Merge pull request #5253 from cfromknecht/amp-invoice

Support paying AMP invoices via SendPaymentV2

channeldb/invoice_test.go

@@ -1294,9 +1294,9 @@ func TestHTLCSet(t *testing.T) {
 	expSet2 := make(map[CircuitKey]*InvoiceHTLC)
 
 	checkHTLCSets := func() {
-		require.Equal(t, expSetNil, inv.HTLCSet(nil))
-		require.Equal(t, expSet1, inv.HTLCSet(setID1))
-		require.Equal(t, expSet2, inv.HTLCSet(setID2))
+		require.Equal(t, expSetNil, inv.HTLCSet(nil, HtlcStateAccepted))
+		require.Equal(t, expSet1, inv.HTLCSet(setID1, HtlcStateAccepted))
+		require.Equal(t, expSet2, inv.HTLCSet(setID2, HtlcStateAccepted))
 	}
 
 	// All HTLC sets should be empty initially.

channeldb/invoices.go

@@ -471,17 +471,16 @@ type Invoice struct {
 	HodlInvoice bool
 }
 
-// HTLCSet returns the set of accepted HTLCs belonging to an invoice. Passing a
-// nil setID will return all accepted HTLCs in the case of legacy or MPP, and no
-// HTLCs in the case of AMP.  Otherwise, the returned set will be filtered by
-// the populated setID which is used to retrieve AMP HTLC sets.
-func (i *Invoice) HTLCSet(setID *[32]byte) map[CircuitKey]*InvoiceHTLC {
+// HTLCSet returns the set of HTLCs belonging to setID and in the provided
+// state. Passing a nil setID will return all HTLCs in the provided state in the
+// case of legacy or MPP, and no HTLCs in the case of AMP.  Otherwise, the
+// returned set will be filtered by the populated setID which is used to
+// retrieve AMP HTLC sets.
+func (i *Invoice) HTLCSet(setID *[32]byte, state HtlcState) map[CircuitKey]*InvoiceHTLC {
 	htlcSet := make(map[CircuitKey]*InvoiceHTLC)
 	for key, htlc := range i.Htlcs {
-		// Only consider accepted mpp htlcs. It is possible that there
-		// are htlcs registered in the invoice database that previously
-		// timed out and are in the canceled state now.
-		if htlc.State != HtlcStateAccepted {
+		// Only add HTLCs that are in the requested HtlcState.
+		if htlc.State != state {
 			continue
 		}
 
@@ -495,6 +494,31 @@ func (i *Invoice) HTLCSet(setID *[32]byte) map[CircuitKey]*InvoiceHTLC {
 	return htlcSet
 }
 
+// HTLCSetCompliment returns the set of all HTLCs not belonging to setID that
+// are in the target state. Passing a nil setID will return no invoices, since
+// all MPP HTLCs are part of the same HTLC set.
+func (i *Invoice) HTLCSetCompliment(setID *[32]byte,
+	state HtlcState) map[CircuitKey]*InvoiceHTLC {
+
+	htlcSet := make(map[CircuitKey]*InvoiceHTLC)
+	for key, htlc := range i.Htlcs {
+		// Only add HTLCs that are in the requested HtlcState.
+		if htlc.State != state {
+			continue
+		}
+
+		// We are constructing the compliment, so filter anything that
+		// matches this set id.
+		if htlc.IsInHTLCSet(setID) {
+			continue
+		}
+
+		htlcSet[key] = htlc
+	}
+
+	return htlcSet
+}
+
 // HtlcState defines the states an htlc paying to an invoice can be in.
 type HtlcState uint8
 
@@ -2039,7 +2063,7 @@ func updateInvoiceState(invoice *Invoice, hash *lntypes.Hash,
 
 		// Sanity check that the user isn't trying to settle or accept a
 		// non-existent HTLC set.
-		if len(invoice.HTLCSet(update.SetID)) == 0 {
+		if len(invoice.HTLCSet(update.SetID, HtlcStateAccepted)) == 0 {
 			return ErrEmptyHTLCSet
 		}
 
@@ -2329,8 +2353,8 @@ func (d *DB) DeleteInvoice(invoicesToDelete []InvoiceDeleteRef) error {
 			// invoice key.
 			key := invoiceAddIndex.Get(addIndexKey[:])
 			if !bytes.Equal(key, invoiceKey) {
-				return fmt.Errorf("unknown invoice in " +
-					"add index")
+				return fmt.Errorf("unknown invoice " +
+					"in add index")
 			}
 
 			// Remove from the add index.

cmd/lncli/cmd_invoice.go

@@ -66,6 +66,11 @@ var addInvoiceCommand = cli.Command{
 				"private channels in order to assist the " +
 				"payer in reaching you",
 		},
+		cli.BoolFlag{
+			Name: "amp",
+			Usage: "creates an AMP invoice. If true, preimage " +
+				"should not be set.",
+		},
 	},
 	Action: actionDecorator(addInvoice),
 }
@@ -119,6 +124,7 @@ func addInvoice(ctx *cli.Context) error {
 		FallbackAddr:    ctx.String("fallback_addr"),
 		Expiry:          ctx.Int64("expiry"),
 		Private:         ctx.Bool("private"),
+		IsAmp:           ctx.Bool("amp"),
 	}
 
 	resp, err := client.AddInvoice(ctxc, invoice)

cmd/lncli/cmd_pay.go

@@ -87,6 +87,12 @@ var (
 			"payment splitting is required to attempt a payment, " +
 			"specified in milli-satoshis",
 	}
+
+	ampFlag = cli.BoolFlag{
+		Name: "amp",
+		Usage: "if set to true, then AMP will be used to complete the " +
+			"payment",
+	}
 )
 
 // paymentFlags returns common flags for sendpayment and payinvoice.
@@ -131,7 +137,7 @@ func paymentFlags() []cli.Flag {
 			Usage: "allow sending a circular payment to self",
 		},
 		dataFlag, inflightUpdatesFlag, maxPartsFlag, jsonFlag,
-		maxShardSizeSatFlag, maxShardSizeMsatFlag,
+		maxShardSizeSatFlag, maxShardSizeMsatFlag, ampFlag,
 	}
 }
 
@@ -287,11 +293,16 @@ func sendPayment(ctx *cli.Context) error {
 		Dest:              destNode,
 		Amt:               amount,
 		DestCustomRecords: make(map[uint64][]byte),
+		Amp:               ctx.Bool(ampFlag.Name),
 	}
 
 	var rHash []byte
 
-	if ctx.Bool("keysend") {
+	switch {
+	case ctx.Bool("keysend") && ctx.Bool(ampFlag.Name):
+		return errors.New("either keysend or amp may be set, but not both")
+
+	case ctx.Bool("keysend"):
 		if ctx.IsSet("payment_hash") {
 			return errors.New("cannot set payment hash when using " +
 				"keysend")
@@ -308,7 +319,7 @@ func sendPayment(ctx *cli.Context) error {
 
 		hash := preimage.Hash()
 		rHash = hash[:]
-	} else {
+	case !ctx.Bool(ampFlag.Name):
 		switch {
 		case ctx.IsSet("payment_hash"):
 			rHash, err = hex.DecodeString(ctx.String("payment_hash"))
@@ -323,7 +334,7 @@ func sendPayment(ctx *cli.Context) error {
 	if err != nil {
 		return err
 	}
-	if len(rHash) != 32 {
+	if !req.Amp && len(rHash) != 32 {
 		return fmt.Errorf("payment hash must be exactly 32 "+
 			"bytes, is instead %v", len(rHash))
 	}

config.go

@@ -338,6 +338,8 @@ type Config struct {
 
 	AcceptKeySend bool `long:"accept-keysend" description:"If true, spontaneous payments through keysend will be accepted. [experimental]"`
 
