    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.ByteBuffer;
    024import java.nio.channels.FileChannel;
    025import java.nio.charset.Charset;
    026import java.nio.file.FileVisitResult;
    027import java.nio.file.Files;
    028import java.nio.file.Path;
    029import java.nio.file.attribute.BasicFileAttributes;
    030import java.util.Arrays;
    031import java.util.Objects;
    032
    033import org.apache.commons.io.RandomAccessFileMode;
    034import org.apache.commons.io.RandomAccessFiles;
    035
    036/**
    037 * <p>
    038 * File filter for matching files containing a "magic number". A magic number
    039 * is a unique series of bytes common to all files of a specific file format.
    040 * For instance, all Java class files begin with the bytes
    041 * {@code 0xCAFEBABE}.
    042 * </p>
    043 * <h2>Using Classic IO</h2>
    044 * <pre>
    045 * File dir = FileUtils.current();
    046 * MagicNumberFileFilter javaClassFileFilter =
    047 *     MagicNumberFileFilter(new byte[] {(byte) 0xCA, (byte) 0xFE,
    048 *       (byte) 0xBA, (byte) 0xBE});
    049 * String[] javaClassFiles = dir.list(javaClassFileFilter);
    050 * for (String javaClassFile : javaClassFiles) {
    051 *     System.out.println(javaClassFile);
    052 * }
    053 * </pre>
    054 *
    055 * <p>
    056 * Sometimes, such as in the case of TAR files, the
    057 * magic number will be offset by a certain number of bytes in the file. In the
    058 * case of TAR archive files, this offset is 257 bytes.
    059 * </p>
    060 *
    061 * <pre>
    062 * File dir = FileUtils.current();
    063 * MagicNumberFileFilter tarFileFilter =
    064 *     MagicNumberFileFilter("ustar", 257);
    065 * String[] tarFiles = dir.list(tarFileFilter);
    066 * for (String tarFile : tarFiles) {
    067 *     System.out.println(tarFile);
    068 * }
    069 * </pre>
    070 * <h2>Using NIO</h2>
    071 * <pre>
    072 * final Path dir = PathUtils.current();
    073 * final AccumulatorPathVisitor visitor = AccumulatorPathVisitor.withLongCounters(MagicNumberFileFilter("ustar", 257));
    074 * //
    075 * // Walk one dir
    076 * Files.<b>walkFileTree</b>(dir, Collections.emptySet(), 1, visitor);
    077 * System.out.println(visitor.getPathCounters());
    078 * System.out.println(visitor.getFileList());
    079 * //
    080 * visitor.getPathCounters().reset();
    081 * //
    082 * // Walk dir tree
    083 * Files.<b>walkFileTree</b>(dir, visitor);
    084 * System.out.println(visitor.getPathCounters());
    085 * System.out.println(visitor.getDirList());
    086 * System.out.println(visitor.getFileList());
    087 * </pre>
    088 * <h2>Deprecating Serialization</h2>
    089 * <p>
    090 * <em>Serialization is deprecated and will be removed in 3.0.</em>
    091 * </p>
    092 *
    093 * <h2>Deprecating Serialization</h2>
    094 * <p>
    095 * <em>Serialization is deprecated and will be removed in 3.0.</em>
    096 * </p>
    097 *
    098 * @since 2.0
    099 * @see FileFilterUtils#magicNumberFileFilter(byte[])
    100 * @see FileFilterUtils#magicNumberFileFilter(String)
    101 * @see FileFilterUtils#magicNumberFileFilter(byte[], long)
    102 * @see FileFilterUtils#magicNumberFileFilter(String, long)
    103 */
    104public class MagicNumberFileFilter extends AbstractFileFilter implements Serializable {
    105
    106    /**
    107     * The serialization version unique identifier.
    108     */
    109    private static final long serialVersionUID = -547733176983104172L;
    110
    111    /**
    112     * The magic number to compare against the file's bytes at the provided
    113     * offset.
    114     */
    115    private final byte[] magicNumbers;
    116
    117    /**
    118     * The offset (in bytes) within the files that the magic number's bytes
    119     * should appear.
