Johan Sørensen

Ruby has a nice new Rack

As someone who’ve used Rails and other ruby web frameworks for quite some time, plus my own dabbling in that domain, I’ve seen how we all go and redo our own webserver interface, while those cheeky python kids keep nagging about WSGI.

So, I’ve been playing with Rack recently, and it’s quite inspired by WSGI. At its core, all a Rack application has to do is answer to a message for call with the environment hash as the arguments and return a tuple looking like [status_code, headers, body_array], like this

require "rack"
class Foo
  def call(env)
    [200, {"Content-Type"=>"text/plain"}, ["Hello world!"]]
HOST_AND_PORT = {:Host => "", :Port => 8080}, HOST_AND_PORT)

in fact, we could even replace that whole class with a lambda that just returns the array:

app = lambda { [200, {"Content-Type" => "text/plain"}, ["Hello lambda world!"]] }, {:Host => "", :Port => 8080})

And we can run our marvelous application under mongrel. Now, a Rack application is basically anything that responds to #call, the nice thing about this is that we can chain Rack applications together, forming some middleware between our main app and the request being served by the browser. So if we call Rack::ShowExceptions#call before calling Foo#call, like this we get some nice views from your nasty little exceptions.

Why is this good? Because as a framework author you’d be able to reuse middleware (Rack applications) from other applications, or as Chris puts it:

bq. Compare “That upload handler you wrote for IOWA is really great, too bad I use Camping.” with “That upload handler you wrote for Rack works great for me too!”

Rack is still a bit rough around the edges, and the API is stupidly simple (“just #call it”), however it does provide a very easy to use API.

Cabinet is a tiny little pseudo-framework I wrote while playing around with Rack last night. Knock yourself out. I think the slogan should be “10x less productive” or “typing boring stuff over convention”. Features Django inspired url dispatching, that’ll make you type lots of regexens for every single thing. “Ruby push-ups” or something like that.

Now, don’t go write your own framework just yet, unless its merely for the sake of fooling around (like “Cabinet” was), ruby already has a bunch; Rails, Nitro, Camping, Merb, Ramaze and the oldskoolers like IOWA and Cerise.


  1. Dr Nic Says:

    Thanks for the intro to Rack; I just haven’t found time to fiddle around with it yet.