/**
 * 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.hdfs.server.datanode;

import static org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.Status.ERROR;
import static org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.Status.ERROR_ACCESS_TOKEN;
import static org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.Status.SUCCESS;
import static org.apache.hadoop.hdfs.server.common.Util.now;
import static org.apache.hadoop.hdfs.server.datanode.DataNode.DN_CLIENTTRACE_FORMAT;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketException;
import java.nio.channels.ClosedChannelException;
import java.util.Arrays;

import org.apache.commons.logging.Log;
import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
import org.apache.hadoop.hdfs.protocol.HdfsConstants;
import org.apache.hadoop.hdfs.protocol.HdfsProtoUtil;
import org.apache.hadoop.hdfs.protocol.datatransfer.BlockConstructionStage;
import org.apache.hadoop.hdfs.protocol.datatransfer.DataTransferProtoUtil;
import org.apache.hadoop.hdfs.protocol.datatransfer.Op;
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.ClientReadStatusProto;
import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.OpBlockChecksumResponseProto;
import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.ReadOpChecksumInfoProto;
import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.Status;
import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
import org.apache.hadoop.hdfs.security.token.block.BlockTokenSecretManager;
import org.apache.hadoop.hdfs.server.common.HdfsServerConstants;
import org.apache.hadoop.hdfs.server.datanode.fsdataset.LengthInputStream;
import org.apache.hadoop.hdfs.server.protocol.DatanodeRegistration;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.MD5Hash;
import org.apache.hadoop.net.NetUtils;
import org.apache.hadoop.net.SocketInputWrapper;
import org.apache.hadoop.security.token.SecretManager.InvalidToken;
import org.apache.hadoop.security.token.Token;
import org.apache.hadoop.util.DataChecksum;

import com.google.protobuf.ByteString;


/**
 * Thread for processing incoming/outgoing data stream.
 */
class DataXceiver extends Receiver implements Runnable {
  public static final Log LOG = DataNode.LOG;
  static final Log ClientTraceLog = DataNode.ClientTraceLog;
  
  private final Socket s;
  private final boolean isLocal; //is a local connection?
  private final String remoteAddress; // address of remote side
  private final String localAddress;  // local address of this daemon
  private final DataNode datanode;
  private final DNConf dnConf;
  private final DataXceiverServer dataXceiverServer;

  private long opStartTime; //the start time of receiving an Op
  private final SocketInputWrapper socketInputWrapper;

  /**
   * Client Name used in previous operation. Not available on first request
   * on the socket.
   */
  private String previousOpClientName;
  
  public static DataXceiver create(Socket s, DataNode dn,
      DataXceiverServer dataXceiverServer) throws IOException {
    
    SocketInputWrapper iw = NetUtils.getInputStream(s);
    return new DataXceiver(s, iw, dn, dataXceiverServer);
  }
  
  private DataXceiver(Socket s, 
      SocketInputWrapper socketInput,
      DataNode datanode, 
      DataXceiverServer dataXceiverServer) throws IOException {
    super(new DataInputStream(new BufferedInputStream(
        socketInput, HdfsConstants.SMALL_BUFFER_SIZE)));

    this.s = s;
    this.socketInputWrapper = socketInput;
    this.isLocal = s.getInetAddress().equals(s.getLocalAddress());
    this.datanode = datanode;
    this.dnConf = datanode.getDnConf();
    this.dataXceiverServer = dataXceiverServer;
    remoteAddress = s.getRemoteSocketAddress().toString();
    localAddress = s.getLocalSocketAddress().toString();

    if (LOG.isDebugEnabled()) {
      LOG.debug("Number of active connections is: "
          + datanode.getXceiverCount());
    }
  }

  /**
   * Update the current thread's name to contain the current status.
   * Use this only after this receiver has started on its thread, i.e.,
   * outside the constructor.
   */
  private void updateCurrentThreadName(String status) {
    StringBuilder sb = new StringBuilder();
    sb.append("DataXceiver for client ");
    if (previousOpClientName != null) {
      sb.append(previousOpClientName).append(" at ");
    }
    sb.append(remoteAddress);
    if (status != null) {
      sb.append(" [").append(status).append("]");
    }
    Thread.currentThread().setName(sb.toString());
  }

