HADOOP-13483. Optimize IPC server protobuf decoding. Contributed by Daryn Sharp.

(cherry picked from commit 580a833496)

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

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

@@ -32,6 +32,7 @@ import org.apache.hadoop.io.Writable;
 import org.apache.hadoop.io.retry.RetryPolicy;
 import org.apache.hadoop.ipc.Client.ConnectionId;
 import org.apache.hadoop.ipc.RPC.RpcInvoker;
+import org.apache.hadoop.ipc.RpcWritable;
 import org.apache.hadoop.ipc.protobuf.ProtobufRpcEngineProtos.RequestHeaderProto;
 import org.apache.hadoop.ipc.protobuf.RpcHeaderProtos.RpcRequestHeaderProto;
 import org.apache.hadoop.ipc.protobuf.RpcHeaderProtos.RpcResponseHeaderProto;
@@ -68,7 +69,7 @@ public class ProtobufRpcEngine implements RpcEngine {
 
   static { // Register the rpcRequest deserializer for WritableRpcEngine 
     org.apache.hadoop.ipc.Server.registerProtocolEngine(
-        RPC.RpcKind.RPC_PROTOCOL_BUFFER, RpcRequestWrapper.class,
+        RPC.RpcKind.RPC_PROTOCOL_BUFFER, RpcWritable.Buffer.class,
         new Server.ProtoBufRpcInvoker());
   }
 
@@ -612,8 +613,9 @@ public class ProtobufRpcEngine implements RpcEngine {
        */
       public Writable call(RPC.Server server, String protocol,
           Writable writableRequest, long receiveTime) throws Exception {
-        RpcRequestWrapper request = (RpcRequestWrapper) writableRequest;
+        RpcWritable.Buffer request = (RpcWritable.Buffer) writableRequest;
-        RequestHeaderProto rpcRequest = request.requestHeader;
+        RequestHeaderProto rpcRequest =
+            request.getValue(RequestHeaderProto.getDefaultInstance());
         String methodName = rpcRequest.getMethodName();
         String protoName = rpcRequest.getDeclaringClassProtocolName();
         long clientVersion = rpcRequest.getClientProtocolVersion();
@@ -632,8 +634,7 @@ public class ProtobufRpcEngine implements RpcEngine {
           throw new RpcNoSuchMethodException(msg);
         }
         Message prototype = service.getRequestPrototype(methodDescriptor);
-        Message param = prototype.newBuilderForType()
+        Message param = request.getValue(prototype);
-            .mergeFrom(request.theRequestRead).build();
 
         Message result;
         long startTime = Time.now();
@@ -663,7 +664,7 @@ public class ProtobufRpcEngine implements RpcEngine {
               exception.getClass().getSimpleName();
           server.updateMetrics(detailedMetricsName, qTime, processingTime);
         }
-        return new RpcResponseWrapper(result);
+        return RpcWritable.wrap(result);
       }
     }
   }