+	AcceptAMP bool `long:"accept-amp" description:"If true, spontaneous payments via AMP will be accepted."`
+
 	KeysendHoldTime time.Duration `long:"keysend-hold-time" description:"If non-zero, keysend payments are accepted but not immediately settled. If the payment isn't settled manually after the specified time, it is canceled automatically. [experimental]"`
 
 	GcCanceledInvoicesOnStartup bool `long:"gc-canceled-invoices-on-startup" description:"If true, we'll attempt to garbage collect canceled invoices upon start."`

feature/default_sets.go

@@ -22,6 +22,7 @@ var defaultSetDesc = setDesc{
 		SetInit:         {}, // I
 		SetNodeAnn:      {}, // N
 		SetInvoice:      {}, // 9
+		SetInvoiceAmp:   {}, // 9A
 		SetLegacyGlobal: {},
 	},
 	lnwire.StaticRemoteKeyRequired: {
@@ -34,9 +35,10 @@ var defaultSetDesc = setDesc{
 		SetNodeAnn: {}, // N
 	},
 	lnwire.PaymentAddrRequired: {
-		SetInit:    {}, // I
-		SetNodeAnn: {}, // N
-		SetInvoice: {}, // 9
+		SetInit:       {}, // I
+		SetNodeAnn:    {}, // N
+		SetInvoice:    {}, // 9
+		SetInvoiceAmp: {}, // 9A
 	},
 	lnwire.MPPOptional: {
 		SetInit:    {}, // I
@@ -54,6 +56,8 @@ var defaultSetDesc = setDesc{
 	lnwire.AMPOptional: {
 		SetInit:    {}, // I
 		SetNodeAnn: {}, // N
-		SetInvoice: {}, // 9
+	},
+	lnwire.AMPRequired: {
+		SetInvoiceAmp: {}, // 9A
 	},
 }

feature/set.go

@@ -22,6 +22,10 @@ const (
 	// SetInvoice identifies features that should be advertised on invoices
 	// generated by the daemon.
 	SetInvoice
+
+	// SetInvoiceAmp identifies the features that should be advertised on
+	// AMP invoices generated by the daemon.
+	SetInvoiceAmp
 )
 
 // String returns a human-readable description of a Set.
@@ -35,6 +39,8 @@ func (s Set) String() string {
 		return "SetNodeAnn"
 	case SetInvoice:
 		return "SetInvoice"
+	case SetInvoiceAmp:
+		return "SetInvoiceAmp"
 	default:
 		return "SetUnknown"
 	}

invoices/invoiceregistry.go

@@ -57,6 +57,10 @@ type RegistryConfig struct {
 	// send payments.
 	AcceptKeySend bool
 
+	// AcceptAMP indicates whether we want to accept spontaneous AMP
+	// payments.
+	AcceptAMP bool
+
 	// GcCanceledInvoicesOnStartup if set, we'll attempt to garbage collect
 	// all canceled invoices upon start.
 	GcCanceledInvoicesOnStartup bool
@@ -884,28 +888,33 @@ func (i *InvoiceRegistry) NotifyExitHopHtlc(rHash lntypes.Hash,
 		amp:                  payload.AMPRecord(),
 	}
 
-	// Process keysend if present. Do this outside of the lock, because
-	// AddInvoice obtains its own lock. This is no problem, because the
-	// operation is idempotent.
-	if i.cfg.AcceptKeySend {
-		if ctx.amp != nil {
-			err := i.processAMP(ctx)
-			if err != nil {
-				ctx.log(fmt.Sprintf("amp error: %v", err))
+	switch {
 
-				return NewFailResolution(
-					circuitKey, currentHeight, ResultAmpError,
-				), nil
-			}
-		} else {
-			err := i.processKeySend(ctx)
-			if err != nil {
-				ctx.log(fmt.Sprintf("keysend error: %v", err))
+	// If we are accepting spontaneous AMP payments and this payload
+	// contains an AMP record, create an AMP invoice that will be settled
+	// below.
+	case i.cfg.AcceptAMP && ctx.amp != nil:
+		err := i.processAMP(ctx)
+		if err != nil {
+			ctx.log(fmt.Sprintf("amp error: %v", err))
 
-				return NewFailResolution(
-					circuitKey, currentHeight, ResultKeySendError,
-				), nil
-			}
+			return NewFailResolution(
+				circuitKey, currentHeight, ResultAmpError,
+			), nil
+		}
+
+	// If we are accepting spontaneous keysend payments, create a regular
+	// invoice that will be settled below. We also enforce that this is only
+	// done when no AMP payload is present since it will only be settle-able
+	// by regular HTLCs.
+	case i.cfg.AcceptKeySend && ctx.amp == nil:
+		err := i.processKeySend(ctx)
+		if err != nil {
+			ctx.log(fmt.Sprintf("keysend error: %v", err))
+
+			return NewFailResolution(
+				circuitKey, currentHeight, ResultKeySendError,
+			), nil
 		}
 	}
 
@@ -1021,15 +1030,8 @@ func (i *InvoiceRegistry) notifyExitHopHtlcLocked(
 		// Also cancel any HTLCs in the HTLC set that are also in the
 		// canceled state with the same failure result.
 		setID := ctx.setID()
-		for key, htlc := range invoice.Htlcs {
-			if htlc.State != channeldb.HtlcStateCanceled {
-				continue
-			}
-
-			if !htlc.IsInHTLCSet(setID) {
-				continue
-			}
-
+		canceledHtlcSet := invoice.HTLCSet(setID, channeldb.HtlcStateCanceled)
+		for key, htlc := range canceledHtlcSet {
 			htlcFailResolution := NewFailResolution(
 				key, int32(htlc.AcceptHeight), res.Outcome,
 			)
@@ -1047,11 +1049,9 @@ func (i *InvoiceRegistry) notifyExitHopHtlcLocked(
 		// Also settle any previously accepted htlcs. If a htlc is
 		// marked as settled, we should follow now and settle the htlc
 		// with our peer.
-		for key, htlc := range invoice.Htlcs {
-			if htlc.State != channeldb.HtlcStateSettled {
-				continue
-			}
-
+		setID := ctx.setID()
+		settledHtlcSet := invoice.HTLCSet(setID, channeldb.HtlcStateSettled)
+		for key, htlc := range settledHtlcSet {
 			preimage := res.Preimage
 			if htlc.AMP != nil && htlc.AMP.Preimage != nil {
 				preimage = *htlc.AMP.Preimage
@@ -1072,6 +1072,23 @@ func (i *InvoiceRegistry) notifyExitHopHtlcLocked(
 			i.notifyHodlSubscribers(htlcSettleResolution)
 		}
 
+		// If concurrent payments were attempted to this invoice before
+		// the current one was ultimately settled, cancel back any of
+		// the HTLCs immediately. As a result of the settle, the HTLCs
+		// in other HTLC sets are automatically converted to a canceled
+		// state when updating the invoice.
+		canceledHtlcSet := invoice.HTLCSetCompliment(
+			setID, channeldb.HtlcStateCanceled,
+		)
+		for key, htlc := range canceledHtlcSet {
+			htlcFailResolution := NewFailResolution(
+				key, int32(htlc.AcceptHeight),
+				ResultInvoiceAlreadySettled,
+			)
+
+			i.notifyHodlSubscribers(htlcFailResolution)
+		}
+
 	// If we accepted the htlc, subscribe to the hodl invoice and return
 	// an accept resolution with the htlc's accept time on it.
 	case *htlcAcceptResolution:

invoices/invoiceregistry_test.go

@@ -1290,7 +1290,7 @@ func TestAMPWithoutMPPPayload(t *testing.T) {
 	ctx := newTestContext(t)
 	defer ctx.cleanup()
 
