[issue #3975] Bugfix NPE on non durable consumer (#3988)

*Motivation*

Trying to fix #3975

When a reset of a cursor is performed with some timestamp on a non-durable
consumer the message finder will fail with null pointer exception due to
`cursor.getName()` being null.

*Modifications*

  - Add method overloading for `newNonDurableCursor()` with subscription name.
  - Fix method getNonDurableSubscription to call `newNonDurableCursor()` with
    proper subscription name
  - Add test to assert issue.

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/ManagedLedger.java

@@ -172,6 +172,7 @@ public interface ManagedLedger {
      * @return the new NonDurableCursor
      */
     ManagedCursor newNonDurableCursor(Position startCursorPosition) throws ManagedLedgerException;
+    ManagedCursor newNonDurableCursor(Position startPosition, String subscriptionName) throws ManagedLedgerException;
 
     /**
      * Delete a ManagedCursor asynchronously.

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

@@ -831,6 +831,16 @@ public ManagedCursor newNonDurableCursor(Position startCursorPosition) throws Ma
         return new NonDurableCursorImpl(bookKeeper, config, this, null, (PositionImpl) startCursorPosition);
     }
 
+    @Override
+    public ManagedCursor newNonDurableCursor(Position startCursorPosition, String cursorName)
+            throws ManagedLedgerException {
+        checkManagedLedgerIsOpen();
+        checkFenced();
+
+        return new NonDurableCursorImpl(bookKeeper, config, this, cursorName,
+                (PositionImpl) startCursorPosition);
+    }
+
     @Override
     public Iterable<ManagedCursor> getCursors() {
         return cursors;

pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentTopic.java

@@ -641,7 +641,7 @@ private CompletableFuture<? extends Subscription> getNonDurableSubscription(Stri
             Position startPosition = new PositionImpl(ledgerId, entryId);
             ManagedCursor cursor = null;
             try {
-                cursor = ledger.newNonDurableCursor(startPosition);
+                cursor = ledger.newNonDurableCursor(startPosition, subscriptionName);
             } catch (ManagedLedgerException e) {
                 subscriptionFuture.completeExceptionally(e);
             }

pulsar-broker/src/test/java/org/apache/pulsar/client/api/TopicReaderTest.java

@@ -34,7 +34,9 @@
 import java.util.concurrent.TimeUnit;
 import org.apache.pulsar.client.impl.BatchMessageIdImpl;
 import org.apache.pulsar.client.impl.MessageImpl;
+import org.apache.pulsar.client.impl.ReaderImpl;
 import org.apache.pulsar.common.policies.data.TopicStats;
+import org.apache.pulsar.common.util.RelativeTimeUtil;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.testng.Assert;
@@ -479,7 +481,7 @@ public void testMessageAvailableAfterRestart() throws Exception {
             assertTrue(reader.hasMessageAvailable());
 
             String readOut = new String(reader.readNext().getData());
-            assertTrue(readOut.equals(content));
+            assertEquals(content, readOut);
             assertFalse(reader.hasMessageAvailable());
         }