/*
    * 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.hbase.io.hfile;
  
  import java.io.ByteArrayOutputStream;
  import java.io.DataInputStream;
  import java.io.DataOutput;
  import java.io.DataOutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.nio.ByteBuffer;
  import java.util.concurrent.locks.Lock;
  import java.util.concurrent.locks.ReentrantLock;
  
  import org.apache.hadoop.fs.FSDataInputStream;
  import org.apache.hadoop.fs.FSDataOutputStream;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.fs.HFileSystem;
  import org.apache.hadoop.hbase.io.ByteBufferInputStream;
  import org.apache.hadoop.hbase.io.FSDataInputStreamWrapper;
  import org.apache.hadoop.hbase.io.encoding.DataBlockEncoding;
  import org.apache.hadoop.hbase.io.encoding.HFileBlockDecodingContext;
  import org.apache.hadoop.hbase.io.encoding.HFileBlockDefaultDecodingContext;
  import org.apache.hadoop.hbase.io.encoding.HFileBlockDefaultEncodingContext;
  import org.apache.hadoop.hbase.io.encoding.HFileBlockEncodingContext;
  import org.apache.hadoop.hbase.util.ByteBufferUtils;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.hbase.util.ChecksumType;
  import org.apache.hadoop.hbase.util.ClassSize;
  import org.apache.hadoop.io.IOUtils;
  
  import com.google.common.annotations.VisibleForTesting;
  import com.google.common.base.Preconditions;
  
  /**
   * Reading {@link HFile} version 1 and 2 blocks, and writing version 2 blocks.
   * <ul>
   * <li>In version 1 all blocks are always compressed or uncompressed, as
   * specified by the {@link HFile}'s compression algorithm, with a type-specific
   * magic record stored in the beginning of the compressed data (i.e. one needs
   * to uncompress the compressed block to determine the block type). There is
   * only a single compression algorithm setting for all blocks. Offset and size
   * information from the block index are required to read a block.
   * <li>In version 2 a block is structured as follows:
   * <ul>
   * <li>header (see Writer#finishBlock())
   * <ul>
   * <li>Magic record identifying the block type (8 bytes)
   * <li>Compressed block size, excluding header, including checksum (4 bytes)
   * <li>Uncompressed block size, excluding header, excluding checksum (4 bytes)
   * <li>The offset of the previous block of the same type (8 bytes). This is
   * used to be able to navigate to the previous block without going to the block
   * <li>For minorVersions &gt;=1, the ordinal describing checksum type (1 byte)
   * <li>For minorVersions &gt;=1, the number of data bytes/checksum chunk (4 bytes)
   * <li>For minorVersions &gt;=1, the size of data on disk, including header,
   * excluding checksums (4 bytes)
   * </ul>
   * </li>
   * <li>Raw/Compressed/Encrypted/Encoded data. The compression algorithm is the
   * same for all the blocks in the {@link HFile}, similarly to what was done in
   * version 1.
   * <li>For minorVersions &gt;=1, a series of 4 byte checksums, one each for
   * the number of bytes specified by bytesPerChecksum.
   * </ul>
   * </ul>
   */
  @InterfaceAudience.Private
  @edu.umd.cs.findbugs.annotations.SuppressWarnings(value="HE_EQUALS_USE_HASHCODE",
    justification="Fix!!! Fine for now bug FIXXXXXXX!!!!")
  public class HFileBlock implements Cacheable {
  
    /**
     * On a checksum failure on a Reader, these many suceeding read
     * requests switch back to using hdfs checksums before auto-reenabling
     * hbase checksum verification.
     */
    static final int CHECKSUM_VERIFICATION_NUM_IO_THRESHOLD = 3;
  
    public static final boolean FILL_HEADER = true;
    public static final boolean DONT_FILL_HEADER = false;
  
   /**
    * The size of block header when blockType is {@link BlockType#ENCODED_DATA}.
    * This extends normal header by adding the id of encoder.
    */
   public static final int ENCODED_HEADER_SIZE = HConstants.HFILEBLOCK_HEADER_SIZE
       + DataBlockEncoding.ID_SIZE;
 
   static final byte[] DUMMY_HEADER_NO_CHECKSUM =
      new byte[HConstants.HFILEBLOCK_HEADER_SIZE_NO_CHECKSUM];
 
   public static final int BYTE_BUFFER_HEAP_SIZE = (int) ClassSize.estimateBase(
       ByteBuffer.wrap(new byte[0], 0, 0).getClass(), false);
 
   // meta.usesHBaseChecksum+offset+nextBlockOnDiskSizeWithHeader
   public static final int EXTRA_SERIALIZATION_SPACE = Bytes.SIZEOF_BYTE + Bytes.SIZEOF_INT
       + Bytes.SIZEOF_LONG;
 
   /**
    * Each checksum value is an integer that can be stored in 4 bytes.
    */
   static final int CHECKSUM_SIZE = Bytes.SIZEOF_INT;
 
   static final CacheableDeserializer<Cacheable> blockDeserializer =
       new CacheableDeserializer<Cacheable>() {
         public HFileBlock deserialize(ByteBuffer buf, boolean reuse) throws IOException{
           buf.limit(buf.limit() - HFileBlock.EXTRA_SERIALIZATION_SPACE).rewind();
           ByteBuffer newByteBuffer;
           if (reuse) {
             newByteBuffer = buf.slice();
           } else {
            newByteBuffer = ByteBuffer.allocate(buf.limit());
            newByteBuffer.put(buf);
           }
           buf.position(buf.limit());
           buf.limit(buf.limit() + HFileBlock.EXTRA_SERIALIZATION_SPACE);
           boolean usesChecksum = buf.get() == (byte)1;
           HFileBlock hFileBlock = new HFileBlock(newByteBuffer, usesChecksum);
           hFileBlock.offset = buf.getLong();
           hFileBlock.nextBlockOnDiskSizeWithHeader = buf.getInt();
           if (hFileBlock.hasNextBlockHeader()) {
             hFileBlock.buf.limit(hFileBlock.buf.limit() - hFileBlock.headerSize());
           }
           return hFileBlock;
         }
 
         @Override
         public int getDeserialiserIdentifier() {
           return deserializerIdentifier;
         }
 
         @Override
         public HFileBlock deserialize(ByteBuffer b) throws IOException {
           return deserialize(b, false);
         }
       };
   private static final int deserializerIdentifier;
   static {
     deserializerIdentifier = CacheableDeserializerIdManager
         .registerDeserializer(blockDeserializer);
   }
 
     // Todo: encapsulate Header related logic in this inner class.
   static class Header {
     // Format of header is:
     // 8 bytes - block magic
     // 4 bytes int - onDiskSizeWithoutHeader
     // 4 bytes int - uncompressedSizeWithoutHeader
     // 8 bytes long - prevBlockOffset
     // The following 3 are only present if header contains checksum information
     // 1 byte - checksum type
     // 4 byte int - bytes per checksum
     // 4 byte int - onDiskDataSizeWithHeader
     static int BLOCK_MAGIC_INDEX = 0;
     static int ON_DISK_SIZE_WITHOUT_HEADER_INDEX = 8;
     static int UNCOMPRESSED_SIZE_WITHOUT_HEADER_INDEX = 12;
     static int PREV_BLOCK_OFFSET_INDEX = 16;
     static int CHECKSUM_TYPE_INDEX = 24;
     static int BYTES_PER_CHECKSUM_INDEX = 25;
     static int ON_DISK_DATA_SIZE_WITH_HEADER_INDEX = 29;
   }
 
   /** Type of block. Header field 0. */
   private BlockType blockType;
 
   /** Size on disk excluding header, including checksum. Header field 1. */
   private int onDiskSizeWithoutHeader;
 
   /** Size of pure data. Does not include header or checksums. Header field 2. */
   private final int uncompressedSizeWithoutHeader;
 
   /** The offset of the previous block on disk. Header field 3. */
   private final long prevBlockOffset;
 
   /**
    * Size on disk of header + data. Excludes checksum. Header field 6,
    * OR calculated from {@link #onDiskSizeWithoutHeader} when using HDFS checksum.
    */
   private final int onDiskDataSizeWithHeader;
 
   /** The in-memory representation of the hfile block */
   private ByteBuffer buf;
 
   /** Meta data that holds meta information on the hfileblock */
   private HFileContext fileContext;
 
   /**
    * The offset of this block in the file. Populated by the reader for
    * convenience of access. This offset is not part of the block header.
    */
   private long offset = -1;
 
   /**
    * The on-disk size of the next block, including the header, obtained by
    * peeking into the first {@link HConstants#HFILEBLOCK_HEADER_SIZE} bytes of the next block's
    * header, or -1 if unknown.
    */
   private int nextBlockOnDiskSizeWithHeader = -1;
 
   /**
    * Creates a new {@link HFile} block from the given fields. This constructor
    * is mostly used when the block data has already been read and uncompressed,
    * and is sitting in a byte buffer.
    *
    * @param blockType the type of this block, see {@link BlockType}
    * @param onDiskSizeWithoutHeader see {@link #onDiskSizeWithoutHeader}
    * @param uncompressedSizeWithoutHeader see {@link #uncompressedSizeWithoutHeader}
    * @param prevBlockOffset see {@link #prevBlockOffset}
    * @param buf block header ({@link HConstants#HFILEBLOCK_HEADER_SIZE} bytes) followed by
    *          uncompressed data. This
    * @param fillHeader when true, parse {@code buf} and override the first 4 header fields.
    * @param offset the file offset the block was read from
    * @param onDiskDataSizeWithHeader see {@link #onDiskDataSizeWithHeader}
    * @param fileContext HFile meta data
    */
   HFileBlock(BlockType blockType, int onDiskSizeWithoutHeader, int uncompressedSizeWithoutHeader,
       long prevBlockOffset, ByteBuffer buf, boolean fillHeader, long offset,
       int onDiskDataSizeWithHeader, HFileContext fileContext) {
     this.blockType = blockType;
     this.onDiskSizeWithoutHeader = onDiskSizeWithoutHeader;
     this.uncompressedSizeWithoutHeader = uncompressedSizeWithoutHeader;
     this.prevBlockOffset = prevBlockOffset;
     this.buf = buf;
     this.offset = offset;
     this.onDiskDataSizeWithHeader = onDiskDataSizeWithHeader;
     this.fileContext = fileContext;
     if (fillHeader)
       overwriteHeader();
     this.buf.rewind();
   }
 
