1 files changed, 233 insertions, 0 deletions

diff --git a/gl/fflush.c b/gl/fflush.c
new file mode 100644
index 0000000..f3689b3
--- /dev/null
+++ b/gl/fflush.c
@@ -0,0 +1,233 @@
+/* fflush.c -- allow flushing input streams
+   Copyright (C) 2007-2023 Free Software Foundation, Inc.
+
+   This file is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
+
+   This file 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 Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Eric Blake. */
+
+#include <config.h>
+
+/* Specification.  */
+#include <stdio.h>
+
+#include <errno.h>
+#include <unistd.h>
+
+#include "freading.h"
+
+#include "stdio-impl.h"
+
+#undef fflush
+
+
+#if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1
+/* GNU libc, BeOS, Haiku, Linux libc5 */
+
+/* Clear the stream's ungetc buffer, preserving the value of ftello (fp).  */
+static void
+clear_ungetc_buffer_preserving_position (FILE *fp)
+{
+  if (fp->_flags & _IO_IN_BACKUP)
+    /* _IO_free_backup_area is a bit complicated.  Simply call fseek.  */
+    fseeko (fp, 0, SEEK_CUR);
+}
+
+#else
+
+/* Clear the stream's ungetc buffer.  May modify the value of ftello (fp).  */
+static void
+clear_ungetc_buffer (FILE *fp)
+{
+# if defined __sferror || defined __DragonFly__ || defined __ANDROID__
+  /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */
+  if (HASUB (fp))
+    {
+      fp_->_p += fp_->_r;
+      fp_->_r = 0;
+    }
+# elif defined __EMX__              /* emx+gcc */
+  if (fp->_ungetc_count > 0)
+    {
+      fp->_ungetc_count = 0;
+      fp->_rcount = - fp->_rcount;
+    }
+# elif defined _IOERR               /* Minix, AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, UnixWare, mingw, MSVC, NonStop Kernel, OpenVMS */
+  /* Nothing to do.  */
+# else                              /* other implementations */
+  fseeko (fp, 0, SEEK_CUR);
+# endif
+}
+
+#endif
+
+#if ! (defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1)
+/* GNU libc, BeOS, Haiku, Linux libc5 */
+
+# if (defined __sferror || defined __DragonFly__ || defined __ANDROID__) && defined __SNPT
+/* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */
+
+static int
+disable_seek_optimization (FILE *fp)
+{
+  int saved_flags = fp_->_flags & (__SOPT | __SNPT);
+  fp_->_flags = (fp_->_flags & ~__SOPT) | __SNPT;
+  return saved_flags;
+}
+
+static void
+restore_seek_optimization (FILE *fp, int saved_flags)
+{
+  fp_->_flags = (fp_->_flags & ~(__SOPT | __SNPT)) | saved_flags;
+}
+
+# else
+
+static void
+update_fpos_cache (_GL_ATTRIBUTE_MAYBE_UNUSED FILE *fp,
+                   _GL_ATTRIBUTE_MAYBE_UNUSED off_t pos)
+{
+#  if defined __sferror || defined __DragonFly__ || defined __ANDROID__
+  /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */
+#   if defined __CYGWIN__ || defined __ANDROID__
+  /* fp_->_offset is typed as an integer.  */
+  fp_->_offset = pos;
+#   else
+  /* fp_->_offset is an fpos_t.  */
+  /* Use a union, since on NetBSD, the compilation flags determine
+     whether fpos_t is typedef'd to off_t or a struct containing a
+     single off_t member.  */
+  union
+    {
+      fpos_t f;
+      off_t o;
+    } u;
+  u.o = pos;
+  fp_->_offset = u.f;
+#   endif
+  fp_->_flags |= __SOFF;
+#  endif
+}
+# endif
+#endif
+
+/* Flush all pending data on STREAM according to POSIX rules.  Both
+   output and seekable input streams are supported.  */
+int
+rpl_fflush (FILE *stream)
+{
+  /* When stream is NULL, POSIX and C99 only require flushing of "output
+     streams and update streams in which the most recent operation was not
+     input", and all implementations do this.
+
+     When stream is "an output stream or an update stream in which the most
+     recent operation was not input", POSIX and C99 requires that fflush
+     writes out any buffered data, and all implementations do this.
+
+     When stream is, however, an input stream or an update stream in
+     which the most recent operation was input, C99 specifies nothing,
+     and POSIX only specifies behavior if the stream is seekable.
+     mingw, in particular, drops the input buffer, leaving the file
+     descriptor positioned at the end of the input buffer. I.e. ftell
+     (stream) is lost.  We don't want to call the implementation's
+     fflush in this case.
+
+     We test ! freading (stream) here, rather than fwriting (stream), because
+     what we need to know is whether the stream holds a "read buffer", and on
+     mingw this is indicated by _IOREAD, regardless of _IOWRT.  */
+  if (stream == NULL || ! freading (stream))
+    return fflush (stream);
+
+#if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1
+  /* GNU libc, BeOS, Haiku, Linux libc5 */
+
+  clear_ungetc_buffer_preserving_position (stream);
+
+  return fflush (stream);
+
+#else
+  {
+    /* What POSIX says:
+       1) About the file-position indicator (-> fseeko, ftello):
+          The file position indicator is incremented by fgetc() and decremented
+          by ungetc():
+          <https://pubs.opengroup.org/onlinepubs/9699919799/functions/fgetc.html>
+            "... the fgetc() function shall ... advance the associated file
+             position indicator for the stream ..."
+          <https://pubs.opengroup.org/onlinepubs/9699919799/functions/ungetc.html>
+            "The file-position indicator is decremented by each successful
+             call to ungetc()..."
+       2) fflush discards bytes pushed back by ungetc:
+          <https://pubs.opengroup.org/onlinepubs/9699919799/functions/fflush.html>
+            "...any characters pushed back onto the stream by ungetc()
+             or ungetwc() that have not subsequently been read from the
+             stream shall be discarded..."
+          This implies implicitly: fflush does not change the file position
+          indicator.
+       3) Effects on the file descriptor, if the file descriptor is capable of
+          seeking:
+          <https://pubs.opengroup.org/onlinepubs/9699919799/functions/fflush.html>
+            "...the file offset of the underlying open file description shall
+             be set to the file position of the stream..."  */
+
+    /* POSIX does not specify fflush behavior for non-seekable input
+       streams.  Some implementations purge unread data, some return
+       EBADF, some do nothing.  */
+    off_t pos = ftello (stream);
+    if (pos == -1)
+      {
+        errno = EBADF;
+        return EOF;
+      }
+
+    /* Clear the ungetc buffer.  */
+    clear_ungetc_buffer (stream);
+
+    /* 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.  */
+    {
+      int result = fpurge (stream);
+      if (result != 0)
+        return result;
+    }
+
+# if (defined __sferror || defined __DragonFly__ || defined __ANDROID__) && defined __SNPT
+    /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */
+
+    {
+      /* Disable seek optimization for the next fseeko call.  This tells the
+         following fseeko call to seek to the desired position directly, rather
+         than to seek to a block-aligned boundary.  */
+      int saved_flags = disable_seek_optimization (stream);
+      int result = fseeko (stream, pos, SEEK_SET);
+
+      restore_seek_optimization (stream, saved_flags);
+      return result;
+    }
+
+# else
+
+    pos = lseek (fileno (stream), pos, SEEK_SET);
+    if (pos == -1)
+      return EOF;
+    /* After a successful lseek, update the file descriptor's position cache
+       in the stream.  */
+    update_fpos_cache (stream, pos);
+
+    return 0;
+
+# endif
+  }
+#endif
+}