lnwallet: add configurable cache for web fee estimator

Add fee.min-update-timeout and fee.max-update-timeout config options to
allow configuration of the web fee estimator cache.

lnwallet/chainfee/estimator.go

@@ -28,14 +28,6 @@ const (
 	// less than this will result in an error.
 	minBlockTarget uint32 = 1
 
-	// minFeeUpdateTimeout represents the minimum interval in which a
-	// WebAPIEstimator will request fresh fees from its API.
-	minFeeUpdateTimeout = 5 * time.Minute
-
-	// maxFeeUpdateTimeout represents the maximum interval in which a
-	// WebAPIEstimator will request fresh fees from its API.
-	maxFeeUpdateTimeout = 20 * time.Minute
-
 	// WebAPIConnectionTimeout specifies the timeout value for connecting
 	// to the api source.
 	WebAPIConnectionTimeout = 5 * time.Second
@@ -739,19 +731,43 @@ type WebAPIEstimator struct {
 	// estimates.
 	noCache bool
 
+	// minFeeUpdateTimeout represents the minimum interval in which the
+	// web estimator will request fresh fees from its API.
+	minFeeUpdateTimeout time.Duration
+
+	// minFeeUpdateTimeout represents the maximum interval in which the
+	// web estimator will request fresh fees from its API.
+	maxFeeUpdateTimeout time.Duration
+
 	quit chan struct{}
 	wg   sync.WaitGroup
 }
 
 // NewWebAPIEstimator creates a new WebAPIEstimator from a given URL and a
 // fallback default fee. The fees are updated whenever a new block is mined.
-func NewWebAPIEstimator(api WebAPIFeeSource, noCache bool) *WebAPIEstimator {
-	return &WebAPIEstimator{
-		apiSource:        api,
-		feeByBlockTarget: make(map[uint32]uint32),
-		noCache:          noCache,
-		quit:             make(chan struct{}),
+func NewWebAPIEstimator(api WebAPIFeeSource, noCache bool,
+	minFeeUpdateTimeout time.Duration,
+	maxFeeUpdateTimeout time.Duration) (*WebAPIEstimator, error) {
+
+	if minFeeUpdateTimeout == 0 || maxFeeUpdateTimeout == 0 {
+		return nil, fmt.Errorf("minFeeUpdateTimeout and " +
+			"maxFeeUpdateTimeout must be greater than 0")
 	}
+
+	if minFeeUpdateTimeout >= maxFeeUpdateTimeout {
+		return nil, fmt.Errorf("minFeeUpdateTimeout target of %v "+
+			"cannot be greater than maxFeeUpdateTimeout of %v",
+			minFeeUpdateTimeout, maxFeeUpdateTimeout)
+	}
+
+	return &WebAPIEstimator{
+		apiSource:           api,
+		feeByBlockTarget:    make(map[uint32]uint32),
+		noCache:             noCache,
+		quit:                make(chan struct{}),
+		minFeeUpdateTimeout: minFeeUpdateTimeout,
+		maxFeeUpdateTimeout: maxFeeUpdateTimeout,
+	}, nil
 }
 
 // EstimateFeePerKW takes in a target for the number of blocks until an initial
@@ -809,7 +825,12 @@ func (w *WebAPIEstimator) Start() error {
 	w.started.Do(func() {
 		log.Infof("Starting web API fee estimator")
 
-		w.updateFeeTicker = time.NewTicker(w.randomFeeUpdateTimeout())
+		feeUpdateTimeout := w.randomFeeUpdateTimeout()
+
+		log.Infof("Web API fee estimator using update timeout of %v",
+			feeUpdateTimeout)
+
+		w.updateFeeTicker = time.NewTicker(feeUpdateTimeout)
 		w.updateFeeEstimates()
 