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

@@ -0,0 +1,184 @@
+/**
+ * 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.ByteArrayInputStream;
+import java.io.DataInput;
+import java.io.DataInputStream;
+import java.io.DataOutput;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.conf.Configurable;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.Writable;
+
+import com.google.protobuf.CodedInputStream;
+import com.google.protobuf.CodedOutputStream;
+import com.google.protobuf.Message;
+
+@InterfaceAudience.Private
+public abstract class RpcWritable implements Writable {
+
+  static RpcWritable wrap(Object o) {
+    if (o instanceof RpcWritable) {
+      return (RpcWritable)o;
+    } else if (o instanceof Message) {
+      return new ProtobufWrapper((Message)o);
+    } else if (o instanceof Writable) {
+      return new WritableWrapper((Writable)o);
+    }
+    throw new IllegalArgumentException("Cannot wrap " + o.getClass());
+  }
+
+  // don't support old inefficient Writable methods.
+  @Override
+  public final void readFields(DataInput in) throws IOException {
+    throw new UnsupportedOperationException();
+  }
+  @Override
+  public final void write(DataOutput out) throws IOException {
+    throw new UnsupportedOperationException();
+  }
+
+  // methods optimized for reduced intermediate byte[] allocations.
+  abstract void writeTo(ResponseBuffer out) throws IOException;
+  abstract <T> T readFrom(ByteBuffer bb) throws IOException;
+
+  // adapter for Writables.
+  static class WritableWrapper extends RpcWritable {
+    private final Writable writable;
+
+    WritableWrapper(Writable writable) {
+      this.writable = writable;
+    }
+
+    @Override
+    public void writeTo(ResponseBuffer out) throws IOException {
+      writable.write(out);
+    }
+
+    @SuppressWarnings("unchecked")
+    @Override
+    <T> T readFrom(ByteBuffer bb) throws IOException {
+      // create a stream that may consume up to the entire ByteBuffer.
+      DataInputStream in = new DataInputStream(new ByteArrayInputStream(
+          bb.array(), bb.position() + bb.arrayOffset(), bb.remaining()));
+      try {
+        writable.readFields(in);
+      } finally {
+        // advance over the bytes read.
+        bb.position(bb.limit() - in.available());
+      }
+      return (T)writable;
+    }
+  }
+
+  // adapter for Protobufs.
+  static class ProtobufWrapper extends RpcWritable {
+    private Message message;
+
+    ProtobufWrapper(Message message) {
+      this.message = message;
+    }
+
+    @Override
+    void writeTo(ResponseBuffer out) throws IOException {
+      int length = message.getSerializedSize();
+      length += CodedOutputStream.computeRawVarint32Size(length);
+      out.ensureCapacity(length);
+      message.writeDelimitedTo(out);
+    }
+
+    @SuppressWarnings("unchecked")
+    @Override
+    <T> T readFrom(ByteBuffer bb) throws IOException {
+      // using the parser with a byte[]-backed coded input stream is the
+      // most efficient way to deserialize a protobuf.  it has a direct
+      // path to the PB ctor that doesn't create multi-layered streams
+      // that internally buffer.
+      CodedInputStream cis = CodedInputStream.newInstance(
+          bb.array(), bb.position() + bb.arrayOffset(), bb.remaining());
+      try {
+        cis.pushLimit(cis.readRawVarint32());
+        message = message.getParserForType().parseFrom(cis);
+        cis.checkLastTagWas(0);
+      } finally {
+        // advance over the bytes read.
+        bb.position(bb.position() + cis.getTotalBytesRead());
+      }
+      return (T)message;
+    }
+  }
+
+  // adapter to allow decoding of writables and protobufs from a byte buffer.
+  static class Buffer extends RpcWritable {
+    private ByteBuffer bb;
+
+    static Buffer wrap(ByteBuffer bb) {
+      return new Buffer(bb);
+    }
+
+    Buffer() {}
+
+    Buffer(ByteBuffer bb) {
+      this.bb = bb;
+    }
+
+    @Override
+    void writeTo(ResponseBuffer out) throws IOException {
+      out.ensureCapacity(bb.remaining());
+      out.write(bb.array(), bb.position() + bb.arrayOffset(), bb.remaining());
+    }
+
+    @SuppressWarnings("unchecked")
+    @Override
+    <T> T readFrom(ByteBuffer bb) throws IOException {
+      // effectively consume the rest of the buffer from the callers
+      // perspective.
+      this.bb = bb.slice();
+      bb.limit(bb.position());
+      return (T)this;
+    }
+
+    public <T> T newInstance(Class<T> valueClass,
+        Configuration conf) throws IOException {
+      T instance;
+      try {
+        // this is much faster than ReflectionUtils!
+        instance = valueClass.newInstance();
+        if (instance instanceof Configurable) {
+          ((Configurable)instance).setConf(conf);
+        }
+      } catch (Exception e) {
+        throw new RuntimeException(e);
+      }
+      return getValue(instance);
+    }
+
+    public <T> T getValue(T value) throws IOException {
+      return RpcWritable.wrap(value).readFrom(bb);
+    }
+
+    int remaining() {
+      return bb.remaining();
+    }
+  }
+}

