Channel vs. Broker vs. Destination in Websocket

Question

What is the difference between channel vs. broker vs. destination in Spring websocket?

I recently started working with a websocket and from what I understood:

registry.addEndpoint("/wsocket/") adds a websocket endpoint which is solely used when clients wants to connect to the websocket service:

this.client.configure({
      brokerURL: `ws://localhost:9022/wsocket`,
      onConnect: () => {
        this.client.subscribe('/quote/fb', message => {
          console.log(message);
        });
      }
    });
    this.client.activate();

config.enableSimpleBroker("/quote") enables a channel/broker, letting clients to subscribe to it and receive messages published/sent over it. Clients are able to subscribe to any /quote/* on the server.

config.setApplicationDestinationPrefixes("/app") sets the application prefix, which clients use to send message directly to the app and not through the broker.

Is my understanding correct?

Answer 1

I think your understanding is correct .

Broker

A message broker acts as an intermediary platform when it comes to processing communication between two applications. In the context of spring websocket :

When you use Spring’s STOMP support, the Spring WebSocket application acts as the STOMP broker to clients. Messages are routed to @Controller message-handling methods or to a simple in-memory broker that keeps track of subscriptions and broadcasts messages to subscribed users. You can also configure Spring to work with a dedicated STOMP broker (such as RabbitMQ, ActiveMQ, and others) for the actual broadcasting of messages. In that case, Spring maintains TCP connections to the broker, relays messages to it, and passes messages from it down to connected WebSocket clients.

Channel

It can be thought of as a logical segregation of messages in one or both directions. For example, there can be three channels. One for request(incoming to the server), second one for response(outgoing from the server) and third one for error (outgoing from the server).

Destination

It can be thought of another level of hierarchical nesting for a channel. I find this image helpful to understand it :

https://docs.spring.io/spring/docs/5.1.3.BUILD-SNAPSHOT/spring-framework-reference/images/message-flow-simple-broker.png [![enter image description here][1]][1]

Clients can use the SEND or SUBSCRIBE commands to send or subscribe for messages, along with a destination header that describes what the message is about and who should receive it. This enables a simple publish-subscribe mechanism that you can use to send messages through the broker to other connected clients or to send messages to the server to request that some work be performed.

I find Spring documentation on this topic to be very helpful : https://docs.spring.io/spring/docs/5.1.3.BUILD-SNAPSHOT/spring-framework-reference/web.html#websocket-stomp-handle-simple-broker .