cas_torrent

a bittorrent client with content-addressed storage

download and upload torrents to/from a CAS filesystem

avoid overwriting files with same path but different content

proof of concept for qBittorrent issue: 4.2.5 overwrites files if file names are the same

similar issue: Never silently overwrite existing files

example use

load torrent file

python3 -m cas_torrent --port 6882 input.torrent

load magnet link

python3 -m cas_torrent --port 6882 magnet:?xt=urn:btih:1234567890123456789012345678901234567890

cas filesystem

all complete files are stored in the sha256 store. sha256 is the most common file hash, more common than the bt2r hash (bittorrent v2 merkle root hash, see def get_bt2_root_hash_of_path(file_path) in src/cas_torrent/cas_torrent.py). storing files by their sha256 hash allows sharing these files with other apps.

cas/sha256/12/34/567890123456789012345678901234567890123456789012345678901234

all directories are stored in the bt2 store. the directories contain symlinks to files in the sha256 store. temporary files are stored here, because their sha256 hash is unknown.

cas/bt2/12/34/567890123456789012345678901234567890123456789012345678901234

if the bt2 hash is unknown (v1-only magnet links and missing metadata), then instead of the bt2 store, the bt1 store is used. as soon as the bt2 hash is known, files are moved to the bt2 store. in most cases, the bt1 store holds only a symlink to the bt2 store, because the bt2 store offers better collision-resistance (sha256 versus sha1).

cas/bt1/12/34/567890123456789012345678901234567890

las filesystem

las = location-addressed storage

presenting torrents only by their info hashes is not user-friendly. users expect the torrent name -- this is provided by the "las store".

las/some_torrent_name/some_file.txt

file path collisions

problem: file path collisions between different torrents.

solution: merge by default, rename if different content.

the file contents are compared by comparing cas store paths:

if identical las file paths are linked to identical cas file paths, then the file contents are identical, and we dont rename the las file paths.

if identical las file paths are linked to different cas file paths, then the file contents are different, and we rename the las file paths.

renaming files

a simple solution is to append " (1)" or " (2)" or " (3)" etc. before the file extension.

another solution would be to append a part of the file hash before the file extension, but that produces longer filenames.

todo

• add tests
• allow multiple CAS filesystems on multiple hard drives, aka "soft raid"
• add this feature to other bittorrent clients