Thursday, April 16th, 2009
Category: Comet
, JavaScript
Brian Moschel and Justin Meyer of JavaScriptMVC have opened their Jabbify chat client into a general purpose Comet service called Jabbify. Some of their claims:
- Automatic Scaling: Jabbify scales to thousands of users per domain with no additional maintenance on your part.
- Instant setup: Download a script and you're developing with Comet in 30 seconds or less.
- Simple to use: Its easy. Really really easy. All you need is the JavaScript API or GET requests, technologies most developers are very familiar with. Simply connect and send your message.
Here's a graphic showing how the service works:
Here's an example of how to use Jabbify to send a message to all users connected to a domain:
HTML:
-
<script type='text/javascript' src='jabbify.js'></script>
-
-
// subscribe to incoming Comet messages
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OpenAjax.hub.subscribe("jabbify.message.create", function(name, results){ alert(name) });
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// connect to the server
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Jabbify.connect({name: "Brian"}, function(){
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// send hello world to all connected users
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Jabbify.send("message", "create", { message: "hello world" });
-
})
-
</script>
The service is currently in beta and is free to use; further:
It will always be free for websites with a small number of concurrent users. We’ve tried to make it as easy as possible to get started with plenty of docs and demos. There’s:
* A downloadable page that runs from the filesystem
* A service overview page
* An API demo
* A keyboard demo
* An open source chat client demo
* API documentation
We’d love to chat with people to see what they think about a service like this.
Friday, March 27th, 2009
Category: Comet, Java
We recently posted on Atmosphere, a new framework designed to provide an abstraction layer over Comet back-ends for Java web applications. At a personal level, this comes at an interesting time as over in the Mozilla Labs we're evaluating different Comet approaches for our upcoming collaboration release. As we looked at various options, we come across some recent postings from Ted Goddard of IceFaces fame explaining their work on making Comet as simple as possible for Java developers, including a podcast and an overview of the IceFaces approach.
Say what you will about JSF, their abstraction layer makes server and client implementation of Comet incredibly simple:
In other words, we can re-use our existing Ajax pipeline, and the application developer only needs to worry about one thing: requesting that a page be rendered. As you can imagine, this is only a few lines of code. With ICEfaces it looks like this:
JAVA:
-
SessionRenderer.addCurrentSession("ajaxian");
-
-
// somewhere else in the presentation tier
-
SessionRenderer.render("ajaxian");
Not only does the application developer not have to worry about low-level protocol details or messaging, they don't even have to worry about what has changed on the page -- this is all taken care of by the declared binding between the page and the model.
To summarize: we have dynamic pages that can be rendered on the server at any time, and the updates are pushed to the browser where the changes are applied to the DOM. From the application developer's point of view, that's all there is to it.
Are you using a stack that makes Comet this easy? Have you been able to successfully implement Comet? Do you get sufficient performance from polling?
2.2 rating from 102 votes
Monday, March 16th, 2009
Category: Comet, Java
Jean-Francois Arcand announced a new Java-based framework that clients can code against for portable Comet support:
Atmosphere 0.1-ALPHA1 is now officially released and support Tomcat, Jetty, Grizzly and GlassFish. Finally a Comet/Ajax Push framework you can build on top of it and deploy everywhere!
One of the cool features of this release is that it auto-detects which server back-end you've deployed it into.
Among the materials in the release notes are two code samples and a PDF discussing what Comet is and the motivation/design behind Atmosphere.
Comet on Java just got easier, which is a welcome development indeed.
Wednesday, March 11th, 2009
Category: Bespin, Canvas, Comet, Presentation
I went along last night to the London Mozilla Labs meetup, where Dion, Ben, and Joe delivered a presentation on Bespin. These are my notes from the event.
Goals
Bespin - initially an experiment, now interested to see how far it can go as a coding environment (among other things).