  /** Return the datanode object. */
  DataNode getDataNode() {return datanode;}

  /**
   * Read/write data from/to the DataXceiverServer.
   */
  public void run() {
    int opsProcessed = 0;
    Op op = null;
    dataXceiverServer.childSockets.add(s);
    try {
      // We process requests in a loop, and stay around for a short timeout.
      // This optimistic behaviour allows the other end to reuse connections.
      // Setting keepalive timeout to 0 disable this behavior.
      do {
        updateCurrentThreadName("Waiting for operation #" + (opsProcessed + 1));

        try {
          if (opsProcessed != 0) {
            assert dnConf.socketKeepaliveTimeout > 0;
            socketInputWrapper.setTimeout(dnConf.socketKeepaliveTimeout);
          } else {
            socketInputWrapper.setTimeout(dnConf.socketTimeout);
          }
          op = readOp();
        } catch (InterruptedIOException ignored) {
          // Time out while we wait for client rpc
          break;
        } catch (IOException err) {
          // Since we optimistically expect the next op, it's quite normal to get EOF here.
          if (opsProcessed > 0 &&
              (err instanceof EOFException || err instanceof ClosedChannelException)) {
            if (LOG.isDebugEnabled()) {
              LOG.debug("Cached " + s.toString() + " closing after " + opsProcessed + " ops");
            }
          } else {
            throw err;
          }
          break;
        }

        // restore normal timeout
        if (opsProcessed != 0) {
          s.setSoTimeout(dnConf.socketTimeout);
        }

        opStartTime = now();
        processOp(op);
        ++opsProcessed;
      } while (!s.isClosed() && dnConf.socketKeepaliveTimeout > 0);
    } catch (Throwable t) {
      LOG.error(datanode.getDisplayName() + ":DataXceiver error processing " +
                ((op == null) ? "unknown" : op.name()) + " operation " +
                " src: " + remoteAddress +
                " dest: " + localAddress, t);
    } finally {
      if (LOG.isDebugEnabled()) {
        LOG.debug(datanode.getDisplayName() + ":Number of active connections is: "
            + datanode.getXceiverCount());
      }
      updateCurrentThreadName("Cleaning up");
      IOUtils.closeStream(in);
      IOUtils.closeSocket(s);
      dataXceiverServer.childSockets.remove(s);
    }
  }

  @Override
  public void readBlock(final ExtendedBlock block,
      final Token<BlockTokenIdentifier> blockToken,
      final String clientName,
      final long blockOffset,
      final long length) throws IOException {
    previousOpClientName = clientName;

    OutputStream baseStream = NetUtils.getOutputStream(s, 
        dnConf.socketWriteTimeout);
    DataOutputStream out = new DataOutputStream(new BufferedOutputStream(
        baseStream, HdfsConstants.SMALL_BUFFER_SIZE));
    checkAccess(out, true, block, blockToken,
        Op.READ_BLOCK, BlockTokenSecretManager.AccessMode.READ);
  
    // send the block
    BlockSender blockSender = null;
    DatanodeRegistration dnR = 
      datanode.getDNRegistrationForBP(block.getBlockPoolId());
    final String clientTraceFmt =
      clientName.length() > 0 && ClientTraceLog.isInfoEnabled()
        ? String.format(DN_CLIENTTRACE_FORMAT, localAddress, remoteAddress,
            "%d", "HDFS_READ", clientName, "%d",
            dnR.getStorageID(), block, "%d")
        : dnR + " Served block " + block + " to " +
            remoteAddress;

    updateCurrentThreadName("Sending block " + block);
    try {
      try {
        blockSender = new BlockSender(block, blockOffset, length,
            true, false, datanode, clientTraceFmt);
      } catch(IOException e) {
        String msg = "opReadBlock " + block + " received exception " + e; 
        LOG.info(msg);
        sendResponse(s, ERROR, msg, dnConf.socketWriteTimeout);
        throw e;
      }
      
