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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

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?
Dumb example

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

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
<video id="video" autoplay></video>
<script>
// simplified
navigator.webkitGetUserMedia({video: true},
function(localMediaStream) {
console.log('getting some video');
var video = document.getElementById('video');
video.src =
/slideshow/nodejs-streams-talk/39693897/window.URL.createObjectURL(localMediaStream);
}, console.log);
</script>

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 ?uri?

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