ROW ROW ROW YOUR BOAT by @zladuric 

We have gathered here today ● How to build Node.js Streams? ● A talk to introduce the topic of streams in JavaScript, how this works in Node.js and how it didn't work out before. ● You're my lab! by @zladuric 

What are we talking about ● The past - what was there before ● The present - what are we doing now ● The future - how you can get and use this ● The client - the browser side of things ● The server - Streams API 

But first - why a stream Regular stuff ● Comes as a whole blob ● Takes up memory ● When action is broken at 95%, redo the whole thing Streamed stuff ● Just like regular, but chunked into bits ● When broken, we can still reuse parts we got ● PIPES!!1 

The past Let's hope it dies! 

All right, I'll tell ya On the client ● Until a few years ago, we could not do much with streams in JS ● Mostly for video/audio transfer with Flash, Java Applets On the server ● Comes largely from unix network sockets ● stdin, stdout, stderr ● Created to streamline (yeah, I know) I/O operations ● In web: Flash Media server, Red5 ● Encoders/decoders, format converters ● Bridges between backend services, more I/O WTF? 

Node.js past ● Streams API was (is?) very volatile ● Backwards compatibility ● Main problems: – Your stream could ignore stream.pause();) – Stream starts right away – whether you're ready or not 

The present Node.js “streams2”: Stability: 2 – Unstable ● Node.js is unstable ;) ● No breaking changes expected for Node.js 0.12 

Stream in Node.js ● All streams are instances of an EventEmmiter (events and listeners/hooks) ● var Readable = require('stream').Readable; – Implement your own _read(); ● var Writable = require('stream').Writable; – Implement your own _write(); ● var Duplex = implement both; ● var Transform = convert input then pass to output – Implement _transform(); and flush(); 

How to be streamin' in Node $(#button).on('click', handler); anyone? 

stream.Readable ● Flowing and non-flowing? ● Common events and methods ● Examples: fs.createReadStream, http.createServer listeners, tcp and net sockets. 

Translate stream events into english When stream says: It means: ● readable “I have stuff to be read.” ● data “Here's a chunk.” ● end “I'm all out, you've read it.” ● close “Bye bye!” (file.close); ● error “Pain starts here.” 

Pushmi-pullyu Flowing mode stream.on('data', function(chunk) { // chunk.length bytes // or if we set encoding, chunk is a string // or if objectMode: true, then values/objs ); Non-flowing: var chunk = stream.read(); 

Borin Simple example ● this.push(); → stream.read(); ● objectMode is handy 

Writable stream ● To implement a writable stream, implement _write method, drain 

Transform streams Splits input into lines ● _transform() - what to do on input data ● _flush – what to do when input ends 

And now pipes! var stream = getSomeReadStream() .pipe(toConverterStream()) .pipe(toEncoderStream()) .pipe(toTransportStream()) .pipe(toTheConsumerStream()); 

Piping examples Read file line by line Top secret Steal Google logo 

Do you use it? 

The client ● WebRTC, WebSockets, Workers – they all stream data ● XMLHttpRequest ● User Media (MediaStream) API, Blob/FileSystem API, Audio, Geolocation etc. 

Example http://jszgb.com/ - hacked to steal selfies // simplified navigator.webkitGetUserMedia({video: true}, function(localMediaStream) { console.log('getting some video'); var video = document.getElementById('video'); video.src = window.URL.createObjectURL(localMediaStream); }, console.log); 

Other useful options, events and methods ● options.highWaterMark = 1024; ● stream.setEncoding('utf-8'); ● pause/resume a stream ● wrap(); - for old libs < Node v0.10 ● pipe()/unpipe(), unshift() ● 'finish', 'close', 'drain' events 

The future ● Node.js is relatively stable ● Whatwg is trying to standardize stream APIs from: Domenic Denicola 

Play time http://thlorenz.github.io/stream-viz/ 

Question time 1. Was my english ok? 2. How boring was I, from 1 – 10? Your turn. Zlatko Đurić