-	ctx.registry.cfg.AcceptKeySend = true
+	ctx.registry.cfg.AcceptAMP = true
 
 	const (
 		shardAmt = lnwire.MilliSatoshi(10)
@@ -1320,37 +1320,37 @@ func TestAMPWithoutMPPPayload(t *testing.T) {
 func TestSpontaneousAmpPayment(t *testing.T) {
 	tests := []struct {
 		name               string
-		keySendEnabled     bool
+		ampEnabled         bool
 		failReconstruction bool
 		numShards          int
 	}{
 		{
 			name:               "enabled valid one shard",
-			keySendEnabled:     true,
+			ampEnabled:         true,
 			failReconstruction: false,
 			numShards:          1,
 		},
 		{
 			name:               "enabled valid multiple shards",
-			keySendEnabled:     true,
+			ampEnabled:         true,
 			failReconstruction: false,
 			numShards:          3,
 		},
 		{
 			name:               "enabled invalid one shard",
-			keySendEnabled:     true,
+			ampEnabled:         true,
 			failReconstruction: true,
 			numShards:          1,
 		},
 		{
 			name:               "enabled invalid multiple shards",
-			keySendEnabled:     true,
+			ampEnabled:         true,
 			failReconstruction: true,
 			numShards:          3,
 		},
 		{
 			name:               "disabled valid multiple shards",
-			keySendEnabled:     false,
+			ampEnabled:         false,
 			failReconstruction: false,
 			numShards:          3,
 		},
@@ -1360,7 +1360,7 @@ func TestSpontaneousAmpPayment(t *testing.T) {
 		test := test
 		t.Run(test.name, func(t *testing.T) {
 			testSpontaneousAmpPayment(
-				t, test.keySendEnabled, test.failReconstruction,
+				t, test.ampEnabled, test.failReconstruction,
 				test.numShards,
 			)
 		})
@@ -1369,14 +1369,14 @@ func TestSpontaneousAmpPayment(t *testing.T) {
 
 // testSpontaneousAmpPayment runs a specific spontaneous AMP test case.
 func testSpontaneousAmpPayment(
-	t *testing.T, keySendEnabled, failReconstruction bool, numShards int) {
+	t *testing.T, ampEnabled, failReconstruction bool, numShards int) {
 
 	defer timeout()()
 
 	ctx := newTestContext(t)
 	defer ctx.cleanup()
 
-	ctx.registry.cfg.AcceptKeySend = keySendEnabled
+	ctx.registry.cfg.AcceptAMP = ampEnabled
 
 	allSubscriptions, err := ctx.registry.SubscribeNotifications(0, 0)
 	require.Nil(t, err)
@@ -1471,7 +1471,7 @@ func testSpontaneousAmpPayment(
 		// When keysend is disabled all HTLC should fail with invoice
 		// not found, since one is not inserted before executing
 		// UpdateInvoice.
-		if !keySendEnabled {
+		if !ampEnabled {
 			require.NotNil(t, resolution)
 			checkFailResolution(t, resolution, ResultInvoiceNotFound)
 			continue
@@ -1515,7 +1515,7 @@ func testSpontaneousAmpPayment(
 	}
 
 	// No need to check the hodl chans when keysend is not enabled.
-	if !keySendEnabled {
+	if !ampEnabled {
 		return
 	}
 

invoices/resolution_result.go

@@ -61,6 +61,10 @@ const (
 	// invoice that is already canceled.
 	ResultInvoiceAlreadyCanceled
 
+	// ResultInvoiceAlreadySettled is returned when trying to pay an invoice
+	// that is already settled.
+	ResultInvoiceAlreadySettled
+
 	// ResultAmountTooLow is returned when an invoice is underpaid.
 	ResultAmountTooLow
 
@@ -106,6 +110,10 @@ const (
 	// payment.
 	ResultMppInProgress
 
+	// ResultHtlcInvoiceTypeMismatch is returned when an AMP HTLC targets a
+	// non-AMP invoice and vice versa.
+	ResultHtlcInvoiceTypeMismatch
+
 	// ResultAmpError is returned when we receive invalid AMP parameters.
 	ResultAmpError
 
@@ -133,6 +141,9 @@ func (f FailResolutionResult) FailureString() string {
 	case ResultInvoiceAlreadyCanceled:
 		return "invoice already canceled"
 
+	case ResultInvoiceAlreadySettled:
+		return "invoice alread settled"
+
 	case ResultAmountTooLow:
 		return "amount too low"
 
@@ -169,6 +180,9 @@ func (f FailResolutionResult) FailureString() string {
 	case ResultMppInProgress:
 		return "mpp reception in progress"
 
+	case ResultHtlcInvoiceTypeMismatch:
+		return "htlc invoice type mismatch"
+
 	case ResultAmpError:
 		return "invalid amp parameters"
 

invoices/update.go

@@ -125,6 +125,21 @@ func updateMpp(ctx *invoiceUpdateCtx,
 	inv *channeldb.Invoice) (*channeldb.InvoiceUpdateDesc,
 	HtlcResolution, error) {
 
+	// Reject HTLCs to AMP invoices if they are missing an AMP payload, and
+	// HTLCs to MPP invoices if they have an AMP payload.
+	switch {
+
+	case inv.Terms.Features.RequiresFeature(lnwire.AMPRequired) &&
+		ctx.amp == nil:
+
+		return nil, ctx.failRes(ResultHtlcInvoiceTypeMismatch), nil
+
+	case !inv.Terms.Features.RequiresFeature(lnwire.AMPRequired) &&
+		ctx.amp != nil:
+
+		return nil, ctx.failRes(ResultHtlcInvoiceTypeMismatch), nil
+	}
+
 	setID := ctx.setID()
 
 	// Start building the accept descriptor.
@@ -168,7 +183,7 @@ func updateMpp(ctx *invoiceUpdateCtx,
 		return nil, ctx.failRes(ResultHtlcSetTotalTooLow), nil
 	}
 
-	htlcSet := inv.HTLCSet(setID)
+	htlcSet := inv.HTLCSet(setID, channeldb.HtlcStateAccepted)
 
 	// Check whether total amt matches other htlcs in the set.
 	var newSetTotal lnwire.MilliSatoshi
@@ -373,7 +388,7 @@ func updateLegacy(ctx *invoiceUpdateCtx,
 	// Don't allow settling the invoice with an old style
 	// htlc if we are already in the process of gathering an
 	// mpp set.
-	for _, htlc := range inv.HTLCSet(nil) {
+	for _, htlc := range inv.HTLCSet(nil, channeldb.HtlcStateAccepted) {
 		if htlc.MppTotalAmt > 0 {
 			return nil, ctx.failRes(ResultMppInProgress), nil
 		}

lnrpc/invoicesrpc/addinvoice.go

@@ -54,6 +54,10 @@ type AddInvoiceConfig struct {
 	// GenInvoiceFeatures returns a feature containing feature bits that
 	// should be advertised on freshly generated invoices.
 	GenInvoiceFeatures func() *lnwire.FeatureVector
+
+	// GenAmpInvoiceFeatures returns a feature containing feature bits that
+	// should be advertised on freshly generated AMP invoices.
+	GenAmpInvoiceFeatures func() *lnwire.FeatureVector
 }
 
 // AddInvoiceData contains the required data to create a new invoice.
@@ -99,17 +103,71 @@ type AddInvoiceData struct {
 	// immediately upon receiving the payment.
 	HodlInvoice bool
 
+	// Amp signals whether or not to create an AMP invoice.
+	//
+	// NOTE: Preimage should always be set to nil when this value is true.
+	Amp bool
+
 	// RouteHints are optional route hints that can each be individually used
 	// to assist in reaching the invoice's destination.
 	RouteHints [][]zpay32.HopHint
 }
 