      // send op status
      writeSuccessWithChecksumInfo(blockSender,
          getStreamWithTimeout(s, dnConf.socketWriteTimeout));

      long read = blockSender.sendBlock(out, baseStream, null); // send data

      if (blockSender.didSendEntireByteRange()) {
        // If we sent the entire range, then we should expect the client
        // to respond with a Status enum.
        try {
          ClientReadStatusProto stat = ClientReadStatusProto.parseFrom(
              HdfsProtoUtil.vintPrefixed(in));
          if (!stat.hasStatus()) {
            LOG.warn("Client " + s.getInetAddress() + " did not send a valid status " +
                     "code after reading. Will close connection.");
            IOUtils.closeStream(out);
          }
        } catch (IOException ioe) {
          LOG.debug("Error reading client status response. Will close connection.", ioe);
          IOUtils.closeStream(out);
        }
      } else {
        IOUtils.closeStream(out);
      }
      datanode.metrics.incrBytesRead((int) read);
      datanode.metrics.incrBlocksRead();
    } catch ( SocketException ignored ) {
      if (LOG.isTraceEnabled()) {
        LOG.trace(dnR + ":Ignoring exception while serving " + block + " to " +
            remoteAddress, ignored);
      }
      // Its ok for remote side to close the connection anytime.
      datanode.metrics.incrBlocksRead();
      IOUtils.closeStream(out);
    } catch ( IOException ioe ) {
      /* What exactly should we do here?
       * Earlier version shutdown() datanode if there is disk error.
       */
      LOG.warn(dnR + ":Got exception while serving " + block + " to "
          + remoteAddress, ioe);
      throw ioe;
    } finally {
      IOUtils.closeStream(blockSender);
    }

    //update metrics
    datanode.metrics.addReadBlockOp(elapsed());
    datanode.metrics.incrReadsFromClient(isLocal);
  }

  @Override
  public void writeBlock(final ExtendedBlock block,
      final Token<BlockTokenIdentifier> blockToken,
      final String clientname,
      final DatanodeInfo[] targets,
      final DatanodeInfo srcDataNode,
      final BlockConstructionStage stage,
      final int pipelineSize,
      final long minBytesRcvd,
      final long maxBytesRcvd,
      final long latestGenerationStamp,
      DataChecksum requestedChecksum) throws IOException {
    previousOpClientName = clientname;
    updateCurrentThreadName("Receiving block " + block);
    final boolean isDatanode = clientname.length() == 0;
    final boolean isClient = !isDatanode;
    final boolean isTransfer = stage == BlockConstructionStage.TRANSFER_RBW
        || stage == BlockConstructionStage.TRANSFER_FINALIZED;

    // check single target for transfer-RBW/Finalized 
    if (isTransfer && targets.length > 0) {
      throw new IOException(stage + " does not support multiple targets "
          + Arrays.asList(targets));
    }

    if (LOG.isDebugEnabled()) {
      LOG.debug("opWriteBlock: stage=" + stage + ", clientname=" + clientname 
      		+ "\n  block  =" + block + ", newGs=" + latestGenerationStamp
      		+ ", bytesRcvd=[" + minBytesRcvd + ", " + maxBytesRcvd + "]"
          + "\n  targets=" + Arrays.asList(targets)
          + "; pipelineSize=" + pipelineSize + ", srcDataNode=" + srcDataNode
          );
      LOG.debug("isDatanode=" + isDatanode
          + ", isClient=" + isClient
          + ", isTransfer=" + isTransfer);
      LOG.debug("writeBlock receive buf size " + s.getReceiveBufferSize() +
                " tcp no delay " + s.getTcpNoDelay());
    }

    // We later mutate block's generation stamp and length, but we need to
    // forward the original version of the block to downstream mirrors, so
    // make a copy here.
    final ExtendedBlock originalBlock = new ExtendedBlock(block);
    block.setNumBytes(dataXceiverServer.estimateBlockSize);
    LOG.info("Receiving block " + block + 
             " src: " + remoteAddress +
             " dest: " + localAddress);

