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.fs;
019
020import java.io.IOException;
021import java.nio.ByteBuffer;
022
023/**
024 * Implementers of this interface provide a read API that writes to a
025 * ByteBuffer, not a byte[].
026 */
027public interface ByteBufferReadable {
028  /**
029   * Reads up to buf.remaining() bytes into buf. Callers should use
030   * buf.limit(..) to control the size of the desired read.
031   * <p/>
032   * After a successful call, buf.position() will be advanced by the number 
033   * of bytes read and buf.limit() should be unchanged.
034   * <p/>
035   * In the case of an exception, the values of buf.position() and buf.limit()
036   * are undefined, and callers should be prepared to recover from this
037   * eventuality.
038   * <p/>
039   * Many implementations will throw {@link UnsupportedOperationException}, so
040   * callers that are not confident in support for this method from the
041   * underlying filesystem should be prepared to handle that exception.
042   * <p/>
043   * Implementations should treat 0-length requests as legitimate, and must not
044   * signal an error upon their receipt.
045   *
046   * @param buf
047   *          the ByteBuffer to receive the results of the read operation.
048   * @return the number of bytes read, possibly zero, or -1 if 
049   *         reach end-of-stream
050   * @throws IOException
051   *           if there is some error performing the read
052   */
053  public int read(ByteBuffer buf) throws IOException;
054}