Prior to this commit, a taker bot that received the orderbook on the
onion message channel would attempt to connect to every maker bot that
had sent an offer, which is not just inefficient but appears to trigger
rate limiting in Tor itself, throwing errors in the SOCKS proxy, at
numbers of around 80 makers, in testing (but could easily happen at
lower levels).
After this commit, we only opportunistically attempt to connect to
makers (using the same OnionPeer.try_to_connect method as before) when
we have already decided to send them a message (e.g. chosen to fill
their offer). This is done by calling try_to_connect only in
OnionMessageChannel._privmsg, and only to the right kind of peer.
The downside of this is that we will send more messages via directory
(at least one additional, for each maker), but clearly the alternative
is not viable.
As part of this update, we ensure that connection attempts are not
accidentally duplicated (see OnionPeer.connecting).
Adam Gibson
cc6d341593