HADOOP-9688. Adding a file missed in the commit 1500843

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1500847 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -0,0 +1,50 @@
+/**
+ * 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.nio.ByteBuffer;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+
+@InterfaceAudience.Private
+public class RpcConstants {
+  private RpcConstants() {
+    // Hidden Constructor
+  }
+  
+  public static final int PING_CALL_ID = -1;
+  
+  public static final byte[] DUMMY_CLIENT_ID = new byte[0];
+  
+  
+  /**
+   * The first four bytes of Hadoop RPC connections
+   */
+  public static final ByteBuffer HEADER = ByteBuffer.wrap("hrpc".getBytes());
+  
+  // 1 : Introduce ping and server does not throw away RPCs
+  // 3 : Introduce the protocol into the RPC connection header
+  // 4 : Introduced SASL security layer
+  // 5 : Introduced use of {@link ArrayPrimitiveWritable$Internal}
+  //     in ObjectWritable to efficiently transmit arrays of primitives
+  // 6 : Made RPC Request header explicit
+  // 7 : Changed Ipc Connection Header to use Protocol buffers
+  // 8 : SASL server always sends a final response
+  // 9 : Changes to protocol for HADOOP-8990
+  public static final byte CURRENT_VERSION = 9;
+}