Coverage Report

Created: 2025-03-06 06:58

/src/wget/lib/fflush.c
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/* fflush.c -- allow flushing input streams
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   Copyright (C) 2007-2025 Free Software Foundation, Inc.
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   This file is free software: you can redistribute it and/or modify
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   it under the terms of the GNU Lesser General Public License as
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   published by the Free Software Foundation; either version 2.1 of the
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   License, or (at your option) any later version.
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   This file is distributed in the hope that it will be useful,
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   but WITHOUT ANY WARRANTY; without even the implied warranty of
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   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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   GNU Lesser General Public License for more details.
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   You should have received a copy of the GNU Lesser General Public License
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   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
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/* Written by Eric Blake. */
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#include <config.h>
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/* Specification.  */
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#include <stdio.h>
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#include <errno.h>
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#include <unistd.h>
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#include "freading.h"
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#include "stdio-impl.h"
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#undef fflush
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#if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1
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/* GNU libc, BeOS, Haiku, Linux libc5 */
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/* Clear the stream's ungetc buffer, preserving the value of ftello (fp).  */
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static void
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clear_ungetc_buffer_preserving_position (FILE *fp)
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0
{
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  if (fp->_flags & _IO_IN_BACKUP)
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    /* _IO_free_backup_area is a bit complicated.  Simply call fseek.  */
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    fseeko (fp, 0, SEEK_CUR);
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0
}
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#else
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/* Clear the stream's ungetc buffer.  May modify the value of ftello (fp).  */
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static void
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clear_ungetc_buffer (FILE *fp)
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{
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# if defined __sferror || defined __DragonFly__ || defined __ANDROID__
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  /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */
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  if (HASUB (fp))
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    {
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      fp_->_p += fp_->_r;
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      fp_->_r = 0;
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    }
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# elif defined __EMX__              /* emx+gcc */
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  if (fp->_ungetc_count > 0)
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    {
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      fp->_ungetc_count = 0;
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      fp->_rcount = - fp->_rcount;
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    }
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# elif defined _IOERR               /* Minix, AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, UnixWare, mingw, MSVC, NonStop Kernel, OpenVMS */
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  /* Nothing to do.  */
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# else                              /* other implementations */
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  fseeko (fp, 0, SEEK_CUR);
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# endif
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}
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#endif
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#if ! (defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1)
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/* GNU libc, BeOS, Haiku, Linux libc5 */
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# if (defined __sferror || defined __DragonFly__ || defined __ANDROID__) && defined __SNPT
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/* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */
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static int
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disable_seek_optimization (FILE *fp)
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{
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  int saved_flags = fp_->_flags & (__SOPT | __SNPT);
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  fp_->_flags = (fp_->_flags & ~__SOPT) | __SNPT;
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  return saved_flags;
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}
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static void
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restore_seek_optimization (FILE *fp, int saved_flags)
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{
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  fp_->_flags = (fp_->_flags & ~(__SOPT | __SNPT)) | saved_flags;
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}
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# else
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static void
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update_fpos_cache (_GL_ATTRIBUTE_MAYBE_UNUSED FILE *fp,
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                   _GL_ATTRIBUTE_MAYBE_UNUSED off_t pos)
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{
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#  if defined __sferror || defined __DragonFly__ || defined __ANDROID__
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  /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */
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#   if defined __CYGWIN__ || defined __ANDROID__
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  /* fp_->_offset is typed as an integer.  */
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  fp_->_offset = pos;
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#   else
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  /* fp_->_offset is an fpos_t.  */
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  /* Use a union, since on NetBSD, the compilation flags determine
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     whether fpos_t is typedef'd to off_t or a struct containing a
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     single off_t member.  */
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  union
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    {
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      fpos_t f;
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      off_t o;
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    } u;
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  u.o = pos;
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  fp_->_offset = u.f;
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#   endif
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  fp_->_flags |= __SOFF;
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#  endif
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}
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# endif
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#endif
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/* Flush all pending data on STREAM according to POSIX rules.  Both
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   output and seekable input streams are supported.  */
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int
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rpl_fflush (FILE *stream)
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{
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  /* When stream is NULL, POSIX and C99 only require flushing of "output
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     streams and update streams in which the most recent operation was not
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     input", and all implementations do this.