-// AddInvoice attempts to add a new invoice to the invoice database. Any
-// duplicated invoices are rejected, therefore all invoices *must* have a
-// unique payment preimage.
-func AddInvoice(ctx context.Context, cfg *AddInvoiceConfig,
-	invoice *AddInvoiceData) (*lntypes.Hash, *channeldb.Invoice, error) {
+// paymentHashAndPreimage returns the payment hash and preimage for this invoice
+// depending on the configuration.
+//
+// For AMP invoices (when Amp flag is true), this method always returns a nil
+// preimage. The hash value can be set externally by the user using the Hash
+// field, or one will be generated randomly. The payment hash here only serves
+// as a unique identifier for insertion into the invoice index, as there is
+// no universal preimage for an AMP payment.
+//
+// For MPP invoices (when Amp flag is false), this method may return nil
+// preimage when create a hodl invoice, but otherwise will always return a
+// non-nil preimage and the corresponding payment hash. The valid combinations
+// are parsed as follows:
+//   - Preimage == nil && Hash == nil -> (random preimage, H(random preimage))
+//   - Preimage != nil && Hash == nil -> (Preimage, H(Preimage))
+//   - Preimage == nil && Hash != nil -> (nil, Hash)
+func (d *AddInvoiceData) paymentHashAndPreimage() (
+	*lntypes.Preimage, lntypes.Hash, error) {
 
+	if d.Amp {
+		return d.ampPaymentHashAndPreimage()
+	}
+
+	return d.mppPaymentHashAndPreimage()
+}
+
+// ampPaymentHashAndPreimage returns the payment hash to use for an AMP invoice.
+// The preimage will always be nil.
+func (d *AddInvoiceData) ampPaymentHashAndPreimage() (*lntypes.Preimage, lntypes.Hash, error) {
+	switch {
+
+	// Preimages cannot be set on AMP invoice.
+	case d.Preimage != nil:
+		return nil, lntypes.Hash{},
+			errors.New("preimage set on AMP invoice")
+
+	// If a specific hash was requested, use that.
+	case d.Hash != nil:
+		return nil, *d.Hash, nil
+
+	// Otherwise generate a random hash value, just needs to be unique to be
+	// added to the invoice index.
+	default:
+		var paymentHash lntypes.Hash
+		if _, err := rand.Read(paymentHash[:]); err != nil {
+			return nil, lntypes.Hash{}, err
+		}
+
+		return nil, paymentHash, nil
+	}
+}
+
+// mppPaymentHashAndPreimage returns the payment hash and preimage to use for an
+// MPP invoice.
+func (d *AddInvoiceData) mppPaymentHashAndPreimage() (*lntypes.Preimage, lntypes.Hash, error) {
 	var (
 		paymentPreimage *lntypes.Preimage
 		paymentHash     lntypes.Hash
@@ -118,28 +176,42 @@ func AddInvoice(ctx context.Context, cfg *AddInvoiceConfig,
 	switch {
 
 	// Only either preimage or hash can be set.
-	case invoice.Preimage != nil && invoice.Hash != nil:
-		return nil, nil,
+	case d.Preimage != nil && d.Hash != nil:
+		return nil, lntypes.Hash{},
 			errors.New("preimage and hash both set")
 
 	// If no hash or preimage is given, generate a random preimage.
-	case invoice.Preimage == nil && invoice.Hash == nil:
+	case d.Preimage == nil && d.Hash == nil:
 		paymentPreimage = &lntypes.Preimage{}
 		if _, err := rand.Read(paymentPreimage[:]); err != nil {
-			return nil, nil, err
+			return nil, lntypes.Hash{}, err
 		}
 		paymentHash = paymentPreimage.Hash()
 
 	// If just a hash is given, we create a hold invoice by setting the
 	// preimage to unknown.
-	case invoice.Preimage == nil && invoice.Hash != nil:
-		paymentHash = *invoice.Hash
+	case d.Preimage == nil && d.Hash != nil:
+		paymentHash = *d.Hash
 
 	// A specific preimage was supplied. Use that for the invoice.
-	case invoice.Preimage != nil && invoice.Hash == nil:
-		preimage := *invoice.Preimage
+	case d.Preimage != nil && d.Hash == nil:
+		preimage := *d.Preimage
 		paymentPreimage = &preimage
-		paymentHash = invoice.Preimage.Hash()
+		paymentHash = d.Preimage.Hash()
+	}
+
+	return paymentPreimage, paymentHash, nil
+}
+
+// AddInvoice attempts to add a new invoice to the invoice database. Any
+// duplicated invoices are rejected, therefore all invoices *must* have a
+// unique payment preimage.
+func AddInvoice(ctx context.Context, cfg *AddInvoiceConfig,
+	invoice *AddInvoiceData) (*lntypes.Hash, *channeldb.Invoice, error) {
+
+	paymentPreimage, paymentHash, err := invoice.paymentHashAndPreimage()
+	if err != nil {
+		return nil, nil, err
 	}
 
 	// The size of the memo, receipt and description hash attached must not
@@ -307,7 +379,12 @@ func AddInvoice(ctx context.Context, cfg *AddInvoiceConfig,
 	}
 
 	// Set our desired invoice features and add them to our list of options.
-	invoiceFeatures := cfg.GenInvoiceFeatures()
+	var invoiceFeatures *lnwire.FeatureVector
+	if invoice.Amp {
+		invoiceFeatures = cfg.GenAmpInvoiceFeatures()
+	} else {
+		invoiceFeatures = cfg.GenInvoiceFeatures()
+	}
 	options = append(options, zpay32.Features(invoiceFeatures))
 
 	// Generate and set a random payment address for this invoice. If the

lnrpc/invoicesrpc/config_active.go

@@ -55,4 +55,8 @@ type Config struct {
 	// GenInvoiceFeatures returns a feature containing feature bits that
 	// should be advertised on freshly generated invoices.
 	GenInvoiceFeatures func() *lnwire.FeatureVector
+
+	// GenAmpInvoiceFeatures returns a feature containing feature bits that
+	// should be advertised on freshly generated AMP invoices.
+	GenAmpInvoiceFeatures func() *lnwire.FeatureVector
 }

lnrpc/invoicesrpc/invoices.swagger.json

@@ -463,6 +463,11 @@
           "type": "string",
           "format": "byte",
           "description": "The payment address of this invoice. This value will be used in MPP\npayments, and also for newer invoies that always require the MPP paylaod\nfor added end-to-end security."
+        },
+        "is_amp": {
+          "type": "boolean",
+          "format": "boolean",
+          "description": "Signals whether or not this is an AMP invoice."
         }
       }
     },

lnrpc/invoicesrpc/invoices_server.go

@@ -308,14 +308,15 @@ func (s *Server) AddHoldInvoice(ctx context.Context,
 	invoice *AddHoldInvoiceRequest) (*AddHoldInvoiceResp, error) {
 
 	addInvoiceCfg := &AddInvoiceConfig{
-		AddInvoice:         s.cfg.InvoiceRegistry.AddInvoice,
-		IsChannelActive:    s.cfg.IsChannelActive,
-		ChainParams:        s.cfg.ChainParams,
-		NodeSigner:         s.cfg.NodeSigner,
-		DefaultCLTVExpiry:  s.cfg.DefaultCLTVExpiry,
-		ChanDB:             s.cfg.RemoteChanDB,
-		Graph:              s.cfg.LocalChanDB.ChannelGraph(),
-		GenInvoiceFeatures: s.cfg.GenInvoiceFeatures,
+		AddInvoice:            s.cfg.InvoiceRegistry.AddInvoice,
+		IsChannelActive:       s.cfg.IsChannelActive,
+		ChainParams:           s.cfg.ChainParams,
+		NodeSigner:            s.cfg.NodeSigner,
+		DefaultCLTVExpiry:     s.cfg.DefaultCLTVExpiry,
+		ChanDB:                s.cfg.RemoteChanDB,
+		Graph:                 s.cfg.LocalChanDB.ChannelGraph(),
+		GenInvoiceFeatures:    s.cfg.GenInvoiceFeatures,
+		GenAmpInvoiceFeatures: s.cfg.GenAmpInvoiceFeatures,
 	}
 
 	hash, err := lntypes.MakeHash(invoice.Hash)

lnrpc/invoicesrpc/utils.go

@@ -147,6 +147,8 @@ func CreateRPCInvoice(invoice *channeldb.Invoice,
 		rpcHtlcs = append(rpcHtlcs, &rpcHtlc)
 	}
 
