HDFS-2512. Add textual error message to data transfer protocol responses. Contributed by Todd Lipcon.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1195693 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -836,6 +836,9 @@ Release 0.23.0 - Unreleased
     HDFS-2436. Change FSNamesystem.setTimes(..) for allowing setting times on
     directories.  (Uma Maheswara Rao G via szetszwo)
 
+    HDFS-2512. Add textual error message to data transfer protocol responses
+    (todd)
+
   OPTIMIZATIONS
 
     HDFS-1458. Improve checkpoint performance by avoiding unnecessary image

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/proto/DataTransferProtos.java

@@ -15,7 +15,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 // Generated by the protocol buffer compiler.  DO NOT EDIT!
 // source: datatransfer.proto
 
@@ -6936,6 +6935,10 @@ public interface BlockOpResponseProtoOrBuilder
     boolean hasChecksumResponse();
     org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.OpBlockChecksumResponseProto getChecksumResponse();
     org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.OpBlockChecksumResponseProtoOrBuilder getChecksumResponseOrBuilder();
+    
+    // optional string message = 4;
+    boolean hasMessage();
+    String getMessage();
   }
   public static final class BlockOpResponseProto extends
       com.google.protobuf.GeneratedMessage
@@ -7021,10 +7024,43 @@ public org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.OpBlockChecksumR
       return checksumResponse_;
     }
     
+    // optional string message = 4;
+    public static final int MESSAGE_FIELD_NUMBER = 4;
+    private java.lang.Object message_;
+    public boolean hasMessage() {
+      return ((bitField0_ & 0x00000008) == 0x00000008);
+    }
+    public String getMessage() {
+      java.lang.Object ref = message_;
+      if (ref instanceof String) {
+        return (String) ref;
+      } else {
+        com.google.protobuf.ByteString bs = 
+            (com.google.protobuf.ByteString) ref;
+        String s = bs.toStringUtf8();
+        if (com.google.protobuf.Internal.isValidUtf8(bs)) {
+          message_ = s;
+        }
+        return s;
+      }
+    }
+    private com.google.protobuf.ByteString getMessageBytes() {
+      java.lang.Object ref = message_;
+      if (ref instanceof String) {
+        com.google.protobuf.ByteString b = 
+            com.google.protobuf.ByteString.copyFromUtf8((String) ref);
+        message_ = b;
+        return b;
+      } else {
+        return (com.google.protobuf.ByteString) ref;
+      }
+    }
+    
     private void initFields() {
       status_ = org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.Status.SUCCESS;
       firstBadLink_ = "";
       checksumResponse_ = org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.OpBlockChecksumResponseProto.getDefaultInstance();
+      message_ = "";
     }
     private byte memoizedIsInitialized = -1;
     public final boolean isInitialized() {
@@ -7057,6 +7093,9 @@ public void writeTo(com.google.protobuf.CodedOutputStream output)
       if (((bitField0_ & 0x00000004) == 0x00000004)) {
         output.writeMessage(3, checksumResponse_);
       }
+      if (((bitField0_ & 0x00000008) == 0x00000008)) {
+        output.writeBytes(4, getMessageBytes());
+      }
       getUnknownFields().writeTo(output);
     }
     
@@ -7078,6 +7117,10 @@ public int getSerializedSize() {
         size += com.google.protobuf.CodedOutputStream
           .computeMessageSize(3, checksumResponse_);
       }
+      if (((bitField0_ & 0x00000008) == 0x00000008)) {
+        size += com.google.protobuf.CodedOutputStream
+          .computeBytesSize(4, getMessageBytes());
+      }
       size += getUnknownFields().getSerializedSize();
       memoizedSerializedSize = size;
       return size;
@@ -7116,6 +7159,11 @@ public boolean equals(final java.lang.Object obj) {
         result = result && getChecksumResponse()
             .equals(other.getChecksumResponse());
       }
+      result = result && (hasMessage() == other.hasMessage());
+      if (hasMessage()) {
+        result = result && getMessage()
+            .equals(other.getMessage());
+      }
       result = result &&
           getUnknownFields().equals(other.getUnknownFields());
       return result;
@@ -7137,6 +7185,10 @@ public int hashCode() {
         hash = (37 * hash) + CHECKSUMRESPONSE_FIELD_NUMBER;
         hash = (53 * hash) + getChecksumResponse().hashCode();
       }
+      if (hasMessage()) {
+        hash = (37 * hash) + MESSAGE_FIELD_NUMBER;
+        hash = (53 * hash) + getMessage().hashCode();
+      }
       hash = (29 * hash) + getUnknownFields().hashCode();
       return hash;
     }
@@ -7264,6 +7316,8 @@ public Builder clear() {
           checksumResponseBuilder_.clear();
         }
         bitField0_ = (bitField0_ & ~0x00000004);
+        message_ = "";
+        bitField0_ = (bitField0_ & ~0x00000008);
         return this;
       }
       
