Java Code Examples for org.apache.hadoop.util.DataChecksum#getBytesPerChecksum()

FanOutOneBlockAsyncDFSOutput(Configuration conf,DistributedFileSystem dfs,
    DFSClient client, ClientProtocol namenode, String clientName, String src, long fileId,
    LocatedBlock locatedBlock, Encryptor encryptor, List<Channel> datanodeList,
    DataChecksum summer, ByteBufAllocator alloc) {
  this.conf = conf;
  this.dfs = dfs;
  this.client = client;
  this.namenode = namenode;
  this.fileId = fileId;
  this.clientName = clientName;
  this.src = src;
  this.block = locatedBlock.getBlock();
  this.locations = locatedBlock.getLocations();
  this.encryptor = encryptor;
  this.datanodeList = datanodeList;
  this.summer = summer;
  this.maxDataLen = MAX_DATA_LEN - (MAX_DATA_LEN % summer.getBytesPerChecksum());
  this.alloc = alloc;
  this.buf = alloc.directBuffer(sendBufSizePRedictor.initialSize());
  this.state = State.STREAMING;
  setupReceiver(conf.getInt(DFS_CLIENT_SOCKET_TIMEOUT_KEY, READ_TIMEOUT));
}
 

private RemoteBlockReader(String file, String bpid, long blockId,
    DataInputStream in, DataChecksum checksum, boolean verifyChecksum,
    long startOffset, long firstChunkOffset, long bytesToRead, Peer peer,
    DatanodeID datanodeID, PeerCache peerCache) {
  // Path is used only for printing block and file information in debug
  super(new Path("/" + Block.BLOCK_FILE_PREFIX + blockId +
                  ":" + bpid + ":of:"+ file)/*too non path-like?*/,
        1, verifyChecksum,
        checksum.getChecksumSize() > 0? checksum : null, 
        checksum.getBytesPerChecksum(),
        checksum.getChecksumSize());

  this.isLocal = DFSClient.isLocalAddress(NetUtils.
      createSocketAddr(datanodeID.getXferAddr()));
  
  this.peer = peer;
  this.datanodeID = datanodeID;
  this.in = in;
  this.checksum = checksum;
  this.startOffset = Math.max( startOffset, 0 );
  this.blockId = blockId;

  // The total number of bytes that we need to transfer from the DN is
  // the amount that the user wants (bytesToRead), plus the padding at
  // the beginning in order to chunk-align. Note that the DN may elect
  // to send more than this amount if the read starts/ends mid-chunk.
  this.bytesNeededToFinish = bytesToRead + (startOffset - firstChunkOffset);

  this.firstChunkOffset = firstChunkOffset;
  lastChunkOffset = firstChunkOffset;
  lastChunkLen = -1;

  bytesPerChecksum = this.checksum.getBytesPerChecksum();
  checksumSize = this.checksum.getChecksumSize();
  this.peerCache = peerCache;
}
 

protected BlockReader(Path file, int numRetries, DataChecksum checksum, boolean verifyChecksum) {
  super(file,
      numRetries,
      verifyChecksum,
      checksum.getChecksumSize() > 0? checksum : null, 
      checksum.getBytesPerChecksum(),
      checksum.getChecksumSize());       
}
 

private MD5Hash calcPartialBlockChecksum(ExtendedBlock block,
    long requestLength, DataChecksum checksum, DataInputStream checksumIn)
    throws IOException {
  final int bytesPerCRC = checksum.getBytesPerChecksum();
  final int csize = checksum.getChecksumSize();
  final byte[] buffer = new byte[4*1024];
  MessageDigest digester = MD5Hash.getDigester();

  long remaining = requestLength / bytesPerCRC * csize;
  for (int toDigest = 0; remaining > 0; remaining -= toDigest) {
    toDigest = checksumIn.read(buffer, 0,
        (int) Math.min(remaining, buffer.length));
    if (toDigest < 0) {
      break;
    }
    digester.update(buffer, 0, toDigest);
  }
  
  int partialLength = (int) (requestLength % bytesPerCRC);
  if (partialLength > 0) {
    byte[] buf = new byte[partialLength];
    final InputStream blockIn = datanode.data.getBlockInputStream(block,
        requestLength - partialLength);
    try {
      // Get the CRC of the partialLength.
      IOUtils.readFully(blockIn, buf, 0, partialLength);
    } finally {
      IOUtils.closeStream(blockIn);
    }
    checksum.update(buf, 0, partialLength);
    byte[] partialCrc = new byte[csize];
    checksum.writeValue(partialCrc, 0, true);
    digester.update(partialCrc);
  }
  return new MD5Hash(digester.digest());
}
 

