/*

 * Copyright 1996-2006 Sun Microsystems, Inc.  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.  Sun designates this

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

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package java.util.zip;

import java.io.SequenceInputStream;

import java.io.ByteArrayInputStream;

import java.io.InputStream;

import java.io.IOException;

import java.io.EOFException;

/**

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

 * the GZIP file format.

 *

 * @see         InflaterInputStream

 * @author      David Connelly

 *

 */

public

class GZIPInputStream extends InflaterInputStream {

    /**

     * CRC-32 for uncompressed data.

     */

    protected CRC32 crc = new CRC32();

    /**

     * Indicates end of input stream.

     */

    protected boolean eos;

    private boolean closed = false;

    /**

     * Check to make sure that this stream has not been closed

     */

    private void ensureOpen() throws IOException {

        if (closed) {

            throw new IOException("Stream closed");

        }

    }

    /**

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

     * @param in the input stream

     * @param size the input buffer size

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

     * @exception IllegalArgumentException if size is <= 0

     */

    public GZIPInputStream(InputStream in, int size) throws IOException {

        super(in, new Inflater(true), size);

        usesDefaultInflater = true;

        readHeader();

        crc.reset();

    }

    /**

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

     * @param in the input stream

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

     */

    public GZIPInputStream(InputStream in) throws IOException {

        this(in, 512);

    }

    /**

     * Reads uncompressed data into an array of bytes. If <code>len</code> is not

     * zero, the method will block until some input can be decompressed; otherwise,

     * no bytes are read and <code>0</code> is returned.

     * @param buf the buffer into which the data is read

     * @param off the start offset in the destination array <code>b</code>

     * @param len the maximum number of bytes read

     * @return  the actual number of bytes read, or -1 if the end of the

     *          compressed input stream is reached

     * @exception  NullPointerException If <code>buf</code> is <code>null</code>.

     * @exception  IndexOutOfBoundsException If <code>off</code> is negative,

     * <code>len</code> is negative, or <code>len</code> is greater than

     * <code>buf.length - off</code>

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

     *                        input data is corrupt

     */

    public int read(byte[] buf, int off, int len) throws IOException {

        ensureOpen();

        if (eos) {

            return -1;

        }

        len = super.read(buf, off, len);

        if (len == -1) {

            readTrailer();

            eos = true;

        } else {

            crc.update(buf, off, len);

        }

        return len;

    }

    /**

     * Closes this input stream and releases any system resources associated

     * with the stream.

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

     */

    public void close() throws IOException {

        if (!closed) {

            super.close();

            eos = true;

            closed = true;

        }

    }

    /**

     * GZIP header magic number.

     */

    public final static int GZIP_MAGIC = 0x8b1f;

    /*

     * File header flags.

     */

    private final static int FTEXT      = 1;    // Extra text

    private final static int FHCRC      = 2;    // Header CRC

    private final static int FEXTRA     = 4;    // Extra field

    private final static int FNAME      = 8;    // File name

    private final static int FCOMMENT   = 16;   // File comment

    /*

     * Reads GZIP member header.

     */

    private void readHeader() throws IOException {

        CheckedInputStream in = new CheckedInputStream(this.in, crc);

        crc.reset();

        // Check header magic

        if (readUShort(in) != GZIP_MAGIC) {

            throw new IOException("Not in GZIP format");

        }

        // Check compression method

        if (readUByte(in) != 8) {

            throw new IOException("Unsupported compression method");

        }

        // Read flags

        int flg = readUByte(in);

        // Skip MTIME, XFL, and OS fields

        skipBytes(in, 6);

        // Skip optional extra field

        if ((flg & FEXTRA) == FEXTRA) {

            skipBytes(in, readUShort(in));

        }

        // Skip optional file name

        if ((flg & FNAME) == FNAME) {

            while (readUByte(in) != 0) ;

        }

        // Skip optional file comment

        if ((flg & FCOMMENT) == FCOMMENT) {

            while (readUByte(in) != 0) ;

        }

        // Check optional header CRC

        if ((flg & FHCRC) == FHCRC) {

            int v = (int)crc.getValue() & 0xffff;

            if (readUShort(in) != v) {

                throw new IOException("Corrupt GZIP header");

            }

        }

    }

    /*

     * Reads GZIP member trailer.

     */

    private void readTrailer() throws IOException {

        InputStream in = this.in;

        int n = inf.getRemaining();

        if (n > 0) {

            in = new SequenceInputStream(

                        new ByteArrayInputStream(buf, len - n, n), in);

        }

        // Uses left-to-right evaluation order

        if ((readUInt(in) != crc.getValue()) ||

            // rfc1952; ISIZE is the input size modulo 2^32

            (readUInt(in) != (inf.getBytesWritten() & 0xffffffffL)))

            throw new IOException("Corrupt GZIP trailer");

    }

    /*

     * Reads unsigned integer in Intel byte order.

     */

    private long readUInt(InputStream in) throws IOException {

        long s = readUShort(in);

        return ((long)readUShort(in) << 16) | s;

    }

    /*

     * Reads unsigned short in Intel byte order.

     */

    private int readUShort(InputStream in) throws IOException {

        int b = readUByte(in);

        return ((int)readUByte(in) << 8) | b;

    }

    /*

     * Reads unsigned byte.

     */

    private int readUByte(InputStream in) throws IOException {

        int b = in.read();

        if (b == -1) {

            throw new EOFException();

        }

        if (b < -1 || b > 255) {

            // Report on this.in, not argument in; see read{Header, Trailer}.

            throw new IOException(this.in.getClass().getName()

                + ".read() returned value out of range -1..255: " + b);

        }

        return b;

    }

    private byte[] tmpbuf = new byte[128];

    /*

     * Skips bytes of input data blocking until all bytes are skipped.

     * Does not assume that the input stream is capable of seeking.

     */

    private void skipBytes(InputStream in, int n) throws IOException {

        while (n > 0) {

            int len = in.read(tmpbuf, 0, n < tmpbuf.length ? n : tmpbuf.length);

            if (len == -1) {

                throw new EOFException();

            }

            n -= len;

        }

    }

}