"The editor of our dreams":
- Accessible from anywhere
- Simple to use, like Textmate - for people who don't want to muck around with low-level details, too much time in version control
- Wicked fast - many editors look okay initially but don't scale well with large files and fast editing
- Rock-solid real-time collaboration - like SubEthaEdit - watch people in our time, e.g. follow someone like Brendan Eich as he codes (given that it's already open source). One of the meta-goals here is to lower the barriers for open-source development.
- Integrated command-line, like Vi
- "Self-hosted" environment - like Emacs. As a programmer, can get into its guts. And can do this kind of thing in real-time - modify the model as it runs (c.f. Eclipse - must re-compile)
Demo
Dion demos interacting with the Bespin editor. (Always good to see how the creators eat their own dogfood.) Ben points out it's fast, thanks to Canvas. Some demos of the command-line, its extensibility, and collaboration features.
Collaboration
Moz hired Joe Walker of Comet/DWR fame a month ago. Joe explains collaboration goals.
Typical scenario - two coders working simultaneously, perhaps chatting over skype.
From Neil Fraser (worked on Google Docs stuff around this) - designed as a "little version control system" - sends out diffs and patches it (see Mobwrite. Bizzarely, the bottleneck is not the network or the patch, but the diff. And exarcebated by the fact that typing faster - doing more work - necessitates more diffing.
Joe shows debug messages in Firebug console - showing diff info going to and from the server
Extra Features
Code nav - heatmap showing all of code and what's been edited. recently. Example of a mashup component you can build.
e.g. IBM coder turned it into a Java compiler - by compiling the Java on the server. Used Bespin's server API. Likewise, the editor is also a distinct component - can use the editor for other (non-IDE) application - e.g. a wiki project using Bespin's editor to edit the wiki. Likewise, the command line is separate. And there's the underlying core, Thunderhead.
Ben further emphasises it's not just a rich client-side editor - server-side code analysis with the RESTful API.
Upcoming Features
Big things:
- Collaboration
- VCS integration - integrate with Mercurial, etc etc
- Ubiquity Integration
- Server Side Javascript - can have different server implementations, could be Ruby etc, and want to implement one in JS
Smaller:
- Some nice commands
- Plan "follow me!"
- Syntax highlighting
- Design concepts
- Templates ("create project Rails")
- Editor functionality
- ... many more - need people to help with it (engaging with the community and supporting contributions in an open-sourcey way is a big theme in this talk)
Fin
They leave us with a clip of Dave Thomas @ RubyConf asking if it's weird to love your software tools, and answering that you have to love your tools. Fair play!
Questions and Answers
Q. Distributed Version Control - will bespin support it? Bespin designed for two basic use cases (a) standard thing - check in to repo etc (b) bespin.mozilla.com - SAAS type model.
Q. What data structure is being used for patch sets? Because a decent structure would make VCS possible. Mobwrite - Neil Fraser's project behind Google Docs - so using that format, but we might expect it to change in the future.
Q. (me) Eating your own dogfood Dogfooding by end of month, when VCS lands or using Appcelerator Titanium to run off local file system.
Q. (about integration with Ubiqutiy I think?) Ubiquity as the runtime and Bespin for authoring. Initially, separate to Ubiquity and then normalised commands with Ubiquity. Now just starting to share components like parser. Next phase, access to virtually all of Ubiquity and will work even without Moz browsers. And the other way round - running Ubiquity commands inside Bespin.
Q. With the collaboration engine, can you do more than code creation, e.g. drawing or spreadsheets? Using Mobwrite, the engine behind Google Docs' collaboration - Mobwrite's restricted to text - as long as there are changes to some structure (ie it can be serialised), it's possible.
Q. Codes and tests in the cloud - should be great for continuous integration There are various people already implementing the Bespin server API for other things too. With the code out in the cloud, very possible to do all sorts of things with the code. John Resig (also Moz) is also interested in this area - also wrt manual tests that are downloaded to various people's browsers and run locally. Maybe could even be automated using the aggregate crowd while the browser isn't doing anything else. Another project is Test Pilot (usability testing).
(On a related note, I mentioned later on it would be interesting to couple the code with real-time user data, e.g. a heatmap overlay on the code showing how much resources each segment used during real-world use.)
