/* GZIPInputStream.java - Input filter for reading gzip file
   Copyright (C) 1999, 2000 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., 59 Temple Place, Suite 330, Boston, MA
02111-1307 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;

/**
 * @author Tom Tromey
 * @date May 17, 1999
 */

/* Written using on-line Java Platform 1.2 API Specification
 * and JCL book.
 * Believed complete and correct.
 */

public class GZIPInputStream extends InflaterInputStream
{
  public static final int GZIP_MAGIC = 0x8b1f;

  public void close () throws IOException
  {
    // Nothing to do here.
    super.close();
  }

  public GZIPInputStream (InputStream istream) throws IOException
  {
    this (istream, 512);
  }

  private final int eof_read () throws IOException
  {
    int r = in.read();
    if (r == -1)
      throw new ZipException ("gzip header corrupted");
    return r & 0xff;
  }

  public GZIPInputStream (InputStream istream, int readsize)
    throws IOException
  {
    super (istream, new Inflater (true), readsize);

    // 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 ();
  }

  public int read (byte[] buf, int off, int len) throws IOException
  {
    if (eos)
      return -1;
    int r = super.read(buf, off, len);
    if (r == -1)
      {
	eos = true;
	int header_crc = read4 ();
	if (crc.getValue() != header_crc)
	  throw new ZipException ("corrupted gzip file");
	// Read final `ISIZE' field.
	// FIXME: should we check this length?
	read4 ();
	return -1;
      }
    crc.update(buf, off, r);
    return r;
  }

  private final int read4 () throws IOException
  {
    int byte0 = in.read();
    int byte1 = in.read();
    int byte2 = in.read();
    int byte3 = in.read();
    if (byte3 < 0)
      throw new ZipException (".zip archive ended prematurely");
    return ((byte3 & 0xFF) << 24) + ((byte2 & 0xFF) << 16)
      + ((byte1 & 0xFF) << 8) + (byte0 & 0xFF);
  }

  // Checksum used by this input stream.
  protected CRC32 crc;

  // Indicates whether end-of-stream has been reached.
  protected boolean eos;

  // Some constants from zlib.
  static final int Z_DEFLATED = 8;
  static final int HEAD_CRC    = 0x02;
  static final int EXTRA_FIELD = 0x04;
  static final int ORIG_NAME   = 0x08;
  static final int COMMENT     = 0x10;
  static final int RESERVED    = 0xe0;
}