@@ -7318,6 +7372,10 @@ public org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.BlockOpResponseP
         } else {
           result.checksumResponse_ = checksumResponseBuilder_.build();
         }
+        if (((from_bitField0_ & 0x00000008) == 0x00000008)) {
+          to_bitField0_ |= 0x00000008;
+        }
+        result.message_ = message_;
         result.bitField0_ = to_bitField0_;
         onBuilt();
         return result;
@@ -7343,6 +7401,9 @@ public Builder mergeFrom(org.apache.hadoop.hdfs.protocol.proto.DataTransferProto
         if (other.hasChecksumResponse()) {
           mergeChecksumResponse(other.getChecksumResponse());
         }
+        if (other.hasMessage()) {
+          setMessage(other.getMessage());
+        }
         this.mergeUnknownFields(other.getUnknownFields());
         return this;
       }
@@ -7409,6 +7470,11 @@ public Builder mergeFrom(
               setChecksumResponse(subBuilder.buildPartial());
               break;
             }
+            case 34: {
+              bitField0_ |= 0x00000008;
+              message_ = input.readBytes();
+              break;
+            }
           }
         }
       }
@@ -7565,6 +7631,42 @@ public org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.OpBlockChecksumR
         return checksumResponseBuilder_;
       }
       
+      // optional string message = 4;
+      private java.lang.Object message_ = "";
+      public boolean hasMessage() {
+        return ((bitField0_ & 0x00000008) == 0x00000008);
+      }
+      public String getMessage() {
+        java.lang.Object ref = message_;
+        if (!(ref instanceof String)) {
+          String s = ((com.google.protobuf.ByteString) ref).toStringUtf8();
+          message_ = s;
+          return s;
+        } else {
+          return (String) ref;
+        }
+      }
+      public Builder setMessage(String value) {
+        if (value == null) {
+    throw new NullPointerException();
+  }
+  bitField0_ |= 0x00000008;
+        message_ = value;
+        onChanged();
+        return this;
+      }
+      public Builder clearMessage() {
+        bitField0_ = (bitField0_ & ~0x00000008);
+        message_ = getDefaultInstance().getMessage();
+        onChanged();
+        return this;
+      }
+      void setMessage(com.google.protobuf.ByteString value) {
+        bitField0_ |= 0x00000008;
+        message_ = value;
+        onChanged();
+      }
+      
       // @@protoc_insertion_point(builder_scope:BlockOpResponseProto)
     }
     
