2022/5/30

RSocket + WebSocket

Reactive Programming

這是一種以資料流為主的程式開發模型，目前比較流行的 Vue, React 也是類似這個概念，畫面上顯示的運算結果或呈現的資料，會隨時跟著資料異動而自動更新。

傳統的程式設計是用 Interative Programming 方法，例如

b:=2;
c:=3;
a:=b+c
// a 為 5
b:=3;
// 當 b 的值異動後，必須重新運算一次 b+c，才能更新 a

Excel 就是使用 Reactive Programming，當在某個儲存格 C1 填寫為 C1=A1+B1，C1 的值，就會隨著 A1 與 B1 異動而自動更新。

RSocket

rsocket 是類似 gRPC 的訊息傳遞協定，支援 TCP, WebSocket, Aeron(UDP)，主要有四種互動的方式

Interaction Model Behavior
fire-and-forget 不需要 response
request-and-response one-to-one 傳統通訊，一個 request，一個response，然後不斷重複
request-response-stream one-to-many 發一個訊息，可連續收到多個 response
channel many-to-many bi-directional stream

Sample

ref: RSocket + WebSocket + Spring Boot = Real Time Application

這個網頁用 spring boot 做了stream 及 channel 兩個 sample server

client 部分是用 rsocket-js，透過 nodejs 啟動

Server

用 Java Sprint Boot 撰寫

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.5</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.vinsguru</groupId>
    <artifactId>rsocket-websocket</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>rsocket-websocket</name>
    <description>Demo project for Spring Boot, RSocket WebSocket</description>

    <properties>
        <java.version>11</java.version>
    </properties>

    <dependencies>

        <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>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>io.projectreactor</groupId>
            <artifactId>reactor-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

resources/application.properties

spring.rsocket.server.port=6565
spring.rsocket.server.mapping-path=/rsocket
spring.rsocket.server.transport=websocket

RsocketWebsocketApplication

package com.vinsguru.rsocketwebsocket;

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

@SpringBootApplication
public class RsocketWebsocketApplication {

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

}

RSocketController

package com.vinsguru.rsocketwebsocket.controller;

import org.springframework.messaging.handler.annotation.MessageMapping;
import org.springframework.stereotype.Controller;
import reactor.core.publisher.Flux;

import java.time.Duration;

@Controller
public class RSocketController {

    @MessageMapping("number.stream")
    public Flux<Integer> responseStream(Integer number) {
        return Flux.range(1, number)
                .delayElements(Duration.ofSeconds(1));
    }

    @MessageMapping("number.channel")
    public Flux<Long> biDirectionalStream(Flux<Long> numberFlux) {
        return numberFlux
                .map(n -> n * n)
                .onErrorReturn(-1L);
    }

}
  1. number.stream 就是 request-response-stream，client 會發送一個 Integer 給 Server，Server 會定時回傳 1, 2 ..... 直到該 Integer 停止
  2. number.channel 是 many-to-many 的傳輸，可連續發送多個 Long 給 Server，Server 會回傳該數的平方

Client

最主要的是 index.js

有兩個部分，分別是 number.stream 與 number.channel

import { RSocketClient, JsonSerializer, IdentitySerializer } from 'rsocket-core';
import RSocketWebSocketClient from 'rsocket-websocket-client';
import {FlowableProcessor} from 'rsocket-flowable';

// backend ws endpoint
const wsURL = 'ws://localhost:6565/rsocket';

// rsocket client
const client = new RSocketClient({
    serializers: {
        data: JsonSerializer,
        metadata: IdentitySerializer
    },
    setup: {
        keepAlive: 60000,
        lifetime: 180000,
        dataMimeType: 'application/json',
        metadataMimeType: 'message/x.rsocket.routing.v0',
    },
    transport: new RSocketWebSocketClient({
        url: wsURL
    })
});
// error handler
const errorHanlder = (e) => console.log(e);

// response handler
const responseHanlder = (payload) => {
    const li = document.createElement('li');
    li.innerText = payload.data;
    li.classList.add('list-group-item', 'small')
    document.getElementById('result').appendChild(li);
}

/////////
//  number.stream
////////
/*

const numberRequester = (socket, value) => {
    socket.requestStream({
        data: value,
        metadata: String.fromCharCode('number.stream'.length) + 'number.stream'
    }).subscribe({
        onError: errorHanlder,
        onNext: responseHanlder,
        onSubscribe: subscription => {
            subscription.request(100); // set it to some max value
        }
    })
}

client.connect().then(sock => {
    document.getElementById('n').addEventListener('change', ({srcElement}) => {
        numberRequester(sock, parseInt(srcElement.value));
    })
}, errorHanlder);
*/

/////////
//  number.channel
////////
// reactive stream processor
const processor = new FlowableProcessor(sub => {});

const numberRequester = (socket, processor) => {
    socket.requestChannel(processor.map(i => {
        return {
            data: i,
            metadata: String.fromCharCode('number.channel'.length) + 'number.channel'
        }
    })).subscribe({
        onError: errorHanlder,
        onNext: responseHanlder,
        onSubscribe: subscription => {
            subscription.request(100); // set it to some max value
        }
    })
}

client.connect().then(sock => {
    numberRequester(sock, processor);
    document.getElementById('n').addEventListener('keyup', ({srcElement}) => {
        if(srcElement.value.length > 0){
            processor.onNext(parseInt(srcElement.value))
        }
    })
}, errorHanlder);

安裝 node_modules

npm install

設定

npm run build

啟動 client

npm run serve

問題

一直找不到如何單獨使用 rsocket-js 的方法，就是不透過 nodejs 提供 網頁 service 的方法。現在很多 js library 只有用在 nodejs 的 sample，但傳統的網頁，應該只要透過 webserver 直接載入 javascript file，就可以使用才對。如果可以這樣用，就可以將 html, js 合併到 sping boot 裡面，也不需要兩個 service port。

References

RSocket 革命，為了 Reactive Programming 而生的高效率通訊協定

RSocket With Spring Boot

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