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

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


#ifndef Foundation_BufferedStreamBuf_INCLUDED
#define Foundation_BufferedStreamBuf_INCLUDED


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


namespace DB
{
class ReadBufferFromIStream;
}

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);
    }

    ~BasicBufferedStreamBuf() { Allocator::deallocate(_pBuffer, _bufsize); }

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

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

        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:
    friend class DB::ReadBufferFromIStream;

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


} // namespace Poco


#endif // Foundation_BufferedStreamBuf_INCLUDED