private RemoteBlockReader(String file, String bpid, long blockId,
    DataInputStream in, DataChecksum checksum, boolean verifyChecksum,
    long startOffset, long firstChunkOffset, long bytesToRead, Peer peer,
    DatanodeID datanodeID, PeerCache peerCache) {
  // Path is used only for printing block and file information in debug
  super(new Path("/" + Block.BLOCK_FILE_PREFIX + blockId +
                  ":" + bpid + ":of:"+ file)/*too non path-like?*/,
        1, verifyChecksum,
        checksum.getChecksumSize() > 0? checksum : null, 
        checksum.getBytesPerChecksum(),
        checksum.getChecksumSize());

  this.isLocal = DFSClient.isLocalAddress(NetUtils.
      createSocketAddr(datanodeID.getXferAddr()));
  
  this.peer = peer;
  this.datanodeID = datanodeID;
  this.in = in;
  this.checksum = checksum;
  this.startOffset = Math.max( startOffset, 0 );
  this.blockId = blockId;

  // The total number of bytes that we need to transfer from the DN is
  // the amount that the user wants (bytesToRead), plus the padding at
  // the beginning in order to chunk-align. Note that the DN may elect
  // to send more than this amount if the read starts/ends mid-chunk.
  this.bytesNeededToFinish = bytesToRead + (startOffset - firstChunkOffset);

  this.firstChunkOffset = firstChunkOffset;
  lastChunkOffset = firstChunkOffset;
  lastChunkLen = -1;

  bytesPerChecksum = this.checksum.getBytesPerChecksum();
  checksumSize = this.checksum.getChecksumSize();
  this.peerCache = peerCache;
}
 

private DFSOutputStream(DFSClient dfsClient, String src, Progressable progress,
    HdfsFileStatus stat, DataChecksum checksum) throws IOException {
  super(getChecksum4Compute(checksum, stat));
  this.dfsClient = dfsClient;
  this.src = src;
  this.fileId = stat.getFileId();
  this.blockSize = stat.getBlockSize();
  this.blockReplication = stat.getReplication();
  this.fileEncryptionInfo = stat.getFileEncryptionInfo();
  this.progress = progress;
  this.cachingStrategy = new AtomicReference<CachingStrategy>(
      dfsClient.getDefaultWriteCachingStrategy());
  if ((progress != null) && DFSClient.LOG.isDebugEnabled()) {
    DFSClient.LOG.debug(
        "Set non-null progress callback on DFSOutputStream " + src);
  }
  
  this.bytesPerChecksum = checksum.getBytesPerChecksum();
  if (bytesPerChecksum <= 0) {
    throw new HadoopIllegalArgumentException(
        "Invalid value: bytesPerChecksum = " + bytesPerChecksum + " <= 0");
  }
  if (blockSize % bytesPerChecksum != 0) {
    throw new HadoopIllegalArgumentException("Invalid values: "
        + DFSConfigKeys.DFS_BYTES_PER_CHECKSUM_KEY + " (=" + bytesPerChecksum
        + ") must divide block size (=" + blockSize + ").");
  }
  this.checksum4WriteBlock = checksum;

  this.dfsclientSlowLogThresholdMs =
    dfsClient.getConf().dfsclientSlowIoWarningThresholdMs;
  this.byteArrayManager = dfsClient.getClientContext().getByteArrayManager();
}
 

private MD5Hash calcPartialBlockChecksum(ExtendedBlock block,
    long requestLength, DataChecksum checksum, DataInputStream checksumIn)
    throws IOException {
  final int bytesPerCRC = checksum.getBytesPerChecksum();
  final int csize = checksum.getChecksumSize();
  final byte[] buffer = new byte[4*1024];
  MessageDigest digester = MD5Hash.getDigester();

  long remaining = requestLength / bytesPerCRC * csize;
  for (int toDigest = 0; remaining > 0; remaining -= toDigest) {
    toDigest = checksumIn.read(buffer, 0,
        (int) Math.min(remaining, buffer.length));
    if (toDigest < 0) {
      break;
    }
    digester.update(buffer, 0, toDigest);
  }
  
