Merge pull request #3691 from halseth/link-bandwitch-amt-aware

lnwallet: Make available balance HTLC fee aware

htlcswitch/link.go

@@ -2163,26 +2163,21 @@ func (l *channelLink) ChanID() lnwire.ChannelID {
 //
 // NOTE: Part of the ChannelLink interface.
 func (l *channelLink) Bandwidth() lnwire.MilliSatoshi {
+	// Get the balance available on the channel for new HTLCs. This takes
+	// the channel reserve into account so HTLCs up to this value won't
+	// violate it.
 	channelBandwidth := l.channel.AvailableBalance()
-	overflowBandwidth := l.overflowQueue.TotalHtlcAmount()
 
 	// To compute the total bandwidth, we'll take the current available
 	// bandwidth, then subtract the overflow bandwidth as we'll eventually
 	// also need to evaluate those HTLC's once space on the commitment
 	// transaction is free.
-	linkBandwidth := channelBandwidth - overflowBandwidth
-
-	// If the channel reserve is greater than the total available balance
-	// of the link, just return 0.
-	reserve := lnwire.NewMSatFromSatoshis(l.channel.LocalChanReserve())
-	if linkBandwidth < reserve {
+	overflowBandwidth := l.overflowQueue.TotalHtlcAmount()
+	if channelBandwidth < overflowBandwidth {
 		return 0
 	}
 
-	// Else the amount that is available to flow through the link at this
-	// point is the available balance minus the reserve amount we are
-	// required to keep as collateral.
-	return linkBandwidth - reserve
+	return channelBandwidth - overflowBandwidth
 }
 
 // AttachMailBox updates the current mailbox used by this link, and hooks up

htlcswitch/link_test.go

@@ -1983,8 +1983,11 @@ func TestChannelLinkBandwidthConsistency(t *testing.T) {
 	)
 
 	// The starting bandwidth of the channel should be exactly the amount
-	// that we created the channel between her and Bob.
-	expectedBandwidth := lnwire.NewMSatFromSatoshis(chanAmt - defaultCommitFee)
+	// that we created the channel between her and Bob, minus the
+	// commitment fee and fee for adding an additional HTLC.
+	expectedBandwidth := lnwire.NewMSatFromSatoshis(
+		chanAmt-defaultCommitFee,
+	) - htlcFee
 	assertLinkBandwidth(t, aliceLink, expectedBandwidth)
 
 	// Next, we'll create an HTLC worth 1 BTC, and send it into the link as
@@ -2657,8 +2660,10 @@ func TestChannelLinkTrimCircuitsPending(t *testing.T) {
 
 	// The starting bandwidth of the channel should be exactly the amount
 	// that we created the channel between her and Bob, minus the commitment
-	// fee.
-	expectedBandwidth := lnwire.NewMSatFromSatoshis(chanAmt - defaultCommitFee)
+	// fee and fee of adding an HTLC.
+	expectedBandwidth := lnwire.NewMSatFromSatoshis(
+		chanAmt-defaultCommitFee,
+	) - htlcFee
 	assertLinkBandwidth(t, alice.link, expectedBandwidth)
 
 	// Capture Alice's starting bandwidth to perform later, relative
@@ -2936,8 +2941,10 @@ func TestChannelLinkTrimCircuitsNoCommit(t *testing.T) {
 
 	// The starting bandwidth of the channel should be exactly the amount
 	// that we created the channel between her and Bob, minus the commitment
-	// fee.
-	expectedBandwidth := lnwire.NewMSatFromSatoshis(chanAmt - defaultCommitFee)
+	// fee and fee for adding an additional HTLC.
+	expectedBandwidth := lnwire.NewMSatFromSatoshis(
+		chanAmt-defaultCommitFee,
+	) - htlcFee
 	assertLinkBandwidth(t, alice.link, expectedBandwidth)
 
 	// Capture Alice's starting bandwidth to perform later, relative
@@ -3192,9 +3199,9 @@ func TestChannelLinkBandwidthChanReserve(t *testing.T) {
 
 	// The starting bandwidth of the channel should be exactly the amount
 	// that we created the channel between her and Bob, minus the channel
-	// reserve.
+	// reserve, commitment fee and fee for adding an additional HTLC.
 	expectedBandwidth := lnwire.NewMSatFromSatoshis(
-		chanAmt - defaultCommitFee - chanReserve)
+		chanAmt-defaultCommitFee-chanReserve) - htlcFee
 	assertLinkBandwidth(t, aliceLink, expectedBandwidth)
 
 	// Next, we'll create an HTLC worth 3 BTC, and send it into the link as