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# Serialization (NvBlastExtSerialization)

## Introduction

This extension defines the Nv::Blast::ExtSerialization class, a modular serialization manager which can be extended to handle data types from different Blast™ modules (such as low-level, Tk, and ExtPhysX).

An ExtSerialization manager is created using the global function NvBlastExtSerializationCreate:

(From now on we'll assume we are using the Nv::Blast namespace.)

    ExtSerialization* ser = NvBlastExtSerializationCreate();

ExtSerialization is capable of loading sets of serializers for different data types and encodings. The NvBlastExtSerialization extension comes with a set of low-level data serializers, with types enumerated in the header NvBlastExtLlSerialization.h.

The low-level serializers are automatically loaded into an ExtSerialization when it is created.

To load serializers for Tk and ExtPhysX assets, you must also load the extensions BlastTk Serialization (NvBlastExtTkSerialization) and ExtPhysX Serialization (NvBlastExtPxSerialization), respectively. See the documentation for those modules.

Each serializer is capable of reading (and writing, if it is not read-only) a single data type in a single encoding (format). Some serializers are read-only, in order to read legacy formats.

The encodings available are enumerated in ExtSerialization::EncodingID. They are currently:

- CapnProtoBinary - Uses Cap'n Proto's binary serialization format
- Raw - For low-level NvBlastAsset and NvBlastFamily types, this is simply a memory copy. For Tk and ExtPx assets, this is the deprecated serialization format from Blast™ 1.0.

## Serialization (writing)

To serialize an object, the serialization manager's write encoding ID must be set to the desired value. By default it is set to EncodingID::CapnProtoBinary, as this is the only encoding which supports writing for all object types (at the present time). When other encodings become available, use ExtSerialization::setSerializationEncoding to set the write encoding to the desired type.

Each serialization module defines the object types it can serialize. ExtSerialization defines the low-level types in NvBlastExtLlSerialization.h:

- LlObjectTypeID::Asset - An NvBlastAsset
- LlObjectTypeID::Family - An NvBlastFamily

To serialize an object, for example an NvBlastAsset, use ExtSerialization::serializeIntoBuffer as follows:

    const NvBlastAsset* asset = ... // Given pointer to an NvBlastAsset

    void* buffer;
    uint64_t size = ser->serializeIntoBuffer(buffer, asset, LlObjectTypeID::Asset);

If successful, the data is written into a buffer allocated using the NvBlastGlobals allocator, written to the "buffer" parameter, and the size of the buffer written is the return value of the function. If the function returns 0, then serialization was unsuccessful. Notice that the second function parameter is actually a void*, so it requires the last parameter to tell it what object it is serializing. A utility wrapper function is given in NvBlastExtLlSerialization.h which performs the same operation with an NvBlastAsset, so one could equivalently use

    void* buffer;
    uint64_t size = NvBlastExtSerializationSerializeAssetIntoBuffer(buffer, *ser, asset);

A corresponding function also exists for NvBlastFamily, as well as other data types supported by other serialization extensions.

This buffer may be written to disk, memory, networked, etc. Since the memory for the buffer is allocated using the allocator in NvBlastGlobals, it may be freed using the same allocator:

    NVBLAST_FREE(buffer)

### Using a Buffer Provider

If you wish to provide the serialization buffer by some means other than the NvBlastGlobals allocator, you may set a "buffer provider" in the serialization manager. A buffer provider is simply a callback that requests a buffer from the user of the necessary size. The user implements the interface ExtSerialization::BufferProvider, and passes a pointer to an instance of one to the serialization manager using ExtSerialization::setBufferProvider.

For example:

    std::vector<char> growableBuffer;

    class MyBufferProvider : public Nv::Blast::ExtSerialization::BufferProvider
    {
    public:
        MyBufferProvider(std::vector<char>& growableBuffer) : m_growableBuffer(growableBuffer) {}

        virtual void*   requestBuffer(size_t size) override
        {
            if (m_growableBuffer.size() < size)
            {
                m_growableBuffer.resize(size);
            }
            return m_growableBuffer.data();
        }

    private:
        std::vector<char>&  m_growableBuffer;
    } myBufferProvider(growableBuffer);

    ser->setBufferProvider(&myBufferProvider);

Passing NULL to setBufferProvider returns the serialization to its default behavior of using the NvBlastGlobals allocator.

## Deserialization (reading)

To deserialize an object, use the ExtSerialization::deserializeFromBuffer method. If you know the type of object in the buffer, you may directly cast the returned pointer to one of that type. For example, if the buffer contains an NvBlastAsset, use:

    const void* buffer = ... // A given buffer, may be read from disk, memory, etc.
    const uint64_t size = ... // The buffer's size in bytes

    NvBlastAsset* asset = static_cast<NvBlastAsset*>(ser->deserializeFromBuffer(buffer, size));

This returns a valid pointer if deserialization was successful, or NULL otherwise. If no serializer is loaded which can handle the object type in the stream in its given encoding, it will fail and return NULL.

Again, the memory for the asset is allocated using NvBlastGlobals, so that the asset may be released using

    NVBLAST_FREE(asset);

## Detecting the Object Type in a Buffer

If you don't know the object type in the buffer, you may use the last (optional) argument in deserializeFromBuffer to return the type:

    uint32_t objTypeID;
    void* obj = ser->deserializeFromBuffer(buffer, size, &objTypeID);

    NVBLAST_CHECK_ERROR(obj != nullptr, "Object could not be read from buffer.", return);

    switch (objTypeID)
    {
    case LlObjectTypeID::Asset:
        handleAssetLoad(static_cast<NvBlastAsset*>(obj));
        break;
    case LlObjectTypeID::Family:
        handleFamilyLoad(static_cast<NvBlastFamily*>(obj));
        break;
    default:
        NVBLAST_LOG_ERROR("Unknown object type ");
    }

### Peeking at and Skipping Buffer Data

If a buffer contains multiple objects, you may peek at the buffer to get object information including object type, encoding, and data size, and skip to the next object in the buffer (whether or not you have chosen to read the current object). For example:

    const void* buffer = ... // The input buffer
    uint64_t size = ... // The input buffer size

    while (size)
    {
        uint64_t objTypeID;
        if (!ser->peekHeader(&objTypeID, NULL, NULL, buffer, size)) // Only reading the object type ID; may pass in NULL for the other header value pointers
        {
            break;  // Read error, stop
        }

        if (objectShouldBeLoaded(objTypeID))    // Some function to determine whether or not we want this object
        {
            void* obj = ser->deserializeFromBuffer(buffer, size);
            // Handle loaded object ...
        }

        // Jump to next object:
        buffer = ser->skipObject(size, buffer); // Updates size as well
    }

## Cleaning Up

When finished with the serialization manager, it may be released using its release() method:

    ser->release();