filestream.h

/***
* ==++==
*
* Copyright (c) Microsoft Corporation. All rights reserved.
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* ==--==
* =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
*
* Asynchronous File streams
*
* For the latest on this and related APIs, please see http://casablanca.codeplex.com.
*
* =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
****/
#pragma once

#ifndef _CASA_FILE_STREAMS_H
#define _CASA_FILE_STREAMS_H

#include "cpprest/details/fileio.h"
#include "cpprest/astreambuf.h"
#include "cpprest/streams.h"
#include <assert.h>

#ifndef _CONCRT_H
#ifndef _LWRCASE_CNCRRNCY
#define _LWRCASE_CNCRRNCY
// Note to reader: we're using lower-case namespace names everywhere, but the 'Concurrency' namespace
// is capitalized for historical reasons. The alias let's us pretend that style issue doesn't exist.
namespace Concurrency { }
namespace concurrency = Concurrency;
#endif
#endif

namespace Concurrency { namespace streams
{
    // Forward declarations
    template<typename _CharType> class file_buffer;

namespace details {
    // This operation queue is NOT thread safe
    class async_operation_queue
    {
        pplx::task<void> m_lastOperation;
    public:
        async_operation_queue()
        {
            m_lastOperation = pplx::task_from_result();
        }

        // It only accepts functors that take no argument and return pplx::task<T>
        // This function may execute op inline, thus it could throw immediately
        template <typename Func>
        auto enqueue_operation(Func &&op) -> decltype(op())
        {
            decltype(op()) res; // res is task<T> , which always has default constructor
            if (m_lastOperation.is_done())
            {
                res = op(); // Exceptions are expected to be thrown directly without catching
                if (res.is_done())
                    return res;
            }
            else
            {
                res = m_lastOperation.then([=] {
                    return op(); // It will cause task unwrapping
                });
            }
            m_lastOperation = res.then([&] (decltype(op())) {
                // This empty task is necessary for keeping the rest of the operations on the list running
                // even when the previous operation gets error.
                // Don't observe exception here.
            });
            return res;
        }

        void wait() const
        {
            m_lastOperation.wait();
        }
    };


    template<typename _CharType>
    class basic_file_buffer : public details::streambuf_state_manager<_CharType>
    {
    public:
        typedef typename basic_streambuf<_CharType>::traits traits;
        typedef typename basic_streambuf<_CharType>::int_type int_type;
        typedef typename basic_streambuf<_CharType>::pos_type pos_type;
        typedef typename basic_streambuf<_CharType>::off_type off_type;

        virtual ~basic_file_buffer()
        {
            if( this->can_read() )
            {
                this->_close_read().wait();
            }

            if (this->can_write())
            {
                this->_close_write().wait();
            }
        }

    protected:

        virtual bool can_seek() const { return this->is_open(); }

        virtual bool has_size() const { return this->is_open(); }

        virtual utility::size64_t size() const
        {
            if (!this->is_open())
                return 0;
            return _get_size(m_info, sizeof(_CharType));
        }


        virtual size_t buffer_size(std::ios_base::openmode direction = std::ios_base::in) const
        {
            if ( direction == std::ios_base::in )
                return m_info->m_buffer_size;
            else
                return 0;
        }

        virtual void set_buffer_size(size_t size, std::ios_base::openmode direction = std::ios_base::in)
        {
            if ( direction == std::ios_base::out ) return;

            m_info->m_buffer_size = size;

            if ( size == 0 && m_info->m_buffer != nullptr )
            {
               delete m_info->m_buffer;
               m_info->m_buffer = nullptr;
            }
        }

        virtual size_t in_avail() const
        {
            pplx::extensibility::scoped_recursive_lock_t lck(m_info->m_lock);

            return _in_avail_unprot();
        }

        size_t _in_avail_unprot() const
        {
            if ( !this->is_open() ) return 0;

