Part of a presentation @ nodemtl meetup. Presenting Kerouac, a real-time webapp featuring a remote GPS tracking device, a webcam and a whole lot of Node.js magic covering some basics of Node.js such as: event emitters and process spawning.

1. How to Hack a Road Trip
with a Webcam, a GSP
and Some Fun
StreetView+ on the cheap
NodeMTL.
com

2. Pascal Deschenes
Technologist, Nu Echo Co-Founder
@pdeschen
http://about.me/pdeschen

3. Outline
● Background
● Base Modules
● Geo Storage
● Real-time Layer
● Web Front
● Demo

4. Background

5. Stop-motion
movie of our
Newfoundland
summer road
trip

6. Base Modules

7. Camelot
Non-Blocking
Webcam Frame
Grabbing and
Remote
Controller

8. Process Spawning
var spawn = require('child_process').spawn;
var arguments = [];
arguments.push(foo);
...
var fswebcam = spawn('fswebcam', arguments);
fswebcam.stderr.on('data', function (data) {
console.log('stdout: ' + data);
});
fswebcam.on('exit', function (code) {
...
});

9. Bancroft
Non-Blocking
GPS Daemon
Client

10. Event Emitting
var events = require('events');
...
/* tap into prototype chain */
sys.inherits(Bancroft, events.EventEmitter);
...
var emitter = events.EventEmitter.call(this);
...
emitter.emit('location', self.location);
...
emitter.emit('error', error);

11. Event Handling
var bancroft = new Bancroft();
bancroft.on('connect', function () {
console.log('connected');
});
bancroft.on('location', function (location) {
console.log('got new location', location);
});

12. Geo Storage

13. Cradle
A high-level,
caching,
CouchDB client

14. Init
var Cradle = require('cradle');
var cradle = new (Cradle.Connection)('http://127.0.0.1', 5984, {cache:
false});
var db = cradle.database('kerouac');
if (!db.exists()) {db.create();}

15. Store
var document = {
timestamp : new Date().getTime(),
location : bancroft.location
};
db.save(uuid(), document, function (err, res) {
console.log(res);
db.saveAttachment(res.id, res.rev,
'frame', 'image/png', frame,
function (err, data) {
...
});
});

16. Delete
db.view('k/coordinates', function (err, rows) {
rows.forEach(function (row) {
console.log('deleting', row);
db.remove(row.key._id, row.key._rev);
});
});

17. Model
{
"_id": "ffdba8b3-e125-4b4e-98fe-0be027aaec40",
"_rev": "2-43d3afdb1909626bc962e44612c57150",
"timestamp": 1311513742115,
"location": {
"timestamp": 1311513742000,
"latitude": 44.423216667,
"longitude": -72.944055,
"altitude": 194.7,
"speed": 0,
"geometries": {
"type": "Point",
"coordinates": [-72.944055, 44.423216667, 194.7]
}
},
"_attachments": {
"frame": {
"content_type": "image/png",
"revpos": 2,
"length": 142666,
"stub": true
}
}

18. Real-time Layer

19. Socket.IO
Sending binary
messages

20. Base64 Encoding
/* server side */
io.sockets.volatile.emit('frame',
{ data : frame.toString('base64') }
);
/* client side */
socket.on('frame', function (frame) {
var img = $('#frame');
img.attr("src",
'data:image/png;base64,' + frame.data);
});

21. Web Front

22. Express
app.get('/map', function (req, res) {
res.render('map', {
title : "Kerouac"
});
});

23. Jade Templates
<?xml version="1.0" encoding="UTF-8"?>
kml(xmlns="http://earth.google.com/kml/2.1")
Document
name Newfoundland RoadTrip
description A dynamically waypoint selection from an ongoing road trip
Style(id="blueLine")
LineStyle
color red
width 4
Placemark
name Blue Line
styleUrl #blueLine
LineString
altitudeMode relative
coordinates
- if (coordinates.length)
- coordinates.forEach(function(coordinate) {
=coordinate
- })

24. REST Handling
app.get('/status', function (req, res) {
res.header('content-type', 'application/json');
var status = messaging.location;
db.view('kerouac/speed_mean', function (err, rows) {
if (rows[0]) {
status['mean'] = rows[0].value.toFixed(2);
} else {
status['mean'] = 'n.a.';
}
var json = JSON.stringify(status);
res.send(json);
});
});

25. Show Time

26. Open Issues
for an upcoming meet-up? volunteers?
How to unit test event emission?
What about native c++ module?
What are the best practices regarding express.js code
organization?
How to distribute Socket.io/Express behind a proxy?

27. Questions?
@pdeschen

28. References
http://nodejs.org/docs/v0.4.9/api/child_processes.html
http://nodejs.org/docs/v0.4.9/api/events.html
http://blog.rassemblr.com/tag/nodejs/
https://github.com/pdeschen/camelot
https://github.com/pdeschen/bancroft
https://github.com/cloudhead/cradle
http://geojson.org/
http://socket.io/
http://expressjs.com/
http://jade-lang.com/