Facsimile

Transparent object mirroring across process boundaries, with change monitoring

Installation

Install with npm

npm i --save facsimile

API

Before you begin:

const Facsimile = require('facsimile');

new Facsimile(hostname)

Create an empty instance of a facsimile node. Hostname is used for data conflict resolution, it may be any value type (string preferably), but types should not be mixed across your network

Facsimile.store

A monitored object used to manage your state. It can be accessed like any other object

Facsimile.sync()

Tells the instance to flush it's state, and request syncronization data from the network

Facsimile.lock(object):Promise

Request exclusive write permissions to an object, promise will not resolve until the lock has been established

NOTE: You must pass an object returned from the Facsimile.state collection

Facsimile.request(object):Promise

Request exclusive write permissions to an object, promise will return a failure if the lock has already been established.

NOTE: You must pass an object returned from the Facsimile.state collection

Facsimile.release(object)

Release lock on object, will throw an error if the object is not owned by host node.

NOTE: You must pass an object returned from the Facsimile.state collection

Facsimile.send(message, payload)

This function must be overloaded as a part of setting up a communications pipeline. For every call made to this, a similar call to Facsimile.receive must be made in the same order as they were dispatched

Facsimile.receive(message, payload)

Receive syncronization data from an external Facsimile instance

Events

Facsimile.on('root_changed', cb)

A node has redefined the global scope object

Facsimile.on('ready', cb)

Creates a listener that will fire any time all known lazy references have been resolved. IE: when a .sync() command has completed.

Facsimile.on('change', function(target:object, property:string, [new:*], [old:*]))

An instance contained inside of the Facsimile store has changed

NOTE: Property may be undefined if mass object change occured

Facsimile.store.*.on([property:string], cb:function(target:object, property:string, [new:*], [old:*]))

Monitor changes on a reference type in a Facsimile.store. Can only be attached to reference types, and will not monitor changes in contained objects.

NOTE: Property may be undefined if mass object change occured

Facsimile.store.*.off([property:string], cb:function)

Destroy an event listener created with Facsimile.store.*.on

Notes on communication

Facsimile instances do not natively support any signalling between the various modules. You must supply a tunnel between the instances, and all messages sent from one node must be sent to all other nodes in the system.

Caveats:

• Messages sent from a node must be relayed in order.
• How messages are interleaved between multiple nodes does not matter
• Messages are committed in 'Last Written' priority
• If the system cannot determine who wrote last, the host with the highest 'hostname' wins

Basic local example

const Facsimile = require('..');

class Network {
	constructor () {
		this._nodes = [];
	}

	add (source) {
		this._nodes.push(source);
		source.send = (message, payload) => this.send(source, message, payload);
	}

	send (source, message, payload)	{
		for (let target of this._nodes) {
			if (target === source) continue ;

			console.log(source._hostname, message, payload);
			target.receive(message, payload);
		}
	}
}

const network = new Network();

// Create our host network
const a = new Facsimile("host");
network.add(a);
a.store = { elements: [1, 2, 3] };

a.store.elements.on(0, (target, property, new_value) => {
	console.log(`Index[0] = ${new_value}`);
});
a.store.elements.on((target, property, new_value) => {
	console.log(`Index[${property}] = ${new_value}`);
});

// Create a subnode, and syncronize them
const b = new Facsimile("client");
network.add(b);
b.on('root_changed', () => {
	console.log("Root element has changed.");
});

async function arrayFunctions() {
	const array = b.store.elements;

	console.log("Locking")
	await b.lock(array);
	console.log("Locked");

	console.log("Trying to create a dead lock");
	try {
		await a.request(a.store.elements);
	} catch (e) {
		console.log("Intentional error:", e);
	}

	b.store.elements[0] = 999;
	b.store.elements[1] = 888;
	b.store.elements.unshift(4);
	b.store.elements.sort((a, b) => (a - b));

	console.log("Unlocking");
	b.release(array);
}

b.on('ready', () => {
	console.log("elements =", b.store.elements);
	arrayFunctions()
});

b.sync();

Contact

@asterick: Twitter | GitHub