# FileTypeDetector.java

    /*
     * 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.pdfbox.util.filetypedetector;

    import java.io.BufferedInputStream;
    import java.io.IOException;
    import java.nio.charset.StandardCharsets;

    /**
     * @author Drew Noakes
     *
     * code taken from https://github.com/drewnoakes/metadata-extractor
     *
     * 2016-01-04
     *
     * latest commit number 73f1a48
     *
     * Examines the a file's first bytes and estimates the file's type.
     */
    public final class FileTypeDetector
    {
        private static final ByteTrie<FileType> root;

        static
        {
            root = new ByteTrie<>();
            root.setDefaultValue(FileType.UNKNOWN);

            // https://en.wikipedia.org/wiki/List_of_file_signatures

            root.addPath(FileType.JPEG, new byte[]{(byte)0xff, (byte)0xd8});
            root.addPath(FileType.TIFF, "II".getBytes(StandardCharsets.ISO_8859_1), new byte[]{0x2a, 0x00});
            root.addPath(FileType.TIFF, "MM".getBytes(StandardCharsets.ISO_8859_1), new byte[]{0x00, 0x2a});
            root.addPath(FileType.PSD, "8BPS".getBytes(StandardCharsets.ISO_8859_1));
            root.addPath(FileType.PNG, new byte[]{(byte)0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, 0x00, 0x00, 0x00, 0x0D, 0x49, 0x48, 0x44, 0x52});
            // TODO technically there are other very rare magic numbers for OS/2 BMP files...
            root.addPath(FileType.BMP, "BM".getBytes(StandardCharsets.ISO_8859_1));
            root.addPath(FileType.GIF, "GIF87a".getBytes(StandardCharsets.ISO_8859_1));
            root.addPath(FileType.GIF, "GIF89a".getBytes(StandardCharsets.ISO_8859_1));
            root.addPath(FileType.ICO, new byte[]{0x00, 0x00, 0x01, 0x00});
            // multiple PCX versions, explicitly listed
            root.addPath(FileType.PCX, new byte[]{0x0A, 0x00, 0x01});
            root.addPath(FileType.PCX, new byte[]{0x0A, 0x02, 0x01});
            root.addPath(FileType.PCX, new byte[]{0x0A, 0x03, 0x01});
            root.addPath(FileType.PCX, new byte[]{0x0A, 0x05, 0x01});
            root.addPath(FileType.RIFF, "RIFF".getBytes(StandardCharsets.ISO_8859_1));

            // https://github.com/drewnoakes/metadata-extractor/issues/217
            // root.addPath(FileType.ARW, "II".getBytes(StandardCharsets.ISO_8859_1), new byte[]{0x2a, 0x00, 0x08, 0x00})
            root.addPath(FileType.CRW, "II".getBytes(StandardCharsets.ISO_8859_1), new byte[]{0x1a, 0x00, 0x00, 0x00}, "HEAPCCDR".getBytes(StandardCharsets.ISO_8859_1));
            root.addPath(FileType.CR2, "II".getBytes(StandardCharsets.ISO_8859_1), new byte[]{0x2a, 0x00, 0x10, 0x00, 0x00, 0x00, 0x43, 0x52});
            root.addPath(FileType.NEF, "MM".getBytes(StandardCharsets.ISO_8859_1), new byte[]{0x00, 0x2a, 0x00, 0x00, 0x00, (byte)0x80, 0x00});
            root.addPath(FileType.ORF, "IIRO".getBytes(StandardCharsets.ISO_8859_1), new byte[]{(byte)0x08, 0x00});
            root.addPath(FileType.ORF, "IIRS".getBytes(StandardCharsets.ISO_8859_1), new byte[]{(byte)0x08, 0x00});
            root.addPath(FileType.RAF, "FUJIFILMCCD-RAW".getBytes(StandardCharsets.ISO_8859_1));
            root.addPath(FileType.RW2, "II".getBytes(StandardCharsets.ISO_8859_1), new byte[]{0x55, 0x00});
        }

        private FileTypeDetector()
        {
        }

        /**
         * Examines the a file's first bytes and estimates the file's type.
         * <p>
         * Requires a {@link BufferedInputStream} in order to mark and reset the stream to the position
         * at which it was provided to this method once completed.
         * <p>
         * Requires the stream to contain at least eight bytes.
         *
         * @param inputStream a buffered input stream of the file to examine.
         * @return the file type.
         * @throws IOException if an IO error occurred or the input stream ended unexpectedly.
         */
        public static FileType detectFileType(final BufferedInputStream inputStream) throws IOException
        {
            if (!inputStream.markSupported())
            {
                throw new IOException("Stream must support mark/reset");
            }

            int maxByteCount = root.getMaxDepth();

            inputStream.mark(maxByteCount);

            byte[] bytes = new byte[maxByteCount];
            int bytesRead = inputStream.read(bytes);

            if (bytesRead == -1)
            {
                throw new IOException("Stream ended before file's magic number could be determined.");
            }

            inputStream.reset();

            //noinspection ConstantConditions
            return root.find(bytes);
        }

        public static FileType detectFileType(final byte[] fileBytes)
        {
            return root.find(fileBytes);
        }
    }