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The Apache PDFBox library is an open source Java tool for working with PDF documents.
/*
* Copyright 2014 The Apache Software Foundation.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.pdfbox.filter;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import javax.imageio.stream.MemoryCacheImageInputStream;
import javax.imageio.stream.MemoryCacheImageOutputStream;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.pdfbox.cos.COSDictionary;
import org.apache.pdfbox.cos.COSName;
/**
*
* This is the filter used for the LZWDecode filter.
*
* @author Ben Litchfield
* @author Tilman Hausherr
*/
public class LZWFilter extends Filter
{
/**
* Log instance.
*/
private static final Log LOG = LogFactory.getLog(LZWFilter.class);
/**
* The LZW clear table code.
*/
public static final long CLEAR_TABLE = 256;
/**
* The LZW end of data code.
*/
public static final long EOD = 257;
//BEWARE: codeTable must be local to each method, because there is only
// one instance of each filter
/**
* {@inheritDoc}
*/
@Override
public DecodeResult decode(InputStream encoded, OutputStream decoded,
COSDictionary parameters, int index) throws IOException
{
int predictor = -1;
int earlyChange = 1;
COSDictionary decodeParams = getDecodeParams(parameters, index);
if (decodeParams != null)
{
predictor = decodeParams.getInt(COSName.PREDICTOR);
earlyChange = decodeParams.getInt(COSName.EARLY_CHANGE, 1);
if (earlyChange != 0 && earlyChange != 1)
{
earlyChange = 1;
}
}
if (predictor > 1)
{
@SuppressWarnings("null")
int colors = Math.min(decodeParams.getInt(COSName.COLORS, 1), 32);
int bitsPerPixel = decodeParams.getInt(COSName.BITS_PER_COMPONENT, 8);
int columns = decodeParams.getInt(COSName.COLUMNS, 1);
ByteArrayOutputStream baos = new ByteArrayOutputStream();
doLZWDecode(encoded, baos, earlyChange);
ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
Predictor.decodePredictor(predictor, colors, bitsPerPixel, columns, bais, decoded);
decoded.flush();
baos.reset();
bais.reset();
}
else
{
doLZWDecode(encoded, decoded, earlyChange);
}
return new DecodeResult(parameters);
}
private void doLZWDecode(InputStream encoded, OutputStream decoded, int earlyChange) throws IOException
{
List codeTable = new ArrayList();
int chunk = 9;
final MemoryCacheImageInputStream in = new MemoryCacheImageInputStream(encoded);
long nextCommand;
long prevCommand = -1;
try
{
while ((nextCommand = in.readBits(chunk)) != EOD)
{
if (nextCommand == CLEAR_TABLE)
{
chunk = 9;
codeTable = createCodeTable();
prevCommand = -1;
}
else
{
if (nextCommand < codeTable.size())
{
byte[] data = codeTable.get((int) nextCommand);
byte firstByte = data[0];
decoded.write(data);
if (prevCommand != -1)
{
checkIndexBounds(codeTable, prevCommand, in);
data = codeTable.get((int) prevCommand);
byte[] newData = Arrays.copyOf(data, data.length + 1);
newData[data.length] = firstByte;
codeTable.add(newData);
}
}
else
{
checkIndexBounds(codeTable, prevCommand, in);
byte[] data = codeTable.get((int) prevCommand);
byte[] newData = Arrays.copyOf(data, data.length + 1);
newData[data.length] = data[0];
decoded.write(newData);
codeTable.add(newData);
}
chunk = calculateChunk(codeTable.size(), earlyChange);
prevCommand = nextCommand;
}
}
}
catch (EOFException ex)
{
LOG.warn("Premature EOF in LZW stream, EOD code missing");
}
decoded.flush();
}
private void checkIndexBounds(List codeTable, long index, MemoryCacheImageInputStream in)
throws IOException
{
if (index < 0)
{
