Juggler communication protocol

Juggler is communication protocol used for communication between back-end and GUI front-end parts of components. As underlying protocol, Juggler uses WebSocket communication and text messages encoding JSON data. Communication between peers is symmetrical full duplex - once client and server establish WebSocket communication, each party can send messages independently of other and no further distinction between client and server is made.

Model

As prerequisite for Juggler communication, each peer should implement data model consisting of local and remote data. Data can be arbitrary application specific JSON serializable data.

Initially, null value is assumed for both local and remote data.

Each peer can freely change local data. Once local data is changed, JSON patch between previous and current local data is generated and transmitted to other peer. Upon receiving data change, other peer applies JSON patch to it’s remote data and notifies of remote data change. This enables continuous synchronization of local and remote data on both peers.

Communication

Juggler provides communication based on continuous synchronization of JSON data and communication based on asynchronous message passing.

Local and remote data synchronization assumes existence of time delayed caching implementation. Once local data changes, peer should wait for predefined time period prior to sending changes to other peer. In this time period, peer expects other local data changes which should all be delivered as single change to other peer. This caching provides optimization of message number and size of data exchanged between peers. At same time, additional communication latency is introduced.

When transfer of data as they are is required, asynchronous message passing should be used. By explicitly sending JSON messages, each peer can transmit arbitrary data. This communication assumes that no additional caching is done by Juggler implementation. Asynchronous message passing is independent of continuous data synchronization communication.

Messages

All messages are UTF-8 encoded JSON data defined by following JSON Schema:

type: object
required:
    - type
    - payload
properties:
    type:
        enum:
            - DATA
            - MESSAGE

DATA messages are used for continuous synchronization of JSON data. It’s payload parameter contains JSON patch value as defined by https://tools.ietf.org/html/rfc6902. This messages are sent by peer once local data changes.

MESSAGE messages provide asynchronous message passing communication.

Implementation

Documentation is available as part of generated API reference: