runtime.rb

require 'hitimes'

module Rack

  class Runtime

    def initialize(app)
      @app = app
    end

    def call(env)
      interval = Hitimes::Interval.now
      status, headers, body = @app.call(env)
      duration = interval.stop

      headers['X-Runtime'] = ("%0.6f" % duration)

      [status, headers, body]
    end

  end
end