            if ( m_info->m_buffer == nullptr || m_info->m_buffill == 0 ) return 0;
            if ( m_info->m_bufoff > m_info->m_rdpos || (m_info->m_bufoff+m_info->m_buffill) < m_info->m_rdpos ) return 0;

            msl::safeint3::SafeInt<size_t> rdpos(m_info->m_rdpos);
            msl::safeint3::SafeInt<size_t> buffill(m_info->m_buffill);
            msl::safeint3::SafeInt<size_t> bufpos = rdpos - m_info->m_bufoff;

            return buffill - bufpos;
        }

        _file_info * _close_stream()
        {
            // indicate that we are no longer open
            auto fileInfo = m_info;
            m_info = nullptr;
            return fileInfo;
        }

        static pplx::task<void> _close_file(_In_ _file_info * fileInfo)
        {
            pplx::task_completion_event<void> result_tce;
            auto callback = new _filestream_callback_close(result_tce);

            if ( !_close_fsb_nolock(&fileInfo, callback) )
            {
                delete callback;
                return pplx::task_from_result();
            }
            return pplx::create_task(result_tce);
        }

        // Workaround GCC compiler bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58972
        void _invoke_parent_close_read()
        {
            streambuf_state_manager<_CharType>::_close_read();
        }

        pplx::task<void> _close_read()
        {
            return m_readOps.enqueue_operation([this]
            {
                _invoke_parent_close_read();

                if (this->can_write())
                {
                    return pplx::task_from_result();
                }
                else
                {
                    // Neither heads are open. Close the underlying device
                    // to indicate that we are no longer open
                    auto fileInfo = _close_stream();

                    return _close_file(fileInfo);
                }
            });
        }

        pplx::task<void> _close_write()
        {
            streambuf_state_manager<_CharType>::_close_write();
            if (this->can_read())
            {
                // Read head is still open. Just flush the write data
                return flush_internal();
            }
            else
            {
                // Neither heads are open. Close the underlying device

                // We need to flush all writes if the file was opened for writing.
                return flush_internal().then([=](pplx::task<void> flushTask) -> pplx::task<void>
                {
                    // swallow exception from flush
                    try
                    {
                        flushTask.wait();
                    }
                    catch(...)
                    {
                    }

                    // indicate that we are no longer open
                    auto fileInfo = this->_close_stream();

                    return this->_close_file(fileInfo);
                });
            }
        }

        virtual pplx::task<int_type> _putc(_CharType ch)
        {
            auto result_tce = pplx::task_completion_event<size_t>();
            auto callback = new _filestream_callback_write<size_t>(m_info, result_tce);

            // Potentially we should consider deprecating this API, it is TERRIBLY inefficient.
            std::shared_ptr<_CharType> sharedCh;
            try
            {
                sharedCh = std::make_shared<_CharType>(ch);
            } catch (const std::bad_alloc &)
            {
                delete callback;
                throw;
            }
            
            size_t written = _putn_fsb(m_info, callback, sharedCh.get(), 1, sizeof(_CharType));
            if (written == sizeof(_CharType))
            {
                delete callback;
                return pplx::task_from_result<int_type>(ch);
            }
            
            return pplx::create_task(result_tce).then([sharedCh](size_t)
            {
                return static_cast<int_type>(*sharedCh);
            });
        }

        _CharType* _alloc(size_t)
        {
            return nullptr;
        }

        void _commit(size_t)
        {
        }

        virtual bool acquire(_Out_ _CharType*& ptr, _Out_ size_t& count)
        {
            ptr = nullptr;
            count = 0;
            return false;
        }

        virtual void release(_Out_writes_ (count) _CharType *, _In_ size_t count)
        {
            (void)(count);
        }

        virtual pplx::task<size_t> _putn(const _CharType *ptr, size_t count)
        {
            auto result_tce = pplx::task_completion_event<size_t>();
            auto callback = new _filestream_callback_write<size_t>(m_info, result_tce);

            size_t written = _putn_fsb(m_info, callback, ptr, count, sizeof(_CharType));

            if ( written != 0 && written != -1 )
            {
                delete callback;
                written = written/sizeof(_CharType);
                return pplx::task_from_result<size_t>(written);
            }
            return pplx::create_task(result_tce);
        }

