/*

 * Copyright (c) 1996, 2010, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.util.zip;

import java.io.OutputStream;

import java.io.IOException;

/**

 * This class implements a stream filter for writing compressed data in

 * the GZIP file format.

 * @author      David Connelly

 *

 */

public

class GZIPOutputStream extends DeflaterOutputStream {

    /**

     * CRC-32 of uncompressed data.

     */

    protected CRC32 crc = new CRC32();

    /*

     * GZIP header magic number.

     */

    private final static int GZIP_MAGIC = 0x8b1f;

    /*

     * Trailer size in bytes.

     *

     */

    private final static int TRAILER_SIZE = 8;

    /**

     * Creates a new output stream with the specified buffer size.

     *

     * <p>The new output stream instance is created as if by invoking

     * the 3-argument constructor GZIPOutputStream(out, size, false).

     *

     * @param out the output stream

     * @param size the output buffer size

     * @exception IOException If an I/O error has occurred.

     */

    public GZIPOutputStream(OutputStream out, int size) throws IOException {

        this(out, size, false);

    }

    /**

     * Creates a new output stream with the specified buffer size and

     * flush mode.

     *

     * @param out the output stream

     * @param size the output buffer size

     * @param syncFlush

     *        if {@code true} invocation of the inherited

     *        {@link DeflaterOutputStream#flush() flush()} method of

     *        this instance flushes the compressor with flush mode

     *        {@link Deflater#SYNC_FLUSH} before flushing the output

     *        stream, otherwise only flushes the output stream

     * @exception IOException If an I/O error has occurred.

     *

     * @since 1.7

     */

    public GZIPOutputStream(OutputStream out, int size, boolean syncFlush)

        throws IOException

    {

        super(out, new Deflater(Deflater.DEFAULT_COMPRESSION, true),

              size,

              syncFlush);

        usesDefaultDeflater = true;

        writeHeader();

        crc.reset();

    }

    /**

     * Creates a new output stream with a default buffer size.

     *

     * <p>The new output stream instance is created as if by invoking

     * the 2-argument constructor GZIPOutputStream(out, false).

     *

     * @param out the output stream

     * @exception IOException If an I/O error has occurred.

     */

    public GZIPOutputStream(OutputStream out) throws IOException {

        this(out, 512, false);

    }

    /**

     * Creates a new output stream with a default buffer size and

     * the specified flush mode.

     *

     * @param out the output stream

     * @param syncFlush

     *        if {@code true} invocation of the inherited

     *        {@link DeflaterOutputStream#flush() flush()} method of

     *        this instance flushes the compressor with flush mode

     *        {@link Deflater#SYNC_FLUSH} before flushing the output

     *        stream, otherwise only flushes the output stream

     *

     * @exception IOException If an I/O error has occurred.

     *

     * @since 1.7

     */

    public GZIPOutputStream(OutputStream out, boolean syncFlush)

        throws IOException

    {

        this(out, 512, syncFlush);

    }

    /**

     * Writes array of bytes to the compressed output stream. This method

     * will block until all the bytes are written.

     * @param buf the data to be written

     * @param off the start offset of the data

     * @param len the length of the data

     * @exception IOException If an I/O error has occurred.

     */

    public synchronized void write(byte[] buf, int off, int len)

        throws IOException

    {

        super.write(buf, off, len);

        crc.update(buf, off, len);

    }

    /**

     * Finishes writing compressed data to the output stream without closing

     * the underlying stream. Use this method when applying multiple filters

     * in succession to the same output stream.

     * @exception IOException if an I/O error has occurred

     */

    public void finish() throws IOException {

        if (!def.finished()) {

            def.finish();

            while (!def.finished()) {

                int len = def.deflate(buf, 0, buf.length);

                if (def.finished() && len <= buf.length - TRAILER_SIZE) {

                    // last deflater buffer. Fit trailer at the end

                    writeTrailer(buf, len);

                    len = len + TRAILER_SIZE;

                    out.write(buf, 0, len);

                    return;

                }

                if (len > 0)

                    out.write(buf, 0, len);

            }

            // if we can't fit the trailer at the end of the last

            // deflater buffer, we write it separately

            byte[] trailer = new byte[TRAILER_SIZE];

            writeTrailer(trailer, 0);

            out.write(trailer);

        }

    }

    /*

     * Writes GZIP member header.

     */

    private void writeHeader() throws IOException {

        out.write(new byte[] {

                      (byte) GZIP_MAGIC,        // Magic number (short)

                      (byte)(GZIP_MAGIC >> 8),  // Magic number (short)

                      Deflater.DEFLATED,        // Compression method (CM)

                      0,                        // Flags (FLG)

                      0,                        // Modification time MTIME (int)

                      0,                        // Modification time MTIME (int)

                      0,                        // Modification time MTIME (int)

                      0,                        // Modification time MTIME (int)

                      0,                        // Extra flags (XFLG)

                      0                         // Operating system (OS)

                  });

    }

    /*

     * Writes GZIP member trailer to a byte array, starting at a given

     * offset.

     */

    private void writeTrailer(byte[] buf, int offset) throws IOException {

        writeInt((int)crc.getValue(), buf, offset); // CRC-32 of uncompr. data

        writeInt(def.getTotalIn(), buf, offset + 4); // Number of uncompr. bytes

    }

    /*

     * Writes integer in Intel byte order to a byte array, starting at a

     * given offset.

     */

    private void writeInt(int i, byte[] buf, int offset) throws IOException {

        writeShort(i & 0xffff, buf, offset);

        writeShort((i >> 16) & 0xffff, buf, offset + 2);

    }

    /*

     * Writes short integer in Intel byte order to a byte array, starting

     * at a given offset

     */

    private void writeShort(int s, byte[] buf, int offset) throws IOException {

        buf[offset] = (byte)(s & 0xff);

        buf[offset + 1] = (byte)((s >> 8) & 0xff);

    }

}