client-ketchup

A simple interface for keeping remote clients up to date with their authoritative state

Initial Motivation

The goal of client-ketchup is to be a small API for managing the states of a constantly changing set of connected clients.

A server might have an enormous application state object but each client only needs to know about different pieces of this data.

When a specific client's state changes, we generate a small set of string-ified patches to send to them so that they can update (or catch-up) their local state.

This helps avoid sending a massive amount of data over whenever we have new state information to each connected client.

The intended use case was for running multiplayer game servers, but an example potential different case might be a websocket powered real-time database.

To Install

$ npm install --save client-ketchup

Usage

/*
 * On our server
 */

// Use this to generate new client state trackers
var CreateClientStateTracker = require('client-ketchup')
// Create a new client state tracker. You'll typically use one of these and add/remove different clients to it
var CST = CreateClientStateTracker({
  differ: require('minimal-object-diff').diff
})

// Add a new client
CST.add('some-client-id-1')

// Update our clients view of the world and then receive a set of JSON stringified patches that we can send over
var minimalPatches = CST.update({foo: 'bar', bazz: 'buzz'})

// Use whatever network protocol you please in order to send updates
myClients['some-client-id-1'].websocket.send(JSON.stringify(minimalPatches))

/*
 * Later on our client
 */
var patchObject = require('minimal-object-diff').patch
var minimalPatches = GetPatchesFromServerSomehow()
var myLocalState = GetLocalState()
myLocalState = patchObject(myLocalState, JSON.parse(minimalPatches))

client-ketchup only concerns itself with helping to keep track of and generate optimized diffs for your client data. The method of transport (websocket, server-sent events, carrier pidgen, etc) is up to the consumer.

Typically you'll already have your network protocol in place and client-ketchup will be added in to reduce bandwidth.

API

CST.{add, del, update}

add

Add a client to our client pool

CST.add('cuid-1')
CST.add('cuid-2', {thisIsOur: 'inital state object'})

del

Remove a client from our client pool

CST.del('cuid-1')

update

Overwrite the clients state and receive JSON patches to send to a client

Applying these patches to the old state creates the new state

CST.add('cuid3', {hello: 'world'})
var patches = CST.update('cuid2', {hello: 'mars'})

// Client `cuid3` now has a state of {hello: 'mars'}

// ... Later ... Likely on one of your clients

var patch = require('minimal-object-diff').patch

var patchedObject = patch({hello: 'world'}, JSON.parse(patches))

console.log(patchedObject)
// => {hello: 'mars'}

TODO:

• I suppose that there should be a way to deal with clients that somehow got out of sync. Maybe accepting a state hash and verifying that it matches our authoritative client state.. And if not.. generate the appropriate patches? Let's handle that if/when it happens

See Also

• minimal-object-diff

License

MIT