multi: make max fee rate configurable

config.go

@@ -681,6 +681,7 @@ func DefaultConfig() Config {
 		},
 		Sweeper: &lncfg.Sweeper{
 			BatchWindowDuration: sweep.DefaultBatchWindowDuration,
+			MaxFeeRate:          sweep.DefaultMaxFeeRate,
 		},
 		Htlcswitch: &lncfg.Htlcswitch{
 			MailboxDeliveryTimeout: htlcswitch.DefaultMailboxDeliveryTimeout,

lncfg/sweeper.go

@@ -3,11 +3,24 @@ package lncfg
 import (
 	"fmt"
 	"time"
+
+	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
+)
+
+const (
+	// MaxFeeRateFloor is the smallest config value allowed for the max fee
+	// rate in sat/vb.
+	MaxFeeRateFloor chainfee.SatPerVByte = 100
+
+	// MaxAllowedFeeRate is the largest fee rate in sat/vb that we allow
+	// when configuring the MaxFeeRate.
+	MaxAllowedFeeRate = 10_000
 )
 
 //nolint:lll
 type Sweeper struct {
-	BatchWindowDuration time.Duration `long:"batchwindowduration" description:"Duration of the sweep batch window. The sweep is held back during the batch window to allow more inputs to be added and thereby lower the fee per input."`
+	BatchWindowDuration time.Duration        `long:"batchwindowduration" description:"Duration of the sweep batch window. The sweep is held back during the batch window to allow more inputs to be added and thereby lower the fee per input."`
+	MaxFeeRate          chainfee.SatPerVByte `long:"maxfeerate" description:"Maximum fee rate in sat/vb that the sweeper is allowed to use when sweeping funds. Setting this value too low can result in transactions not being confirmed in time, causing HTLCs to expire hence potentially losing funds."`
 }
 
 // Validate checks the values configured for the sweeper.
@@ -16,5 +29,15 @@ func (s *Sweeper) Validate() error {
 		return fmt.Errorf("batchwindowduration must be positive")
 	}
 
+	// We require the max fee rate to be at least 100 sat/vbyte.
+	if s.MaxFeeRate < MaxFeeRateFloor {
+		return fmt.Errorf("maxfeerate must be >= 100 sat/vb")
+	}
+
+	// We require the max fee rate to be no greater than 10_000 sat/vbyte.
+	if s.MaxFeeRate > MaxAllowedFeeRate {
+		return fmt.Errorf("maxfeerate must be <= 10000 sat/vb")
+	}
+
 	return nil
 }

sample-lnd.conf

@@ -1578,6 +1578,11 @@
 ; window to allow more inputs to be added and thereby lower the fee per input.
 ; sweeper.batchwindowduration=30s
 
+; The max fee rate in sat/vb which can be used when sweeping funds. Setting
+; this value too low can result in transactions not being confirmed in time,
+; causing HTLCs to expire hence potentially losing funds.
+; sweeper.maxfeerate=1000
+
 
 [htlcswitch]
 

server.go

@@ -1071,7 +1071,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		MaxInputsPerTx:       sweep.DefaultMaxInputsPerTx,
 		MaxSweepAttempts:     sweep.DefaultMaxSweepAttempts,
 		NextAttemptDeltaFunc: sweep.DefaultNextAttemptDeltaFunc,
-		MaxFeeRate:           sweep.DefaultMaxFeeRate,
+		MaxFeeRate:           cfg.Sweeper.MaxFeeRate,
 		FeeRateBucketSize:    sweep.DefaultFeeRateBucketSize,
 	})