Q. Hyperlinking in code? Could you create ~implicit links, e.g. to other parts of the code? Don't have hyperlinks because it's canvas! But will be able to implement these things - would be done as a syntax highlighter extension.
Q. Firstly, the name? Secondly, the offline capability - can I just run it directly off the local file system. With Appcelerator Titanium, would feel like a real desktop app while offline, but can still access the cloud when connected. (No-one answered the name question ;)
Q. Mashups in the browser - loads of scope for in-editor mashups, will it be part of the editor framework Right now, editor has an event bus - events like "he's opened the file, he's hit a key", so can set up events for this kind of thing. It's all based on an asynchronous model, so very possible.
Q. Will there be user testing - to see what people really want? There's a huge list in Bugzilla for these kinds of things. This is a tech preview, missing a ton of functionality. Already improved, but a lot more to do.
Q. Vim or Emacs macros - which will be first? Have implemented Elisp and Javascript, so it's only a matter of time. (cunningly avoided expressing a preference :)
Q. Functional reactive programming (FRP) - Flapjax demonstrates the idea in JS - for pubsub. Would it be possible to extend the current pubsub framework into a FRP framework - avoids bugs around order . Would be good to see something like that.
Q. Are you "re-inventing the web" with this stuff, i.e. finding that canvas doesn't support it? Yes, do have to reinvent a lot of things - people coming together to discuss these things - ARIA etc. Very focused on accessibility. Two ways to do it - (a) hacks like the cut-and-paste to mirror what's happening; (b) longer-term - drive the browsers forward.
Aside - Bespin currently leaks memory. Browsers are now runtimes, so want to build a tool for memory tracking. (a) Log each garbage collection. (b) Graphical view of the heap. After that, tool after that is meta - a directory of all the tools out there.
Q. On a much smaller scale, could it be used as a textarea? Yes, Firefox engineers were keen to look at that.
Q. How much implemented in Javascript? Very much the trend in Moz. cf. Aza Raskin's recent post on doing an extension in Javascript (*cough* Chrome *cough*). All the XUL stuff was necessary at the time. Javascript's not the bottleneck anymore.
Q. The name? (as was previously asked) So with that, let's wrap up.
My colleague Fred has also posted his impressions.
Friday, February 27th, 2009
Category: Comet
Daniel Prieler has created a new library that allows realtime communication in JavaScript between clients. It works by embedding Flash in the page which is connected to a rtmp-flash-server.
JSSO works like this:
The data-transfer and the connection to the server are maintained by a simple embedded Flashmovie in your page. The communication with other clients runs through the local Flashmovie and the Red5-Server.
The data-flow between two clients looks like this:
Javascript/jsSO - Flashmovie - Red5-Server - Flashmovie - Javascript/jsSO
JAVASCRIPT:
-
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// Connect to to a shared object Handler (SOSample) on the Red5-Server and
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// use the objectName "draw". The objectName is identical to a namespace
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// for your data or a chat-room.
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// SOSample is the simplest shared object example of the Red5-server
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jsSO.connect('draw', 'rtmp://localhost/SOSample');
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// On button click set someVar in the shared object
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$(':button').live('click', function(){
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jsSO.set('someVar', 'value');
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});
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-
// Listen to changes on the shared object
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// event = A jquery event object
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// updates = If a var is updated it is set in the updates-object.
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// See code below for usage
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// data = All data in the object
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jsSO.onSync(function(event, updates, data) {
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if (updates.someVar) {
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// someVar was updated
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console.log(data.someVar);
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}
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});
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Wednesday, December 31st, 2008
Category: Comet
How about if all you needed to do was:
JAVASCRIPT:
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var server = new Addressable.Server({ useGears: true });
-
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server.onmessage = function (message) {
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log(message)
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}
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server.connect(function (id, url) {
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log("Connected. Messages will appear here.")
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$("#clientId").html("Client-Url: "+url)
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$("#testForm").attr("action", url)
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})
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function log(msg) {
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var log = $("#log");
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log.html(""+msg + "<br />" + log.html())
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}
-
And you would have Comet end points to play with?
