    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 *      https://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.Serializable;
    022import java.nio.ByteBuffer;
    023import java.nio.channels.FileChannel;
    024import java.nio.charset.Charset;
    025import java.nio.file.FileVisitResult;
    026import java.nio.file.Files;
    027import java.nio.file.Path;
    028import java.nio.file.attribute.BasicFileAttributes;
    029import java.util.Arrays;
    030import java.util.Objects;
    031
    032import org.apache.commons.io.RandomAccessFileMode;
    033import org.apache.commons.io.RandomAccessFiles;
    034
    035/**
    036 * <p>
    037 * File filter for matching files containing a "magic number". A magic number
    038 * is a unique series of bytes common to all files of a specific file format.
    039 * For instance, all Java class files begin with the bytes
    040 * {@code 0xCAFEBABE}.
    041 * </p>
    042 * <h2>Using Classic IO</h2>
    043 * <pre>
    044 * File dir = FileUtils.current();
    045 * MagicNumberFileFilter javaClassFileFilter =
    046 *     MagicNumberFileFilter(new byte[] {(byte) 0xCA, (byte) 0xFE,
    047 *       (byte) 0xBA, (byte) 0xBE});
    048 * String[] javaClassFiles = dir.list(javaClassFileFilter);
    049 * for (String javaClassFile : javaClassFiles) {
    050 *     System.out.println(javaClassFile);
    051 * }
    052 * </pre>
    053 *
    054 * <p>
    055 * Sometimes, such as in the case of TAR files, the
    056 * magic number will be offset by a certain number of bytes in the file. In the
    057 * case of TAR archive files, this offset is 257 bytes.
    058 * </p>
    059 *
    060 * <pre>
    061 * File dir = FileUtils.current();
    062 * MagicNumberFileFilter tarFileFilter =
    063 *     MagicNumberFileFilter("ustar", 257);
    064 * String[] tarFiles = dir.list(tarFileFilter);
    065 * for (String tarFile : tarFiles) {
    066 *     System.out.println(tarFile);
    067 * }
    068 * </pre>
    069 * <h2>Using NIO</h2>
    070 * <pre>
    071 * final Path dir = PathUtils.current();
    072 * final AccumulatorPathVisitor visitor = AccumulatorPathVisitor.withLongCounters(MagicNumberFileFilter("ustar", 257));
    073 * //
    074 * // Walk one directory
    075 * Files.<strong>walkFileTree</strong>(dir, Collections.emptySet(), 1, visitor);
    076 * System.out.println(visitor.getPathCounters());
    077 * System.out.println(visitor.getFileList());
    078 * //
    079 * visitor.getPathCounters().reset();
    080 * //
    081 * // Walk directory tree
    082 * Files.<strong>walkFileTree</strong>(dir, visitor);
    083 * System.out.println(visitor.getPathCounters());
    084 * System.out.println(visitor.getDirList());
    085 * System.out.println(visitor.getFileList());
    086 * </pre>
    087 * <h2>Deprecating Serialization</h2>
    088 * <p>
    089 * <em>Serialization is deprecated and will be removed in 3.0.</em>
    090 * </p>
    091 *
    092 * <h2>Deprecating Serialization</h2>
    093 * <p>
    094 * <em>Serialization is deprecated and will be removed in 3.0.</em>
    095 * </p>
    096 *
    097 * @since 2.0
    098 * @see FileFilterUtils#magicNumberFileFilter(byte[])
    099 * @see FileFilterUtils#magicNumberFileFilter(String)
    100 * @see FileFilterUtils#magicNumberFileFilter(byte[], long)
    101 * @see FileFilterUtils#magicNumberFileFilter(String, long)
    102 */
    103public class MagicNumberFileFilter extends AbstractFileFilter implements Serializable {
    104
    105    /**
    106     * The serialization version unique identifier.
    107     */
    108    private static final long serialVersionUID = -547733176983104172L;
    109
    110    /**
    111     * The magic number to compare against the file's bytes at the provided
    112     * offset.