    // reply to upstream datanode or client 
    final DataOutputStream replyOut = new DataOutputStream(
        new BufferedOutputStream(
            NetUtils.getOutputStream(s, dnConf.socketWriteTimeout),
            HdfsConstants.SMALL_BUFFER_SIZE));
    checkAccess(replyOut, isClient, block, blockToken,
        Op.WRITE_BLOCK, BlockTokenSecretManager.AccessMode.WRITE);

    DataOutputStream mirrorOut = null;  // stream to next target
    DataInputStream mirrorIn = null;    // reply from next target
    Socket mirrorSock = null;           // socket to next target
    BlockReceiver blockReceiver = null; // responsible for data handling
    String mirrorNode = null;           // the name:port of next target
    String firstBadLink = "";           // first datanode that failed in connection setup
    Status mirrorInStatus = SUCCESS;
    try {
      if (isDatanode || 
          stage != BlockConstructionStage.PIPELINE_CLOSE_RECOVERY) {
        // open a block receiver
        blockReceiver = new BlockReceiver(block, in, 
            s.getRemoteSocketAddress().toString(),
            s.getLocalSocketAddress().toString(),
            stage, latestGenerationStamp, minBytesRcvd, maxBytesRcvd,
            clientname, srcDataNode, datanode, requestedChecksum);
      } else {
        datanode.data.recoverClose(block, latestGenerationStamp, minBytesRcvd);
      }

      //
      // Connect to downstream machine, if appropriate
      //
      if (targets.length > 0) {
        InetSocketAddress mirrorTarget = null;
        // Connect to backup machine
        mirrorNode = targets[0].getXferAddr();
        mirrorTarget = NetUtils.createSocketAddr(mirrorNode);
        mirrorSock = datanode.newSocket();
        try {
          int timeoutValue = dnConf.socketTimeout
              + (HdfsServerConstants.READ_TIMEOUT_EXTENSION * targets.length);
          int writeTimeout = dnConf.socketWriteTimeout + 
                      (HdfsServerConstants.WRITE_TIMEOUT_EXTENSION * targets.length);
          NetUtils.connect(mirrorSock, mirrorTarget, timeoutValue);
          mirrorSock.setSoTimeout(timeoutValue);
          mirrorSock.setSendBufferSize(HdfsConstants.DEFAULT_DATA_SOCKET_SIZE);
          mirrorOut = new DataOutputStream(
             new BufferedOutputStream(
                         NetUtils.getOutputStream(mirrorSock, writeTimeout),
                         HdfsConstants.SMALL_BUFFER_SIZE));
          mirrorIn = new DataInputStream(NetUtils.getInputStream(mirrorSock));

          new Sender(mirrorOut).writeBlock(originalBlock, blockToken,
              clientname, targets, srcDataNode, stage, pipelineSize,
              minBytesRcvd, maxBytesRcvd, latestGenerationStamp, requestedChecksum);

          mirrorOut.flush();

          // read connect ack (only for clients, not for replication req)
          if (isClient) {
            BlockOpResponseProto connectAck =
              BlockOpResponseProto.parseFrom(HdfsProtoUtil.vintPrefixed(mirrorIn));
            mirrorInStatus = connectAck.getStatus();
            firstBadLink = connectAck.getFirstBadLink();
            if (LOG.isDebugEnabled() || mirrorInStatus != SUCCESS) {
              LOG.info("Datanode " + targets.length +
                       " got response for connect ack " +
                       " from downstream datanode with firstbadlink as " +
                       firstBadLink);
            }
          }

        } catch (IOException e) {
          if (isClient) {
            BlockOpResponseProto.newBuilder()
              .setStatus(ERROR)
              .setFirstBadLink(mirrorNode)
              .build()
              .writeDelimitedTo(replyOut);
            replyOut.flush();
          }
          IOUtils.closeStream(mirrorOut);
          mirrorOut = null;
          IOUtils.closeStream(mirrorIn);
          mirrorIn = null;
          IOUtils.closeSocket(mirrorSock);
          mirrorSock = null;
          if (isClient) {
            LOG.error(datanode + ":Exception transfering block " +
                      block + " to mirror " + mirrorNode + ": " + e);
            throw e;
          } else {
            LOG.info(datanode + ":Exception transfering block " +
                     block + " to mirror " + mirrorNode +
                     ". continuing without the mirror.", e);
          }
        }
      }

