BufferWriter.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreTypes.h"
#include "Misc/AssertionMacros.h"
#include "HAL/UnrealMemory.h"
#include "Math/NumericLimits.h"
#include "Serialization/Archive.h"
#include "Containers/UnrealString.h"
#include "Logging/LogMacros.h"
#include "Misc/EnumClassFlags.h"
#include "CoreGlobals.h"
 
enum class EBufferWriterFlags : uint8
{
    None =              0x0,    // No Flags
    TakeOwnership =     0x1,    // Archive will take ownership of the passed-in memory and free it on destruction
    AllowResize =       0x2,    // Allow overflow by resizing buffer
};
 
ENUM_CLASS_FLAGS(EBufferWriterFlags);
 
class FBufferWriter final : public FArchive
{
public:
    FBufferWriter(void* Data, int64 Size, EBufferWriterFlags InFlags = EBufferWriterFlags::None)
        : WriterData(Data)
        , WriterPos(0)
        , WriterSize(Size)
        , bFreeOnClose((InFlags & EBufferWriterFlags::TakeOwnership) != EBufferWriterFlags::None)
        , bAllowResize((InFlags & EBufferWriterFlags::AllowResize) != EBufferWriterFlags::None)
    {
        this->SetIsSaving(true);
    }
 
    ~FBufferWriter()
    {
        Close();
    }
    bool Close()
    {
        if (bFreeOnClose)
        {
            FMemory::Free(WriterData);
            WriterData = nullptr;
        }
        return !IsError();
    }
    void Serialize(void* Data, int64 Num)
    {
        const int64 NumBytesToAdd = WriterPos + Num - WriterSize;
        if (NumBytesToAdd > 0)
        {
            if (bAllowResize)
            {
                const int64 NewArrayCount = WriterSize + NumBytesToAdd;
                if (NewArrayCount >= MAX_int32)
                {
                    UE_LOG(LogSerialization, Fatal, TEXT("FBufferWriter does not support data larger than 2GB. Archive name: %s."), *GetArchiveName());
                }
 
                WriterData = FMemory::Realloc(WriterData, NewArrayCount);
                WriterSize = NewArrayCount;
            }
            else
            {
                UE_LOG(LogSerialization, Fatal, TEXT("FBufferWriter overflowed. Archive name: %s."), *GetArchiveName());
            }
        }
 
        check(WriterPos >= 0);
        check((WriterPos + Num) <= WriterSize);
        FMemory::Memcpy((uint8*)WriterData + WriterPos, Data, Num);
        WriterPos += Num;
    }
    int64 Tell()
    {
        return WriterPos;
    }
    int64 TotalSize()
    {
        return WriterSize;
    }
    void Seek(int64 InPos)
    {
        check(InPos >= 0);
        check(InPos <= WriterSize);
        WriterPos = InPos;
    }
    bool AtEnd()
    {
        return WriterPos >= WriterSize;
    }
    template <typename Type>
    Type* SerializeUninitialized()
    {
        check(WriterPos >= 0);
        check((WriterPos + (int64)sizeof(Type)) <= WriterSize);
        Type* Data = reinterpret_cast<Type*>((uint8*)WriterData + WriterPos);
        WriterPos += sizeof(Type);
        return Data;
    }
    virtual FString GetArchiveName() const { return TEXT("FBufferWriter"); }
 
    void* GetWriterData()
    {
        return WriterData;
    }
protected:
    void* WriterData;
    int64 WriterPos;
    int64 WriterSize;
    bool bFreeOnClose;
    bool bAllowResize;
};