        // Temporarily needed until the deprecated putn is removed.
        virtual pplx::task<size_t> _putn(const _CharType *ptr, size_t count, bool copy)
        {
            if (copy)
            {
                auto sharedData = std::make_shared<std::vector<_CharType>>(ptr, ptr + count);
                return _putn(ptr, count).then([sharedData](size_t size)
                {
                    return size;
                });
            }
            else
            {
                return _putn(ptr, count);
            }
        }

        virtual pplx::task<int_type> _bumpc()
        {
            return m_readOps.enqueue_operation([this]()-> pplx::task<int_type> {
                if ( _in_avail_unprot() > 0 )
                {
                    pplx::extensibility::scoped_recursive_lock_t lck(m_info->m_lock);

                    // Check again once the lock is held.

                    if ( _in_avail_unprot() > 0 )
                    {
                        auto bufoff = m_info->m_rdpos - m_info->m_bufoff;
                        _CharType ch = m_info->m_buffer[bufoff*sizeof(_CharType)];
                        m_info->m_rdpos += 1;
                        return pplx::task_from_result<int_type>(ch);
                    }
                }

                auto result_tce = pplx::task_completion_event<int_type>();
                auto callback = new _filestream_callback_bumpc(m_info, result_tce);

                size_t ch = _getn_fsb(m_info, callback, &callback->m_ch, 1, sizeof(_CharType));

                if ( ch == sizeof(_CharType) )
                {
                    pplx::extensibility::scoped_recursive_lock_t lck(m_info->m_lock);
                    m_info->m_rdpos += 1;
                    _CharType ch1 = (_CharType)callback->m_ch;
                    delete callback;
                    return pplx::task_from_result<int_type>(ch1);
                }
                return pplx::create_task(result_tce);
            });
        }

        virtual int_type _sbumpc()
        {
            m_readOps.wait();
            if ( m_info->m_atend ) return traits::eof();

            if ( _in_avail_unprot() == 0 ) return traits::requires_async();

            pplx::extensibility::scoped_recursive_lock_t lck(m_info->m_lock);

            if ( _in_avail_unprot() == 0 ) return traits::requires_async();

            auto bufoff = m_info->m_rdpos - m_info->m_bufoff;
            _CharType ch = m_info->m_buffer[bufoff*sizeof(_CharType)];
            m_info->m_rdpos += 1;
            return (int_type)ch;
        }

        pplx::task<int_type> _getcImpl()
        {
            if ( _in_avail_unprot() > 0 )
            {
                pplx::extensibility::scoped_recursive_lock_t lck(m_info->m_lock);

                // Check again once the lock is held.

                if ( _in_avail_unprot() > 0 )
                {
                    auto bufoff = m_info->m_rdpos - m_info->m_bufoff;
                    _CharType ch = m_info->m_buffer[bufoff*sizeof(_CharType)];
                    return pplx::task_from_result<int_type>(ch);
                }
            }

            auto result_tce = pplx::task_completion_event<int_type>();
            auto callback = new _filestream_callback_getc(m_info, result_tce);

            size_t ch = _getn_fsb(m_info, callback, &callback->m_ch, 1, sizeof(_CharType));

            if ( ch == sizeof(_CharType) )
            {
                pplx::extensibility::scoped_recursive_lock_t lck(m_info->m_lock);
                _CharType ch1 = (_CharType)callback->m_ch;
                delete callback;
                return pplx::task_from_result<int_type>(ch1);
            }
            return pplx::create_task(result_tce);

