How to support WebSocket transport with Spring Boot RSocket server?

Question

TLDR: What is required to configure a Spring Boot application that exposes an RSocket interface that supports the WebSocket transport?

---

I'm learning about RSocket and Spring Boot at the same time, so please bear with me.

In my struggles, I have been able to build a very simple and contrived implementation of a Spring Boot application that consumes an API provided/exposed by a second Spring Boot application using RSocket as the protocol, however, I am only able to achieve this when using the TcpClientTransport.

From my perspective, the WebsocketTransport is much more likely to be used and more useful for client->server architectures, however, I haven't found any working examples or documentation on how to properly configure a Spring Boot application that accepts RSocket messages using WebSocket as the transport.

The odd part is that in my tests it appears that my consumer (client) does establish a WebSocket connection to the server/producer, however, the 'handshake' appears to hang and the connection is never fully established. I've tested with both the JavaScript libraries (rsocket-websocket-client, rsocket-rpc-core, etc), and the Java libraries (io.rsocket.transport.netty.client.WebsocketClientTransport) and the server appears to exhibit the same behavior regardless.

To reiterate, using the TCPTransport I am able to connect to the server and invoke requests just fine, however when using the WebsocketTransport the connection is never established.

What is required of a Spring Boot application that aims to support RSocket via the WebsocketClientTransport, past consuming spring-boot-starter-rsocket as a dependency?.

Server

---

pom.xml

...

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.2.0.M5</version>
    <relativePath/> <!-- lookup parent from repository -->
</parent>

...

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-actuator</artifactId>
    </dependency>

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-rsocket</artifactId>
    </dependency>

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-webflux</artifactId>
    </dependency>

    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
    </dependency>
</dependencies>

...

application.properties

spring.rsocket.server.port=8081
management.endpoints.enabled-by-default=true
management.endpoints.web.exposure.include=*

SpringBootRSocketServerApplication.java

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringBootRSocketServerApplication {

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

UserRSocketController

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.messaging.handler.annotation.MessageMapping;
import org.springframework.stereotype.Controller;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import java.time.Duration;
import java.util.List;
import java.util.Random;
import java.util.stream.Stream;

@Slf4j
@Controller
public class UserRSocketController {

    @Autowired
    private UserRepository userRepository;

    @MessageMapping("usersList")
    public Mono<List<User>> usersList() {
        log.info("Handling usersList request.");
        return Mono.just(this.userRepository.getUsers());
    }

    @MessageMapping("usersStream")
    Flux<User> usersStream(UserStreamRequest request) {
        log.info("Handling request for usersStream.");
        List<User> users = userRepository.getUsers();
        Stream<User> userStream = Stream.generate(() -> {
            Random rand = new Random();
            return users.get(rand.nextInt(users.size()));
        });
        return Flux.fromStream(userStream).delayElements(Duration.ofSeconds(1));
    }

    @MessageMapping("userById")
    public Mono<User> userById(GetUserByIdRequest request) {
        log.info("Handling request for userById id: {}.", request.getId());
        return Mono.just(this.userRepository.getUserById(request.getId()));
    };
}

Startup Logging

 :: Spring Boot ::             (v2.2.0.M5)

2019-09-08 21:40:02,986 INFO  [main] org.springframework.boot.StartupInfoLogger: Starting SpringBootRSocketServerApplication on REDACTED with PID 22540 (REDACTED)
2019-09-08 21:40:02,988 INFO  [main] org.springframework.boot.SpringApplication: No active profile set, falling back to default profiles: default
2019-09-08 21:40:04,103 INFO  [main] org.springframework.boot.actuate.endpoint.web.EndpointLinksResolver: Exposing 14 endpoint(s) beneath base path '/actuator'
2019-09-08 21:40:04,475 INFO  [main] org.springframework.boot.rsocket.netty.NettyRSocketServer: Netty RSocket started on port(s): 8081
2019-09-08 21:40:04,494 INFO  [main] org.springframework.boot.web.embedded.netty.NettyWebServer: Netty started on port(s): 8080
2019-09-08 21:40:04,498 INFO  [main] org.springframework.boot.StartupInfoLogger: Started SpringBootRSocketServerApplication in 1.807 seconds (JVM running for 2.883)

Consumer/Client

---

ClientConfiguration.java

import io.rsocket.RSocket;
import io.rsocket.RSocketFactory;
import io.rsocket.frame.decoder.PayloadDecoder;
import io.rsocket.transport.ClientTransport;
//import io.rsocket.transport.netty.client.TcpClientTransport;
import io.rsocket.transport.netty.client.WebsocketClientTransport;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.messaging.rsocket.MetadataExtractor;
import org.springframework.messaging.rsocket.RSocketRequester;
import org.springframework.messaging.rsocket.RSocketStrategies;
import org.springframework.util.MimeTypeUtils;

