[sftwnd]

Since #1262, PersistentWatcher casts the client to CuratorFrameworkBase to reach the underlying client, because NamespaceFacade does not support getCuratorListenable(). As a result, PersistentWatcher and CuratorCache fail with ClassCastException for any other CuratorFramework implementation, for example a decorator of the public interface. This worked in 5.8.0.

This change uses the underlying client only for CuratorFrameworkBase instances, so namespaced facades keep working (#1259). For any other implementation it falls back to the public getCuratorListenable(). Both start() and close() are covered; the cast in close() was added by #1293.

Two tests are added to TestPersistentWatcher. They use a java.lang.reflect.Proxy-based delegating client and cover:

• watch events;
• the Closed notification;
• de-registration of listeners on close.

Both tests fail on master with ClassCastException and pass with the fix. TestPersistentWatcher, TestCuratorCache* and spotless:check pass locally on JDK 21.

Fixes #1314.

[kezhuw]

LGTM.

Generally speaking, all implementations should come from curator as CuratorFramework itself is constructed from cutator and some of its api (say, usingNamespace) are depended by internal codes. Before #517, there are plenty casts to CuratorFrameworkImpl. That is why I added the "MUST BE" statement.

I guess forwarding could be the only way to meet curator.