/*

  * Licensed to the Apache Software Foundation (ASF) under one or more

  * contributor license agreements.  See the NOTICE file distributed with

  * this work for additional information regarding copyright ownership.

  * The ASF licenses this file to You under the Apache License, Version 2.0

  * (the "License"); you may not use this file except in compliance with

  * the License.  You may obtain a copy of the License at

  *

  *      http://www.apache.org/licenses/LICENSE-2.0

  *

  * Unless required by applicable law or agreed to in writing, software

  * distributed under the License is distributed on an "AS IS" BASIS,

  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

  * See the License for the specific language governing permissions and

  * limitations under the License.

  */

 package org.apache.commons.io.filefilter;

 import java.io.File;

 import java.io.IOException;

 import java.io.RandomAccessFile;

 import java.io.Serializable;

 import java.nio.charset.Charset;

 import java.util.Arrays;

 import org.apache.commons.io.IOUtils;

 /**

  * <p>

  * File filter for matching files containing a "magic number". A magic number

  * is a unique series of bytes common to all files of a specific file format.

  * For instance, all Java class files begin with the bytes

  * <code>0xCAFEBABE</code>.

  * </p>

  *

  * <code><pre>

  * File dir = new File(".");

  * MagicNumberFileFilter javaClassFileFilter =

  *     MagicNumberFileFilter(new byte[] {(byte) 0xCA, (byte) 0xFE,

  *       (byte) 0xBA, (byte) 0xBE});

  * String[] javaClassFiles = dir.list(javaClassFileFilter);

  * for (String javaClassFile : javaClassFiles) {

  *     System.out.println(javaClassFile);

  * }

  * </pre></code>

  *

  * <p>

  * Sometimes, such as in the case of TAR files, the

  * magic number will be offset by a certain number of bytes in the file. In the

  * case of TAR archive files, this offset is 257 bytes.

  * </p>

  *

  * <code><pre>

  * File dir = new File(".");

  * MagicNumberFileFilter tarFileFilter =

  *     MagicNumberFileFilter("ustar", 257);

  * String[] tarFiles = dir.list(tarFileFilter);

  * for (String tarFile : tarFiles) {

  *     System.out.println(tarFile);

  * }

  * </pre></code>

  * @since 2.0

  * @see FileFilterUtils#magicNumberFileFilter(byte[])

  * @see FileFilterUtils#magicNumberFileFilter(String)

  * @see FileFilterUtils#magicNumberFileFilter(byte[], long)

  * @see FileFilterUtils#magicNumberFileFilter(String, long)

  */

 public class MagicNumberFileFilter extends AbstractFileFilter implements

         Serializable {

     /**

      * The serialization version unique identifier.

      */

     private static final long serialVersionUID = -547733176983104172L;

     /**

      * The magic number to compare against the file's bytes at the provided

      * offset.

      */

     private final byte[] magicNumbers;

     /**

      * The offset (in bytes) within the files that the magic number's bytes

      * should appear.

      */

     private final long byteOffset;

     /**

      * <p>

      * Constructs a new MagicNumberFileFilter and associates it with the magic

      * number to test for in files. This constructor assumes a starting offset

      * of <code>0</code>.

      * </p>

      *

      * <p>

      * It is important to note that <em>the array is not cloned</em> and that

      * any changes to the magic number array after construction will affect the

      * behavior of this file filter.

      * </p>

      *

      * <code><pre>

      * MagicNumberFileFilter javaClassFileFilter =

      *     MagicNumberFileFilter(new byte[] {(byte) 0xCA, (byte) 0xFE,

      *       (byte) 0xBA, (byte) 0xBE});

      * </pre></code>

      *

      * @param magicNumber the magic number to look for in the file.

      *

      * @throws IllegalArgumentException if <code>magicNumber</code> is

      *         {@code null}, or contains no bytes.

      */

     public MagicNumberFileFilter(final byte[] magicNumber) {

         this(magicNumber, 0);

     }

     /**

      * <p>

      * Constructs a new MagicNumberFileFilter and associates it with the magic

      * number to test for in files. This constructor assumes a starting offset

      * of <code>0</code>.

      * </p>

      *

      * Example usage:

      * <pre>

      * {@code

      * MagicNumberFileFilter xmlFileFilter =

      *     MagicNumberFileFilter("<?xml");

      * }

      * </pre>

      *

      * @param magicNumber the magic number to look for in the file.

      *        The string is converted to bytes using the platform default charset.

      *

      * @throws IllegalArgumentException if <code>magicNumber</code> is

      *         {@code null} or the empty String.