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

@@ -25,7 +25,6 @@ import static org.apache.hadoop.ipc.RpcConstants.PING_CALL_ID;
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
-import java.io.DataInputStream;
 import java.io.DataOutputStream;
 import java.io.IOException;
 import java.lang.reflect.UndeclaredThrowableException;
@@ -82,8 +81,6 @@ import org.apache.hadoop.fs.CommonConfigurationKeysPublic;
 import org.apache.hadoop.io.IOUtils;
 import org.apache.hadoop.io.Writable;
 import org.apache.hadoop.io.WritableUtils;
-import org.apache.hadoop.ipc.ProtobufRpcEngine.RpcResponseWrapper;
-import org.apache.hadoop.ipc.ProtobufRpcEngine.RpcWrapper;
 import org.apache.hadoop.ipc.RPC.RpcInvoker;
 import org.apache.hadoop.ipc.RPC.VersionMismatch;
 import org.apache.hadoop.ipc.metrics.RpcDetailedMetrics;
@@ -113,7 +110,6 @@ import org.apache.hadoop.security.token.SecretManager;
 import org.apache.hadoop.security.token.SecretManager.InvalidToken;
 import org.apache.hadoop.security.token.TokenIdentifier;
 import org.apache.hadoop.util.ProtoUtil;
-import org.apache.hadoop.util.ReflectionUtils;
 import org.apache.hadoop.util.StringUtils;
 import org.apache.hadoop.util.Time;
 import org.apache.htrace.core.SpanId;
@@ -122,9 +118,7 @@ import org.apache.htrace.core.Tracer;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.protobuf.ByteString;
-import com.google.protobuf.CodedOutputStream;
 import com.google.protobuf.Message;
-import com.google.protobuf.Message.Builder;
 
 /** An abstract IPC service.  IPC calls take a single {@link Writable} as a
  * parameter, and return a {@link Writable} as their value.  A service runs on
@@ -1345,6 +1339,7 @@ public abstract class Server {
    * A WrappedRpcServerException that is suppressed altogether
    * for the purposes of logging.
    */
+  @SuppressWarnings("serial")
   private static class WrappedRpcServerExceptionSuppressed
       extends WrappedRpcServerException {
     public WrappedRpcServerExceptionSuppressed(
@@ -1474,10 +1469,10 @@ public abstract class Server {
       }
     }
 
-    private void saslReadAndProcess(DataInputStream dis) throws
+    private void saslReadAndProcess(RpcWritable.Buffer buffer) throws
     WrappedRpcServerException, IOException, InterruptedException {
       final RpcSaslProto saslMessage =
-          decodeProtobufFromStream(RpcSaslProto.newBuilder(), dis);
+          getMessage(RpcSaslProto.getDefaultInstance(), buffer);
       switch (saslMessage.getState()) {
         case WRAP: {
           if (!saslContextEstablished || !useWrap) {
@@ -1675,7 +1670,7 @@ public abstract class Server {
           RpcConstants.INVALID_RETRY_COUNT, null, this);
       setupResponse(saslCall,
           RpcStatusProto.SUCCESS, null,
-          new RpcResponseWrapper(message), null, null);
+          RpcWritable.wrap(message), null, null);
       saslCall.sendResponse();
     }
 
@@ -1780,7 +1775,7 @@ public abstract class Server {
           dataLengthBuffer.clear();
           data.flip();
           boolean isHeaderRead = connectionContextRead;
-          processOneRpc(data.array());
+          processOneRpc(data);
           data = null;
           if (!isHeaderRead) {
             continue;
@@ -1897,7 +1892,7 @@ public abstract class Server {
      * @throws WrappedRpcServerException - if the header cannot be
      *         deserialized, or the user is not authorized
      */ 
-    private void processConnectionContext(DataInputStream dis)
+    private void processConnectionContext(RpcWritable.Buffer buffer)
         throws WrappedRpcServerException {
       // allow only one connection context during a session
       if (connectionContextRead) {
@@ -1905,8 +1900,7 @@ public abstract class Server {
             RpcErrorCodeProto.FATAL_INVALID_RPC_HEADER,
             "Connection context already processed");
       }
-      connectionContext = decodeProtobufFromStream(
+      connectionContext = getMessage(IpcConnectionContextProto.getDefaultInstance(), buffer);
-          IpcConnectionContextProto.newBuilder(), dis);
       protocolName = connectionContext.hasProtocol() ? connectionContext
           .getProtocol() : null;
 