      // send connect-ack to source for clients and not transfer-RBW/Finalized
      if (isClient && !isTransfer) {
        if (LOG.isDebugEnabled() || mirrorInStatus != SUCCESS) {
          LOG.info("Datanode " + targets.length +
                   " forwarding connect ack to upstream firstbadlink is " +
                   firstBadLink);
        }
        BlockOpResponseProto.newBuilder()
          .setStatus(mirrorInStatus)
          .setFirstBadLink(firstBadLink)
          .build()
          .writeDelimitedTo(replyOut);
        replyOut.flush();
      }

      // receive the block and mirror to the next target
      if (blockReceiver != null) {
        String mirrorAddr = (mirrorSock == null) ? null : mirrorNode;
        blockReceiver.receiveBlock(mirrorOut, mirrorIn, replyOut,
            mirrorAddr, null, targets);

        // send close-ack for transfer-RBW/Finalized 
        if (isTransfer) {
          if (LOG.isTraceEnabled()) {
            LOG.trace("TRANSFER: send close-ack");
          }
          writeResponse(SUCCESS, null, replyOut);
        }
      }

      // update its generation stamp
      if (isClient && 
          stage == BlockConstructionStage.PIPELINE_CLOSE_RECOVERY) {
        block.setGenerationStamp(latestGenerationStamp);
        block.setNumBytes(minBytesRcvd);
      }
      
      // if this write is for a replication request or recovering
      // a failed close for client, then confirm block. For other client-writes,
      // the block is finalized in the PacketResponder.
      if (isDatanode ||
          stage == BlockConstructionStage.PIPELINE_CLOSE_RECOVERY) {
        datanode.closeBlock(block, DataNode.EMPTY_DEL_HINT);
        LOG.info("Received block " + block + 
                 " src: " + remoteAddress +
                 " dest: " + localAddress +
                 " of size " + block.getNumBytes());
      }

      
    } catch (IOException ioe) {
      LOG.info("opWriteBlock " + block + " received exception " + ioe);
      throw ioe;
    } finally {
      // close all opened streams
      IOUtils.closeStream(mirrorOut);
      IOUtils.closeStream(mirrorIn);
      IOUtils.closeStream(replyOut);
      IOUtils.closeSocket(mirrorSock);
      IOUtils.closeStream(blockReceiver);
    }

    //update metrics
    datanode.metrics.addWriteBlockOp(elapsed());
    datanode.metrics.incrWritesFromClient(isLocal);
  }

  @Override
  public void transferBlock(final ExtendedBlock blk,
      final Token<BlockTokenIdentifier> blockToken,
      final String clientName,
      final DatanodeInfo[] targets) throws IOException {
    checkAccess(null, true, blk, blockToken,
        Op.TRANSFER_BLOCK, BlockTokenSecretManager.AccessMode.COPY);
    previousOpClientName = clientName;
    updateCurrentThreadName(Op.TRANSFER_BLOCK + " " + blk);

    final DataOutputStream out = new DataOutputStream(
        NetUtils.getOutputStream(s, dnConf.socketWriteTimeout));
    try {
      datanode.transferReplicaForPipelineRecovery(blk, targets, clientName);
      writeResponse(Status.SUCCESS, null, out);
    } finally {
      IOUtils.closeStream(out);
    }
  }
  
  @Override
  public void blockChecksum(final ExtendedBlock block,
      final Token<BlockTokenIdentifier> blockToken) throws IOException {
    final DataOutputStream out = new DataOutputStream(
        NetUtils.getOutputStream(s, dnConf.socketWriteTimeout));
    checkAccess(out, true, block, blockToken,
        Op.BLOCK_CHECKSUM, BlockTokenSecretManager.AccessMode.READ);
    updateCurrentThreadName("Reading metadata for block " + block);
    final LengthInputStream metadataIn = 
      datanode.data.getMetaDataInputStream(block);
    final DataInputStream checksumIn = new DataInputStream(new BufferedInputStream(
        metadataIn, HdfsConstants.IO_FILE_BUFFER_SIZE));

    updateCurrentThreadName("Getting checksum for block " + block);
    try {
      //read metadata file
      final BlockMetadataHeader header = BlockMetadataHeader.readHeader(checksumIn);
      final DataChecksum checksum = header.getChecksum(); 
      final int bytesPerCRC = checksum.getBytesPerChecksum();
      final long crcPerBlock = (metadataIn.getLength()
          - BlockMetadataHeader.getHeaderSize())/checksum.getChecksumSize();
      
