Nested CRDTs

This project allows creation of CRDTs with nesting. For these CRDTs ether custom behavior or provided behavior can be used.

Usage

Use the create function to create a CRDT. This requires an id and a typeName, which will uniquely identify this CRDT over the network. The typeName will also dictate the behavior of this CRDT, and must be a key in the typeStore, which holds all possible behaviors known in the network. Any child of this CRDT, or any other CRDT interacting with this one, must have the same typeStore, messageHandler and cache. The messageHandler is responsible for distributing messages to all CRDTs in this network, and the cache holds every CRDT previously mentioned in the system, for later storage. The cache is expected to be empty at first, when no CRDTs are associated with it yet.

A default typeStore can be imported (called defaultTypes), and extended with custom types, if needed. It is also possible, however, to forgo these default types, and only use custom ones.

import { create, MessageHandler, defaultTypes } from "nest-crdt"

// MessageHandler must be implemented
const messageHandler: MessageHandler = /* see next section */ undefined as any

// Expected to be empty at first
const cache = new Map()

const syncedSet = create('syncedSet', 'g-set', messageHandler, defaultTypes, cache)

// The 'add' method is a modifier specified for 'g-set' in 'defaultTypes',
// and can therefore be used type-safely here.
syncedSet.add("Text to be added to set.").then(() => {
    // The Promise being resolved doesn't imply that the message
    // has been accepted by every node in the network,
    // only that the sending process has been initiated.
    console.log("Added text to 'syncedSet'!")
})

Message Handler

The messageHandler is responsible for ensuring that messages get delivered to CRDTs, even if they haven't yet been accessed locally, and thus don't exist in the cache.

In order to make sure messages get delivered consistently, however, it may instantiate the target CRDT, once a message arrives for it, adding it to the cache, and deliver the message to it.

An implementation of this strategy can be found in the nest-crdt-tools module, in the CachedMessageHandler class.

Building

To build this project first run npm install to install the node libraries, then run npm run build, to invoke the TypeScript compiler.