BulkDataWriter.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 "Serialization/Archive.h"
#include "Serialization/BulkData.h"
#include "Containers/UnrealString.h"
 
 
class FBulkDataWriter final : public FArchive
{
public:
    FBulkDataWriter( FByteBulkData& InBulkData, bool bIsPersistent = false )
        : BulkData( InBulkData )
        , WriterPos( BulkData.GetBulkDataSize() )
        , WriterSize( WriterPos )
    {
        SetIsSaving( true );
        SetIsPersistent( bIsPersistent );
        Buffer = BulkData.Lock( LOCK_READ_WRITE );
    }
 
    ~FBulkDataWriter()
    {
        // Remove the slack from the allocated bulk data
        BulkData.Realloc( WriterSize );
        BulkData.Unlock();
    }
 
    virtual void Serialize( void* Data, int64 Num )
    {
        // Determine if we need to reallocate the buffer to fit the next item
        const int64 NewPos = WriterPos + Num;
        check( NewPos >= WriterPos );
        if( NewPos > BulkData.GetBulkDataSize() )
        {
            // If so, resize to the new size + 3/8
            Buffer = BulkData.Realloc( NewPos + 3 * NewPos / 8 + 16 );
        }
 
        FMemory::Memcpy( static_cast<unsigned char*>( Buffer ) + WriterPos, Data, Num );
        WriterPos += Num;
        WriterSize = FMath::Max( WriterSize, WriterPos );
    }
 
    using FArchive::operator<<; // For visibility of the overloads we don't override
 
    virtual FArchive& operator<<( class FName& Name ) override
    {
        // FNames are serialized as strings in BulkData
        FString StringName = Name.ToString();
        *this << StringName;
        return *this;
    }
 
    virtual int64 Tell() { return WriterPos; }
    virtual int64 TotalSize() { return WriterSize; }
 
    virtual void Seek( int64 InPos )
    {
        check( InPos >= 0 );
        check( InPos <= WriterSize );
        WriterPos = InPos;
    }
 
    virtual bool AtEnd()
    {
        return WriterPos >= WriterSize;
    }
 
    virtual FString GetArchiveName() const { return TEXT( "FBulkDataWriter" ); }
 
protected:
    FByteBulkData& BulkData;
    void* Buffer;
    int64 WriterPos;
    int64 WriterSize;
};