如何在 Java 中生成 .torrent? [英] How can I generate a .torrent in Java?

问题描述

我想用 Java 生成一个 .torrent 文件，但我不想要一个大的 API 来做任何事情，比如抓取跟踪器、播种等.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?我只生成单个 .zip 文件的 .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

我已经将这段独立的 Java 代码放在一起，以准备一个包含单个文件的 .torrent 文件.

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

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

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() 使用 Java 的 MessageDigest 类散列文件 pieces.然后 createTorrent() 准备一个包含 Torrent 元数据的 元信息字典.然后使用 encode*() 方法将该字典序列化为正确的 bencode 格式并保存在 .torrent 文件中.

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.

有关详细信息，请参阅 BitTorrent 规范.

See the BitTorrent spec for details.

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.HashMap;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;

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 (Map.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<>();
        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");
    }
}

代码使其更紧凑，修复方法可见性，在适当的情况下使用字符文字，使用instanceof Number.最近使用块 I/O 读取文件，因为我正在尝试将其用于实际，而字节 I/O 速度很慢，

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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