[BitTorrent] XML Torrents?

Joseph Ashwood ashwood at msn.com
Sat Mar 12 05:55:23 EST 2005

----- Original Message ----- 
From: "Kenneth Porter" <shiva at sewingwitch.com>
Subject: Re: [BitTorrent] XML Torrents?

> Looking at the spec <http://www.bittorrent.com/protocol.html>, I see a
> filename (or list of filename/length pairs), tracker URL, and a set of
> fragment checksums. Most of the size would be the checksums. How do you
> propose shrinking this to fit in a URL? I suppose you could designate
> trusted peers (eg. initial seeds) to host the checksums.

I believe the concept there is to (as we have been discussing in great 
detail with very mixed results) use Merkle trees, this eliminates the long 
list of hashes at the end. The proposal also includes the presumption that 
multi-file torrents have to be redeigned substantially (again many concepts 
and mixed results). By doing this the necessary elements of the torrent 
become tracker, filename, root hash. There would have to be come changes in 
the formatting of the URI, basically just encoding, but the end result could 
look something like:


I assumed the inclusion of the recently (briefly) discussed hash_function 
argument, and obviously SHA-512, although I am not sure "-" is valid in 
URIs. Any authorities? Even at that we have the option of (assuming the 
tracker or peer protocol is altered to support this, I would vote peer) the 
URL can be reduce to not include the filename either.

Even without the further optimizations at 218 bytes this forms a usably 
sized, if hard to remember, URI. The same information could be stored in any 
other convenient format as well, with bencoding of course being the default, 
an XML definition (even though so many people don't like it), etc. It fits 
easily into a TCP/IP frame, ethernet frame, Wi-Fi frame, but does not fit 
into an ATM frame, not sure about modem frame I haven't looked at that 
information for quite some time. The frame fitting is not critical but it 
can relieve overhead in a system, and was one of the primary reasons for the 
size limits on URI in the beginning (IIRC 4096 bytes to match the maximum 
ethernet frame, and yes I am old school enough to have actually done heavy 
optimization based on this and achieved throughputs higher than the 
theoretical maximum because of it).

I actually think that this poses a very interesting new area for BitTorrent, 
or a BitTorrent-like protocol, and at the very least something that can help 
in optimizing the system.

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