   /**
    * Copy constructor. Creates a shallow copy of {@code that}'s buffer.
    */
   HFileBlock(HFileBlock that) {
     this.blockType = that.blockType;
     this.onDiskSizeWithoutHeader = that.onDiskSizeWithoutHeader;
     this.uncompressedSizeWithoutHeader = that.uncompressedSizeWithoutHeader;
     this.prevBlockOffset = that.prevBlockOffset;
     this.buf = that.buf.duplicate();
     this.offset = that.offset;
     this.onDiskDataSizeWithHeader = that.onDiskDataSizeWithHeader;
     this.fileContext = that.fileContext;
     this.nextBlockOnDiskSizeWithHeader = that.nextBlockOnDiskSizeWithHeader;
   }
 
   /**
    * Creates a block from an existing buffer starting with a header. Rewinds
    * and takes ownership of the buffer. By definition of rewind, ignores the
    * buffer position, but if you slice the buffer beforehand, it will rewind
    * to that point. The reason this has a minorNumber and not a majorNumber is
    * because majorNumbers indicate the format of a HFile whereas minorNumbers
    * indicate the format inside a HFileBlock.
    */
   HFileBlock(ByteBuffer b, boolean usesHBaseChecksum) throws IOException {
     b.rewind();
     blockType = BlockType.read(b);
     onDiskSizeWithoutHeader = b.getInt(Header.ON_DISK_SIZE_WITHOUT_HEADER_INDEX);
     uncompressedSizeWithoutHeader = b.getInt(Header.UNCOMPRESSED_SIZE_WITHOUT_HEADER_INDEX);
     prevBlockOffset = b.getLong(Header.PREV_BLOCK_OFFSET_INDEX);
     HFileContextBuilder contextBuilder = new HFileContextBuilder();
     contextBuilder.withHBaseCheckSum(usesHBaseChecksum);
     if (usesHBaseChecksum) {
       contextBuilder.withChecksumType(ChecksumType.codeToType(b.get(Header.CHECKSUM_TYPE_INDEX)));
       contextBuilder.withBytesPerCheckSum(b.getInt(Header.BYTES_PER_CHECKSUM_INDEX));
       this.onDiskDataSizeWithHeader = b.getInt(Header.ON_DISK_DATA_SIZE_WITH_HEADER_INDEX);
     } else {
       contextBuilder.withChecksumType(ChecksumType.NULL);
       contextBuilder.withBytesPerCheckSum(0);
       this.onDiskDataSizeWithHeader = onDiskSizeWithoutHeader +
                                        HConstants.HFILEBLOCK_HEADER_SIZE_NO_CHECKSUM;
     }
     this.fileContext = contextBuilder.build();
     buf = b;
     buf.rewind();
   }
 
   public BlockType getBlockType() {
     return blockType;
   }
 
   /** @return get data block encoding id that was used to encode this block */
   public short getDataBlockEncodingId() {
     if (blockType != BlockType.ENCODED_DATA) {
       throw new IllegalArgumentException("Querying encoder ID of a block " +
           "of type other than " + BlockType.ENCODED_DATA + ": " + blockType);
     }
     return buf.getShort(headerSize());
   }
 
   /**
    * @return the on-disk size of header + data part + checksum.
    */
   public int getOnDiskSizeWithHeader() {
     return onDiskSizeWithoutHeader + headerSize();
   }
 
   /**
    * @return the on-disk size of the data part + checksum (header excluded).
    */
   public int getOnDiskSizeWithoutHeader() {
     return onDiskSizeWithoutHeader;
   }
 
   /**
    * @return the uncompressed size of data part (header and checksum excluded).
    */
    public int getUncompressedSizeWithoutHeader() {
     return uncompressedSizeWithoutHeader;
   }
 
   /**
    * @return the offset of the previous block of the same type in the file, or
    *         -1 if unknown
    */
   public long getPrevBlockOffset() {
     return prevBlockOffset;
   }
 
   /**
    * Rewinds {@code buf} and writes first 4 header fields. {@code buf} position
    * is modified as side-effect.
    */
   private void overwriteHeader() {
     buf.rewind();
     blockType.write(buf);
     buf.putInt(onDiskSizeWithoutHeader);
     buf.putInt(uncompressedSizeWithoutHeader);
     buf.putLong(prevBlockOffset);
     if (this.fileContext.isUseHBaseChecksum()) {
       buf.put(fileContext.getChecksumType().getCode());
       buf.putInt(fileContext.getBytesPerChecksum());
       buf.putInt(onDiskDataSizeWithHeader);
     }
   }
 
   /**
    * Returns a buffer that does not include the header or checksum.
    *
    * @return the buffer with header skipped and checksum omitted.
    */
   public ByteBuffer getBufferWithoutHeader() {
     ByteBuffer dup = this.buf.duplicate();
     dup.position(headerSize());
     dup.limit(buf.limit() - totalChecksumBytes());
     return dup.slice();
   }
 
   /**
    * Returns the buffer this block stores internally. The clients must not
    * modify the buffer object. This method has to be public because it is
    * used in {@link org.apache.hadoop.hbase.util.CompoundBloomFilter}
    * to avoid object creation on every Bloom filter lookup, but has to
    * be used with caution. Checksum data is not included in the returned
    * buffer but header data is.
    *
    * @return the buffer of this block for read-only operations
    */
   public ByteBuffer getBufferReadOnly() {
     ByteBuffer dup = this.buf.duplicate();
     dup.limit(buf.limit() - totalChecksumBytes());
     return dup.slice();
   }
 
   /**
    * Returns the buffer of this block, including header data. The clients must
    * not modify the buffer object. This method has to be public because it is
    * used in {@link org.apache.hadoop.hbase.io.hfile.bucket.BucketCache} to avoid buffer copy.
    *
    * @return the buffer with header and checksum included for read-only operations
    */
   public ByteBuffer getBufferReadOnlyWithHeader() {
     ByteBuffer dup = this.buf.duplicate();
     return dup.slice();
   }
 
   /**
    * Returns a byte buffer of this block, including header data and checksum, positioned at
    * the beginning of header. The underlying data array is not copied.
    *
    * @return the byte buffer with header and checksum included
    */
   ByteBuffer getBufferWithHeader() {
     ByteBuffer dupBuf = buf.duplicate();
     dupBuf.rewind();
     return dupBuf;
   }
 
   private void sanityCheckAssertion(long valueFromBuf, long valueFromField,
       String fieldName) throws IOException {
     if (valueFromBuf != valueFromField) {
       throw new AssertionError(fieldName + " in the buffer (" + valueFromBuf
           + ") is different from that in the field (" + valueFromField + ")");
     }
   }
 
   private void sanityCheckAssertion(BlockType valueFromBuf, BlockType valueFromField)
       throws IOException {
     if (valueFromBuf != valueFromField) {
       throw new IOException("Block type stored in the buffer: " +
         valueFromBuf + ", block type field: " + valueFromField);
     }
   }
 
   /**
    * Checks if the block is internally consistent, i.e. the first
    * {@link HConstants#HFILEBLOCK_HEADER_SIZE} bytes of the buffer contain a
    * valid header consistent with the fields. Assumes a packed block structure.
    * This function is primary for testing and debugging, and is not
    * thread-safe, because it alters the internal buffer pointer.
    */
   void sanityCheck() throws IOException {
     buf.rewind();
 
     sanityCheckAssertion(BlockType.read(buf), blockType);
 
     sanityCheckAssertion(buf.getInt(), onDiskSizeWithoutHeader,
         "onDiskSizeWithoutHeader");
 
     sanityCheckAssertion(buf.getInt(), uncompressedSizeWithoutHeader,
         "uncompressedSizeWithoutHeader");
 
     sanityCheckAssertion(buf.getLong(), prevBlockOffset, "prevBlocKOffset");
     if (this.fileContext.isUseHBaseChecksum()) {
       sanityCheckAssertion(buf.get(), this.fileContext.getChecksumType().getCode(), "checksumType");
       sanityCheckAssertion(buf.getInt(), this.fileContext.getBytesPerChecksum(), "bytesPerChecksum");
       sanityCheckAssertion(buf.getInt(), onDiskDataSizeWithHeader, "onDiskDataSizeWithHeader");
     }
 
     int cksumBytes = totalChecksumBytes();
     int expectedBufLimit = onDiskDataSizeWithHeader + cksumBytes;
     if (buf.limit() != expectedBufLimit) {
       throw new AssertionError("Expected buffer limit " + expectedBufLimit
           + ", got " + buf.limit());
     }
 
     // We might optionally allocate HFILEBLOCK_HEADER_SIZE more bytes to read the next
     // block's header, so there are two sensible values for buffer capacity.
     int hdrSize = headerSize();
     if (buf.capacity() != expectedBufLimit &&
         buf.capacity() != expectedBufLimit + hdrSize) {
       throw new AssertionError("Invalid buffer capacity: " + buf.capacity() +
           ", expected " + expectedBufLimit + " or " + (expectedBufLimit + hdrSize));
     }
   }
 
