multi: thread bandwidth check amount down to MayAddOutgoingHtlc

Pass htlc amount down to the channel so that we don't need to rely
on minHtlc (and pad it when the channel sets a 0 min htlc). Update
test to just check some sane values since we're no longer relying
on minHtlc amount at all.

routing/bandwidth.go

@@ -12,8 +12,13 @@ import (
 type bandwidthHints interface {
 	// availableChanBandwidth returns the total available bandwidth for a
 	// channel and a bool indicating whether the channel hint was found.
-	// If the channel is unavailable, a zero amount is returned.
-	availableChanBandwidth(channelID uint64) (lnwire.MilliSatoshi, bool)
+	// The amount parameter is used to validate the outgoing htlc amount
+	// that we wish to add to the channel against its flow restrictions. If
+	// a zero amount is provided, the minimum htlc value for the channel
+	// will be used. If the channel is unavailable, a zero amount is
+	// returned.
+	availableChanBandwidth(channelID uint64,
+		amount lnwire.MilliSatoshi) (lnwire.MilliSatoshi, bool)
 }
 
 // getLinkQuery is the function signature used to lookup a link.
@@ -65,7 +70,8 @@ func newBandwidthManager(graph routingGraph, sourceNode route.Vertex,
 // available bandwidth. Note that this function assumes that the channel being
 // queried is one of our local channels, so any failure to retrieve the link
 // is interpreted as the link being offline.
-func (b *bandwidthManager) getBandwidth(cid lnwire.ShortChannelID) lnwire.MilliSatoshi {
+func (b *bandwidthManager) getBandwidth(cid lnwire.ShortChannelID,
+	amount lnwire.MilliSatoshi) lnwire.MilliSatoshi {
 	link, err := b.getLink(cid)
 	if err != nil {
 		// If the link isn't online, then we'll report that it has
@@ -82,7 +88,7 @@ func (b *bandwidthManager) getBandwidth(cid lnwire.ShortChannelID) lnwire.MilliS
 
 	// If our link isn't currently in a state where it can  add another
 	// outgoing htlc, treat the link as unusable.
-	if err := link.MayAddOutgoingHtlc(); err != nil {
+	if err := link.MayAddOutgoingHtlc(amount); err != nil {
 		return 0
 	}
 
@@ -94,8 +100,8 @@ func (b *bandwidthManager) getBandwidth(cid lnwire.ShortChannelID) lnwire.MilliS
 // availableChanBandwidth returns the total available bandwidth for a channel
 // and a bool indicating whether the channel hint was found. If the channel is
 // unavailable, a zero amount is returned.
-func (b *bandwidthManager) availableChanBandwidth(channelID uint64) (
-	lnwire.MilliSatoshi, bool) {
+func (b *bandwidthManager) availableChanBandwidth(channelID uint64,
+	amount lnwire.MilliSatoshi) (lnwire.MilliSatoshi, bool) {
 
 	shortID := lnwire.NewShortChanIDFromInt(channelID)
 	_, ok := b.localChans[shortID]
@@ -103,5 +109,5 @@ func (b *bandwidthManager) availableChanBandwidth(channelID uint64) (
 		return 0, false
 	}
 
-	return b.getBandwidth(shortID), true
+	return b.getBandwidth(shortID, amount), true
 }

routing/bandwidth_test.go

@@ -119,7 +119,7 @@ func TestBandwidthManager(t *testing.T) {
 			require.NoError(t, err)
 
 			bandwidth, found := m.availableChanBandwidth(
-				testCase.channelID,
+				testCase.channelID, 10,
 			)
 			require.Equal(t, testCase.expectedBandwidth, bandwidth)
 			require.Equal(t, testCase.expectFound, found)

routing/integrated_routing_context_test.go

@@ -22,8 +22,8 @@ type mockBandwidthHints struct {
 	hints map[uint64]lnwire.MilliSatoshi
 }
 
-func (m *mockBandwidthHints) availableChanBandwidth(channelID uint64) (
-	lnwire.MilliSatoshi, bool) {
+func (m *mockBandwidthHints) availableChanBandwidth(channelID uint64,
+	_ lnwire.MilliSatoshi) (lnwire.MilliSatoshi, bool) {
 
 	if m.hints == nil {
 		return 0, false

routing/mock_test.go

@@ -760,6 +760,6 @@ func (m *mockLink) EligibleToForward() bool {
 }
 
 // MayAddOutgoingHtlc returns the error configured in our mock.
-func (m *mockLink) MayAddOutgoingHtlc() error {
+func (m *mockLink) MayAddOutgoingHtlc(_ lnwire.MilliSatoshi) error {
 	return m.mayAddOutgoingErr
 }

routing/pathfind.go

@@ -373,7 +373,9 @@ func getOutgoingBalance(node route.Vertex, outgoingChans map[uint64]struct{},
 			}
 		}
 
-		bandwidth, ok := bandwidthHints.availableChanBandwidth(chanID)
+		bandwidth, ok := bandwidthHints.availableChanBandwidth(
+			chanID, 0,
+		)
 
 		// If the bandwidth is not available, use the channel capacity.
 		// This can happen when a channel is added to the graph after

routing/unified_policies.go

@@ -170,7 +170,7 @@ func (u *unifiedPolicy) getPolicyLocal(amt lnwire.MilliSatoshi,
 		// channel. The bandwidth hint is expected to be
 		// available.
 		bandwidth, ok := bandwidthHints.availableChanBandwidth(
-			edge.policy.ChannelID,
+			edge.policy.ChannelID, amt,
 		)
 		if !ok {
 			bandwidth = lnwire.MaxMilliSatoshi