  int partialLength = (int) (requestLength % bytesPerCRC);
  if (partialLength > 0) {
    byte[] buf = new byte[partialLength];
    final InputStream blockIn = datanode.data.getBlockInputStream(block,
        requestLength - partialLength);
    try {
      // Get the CRC of the partialLength.
      IOUtils.readFully(blockIn, buf, 0, partialLength);
    } finally {
      IOUtils.closeStream(blockIn);
    }
    checksum.update(buf, 0, partialLength);
    byte[] partialCrc = new byte[csize];
    checksum.writeValue(partialCrc, 0, true);
    digester.update(partialCrc);
  }
  return new MD5Hash(digester.digest());
}
 

private DFSOutputStream(DFSClient dfsClient, String src, Progressable progress,
    HdfsFileStatus stat, DataChecksum checksum) throws IOException {
  super(getChecksum4Compute(checksum, stat));
  this.dfsClient = dfsClient;
  this.src = src;
  this.fileId = stat.getFileId();
  this.blockSize = stat.getBlockSize();
  this.blockReplication = stat.getReplication();
  this.fileEncryptionInfo = stat.getFileEncryptionInfo();
  this.progress = progress;
  this.cachingStrategy = new AtomicReference<CachingStrategy>(
      dfsClient.getDefaultWriteCachingStrategy());
  if ((progress != null) && DFSClient.LOG.isDebugEnabled()) {
    DFSClient.LOG.debug(
        "Set non-null progress callback on DFSOutputStream " + src);
  }
  
  this.bytesPerChecksum = checksum.getBytesPerChecksum();
  if (bytesPerChecksum <= 0) {
    throw new HadoopIllegalArgumentException(
        "Invalid value: bytesPerChecksum = " + bytesPerChecksum + " <= 0");
  }
  if (blockSize % bytesPerChecksum != 0) {
    throw new HadoopIllegalArgumentException("Invalid values: "
        + DFSConfigKeys.DFS_BYTES_PER_CHECKSUM_KEY + " (=" + bytesPerChecksum
        + ") must divide block size (=" + blockSize + ").");
  }
  this.checksum4WriteBlock = checksum;

  this.dfsclientSlowLogThresholdMs =
    dfsClient.getConf().dfsclientSlowIoWarningThresholdMs;
  this.byteArrayManager = dfsClient.getClientContext().getByteArrayManager();
}
 

@Override
public void blockChecksum(final ExtendedBlock block,
    final Token<BlockTokenIdentifier> blockToken) throws IOException {
  final DataOutputStream out = new DataOutputStream(
      getOutputStream());
  checkAccess(out, true, block, blockToken,
      Op.BLOCK_CHECKSUM, BlockTokenSecretManager.AccessMode.READ);
  // client side now can specify a range of the block for checksum
  long requestLength = block.getNumBytes();
  Preconditions.checkArgument(requestLength >= 0);
  long visibleLength = datanode.data.getReplicaVisibleLength(block);
  boolean partialBlk = requestLength < visibleLength;

  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 csize = checksum.getChecksumSize();
    final int bytesPerCRC = checksum.getBytesPerChecksum();
    final long crcPerBlock = csize <= 0 ? 0 : 
      (metadataIn.getLength() - BlockMetadataHeader.getHeaderSize()) / csize;

    final MD5Hash md5 = partialBlk && crcPerBlock > 0 ? 
        calcPartialBlockChecksum(block, requestLength, checksum, checksumIn)
          : 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()))
        .setCrcType(PBHelper.convert(checksum.getChecksumType())))
      .build()
      .writeDelimitedTo(out);
    out.flush();
  } catch (IOException ioe) {
    LOG.info("blockChecksum " + block + " received exception " + ioe);
    incrDatanodeNetworkErrors();
    throw ioe;
  } finally {
    IOUtils.closeStream(out);
    IOUtils.closeStream(checksumIn);
    IOUtils.closeStream(metadataIn);
  }

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

protected FSOutputSummer(DataChecksum sum) {
  this.sum = sum;
  this.buf = new byte[sum.getBytesPerChecksum() * BUFFER_NUM_CHUNKS];
  this.checksum = new byte[getChecksumSize() * BUFFER_NUM_CHUNKS];
  this.count = 0;
}
 

