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/**
* 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.client.impl;
import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.ReadableByteChannel;
import java.util.EnumSet;
import java.util.UUID;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.ReadOption;
import org.apache.hadoop.hdfs.BlockReader;
import org.apache.hadoop.hdfs.PeerCache;
import org.apache.hadoop.hdfs.net.Peer;
import org.apache.hadoop.hdfs.protocol.DatanodeID;
import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
import org.apache.hadoop.hdfs.protocol.datatransfer.DataTransferProtoUtil;
import org.apache.hadoop.hdfs.protocol.datatransfer.PacketHeader;
import org.apache.hadoop.hdfs.protocol.datatransfer.PacketReceiver;
import org.apache.hadoop.hdfs.protocol.datatransfer.Sender;
import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.BlockOpResponseProto;
import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.ClientReadStatusProto;
import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.ReadOpChecksumInfoProto;
import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.Status;
import org.apache.hadoop.hdfs.protocolPB.PBHelperClient;
import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
import org.apache.hadoop.hdfs.server.datanode.CachingStrategy;
import org.apache.hadoop.hdfs.shortcircuit.ClientMmap;
import org.apache.hadoop.security.token.Token;
import org.apache.hadoop.util.DataChecksum;
import org.apache.hadoop.classification.VisibleForTesting;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import static org.apache.hadoop.hdfs.client.HdfsClientConfigKeys.DFS_CLIENT_BLOCK_READER_REMOTE_BUFFER_SIZE_DEFAULT;
import static org.apache.hadoop.hdfs.client.HdfsClientConfigKeys.DFS_CLIENT_BLOCK_READER_REMOTE_BUFFER_SIZE_KEY;
/**
* This is a wrapper around connection to datanode
* and understands checksum, offset etc.
*
* Terminology:
*
*
block
*
The hdfs block, typically large (~64MB).
*
*
chunk
*
A block is divided into chunks, each comes with a checksum.
* We want transfers to be chunk-aligned, to be able to
* verify checksums.
*
*
packet
*
A grouping of chunks used for transport. It contains a
* header, followed by checksum data, followed by real data.
*
*
* Please see DataNode for the RPC specification.
*
* This is a new implementation introduced in Hadoop 0.23 which
* is more efficient and simpler than the older BlockReader
* implementation. It is renamed to BlockReaderRemote from BlockReaderRemote2.
*
*/
@InterfaceAudience.Private
public class BlockReaderRemote implements BlockReader {
static final Logger LOG = LoggerFactory.getLogger(BlockReaderRemote.class);
static final int TCP_WINDOW_SIZE = 128 * 1024; // 128 KB;
final private Peer peer;
final private DatanodeID datanodeID;
final private PeerCache peerCache;
final private long blockId;
private final ReadableByteChannel in;
private DataChecksum checksum;
private final PacketReceiver packetReceiver = new PacketReceiver(true);
private ByteBuffer curDataSlice = null;
/** offset in block of the last chunk received */
private long lastSeqNo = -1;
/** offset in block where reader wants to actually read */
private long startOffset;
private final String filename;
private final int bytesPerChecksum;
private final int checksumSize;
/**
* The total number of bytes we need to transfer from the DN.
* This is the amount that the user has requested plus some padding
* at the beginning so that the read can begin on a chunk boundary.
*/
private long bytesNeededToFinish;
private final boolean verifyChecksum;
private boolean sentStatusCode = false;
private final int networkDistance;
@VisibleForTesting
public Peer getPeer() {
return peer;
}
@Override
public synchronized int read(byte[] buf, int off, int len)
throws IOException {
boolean logTraceEnabled = LOG.isTraceEnabled();
UUID randomId = null;
if (logTraceEnabled) {
randomId = UUID.randomUUID();
LOG.trace("Starting read #{} file {} from datanode {}",
randomId, filename, datanodeID.getHostName());
}
if (curDataSlice == null ||
curDataSlice.remaining() == 0 && bytesNeededToFinish > 0) {
readNextPacket();
}
if (logTraceEnabled) {
LOG.trace("Finishing read #{}", randomId);
}
if (curDataSlice.remaining() == 0) {
// we're at EOF now
return -1;
}
int nRead = Math.min(curDataSlice.remaining(), len);
curDataSlice.get(buf, off, nRead);
return nRead;
}
@Override
public synchronized int read(ByteBuffer buf) throws IOException {
if (curDataSlice == null ||
(curDataSlice.remaining() == 0 && bytesNeededToFinish > 0)) {
readNextPacket();
}
if (curDataSlice.remaining() == 0) {
// we're at EOF now
return -1;
}
int nRead = Math.min(curDataSlice.remaining(), buf.remaining());
ByteBuffer writeSlice = curDataSlice.duplicate();
writeSlice.limit(writeSlice.position() + nRead);
buf.put(writeSlice);
curDataSlice.position(writeSlice.position());
return nRead;
}
private void readNextPacket() throws IOException {
//Read packet headers.
