Make fflush after ungetc work on BSD platforms.

6 files changed, 152 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index 61347900fb..78f3667256 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2008-03-06  Bruno Haible  <bruno@clisp.org>
+
+	Make fflush after ungetc work on BSD platforms.
+	* lib/fflush.c (rpl_fflush): Discard ungetc buffer if possible.
+	* tests/test-fflush2.c: New file.
+	* tests/test-fflush2.sh: New file.
+	* modules/fflush-tests (Files): Add tests/test-fflush2.sh,
+	tests/test-fflush2.c.
+	(Makefile.am): Build test-fflush2 and run test-fflush2.sh.
+	* doc/posix-functions/fflush.texi: Document fflush after ungetc bug.
+
 2008-03-06  Eric Blake  <ebb9@byu.net>
 
 	Likewise for ftello.
diff --git a/doc/posix-functions/fflush.texi b/doc/posix-functions/fflush.texi
index 2cc9d88113..b1a461bf3b 100644
--- a/doc/posix-functions/fflush.texi
+++ b/doc/posix-functions/fflush.texi
@@ -15,6 +15,11 @@ It doesn't do this on some platforms.
 @item
 @code{fflush} on an input stream changes the position of the stream to the
 end of the previous buffer, on some platforms: mingw.
+@item
+@code{fflush} on an input stream right after @code{ungetc} does not discard
+the @code{ungetc} buffer, on some platforms:
+MacOS X 10.3, FreeBSD 6.0, NetBSD 3.0, OpenBSD 3.8, Cygwin.
+Cygwin.
 @end itemize
 
 Portability problems not fixed by Gnulib:
@@ -26,4 +31,8 @@ contains Unix line terminators (LF), on some platforms: mingw.
 @item
 On Windows platforms (excluding Cygwin), this function does not set @code{errno}
 upon failure.
+@item
+@code{fflush} on an input stream right after @code{ungetc} does not discard
+the @code{ungetc} buffer, on some platforms:
+AIX 5.1, HP-UX 11, IRIX 6.5, OSF/1 5.1, Solaris 10, mingw.
 @end itemize
diff --git a/lib/fflush.c b/lib/fflush.c
index be97769a4a..dfc1a74abd 100644
--- a/lib/fflush.c
+++ b/lib/fflush.c
@@ -1,5 +1,5 @@
 /* fflush.c -- allow flushing input streams
-   Copyright (C) 2007 Free Software Foundation, Inc.
+   Copyright (C) 2007-2008 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
@@ -59,6 +59,46 @@ rpl_fflush (FILE *stream)
   if (stream == NULL || ! freading (stream))
     return fflush (stream);
 
+  /* Clear the ungetc buffer.
+
+     This is needed before fetching the file-position indicator, because
+     1) The file position indicator is incremented by fgetc() and decremented
+        by ungetc():
+        <http://www.opengroup.org/susv3/functions/fgetc.html>
+          "The file-position indicator is decremented by each successful
+           call to ungetc()..."
+        <http://www.opengroup.org/susv3/functions/ungetc.html>
+          "... the fgetc() function shall ... advance the associated file
+        position indicator for the stream ..."
+     2) <http://www.opengroup.org/susv3/functions/ungetc.html> says:
+          "The value of the file-position indicator for the stream after
+           reading or discarding all pushed-back bytes shall be the same
+           as it was before the bytes were pushed back."
+     3) Here we are discarding all pushed-back bytes.
+
+     Unfortunately it is impossible to implement this on platforms with
+     _IOERR, because an ungetc() on this platform prepends the pushed-back
+     bytes to the buffer without an indication of the limit between the
+     pushed-back bytes and the read-ahead bytes.  */
+#if defined __sferror               /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
+  {
+# if defined __NetBSD__ || defined __OpenBSD__
+    struct __sfileext
+      {
+	struct  __sbuf _ub; /* ungetc buffer */
+	/* More fields, not relevant here.  */
+      };
+    if (((struct __sfileext *) stream->_ext._base)->_ub._base != NULL)
+# else
+    if (stream->_ub._base != NULL)
+# endif
+      {
+	stream->_p += stream->_r;
+	stream->_r = 0;
+      }
+  }
+#endif
+
   /* POSIX does not specify fflush behavior for non-seekable input
      streams.  Some implementations purge unread data, some return
      EBADF, some do nothing.  */
diff --git a/modules/fflush-tests b/modules/fflush-tests
index d9ab967e44..d7ed9b1b66 100644
--- a/modules/fflush-tests
+++ b/modules/fflush-tests
@@ -1,5 +1,7 @@
 Files:
 tests/test-fflush.c
+tests/test-fflush2.sh
+tests/test-fflush2.c
 
