with spring boot rsocket capture the cancel frame type - spring-boot

Question

I have a spring boot rsocket implementation where if a client cancels or closes their rsocket request then I want to cancel other subscription registrations on the server.
In the logs on the spring boot server I can see that a cancel message is sent or received:
WARN i.r.t.n.s.WebsocketServerTransport$1 [reactor-http-nio-3] received WebSocket Close Frame - connection is closing
INFO r.u.Loggers$Slf4JLogger [reactor-http-nio-3] cancel()
How do I capture and handle this cancel signal?
I tried cancel endpoints but these don't capture the signal:
#MessageMapping("cancel")
Flux<Object> onCancel() {
log.info("Captured cancel signal");
}
or
#ConnectMapping("cancel")
Flux<Object> onCancel2() {
log.info("Captured cancel2 signal");
}
This question on cancel subscriptions is possibly related, and this question on detecting websocket disconnection

Answer 1

To capture the cancel signal you can use subscribe to onClose() event.
In your controller
#Controller
class RSocketConnectionController {
#ConnectMapping("client-id")
fun onConnect(rSocketRequester: RSocketRequester, clientId: String) {
// rSocketRequester.rsocket().dispose() //to reject connection
rSocketRequester
.rsocket()
.onClose()
.subscribe(null, null, {
log.info("{} just disconnected", clientId)
//TODO here whatever you want
})
}
}
Your client needs to send the SETUP frame properly to invoke this #ConnectMapping. If you use rsocket-js you need to add a payload like this:
const client = new RSocketClient({
// send/receive JSON objects instead of strings/buffers
serializers: {
data: JsonSerializer,
metadata: IdentitySerializer
},
setup: {
//for connection mapping on server
payload: {
data: 'unique-client-id', //TODO you can receive this data on server side
metadata: String.fromCharCode("client-id".length) + "client-id"
},
// ms btw sending keepalive to server
keepAlive: 60000,
.....
}
});

Answer 2

It was not a well set out question. The answer is that
INFO r.u.Loggers$Slf4JLogger [reactor-http-nio-3] cancel()
is seen by a FluxSink that was setup from the original #MessageMapping endpoint.
For example:
#MessageMapping("hello")
Flux<Object> hello(#Payload String message) {
return myService.generateWorld(message);
}
In myService class
public Flux<Object> generateWorld(String hello) {
EmitterProcessor<Object> emitter = EmitterProcessor.create();
FluxSink<Object> sink = emitter.sink(FluxSink.OverflowStrategy.LATEST);
// doing stuff with sink here
sink.next(stuff());
// This part will handle a cancel from the client
sink.onCancel(() -> {log.info("********** SINK.onCancel ***********");});
return Flux.from(emitter));
}
The sink.onCancel() will handle a cancel of the flux to the hello endpoint, from the client.