4.1. Rack

Rack is a modular interface for handling web requests, written in Ruby, with support for many different web servers. It abstracts away the handling of HTTP requests and responses into a single, simple call method that can be used by anything from a plain Ruby script all the way to Rails itself.

Listing 2.1  HelloWorld as a Rack application
class HelloWorld
  def call(env)
    [200, {"Content-Type" => "text/plain"}, ["Hello world!"]]
  end
end