ClickHouse/base/poco/Foundation/include/Poco/UnbufferedStreamBuf.h

//
// UnufferedStreamBuf.h
//
// Library: Foundation
// Package: Streams
// Module:  StreamBuf
//
// Definition of template BasicUnbufferedStreamBuf and class UnbufferedStreamBuf.
//
// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Foundation_UnbufferedStreamBuf_INCLUDED
#define Foundation_UnbufferedStreamBuf_INCLUDED


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


namespace Poco
{


template <typename ch, typename tr>
class BasicUnbufferedStreamBuf : public std::basic_streambuf<ch, tr>
/// This is an implementation of an unbuffered streambuf
/// that greatly simplifies the implementation of
/// custom streambufs of various kinds.
/// Derived classes only have to override the methods
/// readFromDevice() or writeToDevice().
{
protected:
    typedef std::basic_streambuf<ch, tr> Base;
    typedef std::basic_ios<ch, tr> IOS;
    typedef ch char_type;
    typedef tr char_traits;
    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:
    BasicUnbufferedStreamBuf() : _pb(char_traits::eof()), _ispb(false)
    {
        this->setg(0, 0, 0);
        this->setp(0, 0);
    }

    ~BasicUnbufferedStreamBuf() { }

    virtual int_type overflow(int_type c)
    {
        if (c != char_traits::eof())
            return writeToDevice(char_traits::to_char_type(c));
        else
            return c;
    }

    virtual int_type underflow()
    {
        if (_ispb)
        {
            return _pb;
        }
        else
        {
            int_type c = readFromDevice();
            if (c != char_traits::eof())
            {
                _ispb = true;
                _pb = c;
            }
            return c;
        }
    }

    virtual int_type uflow()
    {
        if (_ispb)
        {
            _ispb = false;
            return _pb;
        }
        else
        {
            int_type c = readFromDevice();
            if (c != char_traits::eof())
            {
                _pb = c;
            }
            return c;
        }
    }

    virtual int_type pbackfail(int_type c)
    {
        if (_ispb)
        {
            return char_traits::eof();
        }
        else
        {
            _ispb = true;
            _pb = c;
            return c;
        }
    }

    virtual std::streamsize xsgetn(char_type * p, std::streamsize count)
    /// Some platforms (for example, Compaq C++) have buggy implementations of
    /// xsgetn that handle null buffers incorrectly.
    /// Anyway, it does not hurt to provide an optimized implementation
    /// of xsgetn for this streambuf implementation.
    {
        std::streamsize copied = 0;
        while (count > 0)
        {
            int_type c = uflow();
            if (c == char_traits::eof())
                break;
            *p++ = char_traits::to_char_type(c);
            ++copied;
            --count;
        }
        return copied;
    }

protected:
    static int_type charToInt(char_type c) { return char_traits::to_int_type(c); }

private:
    virtual int_type readFromDevice() { return char_traits::eof(); }

    virtual int_type writeToDevice(char_type) { return char_traits::eof(); }

    int_type _pb;
    bool _ispb;

    BasicUnbufferedStreamBuf(const BasicUnbufferedStreamBuf &);
    BasicUnbufferedStreamBuf & operator=(const BasicUnbufferedStreamBuf &);
};


//
// We provide an instantiation for char.
//
// Visual C++ needs a workaround - explicitly importing the template
// instantiation - to avoid duplicate symbols due to multiple
// instantiations in different libraries.
//
typedef BasicUnbufferedStreamBuf<char, std::char_traits<char>> UnbufferedStreamBuf;


} // namespace Poco


#endif // Foundation_UnbufferedStreamBuf_INCLUDED