Richard Searle

Akka 2.0 provides a clean mechanism for non blocking I/O, abstracting all the details of NIO. The example provided is very detailed but a little large to serve as an introduction. The code below implements a very simple network service: read a length delimited ascii string and print it. The length is a 4 digit human readable number, for ease of testing. The code can then exercised using netcat

nc localhost 9999 <
      val socket = server.accept()
      state(socket) flatMap (_ => LengthBoundedServer.printMessage)

    case Read(socket, bytes) =>
      state(socket)(Chunk(bytes))

    case Closed(socket, cause) =>
      state(socket)(EOF(None))
      state -= socket
  }

}

object LengthBoundedServer {
  import IO._
  def ascii(bytes: ByteString): String = bytes.decodeString("US-ASCII").trim

  def printMessage: IO.Iteratee[Unit] =
    repeat {
      for {
        string <- readMessage
 } yield {
    println(string)
    }
 }
def readMessage: IO.Iteratee[String] =
 for {
   lengthBytes <- take(4)
   len = ascii(lengthBytes).toInt
   bytes <- take(len)
 } yield {
   ascii(bytes)
 }
}
object Main extends App {
 val port = Option(System.getenv("PORT")) map (_.toInt) getOrElse 9999
 val system = ActorSystem()
 val server = system.actorOf(Props(new LengthBoundedServer(port)))
}