    120     */
    121    private final long byteOffset;
    122
    123    /**
    124     * <p>
    125     * Constructs a new MagicNumberFileFilter and associates it with the magic
    126     * number to test for in files. This constructor assumes a starting offset
    127     * of {@code 0}.
    128     * </p>
    129     *
    130     * <p>
    131     * It is important to note that <em>the array is not cloned</em> and that
    132     * any changes to the magic number array after construction will affect the
    133     * behavior of this file filter.
    134     * </p>
    135     *
    136     * <pre>
    137     * MagicNumberFileFilter javaClassFileFilter =
    138     *     MagicNumberFileFilter(new byte[] {(byte) 0xCA, (byte) 0xFE,
    139     *       (byte) 0xBA, (byte) 0xBE});
    140     * </pre>
    141     *
    142     * @param magicNumber the magic number to look for in the file.
    143     *
    144     * @throws IllegalArgumentException if {@code magicNumber} is
    145     *         {@code null}, or contains no bytes.
    146     */
    147    public MagicNumberFileFilter(final byte[] magicNumber) {
    148        this(magicNumber, 0);
    149    }
    150
    151    /**
    152     * <p>
    153     * Constructs a new MagicNumberFileFilter and associates it with the magic
    154     * number to test for in files and the byte offset location in the file to
    155     * to look for that magic number.
    156     * </p>
    157     *
    158     * <pre>
    159     * MagicNumberFileFilter tarFileFilter =
    160     *     MagicNumberFileFilter(new byte[] {0x75, 0x73, 0x74, 0x61, 0x72}, 257);
    161     * </pre>
    162     *
    163     * <pre>
    164     * MagicNumberFileFilter javaClassFileFilter =
    165     *     MagicNumberFileFilter(new byte[] {0xCA, 0xFE, 0xBA, 0xBE}, 0);
    166     * </pre>
    167     *
    168     * @param magicNumbers the magic number to look for in the file.
    169     * @param offset the byte offset in the file to start comparing bytes.
    170     *
    171     * @throws IllegalArgumentException if {@code magicNumber}
    172     *         contains no bytes, or {@code offset}
    173     *         is a negative number.
    174     */
    175    public MagicNumberFileFilter(final byte[] magicNumbers, final long offset) {
    176        Objects.requireNonNull(magicNumbers, "magicNumbers");
    177        if (magicNumbers.length == 0) {
    178            throw new IllegalArgumentException("The magic number must contain at least one byte");
    179        }
    180        if (offset < 0) {
    181            throw new IllegalArgumentException("The offset cannot be negative");
    182        }
    183
    184        this.magicNumbers = magicNumbers.clone();
    185        this.byteOffset = offset;
    186    }
    187
    188    /**
    189     * <p>
    190     * Constructs a new MagicNumberFileFilter and associates it with the magic
    191     * number to test for in files. This constructor assumes a starting offset
    192     * of {@code 0}.
    193     * </p>
    194     *
    195     * Example usage:
    196     * <pre>
    197     * {@code
    198     * MagicNumberFileFilter xmlFileFilter =
    199     *     MagicNumberFileFilter("<?xml");
    200     * }
    201     * </pre>
    202     *
    203     * @param magicNumber the magic number to look for in the file.
    204     *        The string is converted to bytes using the platform default charset.
    205     *
    206     * @throws IllegalArgumentException if {@code magicNumber} is
    207     *         {@code null} or the empty String.
    208     */
    209    public MagicNumberFileFilter(final String magicNumber) {
    210        this(magicNumber, 0);
    211    }
    212
    213    /**
    214     * <p>
    215     * Constructs a new MagicNumberFileFilter and associates it with the magic
    216     * number to test for in files and the byte offset location in the file to
    217     * to look for that magic number.
    218     * </p>
    219     *
    220     * <pre>
    221     * MagicNumberFileFilter tarFileFilter =
    222     *     MagicNumberFileFilter("ustar", 257);
    223     * </pre>
    224     *
    225     * @param magicNumber the magic number to look for in the file.
