Browser creates an SSE connection Connection gets added to an SseBroadcaster. sseBroadcaster.broadcast() sends data. Browser closes SSE connection. Call sseBroadcaster.broadcast again which should result in an IOException being thrown thus causing that specific's SseEventOutputImpl to be closed and thus toClose() to be called from sseBroadcaster which doesnt end up being called. Ive repeated calling sseBroadcaster.broadcast() 6 times and have been able to determine that SseEventOutputImpl never detects an IOException from sending to a closed connection. The following code generates the log statement "Saw this null" for all broadcasts, including those to closed eventSink's.          sseBroadcast.broadcast(event)                 .whenComplete((v, e) -> {                     LOG.infov( "Saw this \{0}" , v);                 });