lib/ftruncate.c

/* ftruncate emulations for native Windows.
   Copyright (C) 1992-2026 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/>.  */

#include <config.h>

/* Specification.  */
#include <unistd.h>

#if HAVE__CHSIZE
/* A native Windows platform.  */

# include <errno.h>

/* We need to test _FILE_OFFSET_BITS for mingw-w64
   and _GL_WINDOWS_64_BIT_OFF_T for MSVC.  */
# if (_FILE_OFFSET_BITS == 64 || _GL_WINDOWS_64_BIT_OFF_T)

/* Large File Support: off_t is 64-bit, but _chsize() takes only a 32-bit
   argument.  Some newer versions of the Windows CRT have a _chsize_s function
   that takes a 64-bit argument, but we cannot rely on that.
   So, define a 64-bit safe SetFileSize function ourselves.  */

/* Ensure that <windows.h> declares GetFileSizeEx.  */
#  if !defined _WIN32_WINNT || (_WIN32_WINNT < _WIN32_WINNT_WIN2K)
#   undef _WIN32_WINNT
#   define _WIN32_WINNT _WIN32_WINNT_WIN2K
#  endif

/* Get declarations of the native Windows API functions.  */
#  define WIN32_LEAN_AND_MEAN
#  include <windows.h>

/* Get _get_osfhandle.  */
#  if GNULIB_MSVC_NOTHROW
#   include "msvc-nothrow.h"
#  else
#   include <io.h>
#  endif

static BOOL
SetFileSize (HANDLE h, LONGLONG size)
{
  LARGE_INTEGER old_size;

  if (!GetFileSizeEx (h, &old_size))
    return FALSE;

  if (size != old_size.QuadPart)
    {
      /* Duplicate the handle, so we are free to modify its file position.  */
      HANDLE curr_process = GetCurrentProcess ();
      HANDLE tmph;

      if (!DuplicateHandle (curr_process,           /* SourceProcessHandle */
                            h,                      /* SourceHandle */
                            curr_process,           /* TargetProcessHandle */
                            (PHANDLE) &tmph,        /* TargetHandle */
                            (DWORD) 0,              /* DesiredAccess */
                            FALSE,                  /* InheritHandle */
                            DUPLICATE_SAME_ACCESS)) /* Options */
        return FALSE;

      if (size < old_size.QuadPart)
        {
          /* Reduce the size.  */
          LONG size_hi = (LONG) (size >> 32);
          if (SetFilePointer (tmph, (LONG) size, &size_hi, FILE_BEGIN)
              == INVALID_SET_FILE_POINTER
              && GetLastError() != NO_ERROR)
            {
              CloseHandle (tmph);
              return FALSE;
            }
          if (!SetEndOfFile (tmph))
            {
              CloseHandle (tmph);
              return FALSE;
            }
        }
      else
        {
          /* Increase the size by adding zero bytes at the end.  */
          static char zero_bytes[1024];
          LONG pos_hi = 0;
          LONG pos_lo = SetFilePointer (tmph, (LONG) 0, &pos_hi, FILE_END);
          if (pos_lo == INVALID_SET_FILE_POINTER
              && GetLastError() != NO_ERROR)
            {
              CloseHandle (tmph);
              return FALSE;
            }
          LONGLONG pos = ((LONGLONG) pos_hi << 32) | (ULONGLONG) (ULONG) pos_lo;
          while (pos < size)
            {
              DWORD written;
              LONGLONG count = size - pos;
              if (count > sizeof (zero_bytes))
                count = sizeof (zero_bytes);
              if (!WriteFile (tmph, zero_bytes, (DWORD) count, &written, NULL)
                  || written == 0)
                {
                  CloseHandle (tmph);
                  return FALSE;
                }
              pos += (ULONGLONG) (ULONG) written;
            }
        }
      /* Close the handle.  */
      CloseHandle (tmph);
    }
  return TRUE;
}

int
ftruncate (int fd, off_t length)
{
  HANDLE handle = (HANDLE) _get_osfhandle (fd);

  if (handle == INVALID_HANDLE_VALUE)
    {
      errno = EBADF;
      return -1;
    }
  if (length < 0)
    {
      errno = EINVAL;
      return -1;
    }
  if (!SetFileSize (handle, length))
    {
      switch (GetLastError ())
        {
        case ERROR_ACCESS_DENIED:
          errno = EACCES;
          break;
        case ERROR_HANDLE_DISK_FULL:
        case ERROR_DISK_FULL:
        case ERROR_DISK_TOO_FRAGMENTED:
          errno = ENOSPC;
          break;
        default:
          errno = EIO;
          break;
        }
      return -1;
    }
  return 0;
}

# else

#  include <io.h>

#  if HAVE_MSVC_INVALID_PARAMETER_HANDLER
#   include "msvc-inval.h"
static int
chsize_nothrow (int fd, long length)
{
  int result;

  TRY_MSVC_INVAL
    {
      result = _chsize (fd, length);
    }
  CATCH_MSVC_INVAL
    {
      result = -1;
      errno = EBADF;
    }
  DONE_MSVC_INVAL;

  return result;
}
#  else
#   define chsize_nothrow _chsize
#  endif

int
ftruncate (int fd, off_t length)
{
  return chsize_nothrow (fd, length);
}

# endif
#endif