That is what Malte has given us with a proof of concept called UniversalComet:
I have developed a JavaScript library that makes it extremely easy to incorporate "comet" or server-push technology into any web application without need for special programming or any special support on the server. Ressources needed on the server are also practically zero.
When you use the JavaScript library, you will receive an URI that identifies the client. Now you can make simple HTTP-GET requests to that URI with a message parameter and the client will receive the message immediately. Because only your application will know the un-guessable URI, the client should be save from unwanted messages. The use of HTTP-GET messages also allows sending messages in a "P2P"-fashion from client to client using JSONP cross-domain-messages.
The function that is passed to the connect-method receives the URI of the client and as soon as messages arrive they will be send to the onmessage-callback.
The JavaScript application uses "channels" to differentiate between different windows that the same client has open at any given time. These are cached in window.name. If you set window.name yourself this value is used. You can also set server.setChannel("myChannel") before you connect to name the channel yourself.
You can check out the demo.
Monday, December 29th, 2008
Category: Comet
Kaazing keeps on moving with its Java Comet server, and just released a new version. It will be interesting to see if real-time connections take off in 2009.
Kaazing is happy to announce the second major release of its Kaazing Gateway, an open source HTML 5 web server, which includes support for HTML 5 WebSockets. With the 8.12 release of Kaazing Gateway delivers even more HTML 5 features such as Server-sent Events, more advanced security services, and extended support for XMPP (Jabber) and STOMP (e.g. ActiveMQ, RabbitMQ, or OpenMQ).
Server-sent events make a substantial contribution to the HTML 5 specification; however, Kaazing Gateway makes that contribution even greater by enabling Broadcast Notifications, which makes it possible to send messages from a TCP-, UDP-, or Multicast-origin and deliver simultaneous updates to tens of thousands of end-users. Applications of Server-sent event broadcasting include sporting event updates, system notifications, financial market updates, and much more.
Kaazing Gateway's HTML 5 emulation libraries also include a number of updates. The libraries now enable any modern browser to support HTML 5 Server-sent Events, and introduce support for HTML 5 postMessage, which facilitates cross document messaging. Kaazing's HTML 5 libraries also include support for HTML 5 Offline Storage, which provides simple DOM-based storage solution. Kaazing Gateway and its client libraries also now provide support W3C Access Controls for Cross-Site Requests, which is a mechanism to enable client-side cross-site requests, better known as Cross-site XmlHttpRequests.
Beyond extended support for HTML 5, Kaazing Gateway 8.12 also provides more advanced XMPP features such as group chat. This release also introduces STOMP-JMS Adapter, which allows you to adapt any existing Java Message Service (JMS) services (e.g. JBoss Messaging, Tibco EMS, OpenMQ, SwiftMQ, WebSphere MQ, etc. ) for use with Kaazing Gateway.
Friday, October 31st, 2008
Category: Comet, HTML
Kaazing has released Kaazing Gateway, an open source HTML 5 WebSocket Server.
The HTML 5 WebSocket specification is a standard that attempts to simplify much of the complexity around achieving bi-directional communications between browsers and servers. The specification provides a simple JavaScript interface that enables developers to open a full-duplex socket connection and connect directly to any TCP-based back-end service (for example, JMS, JMX, IMAP, Jabber, and so on).
Kaazing Gateway makes it possible for developers to take advantage of WebSockets today by providing a JavaScript library that emulates the HTML 5 WebSocket, making it possible to build applications that leverage the WebSocket interface and that can be deployed to both modern and future browsers.
The ultra high-performance server behind Kaazing Gateway can support tens of thousands of concurrent connections on a single node. Multiple instances can be clustered with traditional HTTP load-balancers or DNS round robin, making it possible to support any number of persistent client connections. In addition to large numbers of connections, Kaazing Gateway can also handle high data throughput thanks to its high-performance, staged event driven architecture (SEDA).