/** {@inheritDoc} */
public void validateBlockMetadata(int namespaceId, Block b) throws IOException {
  DatanodeBlockInfo info;
  lock.readLock().lock();
  try {
    info = volumeMap.get(namespaceId, b);
  } finally {
    lock.readLock().unlock();
  }
  if (info == null) {
    throw new IOException("Block " + b + " does not exist in volumeMap.");
  }
  FSVolume v = info.getVolume();
  File tmp = v.getTmpFile(namespaceId, b);
  File f = info.getFile();
  long fileSize;
  if (f == null) {
    f = tmp;
    if (f == null) {
      throw new IOException("Block " + b + " does not exist on disk.");
    }
    if (!f.exists()) {
      throw new IOException("Block " + b + 
                            " block file " + f +
                            " does not exist on disk.");
    }
    fileSize = f.length();
  } else {
    if (info.isFinalized()) {
      info.verifyFinalizedSize();
      fileSize = info.getFinalizedSize();
    } else {
      fileSize = f.length();
    }
  }
  if (b.getNumBytes() > fileSize) {
    throw new IOException("Block " + b + 
                          " length is " + b.getNumBytes()  +
                          " does not match block file length " +
                          f.length());
  }
  File meta = getMetaFile(f, b);
  if (meta == null) {
    throw new IOException("Block " + b + 
                          " metafile does not exist.");
  }
  if (!meta.exists()) {
    throw new IOException("Block " + b + 
                          " metafile " + meta +
                          " does not exist on disk.");
  }
  long metaFileSize = meta.length();
  if (metaFileSize == 0 && fileSize > 0) {
    throw new IOException("Block " + b + " metafile " + meta + " is empty.");
  }
  long stamp = parseGenerationStamp(f, meta);
  if (stamp != b.getGenerationStamp()) {
    throw new IOException("Block " + b + 
                          " genstamp is " + b.getGenerationStamp()  +
                          " does not match meta file stamp " +
                          stamp);
  }
  if (metaFileSize == 0) {
    // no need to check metadata size for 0 size file
    return;
  }
  // verify that checksum file has an integral number of checkum values.
  DataChecksum dcs = BlockMetadataHeader.readHeader(meta).getChecksum();
  int checksumsize = dcs.getChecksumSize();
  long actual = metaFileSize - BlockMetadataHeader.getHeaderSize();
  long numChunksInMeta = actual/checksumsize;
  if (actual % checksumsize != 0) {
    throw new IOException("Block " + b +
                          " has a checksum file of size " + metaFileSize +
                          " but it does not align with checksum size of " +
                          checksumsize);
  }
  int bpc = dcs.getBytesPerChecksum();
  long minDataSize = (numChunksInMeta - 1) * bpc;
  long maxDataSize = numChunksInMeta * bpc;
  if (fileSize > maxDataSize || fileSize <= minDataSize) {
    throw new IOException("Block " + b +
                          " is of size " + f.length() +
                          " but has " + (numChunksInMeta + 1) +
                          " checksums and each checksum size is " +
                          checksumsize + " bytes.");
  }
  // We could crc-check the entire block here, but it will be a costly 
  // operation. Instead we rely on the above check (file length mismatch)
  // to detect corrupt blocks.
}
 

/**
 * Create a new BlockReader specifically to satisfy a read.
 * This method also sends the OP_READ_BLOCK request.
 *
 * @param file  File location
 * @param block  The block object
 * @param blockToken  The block token for security
 * @param startOffset  The read offset, relative to block head
 * @param len  The number of bytes to read
 * @param bufferSize  The IO buffer size (not the client buffer size)
 * @param verifyChecksum  Whether to verify checksum
 * @param clientName  Client name
 * @return New BlockReader instance, or null on error.
 */
public static RemoteBlockReader newBlockReader(String file,
                                   ExtendedBlock block, 
                                   Token<BlockTokenIdentifier> blockToken,
                                   long startOffset, long len,
                                   int bufferSize, boolean verifyChecksum,
                                   String clientName, Peer peer,
                                   DatanodeID datanodeID,
                                   PeerCache peerCache,
                                   CachingStrategy cachingStrategy)
                                     throws IOException {
  // in and out will be closed when sock is closed (by the caller)
  final DataOutputStream out =
      new DataOutputStream(new BufferedOutputStream(peer.getOutputStream()));
  new Sender(out).readBlock(block, blockToken, clientName, startOffset, len,
      verifyChecksum, cachingStrategy);
  
  //
  // Get bytes in block, set streams
  //

  DataInputStream in = new DataInputStream(
      new BufferedInputStream(peer.getInputStream(), bufferSize));
  
  BlockOpResponseProto status = BlockOpResponseProto.parseFrom(
      PBHelper.vintPrefixed(in));
  RemoteBlockReader2.checkSuccess(status, peer, block, file);
  ReadOpChecksumInfoProto checksumInfo =
    status.getReadOpChecksumInfo();
  DataChecksum checksum = DataTransferProtoUtil.fromProto(
      checksumInfo.getChecksum());
  //Warning when we get CHECKSUM_NULL?
  
