/* fchdir replacement.

   Copyright (C) 2006-2017 Free Software Foundation, Inc.

   This program 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 3 of the License, or

   (at your option) any later version.

   This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */

#include <unistd.h>

#include <dirent.h>

#include <errno.h>

#include <fcntl.h>

#include <stdbool.h>

#include <stdlib.h>

#include <string.h>

#include <sys/types.h>

#include <sys/stat.h>

#include "assure.h"

#include "dosname.h"

#include "filenamecat.h"

#ifndef REPLACE_OPEN_DIRECTORY

# define REPLACE_OPEN_DIRECTORY 0

#endif

/* This replacement assumes that a directory is not renamed while opened

   through a file descriptor.

   FIXME: On mingw, this would be possible to enforce if we were to

   also open a HANDLE to each directory currently visited by a file

   descriptor, since mingw refuses to rename any in-use file system

   object.  */

/* Array of file descriptors opened.  If REPLACE_OPEN_DIRECTORY or if it points

   to a directory, it stores info about this directory.  */

typedef struct

{

  char *name;       /* Absolute name of the directory, or NULL.  */

  /* FIXME - add a DIR* member to make dirfd possible on mingw?  */

} dir_info_t;

static dir_info_t *dirs;

static size_t dirs_allocated;

/* Try to ensure dirs has enough room for a slot at index fd; free any

   contents already in that slot.  Return false and set errno to

   ENOMEM on allocation failure.  */

static bool

ensure_dirs_slot (size_t fd)

{

  if (fd < dirs_allocated)

    free (dirs[fd].name);

  else

    {

      size_t new_allocated;

      dir_info_t *new_dirs;

      new_allocated = 2 * dirs_allocated + 1;

      if (new_allocated <= fd)

        new_allocated = fd + 1;

      new_dirs =

        (dirs != NULL

         ? (dir_info_t *) realloc (dirs, new_allocated * sizeof *dirs)

         : (dir_info_t *) malloc (new_allocated * sizeof *dirs));

      if (new_dirs == NULL)

        return false;

      memset (new_dirs + dirs_allocated, 0,

              (new_allocated - dirs_allocated) * sizeof *dirs);

      dirs = new_dirs;

      dirs_allocated = new_allocated;

    }

  return true;

}

/* Return an absolute name of DIR in malloc'd storage.  */

static char *

get_name (char const *dir)

{

  char *cwd;

  char *result;

  int saved_errno;

  if (IS_ABSOLUTE_FILE_NAME (dir))

    return strdup (dir);

  /* We often encounter "."; treat it as a special case.  */

  cwd = getcwd (NULL, 0);

  if (!cwd || (dir[0] == '.' && dir[1] == '\0'))

    return cwd;

  result = mfile_name_concat (cwd, dir, NULL);

  saved_errno = errno;

  free (cwd);

  errno = saved_errno;

  return result;

}

/* Hook into the gnulib replacements for open() and close() to keep track

   of the open file descriptors.  */

/* Close FD, cleaning up any fd to name mapping if fd was visiting a

   directory.  */

void

_gl_unregister_fd (int fd)

{

  if (fd >= 0 && fd < dirs_allocated)

    {

      free (dirs[fd].name);

      dirs[fd].name = NULL;

    }

}

/* Mark FD as visiting FILENAME.  FD must be non-negative, and refer

   to an open file descriptor.  If REPLACE_OPEN_DIRECTORY is non-zero,

   this should only be called if FD is visiting a directory.  Close FD

   and return -1 if there is insufficient memory to track the

   directory name; otherwise return FD.  */

int

_gl_register_fd (int fd, const char *filename)

{

  struct stat statbuf;

  assure (0 <= fd);

  if (REPLACE_OPEN_DIRECTORY

      || (fstat (fd, &statbuf) == 0 && S_ISDIR (statbuf.st_mode)))

    {

      if (!ensure_dirs_slot (fd)

          || (dirs[fd].name = get_name (filename)) == NULL)

        {

          int saved_errno = errno;

          close (fd);

          errno = saved_errno;

          return -1;

        }

    }

  return fd;

}

/* Mark NEWFD as a duplicate of OLDFD; useful from dup, dup2, dup3,

   and fcntl.  Both arguments must be valid and distinct file

   descriptors.  Close NEWFD and return -1 if OLDFD is tracking a

   directory, but there is insufficient memory to track the same

   directory in NEWFD; otherwise return NEWFD.  */

int

_gl_register_dup (int oldfd, int newfd)

{

  assure (0 <= oldfd && 0 <= newfd && oldfd != newfd);

  if (oldfd < dirs_allocated && dirs[oldfd].name)

    {

      /* Duplicated a directory; must ensure newfd is allocated.  */

      if (!ensure_dirs_slot (newfd)

          || (dirs[newfd].name = strdup (dirs[oldfd].name)) == NULL)

        {

          int saved_errno = errno;

          close (newfd);

          errno = saved_errno;

          newfd = -1;

        }

    }

  else if (newfd < dirs_allocated)

    {

      /* Duplicated a non-directory; ensure newfd is cleared.  */

      free (dirs[newfd].name);

      dirs[newfd].name = NULL;

    }

  return newfd;

}

/* If FD is currently visiting a directory, then return the name of

   that directory.  Otherwise, return NULL and set errno.  */

const char *

_gl_directory_name (int fd)

{

  if (0 <= fd && fd < dirs_allocated && dirs[fd].name != NULL)

    return dirs[fd].name;

  /* At this point, fd is either invalid, or open but not a directory.

     If dup2 fails, errno is correctly EBADF.  */

  if (0 <= fd)

    {

      if (dup2 (fd, fd) == fd)

        errno = ENOTDIR;

    }

  else

    errno = EBADF;

  return NULL;

}

/* Implement fchdir() in terms of chdir().  */

int

fchdir (int fd)

{

  const char *name = _gl_directory_name (fd);

  return name ? chdir (name) : -1;

}