2 ways streaming using spring webflux - spring

Question

I'm wondering if it's possible to achieve 2 ways streaming using Spring Webflux?
Basically, I'm looking to make the client to send a flux of data that the server receives maps them to String then return the result, all fluently without having to collect data.
I did it using RSocket but I'm wondering if I can get the same result using http 2.0 (with Spring and Project-Reactor).
Tried doing like this:
1- Client:
public Mono<Void> stream() {
var input = Flux.range(1, 10).delayElements(Duration.ofMillis(500));
return stockWebClient.post()
.uri("/stream")
.body(BodyInserters.fromPublisher(input, Integer.class))
.accept(MediaType.TEXT_EVENT_STREAM)
.retrieve()
.bodyToFlux(String.class)
.log()
.then();
}
2- Server:
#PostMapping(value = "/stream", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
public Flux<String> stream(#RequestBody Integer i) {
return Flux.range(i, i+10).map(n -> String.valueOf(i)).log();
}
Or:
public Flux<String> stream(#RequestBody Flux<Integer> i) {
return i.map(n -> String.valueOf(i)).log();
}
Or:
#PostMapping(value = "/stream", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
public Flux<String> stream(#RequestBody List<Integer> i) {
return Flux.fromIterable(i).map(n -> String.valueOf(i)).log();
}
None worked correctly.

Answer 1

If you want use Server Sent Event you need to return a Flux<ServerSentEvent<String>>.
So your server merthod should be:
#PostMapping(value = "/stream", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
public Flux<ServerSentEvent<String>> stream(#RequestBody Integer i) {
return Flux.range(i, i + 10).map(n -> ServerSentEvent.builder(String.valueOf(n)).build());
}
But in this case the body is only an Integer and your client code becomes:
input.flatMap(i ->
stockWebClient
.post()
.uri("/stream")
.bodyValue(i)
.accept(MediaType.TEXT_EVENT_STREAM)
.retrieve()
.bodyToFlux(new ParameterizedTypeReference<ServerSentEvent<String>>() {})
.mapNotNull(ServerSentEvent::data)
.log())
.blockLast();
You can also do the same with functional endpoint.
If you want to be able to stream data from the client to the server and back you won't be able to use SSE but you can achieve this with websocket.
You will need a HandlerMapping and a WebSocketHandler
public class TestWebSocketHandler implements WebSocketHandler {
#Override
public Mono<Void> handle(WebSocketSession session) {
Flux<WebSocketMessage> output = session.receive()
.map(WebSocketMessage::getPayloadAsText)
.map(Integer::parseInt)
.concatMap(i -> Flux.range(i, i + 10).map(String::valueOf))
.map(session::textMessage);
return session.send(output);
}
}
The configuration with the handler :
#Bean
public TestWebSocketHandler myHandler() {
return new TestWebSocketHandler();
}
#Bean
public HandlerMapping handlerMapping(final TestWebSocketHandler myHandler) {
Map<String, WebSocketHandler> map = new HashMap<>();
map.put("/streamSocket", myHandler);
int order = -1; // before annotated controllers
return new SimpleUrlHandlerMapping(map, order);
}
On the client side:
var input2 = Flux.range(1, 10).delayElements(Duration.ofMillis(500));
WebSocketClient client = new ReactorNettyWebSocketClient();
client.execute(URI.create("http://localhost:8080/streamSocket"), session ->
session.send(input2.map(i -> session.textMessage("" + i))).then(session.receive().map(WebSocketMessage::getPayloadAsText).log().then())
).block();