@@ -8995,19 +9097,20 @@ public Builder clearMd5() {
       "\030\001 \002(\020\022\r\n\005seqno\030\002 \002(\020\022\031\n\021lastPacketInBlo" +
       "ck\030\003 \002(\010\022\017\n\007dataLen\030\004 \002(\017\":\n\020PipelineAck" +
       "Proto\022\r\n\005seqno\030\001 \002(\022\022\027\n\006status\030\002 \003(\0162\007.S" +
-      "tatus\"~\n\024BlockOpResponseProto\022\027\n\006status\030" +
+      "tatus\"\217\001\n\024BlockOpResponseProto\022\027\n\006status" +
-      "\001 \002(\0162\007.Status\022\024\n\014firstBadLink\030\002 \001(\t\0227\n\020" +
+      "\030\001 \002(\0162\007.Status\022\024\n\014firstBadLink\030\002 \001(\t\0227\n" +
-      "checksumResponse\030\003 \001(\0132\035.OpBlockChecksum" +
+      "\020checksumResponse\030\003 \001(\0132\035.OpBlockChecksu" +
-      "ResponseProto\"0\n\025ClientReadStatusProto\022\027" +
+      "mResponseProto\022\017\n\007message\030\004 \001(\t\"0\n\025Clien" +
-      "\n\006status\030\001 \002(\0162\007.Status\"-\n\022DNTransferAck" +
+      "tReadStatusProto\022\027\n\006status\030\001 \002(\0162\007.Statu" +
-      "Proto\022\027\n\006status\030\001 \002(\0162\007.Status\"U\n\034OpBloc",
+      "s\"-\n\022DNTransferAckProto\022\027\n\006status\030\001 \002(\0162",
-      "kChecksumResponseProto\022\023\n\013bytesPerCrc\030\001 " +
+      "\007.Status\"U\n\034OpBlockChecksumResponseProto" +
-      "\002(\r\022\023\n\013crcPerBlock\030\002 \002(\004\022\013\n\003md5\030\003 \002(\014*\202\001" +
+      "\022\023\n\013bytesPerCrc\030\001 \002(\r\022\023\n\013crcPerBlock\030\002 \002" +
-      "\n\006Status\022\013\n\007SUCCESS\020\000\022\t\n\005ERROR\020\001\022\022\n\016ERRO" +
+      "(\004\022\013\n\003md5\030\003 \002(\014*\202\001\n\006Status\022\013\n\007SUCCESS\020\000\022" +
-      "R_CHECKSUM\020\002\022\021\n\rERROR_INVALID\020\003\022\020\n\014ERROR" +
+      "\t\n\005ERROR\020\001\022\022\n\016ERROR_CHECKSUM\020\002\022\021\n\rERROR_" +
-      "_EXISTS\020\004\022\026\n\022ERROR_ACCESS_TOKEN\020\005\022\017\n\013CHE" +
+      "INVALID\020\003\022\020\n\014ERROR_EXISTS\020\004\022\026\n\022ERROR_ACC" +
-      "CKSUM_OK\020\006B>\n%org.apache.hadoop.hdfs.pro" +
+      "ESS_TOKEN\020\005\022\017\n\013CHECKSUM_OK\020\006B>\n%org.apac" +
-      "tocol.protoB\022DataTransferProtos\240\001\001"
+      "he.hadoop.hdfs.protocol.protoB\022DataTrans" +
+      "ferProtos\240\001\001"
     };
     com.google.protobuf.Descriptors.FileDescriptor.InternalDescriptorAssigner assigner =
       new com.google.protobuf.Descriptors.FileDescriptor.InternalDescriptorAssigner() {
@@ -9099,7 +9202,7 @@ public com.google.protobuf.ExtensionRegistry assignDescriptors(
           internal_static_BlockOpResponseProto_fieldAccessorTable = new
             com.google.protobuf.GeneratedMessage.FieldAccessorTable(
               internal_static_BlockOpResponseProto_descriptor,
-              new java.lang.String[] { "Status", "FirstBadLink", "ChecksumResponse", },
+              new java.lang.String[] { "Status", "FirstBadLink", "ChecksumResponse", "Message", },
               org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.BlockOpResponseProto.class,
               org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.BlockOpResponseProto.Builder.class);
           internal_static_ClientReadStatusProto_descriptor =

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/balancer/Balancer.java

@@ -358,7 +358,8 @@ private void receiveResponse(DataInputStream in) throws IOException {
       if (response.getStatus() != Status.SUCCESS) {
         if (response.getStatus() == Status.ERROR_ACCESS_TOKEN)
           throw new IOException("block move failed due to access token error");
-        throw new IOException("block move is failed");
+        throw new IOException("block move is failed: " +
+            response.getMessage());
       }
     }
 

