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/**
 * 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 com.aliyun.odps.io;

import java.io.ByteArrayInputStream;
import java.io.DataOutput;
import java.io.FilterInputStream;
import java.io.InputStream;

/**
 * A reusable {@link InputStream} implementation that reads from an in-memory
 * buffer.
 *
 * 
 * This saves memory over creating a new InputStream and ByteArrayInputStream
 * each time data is read.
 *
 * 

 * Typical usage is something like the following:
 *
 * 
 *
 * InputBuffer buffer = new InputBuffer();
 * while (... loop condition ...) {
 *   byte[] data = ... get data ...;
 *   int dataLength = ... get data length ...;
 *   buffer.reset(data, dataLength);
 *   ... read buffer using InputStream methods ...
 * }
 * 
 *
 * @see DataInputBuffer
 * @see DataOutput
 */
public class InputBuffer extends FilterInputStream {

  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 int getPosition() {
      return pos;
    }

    public int getLength() {
      return count;
    }
  }

  private Buffer buffer;

  /**
   * Constructs a new empty buffer.
   */
  public InputBuffer() {
    this(new Buffer());
  }

  private InputBuffer(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);
  }

  /**
   * 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();
  }

}