def start(relativePath: String)(handler: Request => Response): Subscription = {

...

println("pong 1")
// 2.	create a cancellation token to run an asynchronous computation (hint: use the Future.run companion method)
// ct is a CancellationToken
val working = Future.run() { ct =>
  Future {
    while (ct.nonCancelled) {
      println("pong 2")
        // 3.	in this asynchronous computation, while the token is not
        // cancelled, await the next request from the listener and then
        // respond to it
    ... do some thing
    }
    println("done")
  }
}

...
}