chainfee: method to round up the fee for a given transaction weight

Author: hieblmi

lnwallet/chainfee/rates.go

@@ -71,6 +71,14 @@ func (s SatPerKWeight) FeeForWeight(wu lntypes.WeightUnit) btcutil.Amount {
 	return btcutil.Amount(s) * btcutil.Amount(wu) / 1000
 }
 
+// FeeForWeightRoundUp calculates the fee resulting from this fee rate and the
+// given weight in weight units (wu), rounding up to the nearest satoshi.
+func (s SatPerKWeight) FeeForWeightRoundUp(
+	wu lntypes.WeightUnit) btcutil.Amount {
+
+	return (btcutil.Amount(s)*btcutil.Amount(wu) + 999) / 1000
+}
+
 // FeeForVByte calculates the fee resulting from this fee rate and the given
 // size in vbytes (vb).
 func (s SatPerKWeight) FeeForVByte(vb lntypes.VByte) btcutil.Amount {

lnwallet/chainfee/rates_test.go

@@ -3,6 +3,7 @@ package chainfee
 import (
 	"testing"
 
+	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/stretchr/testify/require"
 )
 
@@ -20,3 +21,13 @@ func TestSatPerVByteConversion(t *testing.T) {
 	// 1 sat/vb should be equal to 250 sat/kw.
 	require.Equal(t, SatPerKWeight(250), rate.FeePerKWeight())
 }
+
+// TestFeeForWeightRoundUp checks that the FeeForWeightRoundUp method correctly
+// rounds up the fee for a given weight.
+func TestFeeForWeightRoundUp(t *testing.T) {
+	feeRate := SatPerVByte(1).FeePerKWeight()
+	txWeight := lntypes.WeightUnit(674) // 674 weight units is 168.5 vb.
+
+	require.EqualValues(t, 168, feeRate.FeeForWeight(txWeight))
+	require.EqualValues(t, 169, feeRate.FeeForWeightRoundUp(txWeight))
+}