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/* GZIPInputStream.java - Input filter for reading gzip file

   Copyright (C) 1999, 2000, 2001, 2002, 2004 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2, or (at your option)

any later version.

GNU Classpath 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 for more details.

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

along with GNU Classpath; see the file COPYING.  If not, write to the

Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301 USA.

Linking this library statically or dynamically with other modules is

making a combined work based on this library.  Thus, the terms and

conditions of the GNU General Public License cover the whole

combination.

As a special exception, the copyright holders of this library give you

permission to link this library with independent modules to produce an

executable, regardless of the license terms of these independent

modules, and to copy and distribute the resulting executable under

terms of your choice, provided that you also meet, for each linked

independent module, the terms and conditions of the license of that

module.  An independent module is a module which is not derived from

or based on this library.  If you modify this library, you may extend

this exception to your version of the library, but you are not

obligated to do so.  If you do not wish to do so, delete this

exception statement from your version. */

package java.util.zip;

import java.io.InputStream;

import java.io.IOException;

/**

 * This filter stream is used to decompress a "GZIP" format stream.

 * The "GZIP" format is described in RFC 1952.

 *

 * @author John Leuner

 * @author Tom Tromey

 * @since JDK 1.1

 */

public class GZIPInputStream

  extends InflaterInputStream

{

  /**

   * The magic number found at the start of a GZIP stream.

   */

  public static final int GZIP_MAGIC = 0x8b1f;

  static final int Z_DEFLATED = 8;

  /**

   * The mask for bit 1 of the flag byte.

   */

  static final int HEAD_CRC = 0x02;

  /**

   * The mask for bit 2 of the flag byte.

   */

  static final int EXTRA_FIELD = 0x04;

  /**

   * The mask for bit 3 of the flag byte.

   */

  static final int ORIG_NAME = 0x08;

  /**

   * The mask for bit 4 of the flag byte.

   */

  static final int COMMENT = 0x10;

  /**

   * The mask for all reserved bits of the flag byte.

   */

  static final int RESERVED = 0xe0;

  /**

   * The CRC-32 checksum value for uncompressed data.

   */

  protected CRC32 crc;

  /**

   * Indicates whether or not the end of the stream has been reached.

   */

  protected boolean eos;

  /**

   * Creates a GZIPInputStream with the default buffer size.

   *

   * @param in The stream to read compressed data from

   *           (in GZIP format).

   *

   * @throws IOException if an error occurs during an I/O operation.

   */

  public GZIPInputStream(InputStream in)

    throws IOException

  {

    this(in, 4096);

  }

  /**

   * Creates a GZIPInputStream with the specified buffer size.

   *

   * @param in The stream to read compressed data from

   *           (in GZIP format).

   * @param size The size of the buffer to use.

   *

   * @throws IOException if an error occurs during an I/O operation.

   * @throws IllegalArgumentException if <code>size</code>

   * is less than or equal to 0.

   */

  public GZIPInputStream(InputStream in, int size)

    throws IOException

  {

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

    // NOTE: header reading code taken from zlib's gzio.c.

    // Read the magic number.

    int magic = eof_read() | (eof_read() << 8);

    if (magic != GZIP_MAGIC)

      throw new ZipException("gzip header corrupted");

    int method = eof_read();

    int flags = eof_read();

    // Test from zlib.

    if (method != Z_DEFLATED || (flags & RESERVED) != 0)

      throw new ZipException("gzip header corrupted");

    // Discard time, xflags, OS code.

    for (int i = 0; i < 6; ++i)

      eof_read();

    // Skip the extra field.

    if ((flags & EXTRA_FIELD) != 0)

      {

        int len = eof_read() | (eof_read() << 8);

        while (len-- != 0)

          eof_read();

      }

    if ((flags & ORIG_NAME) != 0)

      {

        while (true)

          {

            int c = eof_read();

            if (c == 0)

              break;

          }

      }

    if ((flags & COMMENT) != 0)

      {

        while (true)

          {

            int c = eof_read();

            if (c == 0)

              break;

          }

      }

    if ((flags & HEAD_CRC) != 0)

      {

        // FIXME: consider checking CRC of the header.

        eof_read();

        eof_read();

      }

    crc = new CRC32();

  }

  /**

   * Closes the input stream.

   *

   * @throws IOException if an error occurs during an I/O operation.

   */

  public void close()

    throws IOException

  {

    // Nothing to do here.

    super.close();

  }

  private final int eof_read() throws IOException

  {

    int r = in.read();

    if (r == -1)

      throw new ZipException("gzip header corrupted");

    return r & 0xff;

  }

  /**

   * Reads in GZIP-compressed data and stores it in uncompressed form

   * into an array of bytes.  The method will block until either

   * enough input data becomes available or the compressed stream

   * reaches its end.

   *

   * @param buf the buffer into which the uncompressed data will

   *            be stored.

   * @param offset the offset indicating where in <code>buf</code>

   *               the uncompressed data should be placed.

   * @param len the number of uncompressed bytes to be read.

   */

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

  {

    if (eos)

      return -1;

    int r = super.read(buf, offset, len);

    if (r == -1)

      {

        eos = true;

        byte[] tmp = new byte[8];

        // First copy remaining bytes from inflater input buffer.

        int avail = inf.getRemaining();

        System.arraycopy(this.buf, this.len - avail, tmp, 0, avail);

        // Now read remaining bytes from wrapped input stream.

        for (int i = avail; i < 8; ++i)

          {

            tmp[i] = (byte) eof_read();

          }

        // Be careful to avoid sign extension here; CRC32.getValue()

        // returns a long.

        long header_crc = read4(tmp, 0) & 0xffffffffL;

        if (crc.getValue() != header_crc)

          throw new ZipException("corrupted gzip file - crc mismatch");

        int isize = read4(tmp, 4);

        if (inf.getTotalOut() != isize)

          throw new ZipException("corrupted gzip file - size mismatch");

        return -1;

      }

    crc.update(buf, offset, r);

    return r;

  }

  private final int read4(byte[] buf, int offset) throws IOException

  {

    return (((buf[offset + 3] & 0xFF) << 24) + ((buf[offset + 2] & 0xFF) << 16)

            + ((buf[offset + 1] & 0xFF) << 8) + (buf[offset] & 0xFF));

  }

}