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Apache Commons Compress defines an API for working with compression and archive formats. These include bzip2, gzip, pack200, LZMA, XZ, Snappy, traditional Unix Compress, DEFLATE, DEFLATE64, LZ4, Brotli, Zstandard and ar, cpio, jar, tar, zip, dump, 7z, arj.
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/*
 *  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 {
    /**
     * Indicates that the file is encrypted.
     */
    private static final int ENCRYPTION_FLAG = 1 << 0;

    /**
     * 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 filenames are written in utf-8.
     *
     * 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.
     */
    public static final int UFT8_NAMES_FLAG = 1 << 11;

    private boolean languageEncodingFlag = false;
    private boolean dataDescriptorFlag = false;
    private boolean encryptionFlag = false;
    private boolean strongEncryptionFlag = false;

    public GeneralPurposeBit() {
    }

    /**
     * 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.
     */
    public void useUTF8ForNames(boolean b) {
        languageEncodingFlag = b;
    }

    /**
     * whether the current entry uses the data descriptor to store CRC
     * and size information
     */
    public boolean usesDataDescriptor() {
        return dataDescriptorFlag;
    }

    /**
     * whether the current entry will use the data descriptor to store
     * CRC and size information
     */
    public void useDataDescriptor(boolean b) {
        dataDescriptorFlag = b;
    }

    /**
     * whether the current entry is encrypted
     */
    public boolean usesEncryption() {
        return encryptionFlag;
    }

    /**
     * whether the current entry will be encrypted
     */
    public void useEncryption(boolean b) {
        encryptionFlag = b;
    }

    /**
     * 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
     */
    public void useStrongEncryption(boolean b) {
        strongEncryptionFlag = b;
        if (b) {
            useEncryption(true);
        }
    }

    /**
     * Encodes the set bits in a form suitable for ZIP archives.
     */
    public byte[] encode() {
        return 
            ZipShort.getBytes((dataDescriptorFlag ? DATA_DESCRIPTOR_FLAG : 0)
                              |
                              (languageEncodingFlag ? UFT8_NAMES_FLAG : 0)
                              |
                              (encryptionFlag ? ENCRYPTION_FLAG : 0)
                              |
                              (strongEncryptionFlag ? STRONG_ENCRYPTION_FLAG : 0)
                              );
    }

    /**
     * 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
     */
    public static GeneralPurposeBit parse(final byte[] data, final int offset) {
        final int generalPurposeFlag = ZipShort.getValue(data, offset);
        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);
        return b;
    }

    @Override
    public int hashCode() {
        return 3 * (7 * (13 * (17 * (encryptionFlag ? 1 : 0)
                               + (strongEncryptionFlag ? 1 : 0))
                         + (languageEncodingFlag ? 1 : 0))
                    + (dataDescriptorFlag ? 1 : 0));
    }

    @Override
    public boolean equals(Object o) {
        if (!(o instanceof GeneralPurposeBit)) {
            return false;
        }
        GeneralPurposeBit g = (GeneralPurposeBit) o;
        return g.encryptionFlag == encryptionFlag
            && g.strongEncryptionFlag == strongEncryptionFlag
            && g.languageEncodingFlag == languageEncodingFlag
            && g.dataDescriptorFlag == dataDescriptorFlag;
    }
}