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SPEC.md

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This is a rough spec for reference. It is not a complete spec and may not be 100% accurate.

Change Tracking

  • Each Schema instance has a ChangeTree instance, which tracks changes.
  • Whenever a property is changed within a Schema instance, that change is cached inside its ChangeTree.
  • Changes are tracked into separate categories: "all", "changes", and "filtered" (used to encode with StateView's).

Encoding

There are two main types of encoding: the "encode all" and the "encode changes".

  • "encode all" is used when a client joins a room, and the server sends the full state of the room.
  • "encode changes" is used to encode all the pending changes.

Overview

  • Each Schema instance holds a reference to its own ChangeTree instance, which has a unique refId.
  • The root structure has refId of 0.
  • Schema instances are encoded as a sequence of index => value.
  • MapSchema instances have a dynamicIndex encoded sequentially as its index, following by the value (CollectionSchema and SetSchema are encoded in the same way as MapSchema)
  • When encoding a child Schema structure, only its refId is encoded.
  • ArraySchema instances are encoded as a sequence of index + value, where index is the index of the array, and value is the encoded value.
    • When using StateView:
      • On array of primitive types: Not possible to filter particular items. Either all items are encoded, or none.
      • On array of Schema instances: Instead of encoding the index, the refId is encoded instead.

Encoding for a View

This is the process of joining the room:

(The length of each message is part of the WebSocket message frame itself. This is not the case on WebTransport, which is currently experimental; C# does not have a solid implementation yet AFAIK)

Join Room Message {
  Header (uint8) = 10,

  ReconnectionTokenLength (uint8),
  ReconnectionToken (string),

  SerializerIdLength (uint8),
  SerializerId (string),

  Handshake Payload (...all bytes until the end of the message),
}

After receiving this message, the client sends back JOIN_ROOM to confirm the connection, and the server sends back the full room state.

Room State Message {
  Header (uint8) = 14,
  Encoded State (...all bytes until the end of the message),
}

The format of the encoded state depends on the serializer being used. The default serializer is "schema", which is a binary format. The "schema" serializer is the most efficient one, but it's not human-readable. The json serializer is also available, but it's less efficient.