packetReceiver.receiveNextPacket(in);
PacketHeader curHeader = packetReceiver.getHeader();
curDataSlice = packetReceiver.getDataSlice();
assert curDataSlice.capacity() == curHeader.getDataLen();
LOG.trace("DFSClient readNextPacket got header {}", curHeader);
// Sanity check the lengths
if (!curHeader.sanityCheck(lastSeqNo)) {
throw new IOException("BlockReader: error in packet header " +
curHeader);
}
if (curHeader.getDataLen() > 0) {
int chunks = 1 + (curHeader.getDataLen() - 1) / bytesPerChecksum;
int checksumsLen = chunks * checksumSize;
assert packetReceiver.getChecksumSlice().capacity() == checksumsLen :
"checksum slice capacity=" +
packetReceiver.getChecksumSlice().capacity() +
" checksumsLen=" + checksumsLen;
lastSeqNo = curHeader.getSeqno();
if (verifyChecksum && curDataSlice.remaining() > 0) {
// N.B.: the checksum error offset reported here is actually
// relative to the start of the block, not the start of the file.
// This is slightly misleading, but preserves the behavior from
// the older BlockReader.
checksum.verifyChunkedSums(curDataSlice,
packetReceiver.getChecksumSlice(),
filename, curHeader.getOffsetInBlock());
}
bytesNeededToFinish -= curHeader.getDataLen();
}
// First packet will include some data prior to the first byte
// the user requested. Skip it.
if (curHeader.getOffsetInBlock() < startOffset) {
int newPos = (int) (startOffset - curHeader.getOffsetInBlock());
curDataSlice.position(newPos);
}
// If we've now satisfied the whole client read, read one last packet
// header, which should be empty
if (bytesNeededToFinish <= 0) {
readTrailingEmptyPacket();
if (verifyChecksum) {
sendReadResult(Status.CHECKSUM_OK);
} else {
sendReadResult(Status.SUCCESS);
}
}
}
@Override
public synchronized long skip(long n) throws IOException {
/* How can we make sure we don't throw a ChecksumException, at least
* in majority of the cases?. This one throws. */
long skipped = 0;
while (skipped < n) {
long needToSkip = n - skipped;
if (curDataSlice == null ||
curDataSlice.remaining() == 0 && bytesNeededToFinish > 0) {
readNextPacket();
}
if (curDataSlice.remaining() == 0) {
// we're at EOF now
break;
}
int skip = (int)Math.min(curDataSlice.remaining(), needToSkip);
curDataSlice.position(curDataSlice.position() + skip);
skipped += skip;
}
return skipped;
}
private void readTrailingEmptyPacket() throws IOException {
LOG.trace("Reading empty packet at end of read");
packetReceiver.receiveNextPacket(in);
PacketHeader trailer = packetReceiver.getHeader();
if (!trailer.isLastPacketInBlock() ||
trailer.getDataLen() != 0) {
throw new IOException("Expected empty end-of-read packet! Header: " +
trailer);
}
}
protected BlockReaderRemote(String file, long blockId,
DataChecksum checksum, boolean verifyChecksum,
long startOffset, long firstChunkOffset,
long bytesToRead, Peer peer,
DatanodeID datanodeID, PeerCache peerCache,
int networkDistance) {
// Path is used only for printing block and file information in debug
this.peer = peer;
this.datanodeID = datanodeID;
this.in = peer.getInputStreamChannel();
this.checksum = checksum;
this.verifyChecksum = verifyChecksum;
this.startOffset = Math.max( startOffset, 0 );
this.filename = file;
this.peerCache = peerCache;
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);
bytesPerChecksum = this.checksum.getBytesPerChecksum();
checksumSize = this.checksum.getChecksumSize();
this.networkDistance = networkDistance;
}
@Override
public synchronized void close() throws IOException {
packetReceiver.close();
startOffset = -1;
checksum = null;
if (peerCache != null && sentStatusCode) {
peerCache.put(datanodeID, peer);
} else {
peer.close();
}
// in will be closed when its Socket is closed.
