HDDS-506. Fields in AllocateScmBlockResponseProto should be optional. Contributed by Arpit Agarwal.

hadoop-hdds/common/src/main/proto/ScmBlockLocationProtocol.proto

@@ -104,9 +104,9 @@ message AllocateScmBlockResponseProto {
     unknownFailure = 4;
   }
   required Error errorCode = 1;
-  required BlockID blockID = 2;
-  required hadoop.hdds.Pipeline pipeline = 3;
-  required bool createContainer = 4;
+  optional BlockID blockID = 2;
+  optional hadoop.hdds.Pipeline pipeline = 3;
+  optional bool createContainer = 4;
   optional string errorMessage = 5;
 }
 

hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/exceptions/SCMException.java

@@ -118,6 +118,7 @@ public class SCMException extends IOException {
     SCM_NOT_INITIALIZED,
     DUPLICATE_DATANODE,
     NO_SUCH_DATANODE,
-    NO_REPLICA_FOUND
+    NO_REPLICA_FOUND,
+    FAILED_TO_FIND_ACTIVE_PIPELINE
   }
 }

hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/pipelines/PipelineSelector.java

@@ -62,6 +62,7 @@ import java.util.concurrent.TimeUnit;
 
 import static org.apache.hadoop.hdds.scm.exceptions.SCMException.ResultCodes
     .FAILED_TO_CHANGE_PIPELINE_STATE;
+import static org.apache.hadoop.hdds.scm.exceptions.SCMException.ResultCodes.FAILED_TO_FIND_ACTIVE_PIPELINE;
 import static org.apache.hadoop.hdds.server
         .ServerUtils.getOzoneMetaDirPath;
 import static org.apache.hadoop.ozone
@@ -285,6 +286,9 @@ public class PipelineSelector {
       // try to return a pipeline from already allocated pipelines
       PipelineID pipelineId =
               manager.getPipeline(replicationFactor, replicationType);
+      if (pipelineId == null) {
+        throw new SCMException(FAILED_TO_FIND_ACTIVE_PIPELINE);
+      }
       pipeline = pipelineMap.get(pipelineId);
       Preconditions.checkArgument(pipeline.getLifeCycleState() ==
               LifeCycleState.OPEN);