multi: set zero bandwidth hint for channels that do not have any available slots

htlcswitch/interfaces.go

@@ -145,6 +145,10 @@ type ChannelLink interface {
 	// will use this function in forwarding decisions accordingly.
 	EligibleToForward() bool
 
+	// MayAddOutgoingHtlc returns an error if we may not add an outgoing
+	// htlc to the channel.
+	MayAddOutgoingHtlc() error
+
 	// AttachMailBox delivers an active MailBox to the link. The MailBox may
 	// have buffered messages.
 	AttachMailBox(MailBox)

htlcswitch/link.go

@@ -2156,6 +2156,12 @@ func (l *channelLink) Bandwidth() lnwire.MilliSatoshi {
 	return l.channel.AvailableBalance()
 }
 
+// MayAddOutgoingHtlc indicates whether we may add any more outgoing htlcs to
+// this channel.
+func (l *channelLink) MayAddOutgoingHtlc() error {
+	return l.channel.MayAddOutgoingHtlc()
+}
+
 // AttachMailBox updates the current mailbox used by this link, and hooks up
 // the mailbox's message and packet outboxes to the link's upstream and
 // downstream chans, respectively.

htlcswitch/mock.go

@@ -756,6 +756,7 @@ func (f *mockChannelLink) Peer() lnpeer.Peer                            { return
 func (f *mockChannelLink) ChannelPoint() *wire.OutPoint                 { return &wire.OutPoint{} }
 func (f *mockChannelLink) Stop()                                        {}
 func (f *mockChannelLink) EligibleToForward() bool                      { return f.eligible }
+func (f *mockChannelLink) MayAddOutgoingHtlc() error                    { return nil }
 func (f *mockChannelLink) setLiveShortChanID(sid lnwire.ShortChannelID) { f.shortChanID = sid }
 func (f *mockChannelLink) UpdateShortChanID() (lnwire.ShortChannelID, error) {
 	f.eligible = true

