001    /* GZIPOutputStream.java - Create a file in gzip format
002       Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    package java.util.zip;
039    
040    import java.io.IOException;
041    import java.io.OutputStream;
042    
043    /**
044     * This filter stream is used to compress a stream into a "GZIP" stream.
045     * The "GZIP" format is described in RFC 1952.
046     *
047     * @author John Leuner
048     * @author Tom Tromey
049     * @since JDK 1.1
050     */
051    
052    /* Written using on-line Java Platform 1.2 API Specification
053     * and JCL book.
054     * Believed complete and correct.
055     */
056    
057    public class GZIPOutputStream extends DeflaterOutputStream
058    {
059      /**
060       * CRC-32 value for uncompressed data
061       */
062      protected CRC32 crc;
063    
064      /**
065       * Creates a GZIPOutputStream with the default buffer size
066       *
067       * @param out The stream to read data (to be compressed) from
068       *
069       */
070      public GZIPOutputStream(OutputStream out) throws IOException
071      {
072        this(out, 4096);
073      }
074    
075      /**
076       * Creates a GZIPOutputStream with the specified buffer size
077       *
078       * @param out The stream to read compressed data from
079       * @param size Size of the buffer to use
080       */
081      public GZIPOutputStream(OutputStream out, int size) throws IOException
082      {
083        super(out, new Deflater(Deflater.DEFAULT_COMPRESSION, true), size);
084        crc = new CRC32();
085        int mod_time = (int) (System.currentTimeMillis() / 1000L);
086        byte[] gzipHeader =
087          {
088            /* The two magic bytes */
089            (byte) GZIPInputStream.GZIP_MAGIC,
090            (byte) (GZIPInputStream.GZIP_MAGIC >> 8),
091    
092            /* The compression type */
093            (byte) Deflater.DEFLATED,
094    
095            /* The flags (not set) */
096            0,
097    
098            /* The modification time */
099            (byte) mod_time, (byte) (mod_time >> 8),
100            (byte) (mod_time >> 16), (byte) (mod_time >> 24),
101    
102            /* The extra flags */
103            0,
104    
105            /* The OS type (unknown) */
106            (byte) 255
107          };
108    
109        out.write(gzipHeader);
110        //    System.err.println("wrote GZIP header (" + gzipHeader.length + " bytes )");
111      }
112    
113      public synchronized void write(byte[] buf, int off, int len)
114        throws IOException
115      {
116        super.write(buf, off, len);
117        crc.update(buf, off, len);
118      }
119    
120      /**
121       * Writes remaining compressed output data to the output stream
122       * and closes it.
123       */
124      public void close() throws IOException
125      {
126        finish();
127        out.close();
128      }
129    
130      public void finish() throws IOException
131      {
132        super.finish();
133    
134        int totalin = def.getTotalIn();
135        int crcval = (int) (crc.getValue() & 0xffffffff);
136    
137        //    System.err.println("CRC val is " + Integer.toHexString( crcval )                     + " and length " + Integer.toHexString(totalin));
138    
139        byte[] gzipFooter =
140          {
141            (byte) crcval, (byte) (crcval >> 8),
142            (byte) (crcval >> 16), (byte) (crcval >> 24),
143    
144            (byte) totalin, (byte) (totalin >> 8),
145            (byte) (totalin >> 16), (byte) (totalin >> 24)
146          };
147    
148        out.write(gzipFooter);
149      //    System.err.println("wrote GZIP trailer (" + gzipFooter.length + " bytes )");
150      }
151    }