[bittorrent] Use of reserved bits in bt handshake

Justin Cormack justin at street-vision.com
Thu Jul 21 10:19:48 EDT 2005

On 21 Jul 2005, at 15:03, Olaf van der Spek wrote:

> On 7/21/05, Justin Cormack <justin at street-vision.com> wrote:
>> I came across a client today that sets the first bit in the 8 zero
>> bytes in the handshake after 'BitTorrent Protocol'. Anyone know what
>> client this might be and what it might mean?
> Looked at the peer ID?
> Azureus uses -AZ IIRC.

Ah yes, it is.

Another client has connected and has the last bit set to 1. And it  
says it is Bram's.

Unless I have an obscure bug corrupting these bits it looks like  
compatibility is dead...

>> I think it *might* be Azureus, as I think it is the seed for Sun's
>> OpenSolaris torrents.
>> It is of course a completely useless way of specifying protocol
>> extensions as it doesnt allow for any negotiation, all you can do is
> Is it?
> If the other party doesn't support your extensions, don't enable them.

But you dont know if the other party accepts them or not, it will  
just disconnect if it doesnt and probably will never reconnect. So  
for compatibility you cant use them. Basically you cant make a  
backwards compatible client.

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