      //compute block checksum
      final MD5Hash md5 = MD5Hash.digest(checksumIn);

      if (LOG.isDebugEnabled()) {
        LOG.debug("block=" + block + ", bytesPerCRC=" + bytesPerCRC
            + ", crcPerBlock=" + crcPerBlock + ", md5=" + md5);
      }

      //write reply
      BlockOpResponseProto.newBuilder()
        .setStatus(SUCCESS)
        .setChecksumResponse(OpBlockChecksumResponseProto.newBuilder()             
          .setBytesPerCrc(bytesPerCRC)
          .setCrcPerBlock(crcPerBlock)
          .setMd5(ByteString.copyFrom(md5.getDigest()))
          )
        .build()
        .writeDelimitedTo(out);
      out.flush();
    } finally {
      IOUtils.closeStream(out);
      IOUtils.closeStream(checksumIn);
      IOUtils.closeStream(metadataIn);
    }

    //update metrics
    datanode.metrics.addBlockChecksumOp(elapsed());
  }

  @Override
  public void copyBlock(final ExtendedBlock block,
      final Token<BlockTokenIdentifier> blockToken) throws IOException {
    updateCurrentThreadName("Copying block " + block);
    // Read in the header
    if (datanode.isBlockTokenEnabled) {
      try {
        datanode.blockPoolTokenSecretManager.checkAccess(blockToken, null, block,
            BlockTokenSecretManager.AccessMode.COPY);
      } catch (InvalidToken e) {
        LOG.warn("Invalid access token in request from " + remoteAddress
            + " for OP_COPY_BLOCK for block " + block + " : "
            + e.getLocalizedMessage());
        sendResponse(s, ERROR_ACCESS_TOKEN, "Invalid access token", dnConf.socketWriteTimeout);
        return;
      }

    }

    if (!dataXceiverServer.balanceThrottler.acquire()) { // not able to start
      String msg = "Not able to copy block " + block.getBlockId() + " to " 
      + s.getRemoteSocketAddress() + " because threads quota is exceeded."; 
      LOG.info(msg);
      sendResponse(s, ERROR, msg, dnConf.socketWriteTimeout);
      return;
    }

    BlockSender blockSender = null;
    DataOutputStream reply = null;
    boolean isOpSuccess = true;

    try {
      // check if the block exists or not
      blockSender = new BlockSender(block, 0, -1, false, false, datanode, 
          null);

      // set up response stream
      OutputStream baseStream = NetUtils.getOutputStream(
          s, dnConf.socketWriteTimeout);
      reply = new DataOutputStream(new BufferedOutputStream(
          baseStream, HdfsConstants.SMALL_BUFFER_SIZE));

      // send status first
      writeSuccessWithChecksumInfo(blockSender, reply);
      // send block content to the target
      long read = blockSender.sendBlock(reply, baseStream, 
                                        dataXceiverServer.balanceThrottler);

      datanode.metrics.incrBytesRead((int) read);
      datanode.metrics.incrBlocksRead();
      
      LOG.info("Copied block " + block + " to " + s.getRemoteSocketAddress());
    } catch (IOException ioe) {
      isOpSuccess = false;
      LOG.info("opCopyBlock " + block + " received exception " + ioe);
      throw ioe;
    } finally {
      dataXceiverServer.balanceThrottler.release();
      if (isOpSuccess) {
        try {
          // send one last byte to indicate that the resource is cleaned.
          reply.writeChar('d');
        } catch (IOException ignored) {
        }
      }
      IOUtils.closeStream(reply);
      IOUtils.closeStream(blockSender);
    }

