lib-utility/memorystream.h

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/**********************************************************************
 
  Audacity: A Digital Audio Editor
 
  MemoryStream.h
 
  Dmitry Vedenko
 
**********************************************************************/
 
#pragma once
 
#include <array>
#include <cstdint>
#include <list>
#include <vector>
 
#include "IteratorX.h"
 
class UTILITY_API MemoryStream final
{
public:
   using StreamData = std::vector<uint8_t>;
   using StreamChunk = std::pair<const void*, size_t>;
 
private:
   static constexpr size_t ChunkSize =
      1024 * 1024 - // 1Mb
      2 * sizeof(void*) - // account for the list node pointers
      sizeof(size_t); // account for the bytes used member
 
   struct Chunk final
   {
      std::array<uint8_t, ChunkSize> Data;
      size_t BytesUsed { 0 };
 
      // Returns data size left to append
      size_t Append(StreamChunk& dataView);
   };
 
   using ChunksList = std::list<Chunk>;
 
public:
 
   MemoryStream() = default;
   MemoryStream(MemoryStream&&) = default;
 
   void Clear();
 
   void AppendByte(char data);
   void AppendData(const void* data, const size_t length);
 
   // This function possibly has O(size) complexity as it may
   // require copying bytes to a linear chunk
   const void* GetData() const;
   const size_t GetSize() const noexcept;
 
   bool IsEmpty() const noexcept;
 
   struct UTILITY_API Iterator :
       ValueIterator<const StreamChunk, std::forward_iterator_tag>
   {
      Iterator(const Iterator&) = default;
 
      Iterator& operator++();
 
      Iterator operator++(int);
 
      StreamChunk operator*() const;
      StreamChunk operator->() const;
 
      bool operator==(const Iterator& rhs) const noexcept;
      bool operator!=(const Iterator& rhs) const noexcept;
   private:
      Iterator(const MemoryStream* stream, bool isBegin);
      
      const MemoryStream* mStream { nullptr };
      ChunksList::const_iterator mListIterator;
      bool mShowLinearPart { false };
 
      friend class MemoryStream;
   };
 
   Iterator begin() const;
   Iterator end() const;
 
private:
   // This structures are lazily updated by get data
   mutable ChunksList mChunks;
   mutable StreamData mLinearData;
 
   size_t mDataSize { 0 };
};