HADOOP-17680. Allow ProtobufRpcEngine to be extensible (#2905) Contributed by Hector Chaverri.

(cherry picked from commit f40e3eb0590f85bb42d2471992bf5d524628fdd6)

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

@@ -115,7 +115,7 @@ public class ProtobufRpcEngine implements RpcEngine {
                 factory)), false);
   }
 
-  private static class Invoker implements RpcInvocationHandler {
+  protected static class Invoker implements RpcInvocationHandler {
     private final Map<String, Message> returnTypes = 
         new ConcurrentHashMap<String, Message>();
     private boolean isClosed = false;
@@ -126,7 +126,7 @@ public class ProtobufRpcEngine implements RpcEngine {
     private AtomicBoolean fallbackToSimpleAuth;
     private AlignmentContext alignmentContext;
 
-    private Invoker(Class<?> protocol, InetSocketAddress addr,
+    protected Invoker(Class<?> protocol, InetSocketAddress addr,
         UserGroupInformation ticket, Configuration conf, SocketFactory factory,
         int rpcTimeout, RetryPolicy connectionRetryPolicy,
         AtomicBoolean fallbackToSimpleAuth, AlignmentContext alignmentContext)
@@ -141,7 +141,7 @@ public class ProtobufRpcEngine implements RpcEngine {
     /**
      * This constructor takes a connectionId, instead of creating a new one.
      */
-    private Invoker(Class<?> protocol, Client.ConnectionId connId,
+    protected Invoker(Class<?> protocol, Client.ConnectionId connId,
         Configuration conf, SocketFactory factory) {
       this.remoteId = connId;
       this.client = CLIENTS.getClient(conf, factory, RpcWritable.Buffer.class);
@@ -218,8 +218,6 @@ public class ProtobufRpcEngine implements RpcEngine {
         traceScope = tracer.newScope(RpcClientUtil.methodToTraceString(method));
       }
 
-      RequestHeaderProto rpcRequestHeader = constructRpcRequestHeader(method);
-      
       if (LOG.isTraceEnabled()) {
         LOG.trace(Thread.currentThread().getId() + ": Call -> " +
             remoteId + ": " + method.getName() +
@@ -231,7 +229,7 @@ public class ProtobufRpcEngine implements RpcEngine {
       final RpcWritable.Buffer val;
       try {
         val = (RpcWritable.Buffer) client.call(RPC.RpcKind.RPC_PROTOCOL_BUFFER,
-            new RpcProtobufRequest(rpcRequestHeader, theRequest), remoteId,
+            constructRpcRequest(method, theRequest), remoteId,
             fallbackToSimpleAuth, alignmentContext);
 
       } catch (Throwable e) {
@@ -276,6 +274,11 @@ public class ProtobufRpcEngine implements RpcEngine {
       }
     }
 
+    protected Writable constructRpcRequest(Method method, Message theRequest) {
+      RequestHeaderProto rpcRequestHeader = constructRpcRequestHeader(method);
+      return new RpcProtobufRequest(rpcRequestHeader, theRequest);
+    }
+
     private Message getReturnMessage(final Method method,
         final RpcWritable.Buffer buf) throws ServiceException {
       Message prototype = null;
@@ -325,6 +328,14 @@ public class ProtobufRpcEngine implements RpcEngine {
     public ConnectionId getConnectionId() {
       return remoteId;
     }
+
+    protected long getClientProtocolVersion() {
+      return clientProtocolVersion;
+    }
+
+    protected String getProtocolName() {
+      return protocolName;
+    }
   }
 
   @VisibleForTesting
@@ -503,6 +514,13 @@ public class ProtobufRpcEngine implements RpcEngine {
         String declaringClassProtoName = 
             rpcRequest.getDeclaringClassProtocolName();
         long clientVersion = rpcRequest.getClientProtocolVersion();
+        return call(server, connectionProtocolName, request, receiveTime,
+            methodName, declaringClassProtoName, clientVersion);
+      }
+
+      protected Writable call(RPC.Server server, String connectionProtocolName,
+          RpcWritable.Buffer request, long receiveTime, String methodName,
+          String declaringClassProtoName, long clientVersion) throws Exception {
         if (server.verbose)
           LOG.info("Call: connectionProtocolName=" + connectionProtocolName + 
               ", method=" + methodName);