521 lines
16 KiB
Java
521 lines
16 KiB
Java
/* Deflater.java - Compress a data stream
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Copyright (C) 1999, 2000, 2001, 2004 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.util.zip;
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/**
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* This is the Deflater class. The deflater class compresses input
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* with the deflate algorithm described in RFC 1951. It has several
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* compression levels and three different strategies described below.
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*
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* This class is <i>not</i> thread safe. This is inherent in the API, due
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* to the split of deflate and setInput.
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*
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* @author Jochen Hoenicke
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* @author Tom Tromey
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*/
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public class Deflater
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{
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/**
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* The best and slowest compression level. This tries to find very
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* long and distant string repetitions.
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*/
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public static final int BEST_COMPRESSION = 9;
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/**
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* The worst but fastest compression level.
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*/
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public static final int BEST_SPEED = 1;
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/**
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* The default compression level.
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*/
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public static final int DEFAULT_COMPRESSION = -1;
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/**
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* This level won't compress at all but output uncompressed blocks.
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*/
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public static final int NO_COMPRESSION = 0;
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/**
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* The default strategy.
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*/
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public static final int DEFAULT_STRATEGY = 0;
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/**
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* This strategy will only allow longer string repetitions. It is
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* useful for random data with a small character set.
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*/
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public static final int FILTERED = 1;
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/**
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* This strategy will not look for string repetitions at all. It
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* only encodes with Huffman trees (which means, that more common
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* characters get a smaller encoding.
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*/
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public static final int HUFFMAN_ONLY = 2;
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/**
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* The compression method. This is the only method supported so far.
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* There is no need to use this constant at all.
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*/
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public static final int DEFLATED = 8;
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/*
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* The Deflater can do the following state transitions:
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*
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* (1) -> INIT_STATE ----> INIT_FINISHING_STATE ---.
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* / | (2) (5) |
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* / v (5) |
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* (3)| SETDICT_STATE ---> SETDICT_FINISHING_STATE |(3)
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* \ | (3) | ,-------'
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* | | | (3) /
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* v v (5) v v
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* (1) -> BUSY_STATE ----> FINISHING_STATE
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* | (6)
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* v
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* FINISHED_STATE
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* \_____________________________________/
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* | (7)
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* v
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* CLOSED_STATE
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*
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* (1) If we should produce a header we start in INIT_STATE, otherwise
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* we start in BUSY_STATE.
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* (2) A dictionary may be set only when we are in INIT_STATE, then
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* we change the state as indicated.
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* (3) Whether a dictionary is set or not, on the first call of deflate
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* we change to BUSY_STATE.
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* (4) -- intentionally left blank -- :)
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* (5) FINISHING_STATE is entered, when flush() is called to indicate that
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* there is no more INPUT. There are also states indicating, that
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* the header wasn't written yet.
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* (6) FINISHED_STATE is entered, when everything has been flushed to the
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* internal pending output buffer.
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* (7) At any time (7)
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*
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*/
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private static final int IS_SETDICT = 0x01;
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private static final int IS_FLUSHING = 0x04;
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private static final int IS_FINISHING = 0x08;
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private static final int INIT_STATE = 0x00;
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private static final int SETDICT_STATE = 0x01;
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private static final int INIT_FINISHING_STATE = 0x08;
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private static final int SETDICT_FINISHING_STATE = 0x09;
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private static final int BUSY_STATE = 0x10;
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private static final int FLUSHING_STATE = 0x14;
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private static final int FINISHING_STATE = 0x1c;
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private static final int FINISHED_STATE = 0x1e;
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private static final int CLOSED_STATE = 0x7f;
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/** Compression level. */
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private int level;
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/** should we include a header. */
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private boolean noHeader;
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/** The current state. */
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private int state;
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/** The total bytes of output written. */
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private int totalOut;
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/** The pending output. */
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private DeflaterPending pending;
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/** The deflater engine. */
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private DeflaterEngine engine;
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/**
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* Creates a new deflater with default compression level.
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*/
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public Deflater()
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{
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this(DEFAULT_COMPRESSION, false);
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}
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/**
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* Creates a new deflater with given compression level.
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* @param lvl the compression level, a value between NO_COMPRESSION
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* and BEST_COMPRESSION, or DEFAULT_COMPRESSION.
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* @exception IllegalArgumentException if lvl is out of range.
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*/
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public Deflater(int lvl)
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{
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this(lvl, false);
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}
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/**
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* Creates a new deflater with given compression level.
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* @param lvl the compression level, a value between NO_COMPRESSION
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* and BEST_COMPRESSION.
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* @param nowrap true, iff we should suppress the deflate header at the
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* beginning and the adler checksum at the end of the output. This is
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* useful for the GZIP format.
