Spring+WebSocket+STOMP. Message to specific session (NOT user)

Question

I am trying to set up basic message broker on Spring framework, using a recipe I found here

Author claims it has worked well, but I am unable to receive messages on client, though no visible errors were found.

Goal:

What I am trying to do is basically the same - a client connects to server and requests some async operation. After operation completes the client should receive an event. Important note: client is not authenticated by Spring, but an event from async back-end part of the message broker contains his login, so I assumed it would be enough to store concurrent map of Login-SessionId pairs for sending messages directly to particular session.

Client code:

//app.js

var stompClient = null;
var subscription = '/user/queue/response';

//invoked after I hit "connect" button
function connect() {
//reading from input text form
var agentId = $("#agentId").val();

var socket = new SockJS('localhost:5555/cti');
stompClient = Stomp.over(socket);
stompClient.connect({'Login':agentId}, function (frame) {
    setConnected(true);
    console.log('Connected to subscription');
    stompClient.subscribe(subscription, function (response) {
        console.log(response);
    });
});

}

//invoked after I hit "send" button
function send() {

var cmd_str = $("#cmd").val();
var cmd = {
    'command':cmd_str
};
console.log("sending message...");
stompClient.send("/app/request", {}, JSON.stringify(cmd));
console.log("message sent");
}

Here is my configuration.

//message broker configuration

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig extends AbstractWebSocketMessageBrokerConfigurer{


@Override
public void configureMessageBroker(MessageBrokerRegistry config) {
    /** queue prefix for SUBSCRIPTION (FROM server to CLIENT)  */
    config.enableSimpleBroker("/topic");
    /** queue prefix for SENDING messages (FROM client TO server) */
    config.setApplicationDestinationPrefixes("/app");
}


@Override
public void registerStompEndpoints(StompEndpointRegistry registry) {

    registry
            .addEndpoint("/cti")
            .setAllowedOrigins("*")
            .withSockJS();
}

}

Now, after basic config I should implement an application event handler to provide session-related information on client connect.

//application listener

@Service
public class STOMPConnectEventListener implements ApplicationListener<SessionConnectEvent> {

@Autowired
//this is basically a concurrent map for storing pairs "sessionId - login"
WebAgentSessionRegistry webAgentSessionRegistry;

@Override
public void onApplicationEvent(SessionConnectEvent event) {
    StompHeaderAccessor sha = StompHeaderAccessor.wrap(event.getMessage());

    String agentId = sha.getNativeHeader("Login").get(0);
    String sessionId = sha.getSessionId();

    /** add new session to registry */
    webAgentSessionRegistry.addSession(agentId,sessionId);

    //debug: show connected to stdout
    webAgentSessionRegistry.show();

}
}

All good so far. After I run my spring webapp in IDE and connected my "clients" from two browser tabs I got this in IDE console:

session_id / agent_id
-----------------------------
|kecpp1vt|user1|
|10g5e10n|user2|
-----------------------------

Okay, now let's try to implement message mechanics.

//STOMPController


@Controller
public class STOMPController {

@Autowired
//our registry we have already set up earlier
WebAgentSessionRegistry webAgentSessionRegistry;
@Autowired
//a helper service which I will post below
MessageSender sender;

@MessageMapping("/request")
public void handleRequestMessage() throws InterruptedException {

    Map<String,String> params = new HashMap(1);
    params.put("test","test");
    //a custom object for event, not really relevant
    EventMessage msg = new EventMessage("TEST",params);

    //send to user2 (just for the sake of it)
    String s_id = webAgentSessionRegistry.getSessionId("user2");
    System.out.println("Sending message to user2. Target session: "+s_id);
    sender.sendEventToClient(msg,s_id);
    System.out.println("Message sent");

}
}

A service to send messages from any part of the application:

//MessageSender

@Service
public class MessageSender implements IMessageSender{

@Autowired
WebAgentSessionRegistry webAgentSessionRegistry;
@Autowired
SimpMessageSendingOperations messageTemplate;

private String qName = "/queue/response";

private MessageHeaders createHeaders(String sessionId) {
    SimpMessageHeaderAccessor headerAccessor = SimpMessageHeaderAccessor.create(SimpMessageType.MESSAGE);
    headerAccessor.setSessionId(sessionId);
    headerAccessor.setLeaveMutable(true);
    return headerAccessor.getMessageHeaders();
}

@Override
public void sendEventToClient(EventMessage event,String sessionId) {
    messageTemplate.convertAndSendToUser(sessionId,qName,event,createHeaders(sessionId));
}
}

Now, let's try to test it. I run my IDE, opened Chrome and created 2 tabs form which I connected to server. User1 and User2. Result console:

 session_id / agent_id
    -----------------------------
    |kecpp1vt|user1|
    |10g5e10n|user2|
    -----------------------------
Sending message to user2. Target session: 10g5e10n
Message sent

But, as I mentioned in the beginning - user2 got absolutely nothing, though he is connected and subscribed to "/user/queue/response". No errors either.

A question is, where exactly I am missing the point? I have read many articles on the subject, but to no avail. SPR-11309 says it's possible and should work. Maybe, id-s aren't actual session id-s? And well maybe someone knows how to monitor if the message actually has been sent, not dropped by internal Spring mechanics?

SOLUTION UPDATE:

A misconfigured bit:

//WebSocketConfig.java:
....
 @Override
public void configureMessageBroker(MessageBrokerRegistry config) {
    /** queue prefix for SUBSCRIPTION (FROM server to CLIENT)  */
    // + parameter "/queue"
    config.enableSimpleBroker("/topic","/queue");
    /** queue prefix for SENDING messages (FROM client TO server) */
    config.setApplicationDestinationPrefixes("/app");
}
....

I've spent a day debugging internal spring mechanics to find out where exactly it goes wrong:

//AbstractBrokerMessageHandler.java: 
....
protected boolean checkDestinationPrefix(String destination) {
    if ((destination == null) || CollectionUtils.isEmpty(this.destinationPrefixes)) {
        return true;
    }
    for (String prefix : this.destinationPrefixes) {
        if (destination.startsWith(prefix)) {
//guess what? this.destinationPrefixes contains only "/topic". Surprise, surprise
            return true;
        }
    }
    return false;
}
....

Although I have to admit I still think the documentation mentioned that user personal queues aren't to be configured explicitly cause they "already there". Maybe I just got it wrong.

Answer 1

Overall it looks good, but could you change from

config.enableSimpleBroker("/topic");

to

config.enableSimpleBroker("/queue");

... and see if this works? Hope this help.