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     When stream is "an output stream or an update stream in which the most
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     recent operation was not input", POSIX and C99 requires that fflush
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     writes out any buffered data, and all implementations do this.
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     When stream is, however, an input stream or an update stream in
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     which the most recent operation was input, C99 specifies nothing,
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     and POSIX only specifies behavior if the stream is seekable.
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     mingw, in particular, drops the input buffer, leaving the file
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     descriptor positioned at the end of the input buffer. I.e. ftell
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     (stream) is lost.  We don't want to call the implementation's
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     fflush in this case.
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     We test ! freading (stream) here, rather than fwriting (stream), because
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     what we need to know is whether the stream holds a "read buffer", and on
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     mingw this is indicated by _IOREAD, regardless of _IOWRT.  */
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  if (stream == NULL || ! freading (stream))
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0
    return fflush (stream);
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#if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1
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  /* GNU libc, BeOS, Haiku, Linux libc5 */
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  clear_ungetc_buffer_preserving_position (stream);
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  return fflush (stream);
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#else
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  {
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    /* What POSIX says:
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       1) About the file-position indicator (-> fseeko, ftello):
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          The file position indicator is incremented by fgetc() and decremented
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          by ungetc():
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          <https://pubs.opengroup.org/onlinepubs/9699919799/functions/fgetc.html>
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            "... the fgetc() function shall ... advance the associated file
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             position indicator for the stream ..."
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          <https://pubs.opengroup.org/onlinepubs/9699919799/functions/ungetc.html>
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            "The file-position indicator is decremented by each successful
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             call to ungetc()..."
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       2) fflush discards bytes pushed back by ungetc:
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          <https://pubs.opengroup.org/onlinepubs/9699919799/functions/fflush.html>
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            "...any characters pushed back onto the stream by ungetc()
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             or ungetwc() that have not subsequently been read from the
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             stream shall be discarded..."
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          This implies implicitly: fflush does not change the file position
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          indicator.
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       3) Effects on the file descriptor, if the file descriptor is capable of
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          seeking:
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          <https://pubs.opengroup.org/onlinepubs/9699919799/functions/fflush.html>
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            "...the file offset of the underlying open file description shall
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             be set to the file position of the stream..."  */
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    /* POSIX does not specify fflush behavior for non-seekable input
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       streams.  Some implementations purge unread data, some return
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       EBADF, some do nothing.  */
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    off_t pos = ftello (stream);
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    if (pos == -1)
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      {
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        errno = EBADF;
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        return EOF;
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      }
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    /* Clear the ungetc buffer.  */
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    clear_ungetc_buffer (stream);
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    /* To get here, we must be flushing a seekable input stream, so the
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       semantics of fpurge are now appropriate to clear the buffer.  To
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       avoid losing data, the lseek is also necessary.  */
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    {
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      int result = fpurge (stream);
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      if (result != 0)
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        return result;
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    }
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# if (defined __sferror || defined __DragonFly__ || defined __ANDROID__) && defined __SNPT
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    /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */
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    {
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      /* Disable seek optimization for the next fseeko call.  This tells the
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         following fseeko call to seek to the desired position directly, rather
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         than to seek to a block-aligned boundary.  */
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      int saved_flags = disable_seek_optimization (stream);
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      int result = fseeko (stream, pos, SEEK_SET);
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      restore_seek_optimization (stream, saved_flags);
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      return result;
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    }
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# else
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    pos = lseek (fileno (stream), pos, SEEK_SET);
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    if (pos == -1)
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      return EOF;
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    /* After a successful lseek, update the file descriptor's position cache
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       in the stream.  */
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    update_fpos_cache (stream, pos);
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    return 0;
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# endif
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  }
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#endif
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0
}