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* @exception IllegalArgumentException if lvl is out of range.
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*/
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public Deflater(int lvl, boolean nowrap)
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{
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if (lvl == DEFAULT_COMPRESSION)
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lvl = 6;
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else if (lvl < NO_COMPRESSION || lvl > BEST_COMPRESSION)
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throw new IllegalArgumentException();
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pending = new DeflaterPending();
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engine = new DeflaterEngine(pending);
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this.noHeader = nowrap;
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setStrategy(DEFAULT_STRATEGY);
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setLevel(lvl);
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reset();
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}
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/**
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* Resets the deflater. The deflater acts afterwards as if it was
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* just created with the same compression level and strategy as it
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* had before.
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*/
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public void reset()
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{
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state = (noHeader ? BUSY_STATE : INIT_STATE);
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totalOut = 0;
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pending.reset();
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engine.reset();
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}
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/**
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* Frees all objects allocated by the compressor. There's no
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* reason to call this, since you can just rely on garbage
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* collection. Exists only for compatibility against Sun's JDK,
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* where the compressor allocates native memory.
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* If you call any method (even reset) afterwards the behaviour is
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* <i>undefined</i>.
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* @deprecated Just clear all references to deflater instead.
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*/
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public void end()
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{
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engine = null;
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pending = null;
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state = CLOSED_STATE;
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}
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/**
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* Gets the current adler checksum of the data that was processed so
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* far.
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*/
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public int getAdler()
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{
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return engine.getAdler();
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}
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/**
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* Gets the number of input bytes processed so far.
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*/
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public int getTotalIn()
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{
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return engine.getTotalIn();
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}
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/**
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* Gets the number of output bytes so far.
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*/
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public int getTotalOut()
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{
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return totalOut;
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}
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/**
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* Finalizes this object.
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*/
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protected void finalize()
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{
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/* Exists solely for compatibility. We don't have any native state. */
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}
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/**
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* Flushes the current input block. Further calls to deflate() will
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* produce enough output to inflate everything in the current input
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* block. This is not part of Sun's JDK so I have made it package
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* private. It is used by DeflaterOutputStream to implement
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* flush().
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*/
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void flush() {
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state |= IS_FLUSHING;
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}
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/**
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* Finishes the deflater with the current input block. It is an error
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* to give more input after this method was called. This method must
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* be called to force all bytes to be flushed.
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*/
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public void finish() {
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state |= IS_FLUSHING | IS_FINISHING;
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}
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/**
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* Returns true iff the stream was finished and no more output bytes
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* are available.
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*/
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public boolean finished()
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{
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return state == FINISHED_STATE && pending.isFlushed();
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}
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/**
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* Returns true, if the input buffer is empty.
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* You should then call setInput(). <br>
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*
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* <em>NOTE</em>: This method can also return true when the stream
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* was finished.
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*/
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public boolean needsInput()
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{
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return engine.needsInput();
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}
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/**
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* Sets the data which should be compressed next. This should be only
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* called when needsInput indicates that more input is needed.
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* If you call setInput when needsInput() returns false, the
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* previous input that is still pending will be thrown away.
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* The given byte array should not be changed, before needsInput() returns
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* true again.
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* This call is equivalent to <code>setInput(input, 0, input.length)</code>.
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* @param input the buffer containing the input data.
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* @exception IllegalStateException if the buffer was finished() or ended().
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*/
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public void setInput(byte[] input)
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{
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setInput(input, 0, input.length);
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}
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/**
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* Sets the data which should be compressed next. This should be
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* only called when needsInput indicates that more input is needed.
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* The given byte array should not be changed, before needsInput() returns
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* true again.
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* @param input the buffer containing the input data.
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* @param off the start of the data.
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* @param len the length of the data.
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* @exception IllegalStateException if the buffer was finished() or ended()
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* or if previous input is still pending.
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*/
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public void setInput(byte[] input, int off, int len)
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{
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if ((state & IS_FINISHING) != 0)
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throw new IllegalStateException("finish()/end() already called");
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engine.setInput(input, off, len);
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}
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/**
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* Sets the compression level. There is no guarantee of the exact
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* position of the change, but if you call this when needsInput is
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* true the change of compression level will occur somewhere near
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* before the end of the so far given input.
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* @param lvl the new compression level.
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*/
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public void setLevel(int lvl)
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{
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if (lvl == DEFAULT_COMPRESSION)
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lvl = 6;
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else if (lvl < NO_COMPRESSION || lvl > BEST_COMPRESSION)
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throw new IllegalArgumentException();
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if (level != lvl)
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{
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level = lvl;
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engine.setLevel(lvl);
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}
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}
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/**
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* Sets the compression strategy. Strategy is one of
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* DEFAULT_STRATEGY, HUFFMAN_ONLY and FILTERED. For the exact
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* position where the strategy is changed, the same as for
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* setLevel() applies.
