ostream workaround for gcc 4.8.4

include/beast/core/detail/ostream.hpp

@@ -9,7 +9,6 @@
 #define BEAST_DETAIL_OSTREAM_HPP
 
 #include <boost/asio/buffer.hpp>
-#include <boost/utility/base_from_member.hpp>
 #include <memory>
 #include <ostream>
 #include <streambuf>
@@ -53,9 +52,29 @@ operator<<(std::ostream& os,
 
 //------------------------------------------------------------------------------
 
-template<
+struct basic_streambuf_movable_helper :
-    class DynamicBuffer, class CharT, class Traits>
+    std::basic_streambuf<char, std::char_traits<char>>
+{
+    basic_streambuf_movable_helper(
+        basic_streambuf_movable_helper&&) = default;
+};
+
+using basic_streambuf_movable =
+#if 0
+    std::is_move_constructible<basic_streambuf_movable_helper>;
+#else
+    std::false_type;
+#endif
+
+//------------------------------------------------------------------------------
+
+template<class DynamicBuffer,
+    class CharT, class Traits, bool isMovable>
+class ostream_buffer;
+
+template<class DynamicBuffer, class CharT, class Traits>
 class ostream_buffer
+        <DynamicBuffer, CharT, Traits, true>
     : public std::basic_streambuf<CharT, Traits>
 {
     using int_type = typename
@@ -72,45 +91,20 @@ public:
     ostream_buffer(ostream_buffer&&) = default;
     ostream_buffer(ostream_buffer const&) = delete;
 
-    ~ostream_buffer() noexcept;
-
-    explicit
-    ostream_buffer(DynamicBuffer& buf);
-
-    int_type
-    overflow(int_type ch) override;
-
-    int
-    sync() override;
-
-private:
-    void
-    prepare();
-
-    void
-    flush(int extra = 0);
-};
-
-template<class DynamicBuffer, class CharT, class Traits>
-ostream_buffer<DynamicBuffer, CharT, Traits>::
     ~ostream_buffer() noexcept
     {
         sync();
     }
 
-template<class DynamicBuffer, class CharT, class Traits>
+    explicit
-ostream_buffer<DynamicBuffer, CharT, Traits>::
     ostream_buffer(DynamicBuffer& buf)
         : buf_(buf)
     {
         prepare();
     }
 
-template<class DynamicBuffer, class CharT, class Traits>
-auto
-ostream_buffer<DynamicBuffer, CharT, Traits>::
-overflow(int_type ch) ->
     int_type
+    overflow(int_type ch) override
     {
         if(! Traits::eq_int_type(ch, Traits::eof()))
         {
@@ -123,19 +117,16 @@ overflow(int_type ch) ->
         return traits_type::eof();
     }
 
-template<class DynamicBuffer, class CharT, class Traits>
     int
-ostream_buffer<DynamicBuffer, CharT, Traits>::
+    sync() override
-sync()
     {
         flush();
         prepare();
         return 0;
     }
 
-template<class DynamicBuffer, class CharT, class Traits>
+private:
     void
-ostream_buffer<DynamicBuffer, CharT, Traits>::
     prepare()
     {
         using boost::asio::buffer_cast;
@@ -148,15 +139,94 @@ prepare()
             p + buffer_size(mb) / sizeof(CharT) - 1);
     }
 
-template<class DynamicBuffer, class CharT, class Traits>
     void
-ostream_buffer<DynamicBuffer, CharT, Traits>::
+    flush(int extra = 0)
-flush(int extra)
     {
         buf_.commit(
             (this->pptr() - this->pbase() + extra) *
                 sizeof(CharT));
     }
+};
+
+// This nonsense is all to work around a glitch in libstdc++
+// where std::basic_streambuf copy constructor is private:
+// https://github.com/gcc-mirror/gcc/blob/gcc-4_8-branch/libstdc%2B%2B-v3/include/std/streambuf#L799
+
+template<class DynamicBuffer, class CharT, class Traits>
+class ostream_buffer
+        <DynamicBuffer, CharT, Traits, false>
+    : public std::basic_streambuf<CharT, Traits>
+{
+    using int_type = typename
+        std::basic_streambuf<CharT, Traits>::int_type;
+
+    using traits_type = typename
+        std::basic_streambuf<CharT, Traits>::traits_type;
+
+    static std::size_t constexpr max_size = 512;
+
+    DynamicBuffer& buf_;
+
+public:
+    ostream_buffer(ostream_buffer&&) = delete;
+    ostream_buffer(ostream_buffer const&) = delete;
+
+    ~ostream_buffer() noexcept
+    {
+        sync();
+    }
+
+    explicit
+    ostream_buffer(DynamicBuffer& buf)
+        : buf_(buf)
+    {
+        prepare();
+    }
+
+    int_type
+    overflow(int_type ch) override
+    {
+        if(! Traits::eq_int_type(ch, Traits::eof()))
+        {
+            Traits::assign(*this->pptr(), ch);
+            flush(1);
+            prepare();
+            return ch;
+        }
+        flush();
+        return traits_type::eof();
+    }
+
+    int
+    sync() override
+    {
+        flush();
+        prepare();
+        return 0;
+    }
+
+private:
+    void
+    prepare()
+    {
+        using boost::asio::buffer_cast;
+        using boost::asio::buffer_size;
+        auto mbs = buf_.prepare(
+            read_size_helper(buf_, max_size));
+        auto const mb = *mbs.begin();
+        auto const p = buffer_cast<CharT*>(mb);
+        this->setp(p,
+            p + buffer_size(mb) / sizeof(CharT) - 1);
+    }
+
+    void
+    flush(int extra = 0)
+    {
+        buf_.commit(
+            (this->pptr() - this->pbase() + extra) *
+                sizeof(CharT));
+    }
+};
 
