The emitter's removeListener is called twice

[Hokid]

When a client closes WS connection it calls the close method of the SubscriptionContext twice.

Triggered by:

mercurius/lib/subscription.js

Lines 56 to 58 in 01a007d

	socket.on('close', () => {
	subscriptionConnection.close()
	})

And here:

mercurius/lib/subscription-connection.js

Lines 331 to 333 in 01a007d

	if (sc) {
	sc.close && sc.close()
	this.subscriptionContexts.delete(id)

It produces two removeListener calls:

mercurius/lib/subscriber.js

Lines 17 to 19 in 01a007d

	const close = () => {
	this.emitter.removeListener(topic, listener)
	}

If there are two connected clients, and one of them closes the connection, then it is possible that the topic message listeners will be removed for both clients if the emitter implementation does not include a flag to check whether the subscription for a given listener has been removed. For example, mqemitter-redis does not do this and sends an unsubscribe command, so the second client will stop receiving new messages from the topic.

[mcollina]

Thanks for reporting! Would you like to send a Pull Request to address this issue? Remember to add unit tests.

[Hokid]

@mcollina Yes, check please