   @Override
   public String toString() {
     StringBuilder sb = new StringBuilder()
       .append("HFileBlock [")
       .append(" fileOffset=").append(offset)
       .append(" headerSize()=").append(headerSize())
       .append(" blockType=").append(blockType)
       .append(" onDiskSizeWithoutHeader=").append(onDiskSizeWithoutHeader)
       .append(" uncompressedSizeWithoutHeader=").append(uncompressedSizeWithoutHeader)
       .append(" prevBlockOffset=").append(prevBlockOffset)
       .append(" isUseHBaseChecksum()=").append(fileContext.isUseHBaseChecksum());
     if (fileContext.isUseHBaseChecksum()) {
       sb.append(" checksumType=").append(ChecksumType.codeToType(this.buf.get(24)))
         .append(" bytesPerChecksum=").append(this.buf.getInt(24 + 1))
         .append(" onDiskDataSizeWithHeader=").append(onDiskDataSizeWithHeader);
     } else {
       sb.append(" onDiskDataSizeWithHeader=").append(onDiskDataSizeWithHeader)
         .append("(").append(onDiskSizeWithoutHeader)
         .append("+").append(HConstants.HFILEBLOCK_HEADER_SIZE_NO_CHECKSUM).append(")");
     }
     String dataBegin = null;
     if (buf.hasArray()) {
       dataBegin = Bytes.toStringBinary(buf.array(), buf.arrayOffset() + headerSize(),
           Math.min(32, buf.limit() - buf.arrayOffset() - headerSize()));
     } else {
       ByteBuffer bufWithoutHeader = getBufferWithoutHeader();
       byte[] dataBeginBytes = new byte[Math.min(32,
           bufWithoutHeader.limit() - bufWithoutHeader.position())];
       bufWithoutHeader.get(dataBeginBytes);
       dataBegin = Bytes.toStringBinary(dataBeginBytes);
     }
     sb.append(" getOnDiskSizeWithHeader()=").append(getOnDiskSizeWithHeader())
       .append(" totalChecksumBytes()=").append(totalChecksumBytes())
       .append(" isUnpacked()=").append(isUnpacked())
       .append(" buf=[ ").append(buf).append(" ]")
       .append(" dataBeginsWith=").append(dataBegin)
       .append(" fileContext=").append(fileContext)
       .append(" ]");
     return sb.toString();
   }
 
   /**
    * Called after reading a block with provided onDiskSizeWithHeader.
    */
   private static void validateOnDiskSizeWithoutHeader(int expectedOnDiskSizeWithoutHeader,
       int actualOnDiskSizeWithoutHeader, ByteBuffer buf, long offset) throws IOException {
     if (actualOnDiskSizeWithoutHeader != expectedOnDiskSizeWithoutHeader) {
       // We make the read-only copy here instead of when passing the parameter to this function
       // to make duplicates only in failure cases, instead of every single time.
       ByteBuffer bufReadOnly = buf.asReadOnlyBuffer();
       String dataBegin = null;
       byte[] dataBeginBytes = new byte[Math.min(32, bufReadOnly.limit() - bufReadOnly.position())];
       bufReadOnly.get(dataBeginBytes);
       dataBegin = Bytes.toStringBinary(dataBeginBytes);
       String blockInfoMsg =
         "Block offset: " + offset + ", data starts with: " + dataBegin;
       throw new IOException("On-disk size without header provided is "
           + expectedOnDiskSizeWithoutHeader + ", but block "
           + "header contains " + actualOnDiskSizeWithoutHeader + ". " +
           blockInfoMsg);
     }
   }
 
   /**
    * Retrieves the decompressed/decrypted view of this block. An encoded block remains in its
    * encoded structure. Internal structures are shared between instances where applicable.
    */
   HFileBlock unpack(HFileContext fileContext, FSReader reader) throws IOException {
     if (!fileContext.isCompressedOrEncrypted()) {
       // TODO: cannot use our own fileContext here because HFileBlock(ByteBuffer, boolean),
       // which is used for block serialization to L2 cache, does not preserve encoding and
       // encryption details.
       return this;
     }
 
     HFileBlock unpacked = new HFileBlock(this);
     unpacked.allocateBuffer(); // allocates space for the decompressed block
 
     HFileBlockDecodingContext ctx = blockType == BlockType.ENCODED_DATA ?
       reader.getBlockDecodingContext() : reader.getDefaultBlockDecodingContext();
 
     ByteBuffer dup = this.buf.duplicate();
     dup.position(this.headerSize());
     dup = dup.slice();
     ctx.prepareDecoding(unpacked.getOnDiskSizeWithoutHeader(),
       unpacked.getUncompressedSizeWithoutHeader(), unpacked.getBufferWithoutHeader(),
       dup);
 
     // Preserve the next block's header bytes in the new block if we have them.
     if (unpacked.hasNextBlockHeader()) {
       // Both the buffers are limited till checksum bytes and avoid the next block's header.
       // Below call to copyFromBufferToBuffer() will try positional read/write from/to buffers when
       // any of the buffer is DBB. So we change the limit on a dup buffer. No copying just create
       // new BB objects
       ByteBuffer inDup = this.buf.duplicate();
       inDup.limit(inDup.limit() + headerSize());
       ByteBuffer outDup = unpacked.buf.duplicate();
       outDup.limit(outDup.limit() + unpacked.headerSize());
       ByteBufferUtils.copyFromBufferToBuffer(
           outDup,
           inDup,
           this.onDiskDataSizeWithHeader,
           unpacked.headerSize() + unpacked.uncompressedSizeWithoutHeader
               + unpacked.totalChecksumBytes(), unpacked.headerSize());
     }
     return unpacked;
   }
 
   /**
    * Return true when this buffer includes next block's header.
    */
   private boolean hasNextBlockHeader() {
     return nextBlockOnDiskSizeWithHeader > 0;
   }
 
   /**
    * Always allocates a new buffer of the correct size. Copies header bytes
    * from the existing buffer. Does not change header fields.
    * Reserve room to keep checksum bytes too.
    */
   private void allocateBuffer() {
     int cksumBytes = totalChecksumBytes();
     int headerSize = headerSize();
     int capacityNeeded = headerSize + uncompressedSizeWithoutHeader +
         cksumBytes + (hasNextBlockHeader() ? headerSize : 0);
 
     // TODO we need consider allocating offheap here?
     ByteBuffer newBuf = ByteBuffer.allocate(capacityNeeded);
 
     // Copy header bytes into newBuf.
     // newBuf is HBB so no issue in calling array()
     ByteBuffer dup = buf.duplicate();
     dup.position(0);
     dup.get(newBuf.array(), newBuf.arrayOffset(), headerSize);
 
     buf = newBuf;
     // set limit to exclude next block's header
     buf.limit(headerSize + uncompressedSizeWithoutHeader + cksumBytes);
   }
 
   /**
    * Return true when this block's buffer has been unpacked, false otherwise. Note this is a
    * calculated heuristic, not tracked attribute of the block.
    */
   public boolean isUnpacked() {
     final int cksumBytes = totalChecksumBytes();
     final int headerSize = headerSize();
     final int expectedCapacity = headerSize + uncompressedSizeWithoutHeader + cksumBytes;
     final int bufCapacity = buf.capacity();
     return bufCapacity == expectedCapacity || bufCapacity == expectedCapacity + headerSize;
   }
 
   /** An additional sanity-check in case no compression or encryption is being used. */
   public static void verifyUncompressed(ByteBuffer buf, boolean useHBaseChecksum)
       throws IOException {
     int onDiskSizeWithoutHeader = buf.getInt(Header.ON_DISK_SIZE_WITHOUT_HEADER_INDEX);
     int uncompressedSizeWithoutHeader = buf.getInt(Header.UNCOMPRESSED_SIZE_WITHOUT_HEADER_INDEX);
     int onDiskDataSizeWithHeader;
     int checksumBytes = 0;
     if (useHBaseChecksum) {
       onDiskDataSizeWithHeader = buf.getInt(Header.ON_DISK_DATA_SIZE_WITH_HEADER_INDEX);
       checksumBytes = (int) ChecksumUtil.numBytes(onDiskDataSizeWithHeader,
           buf.getInt(Header.BYTES_PER_CHECKSUM_INDEX));
     }
 
     if (onDiskSizeWithoutHeader != uncompressedSizeWithoutHeader + checksumBytes) {
       throw new IOException("Using no compression but "
           + "onDiskSizeWithoutHeader=" + onDiskSizeWithoutHeader + ", "
           + "uncompressedSizeWithoutHeader=" + uncompressedSizeWithoutHeader
           + ", numChecksumbytes=" + checksumBytes);
     }
   }
 
   /**
    * @param expectedType the expected type of this block
    * @throws IOException if this block's type is different than expected
    */
   public void expectType(BlockType expectedType) throws IOException {
     if (blockType != expectedType) {
       throw new IOException("Invalid block type: expected=" + expectedType
           + ", actual=" + blockType);
     }
   }
 
   /** @return the offset of this block in the file it was read from */
   public long getOffset() {
     if (offset < 0) {
       throw new IllegalStateException(
           "HFile block offset not initialized properly");
     }
     return offset;
   }
 
   /**
    * @return a byte stream reading the data + checksum of this block
    */
   public DataInputStream getByteStream() {
     ByteBuffer dup = this.buf.duplicate();
     dup.position(this.headerSize());
     return new DataInputStream(new ByteBufferInputStream(dup));
   }
 