 //------------------------------------------------------------------------------
 
@@ -169,7 +239,8 @@ class ostream_helper<
         DynamicBuffer, CharT, Traits, true>
     : public std::basic_ostream<CharT, Traits>
 {
-    ostream_buffer<DynamicBuffer, CharT, Traits> osb_;
+    ostream_buffer<
+        DynamicBuffer, CharT, Traits, true> osb_;
 
 public:
     explicit
@@ -199,41 +270,48 @@ ostream_helper(
 // This work-around is for libstdc++ versions that
 // don't have a movable std::basic_streambuf
 
-template<class DynamicBuffer, class CharT, class Traits>
+template<class T>
-struct ostream_helper<
+class ostream_helper_base
-        DynamicBuffer, CharT, Traits, false>
-    : private boost::base_from_member<
-        std::unique_ptr<ostream_buffer<
-            DynamicBuffer, CharT, Traits>>>
-    , std::basic_ostream<CharT, Traits>
 {
-    explicit
+protected:
-    ostream_helper(DynamicBuffer& buf);
+    std::unique_ptr<T> member;
 
-    ostream_helper(ostream_helper&& other);
+    ostream_helper_base(
+        ostream_helper_base&&) = default;
+
+    explicit
+    ostream_helper_base(T* t)
+        : member(t)
+    {
+    }
 };
 
 template<class DynamicBuffer, class CharT, class Traits>
-ostream_helper<DynamicBuffer, CharT, Traits, false>::
+class ostream_helper<
+        DynamicBuffer, CharT, Traits, false>
+    : private ostream_helper_base<ostream_buffer<
+        DynamicBuffer, CharT, Traits, false>>
+    , public std::basic_ostream<CharT, Traits>
+{
+public:
+    explicit
     ostream_helper(DynamicBuffer& buf)
-    : boost::base_from_member<std::unique_ptr<
+        : ostream_helper_base<ostream_buffer<
-        ostream_buffer<DynamicBuffer, CharT, Traits>>>(
+            DynamicBuffer, CharT, Traits, false>>(
-            new ostream_buffer<DynamicBuffer, CharT, Traits>(buf))
+                new ostream_buffer<DynamicBuffer,
-    , std::basic_ostream<CharT, Traits>(
+                    CharT, Traits, false>(buf))
-        this->member.get())
+        , std::basic_ostream<CharT, Traits>(this->member.get())
     {
     }
 
-template<class DynamicBuffer, class CharT, class Traits>
-ostream_helper<DynamicBuffer, CharT, Traits, false>::
     ostream_helper(ostream_helper&& other)
-    : boost::base_from_member<std::unique_ptr<
+        : ostream_helper_base<ostream_buffer<
-        ostream_buffer<DynamicBuffer, CharT, Traits>>>(
+            DynamicBuffer, CharT, Traits, false>>(
-            std::move(other.member))
+                std::move(other))
-    , std::basic_ostream<CharT, Traits>(
+        , std::basic_ostream<CharT, Traits>(this->member.get())
-        this->member.get())
     {
     }
+};
 
 } // detail
 } // beast

include/beast/core/ostream.hpp

@@ -80,9 +80,7 @@ implementation_defined
 #else
 detail::ostream_helper<
     DynamicBuffer, char, std::char_traits<char>,
-        std::is_move_constructible<
+        detail::basic_streambuf_movable::value>
-            detail::ostream_buffer<DynamicBuffer,
-                char, std::char_traits<char>>>::value>
 #endif
 ostream(DynamicBuffer& buffer)
 {
@@ -90,9 +88,7 @@ ostream(DynamicBuffer& buffer)
         "DynamicBuffer requirements not met");
     return detail::ostream_helper<
         DynamicBuffer, char, std::char_traits<char>,
-            std::is_move_constructible<
+            detail::basic_streambuf_movable::value>{buffer};
-            detail::ostream_buffer<DynamicBuffer,
-                char, std::char_traits<char>>>::value>{buffer};
 }
 
 } // beast