akka-io-tcp-echo-server-using-iteratee.scala

import akka.actor.IO._
import akka.actor.{Props, IO, IOManager, Actor, ActorSystem}
import akka.event.Logging
import akka.util.ByteString
import java.net.InetSocketAddress

class TCPEchoServer(port: Int) extends Actor {
  val log = Logging(context.system, this)

  val state = IterateeRef.Map.async[IO.Handle]()(context.dispatcher)

  override def preStart {
    IOManager(context.system).listen( new InetSocketAddress(port) )
  }

  def receive = {
    case NewClient(server) => {
      log.info("new client")
      val socket = server.accept()
      state(socket) flatMap (_ => this.write(socket))
    }
    case Read(socket, bytes) => {
      state(socket)(Chunk(bytes))
    }
    case Closed(socket, cause) => {
      state(socket)(EOF(None))
      state -= socket
      log.info("socket closed")
    }
  }

  def ascii(bytes: ByteString): String = bytes.decodeString("US-ASCII")

  def write(socket: IO.SocketHandle): IO.Iteratee[Unit] =
    IO.repeat {
      for {
        string <- readLine
    } yield {
      log.info(string)
      socket.write(ByteString(string))
    }
  }
  def readLine: IO.Iteratee[String] = {
    val CRLF = ByteString("\r\n")
    for {
      line <- IO.takeUntil(CRLF)
    } yield {
      ascii(line)
    }
  }
}

object Main extends App {
  val port = Option(System.getenv("PORT")).map(_.toInt).getOrElse(9999)
  ActorSystem().actorOf(Props(new TCPEchoServer(port)))
}

simple-akka-io-tcp-echo-server.scala

import akka.actor.{Props, IO, IOManager, Actor, ActorSystem}
import java.net.InetSocketAddress

class TCPEchoServer(port: Int) extends Actor {
  override def preStart {
    IOManager(context.system).listen( new InetSocketAddress(port) )
  }

  def receive = {
    case IO.NewClient(server) => server.accept()
    case IO.Read(rHandle, bytes) => rHandle.asSocket.write(bytes.compact)
  }
}

object TCPEchoServer extends App {
  val port = Option(System.getenv("PORT")).map(_.toInt).getOrElse(9999)
  ActorSystem().actorOf(Props(new TCPEchoServer(port)))
}