src/java/org/apache/nutch/util/GZIPUtils.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.nutch.util;

import java.io.ByteArrayOutputStream;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.lang.invoke.MethodHandles;
import java.util.zip.GZIPInputStream;
import java.util.zip.GZIPOutputStream;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * A collection of utility methods for working on GZIPed data.
 */
public class GZIPUtils {

  private static final Logger LOG = LoggerFactory
      .getLogger(MethodHandles.lookup().lookupClass());
  private static final int EXPECTED_COMPRESSION_RATIO = 5;
  private static final int BUF_SIZE = 4096;

  /**
   * Returns an gunzipped copy of the input array. If the gzipped input has been
   * truncated or corrupted, a best-effort attempt is made to unzip as much as
   * possible. If no data can be extracted <code>null</code> is returned.
   */
  public static final byte[] unzipBestEffort(byte[] in) {
    return unzipBestEffort(in, Integer.MAX_VALUE);
  }

  /**
   * Returns an gunzipped copy of the input array, truncated to
   * <code>sizeLimit</code> bytes, if necessary. If the gzipped input has been
   * truncated or corrupted, a best-effort attempt is made to unzip as much as
   * possible. If no data can be extracted <code>null</code> is returned.
   */
  public static final byte[] unzipBestEffort(byte[] in, int sizeLimit) {
    try {
      // decompress using GZIPInputStream
      ByteArrayOutputStream outStream = new ByteArrayOutputStream(
          EXPECTED_COMPRESSION_RATIO * in.length);

      GZIPInputStream inStream = new GZIPInputStream(new ByteArrayInputStream(
          in));

      byte[] buf = new byte[BUF_SIZE];
      int written = 0;
      while (true) {
        try {
          int size = inStream.read(buf);
          if (size <= 0)
            break;
          if ((written + size) > sizeLimit) {
            outStream.write(buf, 0, sizeLimit - written);
            break;
          }
          outStream.write(buf, 0, size);
          written += size;
        } catch (Exception e) {
          break;
        }
      }
      try {
        outStream.close();
      } catch (IOException e) {
      }

      return outStream.toByteArray();

    } catch (IOException e) {
      return null;
    }
  }

  /**
   * Returns an gunzipped copy of the input array.
   * 
   * @throws IOException
   *           if the input cannot be properly decompressed
   */
  public static final byte[] unzip(byte[] in) throws IOException {
    // decompress using GZIPInputStream
    ByteArrayOutputStream outStream = new ByteArrayOutputStream(
        EXPECTED_COMPRESSION_RATIO * in.length);

    GZIPInputStream inStream = new GZIPInputStream(new ByteArrayInputStream(in));

    byte[] buf = new byte[BUF_SIZE];
    while (true) {
      int size = inStream.read(buf);
      if (size <= 0)
        break;
      outStream.write(buf, 0, size);
    }
    outStream.close();

    return outStream.toByteArray();
  }

  /**
   * Returns an gzipped copy of the input array.
   */
  public static final byte[] zip(byte[] in) {
    try {
      // compress using GZIPOutputStream
      ByteArrayOutputStream byteOut = new ByteArrayOutputStream(in.length
          / EXPECTED_COMPRESSION_RATIO);

      GZIPOutputStream outStream = new GZIPOutputStream(byteOut);

      try {
        outStream.write(in);
      } catch (Exception e) {
        LOG.error("Error writing outStream: ", e);
      }

      try {
        outStream.close();
      } catch (IOException e) {
        LOG.error("Error closing outStream: ", e);
      }

      return byteOut.toByteArray();

    } catch (IOException e) {
      LOG.error("Error: ", e);
      return null;
    }
  }

}