  // Read the first chunk offset.
  long firstChunkOffset = checksumInfo.getChunkOffset();
  
  if ( firstChunkOffset < 0 || firstChunkOffset > startOffset ||
      firstChunkOffset <= (startOffset - checksum.getBytesPerChecksum())) {
    throw new IOException("BlockReader: error in first chunk offset (" +
                          firstChunkOffset + ") startOffset is " + 
                          startOffset + " for file " + file);
  }

  return new RemoteBlockReader(file, block.getBlockPoolId(), block.getBlockId(),
      in, checksum, verifyChecksum, startOffset, firstChunkOffset, len,
      peer, datanodeID, peerCache);
}
 

/**
 * Create a new BlockReader specifically to satisfy a read.
 * This method also sends the OP_READ_BLOCK request.
 *
 * @param file  File location
 * @param block  The block object
 * @param blockToken  The block token for security
 * @param startOffset  The read offset, relative to block head
 * @param len  The number of bytes to read
 * @param verifyChecksum  Whether to verify checksum
 * @param clientName  Client name
 * @param peer  The Peer to use
 * @param datanodeID  The DatanodeID this peer is connected to
 * @return New BlockReader instance, or null on error.
 */
public static BlockReader newBlockReader(String file,
                                   ExtendedBlock block,
                                   Token<BlockTokenIdentifier> blockToken,
                                   long startOffset, long len,
                                   boolean verifyChecksum,
                                   String clientName,
                                   Peer peer, DatanodeID datanodeID,
                                   PeerCache peerCache,
                                   CachingStrategy cachingStrategy) throws IOException {
  // in and out will be closed when sock is closed (by the caller)
  final DataOutputStream out = new DataOutputStream(new BufferedOutputStream(
        peer.getOutputStream()));
  new Sender(out).readBlock(block, blockToken, clientName, startOffset, len,
      verifyChecksum, cachingStrategy);

  //
  // Get bytes in block
  //
  DataInputStream in = new DataInputStream(peer.getInputStream());

  BlockOpResponseProto status = BlockOpResponseProto.parseFrom(
      PBHelper.vintPrefixed(in));
  checkSuccess(status, peer, block, file);
  ReadOpChecksumInfoProto checksumInfo =
    status.getReadOpChecksumInfo();
  DataChecksum checksum = DataTransferProtoUtil.fromProto(
      checksumInfo.getChecksum());
  //Warning when we get CHECKSUM_NULL?

  // Read the first chunk offset.
  long firstChunkOffset = checksumInfo.getChunkOffset();

  if ( firstChunkOffset < 0 || firstChunkOffset > startOffset ||
      firstChunkOffset <= (startOffset - checksum.getBytesPerChecksum())) {
    throw new IOException("BlockReader: error in first chunk offset (" +
                          firstChunkOffset + ") startOffset is " +
                          startOffset + " for file " + file);
  }

  return new RemoteBlockReader2(file, block.getBlockPoolId(), block.getBlockId(),
      checksum, verifyChecksum, startOffset, firstChunkOffset, len, peer,
      datanodeID, peerCache);
}
 

static private void truncateBlock(File blockFile, File metaFile,
    long oldlen, long newlen) throws IOException {
  LOG.info("truncateBlock: blockFile=" + blockFile
      + ", metaFile=" + metaFile
      + ", oldlen=" + oldlen
      + ", newlen=" + newlen);

  if (newlen == oldlen) {
    return;
  }
  if (newlen > oldlen) {
    throw new IOException("Cannot truncate block to from oldlen (=" + oldlen
        + ") to newlen (=" + newlen + ")");
  }

  DataChecksum dcs = BlockMetadataHeader.readHeader(metaFile).getChecksum(); 
  int checksumsize = dcs.getChecksumSize();
  int bpc = dcs.getBytesPerChecksum();
  long n = (newlen - 1)/bpc + 1;
  long newmetalen = BlockMetadataHeader.getHeaderSize() + n*checksumsize;
  long lastchunkoffset = (n - 1)*bpc;
  int lastchunksize = (int)(newlen - lastchunkoffset); 
  byte[] b = new byte[Math.max(lastchunksize, checksumsize)]; 

