The problem is the same as already described here: https://issues.jboss.org/browse/UNDERTOW-589 but I cannot observe that behavior. It doesn't matter how many messages are sent after the client closed the connection, the close task is never called.

Another issue is the send(String data, EventCallback callback) function from ServerSentEventConnection. The callback allows me to specify a done(...) and failed(...) method that is called either when the data was successfully submitted or not. In case it was, done(...) gets correctly called but in case the client already closed the connection then I assume failed(...) should be called but it gets never called.