UncompressInputStream.java

/*
 * @(#)UncompressInputStream.java			0.3-3 06/05/2001
 *
 *  This file is part of the HTTPClient package
 *  Copyright (C) 1996-2001 Ronald Tschal�r
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2 of the License, or (at your option) any later version.
 *
 *  This library 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
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free
 *  Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
 *  MA 02111-1307, USA
 *
 *  For questions, suggestions, bug-reports, enhancement-requests etc.
 *  I may be contacted at:
 *
 *  ronald@innovation.ch
 *
 *  The HTTPClient's home page is located at:
 *
 *  http://www.innovation.ch/java/HTTPClient/ 
 *
 */

package HTTPClient;

import java.io.IOException;
import java.io.EOFException;
import java.io.InputStream;
import java.io.FileInputStream;
import java.io.FilterInputStream;


/**
 * This class decompresses an input stream containing data compressed with
 * the unix "compress" utility (LZC, a LZW variant). This code is based
 * heavily on the <var>unlzw.c</var> code in <var>gzip-1.2.4</var> (written
 * by Peter Jannesen) and the original compress code.
 *
 * @version	0.3-3  06/05/2001
 * @author	Ronald Tschal�r
 */
class UncompressInputStream extends FilterInputStream
{
    /**
     * @param is the input stream to decompress
     * @exception IOException if the header is malformed
     */
    public UncompressInputStream(InputStream is)  throws IOException
    {
	super(is);
	parse_header();
    }


    byte[] one = new byte[1];
    public synchronized int read() throws IOException
    {
	int b = in.read(one, 0, 1);
	if (b == 1)
	    return (one[0] & 0xff);
	else
	    return -1;
    }


    // string table stuff
    private static final int TBL_CLEAR = 0x100;
    private static final int TBL_FIRST = TBL_CLEAR + 1;

    private int[]  tab_prefix;
    private byte[] tab_suffix;
    private int[]  zeros = new int[256];
    private byte[] stack;

    // various state
    private boolean block_mode;
    private int  n_bits;
    private int  maxbits;
    private int  maxmaxcode;
    private int  maxcode;
    private int  bitmask;
    private int  oldcode;
    private byte finchar;
    private int  stackp;
    private int  free_ent;

    // input buffer
    private byte[]  data = new byte[10000];
    private int     bit_pos = 0, end = 0, got = 0;
    private boolean eof  = false;
    private static final int EXTRA = 64;


    public synchronized int read(byte[] buf, int off, int len)
	    throws IOException
    {
	if (eof)  return -1;
	int start = off;

	/* Using local copies of various variables speeds things up by as
	 * much as 30% !
	 */
	int[]  l_tab_prefix = tab_prefix;
	byte[] l_tab_suffix = tab_suffix;
	byte[] l_stack      = stack;
	int    l_n_bits     = n_bits;
	int    l_maxcode    = maxcode;
	int    l_maxmaxcode = maxmaxcode;
	int    l_bitmask    = bitmask;
	int    l_oldcode    = oldcode;
	byte   l_finchar    = finchar;
	int    l_stackp     = stackp;
	int    l_free_ent   = free_ent;
	byte[] l_data       = data;
	int    l_bit_pos    = bit_pos;


	// empty stack if stuff still left

	int s_size = l_stack.length - l_stackp;
	if (s_size > 0)
	{
	    int num = (s_size >= len) ? len : s_size ;
	    System.arraycopy(l_stack, l_stackp, buf, off, num);
	    off += num;
	    len -= num;
	    l_stackp += num;
	}

	if (len == 0)
	{
	    stackp = l_stackp;
	    return off-start;
	}


	// loop, filling local buffer until enough data has been decompressed

	main_loop: do
	{
	    if (end < EXTRA)  fill();

	    int bit_in = (got > 0) ? (end - end%l_n_bits)<<3 :
				     (end<<3)-(l_n_bits-1);

	    while (l_bit_pos < bit_in)
	    {
		// check for code-width expansion

		if (l_free_ent > l_maxcode)
		{
		    int n_bytes = l_n_bits << 3;
		    l_bit_pos = (l_bit_pos-1) +
				n_bytes - (l_bit_pos-1+n_bytes) % n_bytes;

		    l_n_bits++;
		    l_maxcode = (l_n_bits==maxbits) ? l_maxmaxcode :
						      (1<<l_n_bits) - 1;


		    l_bitmask = (1<<l_n_bits)-1;
		    l_bit_pos = resetbuf(l_bit_pos);
		    continue main_loop;
		}


		// read next code

		int pos = l_bit_pos>>3;
		int code = (((l_data[pos]&0xFF) | ((l_data[pos+1]&0xFF)<<8) |
			    ((l_data[pos+2]&0xFF)<<16))
			    >> (l_bit_pos & 0x7)) & l_bitmask;
		l_bit_pos += l_n_bits;


		// handle first iteration

		if (l_oldcode == -1)
		{
		    if (code >= 256)
			throw new IOException("corrupt input: " + code +
					      " > 255");
		    l_finchar = (byte) (l_oldcode = code);
		    buf[off++] = l_finchar;
		    len--;
		    continue;
		}


