Akka/Scala detect closed TCP connection?

Question

I'm trying to write a TCP server using Akka and Scala, which will instantiate actors and stop the actors when a client connects and disconnects respectively. I have a TCP binding actor,

 class Server extends Actor{
   import Tcp._
   import context.system

   IO(Tcp) ! Bind(self, new InetSocketAddress("localhost", 9595))

   def receive = {

     case Bound(localAddress) =>
       println("Server Bound")
       println(localAddress)

     case CommandFailed(_: Bind) => context stop self

     case Connected(remote, local)=>
       val handler = context.system.actorOf(Props[ConnHandler])
       val connection = sender()
       connection ! Register(handler)
   }
 }

The above instantiates a TCP listener on localhost:9595 and registers handler actors to each connection.

I then have the receive def in my ConnHandler class defined as such, abbreviated with ... where the code behaves correctly.

case received => {...}
case PeerClosed => {
    println("Stopping")
    //Other actor stopping, cleanup.
    context stop self
}

(See http://doc.akka.io/docs/akka/snapshot/scala/io-tcp.html for the docs I used to write this - it uses more or less the same code in the PeerClosed case)

However, when I close the socket client-side, the actor remains running, and no "Stopping" message is printed.

I have no nearby configured non-Windows machines to test this on, since I believe this to do with me running on Windows because after googling around, I found a still open bug - https://github.com/akka/akka/issues/17122 - which refers to some Close events being missed on Windows-based systems.

Have I made a silly error in my code, or would this be part of the bug linked above?

Although I could write in a case for Received(data) that would close the connection, however, a disconnect caused by the network disconnecting or something would leave the server in an unrecoverable state, requiring the application to be restarted since it would leave a secondary, shared actor in a state that says the client is still connected, and thus, the server would reject further connections from that user.

Edit:

I've worked around this by adding a watchdog timer actor that has a periodic action that fires after some amount of time. The ConnHandler actor will reset the watchdog timer every time an event happens on the connection. Although not ideal, it does what I want to do.

winry winry · Accepted Answer · 2016-12-07T03:01:53

Edit 12/9/2016: ConnHandler will receive a PeerClosed message even when a client Unexpectedly disconnect.

Akka/Scala detect closed TCP connection?

1 Answers