svn merge -c 1210319 from trunk for HADOOP-7875.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23-PB@1230381 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -7,6 +7,9 @@ Release 0.23-PB - Unreleased
     HADOOP-7773. Add support for protocol buffer based RPC engine.
     (suresh)
 
+    HADOOP-7875. Add helper class to unwrap protobuf ServiceException.
+    (suresh)
+
   IMPROVEMENTS
 
     HADOOP-7524 Change RPC to allow multiple protocols including multuple versions of the same protocol (sanjay Radia)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/ProtobufHelper.java

@@ -0,0 +1,46 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.ipc;
+
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+
+import com.google.protobuf.ServiceException;
+
+/**
+ * Helper methods for protobuf related RPC implementation
+ */
+@InterfaceAudience.Private
+public class ProtobufHelper {
+  private ProtobufHelper() {
+    // Hidden constructor for class with only static helper methods
+  }
+
+  /**
+   * Return the RemoteException wrapped in ServiceException as cause.
+   * @param se ServiceException that wraps RemoteException
+   * @return RemoteException wrapped in ServiceException or
+   *         a new IOException that wraps unexpected ServiceException.
+   */
+  public static IOException getRemoteException(ServiceException se) {
+    Throwable e = se.getCause();
+    return ((e instanceof RemoteException) ? (IOException) e : 
+      new IOException(se));
+  }
+}