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataXceiver.java

@@ -48,6 +48,8 @@
 import org.apache.hadoop.hdfs.protocol.datatransfer.Receiver;
 import org.apache.hadoop.hdfs.protocol.datatransfer.Sender;
 import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.BlockOpResponseProto;
+import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.BlockOpResponseProto.Builder;
+import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.BlockOpResponseProtoOrBuilder;
 import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.ClientReadStatusProto;
 import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.OpBlockChecksumResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.Status;
@@ -225,13 +227,14 @@ public void readBlock(final ExtendedBlock block,
         blockSender = new BlockSender(block, blockOffset, length,
             true, true, false, datanode, clientTraceFmt);
       } catch(IOException e) {
-        LOG.info("opReadBlock " + block + " received exception " + e);
+        String msg = "opReadBlock " + block + " received exception " + e; 
-        sendResponse(s, ERROR, datanode.socketWriteTimeout);
+        LOG.info(msg);
+        sendResponse(s, ERROR, msg, datanode.socketWriteTimeout);
         throw e;
       }
       
       // send op status
-      sendResponse(s, SUCCESS, datanode.socketWriteTimeout);
+      sendResponse(s, SUCCESS, null, datanode.socketWriteTimeout);
 
       long read = blockSender.sendBlock(out, baseStream, null); // send data
 
@@ -452,7 +455,7 @@ public void writeBlock(final ExtendedBlock block,
           if (LOG.isTraceEnabled()) {
             LOG.trace("TRANSFER: send close-ack");
           }
-          writeResponse(SUCCESS, replyOut);
+          writeResponse(SUCCESS, null, replyOut);
         }
       }
 
@@ -507,7 +510,7 @@ public void transferBlock(final ExtendedBlock blk,
         NetUtils.getOutputStream(s, datanode.socketWriteTimeout));
     try {
       datanode.transferReplicaForPipelineRecovery(blk, targets, clientName);
-      writeResponse(Status.SUCCESS, out);
+      writeResponse(Status.SUCCESS, null, out);
     } finally {
       IOUtils.closeStream(out);
     }
@@ -577,16 +580,17 @@ public void copyBlock(final ExtendedBlock block,
         LOG.warn("Invalid access token in request from " + remoteAddress
             + " for OP_COPY_BLOCK for block " + block + " : "
             + e.getLocalizedMessage());
-        sendResponse(s, ERROR_ACCESS_TOKEN, datanode.socketWriteTimeout);
+        sendResponse(s, ERROR_ACCESS_TOKEN, "Invalid access token", datanode.socketWriteTimeout);
         return;
       }
 
     }
 
     if (!dataXceiverServer.balanceThrottler.acquire()) { // not able to start
-      LOG.info("Not able to copy block " + block.getBlockId() + " to " 
+      String msg = "Not able to copy block " + block.getBlockId() + " to " 
-          + s.getRemoteSocketAddress() + " because threads quota is exceeded.");
+      + s.getRemoteSocketAddress() + " because threads quota is exceeded."; 
-      sendResponse(s, ERROR, datanode.socketWriteTimeout);
+      LOG.info(msg);
+      sendResponse(s, ERROR, msg, datanode.socketWriteTimeout);
       return;
     }
 
@@ -606,7 +610,7 @@ public void copyBlock(final ExtendedBlock block,
           baseStream, HdfsConstants.SMALL_BUFFER_SIZE));
 
       // send status first
-      writeResponse(SUCCESS, reply);
+      writeResponse(SUCCESS, null, reply);
       // send block content to the target
       long read = blockSender.sendBlock(reply, baseStream, 
                                         dataXceiverServer.balanceThrottler);
@@ -653,21 +657,24 @@ public void replaceBlock(final ExtendedBlock block,
         LOG.warn("Invalid access token in request from " + remoteAddress
             + " for OP_REPLACE_BLOCK for block " + block + " : "
             + e.getLocalizedMessage());
-        sendResponse(s, ERROR_ACCESS_TOKEN, datanode.socketWriteTimeout);
+        sendResponse(s, ERROR_ACCESS_TOKEN, "Invalid access token",
+            datanode.socketWriteTimeout);
         return;
       }
     }
 
     if (!dataXceiverServer.balanceThrottler.acquire()) { // not able to start
-      LOG.warn("Not able to receive block " + block.getBlockId() + " from " 
+      String msg = "Not able to receive block " + block.getBlockId() + " from " 
-          + s.getRemoteSocketAddress() + " because threads quota is exceeded.");
+          + s.getRemoteSocketAddress() + " because threads quota is exceeded."; 
-      sendResponse(s, ERROR, datanode.socketWriteTimeout);
+      LOG.warn(msg);
+      sendResponse(s, ERROR, msg, datanode.socketWriteTimeout);
       return;
     }
 
