From 0fc5301d12d267f2f316a43e65fdf3809e69bec0 Mon Sep 17 00:00:00 2001
From: yyforyongyu <yy2452@columbia.edu>
Date: Mon, 18 Mar 2024 10:56:41 +0800
Subject: [PATCH] lnwallet+sweep: cap conf target used in fee estimator

---
 lnwallet/chainfee/estimator.go | 14 +++++++-------
 sweep/fee_function.go          | 10 ++++++++++
 sweep/fee_function_test.go     | 18 ++++++++++++++++++
 3 files changed, 35 insertions(+), 7 deletions(-)

diff --git a/lnwallet/chainfee/estimator.go b/lnwallet/chainfee/estimator.go
index fa5e04ba1..76c235d1b 100644
--- a/lnwallet/chainfee/estimator.go
+++ b/lnwallet/chainfee/estimator.go
@@ -17,11 +17,11 @@ import (
 )
 
 const (
-	// maxBlockTarget is the highest number of blocks confirmations that
+	// MaxBlockTarget is the highest number of blocks confirmations that
 	// a WebAPIEstimator will cache fees for. This number is chosen
 	// because it's the highest number of confs bitcoind will return a fee
 	// estimate for.
-	maxBlockTarget uint32 = 1008
+	MaxBlockTarget uint32 = 1008
 
 	// minBlockTarget is the lowest number of blocks confirmations that
 	// a WebAPIEstimator will cache fees for. Requesting an estimate for
@@ -463,11 +463,11 @@ func (b *BitcoindEstimator) Stop() error {
 func (b *BitcoindEstimator) EstimateFeePerKW(
 	numBlocks uint32) (SatPerKWeight, error) {
 
-	if numBlocks > maxBlockTarget {
+	if numBlocks > MaxBlockTarget {
 		log.Debugf("conf target %d exceeds the max value, "+
-			"use %d instead.", numBlocks, maxBlockTarget,
+			"use %d instead.", numBlocks, MaxBlockTarget,
 		)
-		numBlocks = maxBlockTarget
+		numBlocks = MaxBlockTarget
 	}
 
 	feeEstimate, err := b.fetchEstimate(numBlocks, b.feeMode)
@@ -761,8 +761,8 @@ func NewWebAPIEstimator(api WebAPIFeeSource, noCache bool) *WebAPIEstimator {
 func (w *WebAPIEstimator) EstimateFeePerKW(numBlocks uint32) (
 	SatPerKWeight, error) {
 
-	if numBlocks > maxBlockTarget {
-		numBlocks = maxBlockTarget
+	if numBlocks > MaxBlockTarget {
+		numBlocks = MaxBlockTarget
 	} else if numBlocks < minBlockTarget {
 		return 0, fmt.Errorf("conf target of %v is too low, minimum "+
 			"accepted is %v", numBlocks, minBlockTarget)
diff --git a/sweep/fee_function.go b/sweep/fee_function.go
index 955ca43a6..59da96d78 100644
--- a/sweep/fee_function.go
+++ b/sweep/fee_function.go
@@ -276,6 +276,16 @@ func (l *LinearFeeFunction) estimateFeeRate(
 		ConfTarget: confTarget,
 	}
 
+	// If the conf target is greater or equal to the max allowed value
+	// (1008), we will use the min relay fee instead.
+	if confTarget >= chainfee.MaxBlockTarget {
+		minFeeRate := l.estimator.RelayFeePerKW()
+		log.Debugf("Conf target %v is greater than max block target, "+
+			"using min relay fee rate %v", confTarget, minFeeRate)
+
+		return minFeeRate, nil
+	}
+
 	// endingFeeRate comes from budget/txWeight, which means the returned
 	// fee rate will always be capped by this value, hence we don't need to
 	// worry about overpay.
diff --git a/sweep/fee_function_test.go b/sweep/fee_function_test.go
index e549d8d64..fb75bcc1c 100644
--- a/sweep/fee_function_test.go
+++ b/sweep/fee_function_test.go
@@ -19,6 +19,7 @@ func TestLinearFeeFunctionNew(t *testing.T) {
 	// Create testing params.
 	maxFeeRate := chainfee.SatPerKWeight(10000)
 	estimatedFeeRate := chainfee.SatPerKWeight(500)
+	minRelayFeeRate := chainfee.SatPerKWeight(100)
 	confTarget := uint32(6)
 
 	// Assert init fee function with zero conf value returns an error.
@@ -62,6 +63,23 @@ func TestLinearFeeFunctionNew(t *testing.T) {
 	rt.ErrorContains(err, "fee rate delta is zero")
 	rt.Nil(f)
 
+	// When the conf target is >= 1008, the min relay fee should be used.
+	//
+	// Mock the fee estimator to reutrn the fee rate.
+	estimator.On("RelayFeePerKW").Return(minRelayFeeRate).Once()
+
+	largeConf := uint32(1008)
+	f, err = NewLinearFeeFunction(maxFeeRate, largeConf, estimator)
+	rt.NoError(err)
+	rt.NotNil(f)
+
+	// Assert the internal state.
+	rt.Equal(minRelayFeeRate, f.startingFeeRate)
+	rt.Equal(maxFeeRate, f.endingFeeRate)
+	rt.Equal(minRelayFeeRate, f.currentFeeRate)
+	rt.NotZero(f.deltaFeeRate)
+	rt.Equal(largeConf, f.width)
+
 	// Check a successfully created fee function.
 	//
 	// Mock the fee estimator to return the fee rate.