      */

     public MagicNumberFileFilter(final String magicNumber) {

         this(magicNumber, 0);

     }

     /**

      * <p>

      * Constructs a new MagicNumberFileFilter and associates it with the magic

      * number to test for in files and the byte offset location in the file to

      * to look for that magic number.

      * </p>

      *

      * <code><pre>

      * MagicNumberFileFilter tarFileFilter =

      *     MagicNumberFileFilter("ustar", 257);

      * </pre></code>

      *

      * @param magicNumber the magic number to look for in the file.

      *        The string is converted to bytes using the platform default charset.

      * @param offset the byte offset in the file to start comparing bytes.

      *

      * @throws IllegalArgumentException if <code>magicNumber</code> is

      *         {@code null} or the empty String, or <code>offset</code> is

      *         a negative number.

      */

     public MagicNumberFileFilter(final String magicNumber, final long offset) {

         if (magicNumber == null) {

             throw new IllegalArgumentException("The magic number cannot be null");

         }

         if (magicNumber.length() == 0) {

             throw new IllegalArgumentException("The magic number must contain at least one byte");

         }

         if (offset < 0) {

             throw new IllegalArgumentException("The offset cannot be negative");

         }

         this.magicNumbers = magicNumber.getBytes(Charset.defaultCharset()); // explicitly uses the platform default charset

         this.byteOffset = offset;

     }

     /**

      * <p>

      * Constructs a new MagicNumberFileFilter and associates it with the magic

      * number to test for in files and the byte offset location in the file to

      * to look for that magic number.

      * </p>

      *

      * <code><pre>

      * MagicNumberFileFilter tarFileFilter =

      *     MagicNumberFileFilter(new byte[] {0x75, 0x73, 0x74, 0x61, 0x72}, 257);

      * </pre></code>

      *

      * <code><pre>

      * MagicNumberFileFilter javaClassFileFilter =

      *     MagicNumberFileFilter(new byte[] {0xCA, 0xFE, 0xBA, 0xBE}, 0);

      * </pre></code>

      *

      * @param magicNumber the magic number to look for in the file.

      * @param offset the byte offset in the file to start comparing bytes.

      *

      * @throws IllegalArgumentException if <code>magicNumber</code> is

      *         {@code null}, or contains no bytes, or <code>offset</code>

      *         is a negative number.

      */

     public MagicNumberFileFilter(final byte[] magicNumber, final long offset) {

         if (magicNumber == null) {

             throw new IllegalArgumentException("The magic number cannot be null");

         }

         if (magicNumber.length == 0) {

             throw new IllegalArgumentException("The magic number must contain at least one byte");

         }

         if (offset < 0) {

             throw new IllegalArgumentException("The offset cannot be negative");

         }

         this.magicNumbers = new byte[magicNumber.length];

         System.arraycopy(magicNumber, 0, this.magicNumbers, 0, magicNumber.length);

         this.byteOffset = offset;

     }

     /**

      * <p>

      * Accepts the provided file if the file contains the file filter's magic

      * number at the specified offset.

      * </p>

      *

      * <p>

      * If any {@link IOException}s occur while reading the file, the file will

      * be rejected.

      * </p>

      *

      * @param file the file to accept or reject.

      *

      * @return {@code true} if the file contains the filter's magic number

      *         at the specified offset, {@code false} otherwise.

      */

     @Override

     public boolean accept(final File file) {

         if (file != null && file.isFile() && file.canRead()) {

             RandomAccessFile randomAccessFile = null;

             try {

                 final byte[] fileBytes = new byte[this.magicNumbers.length];

                 randomAccessFile = new RandomAccessFile(file, "r");

                 randomAccessFile.seek(byteOffset);

                 final int read = randomAccessFile.read(fileBytes);

                 if (read != magicNumbers.length) {

                     return false;

                 }

                 return Arrays.equals(this.magicNumbers, fileBytes);

             } catch (final IOException ioe) {

                 // Do nothing, fall through and do not accept file

             } finally {

                 IOUtils.closeQuietly(randomAccessFile);

             }

         }

         return false;

     }

     /**

      * Returns a String representation of the file filter, which includes the

      * magic number bytes and byte offset.

      *

      * @return a String representation of the file filter.

      */

     @Override

     public String toString() {

         final StringBuilder builder = new StringBuilder(super.toString());

         builder.append("(");

         builder.append(new String(magicNumbers, Charset.defaultCharset()));// TODO perhaps use hex if value is not printable

         builder.append(",");

         builder.append(this.byteOffset);

         builder.append(")");

         return builder.toString();

     }

 }