Akka-http first websocket client only receives the data once from a kafka topic - scala

Question

I am using akka-http websocket to push messages from a kafka topic to websocket clients.
For this purpose, i created a plain kafka consumer (using akka-streams-kafka connector) with offset set to "earliest" so that every new websocket client connecting gets all the data from the beginning.
The problem is that the first connected websocket client gets all the data and other ws clients (connecting after the first client has got all the data) do not get any. The kafka topic has 1million records.
I am using the BroadcastHub from Akka-streams.
Appreciate any suggestions.
lazy private val kafkaPlainSource: Source[String, NotUsed] = {
val consumerSettings = ConsumerSettings(system, new StringDeserializer, new StringDeserializer)
.withBootstrapServers(KAFKA_BROKERS)
.withGroupId(UUID.randomUUID().toString)
.withProperty(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest")
val kafkaSource = Consumer.plainSource(consumerSettings, Subscriptions.topics(KAFKA_TOPIC))
.mapAsync(PARALLELISM) { cr =>
Future {
cr.value
}
}
kafkaSource.toMat(BroadcastHub.sink)(Keep.right).run
}
def logicFlow: Flow[String, String, NotUsed] =
Flow.fromSinkAndSourceCoupled(Sink.ignore, kafkaSource)
val websocketFlow: Flow[Message, Message, Any] = {
Flow[Message]
.map {
case TextMessage.Strict(msg) => msg
case _ => println("ignore streamed message")
}
.via(logicFlow)
.map { msg: String => TextMessage.Strict(msg) }
}
lazy private val streamRoute =
path("stream") {
handleWebSocketMessages {
websocketFlow
.watchTermination() { (_, done) =>
done.onComplete {
case Success(_) =>
log.info("Stream route completed successfully")
case Failure(ex) =>
log.error(s"Stream route completed with failure : $ex")
}
}
}
}
def startServer(): Unit = {
bindingFuture = Http().bindAndHandle(wsRoutes, HOST, PORT)
log.info(s"Server online at http://localhost:9000/")
}
def stopServer(): Unit = {
bindingFuture
.flatMap(_.unbind())
.onComplete{
_ => system.terminate()
log.info("terminated")
}
}