class Rack::Builder

referenced in the application if required.
The +call+ method in this example sets an additional environment key which then can be
All requests through to this application will first be processed by the middleware class.

run lambda { |env| [200, { "content-type" => "text/plain" }, ["OK"]] }
use Middleware

end
end
@app.call(env)
env["rack.some_header"] = "setting an example"
def call(env)

end
@app = app
def initialize(app)
class Middleware

Specifies middleware to use in a stack.

def use(middleware, *args, &block)
  if @map
    mapping, @map = @map, nil
    @use << proc { |app| generate_map(app, mapping) }
  end
  @use << proc { |app| middleware.new(app, *args, &block) }
end