  RandomAccessFile blockRAF = new RandomAccessFile(blockFile, "rw");
  try {
    //truncate blockFile 
    blockRAF.setLength(newlen);
 
    //read last chunk
    blockRAF.seek(lastchunkoffset);
    blockRAF.readFully(b, 0, lastchunksize);
  } finally {
    blockRAF.close();
  }

  //compute checksum
  dcs.update(b, 0, lastchunksize);
  dcs.writeValue(b, 0, false);

  //update metaFile 
  RandomAccessFile metaRAF = new RandomAccessFile(metaFile, "rw");
  try {
    metaRAF.setLength(newmetalen);
    metaRAF.seek(newmetalen - checksumsize);
    metaRAF.write(b, 0, checksumsize);
  } finally {
    metaRAF.close();
  }
}
 

/**
 * Create a new BlockReader specifically to satisfy a read.
 * This method also sends the OP_READ_BLOCK request.
 *
 * @param file  File location
 * @param block  The block object
 * @param blockToken  The block token for security
 * @param startOffset  The read offset, relative to block head
 * @param len  The number of bytes to read
 * @param verifyChecksum  Whether to verify checksum
 * @param clientName  Client name
 * @param peer  The Peer to use
 * @param datanodeID  The DatanodeID this peer is connected to
 * @return New BlockReader instance, or null on error.
 */
public static BlockReader newBlockReader(String file,
                                   ExtendedBlock block,
                                   Token<BlockTokenIdentifier> blockToken,
                                   long startOffset, long len,
                                   boolean verifyChecksum,
                                   String clientName,
                                   Peer peer, DatanodeID datanodeID,
                                   PeerCache peerCache,
                                   CachingStrategy cachingStrategy) throws IOException {
  // in and out will be closed when sock is closed (by the caller)
  final DataOutputStream out = new DataOutputStream(new BufferedOutputStream(
        peer.getOutputStream()));
  new Sender(out).readBlock(block, blockToken, clientName, startOffset, len,
      verifyChecksum, cachingStrategy);

  //
  // Get bytes in block
  //
  DataInputStream in = new DataInputStream(peer.getInputStream());

  BlockOpResponseProto status = BlockOpResponseProto.parseFrom(
      PBHelper.vintPrefixed(in));
  checkSuccess(status, peer, block, file);
  ReadOpChecksumInfoProto checksumInfo =
    status.getReadOpChecksumInfo();
  DataChecksum checksum = DataTransferProtoUtil.fromProto(
      checksumInfo.getChecksum());
  //Warning when we get CHECKSUM_NULL?

  // Read the first chunk offset.
  long firstChunkOffset = checksumInfo.getChunkOffset();

  if ( firstChunkOffset < 0 || firstChunkOffset > startOffset ||
      firstChunkOffset <= (startOffset - checksum.getBytesPerChecksum())) {
    throw new IOException("BlockReader: error in first chunk offset (" +
                          firstChunkOffset + ") startOffset is " +
                          startOffset + " for file " + file);
  }

  return new RemoteBlockReader2(file, block.getBlockPoolId(), block.getBlockId(),
      checksum, verifyChecksum, startOffset, firstChunkOffset, len, peer,
      datanodeID, peerCache);
}
 

public static BlockReader newBlockReader( int dataTransferVersion,
                                   int namespaceId,
                                   Socket sock, String file,
                                   long blockId,
                                   long genStamp,
                                   long startOffset, long len,
                                   int bufferSize, boolean verifyChecksum,
                                   String clientName, long minSpeedBps)
                                   throws IOException {
  // in and out will be closed when sock is closed (by the caller)
  DataOutputStream out = new DataOutputStream(
    new BufferedOutputStream(NetUtils.getOutputStream(sock,HdfsConstants.WRITE_TIMEOUT)));

  //write the header.
  ReadBlockHeader readBlockHeader = new ReadBlockHeader(
      dataTransferVersion, namespaceId, blockId, genStamp, startOffset, len,
      clientName);
  readBlockHeader.writeVersionAndOpCode(out);
  readBlockHeader.write(out);
  out.flush();

  //
  // Get bytes in block, set streams
  //

  DataInputStream in = new DataInputStream(
      new BufferedInputStream(NetUtils.getInputStream(sock),
                              bufferSize));

  if ( in.readShort() != DataTransferProtocol.OP_STATUS_SUCCESS ) {
    throw new IOException("Got error in response to OP_READ_BLOCK " +
                          "self=" + sock.getLocalSocketAddress() +
                          ", remote=" + sock.getRemoteSocketAddress() +
                          " for file " + file +
                          " for block " + blockId);
  }
  DataChecksum checksum = DataChecksum.newDataChecksum( in , new PureJavaCrc32());
  //Warning when we get CHECKSUM_NULL?

