GeneralPurposeBit.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.commons.compress.archivers.zip;
/**
* Parser/encoder for the "general purpose bit" field in ZIP's local file and central directory headers.
*
* @since 1.1
* @NotThreadSafe
*/
public final class GeneralPurposeBit implements Cloneable {
/**
* Indicates that the file is encrypted.
*/
private static final int ENCRYPTION_FLAG = 1 << 0;
/**
* Indicates the size of the sliding dictionary used by the compression method 6 (imploding).
* <ul>
* <li>0: 4096 bytes</li>
* <li>1: 8192 bytes</li>
* </ul>
*/
private static final int SLIDING_DICTIONARY_SIZE_FLAG = 1 << 1;
/**
* Indicates the number of Shannon-Fano trees used by the compression method 6 (imploding).
* <ul>
* <li>0: 2 trees (lengths, distances)</li>
* <li>1: 3 trees (literals, lengths, distances)</li>
* </ul>
*/
private static final int NUMBER_OF_SHANNON_FANO_TREES_FLAG = 1 << 2;
/**
* Indicates that a data descriptor stored after the file contents will hold CRC and size information.
*/
private static final int DATA_DESCRIPTOR_FLAG = 1 << 3;
/**
* Indicates strong encryption.
*/
private static final int STRONG_ENCRYPTION_FLAG = 1 << 6;
/**
* Indicates that file names are written in UTF-8.
*
* <p>
* The only reason this is public is that {@link ZipArchiveOutputStream#EFS_FLAG} was public in Apache Commons Compress 1.0 and we needed a substitute for
* it.
* </p>
*/
public static final int UFT8_NAMES_FLAG = 1 << 11;
/**
* Parses the supported flags from the given archive data.
*
* @param data local file header or a central directory entry.
* @param offset offset at which the general purpose bit starts
* @return parsed flags
*/
public static GeneralPurposeBit parse(final byte[] data, final int offset) {
final int generalPurposeFlag = ZipShort.getValue(data, offset);
final GeneralPurposeBit b = new GeneralPurposeBit();
b.useDataDescriptor((generalPurposeFlag & DATA_DESCRIPTOR_FLAG) != 0);
b.useUTF8ForNames((generalPurposeFlag & UFT8_NAMES_FLAG) != 0);
b.useStrongEncryption((generalPurposeFlag & STRONG_ENCRYPTION_FLAG) != 0);
b.useEncryption((generalPurposeFlag & ENCRYPTION_FLAG) != 0);
b.slidingDictionarySize = (generalPurposeFlag & SLIDING_DICTIONARY_SIZE_FLAG) != 0 ? 8192 : 4096;
b.numberOfShannonFanoTrees = (generalPurposeFlag & NUMBER_OF_SHANNON_FANO_TREES_FLAG) != 0 ? 3 : 2;
return b;
}
private boolean languageEncodingFlag;
private boolean dataDescriptorFlag;
private boolean encryptionFlag;
private boolean strongEncryptionFlag;
private int slidingDictionarySize;
private int numberOfShannonFanoTrees;
public GeneralPurposeBit() {
}
@Override
public Object clone() {
try {
return super.clone();
} catch (final CloneNotSupportedException ex) {
// impossible
throw new UnsupportedOperationException("GeneralPurposeBit is not Cloneable?", ex); // NOSONAR
}
}
/**
* Encodes the set bits in a form suitable for ZIP archives.
*
* @return the encoded general purpose bits
*/
public byte[] encode() {
final byte[] result = new byte[2];
encode(result, 0);
return result;
}
/**
* Encodes the set bits in a form suitable for ZIP archives.
*
* @param buf the output buffer
* @param offset The offset within the output buffer of the first byte to be written. must be non-negative and no larger than {@code buf.length-2}
*/
public void encode(final byte[] buf, final int offset) {
ZipShort.putShort((dataDescriptorFlag ? DATA_DESCRIPTOR_FLAG : 0) | (languageEncodingFlag ? UFT8_NAMES_FLAG : 0)
| (encryptionFlag ? ENCRYPTION_FLAG : 0) | (strongEncryptionFlag ? STRONG_ENCRYPTION_FLAG : 0), buf, offset);
}
@Override
public boolean equals(final Object o) {
if (!(o instanceof GeneralPurposeBit)) {
return false;
}
final GeneralPurposeBit g = (GeneralPurposeBit) o;
return g.encryptionFlag == encryptionFlag && g.strongEncryptionFlag == strongEncryptionFlag && g.languageEncodingFlag == languageEncodingFlag
&& g.dataDescriptorFlag == dataDescriptorFlag;
}
/**
* Returns the number of trees used by the compression method 6 (imploding).
*/
int getNumberOfShannonFanoTrees() {
return numberOfShannonFanoTrees;
}
/**
* Returns the sliding dictionary size used by the compression method 6 (imploding).
*/
int getSlidingDictionarySize() {
return slidingDictionarySize;
}
@Override
public int hashCode() {
return 3 * (7 * (13 * (17 * (encryptionFlag ? 1 : 0) + (strongEncryptionFlag ? 1 : 0)) + (languageEncodingFlag ? 1 : 0))
+ (dataDescriptorFlag ? 1 : 0));
}
/**
* whether the current entry will use the data descriptor to store CRC and size information.
*
* @param b whether the current entry will use the data descriptor to store CRC and size information
*/
public void useDataDescriptor(final boolean b) {
dataDescriptorFlag = b;
}
/**
* whether the current entry will be encrypted.
*
* @param b whether the current entry will be encrypted
*/
public void useEncryption(final boolean b) {
encryptionFlag = b;
}
/**
* whether the current entry uses the data descriptor to store CRC and size information.
*
* @return whether the current entry uses the data descriptor to store CRC and size information
*/
public boolean usesDataDescriptor() {
return dataDescriptorFlag;
}
/**
* whether the current entry is encrypted.
*
* @return whether the current entry is encrypted
*/
public boolean usesEncryption() {
return encryptionFlag;
}
/**
* whether the current entry is encrypted using strong encryption.
*
* @return whether the current entry is encrypted using strong encryption
*/
public boolean usesStrongEncryption() {
return encryptionFlag && strongEncryptionFlag;
}
/**
* whether the current entry will be encrypted using strong encryption.
*
* @param b whether the current entry will be encrypted using strong encryption
*/
public void useStrongEncryption(final boolean b) {
strongEncryptionFlag = b;
if (b) {
useEncryption(true);
}
}
/**
* whether the current entry uses UTF8 for file name and comment.
*
* @return whether the current entry uses UTF8 for file name and comment.
*/
public boolean usesUTF8ForNames() {
return languageEncodingFlag;
}
/**
* whether the current entry will use UTF8 for file name and comment.
*
* @param b whether the current entry will use UTF8 for file name and comment.
*/
public void useUTF8ForNames(final boolean b) {
languageEncodingFlag = b;
}
}