Convert Torrent Files to Magnet Links Using JavaScript

Need to convert torrent files to magnet links programmatically? In this guide, we'll show you how to build a torrent to magnet URL converter using JavaScript, similar to our online torrent to magnet converter.

What are Torrent Files and Magnet Links?

Before we dive into the implementation, let's understand the basics:

• Torrent Files (.torrent): Binary files containing metadata about shared content, including file information and tracker details.
• Magnet Links: URLs that contain the essential information from torrent files, making sharing easier without needing to download a .torrent file.

Required Dependencies

For our implementation, we'll need:

1pnpm add bencode crypto-js base32-encode

• bencode: For decoding torrent file data
• crypto-js: For SHA1 hashing
• base32-encode: For base32 encoding of the info hash

Implementation

Here's the step-by-step implementation:

1import bencode from 'bencode';
2import CryptoJS from 'crypto-js';
3import base32Encode from 'base32-encode';
4
5function convertTorrentToMagnet(torrentBuffer) {
6  // Decode the torrent file
7  const torrentData = bencode.decode(torrentBuffer);
8  
9  // Get the info dictionary
10  const info = torrentData.info;
11  
12  // Encode the info dictionary back to bencoded format
13  const encodedInfo = bencode.encode(info);
14  
15  // Calculate SHA1 hash
16  const infoHash = CryptoJS.SHA1(CryptoJS.lib.WordArray.create(encodedInfo));
17  const infoHashBuffer = Buffer.from(infoHash.toString(CryptoJS.enc.Hex), 'hex');
18  
19  // Convert to base32
20  const base32Hash = base32Encode(infoHashBuffer, 'RFC4648');
21  
22  // Construct the magnet URI
23  let magnetUri = `magnet:?xt=urn:btih:${base32Hash}`;
24  
25  // Add display name if available
26  if (info.name) {
27    magnetUri += `&dn=${encodeURIComponent(info.name.toString())}`;
28  }
29  
30  // Add trackers if available
31  if (torrentData.announce) {
32    magnetUri += `&tr=${encodeURIComponent(torrentData.announce.toString())}`;
33  }
34  
35  if (torrentData['announce-list']) {
36    torrentData['announce-list'].forEach(tracker => {
37      magnetUri += `&tr=${encodeURIComponent(tracker.toString())}`;
38    });
39  }
40  
41  return magnetUri;
42}

How It Works

1. File Reading: First, we read the torrent file as a buffer. In a web application, this can be done using the FileReader API:

1function handleFileSelect(file) {
2  const reader = new FileReader();
3  reader.onload = (e) => {
4    const buffer = Buffer.from(e.target.result);
5    const magnetUri = convertTorrentToMagnet(buffer);
6    // Use the magnet URI
7  };
8  reader.readAsArrayBuffer(file);
9}

2. Decoding: The bencode library decodes the torrent file's bencoded data into a JavaScript object.

3. Hash Calculation: We:

   • Extract the info dictionary
   • Re-encode it to ensure consistent hashing
   • Calculate its SHA1 hash
   • Convert the hash to base32 format

4. URI Construction: The magnet URI is built using:

   • The base32-encoded info hash as the primary identifier
   • The torrent name (if available)
   • Tracker URLs (if available)

Error Handling

Always implement proper error handling:

1function convertTorrentToMagnet(torrentBuffer) {
2  try {
3    // ... implementation ...
4  } catch (error) {
5    console.error('Error converting torrent:', error);
6    throw new Error('Invalid torrent file');
7  }
8}

Security Considerations

When implementing this in a web application:

1. Process files entirely client-side to protect user privacy
2. Validate file size and type before processing
3. Implement proper error boundaries in your React components

Further Resources

• BEP 9 - Extension for Peers to Send Metadata Files
• Magnet URI Scheme Specification
• Our Online Torrent to Magnet Converter

Conclusion

Building a torrent to magnet converter in JavaScript is straightforward with the right libraries. The key is understanding the torrent file structure and magnet URI format. Our implementation provides a secure, client-side solution that respects user privacy by processing files locally in the browser.

Remember to handle errors gracefully and validate inputs to create a robust tool. For a working example, check out our online converter tool which implements these concepts.