The Atlantis release of Kaazing Gateway also comes prepackaged with JavaScript clients for popular message services such as Apache ActiveMQ and RabbittMQ as well as clients for XMPP services such as OpenFire, Jabberd, and other popular chat servers. This makes it easy for you to quickly build web-based chat applications or messaging applications such as stock matrixes, online trading platforms, or online games.
What is the WebSocket API?
JAVASCRIPT:
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interface WebSocket {
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readonly attribute DOMString URL;
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// ready state
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const unsigned short CONNECTING = 0;
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const unsigned short OPEN = 1;
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const unsigned short CLOSED = 2;
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readonly attribute int readyState;
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// networking
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attribute EventListener onopen;
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attribute EventListener onmessage;
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attribute EventListener onclosed;
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void postMessage(in DOMString data);
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void disconnect();
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};
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Wednesday, October 29th, 2008
Category: Comet
Comet is starting to gain steam, although mainly through the term "real-time Web." A couple of the Comet folks posted at the same time, both talking about the technology in different ways.
Ted Goddard answered a bunch of questions in WebSocket is neither Web nor Socket.
- Does WebSocket use TCP ports 81 and 815?
- How does WebSocket make use of an HTTP connection on port 80?
- Does WebSocket obey the same origin policy?
- Is WebSocket restricted to the two-connection limit of HTTP?
- Can WebSocket read and write arbitrarily as with low-level socket APIs?
- How does WebSocket delineate messages?
- How are function call semantics implemented over WebSocket?
- Is WebSocket easy to implement?
- Can we just upgrade HTTP?
Michael Carter had a fun little spin on things in HTML5 WebSocket and WebJneering.
I want to tell you about HTML5, specifically about the advances in bi-directional, asynchronous communication. But I’m troubled. Consider two propositions that I didn’t come up with: 1) Nothing is new, 2) Everything Sucks. Let these simple truths cast a shadow upon the tale you are about to read…
HTML5 provides a new thing called a WebSocket. I’m pretty sad that its not a TCPSocket, but alas, it was easier to throw in a handshake for security than to set up some out-of-bound security method, such as flash’s cross-domain policy files. We can’t connect to existing TCP servers, so we’ll just have to start over and write new WS/TCP servers. No problem. WebSocket will still be our salvation, leading us towards our stateful future.
I was at first overjoyed at the prospect of the World Wide Web’s new status as a real boy. But such feelings were just a precursor to the greatest technology-driven depression of my life. You see, as recently as twenty years ago the world was brimming with real programmers, who knew how to do such amazing things as write programs that conversed with far-away computers by using bsd sockets. We’ve traded those programmers, by and large, for JavaScript kiddies. Its not that the real programmers all died, retired, or gave up with programming; rather, every new programmer of the past decade is a bright-eyed 22 year old who thinks he’s the best thing since Google, what with his domination of rails (, java, or php) and javascript.
Both Michael and Ted will be joining myself, Alex Russell, Dylan, John Fallows, and others at an event tonight in Mountain View covering Comet. If you are in town, join us!
We are using the Google Moderator to help answer questions you want heard, so
add your questions too.
Friday, October 17th, 2008
Category: Comet
Richard Jones has started an interesting series to talk about scaling comet web applications using MochiWeb:
In this series I will detail what I found out empirically about how mochiweb performs with lots of open connections, and show how to build a comet application using mochiweb, where each mochiweb connection is registered with a router which dispatches messages to various users. We end up with a working application that can cope with a million concurrent connections, and crucially, knowing how much RAM we need to make it work.
In part one:
- Build a basic comet mochiweb app that sends clients a message every 10 seconds.
- Tune the Linux kernel to handle lots of TCP connections
- Build a flood-testing tool to open lots of connections (ye olde C10k test)
- Examine how much memory this requires per connection.
Future posts in this series will cover how to build a real message routing system, additional tricks to reduce memory usage, and more testing with 100k and 1m concurrent connections.
Richard walks through the code and setup, step by step and measures the scalable performance, leading too:
That was a reasonable first attempt. 45KB per-connection seems a bit high - I could probably cook something up in C using libevent that could do this with closer to 4.5KB per connection (just a guess, if anyone has experience please leave a comment). If you factor in the amount of code and time it took to do this in Erlang compared with C, I think the increased memory usage is more excusable.