@@ -1981,7 +1975,7 @@ public abstract class Server {
         if (unwrappedData.remaining() == 0) {
           unwrappedDataLengthBuffer.clear();
           unwrappedData.flip();
-          processOneRpc(unwrappedData.array());
+          processOneRpc(unwrappedData);
           unwrappedData = null;
         }
       }
@@ -1998,15 +1992,14 @@ public abstract class Server {
      *         Listener thread
      * @throws InterruptedException
      */
-    private void processOneRpc(byte[] buf)
+    private void processOneRpc(ByteBuffer bb)
         throws IOException, WrappedRpcServerException, InterruptedException {
       int callId = -1;
       int retry = RpcConstants.INVALID_RETRY_COUNT;
       try {
-        final DataInputStream dis =
+        final RpcWritable.Buffer buffer = RpcWritable.Buffer.wrap(bb);
-            new DataInputStream(new ByteArrayInputStream(buf));
         final RpcRequestHeaderProto header =
-            decodeProtobufFromStream(RpcRequestHeaderProto.newBuilder(), dis);
+            getMessage(RpcRequestHeaderProto.getDefaultInstance(), buffer);
         callId = header.getCallId();
         retry = header.getRetryCount();
         if (LOG.isDebugEnabled()) {
@@ -2015,13 +2008,13 @@ public abstract class Server {
         checkRpcHeaders(header);
 
