Prior to this commit, passive observation of orderbook updates by bots
such as ob-watcher was not able to keep track of nicks/bots that had
disconnected and were no longer available, because non-directory peers
do not get the network level disconnection event.
After this commit, the directory nodes forward a variant of the
"peerlist" control message, that was previously used only to send
connection information from one non-directory peer to another (so that
they could establish a new p2p connection if desired). Now a new version
of that message adds an extra "D" field to indicate that this message is
being used to inform that the relevant peer has disconnected from this
directory node.
Bubbling up the on_nick_leave event: it is already the case that the
final on_nick_leave callback is only triggered by the disappearance of a
nick from all available message channels (so that as long as a nick is
perceived as being in at least one available message channel, its
current offers are still maintained in the local database); this logic
is now repeated one layer down, because the disconnection of a nick from
one directory node may not mean it is shut down, so we only pass the
on_nick_leave callback from the OnionMessageChannel object up to the
MessageChannelCollection callback when the active_directories dict
indicates that this particular nick is no longer available on any of our
configured directory nodes.
Adam Gibson
a278b91288