frater secessus

frater secessus

retired snowbird

VA appt, aria2c for torrent file selection

VA appointment: labs

Had a 0715 slot for labs so there were no delays. The lab results will be interpreted by the Dr at my medical appt in a few days.

After I left the facility and found a park to walk the doggo the VA sent this helpful text. Received it an hour after the appointment was over, which makes it of dubious value as a reminder:

late

aria2c

aria2 is a fantastic tool for downloading stuff. It does http/s, ftp, bittorrent (torrents and magnets) and many things I have never seen in the wild. I use it as the backend downloader for youtube-dl since the resume functions and config options are robust.

Problem: sometimes torrents contain multiple files but you only want one (see example below). I use YAAW to monitor progress but it does not appear to honor file selection. Let’s do it on the command line with aria2c

In the examples below we will use a torrent for a linux distribution, which is free to d/l. For convenience and display I will trim the full magnet link down to the bare minimum:

magnet:?xt=urn:btih:febd9a2cb755ec82e6e7a015a8dc497fde9dd507

if online listing is available

According to magnetdl.com1 the file list is:

/ubuntu-ultimate-1.4-dvd.iso (1.94 GB)
/ubuntu-ultimate-1.4-dvd.iso.md5 (62 B) <-- we only want this
/ubuntu-ultimate-1.4-dvd.iso.sha1 (70 B)

It’s ~2gig of data but let’s say I only want the md5 hash (62 bytes). We can issue this command:

aria2c --select-file=2 magnet:?xt=urn:btih:febd9a2cb755ec82e6e7a015a8dc497fde9dd507

This will download only the selected file[s]. It is possible that other file pieces might be downloaded if they share chunks with the target file. They will be fragmentary and deleteable.

if an accurate listing is unavailable

In this scenario we have to pull down a copy of the torrent file to parse locally so we can see the file list in order:

aria2c  --bt-save-metadata=true --follow-torrent=false {link to torrent}

The .torrent file will be downloaded but the files will not.

If we only have a magnet link we use:

aria2c --bt-metadata-only --bt-save-metadata magnet:?xt=urn:btih:febd9a2cb755ec82e6e7a015a8dc497fde9dd507


Saved metadata as /home/mouse/torrent/complete/febd9a2cb755ec82e6e7a015a8dc497fde9dd507.torrent.

Note the .torrent is named after the magnet/hash.

extracting the list from the local .torrent

Once we have a local .torrent file from either method we can

aria2c  --show-file febd9a2cb755ec82e6e7a015a8dc497fde9dd507.torrent

…but it outputs more than we need. Let’s use this:

-----------------------------------------------
aria2c  --show-file febd9a2cb755ec82e6e7a015a8dc497fde9dd507.torrent | grep \|

idx|path/length
  1|./ubuntu-ultimate-1.4-dvd/ubuntu-ultimate-1.4-dvd.iso
   |1.9GiB (2,083,522,560)
  2|./ubuntu-ultimate-1.4-dvd/ubuntu-ultimate-1.4-dvd.iso.md5
   |62B (62)
  3|./ubuntu-ultimate-1.4-dvd/ubuntu-ultimate-1.4-dvd.iso.sha1
   |70B (70)

Yep, there’s our md5 at #2.

So now we can now select-file against

  • a remote .torrent
  • the local torrent
  • magnet link
aria2c --select-file=2 febd9a2cb755ec82e6e7a015a8dc497fde9dd507.torrent

12/16 14:23:16 [NOTICE] Downloading 1 item(s)

12/16 14:23:16 [NOTICE] IPv4 DHT: listening on UDP port 6971

12/16 14:23:16 [NOTICE] IPv4 BitTorrent: listening on TCP port 6890

12/16 14:23:16 [NOTICE] IPv6 BitTorrent: listening on TCP port 6890
[#951c0b 0B/2.1KiB(0%) CN:5 SD:0 DL:0B]
12/16 14:23:17 [NOTICE] Download of selected files was complete.
[#951c0b SEED(0.0) CN:2 SD:0]  
12/16 14:23:40 [NOTICE] Shutdown sequence commencing... Press Ctrl-C again for emergency shutdown.

12/16 14:23:40 [NOTICE] Download complete: ubuntu-ultimate-1.4-dvd

12/16 14:23:40 [NOTICE] Your share ratio was 0.0, uploaded/downloaded=0B/2.1KiB

Download Results:
gid   |stat|avg speed  |path/URI
======+====+===========+=======================================================
951c0b|OK  |   1.3KiB/s|ubuntu-ultimate-1.4-dvd.iso.md5

NOte: I redacted path names for privacy and display. I also bailed out of the seeding session because this was just for demonstration using a tiny file.

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  1. ad- and javascript-blocking recommended; sites like this tend to have NSFW ads ↩

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