In this commit we deprecate the sighash field from the
MuSig2SignSweepReq request in favour of using a psbt serialized sweep
transaction instead. This way the sever gains full transparency about
client sweep requests and can assemble the sighash to sign on its own.
This commit adds optional cooperative musig2 sweep by calling the server
to create a partial signature for the sweep if we'd otherwise be allowed
to spend the htlc. If the cooperative musig2 spend fails, we always fall
back to use the scriptpath spend.
Taproot spends require a different sighash, so we update our HtlcScript
interface to provide the appropriate sighash when sweeping. We also add
distinct Timeout/Success Script functions to allow for tapleaf spends
which have different locking scripts for different paths. Note that the
timeout and success paths will be the same for segwit v0 htlcs, because
it has a single branched script containing all spend paths.
In future iterations, this differentiation of claim scripts can also
be used to use musig2 to collaboratively keyspend P2TR htlcs with the
server. This script can be expressed as PriorityScript (because we'll
try to keyspend as a priority, and then fall back to a tap leaf spend).
As we've done here, segwit v0 spends would just return their single
script for PriorityScript, and the claim would be no different from
our other claims.
In this commit we add the version 3 htlc, which is implemented with
taproot script spending the two payment paths: the claim path case, and
the timeout case.
Fixes#457.
The SignOutputRaw RPC is normally too lenient when it comes to fields
not being set, which is why this used to work previously. But with lnd
in remote signing mode, we need all the extra meta information available
on an input being signed for, so we actually need the pk script being
set.
Loop fully works with a remote signing lnd backend pair after applying
this fix.
We need the newer version of lndclient to get our synced to chain
state. This requires changes to our test mock, so it is separated
into a different commit. Since lndclient is expanding to be used in
projects other than loop, the client interface is embedded in our
mock rather than implementing functions we do not need. Functions that
we already use in tests are updated accordingly.
Note that while this commit bumps us to a version of lndclient that
defaults to requiring lnd 0.11, we do not bump our required version
yet because we are not using any new endpoints.
