config.rb

module Rack
  # Rack::Config modifies the environment using the block given during
  # initialization.
  #
  # Example:
  #     use Rack::Config do |env|
  #       env['my-key'] = 'some-value'
  #     end
  class Config
    def initialize(app, &block)
      @app = app
      @block = block
    end

    def call(env)
      @block.call(env)
      @app.call(env)
    end
  end
end