  // Read the first chunk offset.
  long firstChunkOffset = in.readLong();

  if ( firstChunkOffset < 0 || firstChunkOffset > startOffset ||
      firstChunkOffset >= (startOffset + checksum.getBytesPerChecksum())) {
    throw new IOException("BlockReader: error in first chunk offset (" +
                          firstChunkOffset + ") startOffset is " +
                          startOffset + " for file " + file);
  }

  return new BlockReader(file, blockId, in, checksum, verifyChecksum,
      startOffset, firstChunkOffset, sock, minSpeedBps, dataTransferVersion);
}
 

protected FSOutputSummer(DataChecksum sum) {
  this.sum = sum;
  this.buf = new byte[sum.getBytesPerChecksum() * BUFFER_NUM_CHUNKS];
  this.checksum = new byte[getChecksumSize() * BUFFER_NUM_CHUNKS];
  this.count = 0;
}
 

/**
 * Find out the number of bytes in the block that match its crc.
 *
 * This algorithm assumes that data corruption caused by unexpected
 * datanode shutdown occurs only in the last crc chunk. So it checks
 * only the last chunk.
 *
 * @param blockFile the block file
 * @param genStamp generation stamp of the block
 * @return the number of valid bytes
 */
private long validateIntegrityAndSetLength(File blockFile, long genStamp) {
  try {
    final File metaFile = FsDatasetUtil.getMetaFile(blockFile, genStamp);
    long blockFileLen = blockFile.length();
    long metaFileLen = metaFile.length();
    int crcHeaderLen = DataChecksum.getChecksumHeaderSize();
    if (!blockFile.exists() || blockFileLen == 0 ||
        !metaFile.exists() || metaFileLen < crcHeaderLen) {
      return 0;
    }
    try (DataInputStream checksumIn = new DataInputStream(
        new BufferedInputStream(
            fileIoProvider.getFileInputStream(volume, metaFile),
            ioFileBufferSize))) {
      // read and handle the common header here. For now just a version
      final DataChecksum checksum = BlockMetadataHeader.readDataChecksum(
          checksumIn, metaFile);
      int bytesPerChecksum = checksum.getBytesPerChecksum();
      int checksumSize = checksum.getChecksumSize();
      long numChunks = Math.min(
          (blockFileLen + bytesPerChecksum - 1) / bytesPerChecksum,
          (metaFileLen - crcHeaderLen) / checksumSize);
      if (numChunks == 0) {
        return 0;
      }
      try (InputStream blockIn = fileIoProvider.getFileInputStream(
          volume, blockFile);
           ReplicaInputStreams ris = new ReplicaInputStreams(blockIn,
               checksumIn, volume.obtainReference(), fileIoProvider)) {
        ris.skipChecksumFully((numChunks - 1) * checksumSize);
        long lastChunkStartPos = (numChunks - 1) * bytesPerChecksum;
        ris.skipDataFully(lastChunkStartPos);
        int lastChunkSize = (int) Math.min(
            bytesPerChecksum, blockFileLen - lastChunkStartPos);
        byte[] buf = new byte[lastChunkSize + checksumSize];
        ris.readChecksumFully(buf, lastChunkSize, checksumSize);
        ris.readDataFully(buf, 0, lastChunkSize);
        checksum.update(buf, 0, lastChunkSize);
        long validFileLength;
        if (checksum.compare(buf, lastChunkSize)) { // last chunk matches crc
          validFileLength = lastChunkStartPos + lastChunkSize;
        } else { // last chunk is corrupt
          validFileLength = lastChunkStartPos;
        }
        // truncate if extra bytes are present without CRC
        if (blockFile.length() > validFileLength) {
          try (RandomAccessFile blockRAF =
                   fileIoProvider.getRandomAccessFile(
                       volume, blockFile, "rw")) {
            // truncate blockFile
            blockRAF.setLength(validFileLength);
          }
        }
        return validFileLength;
      }
    }
  } catch (IOException e) {
    FsDatasetImpl.LOG.warn("Getting exception while validating integrity " +
        "and setting length for blockFile", e);
    return 0;
  }
}
 