         if (callId < 0) { // callIds typically used during connection setup
-          processRpcOutOfBandRequest(header, dis);
+          processRpcOutOfBandRequest(header, buffer);
         } else if (!connectionContextRead) {
           throw new WrappedRpcServerException(
               RpcErrorCodeProto.FATAL_INVALID_RPC_HEADER,
               "Connection context not established");
         } else {
-          processRpcRequest(header, dis);
+          processRpcRequest(header, buffer);
         }
       } catch (WrappedRpcServerException wrse) { // inform client of error
         Throwable ioe = wrse.getCause();
@@ -2074,7 +2067,7 @@ public abstract class Server {
      * @throws InterruptedException
      */
     private void processRpcRequest(RpcRequestHeaderProto header,
-        DataInputStream dis) throws WrappedRpcServerException,
+        RpcWritable.Buffer buffer) throws WrappedRpcServerException,
         InterruptedException {
       Class<? extends Writable> rpcRequestClass = 
           getRpcRequestWrapper(header.getRpcKind());
@@ -2088,8 +2081,7 @@ public abstract class Server {
       }
       Writable rpcRequest;
       try { //Read the rpc request
-        rpcRequest = ReflectionUtils.newInstance(rpcRequestClass, conf);
+        rpcRequest = buffer.newInstance(rpcRequestClass, conf);
-        rpcRequest.readFields(dis);
       } catch (Throwable t) { // includes runtime exception from newInstance
         LOG.warn("Unable to read call parameters for client " +
                  getHostAddress() + "on connection protocol " +
@@ -2169,8 +2161,8 @@ public abstract class Server {
      * @throws InterruptedException
      */
     private void processRpcOutOfBandRequest(RpcRequestHeaderProto header,
-        DataInputStream dis) throws WrappedRpcServerException, IOException,
+        RpcWritable.Buffer buffer) throws WrappedRpcServerException,
-        InterruptedException {
+            IOException, InterruptedException {
       final int callId = header.getCallId();
       if (callId == CONNECTION_CONTEXT_CALL_ID) {
         // SASL must be established prior to connection context
@@ -2180,7 +2172,7 @@ public abstract class Server {
               "Connection header sent during SASL negotiation");
         }
         // read and authorize the user
-        processConnectionContext(dis);
+        processConnectionContext(buffer);
       } else if (callId == AuthProtocol.SASL.callId) {
         // if client was switched to simple, ignore first SASL message
         if (authProtocol != AuthProtocol.SASL) {
@@ -2188,7 +2180,7 @@ public abstract class Server {
               RpcErrorCodeProto.FATAL_INVALID_RPC_HEADER,
               "SASL protocol not requested by client");
         }
-        saslReadAndProcess(dis);
+        saslReadAndProcess(buffer);
       } else if (callId == PING_CALL_ID) {
         LOG.debug("Received ping message");
       } else {
@@ -2235,13 +2227,12 @@ public abstract class Server {
      * @throws WrappedRpcServerException - deserialization failed
      */
     @SuppressWarnings("unchecked")
-    private <T extends Message> T decodeProtobufFromStream(Builder builder,
+    <T extends Message> T getMessage(Message message,
-        DataInputStream dis) throws WrappedRpcServerException {
+        RpcWritable.Buffer buffer) throws WrappedRpcServerException {
       try {
-        builder.mergeDelimitedFrom(dis);
+        return (T)buffer.getValue(message);
-        return (T)builder.build();
       } catch (Exception ioe) {
-        Class<?> protoClass = builder.getDefaultInstanceForType().getClass();
+        Class<?> protoClass = message.getClass();
         throw new WrappedRpcServerException(
             RpcErrorCodeProto.FATAL_DESERIALIZING_REQUEST,
             "Error decoding " + protoClass.getSimpleName() + ": "+ ioe);
@@ -2632,19 +2623,13 @@ public abstract class Server {
   private void setupResponse(Call call,
       RpcResponseHeaderProto header, Writable rv) throws IOException {
     ResponseBuffer buf = responseBuffer.get().reset();
-    // adjust capacity on estimated length to reduce resizing copies
+    try {
-    int estimatedLen = header.getSerializedSize();
+      RpcWritable.wrap(header).writeTo(buf);
-    estimatedLen += CodedOutputStream.computeRawVarint32Size(estimatedLen);
+      if (rv != null) {
-    // if it's not a wrapped protobuf, just let it grow on its own
+        RpcWritable.wrap(rv).writeTo(buf);
-    if (rv instanceof RpcWrapper) {
-      estimatedLen += ((RpcWrapper)rv).getLength();
-    }
-    buf.ensureCapacity(estimatedLen);
-    header.writeDelimitedTo(buf);
-    if (rv != null) { // null for exceptions
-      rv.write(buf);
       }
       call.setResponse(ByteBuffer.wrap(buf.toByteArray()));
+    } finally {
       // Discard a large buf and reset it back to smaller size
       // to free up heap.
       if (buf.capacity() > maxRespSize) {
@@ -2653,6 +2638,7 @@ public abstract class Server {
         buf.setCapacity(INITIAL_RESP_BUF_SIZE);
       }
     }
+  }
 
   /**
    * Setup response for the IPC Call on Fatal Error from a 
@@ -2701,7 +2687,7 @@ public abstract class Server {
           .setState(SaslState.WRAP)
           .setToken(ByteString.copyFrom(token))
           .build();
-      setupResponse(call, saslHeader, new RpcResponseWrapper(saslMessage));
+      setupResponse(call, saslHeader, RpcWritable.wrap(saslMessage));
     }
   }
   

