htlcswitch: respect minimum relay fee

When channels fee rates are being considered for an update, the minimum
relay fee should also be considered.

htlcswitch/link_test.go

@@ -3744,6 +3744,7 @@ func TestShouldAdjustCommitFee(t *testing.T) {
 	tests := []struct {
 		netFee       chainfee.SatPerKWeight
 		chanFee      chainfee.SatPerKWeight
+		minRelayFee  chainfee.SatPerKWeight
 		shouldAdjust bool
 	}{
 
@@ -3819,11 +3820,22 @@ func TestShouldAdjustCommitFee(t *testing.T) {
 			chanFee:      1000,
 			shouldAdjust: false,
 		},
+
+		// The network fee is higher than our commitment fee,
+		// hasn't yet crossed our activation threshold, but the
+		// current commitment fee is below the minimum relay fee and
+		// so the fee should be updated.
+		{
+			netFee:       1100,
+			chanFee:      1098,
+			minRelayFee:  1099,
+			shouldAdjust: true,
+		},
 	}
 
 	for i, test := range tests {
 		adjustedFee := shouldAdjustCommitFee(
-			test.netFee, test.chanFee,
+			test.netFee, test.chanFee, test.minRelayFee,
 		)
 
 		if adjustedFee && !test.shouldAdjust {
@@ -4009,6 +4021,13 @@ func TestChannelLinkUpdateCommitFee(t *testing.T) {
 		{"bob", "alice", &lnwire.RevokeAndAck{}, false},
 		{"bob", "alice", &lnwire.CommitSig{}, false},
 		{"alice", "bob", &lnwire.RevokeAndAck{}, false},
+
+		// Third fee update.
+		{"alice", "bob", &lnwire.UpdateFee{}, false},
+		{"alice", "bob", &lnwire.CommitSig{}, false},
+		{"bob", "alice", &lnwire.RevokeAndAck{}, false},
+		{"bob", "alice", &lnwire.CommitSig{}, false},
+		{"alice", "bob", &lnwire.RevokeAndAck{}, false},
 	}
 	n.aliceServer.intersect(createInterceptorFunc("[alice] <-- [bob]",
 		"alice", messages, chanID, false))
@@ -4025,8 +4044,8 @@ func TestChannelLinkUpdateCommitFee(t *testing.T) {
 
 	// triggerFeeUpdate is a helper closure to determine whether a fee
 	// update was triggered and completed properly.
-	triggerFeeUpdate := func(feeEstimate, newFeeRate chainfee.SatPerKWeight,
-		shouldUpdate bool) {
+	triggerFeeUpdate := func(feeEstimate, minRelayFee,
+		newFeeRate chainfee.SatPerKWeight, shouldUpdate bool) {
 
 		t.Helper()
 
@@ -4046,6 +4065,13 @@ func TestChannelLinkUpdateCommitFee(t *testing.T) {
 			t.Fatalf("alice didn't query for the new network fee")
 		}
 
+		// We also send the min relay fee response to Alice.
+		select {
+		case n.feeEstimator.relayFee <- minRelayFee:
+		case <-time.After(time.Second * 5):
+			t.Fatalf("alice didn't query for the min relay fee")
+		}
+
 		// Record the fee rates after the links have processed the fee
 		// update and ensure they are correct based on whether a fee
 		// update should have been triggered.
@@ -4071,20 +4097,28 @@ func TestChannelLinkUpdateCommitFee(t *testing.T) {
 		}, 10*time.Second, time.Second)
 	}
 
+	minRelayFee := startingFeeRate / 3
+
 	// Triggering the link to update the fee of the channel with the same
 	// fee rate should not send a fee update.
-	triggerFeeUpdate(startingFeeRate, startingFeeRate, false)
+	triggerFeeUpdate(startingFeeRate, minRelayFee, startingFeeRate, false)
 
 	// Triggering the link to update the fee of the channel with a much
 	// larger fee rate _should_ send a fee update.
 	newFeeRate := startingFeeRate * 3
-	triggerFeeUpdate(newFeeRate, newFeeRate, true)
+	triggerFeeUpdate(newFeeRate, minRelayFee, newFeeRate, true)
 
 	// Triggering the link to update the fee of the channel with a fee rate
 	// that exceeds its maximum fee allocation should result in a fee rate
 	// corresponding to the maximum fee allocation.
-	const maxFeeRate chainfee.SatPerKWeight = 207182320
-	triggerFeeUpdate(maxFeeRate+1, maxFeeRate, true)
+	const maxFeeRate chainfee.SatPerKWeight = 207180182
+	triggerFeeUpdate(maxFeeRate+1, minRelayFee, maxFeeRate, true)
+
+	// Triggering the link to update the fee of the channel with a fee rate
+	// that is below the current min relay fee rate should result in a fee
+	// rate corresponding to the minimum relay fee.
+	newFeeRate = minRelayFee / 2
+	triggerFeeUpdate(newFeeRate, minRelayFee, minRelayFee, true)
 }
 
 // TestChannelLinkAcceptDuplicatePayment tests that if a link receives an