spring webflux: purely functional way to attach websocket adapter to reactor-netty server

Question

I am not able to figure out a way to attach a WebSocketHandlerAdapter to a reactor netty server.

Requirements: I want to start a reactor netty server and attach http (REST) endpoints and websocket endpoints to the same server. I have gone through the documentation and some sample demo application mentioned in the documentation. They show how to attach a HttpHandlerAdapter to the the HttpServer using newHandler() function. But when it comes to websockets they switch back to using spring boot and annotation examples. I am not able to find how to attach websockets using functional endpoints.

Please point me in the right direction on how to implement this. 1. how do I attach the websocket adapter to the netty server? 2. Should I use HttpServer or TcpServer?

Note: 1. I am not using spring boot. 2. I am not using annotations. 3. Trying to achieve this only using functional webflux end points.

Sample code:

public HandlerMapping webSocketMapping() 
{
  Map<String, WebSocketHandler> map = new HashMap<>();
  map.put("/echo", new EchoTestingWebSocketHandler());
  SimpleUrlHandlerMapping mapping = new SimpleUrlHandlerMapping();
  mapping.setUrlMap(map);
  mapping.setOrder(-1);
  return mapping;
}
public WebSocketHandlerAdapter wsAdapter() 
{
  HandshakeWebSocketService wsService = new HandshakeWebSocketService(new ReactorNettyRequestUpgradeStrategy());
  return new WebSocketHandlerAdapter(wsService);
}

  protected void startServer(String host, int port) 
  {
    HttpServer server = HttpServer.create(host, port);
    server.newHandler(wsAdapter()).block();    //how do I attach the websocket adapter to the netty server
  }

Answer 1

I deal with it this way. and use native reactor-netty

routes.get(rootPath, (req, resp)->{
        // doFilter check the error
        return this.doFilter(request, response, new RequestAttribute())
                .flatMap(requestAttribute -> {
                    WebSocketServerHandle handleObject = injector.getInstance(GameWsHandle.class);
                    return response
                        .header("content-type", "text/plain")
                        .sendWebsocket((in, out) ->
                            this.websocketPublisher3(in, out, handleObject, requestAttribute)
                        );
                });
    })

private Publisher<Void> websocketPublisher3(WebsocketInbound in, WebsocketOutbound out, WebSocketServerHandle handleObject, RequestAttribute requestAttribute) {
        return out
                .withConnection(conn -> {
                    // on connect
                    handleObject.onConnect(conn.channel());
                    conn.channel().attr(AttributeKey.valueOf("request-attribute")).set(requestAttribute);
                    conn.onDispose().subscribe(null, null, () -> {
                            conn.channel().close();
                            handleObject.disconnect(conn.channel());
                            // System.out.println("context.onClose() completed");
                        }
                    );
                    // get message
                    in.aggregateFrames()
                            .receiveFrames()
                            .map(frame -> {
                                if (frame instanceof TextWebSocketFrame) {
                                    handleObject.onTextMessage((TextWebSocketFrame) frame, conn.channel());
                                } else if (frame instanceof BinaryWebSocketFrame) {
                                    handleObject.onBinaryMessage((BinaryWebSocketFrame) frame, conn.channel());
                                } else if (frame instanceof PingWebSocketFrame) {
                                    handleObject.onPingMessage((PingWebSocketFrame) frame, conn.channel());
                                } else if (frame instanceof PongWebSocketFrame) {
                                    handleObject.onPongMessage((PongWebSocketFrame) frame, conn.channel());
                                } else if (frame instanceof CloseWebSocketFrame) {
                                    conn.channel().close();
                                    handleObject.disconnect(conn.channel());
                                }
                                return "";
                            })
                            .blockLast();
                });
    }

Answer 2

Unfortunately, there is no easy way to do that without running up whole SpringBootApplication. Otherwise, you will be required to write whole Spring WebFlux handlers hierarchy by your self. Consider to compose your functional routing with SpringBootApplication:

    @SpringBootApplication
    public class WebSocketApplication {

        public static void main(String[] args) {
            SpringApplication.run(WebSocketApplication.class, args);
        }


        @Bean
        public RouterFunction<ServerResponse> routing() {
            return route(
                    POST("/api/orders"),
                    r -> ok().build()
            );
        }

        @Bean
        public HandlerMapping wsHandlerMapping() {
            HashMap<String, WebSocketHandler> map = new HashMap<>();

            map.put("/ws", new WebSocketHandler() {
                @Override
                public Mono<Void> handle(WebSocketSession session) {
                    return session.send(
                            session.receive()
                                  .map(WebSocketMessage::getPayloadAsText)
                                  .map(tMessage -> "Response From Server: " + tMessage)
                                  .map(session::textMessage)
                    );
                }
            });

            SimpleUrlHandlerMapping mapping = new SimpleUrlHandlerMapping();
            mapping.setUrlMap(map);
            mapping.setOrder(-1);
            return mapping;
        }

        @Bean
        HandlerAdapter wsHandlerAdapter() {
            return new WebSocketHandlerAdapter();
        }
    }

Incase if SpringBoot infra is not the case

try to consider direct interaction with ReactorNetty instead. Reactor Netty Provides pritty good abstraction around native Netty and you may interacti with it in the same functional maner:

ReactorHttpHandlerAdapter handler =
                    new ReactorHttpHandlerAdapter(yourHttpHandlers);

            HttpServer.create()
                      .startRouterAndAwait(routes -> {
                                  routes.ws("/pathToWs", (in, out) -> out.send(in.receive()))
                                        .file("/static/**", ...)
                                        .get("**", handler)
                                        .post("**", handler)
                                        .put("**", handler)
                                        .delete("**", handler);
                              }
                      );