		// handle CLEAR code

		if (code == TBL_CLEAR && block_mode)
		{
		    System.arraycopy(zeros, 0, l_tab_prefix, 0, zeros.length);
		    l_free_ent = TBL_FIRST - 1;

		    int n_bytes = l_n_bits << 3;
		    l_bit_pos = (l_bit_pos-1) +
				n_bytes - (l_bit_pos-1+n_bytes) % n_bytes;
		    l_n_bits  = INIT_BITS;
		    l_maxcode = (1 << l_n_bits) - 1;
		    l_bitmask = l_maxcode;

		    //if (debug)  System.err.println("Code tables reset");

		    l_bit_pos = resetbuf(l_bit_pos);
		    continue main_loop;
		}


		// setup

		int incode = code;
		l_stackp = l_stack.length;


		// Handle KwK case

		if (code >= l_free_ent)
		{
		    if (code > l_free_ent)
			throw new IOException("corrupt input: code=" + code +
					      ", free_ent=" + l_free_ent);
		    
		    l_stack[--l_stackp] = l_finchar;
		    code = l_oldcode;
		}


		// Generate output characters in reverse order

		while (code >= 256)
		{
		    l_stack[--l_stackp] = l_tab_suffix[code];
		    code = l_tab_prefix[code];
		}
		l_finchar  = l_tab_suffix[code];
		buf[off++] = l_finchar;
		len--;


		// And put them out in forward order

		s_size = l_stack.length - l_stackp;
		int num = (s_size >= len) ? len : s_size ;
		System.arraycopy(l_stack, l_stackp, buf, off, num);
		off += num;
		len -= num;
		l_stackp += num;


		// generate new entry in table

		if (l_free_ent < l_maxmaxcode)
		{
		    l_tab_prefix[l_free_ent] = l_oldcode;
		    l_tab_suffix[l_free_ent] = l_finchar;
		    l_free_ent++;
		}


		// Remember previous code

		l_oldcode = incode;


		// if output buffer full, then return

		if (len == 0)
		{
		    n_bits   = l_n_bits;
		    maxcode  = l_maxcode;
		    bitmask  = l_bitmask;
		    oldcode  = l_oldcode;
		    finchar  = l_finchar;
		    stackp   = l_stackp;
		    free_ent = l_free_ent;
		    bit_pos  = l_bit_pos;

		    return off-start;
		}
	    }

	    l_bit_pos = resetbuf(l_bit_pos);
	} while (got > 0);

	n_bits   = l_n_bits;
	maxcode  = l_maxcode;
	bitmask  = l_bitmask;
	oldcode  = l_oldcode;
	finchar  = l_finchar;
	stackp   = l_stackp;
	free_ent = l_free_ent;
	bit_pos  = l_bit_pos;

	eof = true;
	return off-start;
    }


    /**
     * Moves the unread data in the buffer to the beginning and resets
     * the pointers.
     */
    private final int resetbuf(int bit_pos)
    {
	int pos = bit_pos >> 3;
	System.arraycopy(data, pos, data, 0, end-pos);
	end -= pos;
	return 0;
    }


    private final void fill()  throws IOException
    {
	got = in.read(data, end, data.length-1-end);
	if (got > 0)  end += got;
    }


    public synchronized long skip(long num)  throws IOException
    {
	byte[] tmp = new byte[(int) num];
	int got = read(tmp, 0, (int) num);

	if (got > 0)
	    return (long) got;
	else
	    return 0L;
    }


    public synchronized int available()  throws IOException
    {
	if (eof)  return 0;

	return in.available();
    }


    private static final int LZW_MAGIC		= 0x1f9d;
    private static final int MAX_BITS		= 16;
    private static final int INIT_BITS		= 9;
    private static final int HDR_MAXBITS 	= 0x1f;
    private static final int HDR_EXTENDED	= 0x20;
    private static final int HDR_FREE     	= 0x40;
    private static final int HDR_BLOCK_MODE	= 0x80;

    private void parse_header()  throws IOException
    {
	// read in and check magic number 

	int t = in.read();
	if (t < 0)  throw new EOFException("Failed to read magic number");
	int magic = (t & 0xff) << 8;
	t = in.read();
	if (t < 0)  throw new EOFException("Failed to read magic number");
	magic += t & 0xff;
	if (magic != LZW_MAGIC)
	    throw new IOException("Input not in compress format (read " +
				  "magic number 0x" +
				  Integer.toHexString(magic) + ")");


	// read in header byte

	int header = in.read();
	if (header < 0)  throw new EOFException("Failed to read header");

	block_mode = (header & HDR_BLOCK_MODE) > 0;
	maxbits    = header & HDR_MAXBITS;

	if (maxbits > MAX_BITS)
	    throw new IOException("Stream compressed with " + maxbits +
				  " bits, but can only handle " + MAX_BITS +
				  " bits");

	if ((header & HDR_EXTENDED) > 0)
	    throw new IOException("Header extension bit set");

	if ((header & HDR_FREE) > 0)
	    throw new IOException("Header bit 6 set");


	// initialize stuff

	maxmaxcode = 1 << maxbits;
	n_bits     = INIT_BITS;
	maxcode    = (1 << n_bits) - 1;
	bitmask    = maxcode;
	oldcode    = -1;
	finchar    = 0;
	free_ent   = block_mode ? TBL_FIRST : 256;

	tab_prefix = new int[1 << maxbits];
	tab_suffix = new byte[1 << maxbits];
	stack      = new byte[1 << maxbits];
	stackp     = stack.length;

	for (int idx=255; idx>=0; idx--)
	    tab_suffix[idx] = (byte) idx;
    }
}