text: //
  // BufferedStreamBuf.h
  //
  // $Id: //poco/1.3/Foundation/include/Poco/BufferedStreamBuf.h#4 $
  //
  // Library: Foundation
  // Package: Streams
  // Module:  StreamBuf
  //
  // Definition of template BasicBufferedStreamBuf and class BufferedStreamBuf.
  //
  // Copyright (c) 2004-2006, 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_BufferedStreamBuf_INCLUDED
  #define Foundation_BufferedStreamBuf_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> > 
  class BasicBufferedStreamBuf: public std::basic_streambuf<ch, tr>
  	/// This is an implementation of a buffered streambuf
  	/// that greatly simplifies the implementation of
  	/// custom streambufs of various kinds.
  	/// Derived classes only have to override the methods
  	/// readFromDevice() or writeToDevice().
  	///
  	/// This streambuf only supports unidirectional streams.
  	/// In other words, the BasicBufferedStreamBuf can be
  	/// used for the implementation of an istream or an
  	/// ostream, but not for 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:
  	BasicBufferedStreamBuf(std::streamsize bufferSize, openmode mode):
  		_bufsize(bufferSize),
  		_pBuffer(Allocator::allocate(_bufsize)),
  		_mode(mode)
  	{
  		this->setg(_pBuffer + 4, _pBuffer + 4, _pBuffer + 4);
  		this->setp(_pBuffer, _pBuffer + (_bufsize - 1));
  	}
  
  	~BasicBufferedStreamBuf()
  	{
  		Allocator::deallocate(_pBuffer, _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 (flushBuffer() == 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::move(_pBuffer + (4 - putback), this->gptr() - putback, putback);
  
  		int n = readFromDevice(_pBuffer + 4, _bufsize - 4);
  		if (n <= 0) return char_traits::eof();
  
  		this->setg(_pBuffer + (4 - putback), _pBuffer + 4, _pBuffer + 4 + n);
  
  		// return next character
  		return char_traits::to_int_type(*this->gptr());    
  	}
  
  	virtual int sync()
  	{
  		if (this->pptr() && this->pptr() > this->pbase()) 
  		{
  			if (flushBuffer() == -1) return -1;
  		}
  		return 0;
  	}
  
  protected:
  	void setMode(openmode mode)
  	{
  		_mode = mode;
  	}
  	
  	openmode getMode() const
  	{
  		return _mode;
  	}
  
  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 flushBuffer()
  	{
  		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*      _pBuffer;
  	openmode        _mode;
  
  	BasicBufferedStreamBuf(const BasicBufferedStreamBuf&);
  	BasicBufferedStreamBuf& operator = (const BasicBufferedStreamBuf&);
  };
  
  
  //
  // We provide an instantiation for char
  //
  typedef BasicBufferedStreamBuf<char, std::char_traits<char> > BufferedStreamBuf;
  
  
  } // namespace Poco
  
  
  #endif // Foundation_BufferedStreamBuf_INCLUDED
  