SSE connection keeps failing every 5 minutes - spring

Question

I'm exposing a simple SSE endpoint using the SseEmitter Spring API, persisting all the emitters in a ConcurrentHashMap. The timeout for each emitter is set to 24 hours. Every 10 seconds I'm sending a message to all the clients. Clients are subscribed with native EventSource implementation, listening for events of particular name.
Unfortunately, I've noticed that every 5 minutes the connection is lost and reestablished again - even though timeout of emitter was explicitly set to 24 hours. Client's part does log it as an error, however on server side there's nothing. The issue occurs on both Tomcat and Jetty. I'd like to keep the session open without any interruptions, so resetting the connection every 5 minutes is unacceptable. Any ideas why this could be happening?
#RestController
#RequestMapping("api/v1/sse")
class SseController {
private val emitters = ConcurrentHashMap<String, SseEmitter>()
#GetMapping
fun initConnection(#RequestParam token: String): SseEmitter {
logger.info { "Init connection from $token" }
val emitter = SseEmitter(24 * 60 * 60 * 1000)
emitter.onCompletion {
logger.info { "Completion" }
emitters.remove(token)
}
emitter.onTimeout { logger.info { "Timeout " } }
emitter.onError { logger.error(it) { "Error" } }
emitters[token] = emitter
return emitter
}
#Scheduled(fixedRate = 10000)
fun send() {
emitters.forEach { (k, v) ->
logger.info { "Sending message to $k" }
v.send(
SseEmitter.event()
.id(UUID.randomUUID().toString())
.name("randomEvent")
.data("some data")
)
}
}
}
const eventSource = new EventSource(url);
eventSource.addEventListener('randomEvent', (e) =>
console.log(e.data)
);
eventSource.onerror = (e) => console.log(e);

Answer 1

Alright, seems it was an issue with Stackblitz's service worker. I've just implemented the same client-side solution in Chrome's plain console and the disconnecting is no longer happening.