Log Akka Http Response time including transmission of bytes

LogReqRespTimeWithTransportTime.scala

  def akkaResponseTimeLoggingFunction(loggingAdapter: LoggingAdapter,
                                      requestTimestamp: Long,
                                      level: LogLevel = Logging.InfoLevel)(req: HttpRequest)(res: RouteResult): Unit = {
    res match {
      case Complete(resp) =>
        resp.entity.transformDataBytes(Flow[ByteString].watchTermination() {
          case (_, f) =>
            f.foreach { _ =>
              val responseTimestamp: Long = System.nanoTime
              val elapsedTime: Long = (responseTimestamp - requestTimestamp) / 1000000
              val loggingString = s"""Logged Request:${req.method}:${req.uri}:${resp.status}:$elapsedTime"""
              LogEntry(loggingString, level).logTo(loggingAdapter)
            }
        })
      case Rejected(reason) =>
        directives.LogEntry(s"Rejected Reason: ${reason.mkString(",")}", level).logTo(loggingAdapter)
    }
  }

  def printResponseTime(log: LoggingAdapter) = {
    val requestTimestamp = System.nanoTime
    akkaResponseTimeLoggingFunction(log, requestTimestamp)(_)
  }

  val logResponseTime = DebuggingDirectives.logRequestResult(LoggingMagnet(printResponseTime))