/*
* $Id: PDFDecoder.java,v 1.6 2010-06-14 17:32:08 lujke Exp $
*
* Copyright 2004 Sun Microsystems, Inc., 4150 Network Circle,
* Santa Clara, California 95054, U.S.A. All rights reserved.
*
* 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 2.1 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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
package com.sun.pdfview.decode;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;
import com.sun.pdfview.PDFObject;
import com.sun.pdfview.PDFParseException;
import com.sun.pdfview.decrypt.PDFDecrypterFactory;
/**
* A PDF Decoder encapsulates all the methods of decoding a stream of bytes
* based on all the various encoding methods.
* <p>
* You should use the decodeStream() method of this object rather than using
* any of the decoders directly.
*/
public class PDFDecoder {
private static final String FILTER_DCT = "DCT";
private static final String FILTER_DCTDECODE = "DCTDecode";
public final static Set<String> DCT_FILTERS = new HashSet<String>(Arrays.asList(FILTER_DCT, FILTER_DCTDECODE));
/** Creates a new instance of PDFDecoder */
private PDFDecoder() {
}
public static boolean isLastFilter(PDFObject dict, Set<String> filters) throws IOException {
PDFObject filter = dict.getDictRef("Filter");
if (filter == null) {
return false;
} else if (filter.getType() == PDFObject.NAME) {
return filters.contains(filter.getStringValue());
} else {
final PDFObject[] ary = filter.getArray();
return filters.contains(ary[ary.length - 1].getStringValue());
}
}
/**
* Utility class for reading and storing the specification of
* Filters on a stream
*/
private static class FilterSpec
{
PDFObject ary[];
PDFObject params[];
private FilterSpec(PDFObject dict, PDFObject filter) throws IOException {
if (filter.getType() == PDFObject.NAME) {
ary = new PDFObject[1];
ary[0] = filter;
params = new PDFObject[1];
params[0] = dict.getDictRef("DecodeParms");
} else {
ary = filter.getArray();
PDFObject parmsobj = dict.getDictRef("DecodeParms");
if (parmsobj != null) {
params = parmsobj.getArray();
} else {
params = new PDFObject[ary.length];
}
}
}
}
/**
* decode a byte[] stream using the filters specified in the object's
* dictionary (passed as argument 1).
* @param dict the dictionary associated with the stream
* @param streamBuf the data in the stream, as a byte buffer
*/
public static ByteBuffer decodeStream(PDFObject dict, ByteBuffer streamBuf, Set<String> filterLimits)
throws IOException {
PDFObject filter = dict.getDictRef("Filter");
if (filter == null) {
// just apply default decryption
return dict.getDecrypter().decryptBuffer(null, dict, streamBuf);
} else {
// apply filters
FilterSpec spec = new FilterSpec(dict, filter);
// determine whether default encryption applies or if there's a
// specific Crypt filter; it must be the first filter according to
// the errata for PDF1.7
boolean specificCryptFilter =
spec.ary.length != 0 && spec.ary[0].getStringValue().equals("Crypt");
if (!specificCryptFilter) {
// No Crypt filter, so should apply default decryption (if
// present!)
streamBuf = dict.getDecrypter().decryptBuffer(
null, dict, streamBuf);
}
for (int i = 0; i < spec.ary.length; i++) {
String enctype = spec.ary[i].getStringValue();
if (filterLimits.contains(enctype)) {
break;
}
if (enctype == null) {
} else if (enctype.equals("FlateDecode") || enctype.equals("Fl")) {
streamBuf = FlateDecode.decode(dict, streamBuf, spec.params[i]);
} else if (enctype.equals("LZWDecode") || enctype.equals("LZW")) {
streamBuf = LZWDecode.decode(streamBuf, spec.params[i]);
} else if (enctype.equals("ASCII85Decode") || enctype.equals("A85")) {
streamBuf = ASCII85Decode.decode(streamBuf, spec.params[i]);
} else if (enctype.equals("ASCIIHexDecode") || enctype.equals("AHx")) {
streamBuf = ASCIIHexDecode.decode(streamBuf, spec.params[i]);
} else if (enctype.equals("RunLengthDecode") || enctype.equals("RL")) {
streamBuf = RunLengthDecode.decode(streamBuf, spec.params[i]);
} else if (enctype.equals(FILTER_DCTDECODE) || enctype.equals(FILTER_DCT)) {
streamBuf = DCTDecode.decode(dict, streamBuf, spec.params[i]);
} else if (enctype.equals("CCITTFaxDecode") || enctype.equals("CCF")) {
streamBuf = CCITTFaxDecode.decode(dict, streamBuf, spec.params[i]);
} else if (enctype.equals("Crypt")) {
String cfName = getCryptFilterName(spec.params[i]);
streamBuf = dict.getDecrypter().decryptBuffer(cfName, null, streamBuf);
} else {
throw new PDFParseException("Unknown coding method:" + spec.ary[i].getStringValue());
}
}
}
return streamBuf;
}
/**
* The name of the Crypt filter to apply
* @param param the parameters to the Crypt filter
* @return the name of the crypt filter to apply
* @throws IOException if there's a problem reading the objects
*/
private static String getCryptFilterName(PDFObject param) throws IOException {
String cfName = PDFDecrypterFactory.CF_IDENTITY;
if (param != null) {
final PDFObject nameObj = param.getDictRef("Name");
if (nameObj != null && nameObj.getType() == PDFObject.NAME) {
cfName = nameObj.getStringValue();
}
}
return cfName;
}
/**
* Determines whether a stream is encrypted or not; note that encodings
* (e.g., Flate, LZW) are not considered encryptions.
* @param dict the stream dictionary
* @return whether the stream is encrypted
* @throws IOException if the stream dictionary can't be read
*/
public static boolean isEncrypted(PDFObject dict)
throws IOException {
PDFObject filter = dict.getDictRef("Filter");
if (filter == null) {
// just apply default decryption
return dict.getDecrypter().isEncryptionPresent();
} else {
// apply filters
FilterSpec spec = new FilterSpec(dict, filter);
// determine whether default encryption applies or if there's a
// specific Crypt filter; it must be the first filter according to
// the errata for PDF1.7
boolean specificCryptFilter = spec.ary.length != 0 &&
spec.ary[0].getStringValue().equals("Crypt");
if (!specificCryptFilter) {
// No Crypt filter, so we just need to refer to
// the default decrypter
return dict.getDecrypter().isEncryptionPresent();
} else {
String cfName = getCryptFilterName(spec.params[0]);
// see whether the specified crypt filter really decrypts
return dict.getDecrypter().isEncryptionPresent(cfName);
}
}
}
}