    //update metrics    
    datanode.metrics.addCopyBlockOp(elapsed());
  }

  @Override
  public void replaceBlock(final ExtendedBlock block,
      final Token<BlockTokenIdentifier> blockToken,
      final String delHint,
      final DatanodeInfo proxySource) throws IOException {
    updateCurrentThreadName("Replacing block " + block + " from " + delHint);

    /* read header */
    block.setNumBytes(dataXceiverServer.estimateBlockSize);
    if (datanode.isBlockTokenEnabled) {
      try {
        datanode.blockPoolTokenSecretManager.checkAccess(blockToken, null, block,
            BlockTokenSecretManager.AccessMode.REPLACE);
      } catch (InvalidToken e) {
        LOG.warn("Invalid access token in request from " + remoteAddress
            + " for OP_REPLACE_BLOCK for block " + block + " : "
            + e.getLocalizedMessage());
        sendResponse(s, ERROR_ACCESS_TOKEN, "Invalid access token",
            dnConf.socketWriteTimeout);
        return;
      }
    }

    if (!dataXceiverServer.balanceThrottler.acquire()) { // not able to start
      String msg = "Not able to receive block " + block.getBlockId() + " from " 
          + s.getRemoteSocketAddress() + " because threads quota is exceeded."; 
      LOG.warn(msg);
      sendResponse(s, ERROR, msg, dnConf.socketWriteTimeout);
      return;
    }

    Socket proxySock = null;
    DataOutputStream proxyOut = null;
    Status opStatus = SUCCESS;
    String errMsg = null;
    BlockReceiver blockReceiver = null;
    DataInputStream proxyReply = null;
    
    try {
      // get the output stream to the proxy
      InetSocketAddress proxyAddr =
        NetUtils.createSocketAddr(proxySource.getXferAddr());
      proxySock = datanode.newSocket();
      NetUtils.connect(proxySock, proxyAddr, dnConf.socketTimeout);
      proxySock.setSoTimeout(dnConf.socketTimeout);

      OutputStream baseStream = NetUtils.getOutputStream(proxySock, 
          dnConf.socketWriteTimeout);
      proxyOut = new DataOutputStream(new BufferedOutputStream(baseStream,
          HdfsConstants.SMALL_BUFFER_SIZE));

      /* send request to the proxy */
      new Sender(proxyOut).copyBlock(block, blockToken);

      // receive the response from the proxy
      proxyReply = new DataInputStream(new BufferedInputStream(
          NetUtils.getInputStream(proxySock), HdfsConstants.IO_FILE_BUFFER_SIZE));
      BlockOpResponseProto copyResponse = BlockOpResponseProto.parseFrom(
          HdfsProtoUtil.vintPrefixed(proxyReply));

      if (copyResponse.getStatus() != SUCCESS) {
        if (copyResponse.getStatus() == ERROR_ACCESS_TOKEN) {
          throw new IOException("Copy block " + block + " from "
              + proxySock.getRemoteSocketAddress()
              + " failed due to access token error");
        }
        throw new IOException("Copy block " + block + " from "
            + proxySock.getRemoteSocketAddress() + " failed");
      }
      
      // get checksum info about the block we're copying
      ReadOpChecksumInfoProto checksumInfo = copyResponse.getReadOpChecksumInfo();
      DataChecksum remoteChecksum = DataTransferProtoUtil.fromProto(
          checksumInfo.getChecksum());
      // open a block receiver and check if the block does not exist
      blockReceiver = new BlockReceiver(
          block, proxyReply, proxySock.getRemoteSocketAddress().toString(),
          proxySock.getLocalSocketAddress().toString(),
          null, 0, 0, 0, "", null, datanode, remoteChecksum);

      // receive a block
      blockReceiver.receiveBlock(null, null, null, null, 
          dataXceiverServer.balanceThrottler, null);
                    
      // notify name node
      datanode.notifyNamenodeReceivedBlock(block, delHint);

      LOG.info("Moved block " + block + 
          " from " + s.getRemoteSocketAddress());
      