   @Override
   public long heapSize() {
     long size = ClassSize.align(
         ClassSize.OBJECT +
         // Block type, byte buffer and meta references
         3 * ClassSize.REFERENCE +
         // On-disk size, uncompressed size, and next block's on-disk size
         // bytePerChecksum and onDiskDataSize
         4 * Bytes.SIZEOF_INT +
         // This and previous block offset
         2 * Bytes.SIZEOF_LONG +
         // Heap size of the meta object. meta will be always not null.
         fileContext.heapSize()
     );
 
     if (buf != null) {
       // Deep overhead of the byte buffer. Needs to be aligned separately.
       size += ClassSize.align(buf.capacity() + BYTE_BUFFER_HEAP_SIZE);
     }
 
     return ClassSize.align(size);
   }
 
   /**
    * Read from an input stream. Analogous to
    * {@link IOUtils#readFully(InputStream, byte[], int, int)}, but specifies a
    * number of "extra" bytes that would be desirable but not absolutely
    * necessary to read.
    *
    * @param in the input stream to read from
    * @param buf the buffer to read into
    * @param bufOffset the destination offset in the buffer
    * @param necessaryLen the number of bytes that are absolutely necessary to
    *          read
    * @param extraLen the number of extra bytes that would be nice to read
    * @return true if succeeded reading the extra bytes
    * @throws IOException if failed to read the necessary bytes
    */
   public static boolean readWithExtra(InputStream in, byte[] buf,
       int bufOffset, int necessaryLen, int extraLen) throws IOException {
     int bytesRemaining = necessaryLen + extraLen;
     while (bytesRemaining > 0) {
       int ret = in.read(buf, bufOffset, bytesRemaining);
       if (ret == -1 && bytesRemaining <= extraLen) {
         // We could not read the "extra data", but that is OK.
         break;
       }
 
       if (ret < 0) {
         throw new IOException("Premature EOF from inputStream (read "
             + "returned " + ret + ", was trying to read " + necessaryLen
             + " necessary bytes and " + extraLen + " extra bytes, "
             + "successfully read "
             + (necessaryLen + extraLen - bytesRemaining));
       }
       bufOffset += ret;
       bytesRemaining -= ret;
     }
     return bytesRemaining <= 0;
   }
 
   /**
    * Read from an input stream. Analogous to
    * {@link IOUtils#readFully(InputStream, byte[], int, int)}, but uses
    * positional read and specifies a number of "extra" bytes that would be
    * desirable but not absolutely necessary to read.
    *
    * @param in the input stream to read from
    * @param position the position within the stream from which to start reading
    * @param buf the buffer to read into
    * @param bufOffset the destination offset in the buffer
    * @param necessaryLen the number of bytes that are absolutely necessary to
    *     read
    * @param extraLen the number of extra bytes that would be nice to read
    * @return true if and only if extraLen is > 0 and reading those extra bytes
    *     was successful
    * @throws IOException if failed to read the necessary bytes
    */
   @VisibleForTesting
   static boolean positionalReadWithExtra(FSDataInputStream in,
       long position, byte[] buf, int bufOffset, int necessaryLen, int extraLen)
       throws IOException {
     int bytesRemaining = necessaryLen + extraLen;
     int bytesRead = 0;
     while (bytesRead < necessaryLen) {
       int ret = in.read(position, buf, bufOffset, bytesRemaining);
       if (ret < 0) {
         throw new IOException("Premature EOF from inputStream (positional read "
             + "returned " + ret + ", was trying to read " + necessaryLen
             + " necessary bytes and " + extraLen + " extra bytes, "
             + "successfully read " + bytesRead);
       }
       position += ret;
       bufOffset += ret;
       bytesRemaining -= ret;
       bytesRead += ret;
     }
     return bytesRead != necessaryLen && bytesRemaining <= 0;
   }
 
   /**
    * @return the on-disk size of the next block (including the header size)
    *         that was read by peeking into the next block's header
    */
   public int getNextBlockOnDiskSizeWithHeader() {
     return nextBlockOnDiskSizeWithHeader;
   }
 
   /**
    * Unified version 2 {@link HFile} block writer. The intended usage pattern
    * is as follows:
    * <ol>
    * <li>Construct an {@link HFileBlock.Writer}, providing a compression algorithm.
    * <li>Call {@link Writer#startWriting} and get a data stream to write to.
    * <li>Write your data into the stream.
    * <li>Call {@link Writer#writeHeaderAndData(FSDataOutputStream)} as many times as you need to.
    * store the serialized block into an external stream.
    * <li>Repeat to write more blocks.
    * </ol>
    * <p>
    */
   public static class Writer {
 
     private enum State {
       INIT,
       WRITING,
       BLOCK_READY
     };
 
     /** Writer state. Used to ensure the correct usage protocol. */
     private State state = State.INIT;
 
     /** Data block encoder used for data blocks */
     private final HFileDataBlockEncoder dataBlockEncoder;
 
     private HFileBlockEncodingContext dataBlockEncodingCtx;
 
     /** block encoding context for non-data blocks */
     private HFileBlockDefaultEncodingContext defaultBlockEncodingCtx;
 
     /**
      * The stream we use to accumulate data in uncompressed format for each
      * block. We reset this stream at the end of each block and reuse it. The
      * header is written as the first {@link HConstants#HFILEBLOCK_HEADER_SIZE} bytes into this
      * stream.
      */
     private ByteArrayOutputStream baosInMemory;
 
     /**
      * Current block type. Set in {@link #startWriting(BlockType)}. Could be
      * changed in {@link #finishBlock()} from {@link BlockType#DATA}
      * to {@link BlockType#ENCODED_DATA}.
      */
     private BlockType blockType;
 
     /**
      * A stream that we write uncompressed bytes to, which compresses them and
      * writes them to {@link #baosInMemory}.
      */
     private DataOutputStream userDataStream;
 
     // Size of actual data being written. Not considering the block encoding/compression. This
     // includes the header size also.
     private int unencodedDataSizeWritten;
 
     /**
      * Bytes to be written to the file system, including the header. Compressed
      * if compression is turned on. It also includes the checksum data that
      * immediately follows the block data. (header + data + checksums)
      */
     private byte[] onDiskBytesWithHeader;
 
     /**
      * The size of the checksum data on disk. It is used only if data is
      * not compressed. If data is compressed, then the checksums are already
      * part of onDiskBytesWithHeader. If data is uncompressed, then this
      * variable stores the checksum data for this block.
      */
     private byte[] onDiskChecksum;
 
     /**
      * Valid in the READY state. Contains the header and the uncompressed (but
      * potentially encoded, if this is a data block) bytes, so the length is
      * {@link #uncompressedSizeWithoutHeader} +
      * {@link org.apache.hadoop.hbase.HConstants#HFILEBLOCK_HEADER_SIZE}.
      * Does not store checksums.
      */
     private byte[] uncompressedBytesWithHeader;
 
     /**
      * Current block's start offset in the {@link HFile}. Set in
      * {@link #writeHeaderAndData(FSDataOutputStream)}.
      */
     private long startOffset;
 
     /**
      * Offset of previous block by block type. Updated when the next block is
      * started.
      */
     private long[] prevOffsetByType;
 
     /** The offset of the previous block of the same type */
     private long prevOffset;
     /** Meta data that holds information about the hfileblock**/
     private HFileContext fileContext;
 
     /**
      * @param dataBlockEncoder data block encoding algorithm to use
      */
     public Writer(HFileDataBlockEncoder dataBlockEncoder, HFileContext fileContext) {
       this.dataBlockEncoder = dataBlockEncoder != null
           ? dataBlockEncoder : NoOpDataBlockEncoder.INSTANCE;
       defaultBlockEncodingCtx = new HFileBlockDefaultEncodingContext(null,
           HConstants.HFILEBLOCK_DUMMY_HEADER, fileContext);
       dataBlockEncodingCtx = this.dataBlockEncoder
           .newDataBlockEncodingContext(HConstants.HFILEBLOCK_DUMMY_HEADER, fileContext);
 
       if (fileContext.getBytesPerChecksum() < HConstants.HFILEBLOCK_HEADER_SIZE) {
         throw new RuntimeException("Unsupported value of bytesPerChecksum. " +
             " Minimum is " + HConstants.HFILEBLOCK_HEADER_SIZE + " but the configured value is " +
             fileContext.getBytesPerChecksum());
       }
 
       baosInMemory = new ByteArrayOutputStream();
 
       prevOffsetByType = new long[BlockType.values().length];
       for (int i = 0; i < prevOffsetByType.length; ++i)
         prevOffsetByType[i] = -1;
 
       this.fileContext = fileContext;
     }
 
     /**
      * Starts writing into the block. The previous block's data is discarded.
      *
      * @return the stream the user can write their data into
      * @throws IOException
      */
     public DataOutputStream startWriting(BlockType newBlockType)
         throws IOException {
       if (state == State.BLOCK_READY && startOffset != -1) {
         // We had a previous block that was written to a stream at a specific
         // offset. Save that offset as the last offset of a block of that type.
         prevOffsetByType[blockType.getId()] = startOffset;
       }
 
       startOffset = -1;
       blockType = newBlockType;
 
       baosInMemory.reset();
       baosInMemory.write(HConstants.HFILEBLOCK_DUMMY_HEADER);
 
       state = State.WRITING;
 
       // We will compress it later in finishBlock()
       userDataStream = new DataOutputStream(baosInMemory);
       if (newBlockType == BlockType.DATA) {
         this.dataBlockEncoder.startBlockEncoding(dataBlockEncodingCtx, userDataStream);
       }
       this.unencodedDataSizeWritten = 0;
       return userDataStream;
     }
 
     /**
      * Writes the Cell to this block
      * @param cell
      * @throws IOException
      */
     public void write(Cell cell) throws IOException{
       expectState(State.WRITING);
       this.unencodedDataSizeWritten += this.dataBlockEncoder.encode(cell, dataBlockEncodingCtx,
           this.userDataStream);
     }
 
     /**
      * Returns the stream for the user to write to. The block writer takes care
      * of handling compression and buffering for caching on write. Can only be
      * called in the "writing" state.
      *
      * @return the data output stream for the user to write to
      */
     DataOutputStream getUserDataStream() {
       expectState(State.WRITING);
       return userDataStream;
     }
 
