/*
 * realpath.c -- canonicalize pathname by removing symlinks
 * Copyright (C) 1993 Rick Sladkey <jrs@world.std.com>
 * Copyright (C) 2001 Ben Wing.
 *

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, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

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

/* This file has been Mule-ized, June 2001 by Ben Wing.

   Everything in this file now works in terms of internal, not external,
   data.  This is the only way to be safe, and it makes the code cleaner. */

#include <config.h>
#include "lisp.h"

#include "sysfile.h"

#define MAX_READLINKS 32

#if defined (HAVE_SYS_PARAM_H) && !defined (WIN32_NATIVE)
#include <sys/param.h>
#endif

#ifdef WIN32_NATIVE
#include <direct.h>
#endif

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

#if defined(WIN32_NATIVE) || defined(CYGWIN)
#define WIN32_FILENAMES
#endif

/* First char after start of absolute filename. */
#define ABS_START(name) (name + ABS_LENGTH (name))

#if defined (WIN32_NATIVE)
/* Length of start of absolute filename. */
# define ABS_LENGTH(name) (mswindows_abs_start (name))
static int mswindows_abs_start (const Intbyte *name);
# define readlink_and_correct_case mswindows_readlink_and_correct_case
#else
# ifdef CYGWIN
#  ifdef WIN32_FILENAMES
#   define ABS_LENGTH(name) (mswindows_abs_start (name))
static int mswindows_abs_start (const Intbyte * name);
#  else
#   define ABS_LENGTH(name) (IS_DIRECTORY_SEP (*name) ? \
                             (IS_DIRECTORY_SEP (name[1]) ? 2 : 1) : 0)
#  endif
#  define readlink_and_correct_case cygwin_readlink_and_correct_case
# else
#  define ABS_LENGTH(name) (IS_DIRECTORY_SEP (*name) ? 1 : 0)
#  define readlink_and_correct_case qxe_readlink
# endif /* CYGWIN */
#endif /* WIN32_NATIVE */

#if defined (WIN32_NATIVE) || defined (CYGWIN)
#include "syswindows.h"
/* "Emulate" readlink on mswindows - finds real name (i.e. correct
   case) of a file. (#### "readlink" is used extremely misleadingly
   here.  This is much more like "truename"!) UNC servers and shares
   are lower-cased. Directories must be given without trailing
   '/'. One day, this could read Win2K's reparse points. */
static int
mswindows_readlink_and_correct_case (const Intbyte *name, Intbyte *buf,
				     int size)
{
  int len = 0;
  int err = 0;
  const Intbyte *lastname;
  int count = 0;
  const Intbyte *tmp;
  DECLARE_EISTRING (result);
  
  assert (*name);
  
  /* Sort of check we have a valid filename. */
  if (qxestrpbrk (name, "*?|<>\"") || qxestrlen (name) >= PATH_MAX)
    {
      errno = EIO;
      return -1;
    }
  
  /* Find start of filename */
  lastname = name + qxestrlen (name);
  while (lastname > name && !IS_DIRECTORY_SEP (lastname[-1]))
    --lastname;

  /* Count slashes in unc path */
  if (ABS_LENGTH (name) == 2)
    for (tmp = name; *tmp; tmp++)
      if (IS_DIRECTORY_SEP (*tmp))
	count++;

  if (count >= 2 && count < 4)
    {
      eicpy_rawz (result, lastname);
      eilwr (result);
    }
  else
    {
      WIN32_FIND_DATAW find_data;
      Extbyte *nameext;
      HANDLE dir_handle;

      C_STRING_TO_TSTR (name, nameext);
      dir_handle = qxeFindFirstFile (nameext, &find_data);
      if (dir_handle == INVALID_HANDLE_VALUE)
	{
	  errno = ENOENT;
	  return -1;
	}
      eicpy_ext (result, (Extbyte *) find_data.cFileName, Qmswindows_tstr);
      FindClose (dir_handle);
    }

  if ((len = eilen (result)) < size)
    {
      DECLARE_EISTRING (eilastname);

      eicpy_rawz (eilastname, lastname);
      if (eicmp_ei (eilastname, result) == 0)
	/* Signal that the name is already OK. */
	err = EINVAL;
      else
	memcpy (buf, eidata (result), len + 1);
    }
  else
    err = ENAMETOOLONG;

  errno = err;
  return err ? -1 : len;
}
#endif /* WIN32_NATIVE || CYGWIN */

#ifdef CYGWIN
/* Call readlink and try to find out the correct case for the file. */
static int
cygwin_readlink_and_correct_case (const Intbyte *name, Intbyte *buf,
				  int size)
{
  int n = qxe_readlink (name, buf, size);
  if (n < 0 && errno == EINVAL)
    {
      /* The file may exist, but isn't a symlink. Try to find the
         right name. */
      Intbyte *tmp =
	(Intbyte *) ALLOCA (cygwin_posix_to_win32_path_list_buf_size
			    ((char *) name));
      cygwin_posix_to_win32_path_list ((char *) name, (char *) tmp);
      n = mswindows_readlink_and_correct_case (tmp, buf, size);
    }
  return n;
}
#endif /* CYGWIN */