+	isAmp := invoice.Terms.Features.HasFeature(lnwire.AMPOptional)
+
 	rpcInvoice := &lnrpc.Invoice{
 		Memo:            string(invoice.Memo),
 		RHash:           rHash,
@@ -170,8 +172,9 @@ func CreateRPCInvoice(invoice *channeldb.Invoice,
 		State:           state,
 		Htlcs:           rpcHtlcs,
 		Features:        CreateRPCFeatures(invoice.Terms.Features),
-		IsKeysend:       len(invoice.PaymentRequest) == 0,
+		IsKeysend:       len(invoice.PaymentRequest) == 0 && !isAmp,
 		PaymentAddr:     invoice.Terms.PaymentAddr[:],
+		IsAmp:           isAmp,
 	}
 
 	if preimage != nil {

lnrpc/routerrpc/router_backend.go

@@ -696,13 +696,37 @@ func (r *RouterBackend) extractIntentFromSendRequest(
 			payIntent.Amount = *payReq.MilliSat
 		}
 
-		if !payReq.Features.HasFeature(lnwire.MPPOptional) {
+		if !payReq.Features.HasFeature(lnwire.MPPOptional) &&
+			!payReq.Features.HasFeature(lnwire.AMPOptional) {
+
 			payIntent.MaxParts = 1
 		}
 
-		err = payIntent.SetPaymentHash(*payReq.PaymentHash)
-		if err != nil {
-			return nil, err
+		if payReq.Features.HasFeature(lnwire.AMPOptional) {
+			// Generate random SetID and root share.
+			var setID [32]byte
+			_, err = rand.Read(setID[:])
+			if err != nil {
+				return nil, err
+			}
+
+			var rootShare [32]byte
+			_, err = rand.Read(rootShare[:])
+			if err != nil {
+				return nil, err
+			}
+			err := payIntent.SetAMP(&routing.AMPOptions{
+				SetID:     setID,
+				RootShare: rootShare,
+			})
+			if err != nil {
+				return nil, err
+			}
+		} else {
+			err = payIntent.SetPaymentHash(*payReq.PaymentHash)
+			if err != nil {
+				return nil, err
+			}
 		}
 
 		destKey := payReq.Destination.SerializeCompressed()
@@ -765,7 +789,6 @@ func (r *RouterBackend) extractIntentFromSendRequest(
 				ampFeatures := []lnrpc.FeatureBit{
 					lnrpc.FeatureBit_TLV_ONION_OPT,
 					lnrpc.FeatureBit_PAYMENT_ADDR_OPT,
-					lnrpc.FeatureBit_MPP_OPT,
 					lnrpc.FeatureBit_AMP_OPT,
 				}
 

lnrpc/rpc.proto

@@ -3003,6 +3003,11 @@ message Invoice {
     for added end-to-end security.
     */
     bytes payment_addr = 26;
+
+    /*
+    Signals whether or not this is an AMP invoice.
+    */
+    bool is_amp = 27;
 }
 
 enum InvoiceHTLCState {

lnrpc/rpc.swagger.json

@@ -4387,6 +4387,11 @@
           "type": "string",
           "format": "byte",
           "description": "The payment address of this invoice. This value will be used in MPP\npayments, and also for newer invoies that always require the MPP paylaod\nfor added end-to-end security."
+        },
+        "is_amp": {
+          "type": "boolean",
+          "format": "boolean",
+          "description": "Signals whether or not this is an AMP invoice."
         }
       }
     },

lntest/itest/lnd_amp_test.go

@@ -3,6 +3,8 @@ package itest
 import (
 	"context"
 	"crypto/rand"
+	"sort"
+	"testing"
 	"time"
 
 	"github.com/btcsuite/btcutil"
@@ -15,6 +17,152 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+// testSendPaymentAMPInvoice tests that we can send an AMP payment to a
+// specified AMP invoice using SendPaymentV2.
+func testSendPaymentAMPInvoice(net *lntest.NetworkHarness, t *harnessTest) {
+	ctxb := context.Background()
+
+	ctx := newMppTestContext(t, net)
+	defer ctx.shutdownNodes()
+
+	const paymentAmt = btcutil.Amount(300000)
+
+	// Set up a network with three different paths Alice <-> Bob. Channel
+	// capacities are set such that the payment can only succeed if (at
+	// least) three paths are used.
+	//
+	//              _ Eve _
+	//             /       \
+	// Alice -- Carol ---- Bob
+	//      \              /
+	//       \__ Dave ____/
+	//
+	ctx.openChannel(ctx.carol, ctx.bob, 135000)
+	ctx.openChannel(ctx.alice, ctx.carol, 235000)
+	ctx.openChannel(ctx.dave, ctx.bob, 135000)
+	ctx.openChannel(ctx.alice, ctx.dave, 135000)
+	ctx.openChannel(ctx.eve, ctx.bob, 135000)
+	ctx.openChannel(ctx.carol, ctx.eve, 135000)
+
+	defer ctx.closeChannels()
+
+	ctx.waitForChannels()
+
+	// Subscribe to bob's invoices.
+	req := &lnrpc.InvoiceSubscription{}
+	ctxc, cancelSubscription := context.WithCancel(ctxb)
+	bobInvoiceSubscription, err := ctx.bob.SubscribeInvoices(ctxc, req)
+	require.NoError(t.t, err)
+	defer cancelSubscription()
+
+	addInvoiceResp, err := ctx.bob.AddInvoice(context.Background(), &lnrpc.Invoice{
+		Value: int64(paymentAmt),
+		IsAmp: true,
+	})
+	require.NoError(t.t, err)
+
+	// Ensure we get a notification of the invoice being added by Bob.
+	rpcInvoice, err := bobInvoiceSubscription.Recv()
+	require.NoError(t.t, err)
+
+	require.False(t.t, rpcInvoice.Settled) // nolint:staticcheck
+	require.Equal(t.t, lnrpc.Invoice_OPEN, rpcInvoice.State)
+	require.Equal(t.t, int64(0), rpcInvoice.AmtPaidSat)
+	require.Equal(t.t, int64(0), rpcInvoice.AmtPaidMsat)
+
+	require.Equal(t.t, 0, len(rpcInvoice.Htlcs))
+
+	// Increase Dave's fee to make the test deterministic. Otherwise it
+	// would be unpredictable whether pathfinding would go through Charlie
+	// or Dave for the first shard.
+	_, err = ctx.dave.UpdateChannelPolicy(
+		context.Background(),
+		&lnrpc.PolicyUpdateRequest{
+			Scope:         &lnrpc.PolicyUpdateRequest_Global{Global: true},
+			BaseFeeMsat:   500000,
+			FeeRate:       0.001,
+			TimeLockDelta: 40,
+		},
+	)
+	if err != nil {
+		t.Fatalf("dave policy update: %v", err)
+	}
+
+	ctxt, _ := context.WithTimeout(context.Background(), 4*defaultTimeout)
+	payment := sendAndAssertSuccess(
+		ctxt, t, ctx.alice,
+		&routerrpc.SendPaymentRequest{
+			PaymentRequest: addInvoiceResp.PaymentRequest,
+			TimeoutSeconds: 60,
+			FeeLimitMsat:   noFeeLimitMsat,
+		},
+	)
+
+	// Check that Alice split the payment in at least three shards. Because
+	// the hand-off of the htlc to the link is asynchronous (via a mailbox),
+	// there is some non-determinism in the process. Depending on whether
+	// the new pathfinding round is started before or after the htlc is
+	// locked into the channel, different sharding may occur. Therefore we
+	// can only check if the number of shards isn't below the theoretical
+	// minimum.
+	succeeded := 0
+	for _, htlc := range payment.Htlcs {
+		if htlc.Status == lnrpc.HTLCAttempt_SUCCEEDED {
+			succeeded++
+		}
+	}
+
+	const minExpectedShards = 3
+	if succeeded < minExpectedShards {
+		t.Fatalf("expected at least %v shards, but got %v",
+			minExpectedShards, succeeded)
+	}
+
+	// There should now be a settle event for the invoice.
+	rpcInvoice, err = bobInvoiceSubscription.Recv()
+	require.NoError(t.t, err)
+
+	// Also fetch Bob's invoice from ListInvoices and assert it is equal to
+	// the one recevied via the subscription.
+	invoiceResp, err := ctx.bob.ListInvoices(
+		ctxb, &lnrpc.ListInvoiceRequest{},
+	)
+	require.NoError(t.t, err)
+	require.Equal(t.t, 1, len(invoiceResp.Invoices))
+	assertInvoiceEqual(t.t, rpcInvoice, invoiceResp.Invoices[0])
+
+	// Assert that the invoice is settled for the total payment amount and
+	// has the correct payment address.
+	require.True(t.t, rpcInvoice.Settled) // nolint:staticcheck
+	require.Equal(t.t, lnrpc.Invoice_SETTLED, rpcInvoice.State)
+	require.Equal(t.t, int64(paymentAmt), rpcInvoice.AmtPaidSat)
+	require.Equal(t.t, int64(paymentAmt*1000), rpcInvoice.AmtPaidMsat)
+
+	// Finally, assert that the same set id is recorded for each htlc, and
+	// that the preimage hash pair is valid.
+	var setID []byte
+	require.Equal(t.t, succeeded, len(rpcInvoice.Htlcs))
+	for _, htlc := range rpcInvoice.Htlcs {
+		require.NotNil(t.t, htlc.Amp)
+		if setID == nil {
+			setID = make([]byte, 32)
+			copy(setID, htlc.Amp.SetId)
+		}
+		require.Equal(t.t, setID, htlc.Amp.SetId)
+
+		// Parse the child hash and child preimage, and assert they are
+		// well-formed.
+		childHash, err := lntypes.MakeHash(htlc.Amp.Hash)
+		require.NoError(t.t, err)
+		childPreimage, err := lntypes.MakePreimage(htlc.Amp.Preimage)
+		require.NoError(t.t, err)
+
+		// Assert that the preimage actually matches the hashes.
+		validPreimage := childPreimage.Matches(childHash)
+		require.True(t.t, validPreimage)
+	}
+}
+
 // testSendPaymentAMP tests that we can send an AMP payment to a specified
 // destination using SendPaymentV2.
 func testSendPaymentAMP(net *lntest.NetworkHarness, t *harnessTest) {
@@ -64,12 +212,11 @@ func testSendPaymentAMP(net *lntest.NetworkHarness, t *harnessTest) {
 
