When we detect a channel `is_shutdown()` or call on it
`force_shutdown()`, we notify the user with a Event::ChannelClosed
informing about the id and closure reason.
Decorate the user-supplied EventHandler with NetGraphMsgHandler in
the BackgroundProcessor. The resulting handler will intercept
PaymentFailed events in order to update the NetworkGraph in the
background before delegating to the user's event handler.
Previously we'd been expecting to implement anchor outputs before
shipping 0.1, thus reworking our channel fee update process
entirely and leaving it as a future task. However, due to the
difficulty of working with on-chain anchor pools, we are now likely
to ship 0.1 without requiring anchor outputs.
In either case, there isn't a lot of reason to require that users
call an explicit "prevailing feerates have changed" function now
that we have a timer method which is called regularly. Further, we
really should be the ones deciding on the channel feerate in terms
of the users' FeeEstimator, instead of requiring users implement a
second fee-providing interface by calling an update_fee method.
Finally, there is no reason for an update_fee method to be
channel-specific, as we should be updating all (outbound) channel
fees at once.
Thus, we move the update_fee handling to the background, calling it
on the regular 1-minute timer. We also update the regular 1-minute
timer to fire on startup as well as every minute to ensure we get
fee updates even on mobile clients that are rarely, if ever, open
for more than one minute.
It is easy for users to have a bug where they drop a
`BackgroundProcessor` immediately, causing it to start and then
immediately stop. Instead, add a `#[must_use]` tag to provide a
compiler warning for such instances.
The previous commit wraps the background thread's JoinHandle in an
Option. Providing a dedicated method to join hides this implementation
detail from users.
Without stopping the thread when BackgroundProcessor is dropped, it will
run free. In the context of language bindings, it is difficult to know
how long references held by the thread should live. Implement Drop to
stop the thread just as is done when explicitly calling stop().
The specific error from the ChannelManager persister is not asserted for
in test_persist_error. Rather, any error will do. Update the test to use
BackgroundProcessor::stop and assert for the expected value.
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.
