    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.io.filefilter;
    018
    019import java.io.File;
    020import java.io.IOException;
    021import java.io.RandomAccessFile;
    022import java.io.Serializable;
    023import java.nio.charset.Charset;
    024import java.util.Arrays;
    025
    026/**
    027 * <p>
    028 * File filter for matching files containing a "magic number". A magic number
    029 * is a unique series of bytes common to all files of a specific file format.
    030 * For instance, all Java class files begin with the bytes
    031 * <code>0xCAFEBABE</code>.
    032 * </p>
    033 *
    034 * <pre>
    035 * File dir = new File(".");
    036 * MagicNumberFileFilter javaClassFileFilter =
    037 *     MagicNumberFileFilter(new byte[] {(byte) 0xCA, (byte) 0xFE,
    038 *       (byte) 0xBA, (byte) 0xBE});
    039 * String[] javaClassFiles = dir.list(javaClassFileFilter);
    040 * for (String javaClassFile : javaClassFiles) {
    041 *     System.out.println(javaClassFile);
    042 * }
    043 * </pre>
    044 *
    045 * <p>
    046 * Sometimes, such as in the case of TAR files, the
    047 * magic number will be offset by a certain number of bytes in the file. In the
    048 * case of TAR archive files, this offset is 257 bytes.
    049 * </p>
    050 *
    051 * <pre>
    052 * File dir = new File(".");
    053 * MagicNumberFileFilter tarFileFilter =
    054 *     MagicNumberFileFilter("ustar", 257);
    055 * String[] tarFiles = dir.list(tarFileFilter);
    056 * for (String tarFile : tarFiles) {
    057 *     System.out.println(tarFile);
    058 * }
    059 * </pre>
    060 *
    061 * @since 2.0
    062 * @see FileFilterUtils#magicNumberFileFilter(byte[])
    063 * @see FileFilterUtils#magicNumberFileFilter(String)
    064 * @see FileFilterUtils#magicNumberFileFilter(byte[], long)
    065 * @see FileFilterUtils#magicNumberFileFilter(String, long)
    066 */
    067public class MagicNumberFileFilter extends AbstractFileFilter implements
    068        Serializable {
    069
    070    /**
    071     * The serialization version unique identifier.
    072     */
    073    private static final long serialVersionUID = -547733176983104172L;
    074
    075    /**
    076     * The magic number to compare against the file's bytes at the provided
    077     * offset.
    078     */
    079    private final byte[] magicNumbers;
    080
    081    /**
    082     * The offset (in bytes) within the files that the magic number's bytes
    083     * should appear.
    084     */
    085    private final long byteOffset;
    086
    087    /**
    088     * <p>
    089     * Constructs a new MagicNumberFileFilter and associates it with the magic
    090     * number to test for in files. This constructor assumes a starting offset
    091     * of <code>0</code>.
    092     * </p>
    093     *
    094     * <p>
    095     * It is important to note that <em>the array is not cloned</em> and that
    096     * any changes to the magic number array after construction will affect the
    097     * behavior of this file filter.
    098     * </p>
    099     *
    100     * <pre>
    101     * MagicNumberFileFilter javaClassFileFilter =
    102     *     MagicNumberFileFilter(new byte[] {(byte) 0xCA, (byte) 0xFE,
    103     *       (byte) 0xBA, (byte) 0xBE});
    104     * </pre>
    105     *
    106     * @param magicNumber the magic number to look for in the file.
    107     *
    108     * @throws IllegalArgumentException if <code>magicNumber</code> is
    109     *         {@code null}, or contains no bytes.
    110     */
    111    public MagicNumberFileFilter(final byte[] magicNumber) {
    112        this(magicNumber, 0);
    113    }
    114
    115    /**
    116     * <p>
    117     * Constructs a new MagicNumberFileFilter and associates it with the magic
    118     * number to test for in files. This constructor assumes a starting offset
    119     * of <code>0</code>.
    120     * </p>
    121     *
    122     * Example usage:
    123     * <pre>
    124     * {@code
    125     * MagicNumberFileFilter xmlFileFilter =
    126     *     MagicNumberFileFilter("<?xml");
    127     * }
    128     * </pre>
    129     *
    130     * @param magicNumber the magic number to look for in the file.
    131     *        The string is converted to bytes using the platform default charset.
    132     *
    133     * @throws IllegalArgumentException if <code>magicNumber</code> is
    134     *         {@code null} or the empty String.
    135     */
    136    public MagicNumberFileFilter(final String magicNumber) {
    137        this(magicNumber, 0);
    138    }
    139
    140    /**
    141     * <p>
    142     * Constructs a new MagicNumberFileFilter and associates it with the magic
    143     * number to test for in files and the byte offset location in the file to
    144     * to look for that magic number.
