lnrpc: extract fee limit calculation

lnrpc/marshall_utils.go

@@ -0,0 +1,30 @@
+package lnrpc
+
+import (
+	"github.com/btcsuite/btcutil"
+	"github.com/lightningnetwork/lnd/lnwire"
+)
+
+// CalculateFeeLimit returns the fee limit in millisatoshis. If a percentage
+// based fee limit has been requested, we'll factor in the ratio provided with
+// the amount of the payment.
+func CalculateFeeLimit(feeLimit *FeeLimit,
+	amount lnwire.MilliSatoshi) lnwire.MilliSatoshi {
+
+	switch feeLimit.GetLimit().(type) {
+
+	case *FeeLimit_Fixed:
+		return lnwire.NewMSatFromSatoshis(
+			btcutil.Amount(feeLimit.GetFixed()),
+		)
+
+	case *FeeLimit_Percent:
+		return amount * lnwire.MilliSatoshi(feeLimit.GetPercent()) / 100
+
+	default:
+		// If a fee limit was not specified, we'll use the payment's
+		// amount as an upper bound in order to avoid payment attempts
+		// from incurring fees higher than the payment amount itself.
+		return amount
+	}
+}