DataWatch can cause "Error in connection state listener" about kazoo

[bbangert]

What behavior is expected when watching a node that doesn't exist? Immediate error? Silently ignored until it does exist?

[nekto0n]

Not sure. We already have immediate error on first call. What are the choices?

1. Don't set session listener if first read failed.
2. Silently ignore.
3. Raise error every time (immediate and deferred)

I think current implementation is wrong anyway - it blocks session events until _get_data returns and docs say that users should avoid doing that.

Hm... How zookeeper behaves if watched node being removed? How does Curator handles this situation?

[bbangert]

Curator doesn't have any functionality that matches the DataWatch. If the node is deleted, or can't be found on a reconnect, those could just be ignored and if it exists again, and the children are different that before, it calls the function.

[nekto0n]

You mean DataWatch must keep both exists and get watches? If you expose exists method from DataWatch class (which should be a simple cached boolean flag) - that should work.

[nekto0n]

... but removing node causes it's content change, so user must be notified.

[bbangert]

Yep, makes sense. I think it'd be easiest if None was delivered in the event that its removed, since the values have to be string we can use None safely to indicate there is no longer a node.

[nekto0n]

Thanks!