Codeaggregatory
Wednesday 20 June 2012
SQLFire tutorials - 1
SQLFire is a memory-optimized, distributed database management system designed for applications that have demanding scalability and availability requirements. SQLFire offers some of the best features usually only seen in NoSQL databases, such as horizontal scalability, shared-nothing persistence and built in fault tolerance, but does it all while providing a real SQL interface. Applications can manage database tables entirely in memory, or they can persist tables to disk to reload the data after restarting the system. A SQLFire distributed system can be easily scaled out using commodity hardware.
In this post we’ll see how to setup and start a cluster of multiple SQLFire servers. Read more..
The canvas element – Basic usage
The HTML5 Canvas element has its contents rendered with JavaScript. The canvas element makes use of the "context" into which you can issue JavaScript commands to draw anything you want. The canvas is initially blank, and to display something a script first needs to access the rendering context and draw on it. You can obtain the rendering context and it's drawing function by using the getContext method. Read more..
Monday 16 April 2012
Node.js: Templating with Plates
Plates is the templating library in flatiron. Plates binds
data to markup. It's Javascript, Markup and JSON. It works in the browser and
in node.js. All templates are actually valid HTML, with no special characters
for value insertion. The relationship between tags and values is defined
through object literals that are passed to Plates.bind:
You have to install plates before using it
Plates can be used in the program by requiring it.
var http = require('http'),
plates = require(../lib/plates');
var server = http.createServer(function
(req, res) {
res.writeHead(200);
var userSpan = '<span
id="spFirstName">Prajeesh</span> <span
id="spLastName">Prathap</span>'
var userHtml = '<div
id="pnlLogin"></div>';
var map = plates.Map();
map.where('id').is('spFirstName').use('value').as('Prajeesh');
var content
= plates.bind(userHtml, { 'pnlLogin':
userSpan });
res.end(content)
});
server.listen(8083);
Sunday 15 April 2012
Routing using director in Node
Director is a URL router
module which comes as part of the flatiron framework. It works in a browser for single page apps
and in Node.js. It's not a plugin for another framework. It's not dependent on
anything. It's a modern router that was designed from the ground up with
javascript.
Installing flatiron
You can install flatiron
using npm (npm install flatiron –g)
Director handles routing for HTTP requests similar to
journey or express:
var http = require('http');
var director = require(../lib/director');
function sayWelcome(route) {
this.res.writeHead(200, { 'Content-Type':
'text/plain' });
this.res.end('Welcome to
flatiron routing sample');
}
var router = new
director.http.Router({
'': {
get:
sayWelcome
}
});
router.get('/index',
sayWelcome);
router.get('/home',
sayWelcome);
var server = http.createServer(function
(req, res) {
router.dispatch(req, res, function (err)
{
if (err) {
res.writeHead(404);
res.end('Error!!!');
}
})
});
server.listen(8083);
When developing large client-side or server-side
applications it is not always possible to define routes in one location. Usually
individual decoupled components register their own routes with the application
router. Director supports ad-hoc routing also.
router.path(/\/customers\/(\w+)/, function (res) {
this.post(function
(id) {
//sayWelcome('some');
this.res.writeHead(200, { 'Content-Type':
'text/plain' });
this.res.end('Create a
customer with Id = ' + id)
});
this.get(function
(id) {
//sayWelcome('some');
this.res.writeHead(200, { 'Content-Type':
'text/plain' });
this.res.end('Gets a
customer with Id = ' + id)
});
this.get(/\/orders/, function
(id) {
this.res.writeHead(200, { 'Content-Type':
'text/plain' });
this.res.end('Gets orders
for a customer with Id = ' + id)
});
});
Tuesday 10 April 2012
Exception handling in Node
A common problem when
writing Node.js programs is in ensuring all exceptions are handled. Node.js
will helpfully die when exceptions are not caught and handled, which forces
you, the author, to ensure robustness in your Node.js applications. Node emits an uncaughtException event when an exception bubbles
all the way back to the event loop. If a listener is added for this exception,
the default action (which is to print a stack trace and exit) will not occur.
process.on('uncaughtException', function
(ex) {
console.log('Unhandled exception caught: '
+ ex);
process.exit();
});
If you are writing
asynchronous code, you can follow the below given pattern to throw and handle
exceptions in the code. In this pattern the first argument of the callback is err, if an
error happens it is the error, if it doesn't it is null.
var divideAsync = function
(arg1, arg2, callback)
{
if (arg2 == 0) return
callback(new Error('division
by 0 is not possible'));
return callback(null,
arg1 / arg2);
}
divideAsync(9, 0, function
(ex, result) {
if (ex) {
console.log('Error
in division ' + ex);
process.exit();
}
console.log('result ' + result);
});
You can also use the
traditional try {} catch (err) {} to catch exceptions
as given below
console.log('Starting
directory: ' + process.cwd());
try {
process.chdir('/tmp');
console.log('New directory: ' +
process.cwd());
}
catch (err) {
console.log('chdir: ' + err);
process.exit();
}
For synchronous code, if
an error happens you can return an instance of Error object and later check the result for this
object as given below.