lntest/itest/lnd_max_htlcs_test.go

@@ -0,0 +1,229 @@
+package itest
+
+import (
+	"context"
+	"testing"
+
+	"github.com/lightningnetwork/lnd/lnrpc"
+	"github.com/lightningnetwork/lnd/lnrpc/invoicesrpc"
+	"github.com/lightningnetwork/lnd/lnrpc/routerrpc"
+	"github.com/lightningnetwork/lnd/lntest"
+	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/stretchr/testify/require"
+)
+
+// testMaxHtlcPathfind tests the case where we try to send a payment over a
+// channel where we have already reached the limit of the number of htlcs that
+// we may add to the remote party's commitment. This test asserts that we do
+// not attempt to use the full channel at all in our pathfinding.
+func testMaxHtlcPathfind(net *lntest.NetworkHarness, t *harnessTest) {
+	ctxb := context.Background()
+
+	// Setup a channel between Alice and Bob where Alice will only allow
+	// Bob to add a maximum of 5 htlcs to her commitment.
+	maxHtlcs := 5
+
+	ctxt, _ := context.WithTimeout(ctxb, channelOpenTimeout)
+	chanPoint := openChannelAndAssert(
+		ctxt, t, net, net.Alice, net.Bob,
+		lntest.OpenChannelParams{
+			Amt:            1000000,
+			PushAmt:        800000,
+			RemoteMaxHtlcs: uint16(maxHtlcs),
+		},
+	)
+
+	// Wait for Alice and Bob to receive the channel edge from the
+	// funding manager.
+	ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
+	err := net.Alice.WaitForNetworkChannelOpen(ctxt, chanPoint)
+	require.NoError(t.t, err, "alice does not have open channel")
+
+	ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
+	err = net.Bob.WaitForNetworkChannelOpen(ctxt, chanPoint)
+	require.NoError(t.t, err, "bob does not have open channel")
+
+	// Alice and bob should have one channel open with each other now.
+	assertNodeNumChannels(t, net.Alice, 1)
+	assertNodeNumChannels(t, net.Bob, 1)
+
+	// Send our maximum number of htlcs from Bob -> Alice so that we get
+	// to a point where Alice won't accept any more htlcs on the channel.
+	subscriptions := make([]*holdSubscription, maxHtlcs)
+	cancelCtxs := make([]func(), maxHtlcs)
+
+	for i := 0; i < maxHtlcs; i++ {
+		subCtx, cancel := context.WithTimeout(ctxb, defaultTimeout)
+		cancelCtxs[i] = cancel
+
+		subscriptions[i] = acceptHoldInvoice(
+			subCtx, t.t, i, net.Bob, net.Alice,
+		)
+	}
+
+	// Cancel all of our subscriptions on exit.
+	defer func() {
+		for _, cancel := range cancelCtxs {
+			cancel()
+		}
+	}()
+
+	err = assertNumActiveHtlcs([]*lntest.HarnessNode{
+		net.Alice, net.Bob,
+	}, maxHtlcs)
+	require.NoError(t.t, err, "htlcs not active")
+
+	// Now we send a payment from Alice -> Bob to sanity check that our
+	// commitment limit is not applied in the opposite direction.
+	subCtx, cancel := context.WithTimeout(ctxb, defaultTimeout)
+	defer cancel()
+	aliceBobSub := acceptHoldInvoice(
+		subCtx, t.t, maxHtlcs, net.Alice, net.Bob,
+	)
+	err = assertNumActiveHtlcs([]*lntest.HarnessNode{
+		net.Alice, net.Bob,
+	}, maxHtlcs+1)
+	require.NoError(t.t, err, "htlcs not active")
+
+	// Now, we're going to try to send another payment from Bob -> Alice.
+	// We've hit our max remote htlcs, so we expect this payment to spin
+	// out dramatically with pathfinding.
+	ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
+	payment, err := net.Bob.RouterClient.SendPaymentV2(
+		ctxt, &routerrpc.SendPaymentRequest{
+			Amt:            1000,
+			Dest:           net.Alice.PubKey[:],
+			TimeoutSeconds: 60,
+			FeeLimitSat:    1000000,
+			MaxParts:       10,
+			Amp:            true,
+		},
+	)
+	require.NoError(t.t, err, "send payment failed")
+
+	update, err := payment.Recv()
+	require.NoError(t.t, err, "no payment in flight update")
+	require.Equal(t.t, lnrpc.Payment_IN_FLIGHT, update.Status,
+		"payment not inflight")
+
+	update, err = payment.Recv()
+	require.NoError(t.t, err, "no payment failed update")
+	require.Equal(t.t, lnrpc.Payment_FAILED, update.Status)
+	require.Len(t.t, update.Htlcs, 0, "expected no htlcs dispatched")
+
+	// Now that we're done, we cancel all our pending htlcs so that we
+	// can cleanup the channel with a coop close.
+	for _, sub := range subscriptions {
