001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hdfs;
019
020import java.io.IOException;
021import java.net.Socket;
022
023/**
024 * A BlockReader is responsible for reading a single block
025 * from a single datanode.
026 */
027public interface BlockReader {
028
029  /* same interface as inputStream java.io.InputStream#read()
030   * used by DFSInputStream#read()
031   * This violates one rule when there is a checksum error:
032   * "Read should not modify user buffer before successful read"
033   * because it first reads the data to user buffer and then checks
034   * the checksum.
035   */
036  int read(byte[] buf, int off, int len) throws IOException;
037
038  /**
039   * Skip the given number of bytes
040   */
041  long skip(long n) throws IOException;
042
043  void close() throws IOException;
044
045  /**
046   * Read exactly the given amount of data, throwing an exception
047   * if EOF is reached before that amount
048   */
049  void readFully(byte[] buf, int readOffset, int amtToRead) throws IOException;
050
051  /**
052   * Similar to {@link #readFully(byte[], int, int)} except that it will
053   * not throw an exception on EOF. However, it differs from the simple
054   * {@link #read(byte[], int, int)} call in that it is guaranteed to
055   * read the data if it is available. In other words, if this call
056   * does not throw an exception, then either the buffer has been
057   * filled or the next call will return EOF.
058   */
059  int readAll(byte[] buf, int offset, int len) throws IOException;
060
061  /**
062   * Take the socket used to talk to the DN.
063   */
064  Socket takeSocket();
065
066  /**
067   * Whether the BlockReader has reached the end of its input stream
068   * and successfully sent a status code back to the datanode.
069   */
070  boolean hasSentStatusCode();
071
072}