    145     * </p>
    146     *
    147     * <pre>
    148     * MagicNumberFileFilter tarFileFilter =
    149     *     MagicNumberFileFilter("ustar", 257);
    150     * </pre>
    151     *
    152     * @param magicNumber the magic number to look for in the file.
    153     *        The string is converted to bytes using the platform default charset.
    154     * @param offset the byte offset in the file to start comparing bytes.
    155     *
    156     * @throws IllegalArgumentException if <code>magicNumber</code> is
    157     *         {@code null} or the empty String, or <code>offset</code> is
    158     *         a negative number.
    159     */
    160    public MagicNumberFileFilter(final String magicNumber, final long offset) {
    161        if (magicNumber == null) {
    162            throw new IllegalArgumentException("The magic number cannot be null");
    163        }
    164        if (magicNumber.isEmpty()) {
    165            throw new IllegalArgumentException("The magic number must contain at least one byte");
    166        }
    167        if (offset < 0) {
    168            throw new IllegalArgumentException("The offset cannot be negative");
    169        }
    170
    171        this.magicNumbers = magicNumber.getBytes(Charset.defaultCharset()); // explicitly uses the platform default
    172                                                                            // charset
    173        this.byteOffset = offset;
    174    }
    175
    176    /**
    177     * <p>
    178     * Constructs a new MagicNumberFileFilter and associates it with the magic
    179     * number to test for in files and the byte offset location in the file to
    180     * to look for that magic number.
    181     * </p>
    182     *
    183     * <pre>
    184     * MagicNumberFileFilter tarFileFilter =
    185     *     MagicNumberFileFilter(new byte[] {0x75, 0x73, 0x74, 0x61, 0x72}, 257);
    186     * </pre>
    187     *
    188     * <pre>
    189     * MagicNumberFileFilter javaClassFileFilter =
    190     *     MagicNumberFileFilter(new byte[] {0xCA, 0xFE, 0xBA, 0xBE}, 0);
    191     * </pre>
    192     *
    193     * @param magicNumber the magic number to look for in the file.
    194     * @param offset the byte offset in the file to start comparing bytes.
    195     *
    196     * @throws IllegalArgumentException if <code>magicNumber</code> is
    197     *         {@code null}, or contains no bytes, or <code>offset</code>
    198     *         is a negative number.
    199     */
    200    public MagicNumberFileFilter(final byte[] magicNumber, final long offset) {
    201        if (magicNumber == null) {
    202            throw new IllegalArgumentException("The magic number cannot be null");
    203        }
    204        if (magicNumber.length == 0) {
    205            throw new IllegalArgumentException("The magic number must contain at least one byte");
    206        }
    207        if (offset < 0) {
    208            throw new IllegalArgumentException("The offset cannot be negative");
    209        }
    210
    211        this.magicNumbers = new byte[magicNumber.length];
    212        System.arraycopy(magicNumber, 0, this.magicNumbers, 0, magicNumber.length);
    213        this.byteOffset = offset;
    214    }
    215
    216    /**
    217     * <p>
    218     * Accepts the provided file if the file contains the file filter's magic
    219     * number at the specified offset.
    220     * </p>
    221     *
    222     * <p>
    223     * If any {@link IOException}s occur while reading the file, the file will
    224     * be rejected.
    225     * </p>
    226     *
    227     * @param file the file to accept or reject.
    228     *
    229     * @return {@code true} if the file contains the filter's magic number
    230     *         at the specified offset, {@code false} otherwise.
    231     */
    232    @Override
    233    public boolean accept(final File file) {
    234        if (file != null && file.isFile() && file.canRead()) {
    235            try {
    236                try (RandomAccessFile randomAccessFile = new RandomAccessFile(file, "r")) {
    237                    final byte[] fileBytes = new byte[this.magicNumbers.length];
    238                    randomAccessFile.seek(byteOffset);
    239                    final int read = randomAccessFile.read(fileBytes);
    240                    if (read != magicNumbers.length) {
    241                        return false;
    242                    }
    243                    return Arrays.equals(this.magicNumbers, fileBytes);
    244                }
    245            }
    246            catch (final IOException ioe) {
    247                // Do nothing, fall through and do not accept file
    248            }
    249        }
    250
    251        return false;
    252    }
    253
    254    /**
    255     * Returns a String representation of the file filter, which includes the
    256     * magic number bytes and byte offset.
    257     *
    258     * @return a String representation of the file filter.
    259     */
    260    @Override
    261    public String toString() {
    262        final StringBuilder builder = new StringBuilder(super.toString());
    263        builder.append("(");
    264        builder.append(new String(magicNumbers, Charset.defaultCharset()));// TODO perhaps use hex if value is not
    265                                                                           // printable
    266        builder.append(",");
    267        builder.append(this.byteOffset);
    268        builder.append(")");
    269        return builder.toString();
    270    }
    271}