+		ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
+		sub.cancel(ctxt, t.t)
+	}
+
+	ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
+	aliceBobSub.cancel(ctxt, t.t)
+
+	err = assertNumActiveHtlcs([]*lntest.HarnessNode{
+		net.Alice, net.Bob,
+	}, 0)
+	require.NoError(t.t, err, "expected all htlcs canceled")
+
+	ctxt, _ = context.WithTimeout(ctxb, channelCloseTimeout)
+	closeChannelAndAssert(ctxt, t, net, net.Alice, chanPoint, false)
+}
+
+type holdSubscription struct {
+	recipient           invoicesrpc.InvoicesClient
+	hash                lntypes.Hash
+	invSubscription     invoicesrpc.Invoices_SubscribeSingleInvoiceClient
+	paymentSubscription routerrpc.Router_SendPaymentV2Client
+}
+
+// cancel updates a hold invoice to cancel from the recipient and consumes
+// updates from the payer until it has reached a final, failed state.
+func (h *holdSubscription) cancel(ctx context.Context, t *testing.T) {
+	_, err := h.recipient.CancelInvoice(ctx, &invoicesrpc.CancelInvoiceMsg{
+		PaymentHash: h.hash[:],
+	})
+	require.NoError(t, err, "invoice cancel failed")
+
+	invUpdate, err := h.invSubscription.Recv()
+	require.NoError(t, err, "cancel invoice subscribe failed")
+	require.Equal(t, lnrpc.Invoice_CANCELED, invUpdate.State,
+		"expected invoice canceled")
+
+	// We expect one in flight update when our htlc is canceled back, and
+	// another when we fail the payment as a whole.
+	payUpdate, err := h.paymentSubscription.Recv()
+	require.NoError(t, err, "cancel payment subscribe failed")
+	require.Len(t, payUpdate.Htlcs, 1)
+	require.Equal(t, lnrpc.Payment_IN_FLIGHT, payUpdate.Status)
+
+	payUpdate, err = h.paymentSubscription.Recv()
+	require.NoError(t, err, "cancel payment subscribe failed")
+	require.Equal(t, lnrpc.Payment_FAILED, payUpdate.Status,
+		"expected payment failed")
+	require.Equal(t, lnrpc.PaymentFailureReason_FAILURE_REASON_INCORRECT_PAYMENT_DETAILS,
+		payUpdate.FailureReason, "expected unknown details")
+}
+
+// acceptHoldInvoice adds a hold invoice to the recipient node, pays it from
+// the sender and asserts that we have reached the accepted state where htlcs
+// are locked in for the payment.
+func acceptHoldInvoice(ctx context.Context, t *testing.T, idx int, sender,
+	receiver *lntest.HarnessNode) *holdSubscription {
+
+	hash := [lntypes.HashSize]byte{byte(idx + 1)}
+
+	invoice, err := receiver.AddHoldInvoice(
+		ctx, &invoicesrpc.AddHoldInvoiceRequest{
+			ValueMsat: 10000,
+			Hash:      hash[:],
+		},
+	)
+	require.NoError(t, err, "couldn't add invoice")
+
+	invStream, err := receiver.InvoicesClient.SubscribeSingleInvoice(
+		ctx, &invoicesrpc.SubscribeSingleInvoiceRequest{
+			RHash: hash[:],
+		},
+	)
+	require.NoError(t, err, "could not subscribe to invoice")
+
+	inv, err := invStream.Recv()
+	require.NoError(t, err, "invoice open stream failed")
+	require.Equal(t, lnrpc.Invoice_OPEN, inv.State,
+		"expected open")
+
+	payStream, err := sender.RouterClient.SendPaymentV2(
+		ctx, &routerrpc.SendPaymentRequest{
+			PaymentRequest: invoice.PaymentRequest,
+			TimeoutSeconds: 60,
+			FeeLimitSat:    1000000,
+		},
+	)
+	require.NoError(t, err, "send payment failed")
+
+	// Finally, assert that we progress to an accepted state. We expect
+	// the payer to get one update for the creation of the payment, and
+	// another when a htlc is dispatched.
+	payment, err := payStream.Recv()
+	require.NoError(t, err, "payment in flight stream failed")
+	require.Equal(t, lnrpc.Payment_IN_FLIGHT, payment.Status)
+	require.Len(t, payment.Htlcs, 0)
+
+	payment, err = payStream.Recv()
+	require.NoError(t, err, "payment in flight stream failed")
+	require.Equal(t, lnrpc.Payment_IN_FLIGHT, payment.Status)
+	require.Len(t, payment.Htlcs, 1)
+
+	inv, err = invStream.Recv()
+	require.NoError(t, err, "invoice accepted stream failed")
+	require.Equal(t, lnrpc.Invoice_ACCEPTED, inv.State,
+		"expected accepted invoice")
+
+	return &holdSubscription{
+		recipient:           receiver.InvoicesClient,
+		hash:                hash,
+		invSubscription:     invStream,
+		paymentSubscription: payStream,
+	}
+}

