Calculating X-Queue-Time for New Relic instrumentation

gistfile1.rb

now = Time.now.to_f
milliseconds = (now * 1000).to_i
microseconds = (now * 1000000).to_i

env["HTTP_X_MIDDLEWARE_START"] = "t=#{microseconds}"

if env["HTTP_X_REQUEST_START"]
  request_start_milliseconds = env["HTTP_X_REQUEST_START"].to_i
  request_start_microseconds = request_start_milliseconds * 1000

  queue_time_milliseconds = milliseconds - request_start_milliseconds
  queue_time_microseconds = microseconds - request_start_microseconds

  env["HTTP_X_QUEUE_TIME"] = "t=#{queue_time_microseconds}"
  statsd.measure("heroku.router_to_rack", queue_time_milliseconds)
end