throw new IOException("negative array index: " + index + " near offset "
+ in.getStreamPosition());
}
if (index >= codeTable.size())
{
throw new IOException("array index overflow: " + index +
" >= " + codeTable.size() + " near offset "
+ in.getStreamPosition());
}
}
/**
* {@inheritDoc}
*/
@Override
protected void encode(InputStream rawData, OutputStream encoded, COSDictionary parameters)
throws IOException
{
List codeTable = createCodeTable();
int chunk = 9;
byte[] inputPattern = null;
final MemoryCacheImageOutputStream out = new MemoryCacheImageOutputStream(encoded);
out.writeBits(CLEAR_TABLE, chunk);
int foundCode = -1;
int r;
while ((r = rawData.read()) != -1)
{
byte by = (byte) r;
if (inputPattern == null)
{
inputPattern = new byte[] { by };
foundCode = by & 0xff;
}
else
{
inputPattern = Arrays.copyOf(inputPattern, inputPattern.length + 1);
inputPattern[inputPattern.length - 1] = by;
int newFoundCode = findPatternCode(codeTable, inputPattern);
if (newFoundCode == -1)
{
// use previous
chunk = calculateChunk(codeTable.size() - 1, 1);
out.writeBits(foundCode, chunk);
// create new table entry
codeTable.add(inputPattern);
if (codeTable.size() == 4096)
{
// code table is full
out.writeBits(CLEAR_TABLE, chunk);
codeTable = createCodeTable();
}
inputPattern = new byte[] { by };
foundCode = by & 0xff;
}
else
{
foundCode = newFoundCode;
}
}
}
if (foundCode != -1)
{
chunk = calculateChunk(codeTable.size() - 1, 1);
out.writeBits(foundCode, chunk);
}
// PPDFBOX-1977: the decoder wouldn't know that the encoder would output
// an EOD as code, so he would have increased his own code table and
// possibly adjusted the chunk. Therefore, the encoder must behave as
// if the code table had just grown and thus it must be checked it is
// needed to adjust the chunk, based on an increased table size parameter
chunk = calculateChunk(codeTable.size(), 1);
out.writeBits(EOD, chunk);
// pad with 0
out.writeBits(0, 7);
// must do or file will be empty :-(
out.flush();
out.close();
}
/**
* Find the longest matching pattern in the code table.
*
* @param codeTable The LZW code table.
* @param pattern The pattern to be searched for.
* @return The index of the longest matching pattern or -1 if nothing is
* found.
*/
private int findPatternCode(List codeTable, byte[] pattern)
{
int foundCode = -1;
int foundLen = 0;
for (int i = codeTable.size() - 1; i >= 0; --i)
{
if (i <= EOD)
{
// we're in the single byte area
if (foundCode != -1)
{
// we already found pattern with size > 1
return foundCode;
}
else if (pattern.length > 1)
{
// we won't find anything here anyway
return -1;
}
}
byte[] tryPattern = codeTable.get(i);
if ((foundCode != -1 || tryPattern.length > foundLen) && Arrays.equals(tryPattern, pattern))
{
foundCode = i;
foundLen = tryPattern.length;
}
}
return foundCode;
}
/**
* Init the code table with 1 byte entries and the EOD and CLEAR_TABLE
* markers.
*/
private List createCodeTable()
{
List codeTable = new ArrayList(4096);
for (int i = 0; i < 256; ++i)
{
codeTable.add(new byte[] { (byte) (i & 0xFF) });
}
codeTable.add(null); // 256 EOD
codeTable.add(null); // 257 CLEAR_TABLE
return codeTable;
}
/**
* Calculate the appropriate chunk size
*
* @param tabSize the size of the code table
* @param earlyChange 0 or 1 for early chunk increase
*
* @return a value between 9 and 12
*/
private int calculateChunk(int tabSize, int earlyChange)
{
if (tabSize >= 2048 - earlyChange)
{
return 12;
}
if (tabSize >= 1024 - earlyChange)
{
return 11;
}
if (tabSize >= 512 - earlyChange)
{
return 10;
}
return 9;
}
}