lnwallet: modify CoopCloseBalance to not depend on chan commit

Author: Roasbeef

lnwallet/channel.go

@@ -7781,7 +7781,10 @@ func (lc *LightningChannel) CreateCloseProposal(proposedFee btcutil.Amount,
 	// during the channel closing process.
 	ourBalance, theirBalance, err := CoopCloseBalance(
 		lc.channelState.ChanType, lc.channelState.IsInitiator,
-		proposedFee, lc.channelState.LocalCommitment,
+		proposedFee,
+		lc.channelState.LocalCommitment.LocalBalance.ToSatoshis(),
+		lc.channelState.LocalCommitment.RemoteBalance.ToSatoshis(),
+		lc.channelState.LocalCommitment.CommitFee,
 	)
 	if err != nil {
 		return nil, nil, 0, err
@@ -7879,7 +7882,10 @@ func (lc *LightningChannel) CompleteCooperativeClose(
 	// Get the final balances after subtracting the proposed fee.
 	ourBalance, theirBalance, err := CoopCloseBalance(
 		lc.channelState.ChanType, lc.channelState.IsInitiator,
-		proposedFee, lc.channelState.LocalCommitment,
+		proposedFee,
+		lc.channelState.LocalCommitment.LocalBalance.ToSatoshis(),
+		lc.channelState.LocalCommitment.RemoteBalance.ToSatoshis(),
+		lc.channelState.LocalCommitment.CommitFee,
 	)
 	if err != nil {
 		return nil, 0, err

lnwallet/commitment.go

@@ -1033,16 +1033,12 @@ func CreateCommitTx(chanType channeldb.ChannelType,
 // CoopCloseBalance returns the final balances that should be used to create
 // the cooperative close tx, given the channel type and transaction fee.
 func CoopCloseBalance(chanType channeldb.ChannelType, isInitiator bool,
-	coopCloseFee btcutil.Amount, localCommit channeldb.ChannelCommitment) (
-	btcutil.Amount, btcutil.Amount, error) {
-
-	// Get both parties' balances from the latest commitment.
-	ourBalance := localCommit.LocalBalance.ToSatoshis()
-	theirBalance := localCommit.RemoteBalance.ToSatoshis()
+	coopCloseFee, ourBalance, theirBalance,
+	commitFee btcutil.Amount) (btcutil.Amount, btcutil.Amount, error) {
 
 	// We'll make sure we account for the complete balance by adding the
 	// current dangling commitment fee to the balance of the initiator.
-	initiatorDelta := localCommit.CommitFee
+	initiatorDelta := commitFee
 
 	// Since the initiator's balance also is stored after subtracting the
 	// anchor values, add that back in case this was an anchor commitment.