/**
 * Create a new BlockReader specifically to satisfy a read.
 * This method also sends the OP_READ_BLOCK request.
 *
 * @param file  File location
 * @param block  The block object
 * @param blockToken  The block token for security
 * @param startOffset  The read offset, relative to block head
 * @param len  The number of bytes to read
 * @param bufferSize  The IO buffer size (not the client buffer size)
 * @param verifyChecksum  Whether to verify checksum
 * @param clientName  Client name
 * @return New BlockReader instance, or null on error.
 */
public static RemoteBlockReader newBlockReader(String file,
                                   ExtendedBlock block, 
                                   Token<BlockTokenIdentifier> blockToken,
                                   long startOffset, long len,
                                   int bufferSize, boolean verifyChecksum,
                                   String clientName, Peer peer,
                                   DatanodeID datanodeID,
                                   PeerCache peerCache,
                                   CachingStrategy cachingStrategy)
                                     throws IOException {
  // in and out will be closed when sock is closed (by the caller)
  final DataOutputStream out =
      new DataOutputStream(new BufferedOutputStream(peer.getOutputStream()));
  new Sender(out).readBlock(block, blockToken, clientName, startOffset, len,
      verifyChecksum, cachingStrategy);
  
  //
  // Get bytes in block, set streams
  //

  DataInputStream in = new DataInputStream(
      new BufferedInputStream(peer.getInputStream(), bufferSize));
  
  BlockOpResponseProto status = BlockOpResponseProto.parseFrom(
      PBHelper.vintPrefixed(in));
  RemoteBlockReader2.checkSuccess(status, peer, block, file);
  ReadOpChecksumInfoProto checksumInfo =
    status.getReadOpChecksumInfo();
  DataChecksum checksum = DataTransferProtoUtil.fromProto(
      checksumInfo.getChecksum());
  //Warning when we get CHECKSUM_NULL?
  
  // Read the first chunk offset.
  long firstChunkOffset = checksumInfo.getChunkOffset();
  
  if ( firstChunkOffset < 0 || firstChunkOffset > startOffset ||
      firstChunkOffset <= (startOffset - checksum.getBytesPerChecksum())) {
    throw new IOException("BlockReader: error in first chunk offset (" +
                          firstChunkOffset + ") startOffset is " + 
                          startOffset + " for file " + file);
  }

  return new RemoteBlockReader(file, block.getBlockPoolId(), block.getBlockId(),
      in, checksum, verifyChecksum, startOffset, firstChunkOffset, len,
      peer, datanodeID, peerCache);
}
 

static private void truncateBlock(File blockFile, File metaFile,
    long oldlen, long newlen) throws IOException {
  if (newlen == oldlen) {
    return;
  }
  if (newlen > oldlen) {
    throw new IOException("Cannout truncate block to from oldlen (=" + oldlen
        + ") to newlen (=" + newlen + ")");
  }

  DataChecksum dcs = BlockMetadataHeader.readHeader(metaFile).getChecksum(); 
  int checksumsize = dcs.getChecksumSize();
  int bpc = dcs.getBytesPerChecksum();
  long n = (newlen - 1)/bpc + 1;
  long newmetalen = BlockMetadataHeader.getHeaderSize() + n*checksumsize;
  long lastchunkoffset = (n - 1)*bpc;
  int lastchunksize = (int)(newlen - lastchunkoffset); 
  byte[] b = new byte[Math.max(lastchunksize, checksumsize)]; 

  RandomAccessFile blockRAF = new RandomAccessFile(blockFile, "rw");
  try {
    //truncate blockFile 
    blockRAF.setLength(newlen);
 
    //read last chunk
    blockRAF.seek(lastchunkoffset);
    blockRAF.readFully(b, 0, lastchunksize);
  } finally {
    blockRAF.close();
  }

  //compute checksum
  dcs.update(b, 0, lastchunksize);
  dcs.writeValue(b, 0, false);

  //update metaFile 
  RandomAccessFile metaRAF = new RandomAccessFile(metaFile, "rw");
  try {
    metaRAF.setLength(newmetalen);
    metaRAF.seek(newmetalen - checksumsize);
    metaRAF.write(b, 0, checksumsize);
  } finally {
    metaRAF.close();
  }
}