//
   //  ========================================================================
   //  Copyright (c) 1995-2013 Mort Bay Consulting Pty. Ltd.
   //  ------------------------------------------------------------------------
   //  All rights reserved. This program and the accompanying materials
   //  are made available under the terms of the Eclipse Public License v1.0
   //  and Apache License v2.0 which accompanies this distribution.
   //
   //      The Eclipse Public License is available at
  //      http://www.eclipse.org/legal/epl-v10.html
  //
  //      The Apache License v2.0 is available at
  //      http://www.opensource.org/licenses/apache2.0.php
  //
  //  You may elect to redistribute this code under either of these licenses.
  //  ========================================================================
  //
  
  package org.eclipse.jetty.servlets.gzip;
  
  import java.io.IOException;
  import java.io.OutputStream;
  import java.util.zip.CRC32;
  import java.util.zip.Deflater;
  import java.util.zip.DeflaterOutputStream;
  
  /**
   * Reimplementation of {@link java.util.zip.GZIPOutputStream} that supports reusing a {@link Deflater} instance.
   */
  public class GzipOutputStream extends DeflaterOutputStream
  {
  
      private final static byte[] GZIP_HEADER = new byte[]
      { (byte)0x1f, (byte)0x8b, Deflater.DEFLATED, 0, 0, 0, 0, 0, 0, 0 };
  
      private final CRC32 _crc = new CRC32();
  
      public GzipOutputStream(OutputStream out, Deflater deflater, int size) throws IOException
      {
          super(out,deflater,size);
          out.write(GZIP_HEADER);
      }
  
      public synchronized void write(byte[] buf, int off, int len) throws IOException
      {
          super.write(buf,off,len);
          _crc.update(buf,off,len);
      }
  
      public void finish() throws IOException
      {
          if (!def.finished())
          {
              super.finish();
              byte[] trailer = new byte[8];
              writeInt((int)_crc.getValue(),trailer,0);
              writeInt(def.getTotalIn(),trailer,4);
              out.write(trailer);
          }
      }
  
      private void writeInt(int i, byte[] buf, int offset)
      {
          int o = offset;
          buf[o++] = (byte)(i & 0xFF);
          buf[o++] = (byte)((i >>> 8) & 0xFF);
          buf[o++] = (byte)((i >>> 16) & 0xFF);
          buf[o++] = (byte)((i >>> 24) & 0xFF);
      }
  
  }