Base64 Blob Serialization/Deserialization

This demonstrates conversion betweenTArray<uint8> and Base64 encoded strings in JSON:

• DcSerDeBase64.h
• DcSerDeBase64.cpp

// DataConfigExtra/Public/DataConfig/Extra/SerDe/DcSerDeBase64.h
USTRUCT()
struct FDcExtraTestStructWithBase64
{
    GENERATED_BODY()

    UPROPERTY(meta = (DcExtraBase64)) TArray<uint8> BlobField1;
    UPROPERTY(meta = (DcExtraBase64)) TArray<uint8> BlobField2;
};

// DataConfigExtra/Private/DataConfig/Extra/SerDe/DcSerDeBase64.cpp
FString Str = TEXT(R"(
    {
        "BlobField1" : "dGhlc2UgYXJlIG15IHR3aXN0ZWQgd29yZHM=",
        "BlobField2" : "",
    }
)");

Note that we're tagging the BlobField with (meta = (DcExtraBase64)) to explicitly show that we' want this member to be converted into Base64.

UE support arbitrary meta data in the meta = () segment. But beware that the meta data is only available when WITH_EDITORDATA flag is defined. In predicate we check for this DcExtraBase64 like this:

// DataConfigExtra/Private/DataConfig/Extra/SerDe/DcSerDeBase64.cpp
EDcDeserializePredicateResult PredicateIsBase64Blob(FDcDeserializeContext& Ctx)
{
	FArrayProperty* ArrayProperty = DcPropertyUtils::CastFieldVariant<FArrayProperty>(Ctx.TopProperty());

	//	check for only TArray<uint8>
	if (ArrayProperty == nullptr)
		return EDcDeserializePredicateResult::Pass;
	if (!ArrayProperty->Inner->IsA<FByteProperty>())
		return EDcDeserializePredicateResult::Pass;

	return ArrayProperty->HasMetaData(TEXT("DcExtraBase64"))
		? EDcDeserializePredicateResult::Process
		: EDcDeserializePredicateResult::Pass;
}