OggInputStream.java

package de.danoeh.antennapod.core.util.vorbiscommentreader;

import org.apache.commons.io.IOUtils;

import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;

public class OggInputStream extends InputStream {
	private InputStream input;

	/** True if OggInputStream is currently inside an Ogg page. */
	private boolean isInPage;
	private long bytesLeft;

	public OggInputStream(InputStream input) {
		super();
		isInPage = false;
		this.input = input;
	}

	@Override
	public int read() throws IOException {
		if (!isInPage) {
			readOggPage();
		}
		
		if (isInPage && bytesLeft > 0) {
			int result = input.read();
			bytesLeft -= 1;
			if (bytesLeft == 0) {
				isInPage = false;
			}
			return result;
		} 
		return -1;
	}

	private void readOggPage() throws IOException {
		// find OggS
		int[] buffer = new int[4];
		int c = 0;
		boolean isInOggS = false;
		while ((c = input.read()) != -1) {
			switch (c) {
			case 'O':
				isInOggS = true;
				buffer[0] = c;
				break;
			case 'g':
				if (buffer[1] != c) {
					buffer[1] = c;
				} else {
					buffer[2] = c;
				}
				break;
			case 'S':
				buffer[3] = c;
				break;
			default:
				if (isInOggS) {
					Arrays.fill(buffer, 0);
					isInOggS = false;
				}
			}
			if (buffer[0] == 'O' && buffer[1] == 'g' && buffer[2] == 'g'
					&& buffer[3] == 'S') {
				break;
			}
		}
		// read segments
		IOUtils.skipFully(input, 22);
		bytesLeft = 0;
		int numSegments = input.read();
		for (int i = 0; i < numSegments; i++) {
			bytesLeft += input.read();
		}
		isInPage = true;
	}

}