        }

        pplx::task<int_type> _getc()
        {
            return m_readOps.enqueue_operation([this]()-> pplx::task<int_type> {
                return _getcImpl();
            });
        }

        int_type _sgetc()
        {
            m_readOps.wait();
            if ( m_info->m_atend ) return traits::eof();

            if ( _in_avail_unprot() == 0 ) return traits::requires_async();

            pplx::extensibility::scoped_recursive_lock_t lck(m_info->m_lock);

            if ( _in_avail_unprot() == 0 ) return traits::requires_async();

            auto bufoff = m_info->m_rdpos - m_info->m_bufoff;
            _CharType ch = m_info->m_buffer[bufoff*sizeof(_CharType)];
            return (int_type)ch;
        }

        virtual pplx::task<int_type> _nextc()
        {
            return m_readOps.enqueue_operation([this]()-> pplx::task<int_type> {
                _seekrdpos_fsb(m_info, m_info->m_rdpos+1, sizeof(_CharType));
                if ( m_info->m_atend )
                    return pplx::task_from_result(basic_file_buffer<_CharType>::traits::eof());
                return this->_getcImpl();
            });
        }

        virtual pplx::task<int_type> _ungetc()
        {
            return m_readOps.enqueue_operation([this]()-> pplx::task<int_type> {
                if ( m_info->m_rdpos == 0 )
                    return pplx::task_from_result<int_type>(basic_file_buffer<_CharType>::traits::eof());
                _seekrdpos_fsb(m_info, m_info->m_rdpos-1, sizeof(_CharType));
                return this->_getcImpl();
            });
        }

        virtual pplx::task<size_t> _getn(_Out_writes_ (count) _CharType *ptr, _In_ size_t count)
        {
            return m_readOps.enqueue_operation([=] ()-> pplx::task<size_t>{
                if ( m_info->m_atend || count == 0 )
                    return pplx::task_from_result<size_t>(0);

                if ( _in_avail_unprot() >= count )
                {
                    pplx::extensibility::scoped_recursive_lock_t lck(m_info->m_lock);

                    // Check again once the lock is held.

                    if ( _in_avail_unprot() >= count )
                    {
                        auto bufoff = m_info->m_rdpos - m_info->m_bufoff;
                        std::memcpy((void *)ptr, this->m_info->m_buffer+bufoff*sizeof(_CharType), count*sizeof(_CharType));

                        m_info->m_rdpos += count;
                        return pplx::task_from_result<size_t>(count);
                    }
                }

                auto result_tce = pplx::task_completion_event<size_t>();
                auto callback = new _filestream_callback_read(m_info, result_tce);

                size_t read = _getn_fsb(m_info, callback, ptr, count, sizeof(_CharType));

                if ( read != 0 && read != -1)
                {
                    delete callback;
                    pplx::extensibility::scoped_recursive_lock_t lck(m_info->m_lock);
                    m_info->m_rdpos += read/sizeof(_CharType);
                    return pplx::task_from_result<size_t>(read/sizeof(_CharType));
                }
                return pplx::create_task(result_tce);
            });
        }

        size_t _sgetn(_Out_writes_ (count) _CharType *ptr, _In_ size_t count)
        {
            m_readOps.wait();
            if ( m_info->m_atend ) return 0;

            if ( count == 0 || in_avail() == 0 ) return 0;

            pplx::extensibility::scoped_recursive_lock_t lck(m_info->m_lock);

            size_t available = _in_avail_unprot();
            size_t copy = (count < available) ? count : available;

            auto bufoff = m_info->m_rdpos - m_info->m_bufoff;
            std::memcpy((void *)ptr, this->m_info->m_buffer+bufoff*sizeof(_CharType), copy*sizeof(_CharType));

            m_info->m_rdpos += copy;
            m_info->m_atend = (copy < count);
            return copy;
        }

        virtual size_t _scopy(_CharType *, size_t)
        {
            return 0;
        }

        virtual pos_type getpos(std::ios_base::openmode mode) const
        {
            return const_cast<basic_file_buffer*>(this)->seekoff(0, std::ios_base::cur, mode);
        }