     /**
      * Transitions the block writer from the "writing" state to the "block
      * ready" state.  Does nothing if a block is already finished.
      */
     void ensureBlockReady() throws IOException {
       Preconditions.checkState(state != State.INIT,
           "Unexpected state: " + state);
 
       if (state == State.BLOCK_READY)
         return;
 
       // This will set state to BLOCK_READY.
       finishBlock();
     }
 
     /**
      * An internal method that flushes the compressing stream (if using
      * compression), serializes the header, and takes care of the separate
      * uncompressed stream for caching on write, if applicable. Sets block
      * write state to "block ready".
      */
     private void finishBlock() throws IOException {
       if (blockType == BlockType.DATA) {
         BufferGrabbingByteArrayOutputStream baosInMemoryCopy =
             new BufferGrabbingByteArrayOutputStream();
         baosInMemory.writeTo(baosInMemoryCopy);
         this.dataBlockEncoder.endBlockEncoding(dataBlockEncodingCtx, userDataStream,
             baosInMemoryCopy.buf, blockType);
         blockType = dataBlockEncodingCtx.getBlockType();
       }
       userDataStream.flush();
       // This does an array copy, so it is safe to cache this byte array.
       uncompressedBytesWithHeader = baosInMemory.toByteArray();
       prevOffset = prevOffsetByType[blockType.getId()];
 
       // We need to set state before we can package the block up for
       // cache-on-write. In a way, the block is ready, but not yet encoded or
       // compressed.
       state = State.BLOCK_READY;
       if (blockType == BlockType.DATA || blockType == BlockType.ENCODED_DATA) {
         onDiskBytesWithHeader = dataBlockEncodingCtx
             .compressAndEncrypt(uncompressedBytesWithHeader);
       } else {
         onDiskBytesWithHeader = defaultBlockEncodingCtx
             .compressAndEncrypt(uncompressedBytesWithHeader);
       }
       int numBytes = (int) ChecksumUtil.numBytes(
           onDiskBytesWithHeader.length,
           fileContext.getBytesPerChecksum());
 
       // put the header for on disk bytes
       putHeader(onDiskBytesWithHeader, 0,
           onDiskBytesWithHeader.length + numBytes,
           uncompressedBytesWithHeader.length, onDiskBytesWithHeader.length);
       // set the header for the uncompressed bytes (for cache-on-write)
       putHeader(uncompressedBytesWithHeader, 0,
           onDiskBytesWithHeader.length + numBytes,
           uncompressedBytesWithHeader.length, onDiskBytesWithHeader.length);
 
       onDiskChecksum = new byte[numBytes];
       ChecksumUtil.generateChecksums(
           onDiskBytesWithHeader, 0, onDiskBytesWithHeader.length,
           onDiskChecksum, 0, fileContext.getChecksumType(), fileContext.getBytesPerChecksum());
     }
 
     public static class BufferGrabbingByteArrayOutputStream extends ByteArrayOutputStream {
       private byte[] buf;
 
       @Override
       public void write(byte[] b, int off, int len) {
         this.buf = b;
       }
 
       public byte[] getBuffer() {
         return this.buf;
       }
     }
 
     /**
      * Put the header into the given byte array at the given offset.
      * @param onDiskSize size of the block on disk header + data + checksum
      * @param uncompressedSize size of the block after decompression (but
      *          before optional data block decoding) including header
      * @param onDiskDataSize size of the block on disk with header
      *        and data but not including the checksums
      */
     private void putHeader(byte[] dest, int offset, int onDiskSize,
         int uncompressedSize, int onDiskDataSize) {
       offset = blockType.put(dest, offset);
       offset = Bytes.putInt(dest, offset, onDiskSize - HConstants.HFILEBLOCK_HEADER_SIZE);
       offset = Bytes.putInt(dest, offset, uncompressedSize - HConstants.HFILEBLOCK_HEADER_SIZE);
       offset = Bytes.putLong(dest, offset, prevOffset);
       offset = Bytes.putByte(dest, offset, fileContext.getChecksumType().getCode());
       offset = Bytes.putInt(dest, offset, fileContext.getBytesPerChecksum());
       Bytes.putInt(dest, offset, onDiskDataSize);
     }
 
     /**
      * Similar to {@link #writeHeaderAndData(FSDataOutputStream)}, but records
      * the offset of this block so that it can be referenced in the next block
      * of the same type.
      *
      * @param out
      * @throws IOException
      */
     public void writeHeaderAndData(FSDataOutputStream out) throws IOException {
       long offset = out.getPos();
       if (startOffset != -1 && offset != startOffset) {
         throw new IOException("A " + blockType + " block written to a "
             + "stream twice, first at offset " + startOffset + ", then at "
             + offset);
       }
       startOffset = offset;
 
       finishBlockAndWriteHeaderAndData((DataOutputStream) out);
     }
 
     /**
      * Writes the header and the compressed data of this block (or uncompressed
      * data when not using compression) into the given stream. Can be called in
      * the "writing" state or in the "block ready" state. If called in the
      * "writing" state, transitions the writer to the "block ready" state.
      *
      * @param out the output stream to write the
      * @throws IOException
      */
     protected void finishBlockAndWriteHeaderAndData(DataOutputStream out)
       throws IOException {
       ensureBlockReady();
       out.write(onDiskBytesWithHeader);
       out.write(onDiskChecksum);
     }
 
     /**
      * Returns the header or the compressed data (or uncompressed data when not
      * using compression) as a byte array. Can be called in the "writing" state
      * or in the "block ready" state. If called in the "writing" state,
      * transitions the writer to the "block ready" state. This returns
      * the header + data + checksums stored on disk.
      *
      * @return header and data as they would be stored on disk in a byte array
      * @throws IOException
      */
     byte[] getHeaderAndDataForTest() throws IOException {
       ensureBlockReady();
       // This is not very optimal, because we are doing an extra copy.
       // But this method is used only by unit tests.
       byte[] output =
           new byte[onDiskBytesWithHeader.length
               + onDiskChecksum.length];
       System.arraycopy(onDiskBytesWithHeader, 0, output, 0,
           onDiskBytesWithHeader.length);
       System.arraycopy(onDiskChecksum, 0, output,
           onDiskBytesWithHeader.length, onDiskChecksum.length);
       return output;
     }
 
     /**
      * Releases resources used by this writer.
      */
     public void release() {
       if (dataBlockEncodingCtx != null) {
         dataBlockEncodingCtx.close();
         dataBlockEncodingCtx = null;
       }
       if (defaultBlockEncodingCtx != null) {
         defaultBlockEncodingCtx.close();
         defaultBlockEncodingCtx = null;
       }
     }
 
     /**
      * Returns the on-disk size of the data portion of the block. This is the
      * compressed size if compression is enabled. Can only be called in the
      * "block ready" state. Header is not compressed, and its size is not
      * included in the return value.
      *
      * @return the on-disk size of the block, not including the header.
      */
     int getOnDiskSizeWithoutHeader() {
       expectState(State.BLOCK_READY);
       return onDiskBytesWithHeader.length
           + onDiskChecksum.length
           - HConstants.HFILEBLOCK_HEADER_SIZE;
     }
 
     /**
      * Returns the on-disk size of the block. Can only be called in the
      * "block ready" state.
      *
      * @return the on-disk size of the block ready to be written, including the
      *         header size, the data and the checksum data.
      */
     int getOnDiskSizeWithHeader() {
       expectState(State.BLOCK_READY);
       return onDiskBytesWithHeader.length + onDiskChecksum.length;
     }
 
     /**
      * The uncompressed size of the block data. Does not include header size.
      */
     int getUncompressedSizeWithoutHeader() {
       expectState(State.BLOCK_READY);
       return uncompressedBytesWithHeader.length - HConstants.HFILEBLOCK_HEADER_SIZE;
     }
 
     /**
      * The uncompressed size of the block data, including header size.
      */
     int getUncompressedSizeWithHeader() {
       expectState(State.BLOCK_READY);
       return uncompressedBytesWithHeader.length;
     }
 
     /** @return true if a block is being written  */
     public boolean isWriting() {
       return state == State.WRITING;
     }
 
     /**
      * Returns the number of bytes written into the current block so far, or
      * zero if not writing the block at the moment. Note that this will return
      * zero in the "block ready" state as well.
      *
      * @return the number of bytes written
      */
     public int blockSizeWritten() {
       if (state != State.WRITING) return 0;
       return this.unencodedDataSizeWritten;
     }
 
     /**
      * Returns the header followed by the uncompressed data, even if using
      * compression. This is needed for storing uncompressed blocks in the block
      * cache. Can be called in the "writing" state or the "block ready" state.
      * Returns only the header and data, does not include checksum data.
      *
      * @return uncompressed block bytes for caching on write
      */
     ByteBuffer getUncompressedBufferWithHeader() {
       expectState(State.BLOCK_READY);
       return ByteBuffer.wrap(uncompressedBytesWithHeader);
     }
 
     /**
      * Returns the header followed by the on-disk (compressed/encoded/encrypted) data. This is
      * needed for storing packed blocks in the block cache. Expects calling semantics identical to
      * {@link #getUncompressedBufferWithHeader()}. Returns only the header and data,
      * Does not include checksum data.
      *
      * @return packed block bytes for caching on write
      */
     ByteBuffer getOnDiskBufferWithHeader() {
       expectState(State.BLOCK_READY);
       return ByteBuffer.wrap(onDiskBytesWithHeader);
     }
 
     private void expectState(State expectedState) {
       if (state != expectedState) {
         throw new IllegalStateException("Expected state: " + expectedState +
             ", actual state: " + state);
       }
     }
 
