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Topic: WebSocket

WebSpider
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posted on: 07/11/2020 12:57:01 AM

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WebSocket

WebSocket is a protocol to provide bidirectional communication channels over a single TCP connection. It is vital to build the highly interactive real-time web applications like games, chats and bots.

Dependencies:

spring-websocket -- from org.springframework for WebSocket

spring-messaging -- from org.springframework for messaging

jackson-core -- from com.fasterxml.jackson.core for JSON message

jackson-databind -- from com.fasterxml.jackson.core for JSON message

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WebSpider
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posted on: 07/11/2020 12:58:05 AM

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Configuration

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig extends AbstractWebSocketMessageBrokerConfigurer {
 
    @Override
    public void configureMessageBroker(MessageBrokerRegistry config) {
        config.enableSimpleBroker("/topic", "/queue");
        config.setApplicationDestinationPrefixes("/channel");
    }
 
    @Override
    public void registerStompEndpoints(StompEndpointRegistry registry) {
         registry.addEndpoint("/stomp").withSockJS(); 
    }
}

As the annoation @EnableWebSocketMessageBroker suggests, it will enable MESSAGE handling backed by a broker. Here:

".enableSimpleBroker" -- the simple built-in IN-MEMORY (Simple) message broker (Kafka can be a broker for production);

"/topic" -- the destination for subscribers -- a folder holding multiple sub-topics

"/channel" -- the destination for publishers -- a folder holding multiple sub-channels

"/stomp" -- the STOMP's endpoint for connection (STOMP: Simple Text-Orientated Messaging Protocol)

".withSockJS()" -- with SockJS as fallback if WebSocket is not supported by browser.

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WebSpider
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posted on: 07/11/2020 12:59:42 AM

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How it works -- how the broker wire the publish-subscribe mapping internally?

@Controller
public class WebSocketController {

	// publisher send message to --> "/channel/chat"
	//       --> broker relay it to --> "/topic/messages"
        //       --> broker push it to all subscribers
	@MessageMapping("/chat")
	@SendTo("/topic/messages")
	public OutputMessage send(Message message) throws Exception {
	    String time = new SimpleDateFormat("HH:mm").format(new Date());
	    return new OutputMessage(message.getFrom(), message.getText(), time);
	}
}

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WebSpider
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posted on: 07/11/2020 01:01:42 AM

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Example -- JS Client

Connect & Subscribe

function connect() {
    // 'websocket' -- naming context
    // 'api' -- servlet context
    // 'stomp' -- STOMP endpoint
    var socket = new SockJS('/websocket/api/stomp'); 
    stompClient = Stomp.over(socket);
    stompClient.connect({}, function(frame) {
        stompClient.subscribe('/topic/messages', 
            function(messageOutput) { // JS Object <-- Java OutputMessage
                showMessageOutput(JSON.parse(messageOutput.body)); // JS String --> JS Object
            }
        );
   });
}

Publish

function sendMessage() {
    stompClient.send('/channel/chat', 
        {}, // header
	JSON.stringify({...}) // JS Object --> JS String
    );
}

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posted on: 07/12/2020 05:39:39 AM

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WebSocket Security

Once your messaging system is on, you definitely have to regulate as to:

who can connect to STOMP ?

who can send message to /channel as publisher?

who can receive message from /topic as subscriber ?

This is the place where WebSocket Security come into play.

Prerequisite:

	<dependency>
    		<groupId>org.springframework.security</groupId>
    		<artifactId>spring-security-messaging</artifactId>
	</dependency>

Config:

@Configuration
public class WebSocketSecurityConfig extends AbstractSecurityWebSocketMessageBrokerConfigurer {

	// Messages with destination: MESSAGE, SUBSCRIBE
	// Messages w/o  destination: CONNECT, DISCONNECT, UNSUBSCRIBE
	// nullDestMatcher() -- CONNECT, DISCONNECT, UNSUBSCRIBE
	
    @Override
    protected void configureInbound(MessageSecurityMetadataSourceRegistry messages) {
        messages
        
	    // ######## connect #################
            .nullDestMatcher()
	        .authenticated()  // CONNECT, DISCONNECT, UNSUBSCRIBE needs authenticated
        
	    // ######## send #################
            .simpDestMatchers("/channel/**")
	        .hasRole("USER")  // any sessage SENT to "/channel/" will require ROLE_USER
        
	    // ######## receive #################
	    .simpSubscribeDestMatchers("/topic/**", "/queue/*")
                .hasRole("ADMIN") // any message SUBCRIBED for "/topic/ or /queue/" will require ROLE_ADMIN
	    .anyMessage().denyAll();
    }
    
    @Override
    protected boolean sameOriginDisabled() {
        return true;
    }    
}

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