livedb-rethinkdb: Building collaborative apps with ShareJS and RethinkDB Jorge Silva · @thejsj · Developer Evangelist @ RethinkDB

Overview What is Operational Transformation? ShareJS: A Node.js library for OT RethinkDB: A database for realtime apps livedb-rethinkdb: RethinkDB + ShareJS

Text here...

Text here... Text here... User #1 User #2

Text here... Text here... User #1 User #2 How could these two users collaborate?

Every time a user makes an edit, push an updated document

abc User #1 User #2 ‘abc’ Server abc

abc User #1 User #2 ‘abc’ ‘abc’ abc Server abc

abc User #1 User #2 ‘xyz’ xyz 1ms later: Server xyz ‘abc’

xyz User #1 User #2 ‘abc’ ‘xyz’ xyz ‘abc’ ‘xyz’ Server xyz

This system doesn’t take latency into consideration

What if, instead of sending a completely updated document, we just sent the user’s actions?

User #1 User #2 abc { op: [1, ‘bc’] } a Server abc

abc User #1 User #2 abc { op: [1, ‘bc’] } { op: [1, ‘bc’] } Server abc

User #1 User #2 { op: [3, ‘efg’] } 012abc 1ms later: { op: [0, ‘012’ ] } abcefg Server 012efgabc

012efgabc User #1 User #2 012abcefg { op: [3, ‘efg’] } { op: [0, ‘012’ ] } Server 012efgabc

This strategy is not able to accomodate the user’s intentions User #2’s changes are not inserted at the right cursor position.

Merely sending operations to the server doesn’t solve our problem. We need to tranform our operations.

What is Operational Transformation?

A class of algorithms that do multi-site realtime concurrency. Gives you eventual consistency - between multiple users - without retries - without errors - without any data being overwritten http://sharejs.org/

User #1 User #2 { op: [3, ‘def’] } 012abc 1ms later: { op: [0, ‘012’] } abcdef Server 012abcdef { op: [0, ‘012’] } { op: [6, ‘def’] } Transformed into: Transformed into:

012abc User #1 User #2 012abcdef Server 012abcdef { op: [0, ‘012’] } Not Applied Transformed into: { op: [0, ‘012’] } { op: [0, ‘012’] }

012abcdef User #1 User #2 abcdef Server 012abcdef { op: [6, ‘def’] } { op: [6, ‘def’] } Transformed into: { op: [6, ‘def’] } Not Applied

Possible applications Collaborative text and code editors Realtime wikis Any type of concurent text editing Examples: Google Docs, hackpad, etc.

OT is an important tool for building realtime applications

How can I use this in my own projects?

Enter ShareJS “ShareJS is an Operational Transform library for NodeJS & browsers. It lets you easily do live concurrent editing in your app.”

Demo http://livedb-rethinkdb.thejsj.com/

// WebSocket Connection var ws = new WebSocket(‘ws://localhost:8005’); var shareJS = new window.sharejs.Connection(ws); // Textarea var textareaDoc = shareJS.get(‘documents’, ‘helloworld’); textareaDoc.subscribe(); // Wait for document to be ready textareaDoc.whenReady(function () { setTimeout(function () { if (textareaDoc.type && textareaDoc.type.name === ‘text’) { // Attach textarea to document var elem = document.getElementById(‘helloworld’); textareaDoc.attachTextarea(elem); } }); }); ShareJS on the client https://github.com/thejsj/sharejs-rethinkdb-example/blob/master/client/index.html#L102-L124

