/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.hdfs.server.datanode;
import java.io.BufferedInputStream;
import java.io.ByteArrayInputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.util.DataChecksum;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import com.google.common.annotations.VisibleForTesting;
/**
* BlockMetadataHeader manages metadata for data blocks on Datanodes.
* This is not related to the Block related functionality in Namenode.
* The biggest part of data block metadata is CRC for the block.
*/
@InterfaceAudience.Private
@InterfaceStability.Evolving
public class BlockMetadataHeader {
public static final short VERSION = 1;
/**
* Header includes everything except the checksum(s) themselves.
* Version is two bytes. Following it is the DataChecksum
* that occupies 5 bytes.
*/
private final short version;
private DataChecksum checksum = null;
@VisibleForTesting
public BlockMetadataHeader(short version, DataChecksum checksum) {
this.checksum = checksum;
this.version = version;
}
/** Get the version */
public short getVersion() {
return version;
}
/** Get the checksum */
public DataChecksum getChecksum() {
return checksum;
}
/**
* Read the header without changing the position of the FileChannel.
*
* @param fc The FileChannel to read.
* @return the Metadata Header.
* @throws IOException on error.
*/
public static BlockMetadataHeader preadHeader(FileChannel fc)
throws IOException {
byte arr[] = new byte[2 + DataChecksum.HEADER_LEN];
ByteBuffer buf = ByteBuffer.wrap(arr);
while (buf.hasRemaining()) {
if (fc.read(buf, 0) <= 0) {
throw new EOFException("unexpected EOF while reading " +
"metadata file header");
}
}
short version = (short)((arr[0] << 8) | (arr[1] & 0xff));
DataChecksum dataChecksum = DataChecksum.newDataChecksum(arr, 2);
return new BlockMetadataHeader(version, dataChecksum);
}
/**
* This reads all the fields till the beginning of checksum.
* @return Metadata Header
* @throws IOException
*/
public static BlockMetadataHeader readHeader(DataInputStream in) throws IOException {
return readHeader(in.readShort(), in);
}
/**
* Reads header at the top of metadata file and returns the header.
*
* @return metadata header for the block
* @throws IOException
*/
public static BlockMetadataHeader readHeader(File file) throws IOException {
DataInputStream in = null;
try {
in = new DataInputStream(new BufferedInputStream(
new FileInputStream(file)));
return readHeader(in);
} finally {
IOUtils.closeStream(in);
}
}
/**
* Read the header at the beginning of the given block meta file.
* The current file position will be altered by this method.
* If an error occurs, the file is <em>not</em> closed.
*/
static BlockMetadataHeader readHeader(RandomAccessFile raf) throws IOException {
byte[] buf = new byte[getHeaderSize()];
raf.seek(0);
raf.readFully(buf, 0, buf.length);
return readHeader(new DataInputStream(new ByteArrayInputStream(buf)));
}
// Version is already read.
private static BlockMetadataHeader readHeader(short version, DataInputStream in)
throws IOException {
DataChecksum checksum = DataChecksum.newDataChecksum(in);
return new BlockMetadataHeader(version, checksum);
}
/**
* This writes all the fields till the beginning of checksum.
* @param out DataOutputStream
* @throws IOException
*/
@VisibleForTesting
public static void writeHeader(DataOutputStream out,
BlockMetadataHeader header)
throws IOException {
out.writeShort(header.getVersion());
header.getChecksum().writeHeader(out);
}
/**
* Writes all the fields till the beginning of checksum.
* @throws IOException on error
*/
static void writeHeader(DataOutputStream out, DataChecksum checksum)
throws IOException {
writeHeader(out, new BlockMetadataHeader(VERSION, checksum));
}
/**
* Returns the size of the header
*/
public static int getHeaderSize() {
return Short.SIZE/Byte.SIZE + DataChecksum.getChecksumHeaderSize();
}
}