Decompressor.java

/*
 * 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.compress;

import java.io.IOException;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;

/**
 * Specification of a stream-based 'de-compressor' which can be  
 * plugged into a {@link CompressionInputStream} to compress data.
 * This is modelled after {@link java.util.zip.Inflater}
 * 
 */
@InterfaceAudience.Public
@InterfaceStability.Evolving
public interface Decompressor {
  /**
   * Sets input data for decompression. 
   * This should be called if and only if {@link #needsInput()} returns 
   * <code>true</code> indicating that more input data is required.
   * (Both native and non-native versions of various Decompressors require
   * that the data passed in via <code>b[]</code> remain unmodified until
   * the caller is explicitly notified--via {@link #needsInput()}--that the
   * buffer may be safely modified.  With this requirement, an extra
   * buffer-copy can be avoided.)
   * 
   * @param b Input data
   * @param off Start offset
   * @param len Length
   */
  public void setInput(byte[] b, int off, int len);
  
  /**
   * Returns <code>true</code> if the input data buffer is empty and 
   * {@link #setInput(byte[], int, int)} should be called to
   * provide more input. 
   * 
   * @return <code>true</code> if the input data buffer is empty and 
   * {@link #setInput(byte[], int, int)} should be called in
   * order to provide more input.
   */
  public boolean needsInput();
  
  /**
   * Sets preset dictionary for compression. A preset dictionary
   * is used when the history buffer can be predetermined. 
   *
   * @param b Dictionary data bytes
   * @param off Start offset
   * @param len Length
   */
  public void setDictionary(byte[] b, int off, int len);
  
  /**
   * Returns <code>true</code> if a preset dictionary is needed for decompression.
   * @return <code>true</code> if a preset dictionary is needed for decompression
   */
  public boolean needsDictionary();

  /**
   * Returns <code>true</code> if the end of the decompressed 
   * data output stream has been reached. Indicates a concatenated data stream
   * when finished() returns <code>true</code> and {@link #getRemaining()}
   * returns a positive value. finished() will be reset with the
   * {@link #reset()} method.
   * @return <code>true</code> if the end of the decompressed
   * data output stream has been reached.
   */
  public boolean finished();
  
  /**
   * Fills specified buffer with uncompressed data. Returns actual number
   * of bytes of uncompressed data. A return value of 0 indicates that
   * {@link #needsInput()} should be called in order to determine if more
   * input data is required.
   * 
   * @param b Buffer for the compressed data
   * @param off Start offset of the data
   * @param len Size of the buffer
   * @return The actual number of bytes of compressed data.
   * @throws IOException
   */
  public int decompress(byte[] b, int off, int len) throws IOException;

  /**
   * Returns the number of bytes remaining in the compressed data buffer.
   * Indicates a concatenated data stream if {@link #finished()} returns
   * <code>true</code> and getRemaining() returns a positive value. If
   * {@link #finished()} returns <code>true</code> and getRemaining() returns
   * a zero value, indicates that the end of data stream has been reached and
   * is not a concatenated data stream. 
   * @return The number of bytes remaining in the compressed data buffer.
   */
  public int getRemaining();

  /**
   * Resets decompressor and input and output buffers so that a new set of
   * input data can be processed. If {@link #finished()}} returns
   * <code>true</code> and {@link #getRemaining()} returns a positive value,
   * reset() is called before processing of the next data stream in the
   * concatenated data stream. {@link #finished()} will be reset and will
   * return <code>false</code> when reset() is called.
   */
  public void reset();

  /**
   * Closes the decompressor and discards any unprocessed input.
   */
  public void end(); 
}