        virtual pos_type seekpos(pos_type pos, std::ios_base::openmode mode)
        {
            if ( mode == std::ios_base::in )
            {
                m_readOps.wait();
                return (pos_type)_seekrdpos_fsb(m_info, size_t(pos), sizeof(_CharType));
            }
            else if ( (m_info->m_mode & std::ios::ios_base::app) == 0 )
            {
                return (pos_type)_seekwrpos_fsb(m_info, size_t(pos), sizeof(_CharType));
            }
            return (pos_type)Concurrency::streams::char_traits<_CharType>::eof();
        }

        virtual pos_type seekoff(off_type offset, std::ios_base::seekdir way, std::ios_base::openmode mode)
        {
            if ( mode == std::ios_base::in )
            {
                m_readOps.wait();
                switch ( way )
                {
                case std::ios_base::beg:
                    return (pos_type)_seekrdpos_fsb(m_info, size_t(offset), sizeof(_CharType));
                case std::ios_base::cur:
                    return (pos_type)_seekrdpos_fsb(m_info, size_t(m_info->m_rdpos+offset), sizeof(_CharType));
                case std::ios_base::end:
                    return (pos_type)_seekrdtoend_fsb(m_info, int64_t(offset), sizeof(_CharType));
                default:
                    // Fail on invalid input (_S_ios_seekdir_end)
                    assert(false);
                }
            }
            else if ( (m_info->m_mode & std::ios::ios_base::app) == 0 )
            {
                switch ( way )
                {
                case std::ios_base::beg:
                    return (pos_type)_seekwrpos_fsb(m_info, size_t(offset), sizeof(_CharType));
                case std::ios_base::cur:
                    return (pos_type)_seekwrpos_fsb(m_info, size_t(m_info->m_wrpos+offset), sizeof(_CharType));
                case std::ios_base::end:
                    return (pos_type)_seekwrpos_fsb(m_info, size_t(-1), sizeof(_CharType));
                default:
                    // Fail on invalid input (_S_ios_seekdir_end)
                    assert(false);
                }
            }
            return (pos_type)traits::eof();
        }

        virtual pplx::task<bool> _sync()
        {
            return flush_internal().then([](){return true;});
        }

    private:
        template<typename _CharType1> friend class ::concurrency::streams::file_buffer;

        pplx::task<void> flush_internal()
        {
            pplx::task_completion_event<void> result_tce;
            auto callback = utility::details::make_unique<_filestream_callback_write_b>(m_info, result_tce);

            if ( !_sync_fsb(m_info, callback.get()) )
            {
                return pplx::task_from_exception<void>(std::runtime_error("failure to flush stream"));
            }
            callback.release();
            return pplx::create_task(result_tce);
        }

        basic_file_buffer(_In_ _file_info *info) : streambuf_state_manager<_CharType>(info->m_mode), m_info(info) { }

#if !defined(__cplusplus_winrt)
        static pplx::task<std::shared_ptr<basic_streambuf<_CharType>>> open(
            const utility::string_t &_Filename,
            std::ios_base::openmode _Mode = std::ios_base::out,
#ifdef _WIN32
            int _Prot = (int)std::ios_base::_Openprot
#else
            int _Prot = 0 // unsupported on Linux, for now
#endif
            )
        {
            auto result_tce = pplx::task_completion_event<std::shared_ptr<basic_streambuf<_CharType>>>();
            auto callback = new _filestream_callback_open(result_tce);
            _open_fsb_str(callback, _Filename.c_str(), _Mode, _Prot);
            return pplx::create_task(result_tce);
        }