 Depends-on:
 fseeko
@@ -7,6 +9,7 @@ fseeko
 configure.ac:
 
 Makefile.am:
-TESTS += test-fflush
-check_PROGRAMS += test-fflush
+TESTS += test-fflush test-fflush2.sh
+TESTS_ENVIRONMENT += EXEEXT='@EXEEXT@' srcdir='$(srcdir)'
+check_PROGRAMS += test-fflush test-fflush2
 MOSTLYCLEANFILES += test-fflush.txt
diff --git a/tests/test-fflush2.c b/tests/test-fflush2.c
new file mode 100644
index 0000000000..d5d8619c3c
--- /dev/null
+++ b/tests/test-fflush2.c
@@ -0,0 +1,78 @@
+/* Test of POSIX compatible fflush() function.
+   Copyright (C) 2008 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 of the License, 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 <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+#include <stdio.h>
+
+#include <stdlib.h>
+
+/* This test can only be made to work on specific platforms.  */
+#if defined _IO_ferror_unlocked || defined __sferror /* GNU libc, BeOS; FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
+# define ASSERT(expr) \
+  do									     \
+    {									     \
+      if (!(expr))							     \
+        {								     \
+          fprintf (stderr, "%s:%d: assertion failed\n", __FILE__, __LINE__); \
+          abort ();							     \
+        }								     \
+    }									     \
+  while (0)
+#else
+# define ASSERT(expr) \
+  do									     \
+    {									     \
+      if (!(expr))							     \
+        {								     \
+          printf ("Skipping test: expected failure on this platform\n");     \
+          exit (77);							     \
+        }								     \
+    }									     \
+  while (0)
+#endif
+
+int
+main (int argc, char **argv)
+{
+  /* Check that fflush after a non-backup ungetc() call discards the ungetc
+     buffer.  This is mandated by POSIX
+     <http://www.opengroup.org/susv3/functions/ungetc.html>:
+       "The value of the file-position indicator for the stream after
+        reading or discarding all pushed-back bytes shall be the same
+        as it was before the bytes were pushed back."  */
+  int c;
+
+  c = fgetc (stdin);
+  ASSERT (c == '#');
+
+  c = fgetc (stdin);
+  ASSERT (c == '!');
+
+  /* Here the file-position indicator must be 2.  */
+
+  c = ungetc ('@', stdin);
+  ASSERT (c == '@');
+
+  fflush (stdin);
+
+  /* Here the file-position indicator must be 2 again.  */
+
+  c = fgetc (stdin);
+  ASSERT (c == '/');
+
+  return 0;
+}
diff --git a/tests/test-fflush2.sh b/tests/test-fflush2.sh
new file mode 100755
index 0000000000..5c3fc979a6
--- /dev/null
+++ b/tests/test-fflush2.sh
@@ -0,0 +1,8 @@
+#!/bin/sh
+
+# Execute the test only with seekable input stream.
+# The behaviour of fflush() on a non-seekable input stream is undefined.
+./test-fflush2${EXEEXT} < "$srcdir/test-fflush2.sh" || exit $?
+#cat "$srcdir/test-fflush2.sh" | ./test-fflush2${EXEEXT} || exit $?
+
+exit 0