FlexBuffers-CSharp

FlexBuffers is JSON comparable binary format with random value access capabilities. The binary format and data layout was designed at Google as part of FlatBuffers project. This projects brings FlexBuffers as a standalone solution to C# with the focus to convert large JSON files to randomly accessable FlexBuffers.

The main focus of this project is to be used with Unity3D. However current solution has no Unity3D dependencies and should be usable in other C# environments. Please feel free to contribute tests and patches for other environments.

Supported types

As mentioned in the project description, FlexBuffers is a JSON comparable data format. It supports all the types JSON does, but also stores more detailed informations about the values.

Here is the list of supported types, as of November 2019:

• Null represents an absence of a value, specifically useful in collections
• Int represents positive and negative integer numbers, FlexBuffers additionally stores the bit width of the number which can be 8, 16, 32 or 64 bits
• UInt represents only positive numbers, also stores the bit width of 8, 16, 32 or 64 bits
• Float represents a floating point number. The possible bit width is limited to 32 and 64
• Key an internal zero terminated string representation for Map keys. Is not relevant for the end users
• String a length prepanded, zero terminated, UTF-8 encoded text representation
• IndirectInt, IndirectUInt, IndirectFloat are Int, UInt and Float stored by reference. Relevant for end users only if they want to achieve smallest binary size (will be discussed in a separate section)
• Map is similar to JSON object. Keys are strings, values can be any other here listed supported type. Speaking in terms of C# it is a Dictionary<string, dyanmic>
• Vector is similar to JSON array. An array which can host any types. FlexBuffers stores the values together with value type information
• VecorInt, VectorUInt, VectorFloat, VectorKey, VectorString, VectorBool are arrays of a given type. Given this type FlatBuffer does not store the type information for every individual entry and there for achieves smaller buffer size
• VectorInt2, VectorInt3, VectorInt4, VectorUInt2, VectorUInt3, VectorUInt4, VectorFloat2, VectorFloat3, VectorFloat4 is a special type of array which has a fix type and fix size of elements. A vector with non fixed size need to store size, however fix sized vectors don't have to do it as it is encoded in type directly
• Blob stores a byte array
• Bool stores bnoolean values true or false

Creation of FlexBuffer

There are multple ways how we can create a FlexBuffer

Single value

It is posible to store just one value in a FlexBuffer. It is not that probable to do so in day to day business, but was helpful for unit testing the format.

• FlexBuffer.Null() returns a byte array, which represents a FlexBuffer with null as single value.
• FlexBuffer.SingleValue(value) returns a byte array, which represents a FlexBuffer with as single value. The value parameter can be of type long, ulong, string, bool
• FlexBuffer.SingleValue(x, y), FlexBuffer.SingleValue(x, y, z), FlexBuffer.SingleValue(x, y, z, w) creates a typed fixed size vector. Parameters x, y, z, w can be of type long, ulong or double
• FlexBuffer.From(dict) creates a FlexBuffer based on a Dictionary<string, dynamic> instance. It is not the fastest but very convinient way of creating a FlexBuffer. It assumes that the values are of compatible types
• FlexBuffer.From(value) where value is of type IEnumerable will try to create a FlexBuffer with Vector as root element
• FlexBuffer.SingleValue(new byte[]{1, 2, 3})creates a FlexBuffer with Blob as single value.

From JSON

FlexBuffers-CSharp has a special type called JsonToFlexBufferConverter which allows user to convert a JSON string to FlexBuffer byte array.

var buffer = JsonToFlexBufferConverter.Convert("{\"a\":1, \"b\":2}");

JsonToFlexBufferConverter Contains an actualt JSON parser (based on LightJson) and there for converts one byte array (JSON string) directly to another byte aray (FlexBuffer) efficient and with a minimal amount of temporary objects.

FlexBuffer Builder

The FlexBufferBuilder enable users to create FlexBuffers directly form values, without a need for temporary representations. The Root elelemnt can be defined as a Map:

var bytes = FlexBufferBuilder.Map(root =>
{
    root.Add("name", "Maxim");
    root.Add("age", 38);
    root.Add("weight", 72.5);
    root.Map("address", address =>
    {
        address.Add("city", "Bla");
        address.Add("zip", "12345");
        address.Add("countryCode", "XX");
    });
    root.Vector("flags", tags =>
    {
        tags.Add(true);
        tags.Add(false);
        tags.Add(true);
        tags.Add(true);
    });
});

Or as a Vector:

var bytes = FlexBufferBuilder.Vector(root =>
{
    root.AddNull();
    root.Add(new byte[]{1,2,3});
    root.Map(map =>
    {
        map.AddNull("a");
        map.Add("b", new byte[]{3,4,5});
    });
});

FlexBuffers to JSON

As Flexbuffer has JSON compatible types it is very easy to conver a FlexBuffer to JSON.

The FlexBuffer from previous paragraph can be converted to following JSON string: [null,"AQID",{"a":null,"b":"AwQF"}] "AQID" and "AwQF" are Base64 representations of new byte[]{1,2,3} and new byte[]{3,4,5}

Byte array to FlexBuffer value

With FlexBuffers we can extract values directly from the buffer, without any parsing or complex upfront conversions. With var flx = FlxValue.FromBytes(bytes); users can create an instance of a FlexBuffer value which allows conversion to types and access of sub elements. FlxValue struct has following getters:

• ValueType returns the Type enum representing the value type (types are the cases listed Supported Types section)
• IsNull return true or false if the value is null
• AsLong, AsULong, AsDouble, AsBool, AsString and AsBlob tries to interpret the undelying value as expected type and returns the value
• AsVector checks if the underlying value is one of the Vector types and returns an instace of FlxVector struct, which implements IEnumerable<FlxValue> and has a Length getter
• AsMap checks if the underlying value is a Map type and return an instance of FlxMap struct, which implements IEnumerable<KeyValuePair<string, FlxValue>> and also has a Length getter
• ToJson returns a JSON string (see FlexBuffers to JSON section)
• User can wirte flx[0] in order to convert the FlxValue into FlxVector and access the first element of the vector
• When user wirte flx["a"], then FlxValue is converted to FlxMap and value for the key "a" is accessed

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Outlook

As next steps we are cosnidering:

• object graph to FlexBuffer and FlexBuffer to object graph conversion
• profiling and performance tuning

Contribution is welcome.