src/main/java/net/pterodactylus/sonitus/io/mp3/Parser.java

   1 /*
   2  * Sonitus - Mp3Parser.java - Copyright © 2013 David Roden
   3  *
   4  * This program is free software: you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation, either version 3 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 package net.pterodactylus.sonitus.io.mp3;
  19
  20 import java.io.EOFException;
  21 import java.io.IOException;
  22 import java.io.InputStream;
  23
  24 import com.google.common.base.Optional;
  25 import com.google.common.io.ByteStreams;
  26
  27 /**
  28  * A parser for MP3 files. It can recognize (and skip) ID3v2 header tags and
  29  * MPEG audio frames.
  30  * <p/>
  31  * This uses information from <a href="http://mpgedit.org/mpgedit/mpeg_format/mpeghdr.htm">mpgedit.org/mpgedit/mpeg_format/mpeghdr.htm</a>.
  32  *
  33  * @author <a href="mailto:bombe@pterodactylus.net">David ‘Bombe’ Roden</a>
  34  */
  35 public class Parser {
  36
  37         /** The input stream to parse. */
  38         private final InputStream inputStream;
  39
  40         /** The complete ID3v2 tag. */
  41         private final byte[] id3Tag;
  42
  43         /** The current read buffer. */
  44         private final byte[] buffer = new byte[4];
  45
  46         /**
  47          * Creates a new parser.
  48          *
  49          * @param inputStream
  50          *              The input stream to parse
  51          * @throws IOException
  52          *              if an I/O error occurs
  53          */
  54         public Parser(InputStream inputStream) throws IOException {
  55                 this.inputStream = inputStream;
  56                 readFully(inputStream, buffer, 1, 3);
  57                 if ((buffer[1] == 'I') && (buffer[2] == 'D') && (buffer[3] == '3')) {
  58                         readFully(inputStream, buffer, 1, 3);
  59                         byte[] lengthBuffer = new byte[4];
  60                         readFully(inputStream, lengthBuffer, 0, 4);
  61                         int headerLength = (lengthBuffer[0] << 21) | (lengthBuffer[1] << 14) | (lengthBuffer[2] << 7) | lengthBuffer[3];
  62                         id3Tag = new byte[headerLength + 10];
  63                         System.arraycopy(new byte[] { 'I', 'D', '3', buffer[1], buffer[2], buffer[3], lengthBuffer[0], lengthBuffer[1], lengthBuffer[2], lengthBuffer[3] }, 0, id3Tag, 0, 10);
  64                         readFully(inputStream, id3Tag, 10, headerLength);
  65                         readFully(inputStream, buffer, 1, 3);
  66                 } else {
  67                         id3Tag = null;
  68                 }
  69         }
  70
  71         /**
  72          * Returns the ID3v2 tag.
  73          *
  74          * @return The ID3v2 tag, or {@link Optional#absent()} if there is no ID3v2
  75          *         tag
  76          */
  77         public Optional<byte[]> getId3Tag() {
  78                 return Optional.fromNullable(id3Tag);
  79         }
  80
  81         /**
  82          * Returns the next frame.
  83          *
  84          * @return The next frame
  85          * @throws IOException
  86          *              if an I/O error occurs, or EOF is reached
  87          */
  88         public Frame nextFrame() throws IOException {
  89                 while (true) {
  90                         int r = inputStream.read();
  91                         if (r == -1) {
  92                                 throw new EOFException();
  93                         }
  94                         System.arraycopy(buffer, 1, buffer, 0, 3);
  95                         buffer[3] = (byte) r;
  96                         if (Frame.isFrame(buffer, 0, 4)) {
  97                                 int frameLength = Frame.getFrameLength(buffer, 0);
  98                                 if (frameLength != -1) {
  99                                         byte[] content = new byte[frameLength + 4];
 100                                         readFully(inputStream, content, 4, frameLength);
 101                                         System.arraycopy(buffer, 0, content, 0, 4);
 102                                         Optional<Frame> frame = Frame.create(content, 0, frameLength + 4);
 103                                         if (frame.isPresent()) {
 104                                                 return frame.get();
 105                                         }
 106                                 }
 107                         }
 108                 }
 109         }
 110
 111         //
 112         // STATIC METHODS
 113         //
 114
 115         /**
 116          * Reads exactly {@code length} bytes from the given input stream, throwing an
 117          * {@link EOFException} if there are not enough bytes left in the stream.
 118          *
 119          * @param inputStream
 120          *              The input stream to read from
 121          * @param buffer
 122          *              The buffer in which to read
 123          * @param offset
 124          *              The offset at which to start writing into the buffer
 125          * @param length
 126          *              The amount of bytes to read
 127          * @throws IOException
 128          *              if an I/O error occurs, or EOF is reached
 129          */
 130         private static void readFully(InputStream inputStream, byte[] buffer, int offset, int length) throws IOException {
 131                 if (ByteStreams.read(inputStream, buffer, offset, length) < length) {
 132                         throw new EOFException();
 133                 }
 134         }
 135
 136 }