[fix][ml] Fix NPE of getValidPositionAfterSkippedEntries when recovering a terminated managed ledger

[coderzc]

Motivation

Since managedLedger does not create a new ledger when recovering a terminated managed ledger, lead to getValidPositionAfterSkippedEntries will get an NPE.

org.apache.bookkeeper.mledger.ManagedLedgerException$MetaStoreException: java.util.concurrent.CompletionException: java.lang.NullPointerException: Cannot invoke "org.apache.bookkeeper.client.LedgerHandle.getId()" because "this.currentLedger" is null
Caused by: java.util.concurrent.CompletionException: java.lang.NullPointerException: Cannot invoke "org.apache.bookkeeper.client.LedgerHandle.getId()" because "this.currentLedger" is null
	at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:315) ~[?:?]
	at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:320) ~[?:?]
	at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:722) ~[?:?]
	at java.base/java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:482) ~[?:?]
	at org.apache.bookkeeper.common.util.OrderedExecutor$TimedRunnable.run(OrderedExecutor.java:201) [bookkeeper-common-4.16.4.jar:4.16.4]
	at org.apache.bookkeeper.common.util.SingleThreadSafeScheduledExecutorService$SafeRunnable.run(SingleThreadSafeScheduledExecutorService.java:46) [bookkeeper-common-4.16.4.jar:4.16.4]
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539) [?:?]
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) [?:?]
	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304) [?:?]
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136) [?:?]
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635) [?:?]
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) [netty-common-4.1.108.Final.jar:4.1.108.Final]
	at java.base/java.lang.Thread.run(Thread.java:833) [?:?]
Caused by: java.lang.NullPointerException: Cannot invoke "org.apache.bookkeeper.client.LedgerHandle.getId()" because "this.currentLedger" is null

pulsar/managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerImpl.java

Lines 486 to 492 in 3a0f908

	if (state == State.Terminated) {
	// When recovering a terminated managed ledger, we don't need to create
	// a new ledger for writing, since no more writes are allowed.
	// We just move on to the next stage
	initializeCursors(callback);
	return;
	}

pulsar/managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerImpl.java

Lines 3698 to 3712 in 3a0f908

	public PositionImpl getValidPositionAfterSkippedEntries(final PositionImpl position, int skippedEntryNum) {
	PositionImpl skippedPosition = position.getPositionAfterEntries(skippedEntryNum);
	while (!isValidPosition(skippedPosition)) {
	Long nextLedgerId = ledgers.ceilingKey(skippedPosition.getLedgerId() + 1);
	// This means it has jumped to the last position
	if (nextLedgerId == null) {
	if (currentLedgerEntries == 0) {
	return PositionImpl.get(currentLedger.getId(), 0);
	}
	return lastConfirmedEntry.getNext();
	}
	skippedPosition = PositionImpl.get(nextLedgerId, 0);
	}
	return skippedPosition;
	}

this NPE introduced from #22034

Modifications

If currentLedger == null, then return lastConfirmedEntry.getNext() for getValidPositionAfterSkippedEntries to avoid NPE.

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

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• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository:

[lhotari]

LGTM

Test needs addressing the comment raised in a review by shibd

[lhotari]

LGTM