Re: [PATCH] libstdc++: istreambuf_iterator keep attached streambuf

[Jonathan Wakely <jwakely@redhat.com>]

On 23/09/17 09:54 +0300, Petr Ovtchenkov wrote:
>istreambuf_iterator should not forget about attached
>streambuf when it reach EOF.
>
>Checks in debug mode has no infuence more on character
>extraction in istreambuf_iterator increment operators.
>In this aspect behaviour in debug and non-debug mode
>is similar now.
>
>Test for detached srteambuf in istreambuf_iterator:
>When istreambuf_iterator reach EOF of istream, it should not
>forget about attached streambuf.
From fact "EOF in stream reached" not follow that
>stream reach end of life and input operation impossible
>more.
>---
> libstdc++-v3/include/bits/streambuf_iterator.h     | 41 +++++++--------
> .../24_iterators/istreambuf_iterator/3.cc          | 61 ++++++++++++++++++++++
> 2 files changed, 80 insertions(+), 22 deletions(-)
> create mode 100644 libstdc++-v3/testsuite/24_iterators/istreambuf_iterator/3.cc
>
>diff --git a/libstdc++-v3/include/bits/streambuf_iterator.h b/libstdc++-v3/include/bits/streambuf_iterator.h
>index f0451b1..45c3d89 100644
>--- a/libstdc++-v3/include/bits/streambuf_iterator.h
>+++ b/libstdc++-v3/include/bits/streambuf_iterator.h
>@@ -136,12 +136,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>       istreambuf_iterator&
>       operator++()
>       {
>-	__glibcxx_requires_cond(!_M_at_eof(),
>+	__glibcxx_requires_cond(_M_sbuf,
> 				_M_message(__gnu_debug::__msg_inc_istreambuf)
> 				._M_iterator(*this));
> 	if (_M_sbuf)
> 	  {
>+#ifdef _GLIBCXX_DEBUG_PEDANTIC
>+	    int_type _tmp =
>+#endif
> 	    _M_sbuf->sbumpc();
>+#ifdef _GLIBCXX_DEBUG_PEDANTIC
>+	    __glibcxx_requires_cond(!traits_type::eq_int_type(_tmp,traits_type::eof()),
>+				    _M_message(__gnu_debug::__msg_inc_istreambuf)
>+				    ._M_iterator(*this));
>+#endif
> 	    _M_c = traits_type::eof();
> 	  }
> 	return *this;
>@@ -151,14 +159,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>       istreambuf_iterator
>       operator++(int)
>       {
>-	__glibcxx_requires_cond(!_M_at_eof(),
>+        _M_get();
>+	__glibcxx_requires_cond(_M_sbuf
>+				&& !traits_type::eq_int_type(_M_c,traits_type::eof()),
> 				_M_message(__gnu_debug::__msg_inc_istreambuf)
> 				._M_iterator(*this));
>
> 	istreambuf_iterator __old = *this;
> 	if (_M_sbuf)
> 	  {
>-	    __old._M_c = _M_sbuf->sbumpc();
>+	    _M_sbuf->sbumpc();
> 	    _M_c = traits_type::eof();
> 	  }
> 	return __old;
>@@ -177,18 +187,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>       _M_get() const
>       {
> 	const int_type __eof = traits_type::eof();
>-	int_type __ret = __eof;
>-	if (_M_sbuf)
>-	  {
>-	    if (!traits_type::eq_int_type(_M_c, __eof))
>-	      __ret = _M_c;
>-	    else if (!traits_type::eq_int_type((__ret = _M_sbuf->sgetc()),
>-					       __eof))
>-	      _M_c = __ret;
>-	    else
>-	      _M_sbuf = 0;
>-	  }
>-	return __ret;
>+	if (_M_sbuf && traits_type::eq_int_type(_M_c, __eof))
>+          _M_c = _M_sbuf->sgetc();
>+	return _M_c;
>       }
>
>       bool
>@@ -339,7 +340,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>       typedef typename __is_iterator_type::streambuf_type  streambuf_type;
>       typedef typename traits_type::int_type               int_type;
>
>-      if (__first._M_sbuf && !__last._M_sbuf)
>+      if (__first._M_sbuf && (__last == istreambuf_iterator<_CharT>()))
> 	{
> 	  streambuf_type* __sb = __first._M_sbuf;
> 	  int_type __c = __sb->sgetc();
>@@ -374,7 +375,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>       typedef typename __is_iterator_type::streambuf_type  streambuf_type;
>       typedef typename traits_type::int_type               int_type;
>
>-      if (__first._M_sbuf && !__last._M_sbuf)
>+      if (__first._M_sbuf && (__last == istreambuf_iterator<_CharT>()))
> 	{
> 	  const int_type __ival = traits_type::to_int_type(__val);
> 	  streambuf_type* __sb = __first._M_sbuf;
>@@ -395,11 +396,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> 	      else
> 		__c = __sb->snextc();
> 	    }
>-
>-	  if (!traits_type::eq_int_type(__c, traits_type::eof()))
>-	    __first._M_c = __c;
>-	  else
>-	    __first._M_sbuf = 0;
>+	  __first._M_c = __c;
> 	}
>       return __first;
>     }
>diff --git a/libstdc++-v3/testsuite/24_iterators/istreambuf_iterator/3.cc b/libstdc++-v3/testsuite/24_iterators/istreambuf_iterator/3.cc
>new file mode 100644
>index 0000000..803ede4
>--- /dev/null
>+++ b/libstdc++-v3/testsuite/24_iterators/istreambuf_iterator/3.cc
>@@ -0,0 +1,61 @@
>+// { dg-options "-std=gnu++17" }
>+
>+// Copyright (C) 2017 Free Software Foundation, Inc.
>+//
>+// This file is part of the GNU ISO C++ Library.  This library 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, or (at your option)
>+// any later version.
>+
>+// This library 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 library; see the file COPYING3.  If not see
>+// <http://www.gnu.org/licenses/>.
>+
>+#include <algorithm>
>+#include <sstream>
>+#include <iterator>
>+#include <cstring>
>+#include <testsuite_hooks.h>
>+
>+void test03()
>+{
>+  using namespace std;
>+  bool test __attribute__((unused)) = true;
>+
>+  std::stringstream s;
>+  char b[] = "c2ee3d09-43b3-466d-b490-db35999a22cf";
>+  char r[] = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
>+  char q[] = "3c4852d6-d47b-4f46-b05e-b5edc1aa440e";
>+  //          012345678901234567890123456789012345
>+  //          0         1         2         3
>+  s << b;
>+  VERIFY( !s.fail() );
>+
>+  istreambuf_iterator<char> i(s);
>+  copy_n(i, 36, r);
>+  ++i; // EOF reached
>+  VERIFY(i == std::istreambuf_iterator<char>());
>+
>+  VERIFY(memcmp(b, r, 36) == 0);
>+
>+  s << q;
>+  VERIFY(!s.fail());
>+
>+  copy_n(i, 36, r);

This is undefined behaviour. The end-of-stream iterator value cannot
be dereferenced.