@Configuration
public class ClientConfiguration {

    @Bean
    public RSocket rSocket() {
        // ClientTransport transport = TcpClientTransport.create(8081);
        // ^--- TCPTransport works fine

        ClientTransport transport = WebsocketClientTransport.create(8081);
        // ^--- Connection hangs and application startup stalls

        return RSocketFactory
            .connect()
            .mimeType(MetadataExtractor.ROUTING.toString(), MimeTypeUtils.APPLICATION_JSON_VALUE)
            .frameDecoder(PayloadDecoder.ZERO_COPY)
            .transport(transport)
            .start()
            .block();
    }

    @Bean
    RSocketRequester rSocketRequester(RSocketStrategies rSocketStrategies) {
        return RSocketRequester.wrap(rSocket(), MimeTypeUtils.APPLICATION_JSON, MimeTypeUtils.APPLICATION_JSON, rSocketStrategies);
    }
}

Startup Logging

 :: Spring Boot ::             (v2.2.0.M5)

2019-09-08 21:40:52,331 INFO  [main] org.springframework.boot.StartupInfoLogger: Starting SpringBootRsocketConsumerApplication on REDACTED with PID 18904 (REDACTED)
2019-09-08 21:40:52,334 INFO  [main] org.springframework.boot.SpringApplication: No active profile set, falling back to default profiles: default

Answer 1

You only need two things to have an RSocket application exposing endpoints using the websocket transport:

First, you need both webflux and rsocket dependencies as you'll probably need to serve web pages and static resources as well:

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-webflux</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-rsocket</artifactId>
    </dependency>

Then you need to configure the RSocket server accordingly in your application.properties file:

#server.port=8080 this is already the default
spring.rsocket.server.transport=websocket
spring.rsocket.server.mapping-path=/rsocket

You'll find more about that in the Spring Boot reference documentation about RSocket.

The websocket client can now connect to ws://localhost:8080/rsocket.

Note that as of the current 2.2.0 SNAPSHOTs, the RSocket protocol has evolved and the rsocket-js library is currently catching up, especially in the metadata support. You'll find a working sample here as well.

On the Java client side of things, Spring Boot provides you with a RSocketRequester.Builder that's already configured and customized to your needs with codecs and interceptors:

@Component
public class MyService {

    private final RSocketRequester rsocketRequester;

    public MyService(RSocketRequester.Builder builder) {
        this.rsocketRequester = builder
                .connectWebSocket(URI.create("ws://localhost:8080/rsocket"))
                .block();
    }
}

Answer 2

Based on this blog post the correct port to connect to is the port that is configured via server.port=8080.

Server Config

server.port=8080
spring.rsocket.server.port=8081
spring.rsocket.server.mapping-path=/ws
spring.rsocket.server.transport=websocket

Java Consumer Client Configuration

import io.rsocket.RSocket;
import io.rsocket.RSocketFactory;
import io.rsocket.frame.decoder.PayloadDecoder;
import io.rsocket.transport.ClientTransport;
import io.rsocket.transport.netty.client.TcpClientTransport;
import io.rsocket.transport.netty.client.WebsocketClientTransport;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.messaging.rsocket.MetadataExtractor;
import org.springframework.messaging.rsocket.RSocketRequester;
import org.springframework.messaging.rsocket.RSocketStrategies;
import org.springframework.util.MimeTypeUtils;

import java.net.URI;
import java.time.Duration;

@Configuration
public class ClientConfiguration {

    @Bean
    public RSocket rSocket() {
        URI websocketUri = URI.create("ws://127.0.0.1:8080/ws");
        WebsocketClientTransport ws = WebsocketClientTransport.create(websocketUri);
        return RSocketFactory
            .connect()
            .mimeType(
                MetadataExtractor.ROUTING.toString(),
                MimeTypeUtils.APPLICATION_JSON_VALUE)
            .frameDecoder(PayloadDecoder.ZERO_COPY)
            .transport(ws)
            .start()
            .block();
    }

    @Bean
    RSocketRequester rSocketRequester(RSocketStrategies rSocketStrategies) {
        return RSocketRequester.wrap(
            rSocket(),
            MimeTypeUtils.APPLICATION_JSON,
            MetadataExtractor.ROUTING,
            rSocketStrategies);
    }
}

JavaScript Client Configuration

import { RSocketClient, JsonSerializers } from 'rsocket-core';
import RSocketWebSocketClient from 'rsocket-websocket-client';

const transport = new RSocketWebSocketClient({
    url: 'ws://127.0.0.1:8080/ws'
});

const client = new RSocketClient({
    // send/receive JSON objects instead of strings/buffers
    serializers: JsonSerializers,
    setup: {
        // ms btw sending keepalive to server
        keepAlive: 60000,

        // ms timeout if no keepalive response
        lifetime: 180000,

        // format of `data`
        dataMimeType: 'application/json',

        // format of `metadata`
        metadataMimeType: 'application/json',
    },
    transport,
});

client.connect().then((rsocket) => {
    // work with rsocket
});