Tomcat throws IllegalStateException “The remote endpoint was in state [BINARY_FULL_WRITING] …” when calling RemoteEndpoint.Async.sendBinary concurrently on the same session

[Farzad Panahi]

Hi,

I am using tomcat 8.0.23 to terminate my websocket connections. I have
the following code to take care of the incoming messages:

@OnMessage
public void onMsg(Session session, byte[] request) {
        executorService.execute(() ->
                session.getAsyncRemote().sendBinary(
                        ByteBuffer.wrap(getResponse(session,
request)), result -> {
                            if (!result.isOK()) {
                                LOGGER.catching(result.getException());
                            }
                        }
                ));
}

But I get the following exception:

Exception in thread "pool-6-thread-10160"
java.lang.IllegalStateException: The remote endpoint was in state
[BINARY_FULL_WRITING] which is an invalid state for called method
    at 
org.apache.tomcat.websocket.WsRemoteEndpointImplBase$StateMachine.checkState(WsRemoteEndpointImplBase.java:1148)
    at 
org.apache.tomcat.websocket.WsRemoteEndpointImplBase$StateMachine.binaryStart(WsRemoteEndpointImplBase.java:1101)
    at 
org.apache.tomcat.websocket.WsRemoteEndpointImplBase.sendBytesByCompletion(WsRemoteEndpointImplBase.java:152)
    at 
org.apache.tomcat.websocket.WsRemoteEndpointAsync.sendBinary(WsRemoteEndpointAsync.java:65)

>From what I understand from java doc, RemoteEndpoint.Async.sendBinary
should not throw IllegalStateException:

> sendBinary void sendBinary(ByteBuffer data, SendHandler handler)
> Throws: IllegalArgumentException - if either the data or the handler are null.

It is also good to note that RemoEndpoint.Basic (not
RemoteEndpoint.Async) has the following paragraph in java doc:

> If the websocket connection underlying this RemoteEndpoint is busy sending a  
> message when a call is made to send another one, for example if two threads  
> attempt to call a send method concurrently, or if a developer attempts to 
> send a new message while in the middle of sending an existing one, the send 
> method called while the connection is already busy may throw an 
> IllegalStateException.


Is this expected behaviour from tomcat or a possible implementation bug?


Cheers

Farzad

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