HBASE-29831: Fix for NPE in region replication

hbase-server/src/main/java/org/apache/hadoop/hbase/replication/regionserver/RegionReplicaReplicationEndpoint.java

@@ -427,7 +427,6 @@ public void append(TableName tableName, byte[] encodedRegionName, byte[] row,
       // invalidate the cache and check from meta
       RegionLocations locations = null;
       boolean useCache = true;
-      int retries = 0;
       while (true) {
         // get the replicas of the primary region
         try {
@@ -441,12 +440,12 @@ public void append(TableName tableName, byte[] encodedRegionName, byte[] row,
           // keep going to the cache, we will not learn of the replicas and their locations after
           // they come online.
           if (useCache && locations.size() == 1) {
-            if (tableDescriptors.get(tableName).getRegionReplication() > 1 && retries <= 3) {
+            TableDescriptor td = tableDescriptors.get(tableName);
+            if (td != null && td.getRegionReplication() > 1) {
               // Make an obnoxious log here. See how bad this issue is. Add a timer if happening
               // too much.
               LOG.info("Skipping location cache; only one location found for {}", tableName);
               useCache = false;
-              retries++;
               continue;
             }
           }

hbase-server/src/test/java/org/apache/hadoop/hbase/replication/regionserver/TestRegionReplicaReplicationEndpoint.java

@@ -22,6 +22,10 @@
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyBoolean;
+import static org.mockito.ArgumentMatchers.anyInt;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
@@ -42,7 +46,9 @@
 import org.apache.hadoop.hbase.HConstants;
 import org.apache.hadoop.hbase.HRegionLocation;
 import org.apache.hadoop.hbase.HTableDescriptor;
+import org.apache.hadoop.hbase.RegionLocations;
 import org.apache.hadoop.hbase.ReplicationPeerNotFoundException;
+import org.apache.hadoop.hbase.TableDescriptors;
 import org.apache.hadoop.hbase.TableName;
 import org.apache.hadoop.hbase.Waiter;
 import org.apache.hadoop.hbase.client.Admin;
@@ -557,6 +563,59 @@ public void testMetaCacheMissTriggersRefresh() throws Exception {
     }
   }
 
+  @Test
+  public void testNullTableDescriptorDoesNotCauseNPE() throws Exception {
+    TableName tableName = TableName.valueOf(name.getMethodName());
+    int regionReplication = 2;
+    HTableDescriptor htd = HTU.createTableDescriptor(tableName);
+    htd.setRegionReplication(regionReplication);
+    createOrEnableTableWithRetries(htd, true);
+
+    Connection connection = ConnectionFactory.createConnection(HTU.getConfiguration());
+    Table table = connection.getTable(tableName);
+
+    try {
+      HTU.loadNumericRows(table, HBaseTestingUtility.fam1, 0, 100);
+
+      RegionLocator rl = connection.getRegionLocator(tableName);
+      HRegionLocation hrl = rl.getRegionLocation(HConstants.EMPTY_BYTE_ARRAY);
+      byte[] encodedRegionName = hrl.getRegionInfo().getEncodedNameAsBytes();
+      rl.close();
+
+      AtomicLong skippedEdits = new AtomicLong();
+      RegionReplicaReplicationEndpoint.RegionReplicaOutputSink sink =
+        mock(RegionReplicaReplicationEndpoint.RegionReplicaOutputSink.class);
+      when(sink.getSkippedEditsCounter()).thenReturn(skippedEdits);
+
+      TableDescriptors mockTableDescriptors = mock(TableDescriptors.class);
+      when(mockTableDescriptors.get(tableName)).thenReturn(null);
+
+      RegionLocations singleLocation = new RegionLocations(hrl);
+      ClusterConnection mockConnection = mock(ClusterConnection.class);
+      when(mockConnection.locateRegion(eq(tableName), any(byte[].class), anyBoolean(), anyBoolean(),
+        anyInt())).thenReturn(singleLocation);
+      when(mockConnection.getConfiguration()).thenReturn(HTU.getConfiguration());
+
+      RegionReplicaReplicationEndpoint.RegionReplicaSinkWriter sinkWriter =
+        new RegionReplicaReplicationEndpoint.RegionReplicaSinkWriter(sink, mockConnection,
+          Executors.newSingleThreadExecutor(), Integer.MAX_VALUE, mockTableDescriptors);
+
+      Cell cell = CellBuilderFactory.create(CellBuilderType.DEEP_COPY)
+        .setRow(Bytes.toBytes("testRow")).setFamily(HBaseTestingUtility.fam1)
+        .setValue(Bytes.toBytes("testValue")).setType(Type.Put).build();
+
+      Entry entry =
+        new Entry(new WALKeyImpl(encodedRegionName, tableName, 1), new WALEdit().add(cell));
+
+      sinkWriter.append(tableName, encodedRegionName, Bytes.toBytes("testRow"),
+        Lists.newArrayList(entry));
+
+    } finally {
+      table.close();
+      connection.close();
+    }
+  }
+
   @Test
   public void testMetaCacheSkippedForSingleReplicaTable() throws Exception {
     TableName tableName = TableName.valueOf(name.getMethodName());