NPE during websocket disconnect [SPR-14703]

[spring-projects-issues]

Prashant Deva opened SPR-14703 and commented

This is the exception on server

Exception in thread "clientInboundChannel-97" org.springframework.messaging.MessageDeliveryException: Failed to handle GenericMessage [payload=byte[0], headers={simpMessageType=DISCONNECT, stompCommand=DISCONNECT, simpSessionAttributes={org.springframework.messaging.simp.SimpAttributes.COMPLETED=true}, simpSessionId=e4fb909754d849a08526503c2afa7584}] to org.springframework.messaging.support.ExecutorSubscribableChannel$SendTask@329d23a5 in StompBrokerRelay[127.0.0.1:61613]; nested exception is java.lang.NullPointerException
	at org.springframework.messaging.support.ExecutorSubscribableChannel$SendTask.run(ExecutorSubscribableChannel.java:144)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
	at org.springframework.messaging.simp.stomp.StompBrokerRelayMessageHandler$StompConnectionHandler.forward(StompBrokerRelayMessageHandler.java:783)
	at org.springframework.messaging.simp.stomp.StompBrokerRelayMessageHandler.handleMessageInternal(StompBrokerRelayMessageHandler.java:511)
	at org.springframework.messaging.simp.broker.AbstractBrokerMessageHandler.handleMessage(AbstractBrokerMessageHandler.java:238)
	at org.springframework.messaging.support.ExecutorSubscribableChannel$SendTask.run(ExecutorSubscribableChannel.java:135)
	... 3 more

Here is the client side code:

    void setup() throws ExecutionException, InterruptedException
    {

        JettyWebSocketClient webSocketClient = new JettyWebSocketClient();
        List<Transport> transports = new ArrayList<Transport>(1);
        transports.add(new WebSocketTransport(webSocketClient));

        SockJsClient sockJsClient = new SockJsClient(transports);
        sockJsClient.setMessageCodec(new StringMessageCodec());

        stompClient = new WebSocketStompClient(sockJsClient);
        stompClient.setMessageConverter(new StringMessageConverter());
        stompClient.start();

        sessionHandler = new MyStompSessionHandler();
        stompClient.connect(WS_URL, sessionHandler);
    }

    void stop()
    {
        stompSession.disconnect();
        stompClient.stop();
    }

As you can see the client closes the connection gracefully.
It first disconnects the session and then calls stop() on the stompClient.

Doing so should not result in an exception on the server.

---

Affects: 4.2.6

Issue Links:

• exception during websocket server shutdown [SPR-14716] #19281 exception during websocket server shutdown

Referenced from: commits 3bc1121, 07d5f8b, 114b2b6

Backported to: 4.2.8

[spring-projects-issues]

Rossen Stoyanchev commented

Line number based on 4.2.6 should match to here.

Most likely the DISCONNECT frame and the closing of the websocket connection are competing with each other on the server-side. There is actually a way to wait for the DISONNECT to complete through a receipt header before shutting down completely. That said we should be more defensive around this scenario to avoid the NPE. I'll see if I can reproduce it easily. Either way I can add some checks.

[spring-projects-issues]

Rossen Stoyanchev commented

This should now be fixed in snapshots of all 3 target versions.