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* @param stgy the new compression strategy.
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*/
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public void setStrategy(int stgy)
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{
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if (stgy != DEFAULT_STRATEGY && stgy != FILTERED
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&& stgy != HUFFMAN_ONLY)
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throw new IllegalArgumentException();
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engine.setStrategy(stgy);
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}
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/**
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* Deflates the current input block to the given array. It returns
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* the number of bytes compressed, or 0 if either
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* needsInput() or finished() returns true or length is zero.
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* @param output the buffer where to write the compressed data.
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*/
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public int deflate(byte[] output)
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{
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return deflate(output, 0, output.length);
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}
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/**
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* Deflates the current input block to the given array. It returns
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* the number of bytes compressed, or 0 if either
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* needsInput() or finished() returns true or length is zero.
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* @param output the buffer where to write the compressed data.
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* @param offset the offset into the output array.
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* @param length the maximum number of bytes that may be written.
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* @exception IllegalStateException if end() was called.
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* @exception IndexOutOfBoundsException if offset and/or length
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* don't match the array length.
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*/
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public int deflate(byte[] output, int offset, int length)
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{
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int origLength = length;
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if (state == CLOSED_STATE)
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throw new IllegalStateException("Deflater closed");
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if (state < BUSY_STATE)
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{
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/* output header */
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int header = (DEFLATED +
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((DeflaterConstants.MAX_WBITS - 8) << 4)) << 8;
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int level_flags = (level - 1) >> 1;
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if (level_flags < 0 || level_flags > 3)
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level_flags = 3;
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header |= level_flags << 6;
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if ((state & IS_SETDICT) != 0)
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/* Dictionary was set */
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header |= DeflaterConstants.PRESET_DICT;
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header += 31 - (header % 31);
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pending.writeShortMSB(header);
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if ((state & IS_SETDICT) != 0)
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{
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int chksum = engine.getAdler();
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engine.resetAdler();
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pending.writeShortMSB(chksum >> 16);
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pending.writeShortMSB(chksum & 0xffff);
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}
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state = BUSY_STATE | (state & (IS_FLUSHING | IS_FINISHING));
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}
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for (;;)
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{
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int count = pending.flush(output, offset, length);
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offset += count;
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totalOut += count;
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length -= count;
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if (length == 0 || state == FINISHED_STATE)
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break;
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if (!engine.deflate((state & IS_FLUSHING) != 0,
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(state & IS_FINISHING) != 0))
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{
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if (state == BUSY_STATE)
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/* We need more input now */
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return origLength - length;
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else if (state == FLUSHING_STATE)
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{
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if (level != NO_COMPRESSION)
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{
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/* We have to supply some lookahead. 8 bit lookahead
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* are needed by the zlib inflater, and we must fill
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* the next byte, so that all bits are flushed.
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*/
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int neededbits = 8 + ((-pending.getBitCount()) & 7);
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while (neededbits > 0)
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{
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/* write a static tree block consisting solely of
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* an EOF:
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*/
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pending.writeBits(2, 10);
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neededbits -= 10;
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}
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}
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state = BUSY_STATE;
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}
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else if (state == FINISHING_STATE)
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{
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pending.alignToByte();
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/* We have completed the stream */
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if (!noHeader)
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{
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int adler = engine.getAdler();
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pending.writeShortMSB(adler >> 16);
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pending.writeShortMSB(adler & 0xffff);
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}
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state = FINISHED_STATE;
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}
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}
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}
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return origLength - length;
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}
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/**
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* Sets the dictionary which should be used in the deflate process.
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* This call is equivalent to <code>setDictionary(dict, 0,
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* dict.length)</code>.
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* @param dict the dictionary.
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* @exception IllegalStateException if setInput () or deflate ()
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* were already called or another dictionary was already set.
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*/
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public void setDictionary(byte[] dict)
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{
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setDictionary(dict, 0, dict.length);
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}
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/**
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* Sets the dictionary which should be used in the deflate process.
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* The dictionary should be a byte array containing strings that are
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* likely to occur in the data which should be compressed. The
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* dictionary is not stored in the compressed output, only a
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* checksum. To decompress the output you need to supply the same
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* dictionary again.
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* @param dict the dictionary.
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* @param offset an offset into the dictionary.
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* @param length the length of the dictionary.
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* @exception IllegalStateException if setInput () or deflate () were
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* already called or another dictionary was already set.
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*/
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public void setDictionary(byte[] dict, int offset, int length)
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{
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if (state != INIT_STATE)
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throw new IllegalStateException();
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state = SETDICT_STATE;
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engine.setDictionary(dict, offset, length);
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}
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}
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