gnulib/import/getlogin_r.c

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

   Copyright (C) 2005-2007, 2010-2021 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>
/* Don't assume that UNICODE is not defined.  */
# undef GetUserName
# define GetUserName GetUserNameA
#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
}