     Socket proxySock = null;
     DataOutputStream proxyOut = null;
     Status opStatus = SUCCESS;
+    String errMsg = null;
     BlockReceiver blockReceiver = null;
     DataInputStream proxyReply = null;
     
@@ -720,7 +727,8 @@ public void replaceBlock(final ExtendedBlock block,
       
     } catch (IOException ioe) {
       opStatus = ERROR;
-      LOG.info("opReplaceBlock " + block + " received exception " + ioe);
+      errMsg = "opReplaceBlock " + block + " received exception " + ioe; 
+      LOG.info(errMsg);
       throw ioe;
     } finally {
       // receive the last byte that indicates the proxy released its thread resource
@@ -736,7 +744,7 @@ public void replaceBlock(final ExtendedBlock block,
       
       // send response back
       try {
-        sendResponse(s, opStatus, datanode.socketWriteTimeout);
+        sendResponse(s, opStatus, errMsg, datanode.socketWriteTimeout);
       } catch (IOException ioe) {
         LOG.warn("Error writing reply back to " + s.getRemoteSocketAddress());
       }
@@ -759,21 +767,22 @@ private long elapsed() {
    * @param opStatus status message to write
    * @param timeout send timeout
    **/
-  private void sendResponse(Socket s, Status status,
+  private void sendResponse(Socket s, Status status, String message,
       long timeout) throws IOException {
     DataOutputStream reply = 
       new DataOutputStream(NetUtils.getOutputStream(s, timeout));
     
-    writeResponse(status, reply);
+    writeResponse(status, message, reply);
   }
   
-  private void writeResponse(Status status, OutputStream out)
+  private void writeResponse(Status status, String message, OutputStream out)
   throws IOException {
-    BlockOpResponseProto response = BlockOpResponseProto.newBuilder()
+    BlockOpResponseProto.Builder response = BlockOpResponseProto.newBuilder()
-      .setStatus(status)
+      .setStatus(status);
-      .build();
+    if (message != null) {
-    
+      response.setMessage(message);
-    response.writeDelimitedTo(out);
+    }
+    response.build().writeDelimitedTo(out);
     out.flush();
   }
   

hadoop-hdfs-project/hadoop-hdfs/src/proto/datatransfer.proto

@@ -119,6 +119,9 @@ message BlockOpResponseProto {
 
   optional string firstBadLink = 2;
   optional OpBlockChecksumResponseProto checksumResponse = 3;
+
+  /** explanatory text which may be useful to log on the client side */
+  optional string message = 4;
 }
 
 /**

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestDataTransferProtocol.java

@@ -117,10 +117,8 @@ private void sendRecvData(String testDescription,
         throw eof;
       }
 
-      LOG.info("Received: " +
+      LOG.info("Received: " +new String(retBuf));
-          StringUtils.byteToHexString(retBuf));
+      LOG.info("Expected: " + StringUtils.byteToHexString(recvBuf.toByteArray()));
-      LOG.info("Expected: " +
-          StringUtils.byteToHexString(recvBuf.toByteArray()));
       
       if (eofExpected) {
         throw new IOException("Did not recieve IOException when an exception " +
@@ -129,10 +127,8 @@ private void sendRecvData(String testDescription,
       }
       
       byte[] needed = recvBuf.toByteArray();
-      for (int i=0; i<retBuf.length; i++) {
+      assertEquals(StringUtils.byteToHexString(needed),
-        System.out.print(retBuf[i]);
+          StringUtils.byteToHexString(retBuf));
-        assertEquals("checking byte[" + i + "]", needed[i], retBuf[i]);
-      }
     } finally {
       IOUtils.closeSocket(sock);
     }
@@ -166,18 +162,22 @@ private void writeZeroLengthPacket(ExtendedBlock block, String description)
     sendOut.writeInt(0);           // zero checksum
 
