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
021
022import java.util.zip.ZipException;
023
024/**
025 * An extra field who's sole purpose is to align and pad the local file header
026 * so that the entry's data starts at a certain position.
027 *
028 * <p>The padding content of the padding is ignored and not retained
029 * when reading a padding field.</p>
030 *
031 * <p>This enables Commons Compress to create "aligned" archives
032 * similar to Android's zipalign command line tool.</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 = 0;
054
055    public ResourceAlignmentExtraField() {
056    }
057
058    public ResourceAlignmentExtraField(int alignment) {
059        this(alignment, false);
060    }
061
062    public ResourceAlignmentExtraField(int alignment, boolean allowMethodChange) {
063        this(alignment, allowMethodChange, 0);
064    }
065
066    public ResourceAlignmentExtraField(int alignment, boolean allowMethodChange, int padding) {
067        if (alignment < 0 || alignment > 0x7fff) {
068            throw new IllegalArgumentException("Alignment must be between 0 and 0x7fff, was: " + alignment);
069        }
070        this.alignment = (short) alignment;
071        this.allowMethodChange = allowMethodChange;
072        this.padding = padding;
073    }
074
075    /**
076     * Gets requested alignment.
077     *
078     * @return
079     *      requested alignment.
080     */
081    public short getAlignment() {
082        return alignment;
083    }
084
085    /**
086     * Indicates whether method change is allowed when re-compressing the zip file.
087     *
088     * @return
089     *      true if method change is allowed, false otherwise.
090     */
091    public boolean allowMethodChange() {
092        return allowMethodChange;
093    }
094
095    @Override
096    public ZipShort getHeaderId() {
097        return ID;
098    }
099
100    @Override
101    public ZipShort getLocalFileDataLength() {
102        return new ZipShort(BASE_SIZE + padding);
103    }
104
105    @Override
106    public ZipShort getCentralDirectoryLength() {
107        return new ZipShort(BASE_SIZE);
108    }
109
110    @Override
111    public byte[] getLocalFileDataData() {
112        byte[] content = new byte[BASE_SIZE + padding];
113        ZipShort.putShort(alignment | (allowMethodChange ? ALLOW_METHOD_MESSAGE_CHANGE_FLAG : 0),
114                          content, 0);
115        return content;
116    }
117
118    @Override
119    public byte[] getCentralDirectoryData() {
120        return ZipShort.getBytes(alignment | (allowMethodChange ? ALLOW_METHOD_MESSAGE_CHANGE_FLAG : 0));
121    }
122
123    @Override
124    public void parseFromLocalFileData(byte[] buffer, int offset, int length) throws ZipException {
125        parseFromCentralDirectoryData(buffer, offset, length);
126        this.padding = length - BASE_SIZE;
127    }
128
129    @Override
130    public void parseFromCentralDirectoryData(byte[] buffer, int offset, int length) throws ZipException {
131        if (length < BASE_SIZE) {
132            throw new ZipException("Too short content for ResourceAlignmentExtraField (0xa11e): " + length);
133        }
134        int alignmentValue = ZipShort.getValue(buffer, offset);
135        this.alignment = (short) (alignmentValue & (ALLOW_METHOD_MESSAGE_CHANGE_FLAG - 1));
136        this.allowMethodChange = (alignmentValue & ALLOW_METHOD_MESSAGE_CHANGE_FLAG) != 0;
137    }
138}