robert hahn

a darn good web developer

August 16, 2007

The Ideal REST Framework.

Granted, I haven’t been spending all my time looking at everyone’s favorite framework, but from the ones I do know about, it seems really odd that we have an impedance mismatch between HTTP and the classes/methods we use in our framework. I want to spend a few posts exploring how I think a framework should be put together, so that it conforms as much as possible to REST. My code samples will be in Ruby, but I don’t see any reason why you can’t build this in any other language.

Naturally, I start where the HTTP request gets handed off to what we think of as the controller in most frameworks. It seems as though we ought to have a superclass that defines the uniform interface. It would look like this:

class HTTPResource
    def get; end
    def post; end
    def put; end
    def delete; end
    def method_missing m
        @status = 405
        "Method Not Allowed"
    end
end

With it, you would instantiate the resources you want to expose. In this case, I want to build, um, how about a Media Release administration tool, where you can add, edit, and post PRs. Let’s expose a resource called Release.

class Release < HTTPResource
  def get; end
  def put; end
  def delete; end

  private

  def post;end
end

Well, I’m sure you’re tempted to say that you can post a Release, and I’d agree with you, but I wanted to set it up this way to show you something cool: by making post private, any calls to that method would instead be handled by the superclass’ method_missing method, and return a 405 Method Not Allowed. Wow, that’s convenient.

There’s a lot of stuff missing. HTTPResource really ought to get some context together, like a collection of HTTP headers and ready access to query variables. I haven’t yet thought about how that’s going to work yet – it could be that we need instance variables, or it could be that we need classes.

But one thing I thought was pretty cool about this is that this structure seems so simple and natural, you could easily write a commandline script that included these class definitions, and manipulate your app as easily from a script as from a browser. I’m sure you could do it with other frameworks too, but it looks obvious how you’d write such a tool. That seems like a win when it comes times to write tests – just call Release.new.get, for example, and test what gets returned.