 		w.wg.Add(1)
@@ -852,9 +873,11 @@ func (w *WebAPIEstimator) RelayFeePerKW() SatPerKWeight {
 // and maxFeeUpdateTimeout that will be used to determine how often the Estimator
 // should retrieve fresh fees from its API.
 func (w *WebAPIEstimator) randomFeeUpdateTimeout() time.Duration {
-	lower := int64(minFeeUpdateTimeout)
-	upper := int64(maxFeeUpdateTimeout)
-	return time.Duration(prand.Int63n(upper-lower) + lower)
+	lower := int64(w.minFeeUpdateTimeout)
+	upper := int64(w.maxFeeUpdateTimeout)
+	return time.Duration(
+		prand.Int63n(upper-lower) + lower, //nolint:gosec
+	).Round(time.Second)
 }
 
 // getCachedFee takes a conf target and returns the cached fee rate. When the

lnwallet/chainfee/estimator_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"testing"
+	"time"
 
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/stretchr/testify/require"
@@ -142,6 +143,9 @@ func TestWebAPIFeeEstimator(t *testing.T) {
 		// Fee rates are in sat/kb.
 		minFeeRate uint32 = 2000 // 500 sat/kw
 		maxFeeRate uint32 = 4000 // 1000 sat/kw
+
+		minFeeUpdateTimeout = 5 * time.Minute
+		maxFeeUpdateTimeout = 20 * time.Minute
 	)
 
 	testCases := []struct {
@@ -199,7 +203,9 @@ func TestWebAPIFeeEstimator(t *testing.T) {
 	feeSource := &mockFeeSource{}
 	feeSource.On("GetFeeMap").Return(feeRateResp, nil)
 
-	estimator := NewWebAPIEstimator(feeSource, false)
+	estimator, _ := NewWebAPIEstimator(
+		feeSource, false, minFeeUpdateTimeout, maxFeeUpdateTimeout,
+	)
 
 	// Test that requesting a fee when no fees have been cached won't fail.
 	feeRate, err := estimator.EstimateFeePerKW(5)
@@ -247,10 +253,15 @@ func TestGetCachedFee(t *testing.T) {
 
 		minFeeRate uint32 = 100
 		maxFeeRate uint32 = 1000
+
+		minFeeUpdateTimeout = 5 * time.Minute
+		maxFeeUpdateTimeout = 20 * time.Minute
 	)
 
 	// Create a dummy estimator without WebAPIFeeSource.
-	estimator := NewWebAPIEstimator(nil, false)
+	estimator, _ := NewWebAPIEstimator(
+		nil, false, minFeeUpdateTimeout, maxFeeUpdateTimeout,
+	)
 
 	// When the cache is empty, an error should be returned.
 	cachedFee, err := estimator.getCachedFee(minTarget)
@@ -315,3 +326,38 @@ func TestGetCachedFee(t *testing.T) {
 		})
 	}
 }
+
+func TestRandomFeeUpdateTimeout(t *testing.T) {
+	t.Parallel()
+
+	var (
+		minFeeUpdateTimeout = 1 * time.Minute
+		maxFeeUpdateTimeout = 2 * time.Minute
+	)
+
+	estimator, _ := NewWebAPIEstimator(
+		nil, false, minFeeUpdateTimeout, maxFeeUpdateTimeout,
+	)
+
+	for i := 0; i < 1000; i++ {
+		timeout := estimator.randomFeeUpdateTimeout()
+
+		require.GreaterOrEqual(t, timeout, minFeeUpdateTimeout)
+		require.LessOrEqual(t, timeout, maxFeeUpdateTimeout)
+	}
+}
+
+func TestInvalidFeeUpdateTimeout(t *testing.T) {
+	t.Parallel()
+
+	var (
+		minFeeUpdateTimeout = 2 * time.Minute
+		maxFeeUpdateTimeout = 1 * time.Minute
+	)
+
+	_, err := NewWebAPIEstimator(
+		nil, false, minFeeUpdateTimeout, maxFeeUpdateTimeout,
+	)
+	require.Error(t, err, "NewWebAPIEstimator should return an error "+
+		"when minFeeUpdateTimeout > maxFeeUpdateTimeout")
+}