#else
        static pplx::task<std::shared_ptr<basic_streambuf<_CharType>>> open(
            ::Windows::Storage::StorageFile^ file,
            std::ios_base::openmode _Mode = std::ios_base::out)
        {
            auto result_tce = pplx::task_completion_event<std::shared_ptr<basic_streambuf<_CharType>>>();
            auto callback = new _filestream_callback_open(result_tce);
            _open_fsb_stf_str(callback, file, _Mode, 0);
            return pplx::create_task(result_tce);
        }
#endif

        class _filestream_callback_open : public details::_filestream_callback
        {
        public:
            _filestream_callback_open(const pplx::task_completion_event<std::shared_ptr<basic_streambuf<_CharType>>> &op) : m_op(op) { }

            virtual void on_opened(_In_ _file_info *info)
            {
                m_op.set(std::shared_ptr<basic_file_buffer<_CharType>>(new basic_file_buffer<_CharType>(info)));
                delete this;
            }

            virtual void on_error(const std::exception_ptr & e)
            {
                m_op.set_exception(e);
                delete this;
            }

        private:
            pplx::task_completion_event<std::shared_ptr<basic_streambuf<_CharType>>> m_op;
        };

        class _filestream_callback_close : public details::_filestream_callback
        {
        public:
            _filestream_callback_close(const pplx::task_completion_event<void> &op) : m_op(op) { }

            virtual void on_closed()
            {
                m_op.set();
                delete this;
            }

            virtual void on_error(const std::exception_ptr & e)
            {
                m_op.set_exception(e);
                delete this;
            }

        private:
            pplx::task_completion_event<void> m_op;
        };

        template<typename ResultType>
        class _filestream_callback_write : public details::_filestream_callback
        {
        public:
            _filestream_callback_write(_In_ _file_info *info, const pplx::task_completion_event<ResultType> &op) : m_info(info), m_op(op) { }

            virtual void on_completed(size_t result)
            {
                m_op.set((ResultType)result / sizeof(_CharType));
                delete this;
            }

            virtual void on_error(const std::exception_ptr & e)
            {
                m_op.set_exception(e);
                delete this;
            }

        private:
            _file_info *m_info;
            pplx::task_completion_event<ResultType> m_op;
        };

        class _filestream_callback_write_b : public details::_filestream_callback
        {
        public:
            _filestream_callback_write_b(_In_ _file_info *info, const pplx::task_completion_event<void> &op) : m_info(info), m_op(op) { }

            virtual void on_completed(size_t)
            {
                m_op.set();
                delete this;
            }

            virtual void on_error(const std::exception_ptr & e)
            {
                m_op.set_exception(e);
                delete this;
            }

        private:
            _file_info *m_info;
            pplx::task_completion_event<void> m_op;
        };


        class _filestream_callback_read : public details::_filestream_callback
        {
        public:
            _filestream_callback_read(_In_ _file_info *info, const pplx::task_completion_event<size_t> &op) : m_info(info), m_op(op) { }

            virtual void on_completed(size_t result)
            {
                result = result / sizeof(_CharType);
                m_info->m_rdpos += result;
                m_op.set(result);
                delete this;
            }

            virtual void on_error(const std::exception_ptr & e)
            {
                m_op.set_exception(e);
                delete this;
            }

        private:
            _file_info *m_info;
            pplx::task_completion_event<size_t> m_op;
        };

        class _filestream_callback_bumpc : public details::_filestream_callback
        {
        public:
            _filestream_callback_bumpc(_In_ _file_info *info, const pplx::task_completion_event<int_type> &op) : m_ch(0), m_info(info), m_op(op) { }

            virtual void on_completed(size_t result)
            {
                if ( result == sizeof(_CharType) )
                {
                    m_info->m_rdpos += 1;
                    m_op.set(m_ch);
                }
                else
                {
                    m_op.set(traits::eof());
                }
                delete this;
            }

            virtual void on_error(const std::exception_ptr & e)
            {
                m_op.set_exception(e);
                delete this;
            }

            int_type           m_ch;

        private:
            _file_info *m_info;
            pplx::task_completion_event<int_type> m_op;
        };

        class _filestream_callback_getc : public details::_filestream_callback
        {
        public:
            _filestream_callback_getc(_In_ _file_info *info, const pplx::task_completion_event<int_type> &op) : m_ch(0), m_info(info), m_op(op) { }

            virtual void on_completed(size_t result)
            {
                if ( result == sizeof(_CharType) )
                {
                    m_op.set(m_ch);
                }
                else
                {
                    m_op.set(traits::eof());
                }
                delete this;
            }

            int_type           m_ch;

            virtual void on_error(const std::exception_ptr & e)
            {
                m_op.set_exception(e);
                delete this;
            }

        private:
            _file_info *m_info;
            pplx::task_completion_event<int_type> m_op;
        };

