如何在Java中生成.torrent？

Question

我想用Java生成一个.torrent文件，但是我不想要一个大的API，它可以执行诸如抓取跟踪器，种子等操作。这仅适用于生成元数据的客户端。存在哪些轻量级解决方案？我只生成一个.zip文件的.torrent。

谢谢！

Answer 1

我整理了这段独立的Java代码，以准备一个带有单个文件的.torrent文件。

通过调用createTorrent().torrent文件的名称，共享文件的名称和跟踪器URL 来创建.torrent文件。

createTorrent()用于使用Java的类hashPieces()对文件 片段
进行哈希处理MessageDigest。然后createTorrent()准备一个包含洪流元数据的 元信息字典 。然后，使用这些方法以适当的
Bencode 格式序列化该词典，encode*()并将其保存在.torrent文件中。

有关详细信息，请参见BitTorrent规范。

public class Torrent {
    private static void encodeObject(Object o, OutputStream out) throws IOException {
        if (o instanceof String)
            encodeString((String)o, out);
        else if (o instanceof Map)
            encodeMap((Map)o, out);
        else if (o instanceof byte[])
            encodeBytes((byte[])o, out);
        else if (o instanceof Number)
            encodeLong(((Number) o).longValue(), out);
        else
            throw new Error("Unencodable type");
    }
    private static void encodeLong(long value, OutputStream out) throws IOException {
        out.write('i');
        out.write(Long.toString(value).getBytes("US-ASCII"));
        out.write('e');
    }
    private static void encodeBytes(byte[] bytes, OutputStream out) throws IOException {
        out.write(Integer.toString(bytes.length).getBytes("US-ASCII"));
        out.write(':');
        out.write(bytes);
    }
    private static void encodeString(String str, OutputStream out) throws IOException {
        encodeBytes(str.getBytes("UTF-8"), out);
    }
    private static void encodeMap(Map<String,Object> map, OutputStream out) throws IOException{
        // Sort the map. A generic encoder should sort by key bytes
        SortedMap<String,Object> sortedMap = new TreeMap<String, Object>(map);
        out.write('d');
        for (Entry<String, Object> e : sortedMap.entrySet()) {
            encodeString(e.getKey(), out);
            encodeObject(e.getValue(), out);
        }
        out.write('e');
    }
    private static byte[] hashPieces(File file, int pieceLength) throws IOException {
        MessageDigest sha1;
        try {
            sha1 = MessageDigest.getInstance("SHA");
        } catch (NoSuchAlgorithmException e) {
            throw new Error("SHA1 not supported");
        }
        InputStream in = new FileInputStream(file);
        ByteArrayOutputStream pieces = new ByteArrayOutputStream();
        byte[] bytes = new byte[pieceLength];
        int pieceByteCount  = 0, readCount = in.read(bytes, 0, pieceLength);
        while (readCount != -1) {
            pieceByteCount += readCount;
            sha1.update(bytes, 0, readCount);
            if (pieceByteCount == pieceLength) {
                pieceByteCount = 0;
                pieces.write(sha1.digest());
            }
            readCount = in.read(bytes, 0, pieceLength-pieceByteCount);
        }
        in.close();
        if (pieceByteCount > 0)
            pieces.write(sha1.digest());
        return pieces.toByteArray();
    }
    public static void createTorrent(File file, File sharedFile, String announceURL) throws IOException {
        final int pieceLength = 512*1024;
        Map<String,Object> info = new HashMap<String,Object>();
        info.put("name", sharedFile.getName());
        info.put("length", sharedFile.length());
        info.put("piece length", pieceLength);
        info.put("pieces", hashPieces(sharedFile, pieceLength));
        Map<String,Object> metainfo = new HashMap<String,Object>();
        metainfo.put("announce", announceURL);
        metainfo.put("info", info);
        OutputStream out = new FileOutputStream(file);
        encodeMap(metainfo, out);
        out.close();
    }

    public static void main(String[] args) throws Exception {
        createTorrent(new File("C:/x.torrent"), new File("C:/file"), "http://example.com/announce");
    }
}

代码编辑： 使其更紧凑，更清晰地查看方法，在适当的地方使用字符文字，使用instanceof Number。最近 ，我使用块I /
O读取了文件，
因为我试图将其用于实数，而字节I / O只是速度较慢，