 	ctxt, _ := context.WithTimeout(context.Background(), 4*defaultTimeout)
 	payment := sendAndAssertSuccess(
-		ctxt, t, net.Alice,
+		ctxt, t, ctx.alice,
 		&routerrpc.SendPaymentRequest{
-			Dest:           net.Bob.PubKey[:],
+			Dest:           ctx.bob.PubKey[:],
 			Amt:            int64(paymentAmt),
 			FinalCltvDelta: chainreg.DefaultBitcoinTimeLockDelta,
-			MaxParts:       10,
 			TimeoutSeconds: 60,
 			FeeLimitMsat:   noFeeLimitMsat,
 			Amp:            true,
@@ -97,7 +244,7 @@ func testSendPaymentAMP(net *lntest.NetworkHarness, t *harnessTest) {
 	}
 
 	// Fetch Bob's invoices.
-	invoiceResp, err := net.Bob.ListInvoices(
+	invoiceResp, err := ctx.bob.ListInvoices(
 		ctxb, &lnrpc.ListInvoiceRequest{},
 	)
 	require.NoError(t.t, err)
@@ -172,6 +319,13 @@ func testSendToRouteAMP(net *lntest.NetworkHarness, t *harnessTest) {
 
 	ctx.waitForChannels()
 
+	// Subscribe to bob's invoices.
+	req := &lnrpc.InvoiceSubscription{}
+	ctxc, cancelSubscription := context.WithCancel(ctxb)
+	bobInvoiceSubscription, err := ctx.bob.SubscribeInvoices(ctxc, req)
+	require.NoError(t.t, err)
+	defer cancelSubscription()
+
 	// We'll send shards along three routes from Alice.
 	sendRoutes := [numShards][]*lntest.HarnessNode{
 		{ctx.carol, ctx.bob},
@@ -180,7 +334,7 @@ func testSendToRouteAMP(net *lntest.NetworkHarness, t *harnessTest) {
 	}
 
 	payAddr := make([]byte, 32)
-	_, err := rand.Read(payAddr)
+	_, err = rand.Read(payAddr)
 	require.NoError(t.t, err)
 
 	setID := make([]byte, 32)
@@ -193,9 +347,11 @@ func testSendToRouteAMP(net *lntest.NetworkHarness, t *harnessTest) {
 
 	childPreimages := make(map[lntypes.Preimage]uint32)
 	responses := make(chan *lnrpc.HTLCAttempt, len(sendRoutes))
-	for i, hops := range sendRoutes {
+
+	// Define a closure for sending each of the three shards.
+	sendShard := func(i int, hops []*lntest.HarnessNode) {
 		// Build a route for the specified hops.
-		r, err := ctx.buildRoute(ctxb, shardAmt, net.Alice, hops)
+		r, err := ctx.buildRoute(ctxb, shardAmt, ctx.alice, hops)
 		if err != nil {
 			t.Fatalf("unable to build route: %v", err)
 		}
@@ -236,7 +392,7 @@ func testSendToRouteAMP(net *lntest.NetworkHarness, t *harnessTest) {
 		// block as long as the payment is in flight.
 		go func() {
 			ctxt, _ := context.WithTimeout(ctxb, defaultTimeout)
-			resp, err := net.Alice.RouterClient.SendToRouteV2(ctxt, sendReq)
+			resp, err := ctx.alice.RouterClient.SendToRouteV2(ctxt, sendReq)
 			if err != nil {
 				t.Fatalf("unable to send payment: %v", err)
 			}
@@ -245,6 +401,24 @@ func testSendToRouteAMP(net *lntest.NetworkHarness, t *harnessTest) {
 		}()
 	}
 
+	// Send the first shard, this cause Bob to JIT add an invoice.
+	sendShard(0, sendRoutes[0])
+
+	// Ensure we get a notification of the invoice being added by Bob.
+	rpcInvoice, err := bobInvoiceSubscription.Recv()
+	require.NoError(t.t, err)
+
+	require.False(t.t, rpcInvoice.Settled) // nolint:staticcheck
+	require.Equal(t.t, lnrpc.Invoice_OPEN, rpcInvoice.State)
+	require.Equal(t.t, int64(0), rpcInvoice.AmtPaidSat)
+	require.Equal(t.t, int64(0), rpcInvoice.AmtPaidMsat)
+	require.Equal(t.t, payAddr, rpcInvoice.PaymentAddr)
+
+	require.Equal(t.t, 0, len(rpcInvoice.Htlcs))
+
+	sendShard(1, sendRoutes[1])
+	sendShard(2, sendRoutes[2])
+
 	// Assert that all of the child preimages are unique.
 	require.Equal(t.t, len(sendRoutes), len(childPreimages))
 
@@ -282,15 +456,18 @@ func testSendToRouteAMP(net *lntest.NetworkHarness, t *harnessTest) {
 	}
 	childPreimages = childPreimagesCopy
 