var divide = function (arg1,
arg2) {
if (arg2 == 0) return new Error('division by 0 is not possible');
return arg1 / arg2;
}
var x = divide(5, 0);
if (x instanceof Error) {
console.log('Exception logged');
process.exit();
}
Monday 9 April 2012
Buffers in Node – Part 1
Pure javascript, while great
with unicode-encoded strings, does not
handle straight binary data very well. This is fine on the browser, where most
data is in the form of strings. However, node.js servers have to also deal with
TCP streams and reading and writing to the filesystem, both which make it
necessary to deal with purely binary streams of data. Node has several
strategies for manipulating, creating, and consuming streams.
Raw data is stored in
instances of the Buffer
class. A Buffer is
similar to an array of integers but corresponds to a raw memory allocation
outside the V8 heap. A Buffer
cannot be resized.
The Buffer class is a global,
making it very rare that one would need to ever require('buffer').
Converting between Buffers and JavaScript string objects
requires an explicit encoding method. The encodings that are supported are 'ascii', 'utf8', 'usc2', 'base64',
'binary' and 'hex'.
Writing to buffers
new Buffer(size) methods allocates a new buffer
of size octets. Once the buffer is created, the buffer.write method is used to write a string
value to the buffer
var buffer = new Buffer(100);
var stringToWrite = 'Sample text
to add to a buffer';
//Write data to a buffer
buffer.write(stringToWrite,
'utf-8');
//finding the length of buffer
var offset = Buffer.byteLength(stringToWrite);
console.log(offset);
//Appending data to the existing
buffer
buffer.write('. This is
an appended text', offset, 'utf-8');
console.log(buffer.toString('utf-8'));
Copy values to buffer
buffer.copy allows one to copy the contents
of one buffer onto another. The first argument is the target buffer on which to
copy the contents of buffer, and the rest of the arguments allow for copying
only a subsection of the source buffer to somewhere in the middle of the target
buffer. For example:
var helloBuffer = new
Buffer(50);
helloBuffer.write('Hello
', 0, 'utf-8')
var welcomeBuffer = new
Buffer('node.js.');
var helloStringLength = Buffer.byteLength('Hello ');
var welcomeStringLength = Buffer.byteLength('node.js.');
//Copies from welcomeBuffer to
helloBuffer
welcomeBuffer.copy(helloBuffer,
helloStringLength, 0);
console.log(helloBuffer.toString('utf-8'));
Cropping the buffer
buf.slice([start], [end]) method returns a
new buffer which references the same memory as the old, but offset and cropped
by the start (defaults to 0) and end (defaults to buffer.length) indexes. The slice is not a new buffer
and merely references a subset of the memory space. Modifying the slice will also modify the
original buffer. For example:
var nodejsSlice = helloBuffer.slice(helloStringLength, helloStringLength +
welcomeStringLength);
console.log(nodejsSlice.toString());
nodejsSlice.write('Prajeesh');
Sunday 8 April 2012
Node.js application using Socket.io
Socket.io provides real-time communication
between your node.js
server and clients. Socket.IO
allows you to emit and receive custom events. Besides `connect`, `message` and `disconnect`, you can emit
custom events also.
The socket can be
created by the user and used as a client (with connect()) or they can be created by Node and
passed to the user through the 'connection' event of a server.
Installing socket.io on the server
Creating the server
var http = require('http'),
io =
require('socket.io'),
sys =
require('util'),
express =
require('express');
var port = 8083;
var server = express.createServer(function (req,
res) {
// Send HTML headers and message
res.writeHead(200, { 'Content-Type': 'text/html' });
res.end('<h1>Socket server...</h1>');
});
server.listen(port);
var socket = io.listen(server);
socket.sockets.on('connection', function
(client) {
client.on('message', function (data) {
console.log('Message received: ' +
data);
});
client.on('disconnect', function () {
console.log('Disconnected from server!!!');
});
var intervalId = setInterval(function
(message) {
client.send(message);
}, 500, 'From server...');
});
Client code
<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
<script src="socket/socket.io.js"></script>
<script>
var socket = new
io.Socket();
socket.connect('http://localhost:8083');
socket.on('connect', function () {
$('#status').text('Connected');
});
socket.on('message', function (data) {
$('#message').text(data);
});
socket.on('disconnect', function () {
$('#status').text('Disconnected');
});
socket.on('customEvent', function (message) {
$('#customEvent').text(message['time']);
});
</script>
</head>
<body>
<h1>WebSocket Test</h1>
<h2>Status: <span id="status">Waiting</span></h2>
Received
using client.send <pre
id="message"></pre>
<hr />
Received
using client.emit <pre
id="customEvent"></pre>
</body>
</body>
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