| /** |
| * 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; |
| |
| import java.io.Closeable; |
| import java.io.IOException; |
| import java.util.EnumSet; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.fs.ByteBufferReadable; |
| import org.apache.hadoop.fs.ReadOption; |
| import org.apache.hadoop.hdfs.shortcircuit.ClientMmap; |
| import org.apache.hadoop.util.DataChecksum; |
| |
| /** |
| * A BlockReader is responsible for reading a single block |
| * from a single datanode. |
| */ |
| @InterfaceAudience.Private |
| public interface BlockReader extends ByteBufferReadable, Closeable { |
| |
| |
| /* same interface as inputStream java.io.InputStream#read() |
| * used by DFSInputStream#read() |
| * This violates one rule when there is a checksum error: |
| * "Read should not modify user buffer before successful read" |
| * because it first reads the data to user buffer and then checks |
| * the checksum. |
| * Note: this must return -1 on EOF, even in the case of a 0-byte read. |
| * See HDFS-5762 for details. |
| */ |
| int read(byte[] buf, int off, int len) throws IOException; |
| |
| /** |
| * Skip the given number of bytes |
| */ |
| long skip(long n) throws IOException; |
| |
| /** |
| * Returns an estimate of the number of bytes that can be read |
| * (or skipped over) from this input stream without performing |
| * network I/O. |
| * This may return more than what is actually present in the block. |
| */ |
| int available(); |
| |
| /** |
| * Close the block reader. |
| * |
| * @throws IOException |
| */ |
| @Override // java.io.Closeable |
| void close() throws IOException; |
| |
| /** |
| * Read exactly the given amount of data, throwing an exception |
| * if EOF is reached before that amount |
| */ |
| void readFully(byte[] buf, int readOffset, int amtToRead) throws IOException; |
| |
| /** |
| * Similar to {@link #readFully(byte[], int, int)} except that it will |
| * not throw an exception on EOF. However, it differs from the simple |
| * {@link #read(byte[], int, int)} call in that it is guaranteed to |
| * read the data if it is available. In other words, if this call |
| * does not throw an exception, then either the buffer has been |
| * filled or the next call will return EOF. |
| */ |
| int readAll(byte[] buf, int offset, int len) throws IOException; |
| |
| /** |
| * @return true only if this is a short-circuit read. |
| * All short-circuit reads are also local. |
| */ |
| boolean isShortCircuit(); |
| |
| /** |
| * Get a ClientMmap object for this BlockReader. |
| * |
| * @param opts The read options to use. |
| * @return The ClientMmap object, or null if mmap is not |
| * supported. |
| */ |
| ClientMmap getClientMmap(EnumSet<ReadOption> opts); |
| |
| /** |
| * @return The DataChecksum used by the read block |
| */ |
| DataChecksum getDataChecksum(); |
| |
| /** |
| * Return the network distance between local machine and the remote machine. |
| */ |
| int getNetworkDistance(); |
| } |