Here you can find some useful Infobits for Developers. this is by no chance an RFC, not even remotely, but it contains information, which often gets overlooked or buried in long RFCs (or is to current to appear in RFCs already). Most of it will be forum-answers, or answers to E-Mails from me or others.
First from a_guest_in_the_machine from gnutellaforums.com: The initial handshake goes like this (contradicting current specs):
GNUTELLA/0.6 200 (...)\r\n
(optional server specifics)\r\n
And now, at this point you are offically connected, and we remain so indefinately. And from what the documents say, you should now be able to send and receive ping/pong/query/queryhits.