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The simple broker was enabled without heartbeats, so the CONNECTED frame advertised heart-beat:0,0 and an idle connection carried no traffic. A reverse proxy in front of the API closes such a connection once its read timeout passes (60 seconds by default in nginx). The simple broker keeps nothing for a subscriber that is not connected, so messages published before the client reconnects are lost, e.g. student status updates in the Classroom Monitor. The broker now sends a heartbeat every 20 seconds and requires none from clients, since browsers throttle timers in background tabs and a required client heartbeat would get those connections closed. Heartbeats are scheduled on Spring's own messageBrokerTaskScheduler.
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The simple broker is enabled without heartbeats, so the CONNECTED frame advertises
heart-beat:0,0and an idle connection carries no traffic at all. A reverse proxy in front of the API closes such a connection once its read timeout passes; with nginx's defaultproxy_read_timeoutan idle Classroom Monitor socket was closed with code 1006 after 60 seconds. The simple broker keeps nothing for a subscriber that is not connected, so student status updates published before the client reconnects are lost.The broker now sends a heartbeat every 20 seconds and requires none from clients. Requiring client heartbeats was rejected because browsers throttle timers in background tabs to about once a minute, which would get the socket of a teacher who switched tabs closed. The heartbeat task runs on Spring's own
messageBrokerTaskScheduler, injected lazily as the Spring reference documentation describes.Testing:
WebSocketConfigTeststarts the WebSocket messaging configuration and asserts the broker's heartbeat value and task scheduler. Both tests fail on develop and pass with this change. On a deployment behind nginx the CONNECTED frame readheart-beat:20000,0, heartbeats arrived every 20 seconds, and an idle socket stayed open for 173 seconds.