/* Copyright (C) 1991-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or

   modify it under the terms of the GNU Lesser General Public

   License as published by the Free Software Foundation; either

   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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

   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with the GNU C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

#include <errno.h>

#include <unistd.h>

#include <string.h>

#include <stdio.h>

#include <limits.h>

#include <fcntl.h>

#include <utmp.h>

static char name[UT_NAMESIZE + 1];

/* Return the login name of the user, or NULL if it can't be determined.

   The returned pointer, if not NULL, is good only until the next call.  */

#ifdef STATIC

STATIC

#endif

char *

getlogin (void)

{

  char tty_pathname[2 + 2 * NAME_MAX];

  char *real_tty_path = tty_pathname;

  int err;

  char *result = NULL;

  struct utmp *ut, line, buffer;

  /* Get name of tty connected to fd 0.  Return NULL if not a tty or

     if fd 0 isn't open.  Note that a lot of documentation says that

     getlogin() is based on the controlling terminal---what they

     really mean is "the terminal connected to standard input".  The

     getlogin() implementation of DEC Unix, SunOS, Solaris, HP-UX all

     return NULL if fd 0 has been closed, so this is the compatible

     thing to do.  Note that ttyname(open("/dev/tty")) on those

     systems returns /dev/tty, so that is not a possible solution for

     getlogin().  */

  err = __ttyname_r (0, real_tty_path, sizeof (tty_pathname));

  if (err != 0)

    {

      __set_errno (err);

      return NULL;

    }

  real_tty_path += 5;		/* Remove "/dev/".  */

  __setutent ();

  strncpy (line.ut_line, real_tty_path, sizeof line.ut_line);

  if (__getutline_r (&line, &buffer, &ut) < 0)

    {

      if (errno == ESRCH)

	/* The caller expects ENOENT if nothing is found.  */

	__set_errno (ENOENT);

      result = NULL;

    }

  else

    {

      strncpy (name, ut->ut_user, UT_NAMESIZE);

      name[UT_NAMESIZE] = '\0';

      result = name;

    }

  __endutent ();

  return result;

}