    113     */
    114    private final byte[] magicNumbers;
    115
    116    /**
    117     * The offset (in bytes) within the files that the magic number's bytes
    118     * should appear.
    119     */
    120    private final long byteOffset;
    121
    122    /**
    123     * <p>
    124     * Constructs a new MagicNumberFileFilter and associates it with the magic
    125     * number to test for in files. This constructor assumes a starting offset
    126     * of {@code 0}.
    127     * </p>
    128     *
    129     * <p>
    130     * It is important to note that <em>the array is not cloned</em> and that
    131     * any changes to the magic number array after construction will affect the
    132     * behavior of this file filter.
    133     * </p>
    134     *
    135     * <pre>
    136     * MagicNumberFileFilter javaClassFileFilter =
    137     *     MagicNumberFileFilter(new byte[] {(byte) 0xCA, (byte) 0xFE,
    138     *       (byte) 0xBA, (byte) 0xBE});
    139     * </pre>
    140     *
    141     * @param magicNumber the magic number to look for in the file.
    142     * @throws IllegalArgumentException if {@code magicNumber} is
    143     *         {@code null}, or contains no bytes.
    144     */
    145    public MagicNumberFileFilter(final byte[] magicNumber) {
    146        this(magicNumber, 0);
    147    }
    148
    149    /**
    150     * <p>
    151     * Constructs a new MagicNumberFileFilter and associates it with the magic
    152     * number to test for in files and the byte offset location in the file to
    153     * to look for that magic number.
    154     * </p>
    155     *
    156     * <pre>
    157     * MagicNumberFileFilter tarFileFilter =
    158     *     MagicNumberFileFilter(new byte[] {0x75, 0x73, 0x74, 0x61, 0x72}, 257);
    159     * </pre>
    160     *
    161     * <pre>
    162     * MagicNumberFileFilter javaClassFileFilter =
    163     *     MagicNumberFileFilter(new byte[] {0xCA, 0xFE, 0xBA, 0xBE}, 0);
    164     * </pre>
    165     *
    166     * @param magicNumbers the magic number to look for in the file.
    167     * @param offset the byte offset in the file to start comparing bytes.
    168     * @throws IllegalArgumentException if {@code magicNumber}
    169     *         contains no bytes, or {@code offset}
    170     *         is a negative number.
    171     */
    172    public MagicNumberFileFilter(final byte[] magicNumbers, final long offset) {
    173        Objects.requireNonNull(magicNumbers, "magicNumbers");
    174        if (magicNumbers.length == 0) {
    175            throw new IllegalArgumentException("The magic number must contain at least one byte");
    176        }
    177        if (offset < 0) {
    178            throw new IllegalArgumentException("The offset cannot be negative");
    179        }
    180
    181        this.magicNumbers = magicNumbers.clone();
    182        this.byteOffset = offset;
    183    }
    184
    185    /**
    186     * <p>
    187     * Constructs a new MagicNumberFileFilter and associates it with the magic
    188     * number to test for in files. This constructor assumes a starting offset
    189     * of {@code 0}.
    190     * </p>
    191     *
    192     * Example usage:
    193     * <pre>
    194     * {@code
    195     * MagicNumberFileFilter xmlFileFilter =
    196     *     MagicNumberFileFilter("<?xml");
    197     * }
    198     * </pre>
    199     *
    200     * @param magicNumber the magic number to look for in the file.
    201     *        The string is converted to bytes using the platform default charset.
    202     *
    203     * @throws IllegalArgumentException if {@code magicNumber} is
    204     *         {@code null} or the empty String.
    205     */
    206    public MagicNumberFileFilter(final String magicNumber) {
    207        this(magicNumber, 0);
    208    }
    209
    210    /**
    211     * <p>
    212     * Constructs a new MagicNumberFileFilter and associates it with the magic
    213     * number to test for in files and the byte offset location in the file to
    214     * to look for that magic number.
