class Rack::Runtime

too.
time, or before all the other middlewares to include time for them,
You can put it right before the application to see the processing
time of the request, in seconds
Sets an “x-runtime” response header, indicating the response

def call(env) 

def call(env)
  start_time = Utils.clock_time
  _, headers, _ = response = @app.call(env)
  request_time = Utils.clock_time - start_time
  unless headers.key?(@header_name)
    headers[@header_name] = FORMAT_STRING % request_time
  end
  response
end

def initialize(app, name = nil) 

def initialize(app, name = nil)
  @app = app
  @header_name = HEADER_NAME
  @header_name += "-#{name.to_s.downcase}" if name
end