lnwallet: allow callers to specify fee for funding transaction in funding flow

In this commit, we modify the funding reservation workflow slightly to
allow callers to specify their own custom fee when initialization a
funding workflow. This gives power-users the ability to control exactly
how much in fees are paid for each new funding transaction.

lnwallet/reservation.go

@@ -134,7 +134,7 @@ type ChannelReservation struct {
 // used only internally by lnwallet. In order to concurrent safety, the
 // creation of all channel reservations should be carried out via the
 // lnwallet.InitChannelReservation interface.
-func NewChannelReservation(capacity, fundingAmt, feePerKw btcutil.Amount,
+func NewChannelReservation(capacity, fundingAmt, commitFeePerKw btcutil.Amount,
 	wallet *LightningWallet, id uint64, pushMSat lnwire.MilliSatoshi,
 	chainHash *chainhash.Hash) *ChannelReservation {
 
@@ -144,7 +144,9 @@ func NewChannelReservation(capacity, fundingAmt, feePerKw btcutil.Amount,
 		initiator    bool
 	)
 
-	commitFee := btcutil.Amount((int64(feePerKw) * CommitWeight) / 1000)
+	commitFee := btcutil.Amount(
+		(int64(commitFeePerKw) * CommitWeight) / 1000,
+	)
 
 	fundingMSat := lnwire.NewMSatFromSatoshis(fundingAmt)
 	capacityMSat := lnwire.NewMSatFromSatoshis(capacity)
@@ -213,13 +215,13 @@ func NewChannelReservation(capacity, fundingAmt, feePerKw btcutil.Amount,
 			LocalCommitment: channeldb.ChannelCommitment{
 				LocalBalance:  ourBalance,
 				RemoteBalance: theirBalance,
-				FeePerKw:      feePerKw,
+				FeePerKw:      commitFeePerKw,
 				CommitFee:     commitFee,
 			},
 			RemoteCommitment: channeldb.ChannelCommitment{
 				LocalBalance:  ourBalance,
 				RemoteBalance: theirBalance,
-				FeePerKw:      feePerKw,
+				FeePerKw:      commitFeePerKw,
 				CommitFee:     commitFee,
 			},
 			Db: wallet.Cfg.Database,

lnwallet/wallet.go

@@ -94,11 +94,15 @@ type initFundingReserveMsg struct {
 	// amount of funds the remote party contributes (if any).
 	capacity btcutil.Amount
 
-	// feePerKw is the accepted satoshis/Kw fee for the funding
+	// commitFeePerKw is the starting accepted satoshis/Kw fee for the set
-	// transaction. In order to ensure timely confirmation, it is
+	// of initial commitment transactions. In order to ensure timely
-	// recommended that this fee should be generous, paying some multiple
+	// confirmation, it is recommended that this fee should be generous,
-	// of the accepted base fee rate of the network.
+	// paying some multiple of the accepted base fee rate of the network.
-	feePerKw btcutil.Amount
+	commitFeePerKw btcutil.Amount
+
+	// fundingFeePerWeight is the fee rate in satoshis per eight unit to
+	// use for the initial funding transaction.
+	fundingFeePerWeight btcutil.Amount
 
 	// pushMSat is the number of milli-satoshis that should be pushed over
 	// the responder as part of the initial channel creation.
@@ -443,7 +447,7 @@ out:
 // commitment transaction is valid.
 func (l *LightningWallet) InitChannelReservation(
 	capacity, ourFundAmt btcutil.Amount, pushMSat lnwire.MilliSatoshi,
-	feePerKw btcutil.Amount,
+	commitFeePerKw, fundingFeePerWeight btcutil.Amount,
 	theirID *btcec.PublicKey, theirAddr *net.TCPAddr,
 	chainHash *chainhash.Hash) (*ChannelReservation, error) {
 
