lnwallet: prevent static fee estimator fees from being modified

Modifying the static fees is not thread safe. In this commit the fees
are made immutable.

lnwallet/channel_test.go

@@ -1131,7 +1131,7 @@ func TestHTLCSigNumber(t *testing.T) {
 	}
 
 	// Calculate two values that will be below and above Bob's dust limit.
-	estimator := &StaticFeeEstimator{FeePerKW: 6000}
+	estimator := NewStaticFeeEstimator(6000, 0)
 	feePerKw, err := estimator.EstimateFeePerKW(1)
 	if err != nil {
 		t.Fatalf("unable to get fee: %v", err)

lnwallet/fee_estimator.go

@@ -68,22 +68,33 @@ type FeeEstimator interface {
 
 // StaticFeeEstimator will return a static value for all fee calculation
 // requests. It is designed to be replaced by a proper fee calculation
-// implementation.
+// implementation. The fees are not accessible directly, because changing them
+// would not be thread safe.
 type StaticFeeEstimator struct {
-	// FeePerKW is the static fee rate in satoshis-per-vbyte that will be
+	// feePerKW is the static fee rate in satoshis-per-vbyte that will be
 	// returned by this fee estimator.
-	FeePerKW SatPerKWeight
+	feePerKW SatPerKWeight
 
-	// RelayFee is the minimum fee rate required for transactions to be
+	// relayFee is the minimum fee rate required for transactions to be
 	// relayed.
-	RelayFee SatPerKWeight
+	relayFee SatPerKWeight
+}
+
+// NewStaticFeeEstimator returns a new static fee estimator instance.
+func NewStaticFeeEstimator(feePerKW,
+	relayFee SatPerKWeight) *StaticFeeEstimator {
+
+	return &StaticFeeEstimator{
+		feePerKW: feePerKW,
+		relayFee: relayFee,
+	}
 }
 
 // EstimateFeePerKW will return a static value for fee calculations.
 //
 // NOTE: This method is part of the FeeEstimator interface.
 func (e StaticFeeEstimator) EstimateFeePerKW(numBlocks uint32) (SatPerKWeight, error) {
-	return e.FeePerKW, nil
+	return e.feePerKW, nil
 }
 
 // RelayFeePerKW returns the minimum fee rate required for transactions to be
@@ -91,7 +102,7 @@ func (e StaticFeeEstimator) EstimateFeePerKW(numBlocks uint32) (SatPerKWeight, e
 //
 // NOTE: This method is part of the FeeEstimator interface.
 func (e StaticFeeEstimator) RelayFeePerKW() SatPerKWeight {
-	return e.RelayFee
+	return e.relayFee
 }
 
 // Start signals the FeeEstimator to start any processes or goroutines

lnwallet/fee_estimator_test.go

@@ -74,9 +74,7 @@ func TestStaticFeeEstimator(t *testing.T) {
 
 	const feePerKw = lnwallet.FeePerKwFloor
 
-	feeEstimator := &lnwallet.StaticFeeEstimator{
-		FeePerKW: feePerKw,
-	}
+	feeEstimator := lnwallet.NewStaticFeeEstimator(feePerKw, 0)
 	if err := feeEstimator.Start(); err != nil {
 		t.Fatalf("unable to start fee estimator: %v", err)
 	}

lnwallet/interface_test.go

@@ -368,7 +368,7 @@ func createTestWallet(tempTestDir string, miningNode *rpctest.Harness,
 		WalletController: wc,
 		Signer:           signer,
 		ChainIO:          bio,
-		FeeEstimator:     lnwallet.StaticFeeEstimator{FeePerKW: 2500},
+		FeeEstimator:     lnwallet.NewStaticFeeEstimator(2500, 0),
 		DefaultConstraints: channeldb.ChannelConstraints{
 			DustLimit:        500,
 			MaxPendingAmount: lnwire.NewMSatFromSatoshis(btcutil.SatoshiPerBitcoin) * 100,
@@ -2440,7 +2440,7 @@ func runTests(t *testing.T, walletDriver *lnwallet.WalletDriver,
 			}
 
 		case "neutrino":
-			feeEstimator = lnwallet.StaticFeeEstimator{FeePerKW: 62500}
+			feeEstimator = lnwallet.NewStaticFeeEstimator(62500, 0)
 
 			// Set some package-level variable to speed up
 			// operation for tests.

lnwallet/test_utils.go

@@ -229,7 +229,7 @@ func CreateTestChannels() (*LightningChannel, *LightningChannel, func(), error)
 		return nil, nil, nil, err
 	}
 
-	estimator := &StaticFeeEstimator{FeePerKW: 6000}
+	estimator := NewStaticFeeEstimator(6000, 0)
 	feePerKw, err := estimator.EstimateFeePerKW(1)
 	if err != nil {
 		return nil, nil, nil, err