webshare-api/src/torrent.js

// Minimal bencode encoder (Buffers for binary fields)
function bencode(v) {
    if (Number.isInteger(v))  return Buffer.from(`i${v}e`);
    if (Buffer.isBuffer(v))   return Buffer.concat([Buffer.from(`${v.length}:`), v]);
    if (typeof v === 'string') {
        const b = Buffer.from(v, 'utf8');
        return Buffer.concat([Buffer.from(`${b.length}:`), b]);
    }
    if (Array.isArray(v))
        return Buffer.concat([Buffer.from('l'), ...v.map(bencode), Buffer.from('e')]);
    // dict — keys must be sorted for valid bencoding
    const keys = Object.keys(v).sort();
    return Buffer.concat([
        Buffer.from('d'),
        ...keys.flatMap(k => [bencode(k), bencode(v[k])]),
        Buffer.from('e'),
    ]);
}

// Minimal bencode decoder — returns Buffers for byte strings
function bdecode(buf, pos = { i: 0 }) {
    const c = buf[pos.i];
    if (c === 0x69) { // 'i'
        pos.i++;
        const end = buf.indexOf(0x65, pos.i); // 'e'
        const n = parseInt(buf.slice(pos.i, end).toString(), 10);
        pos.i = end + 1;
        return n;
    }
    if (c === 0x6c) { // 'l'
        pos.i++;
        const arr = [];
        while (buf[pos.i] !== 0x65) arr.push(bdecode(buf, pos));
        pos.i++;
        return arr;
    }
    if (c === 0x64) { // 'd'
        pos.i++;
        const obj = {};
        while (buf[pos.i] !== 0x65) {
            const key = bdecode(buf, pos).toString('utf8');
            obj[key] = bdecode(buf, pos);
        }
        pos.i++;
        return obj;
    }
    // byte string: "N:..."
    const colon = buf.indexOf(0x3a, pos.i); // ':'
    const len = parseInt(buf.slice(pos.i, colon).toString(), 10);
    pos.i = colon + 1 + len;
    return buf.slice(colon + 1, pos.i);
}

// Build a minimal .torrent with an HTTP webseed and zeroed piece hashes.
// Our fake qBittorrent skips hash verification so the zeroed hashes are fine.
function makeTorrent({ name, size, webseedUrl }) {
    const PIECE_LEN = 512 * 1024; // 512 KB
    const numPieces = Math.max(1, Math.ceil((size || 1) / PIECE_LEN));
    const pieces = Buffer.alloc(20 * numPieces, 0);

    return bencode({
        'comment':    'Webshare direct download',
        'created by': 'webshare-api',
        'info': {
            'length':       size || 0,
            'name':         name,
            'piece length': PIECE_LEN,
            'pieces':       pieces,
        },
        'url-list': webseedUrl,
    });
}

// Extract the url-list value from a raw .torrent buffer
function extractWebseed(torrentBuf) {
    try {
        const d = bdecode(torrentBuf);
        const ul = d['url-list'];
        if (!ul) return null;
        if (Buffer.isBuffer(ul)) return ul.toString('utf8');
        if (Array.isArray(ul) && ul.length) return ul[0].toString('utf8');
        return null;
    } catch { return null; }
}

// Compute the real torrent info hash (SHA1 of the bencoded info dict).
// Sonarr tracks downloads by this hash — using any other hash causes mismatch.
function extractInfoHash(torrentBuf) {
    try {
        const crypto = require('crypto');
        const d = bdecode(torrentBuf);
        if (!d.info) return null;
        return crypto.createHash('sha1').update(bencode(d.info)).digest('hex');
    } catch { return null; }
}

module.exports = { makeTorrent, extractWebseed, extractInfoHash };