Wrapping my brain around long polling with Orbited/Rails

posted 02 Nov 2009

I’ve been reading about Comet/long polling for a while now. It seems to be becoming a popular topic of discussion. There are a lot of opinions and theories on it. Not having any experience with it myself, I’ve only pseudo-understood what it was.

Wikipedia has a nice breakdown of what it is. Basically, it is a way for a web application to ‘push’ data to the client using long running HTTP requests.

Now that I’ve gotten around to reading up on it, I decided a week or so ago to try and do a simple implementation of it. I noticed that a lot of people use the chat room concept with Comet, so I decided to try and make a simple app that implemented a chat room. Kind of like when I discovered Ruby on Rails, I decided to do the quintessential ‘make a blog with rails’ experiment.

Try #1 – Nginx push module

Without knowing any better, I decided to try out the new-ish Nginx http push module. I’m familiar enough with Nginx. I figured it would be easy. It sort of was.

I followed the instructions for install Nginx with the http push module. Everything seemed to work as advertised. I even tried the sample code from Nginx & Comet: Low Latency Server Push. Everything worked as advertised. I was pretty impressed.

In my app I used the delayed_job plugin to queue messages to be sent to the publish URL. For the most part it appeared to be working correctly. I could see the messages entering the queue and I could see that they were getting published to my Nginx polling server.

Unfortunately, my Javascript/Prototype skills are clearly not up to par. I was unable to get my chat room to work reliably. It would only receive messages sometimes and it seemed to lose track of my polling server.

I spent a day trying to figure out what I was doing wrong and finally threw my hands up in defeat, grabbed my Xbox controller, and cooled off to some Borderlands.

Try #2 – Orbited

The difference between my first try and this try were night and day. The Orbited setup was seemingly simpler than my Nginx one.

Orbited is a Python server using the Twisted framework. Twisted is an extremely stable/reliable networking framework. It has been around for as long as I have been using Python

Instead of having to have Nginx running + Apache + the delayed job runner running, I could slim it down to just Apache + Orbited. Also the Orbited plugin made integration into Rails extremely easy. Installing the plugin created a config file with defaults set the same as the defaults in the Orbited config. So I really didn’t have to configure it to point to Orbited at all.

In my HTML template I had to add the following to my head section:

<%= orbited_javascript %>

And then for the chat channels I just did:

<%= stomp_connect(params[:slug]) %>

The params[:slug] variable is set to whatever my current chat channel is. It was really simple.

In my messages controller I have a private method called send_message_via_orbited(message). This method sends newly created messages to the default Orbited STOMP service(MorbidQ) and then to my channel’s page.

def send_message_via_orbited(message)
  orbited_data = render_to_string :update do |page|
    page.insert_html :bottom, 
		'messages', 
		:partial => 'channels/message', 
		:locals => {:message => message}
    page['message_form'].down('form').reset
  end
  Orbited.send_data(message.channel.name, orbited_data)
end

All this code does is updated the messages div with the new message. This is done via RJS which sends Javascript through Orbited to the page where it is eval’d.

Aaaaaaand done!

Orbited was extremely easy and worked pretty reliably for the little bit of testing that I did. You can browse the source on GitHub, I called it pollchat.

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