When an HTLC has been failed, we track it up until the point there
exists no broadcastable commitment transaction which has the HTLC
present, at which point Channel returns the HTLCSource back to the
ChannelManager, which fails the HTLC backwards appropriately.
When an HTLC is fulfilled, however, we fulfill on the backwards path
immediately. This is great for claiming upstream HTLCs, but when we
want to track pending payments, we need to ensure we can check with
ChannelMonitor data to rebuild pending payments. In order to do so,
we need an event similar to the HTLC failure event, but for
fulfills instead.
Specifically, if we force-close a channel, we remove its off-chain
`Channel` object entirely, at which point, on reload, we may notice
HTLC(s) which are not present in our pending payments map (as they
may have received a payment preimage, but not fully committed to
it). Thus, we'd conclude we still have a retryable payment, which
is untrue.
This commit does so, informing the ChannelManager via a new return
element where appropriate of the HTLCSource corresponding to the
failed HTLC.
During the event of a channel close, if the funding transaction
is yet to be broadcasted then a DiscardFunding event is issued
along with the ChannelClose event.
If a counterparty (or an old channel of ours) uses a non-segwit
script for their cooperative close payout, they may include an
output which is unbroadcastable due to not meeting the network dust
limit.
Here we check for this condition, force-closing the channel instead
if we find an output in the closing transaction which does not meet
the limit.
There is little reason for users to be paying out to non-Segwit
scripts when closing channels at this point. Given we will soon, in
rare cases, force-close during shutdown when a counterparty closes
to a non-Segwit script, we should also require it of our own users.
546 sat/vbyte is the current default dust limit on most
implementations, matching the network dust limit for P2SH outputs.
Implementations don't currently appear to send any larger dust
limits, and allowing a larger dust limit implies higher payment
failure risk, so we'd like to be as tight as we can here.
330 sat/vbyte, the current value, is not sufficient to ensure a
future segwit script longer than 32 bytes meets the dust limit if
used for a shutdown script. Thus, we can either check the value
on shutdown or we can simply require segwit outputs and require a
dust value of no less than 354 sat/vbyte.
We swap the minimum dust value to 354 sat/vbyte here, requiring
segwit scripts in a future commit.
See https://github.com/lightningnetwork/lightning-rfc/issues/905
CounterpartyForwardingInfo is public (previously exposed with a
`pub use`), and used inside of ChannelCounterparty in
channelmanager.rs. However, it is defined in channel.rs, away from
where it is used.
This would be fine, except that the bindings generator is somewhat
confused by this - it doesn't currently support interpreting
`pub use` as a struct to expose, instead ignoring it.
Fixes https://github.com/lightningdevkit/ldk-garbagecollected/issues/44
When communicating the maximum fee we're willing to accept on a
cooperative closing transaction to our peer, we currently tell them
we'll accept `u64::max_value()` if they're the ones who have to pay
it. Spec-wise this is fine - they aren't allowed to try to claim
our balance, and we don't care how much of their own funds they
want to spend on transaction fees.
However, the Eclair folks prefer to check all values on the wire
do not exceed 21 million BTC, which seems like generally good
practice to avoid overflows and such issues. Thus, our close
messages are rejected by Eclair.
Here we simply relax our stated maximum to be the real value - our
counterparty's current balance in satoshis.
Fixes#1071
This adds the new range-based closing_signed negotiation specified
in https://github.com/lightningnetwork/lightning-rfc/pull/847 as
well as cleans up the existing closing_signed negotiation to unify
the new codepaths and the old ones.
Note that because the new range-based closing_signed negotiation
allows the channel fundee to ultimately select the fee out of a
range specified by the funder, which we, of course, always select
the highest allowed amount from. Thus, we've added an extra round
of closing_signed in the common case as we will not simply accept
the first fee we see, always preferring to make the funder pay as
much as they're willing to.
When we added the support for external signing, many of the
signing functions were allowed to return an error, closing the
channel in such a case. `sign_closing_transaction` is one such
function which can now return an error, except instead of handling
it properly we'd simply never send a `closing_signed` message,
hanging the channel until users intervene and force-close it.
Piping the channel-closing error back through the various callsites
(several of which already have pending results by the time they
call `maybe_propose_first_closing_signed`) may be rather
complicated, so instead we simply attempt to propose the initial
`closing_signed` in `get_and_clear_pending_msg_events` like we do
for holding-cell freeing.
Further, since we now (possibly) generate a `ChannelMonitorUpdate`
on `shutdown`, we may need to wait for monitor updating to complete
before we can send a `closing_signed`, meaning we need to handle
the send asynchronously anyway.
This simplifies a few function interfaces and has no impact on
behavior, aside from a few message-ordering edge-cases, as seen in
the two small test changes required.
We're supposed to write `Channel` to disk as if
`remove_uncommitted_htlcs_and_mark_paused` had just run, however we
were writing `last_sent_closing_fee` to disk (if it is not-None),
whereas `remove_uncommitted_htlcs_and_mark_paused` clears it.
Indeed, the BOLTs say fee "... negotiation restarts on
reconnection."
We don't actually yet support `warning` messages as there are
issues left to resolve in the spec PR, but there's nothing to stop
us adding an internal enum variant for sending a warning message
before we actually support doing so.
Inbound fee udpates are rather broken in lightning as they can
impact the non-fundee despite the funder paying the fee, but only
in the dust exposure it places on the fundee.
At least lnd is fairly aggressively high in their (non-anchor) fee
estimation, running the risk of force-closure. Further, because we
relied on a fee estimator we don't have full control over, we
were assuming our users' fees are particularly conservative, and
thus were at a lot of risk to force-closures.
This converts our fee limiting to use an absurd upper bound,
focusing on whether we are over-exposed to in-flight dust when we
receive an update_fee.
If we receive an update_fee but do not receive a commitment_signed,
we should not persist the pending fee update to disk or hold on to
it after our peer disconnects.
In order to make the code the most readable, we add a state enum
which matches the relevant states from InboundHTLCState, allowing
for more simple code comparison between inbound HTLC handling and
update_fee handling.
When we send an update_fee to our counterparty on an outbound
channel, if we need to re-send a commitment update after
reconnection, the update_fee must be present in the re-sent
commitment update messages. However, wewere always setting the
update_fee field in the commitment update to None, causing us to
generate invalid commitment signatures and get channel
force-closures.
This fixes the issue by correctly detecting when an update_fee
needs to be re-sent, doing so when required.
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.