In future posts I’ll cover building a message router (so we can uncomment lines 25 and 41-43 in mochiconntest_web.erl) and talk about some ways to reduce the overall memory usage. I’ll also share the results of testing with 100k and 1M connections.
Monday, October 6th, 2008
Category: Comet, JavaScript, Library
Michael Carter et al have been working on js.io, a client library that gives you networking, including Comet like support, via JavaScript.
The low level work can sit upon Comet APIs, and in the future, Web Sockets, and you get high level APIs to protocols such as:
- amqp
- imap
- irc
- ldap
- smtp
- ssh
- stomp
- telnet
- xmpp
There are some demos such as LiveHelp that uses Orbited as the backend.
Thursday, September 18th, 2008
Category: Announcements, Comet, Framework
ZK 3.5, the latest version of the server-side Ajax framework, is out with a raft of new features. Three of those features really stand out for me:
- Comet server push
- Customization of look and feel
- Performance monitoring
Server push via polling has been available in ZK for a while, and Comet in the ZK "Enterprise Edition," but now it is available to everyone. And it is pretty easy to use: "The implementation of server push is transparent to developers. ZK chooses which implementation to use according to the edition of ZK automatically, but it is configurable."
Customization of look and feel has gotten much easier. ZK has followed the example of a number of other frameworks in styling its widgets with predictably named CSS styles. Changing the look and feel of an application is now as easy as changing the ZK widget style sheet. Styles can further be overridden on a widget instance-by-instance basis.
Performance monitoring is perhaps the most exciting new feature. Client-side tools such as YSlow can guide optimization efforts and give you point in time performance snapshots. But critical applications need to be monitored and tracked end to end over their lifespan. With ZK 3.5, you now have the plumbing to instrument your application to capture five data points for each request:
- T1, the time browser sends a request to server
- T2, the time server receives a request
- T3, the time server sends a request to browser
- T4, the time browser receives a request from server
- T5, the time the browser finishes processing a request
ZKStudio 0.8.2
There's also a new version of ZKStudio for Eclipse out. The major change is that it now supports auto update via http://studioupdate.zkoss.org/studio/update
Tuesday, September 16th, 2008
Category: Comet, DWR
Joe Walker of DWR fame on Comet at @media Ajax.
Motivation for Comet
Interested in what our friends are up to, even if no-one else cares (as twitter illustrates). And also interested in what systems/things are doing, not just people. Chat (meebo), collaborative editing (google docs), streaming financial data (lightstreamer), async updates (yes.com), online gaming, async server processing (polar rose, i.e. shift processing complexity to the server - note this could be seen as an alternative to Gears-style local processing in some situations).
The web was designed to be connectionless - Comet blatently aims to make it connected.
Performance
Actually does scale. Joe shows the following graph:
Technical
Seven ways (!) to implement Comet.
Long polling - "slow" XHR request. Server doesn't answer immediately. Special part of HTTP to do this - chunked mode. However, IE "lies to you" - keeps saying it's got something, but you can't actually inspect it.
Forever frame - Send text/plain and 4k whitespace to flush IE's buffer. Flush with script tag for each data block. Must keep restarting to avoid memory leak.
Script tags - Dynamic script blocks, can point to any domain.
WebSockets - HTML 5 standard. Cleaner solution.
ActiveXObject("htmlfile") - htmlfile is an activeX control similar to XHR. Normally causes "clicking" noise in browser, but there's a hack to turn it off in most cases. Obviously, this only works in IE. Most bizzare thing is you get 49 Javascript before garbage collection, leading to hair-pulling moments when you try to work out why your 50th command isn't executing!
Mime messaging - "What push was built on 11 years ago" - x-multipart-replace. Works really well, though with memory leakage issues, but not in IE and historically not in the other browsers either.
Flash remoting
Forever GIF (bonus technique) - keep sending out new slices of an animated GIF!
