| /** |
| * 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.IOException; |
| import java.nio.ByteBuffer; |
| import java.util.EnumSet; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.fs.ReadOption; |
| import org.apache.hadoop.hdfs.BlockReader; |
| import org.apache.hadoop.hdfs.ReplicaAccessor; |
| import org.apache.hadoop.hdfs.shortcircuit.ClientMmap; |
| |
| /** |
| * An ExternalBlockReader uses pluggable ReplicaAccessor objects to read from |
| * replicas. |
| */ |
| @InterfaceAudience.Private |
| public final class ExternalBlockReader implements BlockReader { |
| private final ReplicaAccessor accessor; |
| private final long visibleLength; |
| private long pos; |
| |
| ExternalBlockReader(ReplicaAccessor accessor, long visibleLength, |
| long startOffset) { |
| this.accessor = accessor; |
| this.visibleLength = visibleLength; |
| this.pos = startOffset; |
| } |
| |
| @Override |
| public int read(byte[] buf, int off, int len) throws IOException { |
| int nread = accessor.read(pos, buf, off, len); |
| if (nread < 0) { |
| return nread; |
| } |
| pos += nread; |
| return nread; |
| } |
| |
| @Override |
| public int read(ByteBuffer buf) throws IOException { |
| int nread = accessor.read(pos, buf); |
| if (nread < 0) { |
| return nread; |
| } |
| pos += nread; |
| return nread; |
| } |
| |
| @Override |
| public long skip(long n) throws IOException { |
| // You cannot skip backwards |
| if (n <= 0) { |
| return 0; |
| } |
| // You can't skip past the last offset that we want to read with this |
| // block reader. |
| long oldPos = pos; |
| pos += n; |
| if (pos > visibleLength) { |
| pos = visibleLength; |
| } |
| return pos - oldPos; |
| } |
| |
| @Override |
| public int available() { |
| // We return the amount of bytes between the current offset and the visible |
| // length. Some of the other block readers return a shorter length than |
| // that. The only advantage to returning a shorter length is that the |
| // DFSInputStream will trash your block reader and create a new one if |
| // someone tries to seek() beyond the available() region. |
| long diff = visibleLength - pos; |
| if (diff > Integer.MAX_VALUE) { |
| return Integer.MAX_VALUE; |
| } else { |
| return (int)diff; |
| } |
| } |
| |
| @Override |
| public void close() throws IOException { |
| accessor.close(); |
| } |
| |
| @Override |
| public void readFully(byte[] buf, int offset, int len) throws IOException { |
| BlockReaderUtil.readFully(this, buf, offset, len); |
| } |
| |
| @Override |
| public int readAll(byte[] buf, int offset, int len) throws IOException { |
| return BlockReaderUtil.readAll(this, buf, offset, len); |
| } |
| |
| @Override |
| public boolean isShortCircuit() { |
| return accessor.isShortCircuit(); |
| } |
| |
| @Override |
| public ClientMmap getClientMmap(EnumSet<ReadOption> opts) { |
| // For now, pluggable ReplicaAccessors do not support zero-copy. |
| return null; |
| } |
| |
| @Override |
| public int getNetworkDistance() { |
| return accessor.getNetworkDistance(); |
| } |
| } |