/* provide consistent interface to chown for systems that don't interpret

   an ID of -1 as meaning "don't change the corresponding ID".

   Copyright (C) 1997, 2004-2007, 2009-2018 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 <https://www.gnu.org/licenses/>.  */

/* written by Jim Meyering */

#include <config.h>

/* Specification.  */

#include <unistd.h>

#include <errno.h>

#include <fcntl.h>

#include <stdbool.h>

#include <string.h>

#include <sys/stat.h>

#if !HAVE_CHOWN

/* Simple stub that always fails with ENOSYS, for mingw.  */

int

chown (const char *file _GL_UNUSED, uid_t uid _GL_UNUSED,

       gid_t gid _GL_UNUSED)

{

  errno = ENOSYS;

  return -1;

}

#else /* HAVE_CHOWN */

/* Below we refer to the system's chown().  */

# undef chown

/* Provide a more-closely POSIX-conforming version of chown on

   systems with one or both of the following problems:

   - chown doesn't treat an ID of -1 as meaning

   "don't change the corresponding ID".

   - chown doesn't dereference symlinks.  */

int

rpl_chown (const char *file, uid_t uid, gid_t gid)

{

  struct stat st;

  bool stat_valid = false;

  int result;

# if CHOWN_CHANGE_TIME_BUG

  if (gid != (gid_t) -1 || uid != (uid_t) -1)

    {

      if (stat (file, &st))

        return -1;

      stat_valid = true;

    }

# endif

# if CHOWN_FAILS_TO_HONOR_ID_OF_NEGATIVE_ONE

  if (gid == (gid_t) -1 || uid == (uid_t) -1)

    {

      /* Stat file to get id(s) that should remain unchanged.  */

      if (!stat_valid && stat (file, &st))

        return -1;

      if (gid == (gid_t) -1)

        gid = st.st_gid;

      if (uid == (uid_t) -1)

        uid = st.st_uid;

    }

# endif

# if CHOWN_MODIFIES_SYMLINK

  {

    /* Handle the case in which the system-supplied chown function

       does *not* follow symlinks.  Instead, it changes permissions

       on the symlink itself.  To work around that, we open the

       file (but this can fail due to lack of read or write permission) and

       use fchown on the resulting descriptor.  */

    int open_flags = O_NONBLOCK | O_NOCTTY;

    int fd = open (file, O_RDONLY | open_flags);

    if (0 <= fd

        || (errno == EACCES

            && 0 <= (fd = open (file, O_WRONLY | open_flags))))

      {

        int saved_errno;

        bool fchown_socket_failure;

        result = fchown (fd, uid, gid);

        saved_errno = errno;

        /* POSIX says fchown can fail with errno == EINVAL on sockets

           and pipes, so fall back on chown in that case.  */

        fchown_socket_failure =

          (result != 0 && saved_errno == EINVAL

           && fstat (fd, &st) == 0

           && (S_ISFIFO (st.st_mode) || S_ISSOCK (st.st_mode)));

        close (fd);

        if (! fchown_socket_failure)

          {

            errno = saved_errno;

            return result;

          }

      }

    else if (errno != EACCES)

      return -1;

  }

# endif

# if CHOWN_TRAILING_SLASH_BUG

  if (!stat_valid)

    {

      size_t len = strlen (file);

      if (len && file[len - 1] == '/' && stat (file, &st))

        return -1;

    }

# endif

  result = chown (file, uid, gid);

# if CHOWN_CHANGE_TIME_BUG

  if (result == 0 && stat_valid

      && (uid == st.st_uid || uid == (uid_t) -1)

      && (gid == st.st_gid || gid == (gid_t) -1))

    {

      /* No change in ownership, but at least one argument was not -1,

         so we are required to update ctime.  Since chown succeeded,

         we assume that chmod will do likewise.  Fortunately, on all

         known systems where a 'no-op' chown skips the ctime update, a

         'no-op' chmod still does the trick.  */

      result = chmod (file, st.st_mode & (S_IRWXU | S_IRWXG | S_IRWXO

                                          | S_ISUID | S_ISGID | S_ISVTX));

    }

# endif

  return result;

}

#endif /* HAVE_CHOWN */