Technical Issues
Co-ordination when browser has multiple tabs open to the same server - using window.name or cookies, but better solution is multi-home DNS - each call points to the server using a different name (1.example.com, 2.example.com etc all pointing to the same IP address).
Issues detecting when browser or connection has broken.
Proxies which don't let the stream go through in real-time - hold on to the chunks for a while before releasing them all at once. Can detect if this is happening from the browser using a timestamp technique.
... so just like with Ajax, we have to come up with hacks, likewise with Comet. Facebook and GMail show it's possible to work around these problems and get Comet working at scale.
API Styles
e.g. with WebSocket you're simply posting and receiving data. Event handlers for onOpen, onRead etc. Joe says this will be too low-level in many cases, hence the following styles.
PubSub - e.g. cometd. Low coupling (server-browser separation - Joe describes demo where servers hot-swapped without affecting client), inter-language interop. Good analogy to SOAP, which has gradually shifted from RPC to document exchange.
API - this looks to me like Ruby's remote JS - server controls what's happening on the browser. e.g. Effect.shake("price") on the server will make the price div shake on the client.
Data Syc API - Keep changing/updating data store. Simplest to understand.
Tuesday, July 8th, 2008
Category: Comet
JAVASCRIPT:
-
-
var conn = new WebSocket("ws://www.example.com/livedemo");
-
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conn.onopen = function(evt) { alert("Conn opened"); }
-
conn.onread = function(evt) { alert("Read: " + evt.data); }
-
conn.onclose = function(evt) { alert("Conn closed"); }
-
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conn.send("Hello World")
-
What if that code was part of an HTML standard? Would that make you feel better about Comet-style applications? Well, Michael Carter has pointed us to the HTML 5 discussions that give us WebSocket:
The HTML5 specification now offers WebSocket, a full-duplex communications channel that operates over a single socket. I have been listening closely, and in some cases contributing, to the process of ensuring that WebSocket will:
- Seamlessly traverse firewalls and routers
- Allow duly authorized cross-domain communication
- Integrate well with cookie-based authentication
- Integrate with existing HTTP load balancers
- Be compatible with binary data
He goes on to discuss how WebSocket is not the same as a TCP socket itself, and what that means as we develop real-time applications.
Tuesday, July 1st, 2008
Category: Comet
Michael Carter of Orbited has written about how he now likes to call Comet sockets in the browser, and has an implementation available that looks like this:
JAVASCRIPT:
-
-
var conn = new TCPSocket(hostname, port)
-
-
conn.onopen = function() { alert('connection opened!') }
-
conn.onread = function(data) { alert('RECEIVE: ' + data) }
-
conn.onclose = function(data) { alert('connection closed!') }
-
-
conn.send('Hello World');
-
The above code code is all you need to know. It will open a TCP connection to hostname:port, and will send the data “Hello Worldâ€. Any data the server sends back will be alerted with the onread handler.
The exact mechanism behind this innovation is pretty straightforward: Orbited is a router and firewall for incoming TCPSocket connections from the browser. It uses Comet techniques to establish bi-directional communication with the browser, then forwards all data over a raw TCP socket to the end point. Configuration allows access control enforcement so that the TCPSocket can only be connected to pre-approved end-points, so that the Orbited server isn’t an open relay.
While this presents a paradigm shift in the way developers are tackling real-time, web-based applications today, it’s actually a return to the original method of writing network applications. Instead of writing applications based on web frameworks and throwing a Comet server in the mix, you can simply use the client-server architecture where the browser is the client, and the server is an arbitrary TCP server.
Monday, May 12th, 2008
Category: Comet, Games
Piotr Dachtera took his 64pola.pl, and created a scalable version using Comet. Dylan reports it as "a Jetty-powered Comet app that uses dojox.cometd on the client-side. It’s a solid implementation that shows chess moves in real-time, and to date is the best all-around Comet game I’ve seen that is live to the world."
Mathieu Nouzareth then commented that Cafe.com, a Flash based gaming platform also uses Jetty and Comet techniques (compared to AMF etc).
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