Gnutella response codes?

Is there any reference to what each client's response codes mean what?

Bearshare sends the useful 'GNUTELLA/0.6 503 Full' one but I noticed Limewire sending 'GNUTELLA/0.6 593 Hi' which means nothing to me.
Also any others you know about would be useful.

I'm writing a intelligent GWebCache and I'm looking at more ways to find Ultrapeers and make clients connect faster.

One main thing I'm thinking about is sending a crawler request to known ultrapeers.
This has two benefits: It allows me to see how full it is and it allows me to find more ultrapeers.
There is no point sending users to a full/dead ultrapeer.

Feedback and suggestions are welcome.
Having a list of response codes would help a lot.