Why is a client.subscribe callback being called twice?

[rriesebos]

When toying around with a remote master, I noticed that the callback passed to the subscribe method is called twice on the client that made a move (suggesting that there were two state changes), while it is only called once on the other clients.

At first I thought this was because the client runs the game in parallel, and the optimistic update causes a local state change - resulting in an additional invocation of the callback. But adding client: false to the moves in the game definition does not seem to resolve the issue, suggesting that either the move is not prevented on the client or something else causes the second callback invocation.

It would be greatly appreciated if someone could shine some light on this issue.

[delucis]

Your intuition is correct. Even with client: false the client itself still runs some logic, at least as far as to discover that move is disabled on the client. Then — even if the state hasn’t changed — it calls the subscriber callbacks. So, as you suspected, the client making the move has its callbacks called twice: once from the local “optimistic” update (even if it didn’t actually produce a state change), and then again when the remote update arrives.

[rriesebos]

Thanks for clearing that up! While it does not really seem intuitive to me, it's good to know that that's the intended behaviour.