-	// Fetch Bob's invoices.
-	invoiceResp, err := net.Bob.ListInvoices(
+	// There should now be a settle event for the invoice.
+	rpcInvoice, err = bobInvoiceSubscription.Recv()
+	require.NoError(t.t, err)
+
+	// Also fetch Bob's invoice from ListInvoices and assert it is equal to
+	// the one recevied via the subscription.
+	invoiceResp, err := ctx.bob.ListInvoices(
 		ctxb, &lnrpc.ListInvoiceRequest{},
 	)
 	require.NoError(t.t, err)
-
-	// There should only be one invoice.
 	require.Equal(t.t, 1, len(invoiceResp.Invoices))
-	rpcInvoice := invoiceResp.Invoices[0]
+	assertInvoiceEqual(t.t, rpcInvoice, invoiceResp.Invoices[0])
 
 	// Assert that the invoice is settled for the total payment amount and
 	// has the correct payment address.
@@ -330,3 +507,60 @@ func testSendToRouteAMP(net *lntest.NetworkHarness, t *harnessTest) {
 		delete(childPreimages, childPreimage)
 	}
 }
+
+// assertInvoiceEqual asserts that two lnrpc.Invoices are equivalent. A custom
+// comparison function is defined for these tests, since proto message returned
+// from unary and streaming RPCs (as of protobuf 1.23.0 and grpc 1.29.1) aren't
+// consistent with the private fields set on the messages. As a result, we avoid
+// using require.Equal and test only the actual data members.
+func assertInvoiceEqual(t *testing.T, a, b *lnrpc.Invoice) {
+	t.Helper()
+
+	// Ensure the HTLCs are sorted properly before attempting to compare.
+	sort.Slice(a.Htlcs, func(i, j int) bool {
+		return a.Htlcs[i].ChanId < a.Htlcs[j].ChanId
+	})
+	sort.Slice(b.Htlcs, func(i, j int) bool {
+		return b.Htlcs[i].ChanId < b.Htlcs[j].ChanId
+	})
+
+	require.Equal(t, a.Memo, b.Memo)
+	require.Equal(t, a.RPreimage, b.RPreimage)
+	require.Equal(t, a.RHash, b.RHash)
+	require.Equal(t, a.Value, b.Value)
+	require.Equal(t, a.ValueMsat, b.ValueMsat)
+	require.Equal(t, a.CreationDate, b.CreationDate)
+	require.Equal(t, a.SettleDate, b.SettleDate)
+	require.Equal(t, a.PaymentRequest, b.PaymentRequest)
+	require.Equal(t, a.DescriptionHash, b.DescriptionHash)
+	require.Equal(t, a.Expiry, b.Expiry)
+	require.Equal(t, a.FallbackAddr, b.FallbackAddr)
+	require.Equal(t, a.CltvExpiry, b.CltvExpiry)
+	require.Equal(t, a.RouteHints, b.RouteHints)
+	require.Equal(t, a.Private, b.Private)
+	require.Equal(t, a.AddIndex, b.AddIndex)
+	require.Equal(t, a.SettleIndex, b.SettleIndex)
+	require.Equal(t, a.AmtPaidSat, b.AmtPaidSat)
+	require.Equal(t, a.AmtPaidMsat, b.AmtPaidMsat)
+	require.Equal(t, a.State, b.State)
+	require.Equal(t, a.Features, b.Features)
+	require.Equal(t, a.IsKeysend, b.IsKeysend)
+	require.Equal(t, a.PaymentAddr, b.PaymentAddr)
+	require.Equal(t, a.IsAmp, b.IsAmp)
+
+	require.Equal(t, len(a.Htlcs), len(b.Htlcs))
+	for i := range a.Htlcs {
+		htlcA, htlcB := a.Htlcs[i], b.Htlcs[i]
+		require.Equal(t, htlcA.ChanId, htlcB.ChanId)
+		require.Equal(t, htlcA.HtlcIndex, htlcB.HtlcIndex)
+		require.Equal(t, htlcA.AmtMsat, htlcB.AmtMsat)
+		require.Equal(t, htlcA.AcceptHeight, htlcB.AcceptHeight)
+		require.Equal(t, htlcA.AcceptTime, htlcB.AcceptTime)
+		require.Equal(t, htlcA.ResolveTime, htlcB.ResolveTime)
+		require.Equal(t, htlcA.ExpiryHeight, htlcB.ExpiryHeight)
+		require.Equal(t, htlcA.State, htlcB.State)
+		require.Equal(t, htlcA.CustomRecords, htlcB.CustomRecords)
+		require.Equal(t, htlcA.MppTotalAmtMsat, htlcB.MppTotalAmtMsat)
+		require.Equal(t, htlcA.Amp, htlcB.Amp)
+	}
+}

lntest/itest/lnd_mpp_test.go

@@ -55,7 +55,7 @@ func testSendToRouteMultiPath(net *lntest.NetworkHarness, t *harnessTest) {
 
 	// Make Bob create an invoice for Alice to pay.
 	payReqs, rHashes, invoices, err := createPayReqs(
-		net.Bob, paymentAmt, 1,
+		ctx.bob, paymentAmt, 1,
 	)
 	if err != nil {
 		t.Fatalf("unable to create pay reqs: %v", err)
@@ -65,7 +65,7 @@ func testSendToRouteMultiPath(net *lntest.NetworkHarness, t *harnessTest) {
 	payReq := payReqs[0]
 
 	ctxt, _ := context.WithTimeout(ctxb, defaultTimeout)
-	decodeResp, err := net.Bob.DecodePayReq(
+	decodeResp, err := ctx.bob.DecodePayReq(
 		ctxt, &lnrpc.PayReqString{PayReq: payReq},
 	)
 	if err != nil {
@@ -84,7 +84,7 @@ func testSendToRouteMultiPath(net *lntest.NetworkHarness, t *harnessTest) {
 	responses := make(chan *lnrpc.HTLCAttempt, len(sendRoutes))
 	for _, hops := range sendRoutes {
 		// Build a route for the specified hops.
-		r, err := ctx.buildRoute(ctxb, shardAmt, net.Alice, hops)
+		r, err := ctx.buildRoute(ctxb, shardAmt, ctx.alice, hops)
 		if err != nil {
 			t.Fatalf("unable to build route: %v", err)
 		}
@@ -107,7 +107,7 @@ func testSendToRouteMultiPath(net *lntest.NetworkHarness, t *harnessTest) {
 		// block as long as the payment is in flight.
 		go func() {
 			ctxt, _ := context.WithTimeout(ctxb, defaultTimeout)
-			resp, err := net.Alice.RouterClient.SendToRouteV2(ctxt, sendReq)
+			resp, err := ctx.alice.RouterClient.SendToRouteV2(ctxt, sendReq)
 			if err != nil {
 				t.Fatalf("unable to send payment: %v", err)
 			}
@@ -234,10 +234,10 @@ func testSendToRouteMultiPath(net *lntest.NetworkHarness, t *harnessTest) {
 
 	// Finally check that the payment shows up with three settled HTLCs in
 	// Alice's list of payments...
-	assertNumHtlcs(net.Alice, 3)
+	assertNumHtlcs(ctx.alice, 3)
 
 	// ...and in Bob's list of paid invoices.
-	assertSettledInvoice(net.Bob, rHash, 3)
+	assertSettledInvoice(ctx.bob, rHash, 3)
 }
 
 type mppTestContext struct {
@@ -257,6 +257,16 @@ func newMppTestContext(t *harnessTest,
 
 	ctxb := context.Background()
 
+	alice, err := net.NewNode("alice", nil)
+	if err != nil {
+		t.Fatalf("unable to create alice: %v", err)
+	}
+
+	bob, err := net.NewNode("bob", []string{"--accept-amp"})
+	if err != nil {
+		t.Fatalf("unable to create bob: %v", err)
+	}
+
 	// Create a five-node context consisting of Alice, Bob and three new
 	// nodes.
 	carol, err := net.NewNode("carol", nil)
@@ -275,7 +285,7 @@ func newMppTestContext(t *harnessTest,
 	}
 