}
/**
* When the reader reaches end of the read, it sends a status response
* (e.g. CHECKSUM_OK) to the DN. Failure to do so could lead to the DN
* closing our connection (which we will re-open), but won't affect
* data correctness.
*/
void sendReadResult(Status statusCode) {
assert !sentStatusCode : "already sent status code to " + peer;
try {
writeReadResult(peer.getOutputStream(), statusCode);
sentStatusCode = true;
} catch (IOException e) {
// It's ok not to be able to send this. But something is probably wrong.
LOG.info("Could not send read status (" + statusCode + ") to datanode " +
peer.getRemoteAddressString() + ": " + e.getMessage());
}
}
/**
* Serialize the actual read result on the wire.
*/
static void writeReadResult(OutputStream out, Status statusCode)
throws IOException {
ClientReadStatusProto.newBuilder()
.setStatus(statusCode)
.build()
.writeDelimitedTo(out);
out.flush();
}
/**
* File name to print when accessing a block directly (from servlets)
* @param s Address of the block location
* @param poolId Block pool ID of the block
* @param blockId Block ID of the block
* @return string that has a file name for debug purposes
*/
public static String getFileName(final InetSocketAddress s,
final String poolId, final long blockId) {
return s.toString() + ":" + poolId + ":" + blockId;
}
@Override
public int readAll(byte[] buf, int offset, int len) throws IOException {
return BlockReaderUtil.readAll(this, buf, offset, len);
}
@Override
public void readFully(byte[] buf, int off, int len) throws IOException {
BlockReaderUtil.readFully(this, buf, off, len);
}
/**
* 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.
* @param peerCache Caches TCP and UNIX domain sockets for reuse.
* @param cachingStrategy Caching strategy to use when reading the block.
* @param networkDistance Return the distance between two nodes by
* comparing their network paths.
* @param configuration Configuration of client.
* @return New BlockReader instance, or null on error.
*/
public static BlockReader newBlockReader(String file,
ExtendedBlock block,
Token blockToken,
long startOffset, long len,
boolean verifyChecksum,
String clientName,
Peer peer, DatanodeID datanodeID,
PeerCache peerCache,
CachingStrategy cachingStrategy,
int networkDistance, Configuration configuration) throws IOException {
// in and out will be closed when sock is closed (by the caller)
int bufferSize = configuration.getInt(
DFS_CLIENT_BLOCK_READER_REMOTE_BUFFER_SIZE_KEY,
DFS_CLIENT_BLOCK_READER_REMOTE_BUFFER_SIZE_DEFAULT);
final DataOutputStream out = new DataOutputStream(new BufferedOutputStream(
peer.getOutputStream(), bufferSize));
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(
PBHelperClient.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 BlockReaderRemote(file, block.getBlockId(), checksum,
verifyChecksum, startOffset, firstChunkOffset, len, peer, datanodeID,
peerCache, networkDistance);
}
static void checkSuccess(
BlockOpResponseProto status, Peer peer,
ExtendedBlock block, String file)
throws IOException {
String logInfo = "for OP_READ_BLOCK"
+ ", self=" + peer.getLocalAddressString()
+ ", remote=" + peer.getRemoteAddressString()
+ ", for file " + file
+ ", for pool " + block.getBlockPoolId()
+ " block " + block.getBlockId() + "_" + block.getGenerationStamp();
DataTransferProtoUtil.checkBlockOpStatus(status, logInfo);
}
@Override
public int available() {
// An optimistic estimate of how much data is available
// to us without doing network I/O.
return TCP_WINDOW_SIZE;
}
@Override
public boolean isShortCircuit() {
return false;
}
@Override
public ClientMmap getClientMmap(EnumSet opts) {
return null;
}
@Override
public DataChecksum getDataChecksum() {
return checksum;
}
@Override
public int getNetworkDistance() {
return networkDistance;
}
}
