Message to a client from the server

Question

Hi, I have to design a client/server system emulated on a website running Ruby on Rails that should work like this:

a page is requested by a web browser and once it's opened the server can push messages to it

I know this is not possible "naturally" but I was thinking of a sort of "java applet" that is running on that page, listening on a port for messages to be sent by the hosting server. This should be done opening a sort of a socket that listens on some port where the server can connect to send its messages.

Can this be done? Do I have to develop a java server thread or can I simply address the client applet via it's ip address and port and use any web service connection from the server?

thanks, Luca

Answer 1

The easiest way to do that is to use Javascript to emulate the push mechanism. Polling in regular intervals using AJAX is sufficient in most cases. Have also a look at Comet.

Answer 2

An alternative to using a java applet may be to use a combination of javascript and an approach known as Comet. In a nutshell, Comet is a way to enable server push over HTTP. I'm not really a ruby on rails guy, but a quick google search for ruby on rails and comet nets a fair amount of useful information.

Answer 3

have you looked at juggernaut

Answer 4

If you want go the applet route, you need to make the connection from applet to the same server where the web page is served. The applet can't listen. Once the TCP connection is established, it's a 2-way channel, you can pull or push as long as your protocol allows it. This is how it's done with most Applet-based chat clients.

More and more people are simply using long polling in Javascript. It's pretty involved to get a reliable long polling system running, I would suggest you to use a framework. For example,

http://cometdproject.dojotoolkit.org/

Answer 5

Comet is definately what you want. Depending on your needs, you can host your own comet server, or use a SaaS solution, such as WebSync On-Demand (disclaimer: I work there). Using the SaaS stuff, you get server-push capabilities without having to actually run your own comet server.