     /**
      * Takes the given {@link BlockWritable} instance, creates a new block of
      * its appropriate type, writes the writable into this block, and flushes
      * the block into the output stream. The writer is instructed not to buffer
      * uncompressed bytes for cache-on-write.
      *
      * @param bw the block-writable object to write as a block
      * @param out the file system output stream
      * @throws IOException
      */
     public void writeBlock(BlockWritable bw, FSDataOutputStream out)
         throws IOException {
       bw.writeToBlock(startWriting(bw.getBlockType()));
       writeHeaderAndData(out);
     }
 
     /**
      * Creates a new HFileBlock. Checksums have already been validated, so
      * the byte buffer passed into the constructor of this newly created
      * block does not have checksum data even though the header minor
      * version is MINOR_VERSION_WITH_CHECKSUM. This is indicated by setting a
      * 0 value in bytesPerChecksum.
      */
     public HFileBlock getBlockForCaching(CacheConfig cacheConf) {
       HFileContext newContext = new HFileContextBuilder()
                                 .withBlockSize(fileContext.getBlocksize())
                                 .withBytesPerCheckSum(0)
                                 .withChecksumType(ChecksumType.NULL) // no checksums in cached data
                                 .withCompression(fileContext.getCompression())
                                 .withDataBlockEncoding(fileContext.getDataBlockEncoding())
                                 .withHBaseCheckSum(fileContext.isUseHBaseChecksum())
                                 .withCompressTags(fileContext.isCompressTags())
                                 .withIncludesMvcc(fileContext.isIncludesMvcc())
                                 .withIncludesTags(fileContext.isIncludesTags())
                                 .build();
       return new HFileBlock(blockType, getOnDiskSizeWithoutHeader(),
           getUncompressedSizeWithoutHeader(), prevOffset,
           cacheConf.shouldCacheCompressed(blockType.getCategory()) ?
             getOnDiskBufferWithHeader() :
             getUncompressedBufferWithHeader(),
           FILL_HEADER, startOffset,
           onDiskBytesWithHeader.length + onDiskChecksum.length, newContext);
     }
   }
 
   /** Something that can be written into a block. */
   public interface BlockWritable {
 
     /** The type of block this data should use. */
     BlockType getBlockType();
 
     /**
      * Writes the block to the provided stream. Must not write any magic
      * records.
      *
      * @param out a stream to write uncompressed data into
      */
     void writeToBlock(DataOutput out) throws IOException;
   }
 
   // Block readers and writers
 
   /** An interface allowing to iterate {@link HFileBlock}s. */
   public interface BlockIterator {
 
     /**
      * Get the next block, or null if there are no more blocks to iterate.
      */
     HFileBlock nextBlock() throws IOException;
 
     /**
      * Similar to {@link #nextBlock()} but checks block type, throws an
      * exception if incorrect, and returns the HFile block
      */
     HFileBlock nextBlockWithBlockType(BlockType blockType) throws IOException;
   }
 
   /** A full-fledged reader with iteration ability. */
   public interface FSReader {
 
     /**
      * Reads the block at the given offset in the file with the given on-disk
      * size and uncompressed size.
      *
      * @param offset
      * @param onDiskSize the on-disk size of the entire block, including all
      *          applicable headers, or -1 if unknown
      * @param uncompressedSize the uncompressed size of the compressed part of
      *          the block, or -1 if unknown
      * @return the newly read block
      */
     HFileBlock readBlockData(long offset, long onDiskSize,
         int uncompressedSize, boolean pread) throws IOException;
 
     /**
      * Creates a block iterator over the given portion of the {@link HFile}.
      * The iterator returns blocks starting with offset such that offset &lt;=
      * startOffset &lt; endOffset. Returned blocks are always unpacked.
      *
      * @param startOffset the offset of the block to start iteration with
      * @param endOffset the offset to end iteration at (exclusive)
      * @return an iterator of blocks between the two given offsets
      */
     BlockIterator blockRange(long startOffset, long endOffset);
 
     /** Closes the backing streams */
     void closeStreams() throws IOException;
 
     /** Get a decoder for {@link BlockType#ENCODED_DATA} blocks from this file. */
     HFileBlockDecodingContext getBlockDecodingContext();
 
     /** Get the default decoder for blocks from this file. */
     HFileBlockDecodingContext getDefaultBlockDecodingContext();
 
     /**
      * To close the stream's socket. Note: This can be concurrently called from multiple threads and
      * implementation should take care of thread safety.
      */
     void unbufferStream();
   }
 
   /**
    * A common implementation of some methods of {@link FSReader} and some
    * tools for implementing HFile format version-specific block readers.
    */
   private abstract static class AbstractFSReader implements FSReader {
     /** Compression algorithm used by the {@link HFile} */
 
     /** The size of the file we are reading from, or -1 if unknown. */
     protected long fileSize;
 
     /** The size of the header */
     protected final int hdrSize;
 
     /** The filesystem used to access data */
     protected HFileSystem hfs;
 
     /** The path (if any) where this data is coming from */
     protected Path path;
 
     protected final Lock streamLock = new ReentrantLock();
 
     /** The default buffer size for our buffered streams */
     public static final int DEFAULT_BUFFER_SIZE = 1 << 20;
 
     protected HFileContext fileContext;
 
     public AbstractFSReader(long fileSize, HFileSystem hfs, Path path, HFileContext fileContext)
         throws IOException {
       this.fileSize = fileSize;
       this.hfs = hfs;
       this.path = path;
       this.fileContext = fileContext;
       this.hdrSize = headerSize(fileContext.isUseHBaseChecksum());
     }
 
     @Override
     public BlockIterator blockRange(final long startOffset,
         final long endOffset) {
       final FSReader owner = this; // handle for inner class
       return new BlockIterator() {
         private long offset = startOffset;
 
         @Override
         public HFileBlock nextBlock() throws IOException {
           if (offset >= endOffset)
             return null;
           HFileBlock b = readBlockData(offset, -1, -1, false);
           offset += b.getOnDiskSizeWithHeader();
           return b.unpack(fileContext, owner);
         }
 
         @Override
         public HFileBlock nextBlockWithBlockType(BlockType blockType)
             throws IOException {
           HFileBlock blk = nextBlock();
           if (blk.getBlockType() != blockType) {
             throw new IOException("Expected block of type " + blockType
                 + " but found " + blk.getBlockType());
           }
           return blk;
         }
       };
     }
 
     /**
      * Does a positional read or a seek and read into the given buffer. Returns
      * the on-disk size of the next block, or -1 if it could not be determined.
      *
      * @param dest destination buffer
      * @param destOffset offset in the destination buffer
      * @param size size of the block to be read
      * @param peekIntoNextBlock whether to read the next block's on-disk size
      * @param fileOffset position in the stream to read at
      * @param pread whether we should do a positional read
      * @param istream The input source of data
      * @return the on-disk size of the next block with header size included, or
      *         -1 if it could not be determined
      * @throws IOException
      */
     protected int readAtOffset(FSDataInputStream istream, byte[] dest, int destOffset, int size,
         boolean peekIntoNextBlock, long fileOffset, boolean pread) throws IOException {
       if (peekIntoNextBlock &&
           destOffset + size + hdrSize > dest.length) {
         // We are asked to read the next block's header as well, but there is
         // not enough room in the array.
         throw new IOException("Attempted to read " + size + " bytes and " +
             hdrSize + " bytes of next header into a " + dest.length +
             "-byte array at offset " + destOffset);
       }
 
       if (!pread && streamLock.tryLock()) {
         // Seek + read. Better for scanning.
         try {
           HFileUtil.seekOnMultipleSources(istream, fileOffset);
 
           long realOffset = istream.getPos();
           if (realOffset != fileOffset) {
             throw new IOException("Tried to seek to " + fileOffset + " to "
                 + "read " + size + " bytes, but pos=" + realOffset
                 + " after seek");
           }
 
           if (!peekIntoNextBlock) {
             IOUtils.readFully(istream, dest, destOffset, size);
             return -1;
           }
 
           // Try to read the next block header.
           if (!readWithExtra(istream, dest, destOffset, size, hdrSize))
             return -1;
         } finally {
           streamLock.unlock();
         }
       } else {
         // Positional read. Better for random reads; or when the streamLock is already locked.
         int extraSize = peekIntoNextBlock ? hdrSize : 0;
         if (!positionalReadWithExtra(istream, fileOffset, dest, destOffset,
             size, extraSize)) {
           return -1;
         }
       }
 
       assert peekIntoNextBlock;
       return Bytes.toInt(dest, destOffset + size + BlockType.MAGIC_LENGTH) + hdrSize;
     }
 
   }
 
   /**
    * We always prefetch the header of the next block, so that we know its
    * on-disk size in advance and can read it in one operation.
    */
   private static class PrefetchedHeader {
     long offset = -1;
     byte[] header = new byte[HConstants.HFILEBLOCK_HEADER_SIZE];
     final ByteBuffer buf = ByteBuffer.wrap(header, 0, HConstants.HFILEBLOCK_HEADER_SIZE);
   }
 
   /** Reads version 2 blocks from the filesystem. */
   static class FSReaderImpl extends AbstractFSReader {
     /** The file system stream of the underlying {@link HFile} that
      * does or doesn't do checksum validations in the filesystem */
     protected FSDataInputStreamWrapper streamWrapper;
 
     private HFileBlockDecodingContext encodedBlockDecodingCtx;
 
     /** Default context used when BlockType != {@link BlockType#ENCODED_DATA}. */
     private final HFileBlockDefaultDecodingContext defaultDecodingCtx;
 
     private ThreadLocal<PrefetchedHeader> prefetchedHeaderForThread =
         new ThreadLocal<PrefetchedHeader>() {
           @Override
           public PrefetchedHeader initialValue() {
             return new PrefetchedHeader();
           }
         };
 
     public FSReaderImpl(FSDataInputStreamWrapper stream, long fileSize, HFileSystem hfs, Path path,
         HFileContext fileContext) throws IOException {
       super(fileSize, hfs, path, fileContext);
       this.streamWrapper = stream;
       // Older versions of HBase didn't support checksum.
       this.streamWrapper.prepareForBlockReader(!fileContext.isUseHBaseChecksum());
       defaultDecodingCtx = new HFileBlockDefaultDecodingContext(fileContext);
       encodedBlockDecodingCtx = defaultDecodingCtx;
     }
 
