In this commit, we add a TCP fallback option for the
DNSSeedBootstrapper. We’ve received many reports of users unable to
bootstrap properly to the network due to the size of the SRV records we
currently return. It has been observed that many revolvers will simply
truncate and ignore the response due to the (current size).
To resolve (no pun intended) we now attempt to detect this failure mode
and will fallback to a manual TCP resolution in the case that our SRV
query over UDP fails. We do this by querying the special record at the
"soa." sub-domain of supporting DNS servers. The retuned IP address
will be the IP address of the authoritative DNS server. Once we have
this IP address, we'll connect manually over TCP to request the SRV
record. This is necessary as the records we return are currently too
large for a class of resolvers, causing them to be filtered out.
This commit adds a new interface the to discovery package:
NetworkPeerBootstrapper. The NetworkPeerBootstrapper interface is meant
to be used to bootstrap a new peer joining the network to the set of
existing active peers within the network. Callers are encouraged to
utilize several boostrappers in series as redundant sources of
information. The MultiSourceBootstrap function will takes a set of
boostrappers, and compose their outputs into a single unified set of
addresses.
Two concrete implementations of the NetworkPeerBootstrapper interface
have been added as a part of this commit: the ChannelGraphBootstrapper
and the DNSSeedBootstrapper. The former will utilize the authenticated
node advertisements within the calling nodes view to boostrap new
connections. The latter will use a set of BOLT-0010 compliant DNS seeds
to query. This DNS seeding more will likely be used by nodes initial
joining the network, as they may not yet have the channel graph as they
haven’t connected to any peers.