// WebSocket Connection var ws = new WebSocket(‘ws://localhost:8005’); var shareJS = new window.sharejs.Connection(ws); // Textarea var textareaDoc = shareJS.get(‘documents’, ‘helloworld’); textareaDoc.subscribe(); // Wait for document to be ready textareaDoc.whenReady(function () { setTimeout(function () { if (textareaDoc.type && textareaDoc.type.name === ‘text’) { // Attach textarea to document var elem = document.getElementById(‘helloworld’); textareaDoc.attachTextarea(elem); } }); }); ShareJS on the client https://github.com/thejsj/sharejs-rethinkdb-example/blob/master/client/index.html#L102-L124

var sharejs = require(‘share’); var livedb = require(‘livedb’); // Connect to the database var db = require(‘livedb-rethinkdb’)({ host: ‘localhost’, port: 28015, db: ‘sharejs’ }); var backend = livedb.client(db); // Attach livedb instances to ShareJS var share = sharejs.server.createClient({ backend: backend }); ShareJS on the server: database https://github.com/thejsj/sharejs-rethinkdb-example/blob/master/server/livedb-client.js

var sharejs = require(‘share’); var livedb = require(‘livedb’); // Connect to the database var db = require(‘livedb-rethinkdb’)({ host: ‘localhost’, port: 28015, db: ‘sharejs’ }); var backend = livedb.client(db); // Attach livedb instances to ShareJS var share = sharejs.server.createClient({ backend: backend }); ShareJS on the server: database https://github.com/thejsj/sharejs-rethinkdb-example/blob/master/server/livedb-client.js

var wss = new WebSocketServer(); var Duplex = require(‘stream’).Duplex; var share = sharejs.server.createClient({ backend: backend }); // On socket connection wss.on(‘connection’, function () { var stream = new Duplex({ objectMode: true }); stream._write = function (chunk, encoding, callback) { client.send(JSON.stringify(chunk)); return callback(); }; client.on(‘message’, function (data) { return stream.push(JSON.parse(data)); }); return share.listen(stream); }); ShareJS on the server https://github.com/thejsj/sharejs-rethinkdb-example/blob/master/server/socket-handler.js#L8-L49

var wss = new WebSocketServer(); var Duplex = require(‘stream’).Duplex; var share = sharejs.server.createClient({ backend: backend }); // On socket connection wss.on(‘connection’, function () { var stream = new Duplex({ objectMode: true }); stream._write = function (chunk, encoding, callback) { client.send(JSON.stringify(chunk)); return callback(); }; client.on(‘message’, function (data) { return stream.push(JSON.parse(data)); }); return share.listen(stream); }); ShareJS on the server https://github.com/thejsj/sharejs-rethinkdb-example/blob/master/server/socket-handler.js#L8-L49

Open source database for building realtime applications NoSQL database that stores schemaless JSON documents Distributed database that is easy to scale What is RethinkDB?

Subscribe to change notifications from database queries No more polling – the database pushes changes to your app Reduce the amount of plumbing needed to stream live updates Built for realtime

var r = require(‘rethinkdb’); r .db(‘share_js’) .table(‘documents’) .filter({ name: ‘helloworld’ }) .run(conn) .then(function (cursor) { // Go through every row returned by the query cursor.each(function (row) { console.log(row); }); }); Changefeeds

var r = require(‘rethinkdb’); r .db(‘share_js’) .table(‘documents’) .filter({ name: ‘helloworld’ }) .run(conn) .then(function (cursor) { // Go through every row returned by the query cursor.each(function (row) { console.log(row); }); }); Changefeeds

var r = require(‘rethinkdb’); r .db(‘share_js’) .table(‘documents’) .filter({ name: ‘helloworld’ }) .changes() .run(conn) .then(function (cursor) { // Gets fired every time a row changes cursor.each(function (row) { console.log(row); }); }); Changefeeds

ShareJS & RethinkDB npm install sharejs livedb livedb-rethinkdb --save

Access documents

Access every single operation

Listen for new operations

Try it! https://github.com/thejsj/sharejs-rethinkdb-example

ShareJS http://sharejs.org/ | https://github.com/share/ShareJS RethinkDB http://rethinkdb.com/ | @rethinkdb livedb-rethinkdb https://github.com/thejsj/livedb-rethinkdb Twitter @thejsj Questions?