memorystream.h

/*********************************************************************************************************************************************/
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/*                                                                                                                                           */
/*  Copyright (c) SILVERCODERS Ltd, http://silvercoders.com                                                                                  */
/*  Project homepage: https://github.com/docwire/docwire                                                                                     */
/*                                                                                                                                           */
/*  SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-DocWire-Commercial                                                                  */
/*********************************************************************************************************************************************/
 
#ifndef DOCWIRE_MEMORY_STREAM_H
#define DOCWIRE_MEMORY_STREAM_H
 
#include <istream>
#include <span>
 
namespace docwire
{
 
class imemorystreambuf : public std::streambuf
{
    std::span<const std::byte> m_source;
 
public:
    explicit imemorystreambuf(std::span<const std::byte> source) :
        m_source(source)
    {
        char* p = const_cast<char*>(reinterpret_cast<const char*>(m_source.data()));
        setg(p, p, p + m_source.size());
    }
 
    std::streampos seekpos(std::streampos sp, std::ios_base::openmode which = std::ios_base::in) override
    {
        if (which != std::ios_base::in || sp < 0 || sp > m_source.size())
            return -1;
        char* p = const_cast<char*>(reinterpret_cast<const char*>(m_source.data()));
        setg(p, p + sp, p + m_source.size());
        return sp;
    }
 
    std::streampos seekoff(std::streamoff off, std::ios_base::seekdir way, std::ios_base::openmode which = std::ios_base::in) override
    {
        if (which != std::ios_base::in)
            return -1;
        switch (way)
        {
            case std::ios_base::beg:
                return seekpos(off, which);
            case std::ios_base::cur:
                return seekpos(gptr() - eback() + off, which);
            case std::ios_base::end:
                return seekpos(m_source.size() + off , which);
            default:
                return -1;
        }
    }
};
 
class imemorystream : public std::istream
{
public:
    explicit imemorystream(std::span<const std::byte> source)
        : std::istream(&m_streambuf), m_streambuf(source)
    {}
 
private:
    imemorystreambuf m_streambuf;
};
 
} // namespace docwire
 
#endif // DOCWIRE_MEMORY_STREAM_H