Support Custom Per-File Paths and Automatic File Matching for V2 Torrents

[oldominion]

Feature Request:

In BitTorrent v2 each file is hashed individually using Merkle trees, which means that every file has its own unique root hash. I propose adding support for custom per-file paths for v2 torrents and adding functionality for automatic scanning of a list of user-specified base directories to match files in newly imported magnet/torrent files, or after files have been moved manually by the user.

I would like to propose the following enhancements to libtorrent:

1. Custom Per-File Paths for V2 Torrents:

Objective: Allow users to specify custom file paths for each file in a torrent, rather than enforcing the predefined folder structure and file names.

Benefits:

• Enables users to seed files organized according to their personal preferences.
• Removes the need to duplicate or rearrange files just to match the torrent's original structure.
• Encourages continued seeding by reducing storage redundancy and preserving user file organization.

2. Automatic File Matching in User-Specified Directories:

Objective: Implement functionality to automatically scan a list of user-defined base directories to find files that match those in newly added magnet or torrent files.

Implementation Suggestion:
Maintain an index of files and their sizes within the specified directories to expedite the scanning process. Only bother to calculate file hashes when a file size matches the expected size.

Benefits:

• Simplifies the process of seeding existing files without manual intervention.
• Reduces the time and computational resources required for file verification.
• Enhances user experience by automating the matching process.

Use Case Example:

A user has a collection of audio files organized by genre with personal naming conventions.
When downloading a torrent that contains some of these files, libtorrent would scan the specified directories, recognize matching files based on size (and hash when necessary), and use them for seeding without requiring the user to move or rename their files.

Conclusion:

Implementing these features would greatly enhance libtorrent's flexibility and user-friendliness. By allowing custom file paths and automating file matching, users are more likely to continue seeding, contributing to a healthier torrent ecosystem.