lntest/itest/lnd_test_list_on_test.go

@@ -322,4 +322,8 @@ var allTestCases = []*testCase{
 		name: "etcd_failover",
 		test: testEtcdFailover,
 	},
+	{
+		name: "max htlc pathfind",
+		test: testMaxHtlcPathfind,
+	},
 }

lnwallet/channel.go

@@ -4924,7 +4924,49 @@ func (lc *LightningChannel) AddHTLC(htlc *lnwire.UpdateAddHTLC,
 	lc.Lock()
 	defer lc.Unlock()
 
-	pd := &PaymentDescriptor{
+	pd := lc.htlcAddDescriptor(htlc, openKey)
+	if err := lc.validateAddHtlc(pd); err != nil {
+		return 0, err
+	}
+
+	lc.localUpdateLog.appendHtlc(pd)
+
+	return pd.HtlcIndex, nil
+}
+
+// MayAddOutgoingHtlc validates whether we can add an outgoing htlc to this
+// channel. We don't have a value or circuit for this htlc, because we just
+// want to test that we have slots for a potential htlc so we use a "mock"
+// htlc to validate a potential commitment state with one more outgoing htlc.
+func (lc *LightningChannel) MayAddOutgoingHtlc() error {
+	lc.Lock()
+	defer lc.Unlock()
+
+	// Create a "mock" outgoing htlc, using the smallest amount we can add
+	// to the commitment so that we validate commitment slots rather than
+	// available balance, since our actual htlc amount is unknown at this
+	// stage.
+	pd := lc.htlcAddDescriptor(
+		&lnwire.UpdateAddHTLC{
+			Amount: lc.channelState.LocalChanCfg.MinHTLC,
+		},
+		&channeldb.CircuitKey{},
+	)
+
+	if err := lc.validateAddHtlc(pd); err != nil {
+		lc.log.Debugf("May add outgoing htlc rejected: %v", err)
+		return err
+	}
+
+	return nil
+}
+
+// htlcAddDescriptor returns a payment descriptor for the htlc and open key
+// provided to add to our local update log.
+func (lc *LightningChannel) htlcAddDescriptor(htlc *lnwire.UpdateAddHTLC,
+	openKey *channeldb.CircuitKey) *PaymentDescriptor {
+
+	return &PaymentDescriptor{
 		EntryType:      Add,
 		RHash:          PaymentHash(htlc.PaymentHash),
 		Timeout:        htlc.Expiry,
@@ -4934,7 +4976,11 @@ func (lc *LightningChannel) AddHTLC(htlc *lnwire.UpdateAddHTLC,
 		OnionBlob:      htlc.OnionBlob[:],
 		OpenCircuitKey: openKey,
 	}
+}
 
+// validateAddHtlc validates the addition of an outgoing htlc to our local and
+// remote commitments.
+func (lc *LightningChannel) validateAddHtlc(pd *PaymentDescriptor) error {
 	// Make sure adding this HTLC won't violate any of the constraints we
 	// must keep on the commitment transactions.
 	remoteACKedIndex := lc.localCommitChain.tail().theirMessageIndex
@@ -4945,7 +4991,7 @@ func (lc *LightningChannel) AddHTLC(htlc *lnwire.UpdateAddHTLC,
 		remoteACKedIndex, lc.localUpdateLog.logIndex, true, pd, nil,
 	)
 	if err != nil {
-		return 0, err
+		return err
 	}
 
 	// We must also check whether it can be added to our own commitment
@@ -4958,12 +5004,10 @@ func (lc *LightningChannel) AddHTLC(htlc *lnwire.UpdateAddHTLC,
 		false, pd, nil,
 	)
 	if err != nil {
-		return 0, err
+		return err
 	}
 
-	lc.localUpdateLog.appendHtlc(pd)
-
-	return pd.HtlcIndex, nil
+	return nil
 }
 
 // ReceiveHTLC adds an HTLC to the state machine's remote update log. This

server.go

@@ -718,6 +718,12 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 			return 0
 		}
 
+		// 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 {
+			return 0
+		}
+
 		// Otherwise, we'll return the current best estimate
 		// for the available bandwidth for the link.
 		return link.Bandwidth()