/* Provide a working getlogin_r for systems which lack it.

   Copyright (C) 2005-2007, 2010-2018 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, 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 Paul Eggert, Derek Price, and Bruno Haible.  */

#include <config.h>

/* Specification.  */

#include <unistd.h>

#include <errno.h>

#include <string.h>

#include "malloca.h"

#if defined _WIN32 && ! defined __CYGWIN__

# define WIN32_LEAN_AND_MEAN

# include <windows.h>

#else

# if !HAVE_DECL_GETLOGIN

extern char *getlogin (void);

# endif

#endif

/* See unistd.in.h for documentation.  */

int

getlogin_r (char *name, size_t size)

{

#undef getlogin_r

#if defined _WIN32 && ! defined __CYGWIN__

  /* Native Windows platform.  */

  DWORD sz;

  /* When size > 0x7fff, the doc says that GetUserName will fail.

     Actually, on Windows XP SP3, it succeeds.  But let's be safe,

     for the sake of older Windows versions.  */

  if (size > 0x7fff)

    size = 0x7fff;

  sz = size;

  if (!GetUserName (name, &sz))

    {

      if (GetLastError () == ERROR_INSUFFICIENT_BUFFER)

        /* In this case, the doc says that sz contains the required size, but

           actually, on Windows XP SP3, it contains 2 * the required size.  */

        return ERANGE;

      else

        return ENOENT;

    }

  return 0;

#elif HAVE_GETLOGIN_R

  /* Platform with a getlogin_r() function.  */

  int ret = getlogin_r (name, size);

  if (ret == 0)

    {

      const char *nul = memchr (name, '\0', size);

      if (nul == NULL)

        /* name contains a truncated result.  */

        return ERANGE;

      if (size > 0 && nul == name + size - 1)

        {

          /* strlen(name) == size-1.  Determine whether the untruncated result

             would have had length size-1 or size.  */

          char *room = (char *) malloca (size + 1);

          if (room == NULL)

            return ENOMEM;

          ret = getlogin_r (room, size + 1);

          /* The untruncated result should be the same as in the first call.  */

          if (ret == 0 && memcmp (name, room, size) != 0)

            /* The untruncated result would have been different.  */

            ret = ERANGE;

          freea (room);

        }

    }

  return ret;

#else

  /* Platform with a getlogin() function.  */

  char *n;

  size_t nlen;

  errno = 0;

  n = getlogin ();

  if (!n)

    /* ENOENT is a reasonable errno value if getlogin returns NULL.  */

    return (errno != 0 ? errno : ENOENT);

  nlen = strlen (n);

  if (size <= nlen)

    return ERANGE;

  memcpy (name, n, nlen + 1);

  return 0;

#endif

}