 	// Connect nodes to ensure propagation of channels.
-	nodes := []*lntest.HarnessNode{net.Alice, net.Bob, carol, dave, eve}
+	nodes := []*lntest.HarnessNode{alice, bob, carol, dave, eve}
 	for i := 0; i < len(nodes); i++ {
 		for j := i + 1; j < len(nodes); j++ {
 			ctxt, _ := context.WithTimeout(ctxb, defaultTimeout)
@@ -288,8 +298,8 @@ func newMppTestContext(t *harnessTest,
 	ctx := mppTestContext{
 		t:     t,
 		net:   net,
-		alice: net.Alice,
-		bob:   net.Bob,
+		alice: alice,
+		bob:   bob,
 		carol: carol,
 		dave:  dave,
 		eve:   eve,

lntest/itest/lnd_send_multi_path_payment_test.go

@@ -59,7 +59,7 @@ func testSendMultiPathPayment(net *lntest.NetworkHarness, t *harnessTest) {
 	// Our first test will be Alice paying Bob using a SendPayment call.
 	// Let Bob create an invoice for Alice to pay.
 	payReqs, rHashes, invoices, err := createPayReqs(
-		net.Bob, paymentAmt, 1,
+		ctx.bob, paymentAmt, 1,
 	)
 	if err != nil {
 		t.Fatalf("unable to create pay reqs: %v", err)
@@ -70,7 +70,7 @@ func testSendMultiPathPayment(net *lntest.NetworkHarness, t *harnessTest) {
 
 	ctxt, _ := context.WithTimeout(ctxb, defaultTimeout)
 	payment := sendAndAssertSuccess(
-		ctxt, t, net.Alice,
+		ctxt, t, ctx.alice,
 		&routerrpc.SendPaymentRequest{
 			PaymentRequest: payReq,
 			MaxParts:       10,

lntest/itest/lnd_test_list_on_test.go

@@ -278,7 +278,10 @@ var allTestCases = []*testCase{
 		name: "sendpayment amp",
 		test: testSendPaymentAMP,
 	},
-
+	{
+		name: "sendpayment amp invoice",
+		test: testSendPaymentAMPInvoice,
+	},
 	{
 		name: "send multi path payment",
 		test: testSendMultiPathPayment,

lntest/node.go

@@ -210,6 +210,7 @@ type NodeConfig struct {
 	ProfilePort int
 
 	AcceptKeySend bool
+	AcceptAMP     bool
 
 	FeeURL string
 
@@ -297,6 +298,10 @@ func (cfg NodeConfig) genArgs() []string {
 		args = append(args, "--accept-keysend")
 	}
 
+	if cfg.AcceptAMP {
+		args = append(args, "--accept-amp")
+	}
+
 	if cfg.Etcd {
 		args = append(args, "--db.backend=etcd")
 		args = append(args, "--db.etcd.embedded")

routing/payment_session.go

@@ -296,9 +296,12 @@ func (p *paymentSession) RequestRoute(maxAmt, feeLimit lnwire.MilliSatoshi,
 				return nil, errNoPathFound
 			}
 
-			if !p.payment.DestFeatures.HasFeature(lnwire.MPPOptional) {
+			destFeatures := p.payment.DestFeatures
+			if !destFeatures.HasFeature(lnwire.MPPOptional) &&
+				!destFeatures.HasFeature(lnwire.AMPOptional) {
+
 				p.log.Debug("not splitting because " +
-					"destination doesn't declare MPP")
+					"destination doesn't declare MPP or AMP")
 
 				return nil, errNoPathFound
 			}

rpcserver.go

@@ -661,6 +661,9 @@ func (r *rpcServer) addDeps(s *server, macService *macaroons.Service,
 	genInvoiceFeatures := func() *lnwire.FeatureVector {
 		return s.featureMgr.Get(feature.SetInvoice)
 	}
+	genAmpInvoiceFeatures := func() *lnwire.FeatureVector {
+		return s.featureMgr.Get(feature.SetInvoiceAmp)
+	}
 
 	var (
 		subServers     []lnrpc.SubServer
@@ -677,7 +680,8 @@ func (r *rpcServer) addDeps(s *server, macService *macaroons.Service,
 		s.htlcSwitch, r.cfg.ActiveNetParams.Params, s.chanRouter,
 		routerBackend, s.nodeSigner, s.localChanDB, s.remoteChanDB,
 		s.sweeper, tower, s.towerClient, s.anchorTowerClient,
-		r.cfg.net.ResolveTCPAddr, genInvoiceFeatures, rpcsLog,
+		r.cfg.net.ResolveTCPAddr, genInvoiceFeatures,
+		genAmpInvoiceFeatures, rpcsLog,
 	)
 	if err != nil {
 		return err
@@ -4796,6 +4800,9 @@ func (r *rpcServer) AddInvoice(ctx context.Context,
 		GenInvoiceFeatures: func() *lnwire.FeatureVector {
 			return r.server.featureMgr.Get(feature.SetInvoice)
 		},
+		GenAmpInvoiceFeatures: func() *lnwire.FeatureVector {
+			return r.server.featureMgr.Get(feature.SetInvoiceAmp)
+		},
 	}
 
 	value, err := lnrpc.UnmarshallAmt(invoice.Value, invoice.ValueMsat)
@@ -4817,6 +4824,7 @@ func (r *rpcServer) AddInvoice(ctx context.Context,
 		CltvExpiry:      invoice.CltvExpiry,
 		Private:         invoice.Private,
 		RouteHints:      routeHints,
+		Amp:             invoice.IsAmp,
 	}
 
 	if invoice.RPreimage != nil {

sample-lnd.conf

@@ -375,6 +375,10 @@
 ; automatically. [experimental]
 ; keysend-hold-time=true
 
+; If true, spontaneous payments through AMP will be accepted. Payments to AMP
+; invoices will be accepted regardless of this setting.
+; accept-amp=true
+
 ; If set, lnd will use anchor channels by default if the remote channel party
 ; supports them. Note that lnd will require 1 UTXO to be reserved for this
 ; channel type if it is enabled.

server.go

@@ -427,6 +427,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		HtlcHoldDuration:            invoices.DefaultHtlcHoldDuration,
 		Clock:                       clock.NewDefaultClock(),
 		AcceptKeySend:               cfg.AcceptKeySend,
+		AcceptAMP:                   cfg.AcceptAMP,
 		GcCanceledInvoicesOnStartup: cfg.GcCanceledInvoicesOnStartup,
 		GcCanceledInvoicesOnTheFly:  cfg.GcCanceledInvoicesOnTheFly,
 		KeysendHoldTime:             cfg.KeysendHoldTime,

subrpcserver_config.go

@@ -100,6 +100,7 @@ func (s *subRPCServerConfigs) PopulateDependencies(cfg *Config,
 	anchorTowerClient wtclient.Client,
 	tcpResolver lncfg.TCPResolver,
 	genInvoiceFeatures func() *lnwire.FeatureVector,
+	genAmpInvoiceFeatures func() *lnwire.FeatureVector,
 	rpcLogger btclog.Logger) error {
 
 	// First, we'll use reflect to obtain a version of the config struct
@@ -230,6 +231,9 @@ func (s *subRPCServerConfigs) PopulateDependencies(cfg *Config,
 			subCfgValue.FieldByName("GenInvoiceFeatures").Set(
 				reflect.ValueOf(genInvoiceFeatures),
 			)
+			subCfgValue.FieldByName("GenAmpInvoiceFeatures").Set(
+				reflect.ValueOf(genAmpInvoiceFeatures),
+			)
 
 		// RouterRPC isn't conditionally compiled and doesn't need to be
 		// populated using reflection.