001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 * http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.commons.compress.archivers.zip;
020
021import java.util.zip.ZipException;
022
023/**
024 * An extra field who's sole purpose is to align and pad the local file header so that the entry's data starts at a certain position.
025 *
026 * <p>
027 * The padding content of the padding is ignored and not retained when reading a padding field.
028 * </p>
029 *
030 * <p>
031 * This enables Commons Compress to create "aligned" archives similar to Android's {@code zipalign} command line tool.
032 * </p>
033 *
034 * @since 1.14
035 * @see "https://developer.android.com/studio/command-line/zipalign.html"
036 * @see ZipArchiveEntry#setAlignment
037 */
038public class ResourceAlignmentExtraField implements ZipExtraField {
039
040    /**
041     * Extra field id used for storing alignment and padding.
042     */
043    public static final ZipShort ID = new ZipShort(0xa11e);
044
045    public static final int BASE_SIZE = 2;
046
047    private static final int ALLOW_METHOD_MESSAGE_CHANGE_FLAG = 0x8000;
048
049    private short alignment;
050
051    private boolean allowMethodChange;
052
053    private int padding;
054
055    public ResourceAlignmentExtraField() {
056    }
057
058    public ResourceAlignmentExtraField(final int alignment) {
059        this(alignment, false);
060    }
061
062    public ResourceAlignmentExtraField(final int alignment, final boolean allowMethodChange) {
063        this(alignment, allowMethodChange, 0);
064    }
065
066    public ResourceAlignmentExtraField(final int alignment, final boolean allowMethodChange, final int padding) {
067        if (alignment < 0 || alignment > 0x7fff) {
068            throw new IllegalArgumentException("Alignment must be between 0 and 0x7fff, was: " + alignment);
069        }
070        if (padding < 0) {
071            throw new IllegalArgumentException("Padding must not be negative, was: " + padding);
072        }
073        this.alignment = (short) alignment;
074        this.allowMethodChange = allowMethodChange;
075        this.padding = padding;
076    }
077
078    /**
079     * Indicates whether method change is allowed when re-compressing the ZIP file.
080     *
081     * @return true if method change is allowed, false otherwise.
082     */
083    public boolean allowMethodChange() {
084        return allowMethodChange;
085    }
086
087    /**
088     * Gets requested alignment.
089     *
090     * @return requested alignment.
091     */
092    public short getAlignment() {
093        return alignment;
094    }
095
096    @Override
097    public byte[] getCentralDirectoryData() {
098        return ZipShort.getBytes(alignment | (allowMethodChange ? ALLOW_METHOD_MESSAGE_CHANGE_FLAG : 0));
099    }
100
101    @Override
102    public ZipShort getCentralDirectoryLength() {
103        return new ZipShort(BASE_SIZE);
104    }
105
106    @Override
107    public ZipShort getHeaderId() {
108        return ID;
109    }
110
111    @Override
112    public byte[] getLocalFileDataData() {
113        final byte[] content = new byte[BASE_SIZE + padding];
114        ZipShort.putShort(alignment | (allowMethodChange ? ALLOW_METHOD_MESSAGE_CHANGE_FLAG : 0), content, 0);
115        return content;
116    }
117
118    @Override
119    public ZipShort getLocalFileDataLength() {
120        return new ZipShort(BASE_SIZE + padding);
121    }
122
123    @Override
124    public void parseFromCentralDirectoryData(final byte[] buffer, final int offset, final int length) throws ZipException {
125        if (length < BASE_SIZE) {
126            throw new ZipException("Too short content for ResourceAlignmentExtraField (0xa11e): " + length);
127        }
128        final int alignmentValue = ZipShort.getValue(buffer, offset);
129        this.alignment = (short) (alignmentValue & ALLOW_METHOD_MESSAGE_CHANGE_FLAG - 1);
130        this.allowMethodChange = (alignmentValue & ALLOW_METHOD_MESSAGE_CHANGE_FLAG) != 0;
131    }
132
133    @Override
134    public void parseFromLocalFileData(final byte[] buffer, final int offset, final int length) throws ZipException {
135        parseFromCentralDirectoryData(buffer, offset, length);
136        this.padding = length - BASE_SIZE;
137    }
138}