/**
* 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.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.zip.Checksum;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.util.DataChecksum;
/**
* 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.
*/
public class BlockMetadataHeader {
static final short METADATA_VERSION = FSDataset.METADATA_VERSION;
/**
* Header includes everything except the checksum(s) themselves.
* Version is two bytes. Following it is the DataChecksum
* that occupies 5 bytes.
*/
private short version;
private DataChecksum checksum = null;
BlockMetadataHeader(short version, DataChecksum checksum) {
this.checksum = checksum;
this.version = version;
}
public short getVersion() {
return version;
}
public DataChecksum getChecksum() {
return checksum;
}
/**
* This reads all the fields till the beginning of checksum.
* @param in
* @return Metadata Header
* @throws IOException
*/
public static BlockMetadataHeader readHeader(DataInputStream in) throws IOException {
return readHeader(in.readShort(), in);
}
/**
* This reads all the fields till the beginning of checksum.
* @param in
* @param checksumImpl
* @return Metadata Header
* @throws IOException
*/
public static BlockMetadataHeader readHeader(DataInputStream in,
Checksum checksumImpl) throws IOException {
return readHeader(in.readShort(), in, checksumImpl);
}
/**
* Reads header at the top of metadata file and returns the header.
*
* @param dataset
* @param block
* @return
* @throws IOException
*/
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);
}
}
// Version is already read.
private static BlockMetadataHeader readHeader(short version, DataInputStream in)
throws IOException {
DataChecksum checksum = DataChecksum.newDataChecksum(in);
return new BlockMetadataHeader(version, checksum);
}
// Version is already read.
private static BlockMetadataHeader readHeader(short version, DataInputStream in,
Checksum checksumImpl)
throws IOException {
DataChecksum checksum = DataChecksum.newDataChecksum(in, checksumImpl);
return new BlockMetadataHeader(version, checksum);
}
/**
* This writes all the fields till the beginning of checksum.
* @param out DataOutputStream
* @param header
* @return
* @throws IOException
*/
private 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.
* @param out
* @param checksum
* @throws IOException
*/
static void writeHeader(DataOutputStream out, DataChecksum checksum)
throws IOException {
writeHeader(out, new BlockMetadataHeader(METADATA_VERSION, checksum));
}
/**
* Returns the size of the header
*/
static int getHeaderSize() {
return Short.SIZE/Byte.SIZE + DataChecksum.getChecksumHeaderSize();
}
}