[BitTorrent] hash-based requests

Elliott Mitchell ehem at m5p.com
Tue Feb 15 19:41:09 EST 2005


>From: Justin Cormack <justin at street-vision.com>
>  
> > If HAVE messages are somehow indexed to tree location, then it works
> > pretty well.
> 
> You can encode the path down a binary tree (left = 0, 1 = right) as the
> HAVE message payload. Thats fairly independent of how (if at all) you
> actually index your nodes. You can with non binary trees too if you insist...

Problem is this turns back into a variable length string.

> > > The other alternative is a two-phase protocol where you first obtain the Merkle
> > > tree before you can do anything else.
> > 
> > I'm working on a sample implementation which computes the hashes, and
> > uses a midsize branching factor. Turns out working with n-ary trees isn't
> > always easy.  %-)
> 
> Its almost never worth it. Possbly never... Whats your reason for not using
> binary?

I'm working with block size divided by hash size as the branching factor.
This results in a node fitting into a single message. At the same time
a block of hashes can be accounted for like a payload block. Should also
mollify the folks looking for a flatish tree (2TB with only 3 levels).

Problem is computing the indicies correctly.  %-)


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