From ea2a58e80f61ccfd28f2b834e022a7a410c1b247 Mon Sep 17 00:00:00 2001
From: "Johan T. Halseth" <johanth@gmail.com>
Date: Fri, 6 Mar 2020 16:11:49 +0100
Subject: [PATCH] fundingmanager+lnwallet: enable anchor commitments

If both nodes are signalling the feature, make all opened channels using
this type.
---
 fundingmanager.go       | 14 ++++++++++++++
 lnwallet/reservation.go | 33 +++++++++++++++++++++++++++++++--
 2 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/fundingmanager.go b/fundingmanager.go
index bf4ed31b0..3e28f2a87 100644
--- a/fundingmanager.go
+++ b/fundingmanager.go
@@ -1111,6 +1111,20 @@ func (f *fundingManager) processFundingOpen(msg *lnwire.OpenChannel,
 func commitmentType(localFeatures,
 	remoteFeatures *lnwire.FeatureVector) lnwallet.CommitmentType {
 
+	// If both peers are signalling support for anchor commitments, this
+	// implicitly mean we'll create the channel of this type. Note that
+	// this also enables tweakless commitments, as anchor commitments are
+	// always tweakless.
+	localAnchors := localFeatures.HasFeature(
+		lnwire.AnchorsOptional,
+	)
+	remoteAnchors := remoteFeatures.HasFeature(
+		lnwire.AnchorsOptional,
+	)
+	if localAnchors && remoteAnchors {
+		return lnwallet.CommitmentTypeAnchors
+	}
+
 	localTweakless := localFeatures.HasFeature(
 		lnwire.StaticRemoteKeyOptional,
 	)
diff --git a/lnwallet/reservation.go b/lnwallet/reservation.go
index ba4c631ef..823aec4ae 100644
--- a/lnwallet/reservation.go
+++ b/lnwallet/reservation.go
@@ -27,6 +27,11 @@ const (
 	// CommitmentTypeTweakless is a newer commitment format where the
 	// to_remote key is static.
 	CommitmentTypeTweakless
+
+	// CommitmentTypeAnchors is a commitment type that is tweakless, and
+	// has extra anchor ouputs in order to bump the fee of the commitment
+	// transaction.
+	CommitmentTypeAnchors
 )
 
 // String returns the name of the CommitmentType.
@@ -36,6 +41,8 @@ func (c CommitmentType) String() string {
 		return "legacy"
 	case CommitmentTypeTweakless:
 		return "tweakless"
+	case CommitmentTypeAnchors:
+		return "anchors"
 	default:
 		return "invalid"
 	}
@@ -172,12 +179,25 @@ func NewChannelReservation(capacity, localFundingAmt btcutil.Amount,
 		initiator    bool
 	)
 
-	commitFee := commitFeePerKw.FeeForWeight(input.CommitWeight)
+	// Based on the channel type, we determine the initial commit weight
+	// and fee.
+	commitWeight := int64(input.CommitWeight)
+	if commitType == CommitmentTypeAnchors {
+		commitWeight = input.AnchorCommitWeight
+	}
+	commitFee := commitFeePerKw.FeeForWeight(commitWeight)
+
 	localFundingMSat := lnwire.NewMSatFromSatoshis(localFundingAmt)
 	// TODO(halseth): make method take remote funding amount directly
 	// instead of inferring it from capacity and local amt.
 	capacityMSat := lnwire.NewMSatFromSatoshis(capacity)
+
+	// The total fee paid by the initiator will be the commitment fee in
+	// addition to the two anchor outputs.
 	feeMSat := lnwire.NewMSatFromSatoshis(commitFee)
+	if commitType == CommitmentTypeAnchors {
+		feeMSat += 2 * lnwire.NewMSatFromSatoshis(anchorSize)
+	}
 
 	// If we're the responder to a single-funder reservation, then we have
 	// no initial balance in the channel unless the remote party is pushing
@@ -257,7 +277,11 @@ func NewChannelReservation(capacity, localFundingAmt btcutil.Amount,
 	// non-zero push amt (there's no pushing for dual funder), then this is
 	// a single-funder channel.
 	if ourBalance == 0 || theirBalance == 0 || pushMSat != 0 {
-		if commitType == CommitmentTypeTweakless {
+		// Both the tweakless type and the anchor type is tweakless,
+		// hence set the bit.
+		if commitType == CommitmentTypeTweakless ||
+			commitType == CommitmentTypeAnchors {
+
 			chanType |= channeldb.SingleFunderTweaklessBit
 		} else {
 			chanType |= channeldb.SingleFunderBit
@@ -277,6 +301,11 @@ func NewChannelReservation(capacity, localFundingAmt btcutil.Amount,
 		chanType |= channeldb.DualFunderBit
 	}
 
+	// We are adding anchor outputs to our commitment.
+	if commitType == CommitmentTypeAnchors {
+		chanType |= channeldb.AnchorOutputsBit
+	}
+
 	return &ChannelReservation{
 		ourContribution: &ChannelContribution{
 			FundingAmount: ourBalance.ToSatoshis(),