        _file_info *m_info;
        async_operation_queue m_readOps;
    };

    } // namespace details

    template<typename _CharType>
    class file_buffer
    {
    public:
#if !defined(__cplusplus_winrt)
        static pplx::task<streambuf<_CharType>> open(
            const utility::string_t &file_name,
            std::ios_base::openmode mode = std::ios_base::out,
#ifdef _WIN32
            int prot = _SH_DENYRD
#else
            int prot = 0 // unsupported on Linux
#endif
            )
        {
            auto bfb = details::basic_file_buffer<_CharType>::open(file_name, mode, prot);
            return bfb.then([](pplx::task<std::shared_ptr<details::basic_streambuf<_CharType>>> op) -> streambuf<_CharType>
                {
                    return streambuf<_CharType>(op.get());
                });
        }

#else
        static pplx::task<streambuf<_CharType>> open(
            ::Windows::Storage::StorageFile^ file,
            std::ios_base::openmode mode = std::ios_base::out)
        {
            auto bfb = details::basic_file_buffer<_CharType>::open(file, mode);
            return bfb.then([](pplx::task<std::shared_ptr<details::basic_streambuf<_CharType>>> op) -> streambuf<_CharType>
                {
                    return streambuf<_CharType>(op.get());
                });
        }
#endif
    };


    template<typename _CharType>
    class file_stream
    {
    public:

#if !defined(__cplusplus_winrt)
        static pplx::task<streams::basic_istream<_CharType>> open_istream(
            const utility::string_t &file_name,
            std::ios_base::openmode mode = std::ios_base::in,
#ifdef _WIN32
            int prot = (int) std::ios_base::_Openprot
#else
            int prot = 0
#endif
            )
        {
            mode |= std::ios_base::in;
            return streams::file_buffer<_CharType>::open(file_name, mode, prot)
                .then([](streams::streambuf<_CharType> buf) -> basic_istream<_CharType>
                {
                    return basic_istream<_CharType>(buf);
                });
        }

        static pplx::task<streams::basic_ostream<_CharType>> open_ostream(
            const utility::string_t &file_name,
            std::ios_base::openmode mode = std::ios_base::out,
#ifdef _WIN32
            int prot = (int) std::ios_base::_Openprot
#else
            int prot = 0
#endif
            )
        {
            mode |= std::ios_base::out;
            return streams::file_buffer<_CharType>::open(file_name, mode, prot)
                .then([](streams::streambuf<_CharType> buf) -> basic_ostream<_CharType>
                {
                    return basic_ostream<_CharType>(buf);
                });
        }
#else
        static pplx::task<streams::basic_istream<_CharType>> open_istream(
            ::Windows::Storage::StorageFile^ file,
            std::ios_base::openmode mode = std::ios_base::in)
        {
            mode |= std::ios_base::in;
            return streams::file_buffer<_CharType>::open(file, mode)
                .then([](streams::streambuf<_CharType> buf) -> basic_istream<_CharType>
                {
                    return basic_istream<_CharType>(buf);
                });
        }

        static pplx::task<streams::basic_ostream<_CharType>> open_ostream(
            ::Windows::Storage::StorageFile^ file,
            std::ios_base::openmode mode = std::ios_base::out)
        {
            mode |= std::ios_base::out;
            return streams::file_buffer<_CharType>::open(file, mode)
                .then([](streams::streambuf<_CharType> buf) -> basic_ostream<_CharType>
                {
                    return basic_ostream<_CharType>(buf);
                });
        }
#endif
    };

    typedef file_stream<uint8_t> fstream;
}} // namespace concurrency::streams

#endif