    } catch (IOException ioe) {
      opStatus = ERROR;
      errMsg = "opReplaceBlock " + block + " received exception " + ioe; 
      LOG.info(errMsg);
      throw ioe;
    } finally {
      // receive the last byte that indicates the proxy released its thread resource
      if (opStatus == SUCCESS) {
        try {
          proxyReply.readChar();
        } catch (IOException ignored) {
        }
      }
      
      // now release the thread resource
      dataXceiverServer.balanceThrottler.release();
      
      // send response back
      try {
        sendResponse(s, opStatus, errMsg, dnConf.socketWriteTimeout);
      } catch (IOException ioe) {
        LOG.warn("Error writing reply back to " + s.getRemoteSocketAddress());
      }
      IOUtils.closeStream(proxyOut);
      IOUtils.closeStream(blockReceiver);
      IOUtils.closeStream(proxyReply);
    }

    //update metrics
    datanode.metrics.addReplaceBlockOp(elapsed());
  }

  private long elapsed() {
    return now() - opStartTime;
  }

  /**
   * Utility function for sending a response.
   * @param s socket to write to
   * @param opStatus status message to write
   * @param timeout send timeout
   **/
  private static void sendResponse(Socket s, Status status, String message,
      long timeout) throws IOException {
    DataOutputStream reply = getStreamWithTimeout(s, timeout);
    
    writeResponse(status, message, reply);
  }
  
  private static DataOutputStream getStreamWithTimeout(Socket s, long timeout)
      throws IOException {
    return new DataOutputStream(NetUtils.getOutputStream(s, timeout));
  }

  private static void writeResponse(Status status, String message, OutputStream out)
  throws IOException {
    BlockOpResponseProto.Builder response = BlockOpResponseProto.newBuilder()
      .setStatus(status);
    if (message != null) {
      response.setMessage(message);
    }
    response.build().writeDelimitedTo(out);
    out.flush();
  }
  
  private void writeSuccessWithChecksumInfo(BlockSender blockSender,
      DataOutputStream out) throws IOException {

    ReadOpChecksumInfoProto ckInfo = ReadOpChecksumInfoProto.newBuilder()
      .setChecksum(DataTransferProtoUtil.toProto(blockSender.getChecksum()))
      .setChunkOffset(blockSender.getOffset())
      .build();
      
    BlockOpResponseProto response = BlockOpResponseProto.newBuilder()
      .setStatus(SUCCESS)
      .setReadOpChecksumInfo(ckInfo)
      .build();
    response.writeDelimitedTo(out);
    out.flush();
  }
  

  private void checkAccess(DataOutputStream out, final boolean reply, 
      final ExtendedBlock blk,
      final Token<BlockTokenIdentifier> t,
      final Op op,
      final BlockTokenSecretManager.AccessMode mode) throws IOException {
    if (datanode.isBlockTokenEnabled) {
      if (LOG.isDebugEnabled()) {
        LOG.debug("Checking block access token for block '" + blk.getBlockId()
            + "' with mode '" + mode + "'");
      }
      try {
        datanode.blockPoolTokenSecretManager.checkAccess(t, null, blk, mode);
      } catch(InvalidToken e) {
        try {
          if (reply) {
            if (out == null) {
              out = new DataOutputStream(
                  NetUtils.getOutputStream(s, dnConf.socketWriteTimeout));
            }
            
            BlockOpResponseProto.Builder resp = BlockOpResponseProto.newBuilder()
              .setStatus(ERROR_ACCESS_TOKEN);
            if (mode == BlockTokenSecretManager.AccessMode.WRITE) {
              DatanodeRegistration dnR = 
                datanode.getDNRegistrationForBP(blk.getBlockPoolId());
              resp.setFirstBadLink(dnR.getXferAddr());
            }
            resp.build().writeDelimitedTo(out);
            out.flush();
          }
          LOG.warn("Block token verification failed: op=" + op
              + ", remoteAddress=" + remoteAddress
              + ", message=" + e.getLocalizedMessage());
          throw e;
        } finally {
          IOUtils.closeStream(out);
        }
      }
    }
  }
}