@@ -451,15 +455,16 @@ func (l *LightningWallet) InitChannelReservation(
 	respChan := make(chan *ChannelReservation, 1)
 
 	l.msgChan <- &initFundingReserveMsg{
-		chainHash:     chainHash,
+		chainHash:           chainHash,
-		nodeID:        theirID,
+		nodeID:              theirID,
-		nodeAddr:      theirAddr,
+		nodeAddr:            theirAddr,
-		fundingAmount: ourFundAmt,
+		fundingAmount:       ourFundAmt,
-		capacity:      capacity,
+		capacity:            capacity,
-		feePerKw:      feePerKw,
+		commitFeePerKw:      commitFeePerKw,
-		pushMSat:      pushMSat,
+		fundingFeePerWeight: fundingFeePerWeight,
-		err:           errChan,
+		pushMSat:            pushMSat,
-		resp:          respChan,
+		err:                 errChan,
+		resp:                respChan,
 	}
 
 	return <-respChan, <-errChan
@@ -488,7 +493,7 @@ func (l *LightningWallet) handleFundingReserveRequest(req *initFundingReserveMsg
 
 	id := atomic.AddUint64(&l.nextFundingID, 1)
 	reservation := NewChannelReservation(req.capacity, req.fundingAmount,
-		req.feePerKw, l, id, req.pushMSat, l.Cfg.NetParams.GenesisHash)
+		req.commitFeePerKw, l, id, req.pushMSat, l.Cfg.NetParams.GenesisHash)
 
 	// Grab the mutex on the ChannelReservation to ensure thread-safety
 	reservation.Lock()
@@ -501,14 +506,12 @@ func (l *LightningWallet) handleFundingReserveRequest(req *initFundingReserveMsg
 	// don't need to perform any coin selection. Otherwise, attempt to
 	// obtain enough coins to meet the required funding amount.
 	if req.fundingAmount != 0 {
-		// Coin selection is done on the basis of sat-per-weight, so
+		// Coin selection is done on the basis of sat-per-weight, we'll
-		// we'll query the fee estimator for a fee to use to ensure the
+		// use the passed sat/byte passed in to perform coin selection.
-		// funding transaction gets into the _next_  block.
+		err := l.selectCoinsAndChange(
-		//
+			req.fundingFeePerWeight, req.fundingAmount,
-		// TODO(roasbeef): shouldn't be targeting next block
+			reservation.ourContribution,
-		satPerWeight := l.Cfg.FeeEstimator.EstimateFeePerWeight(1)
+		)
-		err := l.selectCoinsAndChange(satPerWeight, req.fundingAmount,
-			reservation.ourContribution)
 		if err != nil {
 			req.err <- err
 			req.resp <- nil
@@ -1255,7 +1258,7 @@ func (l *LightningWallet) handleSingleFunderSigs(req *addSingleFunderSigsMsg) {
 // within the passed contribution's inputs. If necessary, a change address will
 // also be generated.
 // TODO(roasbeef): remove hardcoded fees and req'd confs for outputs.
-func (l *LightningWallet) selectCoinsAndChange(feeRatePerWeight uint64,
+func (l *LightningWallet) selectCoinsAndChange(feeRatePerWeight btcutil.Amount,
 	amt btcutil.Amount, contribution *ChannelContribution) error {
 
 	// We hold the coin select mutex while querying for outputs, and
@@ -1264,8 +1267,8 @@ func (l *LightningWallet) selectCoinsAndChange(feeRatePerWeight uint64,
 	l.coinSelectMtx.Lock()
 	defer l.coinSelectMtx.Unlock()
 
-	walletLog.Infof("Performing coin selection using %v sat/weight as fee "+
+	walletLog.Infof("Performing funding tx coin selection using %v "+
-		"rate", feeRatePerWeight)
+		"sat/weight as fee rate", int64(feeRatePerWeight))
 
 	// Find all unlocked unspent witness outputs with greater than 1
 	// confirmation.
@@ -1387,7 +1390,7 @@ func selectInputs(amt btcutil.Amount, coins []*Utxo) (btcutil.Amount, []*Utxo, e
 // change output to fund amt satoshis, adhering to the specified fee rate. The
 // specified fee rate should be expressed in sat/byte for coin selection to
 // function properly.
-func coinSelect(feeRatePerWeight uint64, amt btcutil.Amount,
+func coinSelect(feeRatePerWeight, amt btcutil.Amount,
 	coins []*Utxo) ([]*Utxo, btcutil.Amount, error) {
 
 	amtNeeded := amt
@@ -1432,7 +1435,8 @@ func coinSelect(feeRatePerWeight uint64, amt btcutil.Amount,
 		// coin amount by the estimate required fee, performing another
 		// round of coin selection.
 		requiredFee := btcutil.Amount(
-			uint64(weightEstimate.Weight()) * feeRatePerWeight)
+			uint64(weightEstimate.Weight()) * uint64(feeRatePerWeight),
+		)
 		if overShootAmt < requiredFee {
 			amtNeeded = amt + requiredFee
 			continue