    226     *        The string is converted to bytes using the platform default charset.
    227     * @param offset the byte offset in the file to start comparing bytes.
    228     *
    229     * @throws IllegalArgumentException if {@code magicNumber} is
    230     *         the empty String, or {@code offset} is
    231     *         a negative number.
    232     */
    233    public MagicNumberFileFilter(final String magicNumber, final long offset) {
    234        Objects.requireNonNull(magicNumber, "magicNumber");
    235        if (magicNumber.isEmpty()) {
    236            throw new IllegalArgumentException("The magic number must contain at least one byte");
    237        }
    238        if (offset < 0) {
    239            throw new IllegalArgumentException("The offset cannot be negative");
    240        }
    241
    242        this.magicNumbers = magicNumber.getBytes(Charset.defaultCharset()); // explicitly uses the platform default charset
    243        this.byteOffset = offset;
    244    }
    245
    246    /**
    247     * <p>
    248     * Accepts the provided file if the file contains the file filter's magic
    249     * number at the specified offset.
    250     * </p>
    251     *
    252     * <p>
    253     * If any {@link IOException}s occur while reading the file, the file will
    254     * be rejected.
    255     * </p>
    256     *
    257     * @param file the file to accept or reject.
    258     *
    259     * @return {@code true} if the file contains the filter's magic number
    260     *         at the specified offset, {@code false} otherwise.
    261     */
    262    @Override
    263    public boolean accept(final File file) {
    264        if (file != null && file.isFile() && file.canRead()) {
    265            try (RandomAccessFile randomAccessFile = RandomAccessFileMode.READ_ONLY.create(file)) {
    266                return Arrays.equals(magicNumbers, RandomAccessFiles.read(randomAccessFile, byteOffset, magicNumbers.length));
    267            } catch (final IOException ignored) {
    268                // Do nothing, fall through and do not accept file
    269            }
    270        }
    271        return false;
    272    }
    273
    274    /**
    275     * <p>
    276     * Accepts the provided file if the file contains the file filter's magic
    277     * number at the specified offset.
    278     * </p>
    279     *
    280     * <p>
    281     * If any {@link IOException}s occur while reading the file, the file will
    282     * be rejected.
    283     * </p>
    284     * @param file the file to accept or reject.
    285     *
    286     * @return {@code true} if the file contains the filter's magic number
    287     *         at the specified offset, {@code false} otherwise.
    288     * @since 2.9.0
    289     */
    290    @Override
    291    public FileVisitResult accept(final Path file, final BasicFileAttributes attributes) {
    292        if (file != null && Files.isRegularFile(file) && Files.isReadable(file)) {
    293            try {
    294                try (FileChannel fileChannel = FileChannel.open(file)) {
    295                    final ByteBuffer byteBuffer = ByteBuffer.allocate(this.magicNumbers.length);
    296                    fileChannel.position(byteOffset);
    297                    final int read = fileChannel.read(byteBuffer);
    298                    if (read != magicNumbers.length) {
    299                        return FileVisitResult.TERMINATE;
    300                    }
    301                    return toFileVisitResult(Arrays.equals(this.magicNumbers, byteBuffer.array()));
    302                }
    303            }
    304            catch (final IOException ignored) {
    305                // Do nothing, fall through and do not accept file
    306            }
    307        }
    308        return FileVisitResult.TERMINATE;
    309    }
    310
    311    /**
    312     * Returns a String representation of the file filter, which includes the
    313     * magic number bytes and byte offset.
    314     *
    315     * @return a String representation of the file filter.
    316     */
    317    @Override
    318    public String toString() {
    319        final StringBuilder builder = new StringBuilder(super.toString());
    320        builder.append("(");
    321        // TODO perhaps use hex if value is not printable
    322        builder.append(new String(magicNumbers, Charset.defaultCharset()));
    323        builder.append(",");
    324        builder.append(this.byteOffset);
    325        builder.append(")");
    326        return builder.toString();
    327    }
    328}