    215     * </p>
    216     *
    217     * <pre>
    218     * MagicNumberFileFilter tarFileFilter = MagicNumberFileFilter("ustar", 257);
    219     * </pre>
    220     * <p>
    221     * This method uses the virtual machine's {@linkplain Charset#defaultCharset() default charset}.
    222     * </p>
    223     *
    224     * @param magicNumber the magic number to look for in the file.
    225     *        The string is converted to bytes using the platform default charset.
    226     * @param offset the byte offset in the file to start comparing bytes.
    227     * @throws IllegalArgumentException if {@code magicNumber} is
    228     *         the empty String, or {@code offset} is
    229     *         a negative number.
    230     */
    231    public MagicNumberFileFilter(final String magicNumber, final long offset) {
    232        this(magicNumber.getBytes(Charset.defaultCharset()), offset);
    233    }
    234
    235    /**
    236     * <p>
    237     * Accepts the provided file if the file contains the file filter's magic
    238     * number at the specified offset.
    239     * </p>
    240     *
    241     * <p>
    242     * If any {@link IOException}s occur while reading the file, the file will
    243     * be rejected.
    244     * </p>
    245     *
    246     * @param file the file to accept or reject.
    247     * @return {@code true} if the file contains the filter's magic number
    248     *         at the specified offset, {@code false} otherwise.
    249     */
    250    @Override
    251    public boolean accept(final File file) {
    252        if (isFile(file) && file.canRead()) {
    253            try {
    254                return RandomAccessFileMode.READ_ONLY.apply(file.toPath(),
    255                        raf -> Arrays.equals(magicNumbers, RandomAccessFiles.read(raf, byteOffset, magicNumbers.length)));
    256            } catch (final IOException ignored) {
    257                // Do nothing, fall through and do not accept file
    258            }
    259        }
    260        return false;
    261    }
    262
    263    /**
    264     * <p>
    265     * Accepts the provided file if the file contains the file filter's magic
    266     * number at the specified offset.
    267     * </p>
    268     * <p>
    269     * If any {@link IOException}s occur while reading the file, the file will
    270     * be rejected.
    271     *
    272     * </p>
    273     *
    274     * @param file the file to accept or reject.
    275     * @param attributes the path's basic attributes (may be null).
    276     * @return {@code true} if the file contains the filter's magic number
    277     *         at the specified offset, {@code false} otherwise.
    278     * @since 2.9.0
    279     */
    280    @Override
    281    public FileVisitResult accept(final Path file, final BasicFileAttributes attributes) {
    282        if (file != null && Files.isRegularFile(file) && Files.isReadable(file)) {
    283            try {
    284                try (FileChannel fileChannel = FileChannel.open(file)) {
    285                    final ByteBuffer byteBuffer = ByteBuffer.allocate(this.magicNumbers.length);
    286                    fileChannel.position(byteOffset);
    287                    final int read = fileChannel.read(byteBuffer);
    288                    if (read != magicNumbers.length) {
    289                        return FileVisitResult.TERMINATE;
    290                    }
    291                    return toFileVisitResult(Arrays.equals(this.magicNumbers, byteBuffer.array()));
    292                }
    293            } catch (final IOException ignored) {
    294                // Do nothing, fall through and do not accept file
    295            }
    296        }
    297        return FileVisitResult.TERMINATE;
    298    }
    299
    300    /**
    301     * Returns a String representation of the file filter, which includes the
    302     * magic number bytes and byte offset.
    303     *
    304     * @return a String representation of the file filter.
    305     */
    306    @Override
    307    public String toString() {
    308        final StringBuilder builder = new StringBuilder(super.toString());
    309        builder.append("(");
    310        // TODO perhaps use hex if value is not printable
    311        builder.append(new String(magicNumbers, Charset.defaultCharset()));
    312        builder.append(",");
    313        builder.append(this.byteOffset);
    314        builder.append(")");
    315        return builder.toString();
    316    }
    317}