     /**
      * A constructor that reads files with the latest minor version.
      * This is used by unit tests only.
      */
     FSReaderImpl(FSDataInputStream istream, long fileSize, HFileContext fileContext)
     throws IOException {
       this(new FSDataInputStreamWrapper(istream), fileSize, null, null, fileContext);
     }
 
     /**
      * Reads a version 2 block (version 1 blocks not supported and not expected). Tries to do as
      * little memory allocation as possible, using the provided on-disk size.
      *
      * @param offset the offset in the stream to read at
      * @param onDiskSizeWithHeaderL the on-disk size of the block, including
      *          the header, or -1 if unknown
      * @param uncompressedSize the uncompressed size of the the block. Always
      *          expected to be -1. This parameter is only used in version 1.
      * @param pread whether to use a positional read
      */
     @Override
     public HFileBlock readBlockData(long offset, long onDiskSizeWithHeaderL,
         int uncompressedSize, boolean pread)
     throws IOException {
 
       // get a copy of the current state of whether to validate
       // hbase checksums or not for this read call. This is not
       // thread-safe but the one constaint is that if we decide
       // to skip hbase checksum verification then we are
       // guaranteed to use hdfs checksum verification.
       boolean doVerificationThruHBaseChecksum = streamWrapper.shouldUseHBaseChecksum();
       FSDataInputStream is = streamWrapper.getStream(doVerificationThruHBaseChecksum);
 
       HFileBlock blk = readBlockDataInternal(is, offset, (int) onDiskSizeWithHeaderL,
           uncompressedSize, pread, doVerificationThruHBaseChecksum);
       if (blk == null) {
         HFile.LOG.warn("HBase checksum verification failed for file " +
                        path + " at offset " +
                        offset + " filesize " + fileSize +
                        ". Retrying read with HDFS checksums turned on...");
 
         if (!doVerificationThruHBaseChecksum) {
           String msg = "HBase checksum verification failed for file " +
                        path + " at offset " +
                        offset + " filesize " + fileSize +
                        " but this cannot happen because doVerify is " +
                        doVerificationThruHBaseChecksum;
           HFile.LOG.warn(msg);
           throw new IOException(msg); // cannot happen case here
         }
         HFile.checksumFailures.incrementAndGet(); // update metrics
 
         // If we have a checksum failure, we fall back into a mode where
         // the next few reads use HDFS level checksums. We aim to make the
         // next CHECKSUM_VERIFICATION_NUM_IO_THRESHOLD reads avoid
         // hbase checksum verification, but since this value is set without
         // holding any locks, it can so happen that we might actually do
         // a few more than precisely this number.
         is = this.streamWrapper.fallbackToFsChecksum(CHECKSUM_VERIFICATION_NUM_IO_THRESHOLD);
         doVerificationThruHBaseChecksum = false;
         blk = readBlockDataInternal(is, offset, (int) onDiskSizeWithHeaderL, uncompressedSize,
             pread, doVerificationThruHBaseChecksum);
         if (blk != null) {
           HFile.LOG.warn("HDFS checksum verification suceeded for file " +
                          path + " at offset " +
                          offset + " filesize " + fileSize);
         }
       }
       if (blk == null && !doVerificationThruHBaseChecksum) {
         String msg = "readBlockData failed, possibly due to " +
                      "checksum verification failed for file " + path +
                      " at offset " + offset + " filesize " + fileSize;
         HFile.LOG.warn(msg);
         throw new IOException(msg);
       }
 
       // If there is a checksum mismatch earlier, then retry with
       // HBase checksums switched off and use HDFS checksum verification.
       // This triggers HDFS to detect and fix corrupt replicas. The
       // next checksumOffCount read requests will use HDFS checksums.
       // The decrementing of this.checksumOffCount is not thread-safe,
       // but it is harmless because eventually checksumOffCount will be
       // a negative number.
       streamWrapper.checksumOk();
       return blk;
     }
 
     /**
      * Reads a version 2 block.
      *
      * @param offset the offset in the stream to read at
      * @param onDiskSizeWithHeader the on-disk size of the block, including
      *          the header, or -1 if unknown
      * @param uncompressedSize the uncompressed size of the the block. Always
      *          expected to be -1. This parameter is only used in version 1.
      * @param pread whether to use a positional read
      * @param verifyChecksum Whether to use HBase checksums.
      *        If HBase checksum is switched off, then use HDFS checksum.
      * @return the HFileBlock or null if there is a HBase checksum mismatch
      */
     protected HFileBlock readBlockDataInternal(FSDataInputStream is, long offset,
         int onDiskSizeWithHeader, int uncompressedSize, boolean pread,
         boolean verifyChecksum)
     throws IOException {
       if (offset < 0) {
         throw new IOException("Invalid offset=" + offset + " trying to read "
             + "block (onDiskSize=" + onDiskSizeWithHeader
             + ", uncompressedSize=" + uncompressedSize + ")");
       }
 
       if (uncompressedSize != -1) {
         throw new IOException("Version 2 block reader API does not need " +
             "the uncompressed size parameter");
       }
 
       if ((onDiskSizeWithHeader < hdrSize && onDiskSizeWithHeader != -1)
           || onDiskSizeWithHeader >= Integer.MAX_VALUE) {
         throw new IOException("Invalid onDisksize=" + onDiskSizeWithHeader
             + ": expected to be at least " + hdrSize
             + " and at most " + Integer.MAX_VALUE + ", or -1 (offset="
             + offset + ", uncompressedSize=" + uncompressedSize + ")");
       }
 
       // See if we can avoid reading the header. This is desirable, because
       // we will not incur a backward seek operation if we have already
       // read this block's header as part of the previous read's look-ahead.
       // And we also want to skip reading the header again if it has already
       // been read.
       // TODO: How often does this optimization fire? Has to be same thread so the thread local
       // is pertinent and we have to be reading next block as in a big scan.
       PrefetchedHeader prefetchedHeader = prefetchedHeaderForThread.get();
       ByteBuffer headerBuf = prefetchedHeader.offset == offset? prefetchedHeader.buf: null;
 
       // Allocate enough space to fit the next block's header too.
       int nextBlockOnDiskSize = 0;
       byte[] onDiskBlock = null;
 
       if (onDiskSizeWithHeader > 0) {
         // We know the total on-disk size. Read the entire block into memory,
         // then parse the header. This code path is used when
         // doing a random read operation relying on the block index, as well as
         // when the client knows the on-disk size from peeking into the next
         // block's header (e.g. this block's header) when reading the previous
         // block. This is the faster and more preferable case.
 
         // Size that we have to skip in case we have already read the header.
         int preReadHeaderSize = headerBuf == null ? 0 : hdrSize;
         onDiskBlock = new byte[onDiskSizeWithHeader + hdrSize]; // room for this block plus the
                                                                 // next block's header
         nextBlockOnDiskSize = readAtOffset(is, onDiskBlock,
             preReadHeaderSize, onDiskSizeWithHeader - preReadHeaderSize,
             true, offset + preReadHeaderSize, pread);
         if (headerBuf != null) {
           // the header has been read when reading the previous block, copy
           // to this block's header
           // headerBuf is HBB
           assert headerBuf.hasArray();
           System.arraycopy(headerBuf.array(),
               headerBuf.arrayOffset(), onDiskBlock, 0, hdrSize);
         } else {
           headerBuf = ByteBuffer.wrap(onDiskBlock, 0, hdrSize);
         }
         // if the caller specifies a onDiskSizeWithHeader, validate it.
         int expectedOnDiskSizeWithoutHeader = onDiskSizeWithHeader - hdrSize;
         int actualOnDiskSizeWithoutHeader =
             headerBuf.getInt(Header.ON_DISK_SIZE_WITHOUT_HEADER_INDEX);
         validateOnDiskSizeWithoutHeader(expectedOnDiskSizeWithoutHeader,
             actualOnDiskSizeWithoutHeader, headerBuf, offset);
       } else {
         // Check headerBuf to see if we have read this block's header as part of
         // reading the previous block. This is an optimization of peeking into
         // the next block's header (e.g.this block's header) when reading the
         // previous block. This is the faster and more preferable case. If the
         // header is already there, don't read the header again.
 
