Update Topic Subscriptions Middleware

The BabDev\WebSocket\Server\WAMP\Middleware\UpdateTopicSubscriptions class is a server middleware which updates the topic registry as connections are opened and closed.

Topic Registration

A topic is added to the topic registry when the first connection subscribes to it, and is removed from the registry once its last subscriber unsubscribes or disconnects.

If the decorated middleware throws while processing a "SUBSCRIBE" message (for example, when no route matches the topic or the message handler rejects the subscription), the subscription is rolled back before the exception is rethrown, so the connection is not left subscribed to the topic.

Position in Middleware Stack

It is recommended that this middleware is decorated by the BabDev\WebSocket\Server\WAMP\Middleware\ParseWAMPMessage middleware in your application (see the message flow section from the architecture documentation to see the recommended stack with all optional middleware), however it can be decorated by any WAMP server middleware.

It is also recommended that this middleware decorates the BabDev\WebSocket\Server\WAMP\Middleware\DispatchMessageToHandler middleware, but it can decorate any WAMP server middleware.