HDFS-13758. DatanodeManager should throw exception if it has BlockRecoveryCommand but the block is not under construction. Contributed by chencan.

(cherry picked from commit 04c8b5dbb669cf9d47601311233325b32372dd07)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeManager.java

@@ -1468,7 +1468,7 @@ public class DatanodeManager {
   }
 
   private BlockRecoveryCommand getBlockRecoveryCommand(String blockPoolId,
-      DatanodeDescriptor nodeinfo) {
+      DatanodeDescriptor nodeinfo) throws IOException {
     BlockInfo[] blocks = nodeinfo.getLeaseRecoveryCommand(Integer.MAX_VALUE);
     if (blocks == null) {
       return null;
@@ -1476,7 +1476,10 @@ public class DatanodeManager {
     BlockRecoveryCommand brCommand = new BlockRecoveryCommand(blocks.length);
     for (BlockInfo b : blocks) {
       BlockUnderConstructionFeature uc = b.getUnderConstructionFeature();
-      assert uc != null;
+      if(uc == null) {
+        throw new IOException("Recovery block " + b +
+            "where it is not under construction.");
+      }
       final DatanodeStorageInfo[] storages = uc.getExpectedStorageLocations();
       // Skip stale nodes during recovery
       final List<DatanodeStorageInfo> recoveryLocations =