src/main/java/com/pt/service/TorrentService.java

package com.pt.service;

import com.pt.entity.TorrentMeta;
import com.pt.repository.TorrentMetaRepository;
import com.pt.utils.BencodeUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.io.*;
import java.security.MessageDigest;
import java.time.LocalDateTime;
import java.util.LinkedHashMap;
import java.util.Map;

@Service
public class TorrentService {

    //  Tracker 服务器的 announce 地址
    private static final String ANNOUNCE_URL = "http://localhost:8080/announce";
    private static final int PIECE_LENGTH = 256 * 1024;

    @Autowired
    private TorrentMetaRepository torrentMetaRepository;

    public byte[] generateTorrentBytes(String sourceFilePath) throws Exception {
        File sourceFile = new File(sourceFilePath);

        // 构造 info 字典
        Map<String, Object> infoDict = new LinkedHashMap<>();
        infoDict.put("name", sourceFile.getName());
        infoDict.put("length", sourceFile.length());
        infoDict.put("piece length", PIECE_LENGTH);
        infoDict.put("pieces", calcPiecesHashes(sourceFile));

        // 构造完整 torrent 字典
        Map<String, Object> torrentDict = new LinkedHashMap<>();
        torrentDict.put("announce", ANNOUNCE_URL);
        torrentDict.put("info", infoDict);

        // 编码成种子数据字节数组
        byte[] bencodedTorrent = BencodeUtils.encode(torrentDict);

        // 计算 info_hash 并保存到数据库（如果需要的话）
        MessageDigest sha1 = MessageDigest.getInstance("SHA-1");
        byte[] infoEncoded = BencodeUtils.encode(infoDict);
        sha1.update(infoEncoded);
        String infoHash = bytesToHex(sha1.digest());

        TorrentMeta meta = new TorrentMeta();
        meta.setFilename(sourceFile.getName());
        meta.setInfoHash(infoHash);
        meta.setSize(sourceFile.length());
        meta.setUploadTime(LocalDateTime.now());
        torrentMetaRepository.save(meta);

        return bencodedTorrent;
    }


    private byte[] calcPiecesHashes(File file) throws Exception {
        MessageDigest sha1 = MessageDigest.getInstance("SHA-1");
        try (InputStream fis = new FileInputStream(file)) {
            byte[] buffer = new byte[PIECE_LENGTH];
            ByteArrayOutputStream piecesBuffer = new ByteArrayOutputStream();

            int read;
            while ((read = fis.read(buffer)) > 0) {
                sha1.reset();
                sha1.update(buffer, 0, read);
                piecesBuffer.write(sha1.digest());
            }
            return piecesBuffer.toByteArray();
        }
    }

    private String bytesToHex(byte[] bytes) {
        StringBuilder sb = new StringBuilder();
        for (byte b : bytes) {
            sb.append(String.format("%02x", b));
        }
        return sb.toString();
    }
}