         // Unfortunately, we still have to do a separate read operation to
         // read the header.
         if (headerBuf == null) {
           // From the header, determine the on-disk size of the given hfile
           // block, and read the remaining data, thereby incurring two read
           // operations. This might happen when we are doing the first read
           // in a series of reads or a random read, and we don't have access
           // to the block index. This is costly and should happen very rarely.
           headerBuf = ByteBuffer.allocate(hdrSize);
           // headerBuf is HBB
           readAtOffset(is, headerBuf.array(), headerBuf.arrayOffset(),
               hdrSize, false, offset, pread);
         }
         int onDiskSizeWithoutHeader = headerBuf.getInt(Header.ON_DISK_SIZE_WITHOUT_HEADER_INDEX);
         onDiskSizeWithHeader = onDiskSizeWithoutHeader + hdrSize;
         onDiskBlock = new byte[onDiskSizeWithHeader + hdrSize];
         System.arraycopy(headerBuf.array(), headerBuf.arrayOffset(), onDiskBlock, 0, hdrSize);
         nextBlockOnDiskSize =
           readAtOffset(is, onDiskBlock, hdrSize, onDiskSizeWithHeader - hdrSize, true,
               offset + hdrSize, pread);
       }
       ByteBuffer onDiskBlockByteBuffer = ByteBuffer.wrap(onDiskBlock, 0, onDiskSizeWithHeader);
 
       if (!fileContext.isCompressedOrEncrypted()) {
         verifyUncompressed(headerBuf, fileContext.isUseHBaseChecksum());
       }
 
       if (verifyChecksum && !validateChecksum(offset, onDiskBlockByteBuffer, hdrSize)) {
         return null;             // checksum mismatch
       }
 
       // The onDiskBlock will become the headerAndDataBuffer for this block.
       // If nextBlockOnDiskSizeWithHeader is not zero, the onDiskBlock already
       // contains the header of next block, so no need to set next
       // block's header in it.
        HFileBlock b = new HFileBlock(onDiskBlockByteBuffer, this.fileContext.isUseHBaseChecksum());
 
       b.nextBlockOnDiskSizeWithHeader = nextBlockOnDiskSize;
 
       // Set prefetched header
       if (b.hasNextBlockHeader()) {
         prefetchedHeader.offset = offset + b.getOnDiskSizeWithHeader();
         System.arraycopy(onDiskBlock, onDiskSizeWithHeader, prefetchedHeader.header, 0, hdrSize);
       }
 
       b.offset = offset;
       b.fileContext.setIncludesTags(this.fileContext.isIncludesTags());
       b.fileContext.setIncludesMvcc(this.fileContext.isIncludesMvcc());
       return b;
     }
 
     void setIncludesMemstoreTS(boolean includesMemstoreTS) {
       this.fileContext.setIncludesMvcc(includesMemstoreTS);
     }
 
     void setDataBlockEncoder(HFileDataBlockEncoder encoder) {
       encodedBlockDecodingCtx = encoder.newDataBlockDecodingContext(this.fileContext);
     }
 
     @Override
     public HFileBlockDecodingContext getBlockDecodingContext() {
       return this.encodedBlockDecodingCtx;
     }
 
     @Override
     public HFileBlockDecodingContext getDefaultBlockDecodingContext() {
       return this.defaultDecodingCtx;
     }
 
     /**
      * Generates the checksum for the header as well as the data and then validates it.
      * If the block doesn't uses checksum, returns false.
      * @return True if checksum matches, else false.
      */
     protected boolean validateChecksum(long offset, ByteBuffer data, int hdrSize)
         throws IOException {
       // If this is an older version of the block that does not have checksums, then return false
       // indicating that checksum verification did not succeed. Actually, this method should never
       // be called when the minorVersion is 0, thus this is a defensive check for a cannot-happen
       // case. Since this is a cannot-happen case, it is better to return false to indicate a
       // checksum validation failure.
       if (!fileContext.isUseHBaseChecksum()) {
         return false;
       }
       return ChecksumUtil.validateChecksum(data, path, offset, hdrSize);
     }
 
     @Override
     public void closeStreams() throws IOException {
       streamWrapper.close();
     }
 
     @Override
     public void unbufferStream() {
       // To handle concurrent reads, ensure that no other client is accessing the streams while we
       // unbuffer it.
       if (streamLock.tryLock()) {
         try {
           this.streamWrapper.unbuffer();
         } finally {
           streamLock.unlock();
         }
       }
     }
 
     @Override
     public String toString() {
       return "hfs=" + hfs + ", path=" + path + ", fileContext=" + fileContext;
     }
   }
 
   @Override
   public int getSerializedLength() {
     if (buf != null) {
       // include extra bytes for the next header when it's available.
       int extraSpace = hasNextBlockHeader() ? headerSize() : 0;
       return this.buf.limit() + extraSpace + HFileBlock.EXTRA_SERIALIZATION_SPACE;
     }
     return 0;
   }
 
   @Override
   public void serialize(ByteBuffer destination) {
     ByteBufferUtils.copyFromBufferToBuffer(destination, this.buf, 0, getSerializedLength()
         - EXTRA_SERIALIZATION_SPACE);
     serializeExtraInfo(destination);
   }
 
   public void serializeExtraInfo(ByteBuffer destination) {
     destination.put(this.fileContext.isUseHBaseChecksum() ? (byte) 1 : (byte) 0);
     destination.putLong(this.offset);
     destination.putInt(this.nextBlockOnDiskSizeWithHeader);
     destination.rewind();
   }
 
   @Override
   public CacheableDeserializer<Cacheable> getDeserializer() {
     return HFileBlock.blockDeserializer;
   }
 
   @Override
   public boolean equals(Object comparison) {
     if (this == comparison) {
       return true;
     }
     if (comparison == null) {
       return false;
     }
     if (comparison.getClass() != this.getClass()) {
       return false;
     }
 
     HFileBlock castedComparison = (HFileBlock) comparison;
 
     if (castedComparison.blockType != this.blockType) {
       return false;
     }
     if (castedComparison.nextBlockOnDiskSizeWithHeader != this.nextBlockOnDiskSizeWithHeader) {
       return false;
     }
     if (castedComparison.offset != this.offset) {
       return false;
     }
     if (castedComparison.onDiskSizeWithoutHeader != this.onDiskSizeWithoutHeader) {
       return false;
     }
     if (castedComparison.prevBlockOffset != this.prevBlockOffset) {
       return false;
     }
     if (castedComparison.uncompressedSizeWithoutHeader != this.uncompressedSizeWithoutHeader) {
       return false;
     }
     if (ByteBufferUtils.compareTo(this.buf, 0, this.buf.limit(), castedComparison.buf, 0,
         castedComparison.buf.limit()) != 0) {
       return false;
     }
     return true;
   }
 
   public DataBlockEncoding getDataBlockEncoding() {
     if (blockType == BlockType.ENCODED_DATA) {
       return DataBlockEncoding.getEncodingById(getDataBlockEncodingId());
     }
     return DataBlockEncoding.NONE;
   }
 
   byte getChecksumType() {
     return this.fileContext.getChecksumType().getCode();
   }
 
   int getBytesPerChecksum() {
     return this.fileContext.getBytesPerChecksum();
   }
 
   /** @return the size of data on disk + header. Excludes checksum. */
   int getOnDiskDataSizeWithHeader() {
     return this.onDiskDataSizeWithHeader;
   }
 
   /**
    * Calculate the number of bytes required to store all the checksums for this block. Each
    * checksum value is a 4 byte integer ({@link HFileBlock#CHECKSUM_SIZE}).
    */
   int totalChecksumBytes() {
     return HFileBlock.totalChecksumBytes(this.fileContext, onDiskDataSizeWithHeader);
   }
 
   private static int totalChecksumBytes(HFileContext fileContext, int onDiskDataSizeWithHeader) {
     // If the hfile block has minorVersion 0, then there are no checksum
     // data to validate. Similarly, a zero value in this.bytesPerChecksum
     // indicates that cached blocks do not have checksum data because
     // checksums were already validated when the block was read from disk.
     if (!fileContext.isUseHBaseChecksum() || fileContext.getBytesPerChecksum() == 0) {
       return 0;
     }
     return (int) ChecksumUtil.numBytes(onDiskDataSizeWithHeader,
         fileContext.getBytesPerChecksum());
   }
 
   /**
    * Returns the size of this block header.
    */
   public int headerSize() {
     return headerSize(this.fileContext.isUseHBaseChecksum());
   }
 
   /**
    * Maps a minor version to the size of the header.
    */
   public static int headerSize(boolean usesHBaseChecksum) {
     if (usesHBaseChecksum) {
       return HConstants.HFILEBLOCK_HEADER_SIZE;
     }
     return HConstants.HFILEBLOCK_HEADER_SIZE_NO_CHECKSUM;
   }
 
   /**
    * Return the appropriate DUMMY_HEADER for the minor version
    */
   public byte[] getDummyHeaderForVersion() {
     return getDummyHeaderForVersion(this.fileContext.isUseHBaseChecksum());
   }
 
   /**
    * Return the appropriate DUMMY_HEADER for the minor version
    */
   static private byte[] getDummyHeaderForVersion(boolean usesHBaseChecksum) {
     if (usesHBaseChecksum) {
       return HConstants.HFILEBLOCK_DUMMY_HEADER;
     }
     return DUMMY_HEADER_NO_CHECKSUM;
   }
 
   /**
    * @return the HFileContext used to create this HFileBlock. Not necessary the
    * fileContext for the file from which this block's data was originally read.
    */
   public HFileContext getHFileContext() {
     return this.fileContext;
   }
 
   /**
    * Convert the contents of the block header into a human readable string.
    * This is mostly helpful for debugging. This assumes that the block
    * has minor version > 0.
    */
   static String toStringHeader(ByteBuffer buf) throws IOException {
     byte[] magicBuf = new byte[Math.min(buf.limit() - buf.position(), BlockType.MAGIC_LENGTH)];
     buf.get(magicBuf);
     BlockType bt = BlockType.parse(magicBuf, 0, BlockType.MAGIC_LENGTH);
     int compressedBlockSizeNoHeader = buf.getInt();
     int uncompressedBlockSizeNoHeader = buf.getInt();
     long prevBlockOffset = buf.getLong();
     byte cksumtype = buf.get();
     long bytesPerChecksum = buf.getInt();
     long onDiskDataSizeWithHeader = buf.getInt();
     return " Header dump: magic: " + Bytes.toString(magicBuf) +
                    " blockType " + bt +
                    " compressedBlockSizeNoHeader " +
                    compressedBlockSizeNoHeader +
                    " uncompressedBlockSizeNoHeader " +
                    uncompressedBlockSizeNoHeader +
                    " prevBlockOffset " + prevBlockOffset +
                    " checksumType " + ChecksumType.codeToType(cksumtype) +
                    " bytesPerChecksum " + bytesPerChecksum +
                    " onDiskDataSizeWithHeader " + onDiskDataSizeWithHeader;
   }
 }