How to use Spring Reactive WebSocket and transform it into the Flux stream? - spring-websocket

Question

There is some WebSocketClient example on Spring documentation:
WebSocketClient client = new ReactorNettyWebSocketClient();
client.execute("ws://localhost:8080/echo"), session -> {...}).blockMillis(5000);
Im not sure how to handle stream of incomming data?
Inside that block {...}.
I mean: how can I filter incoming data and cast it into Flux?
Here is what I want to get.
#GetMapping("/stream", produces = MediaType.APPLICATION_STREAM_JSON_VALUE)
public Flux<MyRecourse> getStreaming() {
// get some data from WebSocket (CoinCap service).
// Transform that data into MyRecourse object
// Return stream to a client
}

Answer 1

Just take a look into that WebSocketSession param of the WebSocketHandler.handle() lambda:
/**
* Get the flux of incoming messages.
*/
Flux<WebSocketMessage> receive();
See Spring WebFlux Workshop for more information.
UPDATE
Let's try this!
Mono<Void> sessionMono =
client.execute(new URI("ws://localhost:8080/echo"),
session ->
Mono.empty()
.subscriberContext(Context.of(WebSocketSession.class, session))
.then());
return sessionMono
.thenMany(
Mono.subscriberContext()
.flatMapMany(c -> c
.get(WebSocketSession.class)
.receive()))
.map(WebSocketMessage::getPayloadAsText);
UPDATE 2
Or another option but with blocked subscription:
EmitterProcessor<String> output = EmitterProcessor.create();
client.execute(new URI("ws://localhost:8080/echo"),
session ->
session.receive()
.map(WebSocketMessage::getPayloadAsText)
.subscribeWith(output)
.then())
.block(Duration.ofMillis(5000));
return output;
UPDATE 3
The working Spring Boot application on the matter: https://github.com/artembilan/webflux-websocket-demo
The main code is like:
EmitterProcessor<String> output = EmitterProcessor.create();
Mono<Void> sessionMono =
client.execute(new URI("ws://localhost:8080/echo"),
session -> session.receive()
.map(WebSocketMessage::getPayloadAsText)
.subscribeWith(output)
.then());
return output.doOnSubscribe(s -> sessionMono.subscribe());