#ifdef WIN32_FILENAMES
#ifndef ELOOP
#define ELOOP 10062 /* = WSAELOOP in winsock.h */
#endif
/* Length of start of absolute filename. */
static int 
mswindows_abs_start (const Intbyte *name)
{
  if (isalpha (*name) && IS_DEVICE_SEP (name[1])
      && IS_DIRECTORY_SEP (name[2]))
    return 3;
  else if (IS_DIRECTORY_SEP (*name))
    return IS_DIRECTORY_SEP (name[1]) ? 2 : 1;
  else 
    return 0;
}
#endif /* WIN32_NATIVE */

/* Mule Note: This function works with and returns
   internally-formatted strings. */

Intbyte *
qxe_realpath (const Intbyte *path, Intbyte *resolved_path)
{
  Intbyte copy_path[PATH_MAX];
  Intbyte *new_path = resolved_path;
  Intbyte *max_path;
#if defined (HAVE_READLINK) || defined (WIN32_NATIVE)
  int readlinks = 0;
  Intbyte link_path[PATH_MAX];
  int n;
  int abslen = ABS_LENGTH (path);
#endif

  /* Make a copy of the source path since we may need to modify it. */
  qxestrcpy (copy_path, path);
  path = copy_path;
  max_path = copy_path + PATH_MAX - 2;

  if (0)
    ;
#ifdef WIN32_FILENAMES
  /* Check for c:/... or //server/... */
  else if (abslen == 2 || abslen == 3)
    {
      qxestrncpy (new_path, path, abslen);
      /* Make sure drive letter is lowercased. */
      if (abslen == 3)
	*new_path = tolower (*new_path);
      new_path += abslen;
      path += abslen;
    }
#endif
#ifdef WIN32_NATIVE
  /* No drive letter, but a beginning slash? Prepend drive letter. */
  else if (abslen == 1)
    {
      get_initial_directory (new_path, PATH_MAX - 1);
      new_path += 3;
      path++;
    }
  /* Just a path name, prepend the current directory */
  else if (1)
    {
      get_initial_directory (new_path, PATH_MAX - 1);
      new_path += qxestrlen (new_path);
      if (!IS_DIRECTORY_SEP (new_path[-1]))
	*new_path++ = DIRECTORY_SEP;
    }
#else
  /* If it's a relative pathname use get_initial_directory for starters. */
  else if (abslen == 0)
    {
      get_initial_directory (new_path, PATH_MAX - 1);
      new_path += qxestrlen (new_path);
      if (!IS_DIRECTORY_SEP (new_path[-1]))
	*new_path++ = DIRECTORY_SEP;
    }
  else
    {
      /* Copy first directory sep. May have two on cygwin. */
      qxestrncpy (new_path, path, abslen);
      new_path += abslen;
      path += abslen;
    }
#endif
  /* Expand each slash-separated pathname component. */
  while (*path != '\0')
    {
      /* Ignore stray "/". */
      if (IS_DIRECTORY_SEP (*path))
	{
	  path++;
	  continue;
	}

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

	  /* Handle ".." */
	  if (path[1] == '.' &&
	      (path[2] == '\0' || IS_DIRECTORY_SEP (path[2])))
	    {
	      path += 2;

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

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

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

#if defined (HAVE_READLINK) || defined (WIN32_NATIVE)
      /* See if latest pathname component is a symlink or needs case
	 correction. */
      *new_path = '\0';
      n = readlink_and_correct_case (resolved_path, link_path, PATH_MAX - 1);

      if (n < 0)
	{
	  /* EINVAL means the file exists but isn't a symlink or doesn't
	     need case correction. */
#ifdef CYGWIN
	  if (errno != EINVAL && errno != ENOENT)
#else
	  if (errno != EINVAL) 
#endif
	    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 (ABS_LENGTH (link_path) > 0)
	    /* Start over for an absolute symlink. */
	    new_path = resolved_path + ABS_LENGTH (link_path) - 1;
	  else
	    /* Otherwise back up over this component. */
	    for (--new_path; !IS_DIRECTORY_SEP (*new_path); --new_path)
	      assert (new_path > resolved_path);

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

	  /* Insert symlink contents into path. */
	  qxestrcat (link_path, path);
	  qxestrcpy (copy_path, link_path);
	  path = copy_path;
	}
#endif /* HAVE_READLINK || WIN32_NATIVE */
      *new_path++ = DIRECTORY_SEP;
    }

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

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

  return resolved_path;
}