useDirectives2.scala

import io.prometheus.client.{Gauge, Histogram}

def reportRequestMetrics(request: HttpRequest): Try[RouteResult] => Unit = {
  requestsInProgress.inc()
  val requestTimer = requestLatencySeconds.startTimer()

  result => {
    requestsInProgress.dec()
    result match {
      case Success(Complete(_)) => requestTimer.observeDuration()
      case _ => // do nothing
    }
  }
}