Add custom MP3 parser.

[sonitus.git] / src / main / java / net / pterodactylus / sonitus / io / mp3 / Parser.java

diff --git a/src/main/java/net/pterodactylus/sonitus/io/mp3/Parser.java b/src/main/java/net/pterodactylus/sonitus/io/mp3/Parser.java
new file mode 100644 (file)
index 0000000..eb2b441
--- /dev/null
+++ b/src/main/java/net/pterodactylus/sonitus/io/mp3/Parser.java
@@ -0,0 +1,126 @@
+/*
+ * Sonitus - Mp3Parser.java - Copyright © 2013 David Roden
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package net.pterodactylus.sonitus.io.mp3;
+
+import java.io.EOFException;
+import java.io.IOException;
+import java.io.InputStream;
+
+import com.google.common.base.Optional;
+import com.google.common.io.ByteStreams;
+
+/**
+ * A parser for MP3 files. It can recognize (and skip) ID3v2 header tags and
+ * MPEG audio frames.
+ *
+ * @author <a href="mailto:bombe@pterodactylus.net">David ‘Bombe’ Roden</a>
+ */
+public class Parser {
+
+       /** The input stream to parse. */
+       private final InputStream inputStream;
+
+       /** The complete ID3v2 tag. */
+       private final byte[] id3Tag;
+
+       /** The current read buffer. */
+       private final byte[] buffer = new byte[4];
+
+       /**
+        * Creates a new parser.
+        *
+        * @param inputStream
+        *              The input stream to parse
+        * @throws IOException
+        *              if an I/O error occurs
+        */
+       public Parser(InputStream inputStream) throws IOException {
+               this.inputStream = inputStream;
+               readFully(inputStream, buffer, 0, 3);
+               if ((buffer[0] == 'I') && (buffer[1] == 'D') && (buffer[2] == '3')) {
+                       readFully(inputStream, buffer, 0, 3);
+                       byte[] lengthBuffer = new byte[4];
+                       readFully(inputStream, lengthBuffer, 0, 4);
+                       int headerLength = (lengthBuffer[0] << 21) | (lengthBuffer[1] << 14) | (lengthBuffer[2] << 7) | lengthBuffer[3];
+                       id3Tag = new byte[headerLength + 10];
+                       System.arraycopy(new byte[] { 'I', 'D', '3', buffer[0], buffer[1], buffer[2], lengthBuffer[0], lengthBuffer[1], lengthBuffer[2], lengthBuffer[3] }, 0, id3Tag, 0, 10);
+                       readFully(inputStream, id3Tag, 10, headerLength);
+                       readFully(inputStream, buffer, 0, 3);
+               } else {
+                       id3Tag = null;
+               }
+       }
+
+       /**
+        * Returns the ID3v2 tag.
+        *
+        * @return The ID3v2 tag, or {@link Optional#absent()} if there is no ID3v2
+        *         tag
+        */
+       public Optional<byte[]> getId3Tag() {
+               return Optional.fromNullable(id3Tag);
+       }
+
+       /**
+        * Returns the next frame.
+        *
+        * @return The next frame
+        * @throws IOException
+        *              if an I/O error occurs, or EOF is reached
+        */
+       public Frame nextFrame() throws IOException {
+               while (true) {
+                       int r = inputStream.read();
+                       if (r == -1) {
+                               throw new EOFException();
+                       }
+                       System.arraycopy(buffer, 1, buffer, 0, 3);
+                       buffer[3] = (byte) r;
+                       Optional<Frame> frame = Frame.create(buffer, 0, 4);
+                       if (frame.isPresent()) {
+                               return frame.get();
+                       }
+               }
+       }
+
+       //
+       // STATIC METHODS
+       //
+
+       /**
+        * Reads exactly {@code length} bytes from the given input stream, throwing an
+        * {@link EOFException} if there are not enough bytes left in the stream.
+        *
+        * @param inputStream
+        *              The input stream to read from
+        * @param buffer
+        *              The buffer in which to read
+        * @param offset
+        *              The offset at which to start writing into the buffer
+        * @param length
+        *              The amount of bytes to read
+        * @throws IOException
+        *              if an I/O error occurs, or EOF is reached
+        */
+       private static void readFully(InputStream inputStream, byte[] buffer, int offset, int length) throws IOException {
+               if (ByteStreams.read(inputStream, buffer, offset, length) < length) {
+                       throw new EOFException();
+               }
+       }
+
+}