = '/';
    }
  else
    {
      *new_path++ = '/';
      path++;
    }

  /* Expand each slash-separated pathname component. */
  while (*path != '\0')
    {
      /* Ignore stray "/". */
      if (*path == '/')
    {
      path++;
      continue;
    }

      if (*path == '.')
    {
      /* Ignore ".". */
      if (path[1] == '\0' || path[1] == '/')
        {
          path++;
          continue;
        }

      if (path[1] == '.')
        {
          if (path[2] == '\0' || path[2] == '/')
        {
          path += 2;

          /* Ignore ".." at root. */
          if (new_path == resolved_path + 1)
            continue;

          /* Handle ".." by backing up. */
          while ((--new_path)[-1] != '/')
            ;
          continue;
        }
        }
    }

      /* Safely copy the next pathname component. */
      while (*path != '\0' && *path != '/')
    {
      if (path > max_path)
        {
          errno = ENAMETOOLONG;
          return NULL;
        }
      *new_path++ = *path++;
    }

#ifdef S_IFLNK
      /* See if latest pathname component is a symlink. */
      *new_path = '\0';
      n = readlink(resolved_path, link_path, PATH_MAX - 1);

      if (n < 0)
    {
      /* EINVAL means the file exists but isn't a symlink. */
      if (errno != EINVAL)
        return NULL;
    }
      else
    {
      /* Protect against infinite loops. */
      if (readlinks++ > MAX_READLINKS)
        {
          errno = ELOOP;
          return NULL;
        }

      /* Note: readlink doesn't add the null byte. */
      link_path[n] = '\0';

      if (*link_path == '/')
        /* Start over for an absolute symlink. */
        new_path = resolved_path;
      else
        /* Otherwise back up over this component. */
        while (*(--new_path) != '/')
          ;

      /* Safe sex check. */
      if (strlen(path) + n >= PATH_MAX)
        {
          errno = ENAMETOOLONG;
          return NULL;
        }

      /* Insert symlink contents into path. */
      strcat(link_path, path);
      strcpy(copy_path, link_path);
      path = copy_path;
    }
#endif /* S_IFLNK */
      *new_path++ = '/';
    }

  /* Delete trailing slash but don't whomp a lone slash. */
  if (new_path != resolved_path + 1 && new_path[-1] == '/')
    new_path--;

  /* Make sure it's null terminated. */
  *new_path = '\0';
  return resolved_path;
}