text: /**
   * 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.io;
  
  import org.apache.hadoop.io.CompatibleWritable.CompatibleDataInput;
  
  import java.io.*;
  
  /** A reusable {@link DataInput} implementation that reads from an in-memory
   * buffer.
   *
   * <p>This saves memory over creating a new DataInputStream and
   * ByteArrayInputStream each time data is read.
   *
   * <p>Typical usage is something like the following:<pre>
   *
   * DataInputBuffer buffer = new DataInputBuffer();
   * while (... loop condition ...) {
   *   byte[] data = ... get data ...;
   *   int dataLength = ... get data length ...;
   *   buffer.reset(data, dataLength);
   *   ... read buffer using DataInput methods ...
   * }
   * </pre>
   *  
   */
  public class DataInputBuffer extends DataInputStream implements CompatibleDataInput {
    private static class Buffer extends ByteArrayInputStream {
      public Buffer() {
        super(new byte[] {});
      }
  
      public void reset(byte[] input, int start, int length) {
        this.buf = input;
        this.count = start+length;
        this.mark = start;
        this.pos = start;
      }
  
      public byte[] getData() { return buf; }
      public int getPosition() { return pos; }
      public int getLength() { return count; }
    }
  
    private Buffer buffer;
    
    /** Constructs a new empty buffer. */
    public DataInputBuffer() {
      this(new Buffer());
    }
  
    private DataInputBuffer(Buffer buffer) {
      super(buffer);
      this.buffer = buffer;
    }
  
    /** Resets the data that the buffer reads. */
    public void reset(byte[] input, int length) {
      buffer.reset(input, 0, length);
    }
  
    /** Resets the data that the buffer reads. */
    public void reset(byte[] input, int start, int length) {
      buffer.reset(input, start, length);
    }
    
    public byte[] getData() {
      return buffer.getData();
    }
  
    /** Returns the current position in the input. */
    public int getPosition() { return buffer.getPosition(); }
  
    /** Returns the length of the input. */
    public int getLength() { return buffer.getLength(); }
  
    @Override
    public boolean canReadNextVersion() {
      return buffer.getPosition() < buffer.getLength();
    }
  }
  