     //ok finally write a block with 0 len
-    sendResponse(Status.SUCCESS, "", recvOut);
+    sendResponse(Status.SUCCESS, "", null, recvOut);
     new PipelineAck(100, new Status[]{Status.SUCCESS}).write(recvOut);
     sendRecvData(description, false);
   }
   
   private void sendResponse(Status status, String firstBadLink,
+      String message,
       DataOutputStream out)
   throws IOException {
     Builder builder = BlockOpResponseProto.newBuilder().setStatus(status);
     if (firstBadLink != null) {
       builder.setFirstBadLink(firstBadLink);
     }
+    if (message != null) {
+      builder.setMessage(message);
+    }
     builder.build()
       .writeDelimitedTo(out);
   }
@@ -190,11 +190,11 @@ private void testWrite(ExtendedBlock block, BlockConstructionStage stage, long n
         new DatanodeInfo[1], null, stage,
         0, block.getNumBytes(), block.getNumBytes(), newGS);
     if (eofExcepted) {
-      sendResponse(Status.ERROR, null, recvOut);
+      sendResponse(Status.ERROR, null, null, recvOut);
       sendRecvData(description, true);
     } else if (stage == BlockConstructionStage.PIPELINE_CLOSE_RECOVERY) {
       //ok finally write a block with 0 len
-      sendResponse(Status.SUCCESS, "", recvOut);
+      sendResponse(Status.SUCCESS, "", null, recvOut);
       sendRecvData(description, false);
     } else {
       writeZeroLengthPacket(block, description);
@@ -383,7 +383,7 @@ private void testWrite(ExtendedBlock block, BlockConstructionStage stage, long n
     // bad bytes per checksum
     sendOut.writeInt(-1-random.nextInt(oneMil));
     recvBuf.reset();
-    sendResponse(Status.ERROR, null, recvOut);
+    sendResponse(Status.ERROR, null, null, recvOut);
     sendRecvData("wrong bytesPerChecksum while writing", true);
 
     sendBuf.reset();
@@ -403,7 +403,7 @@ private void testWrite(ExtendedBlock block, BlockConstructionStage stage, long n
       -1 - random.nextInt(oneMil)); // bad datalen
     hdr.write(sendOut);
 
-    sendResponse(Status.SUCCESS, "", recvOut);
+    sendResponse(Status.SUCCESS, "", null, recvOut);
     new PipelineAck(100, new Status[]{Status.ERROR}).write(recvOut);
     sendRecvData("negative DATA_CHUNK len while writing block " + newBlockId, 
                  true);
@@ -428,7 +428,7 @@ private void testWrite(ExtendedBlock block, BlockConstructionStage stage, long n
     sendOut.writeInt(0);           // zero checksum
     sendOut.flush();
     //ok finally write a block with 0 len
-    sendResponse(Status.SUCCESS, "", recvOut);
+    sendResponse(Status.SUCCESS, "", null, recvOut);
     new PipelineAck(100, new Status[]{Status.SUCCESS}).write(recvOut);
     sendRecvData("Writing a zero len block blockid " + newBlockId, false);
     
@@ -462,7 +462,7 @@ private void testWrite(ExtendedBlock block, BlockConstructionStage stage, long n
     
     // negative length is ok. Datanode assumes we want to read the whole block.
     recvBuf.reset();
-    sendResponse(Status.SUCCESS, null, recvOut);
+    sendResponse(Status.SUCCESS, null, null, recvOut);
     sendBuf.reset();
     sender.readBlock(blk, BlockTokenSecretManager.DUMMY_TOKEN, "cl",
         0L, -1L-random.nextInt(oneMil));
@@ -471,7 +471,11 @@ private void testWrite(ExtendedBlock block, BlockConstructionStage stage, long n
     
     // length is more than size of block.
     recvBuf.reset();
-    sendResponse(Status.ERROR, null, recvOut);
+    sendResponse(Status.ERROR, null,
+        "opReadBlock " + firstBlock +
+        " received exception java.io.IOException:  " +
+        "Offset 0 and length 4097 don't match block " + firstBlock + " ( blockLen 4096 )",
+        recvOut);
     sendBuf.reset();
     sender.readBlock(blk, BlockTokenSecretManager.DUMMY_TOKEN, "cl",
         0L, fileLen+1);