RayRoestenburg / scala-io-exercise-1

If you don't have a working Scala development setup yet, please see the setup instructions

Exercise 1

In this exercise you will learn about a pattern known as the Receptionist.

The Receptionist has the following responsibilities:

• Receive messages from the outside world using some endpoint.
• Create child actors.
• delegate to child actors to do the work. The child actors respond back to the receptionist for a request/response interaction (or the receptionist notifies child actors 'fire and forget style' which is not part of this exercise.)
• Supervise the child actors. (the default supervision strategy is used, supervision is not part of this exercise.)

Objective

The objective of this exercise is to get familiar with the Receptionist pattern. You will learn how a child actor is created by the Receptionist and how work is delegated to the child actor. Although Spray is used in the exercise it is not required to know Spray to complete the exercise, since all required code to hook up to HTTP is provided.

What is already prepared

A Main App which uses the Spray-can HTTP IO extension. This Main app creates the ActorSystem, starts the HTTP extension and registers the Receptionist Actor as HTTP listener. If you comment out the ReverseActorSpec the /reverse path should work. The Receptionist listens on the path "/reverse" for a HTTP POST of a JSON entity, for instance:

{ 
  "value" : "reverse this!"
}   

An example using the httpie command line tool:

  http POST localhost:8000/reverse value="reverse this\\!"

The result should be something like:

HTTP/1.1 200 OK
{
  "value": "!siht esrever"
}

In this exercise you will replace the default string reversal code inside the ReverseRoute (which is mixed into the Receptionist) with a call to a child actor: the ReverseActor.

The Exercise

Look for the TODO's in the project and follow the instructions. The following tasks will need to be completed:

Implement the ReverseActor (reverse a string and send back to sender).

• define ReverseActor
• define Reverse case class and ReverseResult case class
• Make the existing ReverseActorSpec pass.
• create the child reverse actor in the Receptionist
• remove the direct implementation and delegate to the ReverseActor.

The Receptionist receives a ReverseRequest which needs to be converted to the message that the ReverseActor understands.

• use the ask pattern, mapTo a typed future
• run the tests, all tests should pass

Run the application

• Run the application by using 'sbt run' from the project root (this starts the spray-can server on localhost:8000)

• Test with httpie (or curl or your fav HTTP command line tool) The example below shows a call using httpie:

  http POST localhost:8000/reverse value="reverse this\!"

Next Exercise

A better way to create the child ReverseActor for easier unit testing of the Receptionist. Go to Exercise 2