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BufferedBidirectionalStreamBuf.h

//
// BufferedBidirectionalStreamBuf.h
//
// $Id: //poco/1.2/Foundation/include/Poco/BufferedBidirectionalStreamBuf.h#1 $
//
// Library: Foundation
// Package: Streams
// Module:  StreamBuf
//
// Definition of template BasicBufferedBidirectionalStreamBuf and class BufferedBidirectionalStreamBuf.
//
// Copyright (c) 2005-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
// 
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#ifndef Foundation_BufferedBidirectionalStreamBuf_INCLUDED
#define Foundation_BufferedBidirectionalStreamBuf_INCLUDED


#include "Poco/Foundation.h"
#include "Poco/BufferAllocator.h"
#include "Poco/StreamUtil.h"
#include <streambuf>
#include <iosfwd>
#include <ios>


namespace Poco {


template<typename ch, typename tr, typename ba = BufferAllocator<ch> > 
00055 class BasicBufferedBidirectionalStreamBuf: public std::basic_streambuf<ch, tr>
      /// This is an implementation of a buffered bidirectional 
      /// streambuf that greatly simplifies the implementation of
      /// custom streambufs of various kinds.
      /// Derived classes only have to override the methods
      /// readFromDevice() or writeToDevice().
      ///
      /// In contrast to BasicBufferedStreambuf, this class supports
      /// simultaneous read and write access, so in addition to
      /// istream and ostream this streambuf can also be used
      /// for implementing an iostream.
{
protected:
      typedef std::basic_streambuf<ch, tr> Base;
      typedef std::basic_ios<ch, tr> IOS;
      typedef ch char_type;
      typedef tr char_traits;
      typedef ba Allocator;
      typedef typename Base::int_type int_type;
      typedef typename Base::pos_type pos_type;
      typedef typename Base::off_type off_type;
      typedef typename IOS::openmode openmode;

public:
      BasicBufferedBidirectionalStreamBuf(std::streamsize bufferSize, openmode mode):
            _bufsize(bufferSize),
            _pReadBuffer(Allocator::allocate(_bufsize)),
            _pWriteBuffer(Allocator::allocate(_bufsize)),
            _mode(mode)
      {
            this->setg(_pReadBuffer + 4, _pReadBuffer + 4, _pReadBuffer + 4);
            this->setp(_pWriteBuffer, _pWriteBuffer + (_bufsize - 1));
      }

      ~BasicBufferedBidirectionalStreamBuf()
      {
            Allocator::deallocate(_pReadBuffer, _bufsize);
            Allocator::deallocate(_pWriteBuffer, _bufsize);
      }

      virtual int_type overflow(int_type c)
      {
            if (!(_mode & IOS::out)) return char_traits::eof();

            if (c != char_traits::eof()) 
            {
                  *this->pptr() = char_traits::to_char_type(c);
                  this->pbump(1);
            }
            if (flush_buffer() == std::streamsize(-1)) return char_traits::eof();

            return c;
      }

      virtual int_type underflow()
      {
            if (!(_mode & IOS::in)) return char_traits::eof();

            if (this->gptr() && (this->gptr() < this->egptr()))
                  return char_traits::to_int_type(*this->gptr());

            int putback = int(this->gptr() - this->eback());
            if (putback > 4) putback = 4;

            char_traits::copy(_pReadBuffer + (4 - putback), this->gptr() - putback, putback);

            int n = readFromDevice(_pReadBuffer + 4, _bufsize - 4);
            if (n <= 0) return char_traits::eof();

            this->setg(_pReadBuffer + (4 - putback), _pReadBuffer + 4, _pReadBuffer + 4 + n);

            // return next character
            return char_traits::to_int_type(*this->gptr());    
      }

      virtual int sync()
      {
            if (this->pptr() && this->pptr() > this->pbase()) 
            {
                  if (flush_buffer() == -1) return -1;
            }
            return 0;
      }

private:
      virtual int readFromDevice(char_type* buffer, std::streamsize length)
      {
            return 0;
      }

      virtual int writeToDevice(const char_type* buffer, std::streamsize length)
      {
            return 0;
      }

      int flush_buffer()
      {
            int n = int(this->pptr() - this->pbase());
            if (writeToDevice(this->pbase(), n) == n) 
            {
                  this->pbump(-n);
                  return n;
            }
            return -1;
      }

      std::streamsize _bufsize;
      char_type*      _pReadBuffer;
      char_type*      _pWriteBuffer;
      openmode        _mode;
};


//
// We provide an instantiation for char
//
typedef BasicBufferedBidirectionalStreamBuf<char, std::char_traits<char> > BufferedBidirectionalStreamBuf;


} // namespace Poco


#endif // Foundation_BufferedBidirectionalStreamBuf_INCLUDED

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