How can invalid websocket requests be gracefully handled in Play 2.6? - scala

Question

We have a play 2.6 app which uses websockets. This is working great, but in our error logs we occasionally see the following:
[ERROR] [08/25/2017 16:00:44.770] [play-dev-mode-akka.actor.default-dispatcher-35] [akka.actor.ActorSystemImpl(play-dev-mode)] Internal server error, sending 500 response
java.lang.RuntimeException: WebSocket returned for non WebSocket request
at scala.sys.package$.error(package.scala:27)
at play.core.server.AkkaHttpServer.executeHandler(AkkaHttpServer.scala:271)
at play.core.server.AkkaHttpServer.handleRequest(AkkaHttpServer.scala:201)
at play.core.server.AkkaHttpServer.$anonfun$createServerBinding$3(AkkaHttpServer.scala:107)
at akka.stream.impl.fusing.MapAsync$$anon$23.onPush(Ops.scala:1172)
at akka.stream.impl.fusing.GraphInterpreter.processPush(GraphInterpreter.scala:499)
at akka.stream.impl.fusing.GraphInterpreter.processEvent(GraphInterpreter.scala:462)
at akka.stream.impl.fusing.GraphInterpreter.execute(GraphInterpreter.scala:368)
at akka.stream.impl.fusing.GraphInterpreterShell.runBatch(ActorGraphInterpreter.scala:571)
at akka.stream.impl.fusing.GraphInterpreterShell$AsyncInput.execute(ActorGraphInterpreter.scala:457)
at akka.stream.impl.fusing.GraphInterpreterShell.processEvent(ActorGraphInterpreter.scala:546)
at akka.stream.impl.fusing.ActorGraphInterpreter.akka$stream$impl$fusing$ActorGraphInterpreter$$processEvent(ActorGraphInterpreter.scala:725)
at akka.stream.impl.fusing.ActorGraphInterpreter$$anonfun$receive$1.applyOrElse(ActorGraphInterpreter.scala:740)
at akka.actor.Actor.aroundReceive(Actor.scala:513)
at akka.actor.Actcorrectlyor.aroundReceive$(Actor.scala:511)
at akka.stream.impl.fusing.ActorGraphInterpreter.aroundReceive(ActorGraphInterpreter.scala:650)
at akka.actor.ActorCell.receiveMessage(ActorCell.scala:527)
at akka.actor.ActorCell.invoke(ActorCell.scala:496)
at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:257)
at akka.dispatch.Mailbox.run(Mailbox.scala:224)
at akka.dispatch.Mailbox.exec(Mailbox.scala:234)
at akka.dispatch.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
at akka.dispatch.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
at akka.dispatch.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
at akka.dispatch.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)
After a little sleuthing it seems this occurs when an HTTP request without the correct Connection and/or Upgrade headers is made. The play source is here.
We would like to log more detailed information to determine why this is happening (we suspect header-stripping firewalls), but unfortunately our websocket handler is never invoked (nothing is printed to console) when the error occurs:
def ws = WebSocketcorrectly.acceptOrResult[String, String] { implicit request =>
println("Hello world") // Only printed for requests with valid headers
...
}
How can we insert some logging statements with access to the request headers and IP?