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require 'rack/utils'
module Rack
# Sets an "X-Runtime" response header, indicating the response
# time of the request, in seconds
# You can put it right before the application to see the processing
# time, or before all the other middlewares to include time for them,
# too.
class Runtime
FORMAT_STRING = "%0.6f".freeze # :nodoc:
HEADER_NAME = "X-Runtime".freeze # :nodoc:
def initialize(app, name = nil)
@app = app
@header_name = HEADER_NAME
@header_name += "-#{name}" if name
def call(env)
start_time = Utils.clock_time
status, headers, body =
request_time = Utils.clock_time - start_time
unless headers.has_key?(@header_name)
headers[@header_name] = FORMAT_STRING % request_time
[status, headers, body]
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