怎样才能在Java中的.torrent？ [英] How can I generate a .torrent in Java?

问题描述

我要生成Java中的.torrent文件，但我不想要一个大的API，它确实像刮跟踪器，播种等，这仅仅是生成的元数据的客户端什么。什么轻量级的解决方案存在？我只产生一个单一的.zip文件的的.torrent。

I want to generate a .torrent file in Java, but I don't want a big API that does anything like scraping trackers, seeding, etc. This is just for a client that generates meta data. What lightweight solutions exist? I am only generating a .torrent of a single .zip file.

谢谢！

推荐答案

我已经把这个自成体系的Java件code至prepare与单个文件的.torrent文件。

I have put together this self-contained piece of Java code to prepare a .torrent file with a single file.

该文件的.torrent通过调用创建 createTorrent（）传递的.torrent文件的名称，共享文件和跟踪URL的名称。

The .torrent file is created by calling createTorrent() passing the name of the .torrent file, the name of the shared file and the tracker URL.

createTorrent（）使用 hashPieces（）散列文件的片的使用Java的消息摘要类。然后 createTorrent（） prepares一个的元信息字典的包含洪流元数据。这本词典，然后在适当的奔code 的使用连接code *格式（）方法并保存在一个序列化。 torrent文件。

createTorrent() uses hashPieces() to hash the file pieces using Java's MessageDigest class. Then createTorrent() prepares a meta info dictionary containing the torrent meta-data. This dictionary is then serialized in the proper bencode format using the encode*() methods and saved in a .torrent file.

详见 BitTorrent的规范。

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");
    }
}

code编辑：将此更紧凑一点，解决方法可视性，使用字符常量在适当情况下使用的instanceof数。而最近的使用块读取文件I / O 的，因为我试图使用它的真正的和字节I / O仅仅是缓慢的，

Code edits: Make this a bit more compact, fix methods visibility, use character literals where appropriate, use instanceof Number. And more recently read the file using block I/O because I 'm trying to use it for real and byte I/O is just slow,

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