HelloWorldJustService.scala

  val service = HttpService {
    // pure example
    case GET -> Root / "hello" / name =>
      Ok(Json.obj("message" -> Json.fromString(s"Hello, ${name}")))


    case request @ POST -> Root / "hello" / name =>
      for {
        // Decode a user request - simplest way to access the request body
	greeting <- request.as(jsonOf[Greeting])
        resp <- Ok(Json.obj("message" -> Json.fromString(s"${greeting.greeting}, ${name}")))
      } yield resp


    case request @ PUT -> Root / "hello" / name => {
      // request.as returns a Task; attempt converts it to a task that
      // will return a (scalaz) Either (\/) of either a throwable or the result
      // Use flatMap here rather than map, because flatMap allows you to return
      // the objects wrapped in a Task that the http4s api provides, and they flatten
      // to one level of Task, rather than a Task[Task[Response]] as they would with
      // simple map.
      // If you're integrating with FS2-based code, map may be better
      request.as(jsonOf[ExtendedGreeting]).attempt.flatMap {
        // check that the exception is caused by a decoding failure
        // and use the Circe show capabilities to print out a vaguely
        // useful error message in the response
        case -\/(f) => f.getCause match {
          case (d: DecodingFailure) => BadRequest(d.show)
          case _ => BadRequest(f.toString)
        }
        // Handle the happy path
        case \/-(greeting) =>  Ok(Json.obj("message" -> Json.fromString(s"${greeting.greeting.greeting}, ${name}")))
      }
    }
  }