MessageService.kt

interface MessageService {
    @Send(topic = "messages/send", qos = QoS.TWO)
    fun send(@Data message: Message)

    @Receive(topic = "messages/receive")
    fun receive(): Observable<Message>

    @Subscribe(topic = "messages/receive", qos = QoS.ONE)
    fun subscribe(): Observable<Message>

    @Unsubscribe(topics = ["messages/receive"])
    fun unsubscribe()
}