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/ipc/TestRpcWritable.java

@@ -0,0 +1,129 @@
+/**
+ * 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.ByteArrayOutputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.io.Writable;
+import org.apache.hadoop.ipc.protobuf.TestProtos.EchoRequestProto;
+import org.apache.hadoop.util.Time;
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.google.protobuf.Message;
+
+public class TestRpcWritable {//extends TestRpcBase {
+
+  static Writable writable = new LongWritable(Time.now());
+  static Message message1 =
+      EchoRequestProto.newBuilder().setMessage("testing1").build();
+  static Message message2 =
+      EchoRequestProto.newBuilder().setMessage("testing2").build();
+
+  @Test
+  public void testWritableWrapper() throws IOException {
+    // serial writable in byte buffer
+    ByteArrayOutputStream baos = new ByteArrayOutputStream();
+    writable.write(new DataOutputStream(baos));
+    ByteBuffer bb = ByteBuffer.wrap(baos.toByteArray());
+
+    // deserial
+    LongWritable actual = RpcWritable.wrap(new LongWritable())
+        .readFrom(bb);
+    Assert.assertEquals(writable, actual);
+    Assert.assertEquals(0, bb.remaining());
+  }
+
+  @Test
+  public void testProtobufWrapper() throws IOException {
+    ByteArrayOutputStream baos = new ByteArrayOutputStream();
+    message1.writeDelimitedTo(baos);
+    ByteBuffer bb = ByteBuffer.wrap(baos.toByteArray());
+
+    Message actual = RpcWritable.wrap(EchoRequestProto.getDefaultInstance())
+        .readFrom(bb);
+    Assert.assertEquals(message1, actual);
+    Assert.assertEquals(0, bb.remaining());
+  }
+
+  @Test
+  public void testBufferWrapper() throws IOException {
+    ByteArrayOutputStream baos = new ByteArrayOutputStream();
+    DataOutputStream dos = new DataOutputStream(baos);
+    message1.writeDelimitedTo(dos);
+    message2.writeDelimitedTo(dos);
+    writable.write(dos);
+
+    ByteBuffer bb = ByteBuffer.wrap(baos.toByteArray());
+    RpcWritable.Buffer buf = RpcWritable.Buffer.wrap(bb);
+    Assert.assertEquals(baos.size(), bb.remaining());
+    Assert.assertEquals(baos.size(), buf.remaining());
+
+    Object actual = buf.getValue(EchoRequestProto.getDefaultInstance());
+    Assert.assertEquals(message1, actual);
+    Assert.assertTrue(bb.remaining() > 0);
+    Assert.assertEquals(bb.remaining(), buf.remaining());
+
+    actual = buf.getValue(EchoRequestProto.getDefaultInstance());
+    Assert.assertEquals(message2, actual);
+    Assert.assertTrue(bb.remaining() > 0);
+    Assert.assertEquals(bb.remaining(), buf.remaining());
+
+    actual = buf.newInstance(LongWritable.class, null);
+    Assert.assertEquals(writable, actual);
+    Assert.assertEquals(0, bb.remaining());
+    Assert.assertEquals(0, buf.remaining());
+  }
+
+  @Test
+  public void testBufferWrapperNested() throws IOException {
+    ByteArrayOutputStream baos = new ByteArrayOutputStream();
+    DataOutputStream dos = new DataOutputStream(baos);
+    writable.write(dos);
+    message1.writeDelimitedTo(dos);
+    message2.writeDelimitedTo(dos);
+    ByteBuffer bb = ByteBuffer.wrap(baos.toByteArray());
+    RpcWritable.Buffer buf1 = RpcWritable.Buffer.wrap(bb);
+    Assert.assertEquals(baos.size(), bb.remaining());
+    Assert.assertEquals(baos.size(), buf1.remaining());
+
+    Object actual = buf1.newInstance(LongWritable.class, null);
+    Assert.assertEquals(writable, actual);
+    int left = bb.remaining();
+    Assert.assertTrue(left > 0);
+    Assert.assertEquals(left, buf1.remaining());
+
+    // original bb now appears empty, but rpc writable has a slice of the bb.
+    RpcWritable.Buffer buf2 = buf1.newInstance(RpcWritable.Buffer.class, null);
+    Assert.assertEquals(0, bb.remaining());
+    Assert.assertEquals(0, buf1.remaining());
+    Assert.assertEquals(left, buf2.remaining());
+
+    actual = buf2.getValue(EchoRequestProto.getDefaultInstance());
+    Assert.assertEquals(message1, actual);
+    Assert.assertTrue(buf2.remaining() > 0);
+
+    actual = buf2.getValue(EchoRequestProto.getDefaultInstance());
+    Assert.assertEquals(message2, actual);
+    Assert.assertEquals(0, buf2.remaining());
+  }
+}