Re: stdin seekable failure

[Eric Blake]

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According to Paul Eggert on 4/11/2007 12:41 PM:
> Eric Blake <address@hidden> writes:
> 
>> Maybe the closeout module needs to be updated to worry about stdin as well
>> as stdout/stderr?
> 
> Coreutils doesn't need that, as it doesn't have the problem.  The two
> apps that I thought might have the problem solve it in a different
> way.  'head' bypasses stdio.  'od -N' sets the stdio input buffer size
> to 1 (which is slow and goes beyond what POSIX requires, but it does
> work).
> 
> So I suggest creating a new module 'closein' instead.

Done like so.

2007-04-12  Eric Blake  <address@hidden>

        Work around glibc's failure to reset seekable stdin on exit.
        * modules/closein: New module.
        * lib/closein.c: New file.
        * lib/closein.h: Likewise.
        * m4/closein.m4: Likewise.
        * MODULES.html.sh (File stream based Input/Output): Document it.

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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diff --git a/ChangeLog b/ChangeLog
index efda62b..fe02dd9 100644
diff --git a/MODULES.html.sh b/MODULES.html.sh
index 3f13fa3..277b09d 100755
--- a/MODULES.html.sh
+++ b/MODULES.html.sh
@@ -2192,6 +2192,7 @@ func_all_modules ()
 
   func_begin_table
   func_module close-stream
+  func_module closein
   func_module closeout
   func_module fopen-safer
   func_module fpending
diff --git a/lib/closein.c b/lib/closein.c
new file mode 100644
index 0000000..1aade1d
--- /dev/null
+++ b/lib/closein.c
@@ -0,0 +1,100 @@
+/* Close standard input, rewinding seekable stdin if necessary.
+
+   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.  */
+
+#include <config.h>
+
+#include "closein.h"
+#include "closeout.h"
+
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "gettext.h"
+#define _(msgid) gettext (msgid)
+
+#include "close-stream.h"
+#include "error.h"
+#include "exitfail.h"
+#include "quotearg.h"
+
+static const char *file_name;
+
+/* Set the file name to be reported in the event an error is detected
+   on stdin by close_stdin.  See also close_stdout_set_file_name, if
+   an error is detected when closing stdout.  */
+void
+close_stdin_set_file_name (const char *file)
+{
+  file_name = file;
+}
+
+/* Close standard input, rewinding any unused input if stdin is
+   seekable.  On error, issue a diagnostic and _exit with status
+   'exit_failure'.  Then call close_stdout.
+
+   Most programs can get by with close_stdout.  close_stdin is only
+   needed when a program wants to guarantee that partially read input
+   from seekable stdin is not consumed, for any subsequent clients.
+   For example, POSIX requires that these two commands behave alike:
+
+     (sed -ne 1q; cat) < file
+     tail -n 1 file
+
+   Since close_stdin is commonly registered via 'atexit', POSIX
+   and the C standard both say that it should not call 'exit',
+   because the behavior is undefined if 'exit' is called more than
+   once.  So it calls '_exit' instead of 'exit'.  If close_stdin
+   is registered via atexit before other functions are registered,
+   the other functions can act before this _exit is invoked.
+
+   Applications that use close_stdout should flush any streams other
+   than stdin, stdout, and stderr before exiting, since the call to
+   _exit will bypass other buffer flushing.  Applications should be
+   flushing and closing other streams anyway, to check for I/O errors.
+   Also, applications should not use tmpfile, since _exit can bypass
+   the removal of these files.
+
+   It's important to detect such failures and exit nonzero because many
+   tools (most notably `make' and other build-management systems) depend
+   on being able to detect failure in other tools via their exit status.  */
+
+void
+close_stdin (void)
+{
+  bool fail = false;
+  if (close_stream (stdin) != 0)
+    {
+      char const *close_error = _("error closing file");
+      if (file_name)
+       error (0, errno, "%s: %s", quotearg_colon (file_name),
+              close_error);
+      else
+       error (0, errno, "%s", close_error);
+
+      /* Defer failure until after closing stdout, since the output
+        can still usefully be flushed.  */
+      fail = true;
+    }
+
+  close_stdout ();
+
+  if (fail)
+    _exit (exit_failure);
+}
diff --git a/lib/closein.h b/lib/closein.h
new file mode 100644
index 0000000..43a713d
--- /dev/null
+++ b/lib/closein.h
@@ -0,0 +1,33 @@
+/* Close standard input, rewinding seekable stdin if necessary.
+
+   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.  */
+
+#ifndef _GL_CLOSEIN_H
+# define _GL_CLOSEIN_H 1
+
+# ifdef __cplusplus
+extern "C" {
+# endif
+
+void close_stdin_set_file_name (const char *file);
+void close_stdin (void);
+
+# ifdef __cplusplus
+}
+# endif
+
+#endif
diff --git a/m4/closein.m4 b/m4/closein.m4
new file mode 100644
index 0000000..bf8ff38
--- /dev/null
+++ b/m4/closein.m4
@@ -0,0 +1,13 @@
+# closein.m4 serial 1
+dnl Copyright (C) 2007 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_CLOSEIN],
+[
+  AC_LIBOBJ([closein])
+
+  dnl Prerequisites of lib/closein.c.
+  :
+])
diff --git a/modules/closein b/modules/closein
new file mode 100644
index 0000000..fefeae3
--- /dev/null
+++ b/modules/closein
@@ -0,0 +1,26 @@
+Description:
+Close all standard streams, resetting seekable stdin if needed, and exiting 
with a diagnostic on error.
+
+Files:
+lib/closein.h
+lib/closein.c
+m4/closein.m4
+
+Depends-on:
+closeout
+fflush
+stdbool
+
+configure.ac:
+gl_CLOSEIN
+
+Makefile.am:
+
+Include:
+"closein.h"
+
+License:
+GPL
+
+Maintainer:
+Eric Blake