/* fflush.c -- allow flushing input streams
   Copyright (C) 2007 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 2, 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, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

/* Written by Eric Blake. */

#include <config.h>

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

#include <errno.h>
#include <unistd.h>

#include "freading.h"
#include "fpurge.h"

#undef fflush

/* Flush all pending data on STREAM according to POSIX rules.  Both
   output and seekable input streams are supported.  */
int
rpl_fflush (FILE *stream)
{
  int result;
  off_t pos;

  /* When stream is NULL, POSIX only requires flushing of output
     streams.  C89 guarantees behavior of output streams, and fflush
     should be safe on read-write streams that are not currently
     reading.  */
  if (! stream || ! freading (stream))
    return fflush (stream);

  /* POSIX does not specify fflush behavior for non-seekable input
     streams.  */
  pos = ftello (stream);
  if (pos == -1)
    {
      errno = EBADF;
      return EOF;
    }

  /* To get here, we must be flushing a seekable input stream, so the
     semantics of fpurge are now appropriate to clear the buffer.  To
     avoid losing data, the lseek is also necessary.  */
  result = fpurge (stream);
  if (result != 0)
    return result;
  pos = lseek (fileno (stream), pos, SEEK_SET);
  if (pos == -1)
    return EOF;
#if defined __sferror               /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
  stream->_offset = pos;
  stream->_flags |= __SOFF;
#endif
  return 0;
}