[JAMES-3177] NPE upon SelectedMailboxImpl event processing

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.6.0
• Component/s: IMAPServer
• Labels: bug
• Assignee: Unassigned
• Reporter: Benoit Tellier
• Created: 11/May/20 06:17
• Updated: 05/Oct/20 07:47
• Resolved: 23/Jul/20 07:54

Description

We noticed the following exception:

 	java.lang.NullPointerException: null
	at org.apache.james.imap.processor.base.SelectedMailboxImpl.mailboxEvent(SelectedMailboxImpl.java:363)
	at org.apache.james.imap.processor.base.SelectedMailboxImpl.event(SelectedMailboxImpl.java:308)
	at org.apache.james.mailbox.events.MailboxListenerExecutor.execute(MailboxListenerExecutor.java:42)
	at org.apache.james.mailbox.events.EventDispatcher.lambda$executeListener$6(EventDispatcher.java:105)
	at reactor.core.publisher.MonoFromPublisher.subscribe(MonoFromPublisher.java:55)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4087)
	at reactor.core.publisher.MonoSubscribeOn$SubscribeOnSubscriber.run(MonoSubscribeOn.java:124)
	at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:84)
	at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:37)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)

In order not to miss updates, SelectedMailboxImpl starts processing events before have completed it's initialization. Thus, if a concurrent mailbox operation happens, the `event` method can be executed before the applicableFlags variable is initialized. Leading to the above null pointer exception.

We should rely on indempoteance of the add only set (applicableFlags) to keep track of applicable flags changes during the initialization. Merging them with the one being stored ensures the data is up to date.