Currently the base fee we apply is always the expected cost to
claim an HTLC on-chain in case of closure. This results in
significantly higher than market rate fees [1], and doesn't really
match the actual forwarding trust model anyway - as long as
channel counterparties are honest, our HTLCs shouldn't end up
on-chain no matter what the HTLC sender/recipient do.
While some users may wish to use a feerate that implies they will
not lose funds even if they go to chain (assuming no flood-and-loot
style attacks), they should do so by calculating fees themselves;
since they're already charging well above market-rate,
over-estimating some won't have a large impact.
Worse, we current re-calculate fees at forward-time, not based on
the fee we set in the channel_update. This means that the fees
others expect to pay us (and which they calculate their route based
on), is not what we actually want to charge, and that any attempt
to forward through us is inherently race-y.
This commit adds a configuration knob to set the base fee
explicitly, defaulting to 1 sat, which appears to be market-rate
today.
[1] Note that due to an msat-vs-sat bug we currently actually
charge 1000x *less* than the calculated cost.
If we are a public node and have a private channel, our
counterparty needs to know the fees which we will charge to forward
payments to them. Without sending them a channel_update, they have
no way to learn that information, resulting in the channel being
effectively useless for outbound-from-us payments.
This commit fixes our lack of channel_update messages to private
channel counterparties, ensuring we always send them a
channel_update after the channel funding is confirmed.
