RFR: 8332303: Better JMX interoperability with older JDKs, after removing Subject Delegation

[Kevin Walls]

On Wed, 15 May 2024 22:44:03 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>> Running JConsole from a previous JDK, and attaching to jdk-23 (after [JDK-8326666](https://bugs.openjdk.org/browse/JDK-8326666): Remove the Java Management Extension (JMX) Subject Delegation feature), the MBean tab is blank.
>> 
>> In javax/management/remote/rmi/RMIConnectionImpl.java:
>> addNotificationListener rejects a non-null delegationSubjects array, but older JDKs will send such an array. It could accept the array, and only reject/throw if it contains a non-null Subject (i.e. if an attempt to use subject delegation is really happening).
>> 
>> Manually testing JConsole, the MBean tab is fully populated and usable.
>
> src/java.management.rmi/share/classes/javax/management/remote/rmi/RMIConnectionImpl.java line 979:
> 
>> 977:             for (Subject s: delegationSubjects) {
>> 978:                 if (s != null) {
>> 979:                     throw new UnsupportedOperationException("Subject Delegation has been removed.");
> 
> Q1: Would it make sense to provide any details about the non-null `delegationSubject` element?
> Q2: Does this fix needs a CSR? My guess is that this issue is very minor, so CSR is not needed.

Q1 We have a couple of places where we use that text, when a non-null Subject is given.  It's quite generic and that is a good fit.  Your app would have to go to a significant effort to use the Subject Delegation feature, and we aren't aware of any apps that use it.  If JConsole were using the feature, you would know as you would have had to specifically configure it somehow (as well as on the remote end with SM and policies), so I really think the generic message is explicit enough.

Q2 Yes, Daniel very quickly added the CSR flag.  I was presuming that "paperwork" would need doing, although yes as spec changes go, it is very very minor.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19253#discussion_r1602917924