[custom channels 4/5]: Extract PART4 from mega staging branch

config_builder.go

@@ -42,6 +42,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwallet/btcwallet"
+	"github.com/lightningnetwork/lnd/lnwallet/chancloser"
 	"github.com/lightningnetwork/lnd/lnwallet/rpcwallet"
 	"github.com/lightningnetwork/lnd/macaroons"
 	"github.com/lightningnetwork/lnd/msgmux"
@@ -182,6 +183,10 @@ type AuxComponents struct {
 	// AuxDataParser is an optional data parser that can be used to parse
 	// auxiliary data for certain custom channel types.
 	AuxDataParser fn.Option[AuxDataParser]
+
+	// AuxChanCloser is an optional channel closer that can be used to
+	// modify the way a coop-close transaction is constructed.
+	AuxChanCloser fn.Option[chancloser.AuxChanCloser]
 }
 
 // DefaultWalletImpl is the default implementation of our normal, btcwallet

contractcourt/htlc_incoming_contest_resolver.go

@@ -308,7 +308,7 @@ func (h *htlcIncomingContestResolver) Resolve(
 
 		resolution, err := h.Registry.NotifyExitHopHtlc(
 			h.htlc.RHash, h.htlc.Amt, h.htlcExpiry, currentHeight,
-			circuitKey, hodlQueue.ChanIn(), payload,
+			circuitKey, hodlQueue.ChanIn(), nil, payload,
 		)
 		if err != nil {
 			return nil, err

contractcourt/interfaces.go

@@ -30,6 +30,7 @@ type Registry interface {
 	NotifyExitHopHtlc(payHash lntypes.Hash, paidAmount lnwire.MilliSatoshi,
 		expiry uint32, currentHeight int32,
 		circuitKey models.CircuitKey, hodlChan chan<- interface{},
+		wireCustomRecords lnwire.CustomRecords,
 		payload invoices.Payload) (invoices.HtlcResolution, error)
 
 	// HodlUnsubscribeAll unsubscribes from all htlc resolutions.

contractcourt/mock_registry_test.go

@@ -26,6 +26,7 @@ type mockRegistry struct {
 func (r *mockRegistry) NotifyExitHopHtlc(payHash lntypes.Hash,
 	paidAmount lnwire.MilliSatoshi, expiry uint32, currentHeight int32,
 	circuitKey models.CircuitKey, hodlChan chan<- interface{},
+	wireCustomRecords lnwire.CustomRecords,
 	payload invoices.Payload) (invoices.HtlcResolution, error) {
 
 	r.notifyChan <- notifyExitHopData{

htlcswitch/interfaces.go

@@ -33,6 +33,7 @@ type InvoiceDatabase interface {
 	NotifyExitHopHtlc(payHash lntypes.Hash, paidAmount lnwire.MilliSatoshi,
 		expiry uint32, currentHeight int32,
 		circuitKey models.CircuitKey, hodlChan chan<- interface{},
+		wireCustomRecords lnwire.CustomRecords,
 		payload invoices.Payload) (invoices.HtlcResolution, error)
 
 	// CancelInvoice attempts to cancel the invoice corresponding to the

htlcswitch/link.go

@@ -3846,7 +3846,7 @@ func (l *channelLink) processExitHop(add lnwire.UpdateAddHTLC,
 
 	event, err := l.cfg.Registry.NotifyExitHopHtlc(
 		invoiceHash, add.Amount, add.Expiry, int32(heightNow),
-		circuitKey, l.hodlQueue.ChanIn(), payload,
+		circuitKey, l.hodlQueue.ChanIn(), add.CustomRecords, payload,
 	)
 	if err != nil {
 		return err

htlcswitch/mock.go

@@ -1014,6 +1014,7 @@ func newMockRegistry(minDelta uint32) *mockInvoiceRegistry {
 		panic(err)
 	}
 
+	modifierMock := &invoices.MockHtlcModifier{}
 	registry := invoices.NewRegistry(
 		cdb,
 		invoices.NewInvoiceExpiryWatcher(
@@ -1022,6 +1023,7 @@ func newMockRegistry(minDelta uint32) *mockInvoiceRegistry {
 		),
 		&invoices.RegistryConfig{
 			FinalCltvRejectDelta: 5,
+			HtlcInterceptor:      modifierMock,
 		},
 	)
 	registry.Start()
@@ -1047,11 +1049,12 @@ func (i *mockInvoiceRegistry) SettleHodlInvoice(
 func (i *mockInvoiceRegistry) NotifyExitHopHtlc(rhash lntypes.Hash,
 	amt lnwire.MilliSatoshi, expiry uint32, currentHeight int32,
 	circuitKey models.CircuitKey, hodlChan chan<- interface{},
+	wireCustomRecords lnwire.CustomRecords,
 	payload invoices.Payload) (invoices.HtlcResolution, error) {
 
 	event, err := i.registry.NotifyExitHopHtlc(
-		rhash, amt, expiry, currentHeight, circuitKey, hodlChan,
-		payload,
+		rhash, amt, expiry, currentHeight, circuitKey,
+		hodlChan, wireCustomRecords, payload,
 	)
 	if err != nil {
 		return nil, err

invoices/interface.go

@@ -207,3 +207,71 @@ type InvoiceUpdater interface {
 	// Finalize finalizes the update before it is written to the database.
 	Finalize(updateType UpdateType) error
 }
+
+// HtlcModifyRequest is the request that is passed to the client via callback
+// during a HTLC interceptor session. The request contains the invoice that the
+// given HTLC is attempting to settle.
+type HtlcModifyRequest struct {
+	// WireCustomRecords are the custom records that were parsed from the
+	// HTLC wire message. These are the records of the current HTLC to be
+	// accepted/settled. All previously accepted/settled HTLCs for the same
+	// invoice are present in the Invoice field below.
+	WireCustomRecords lnwire.CustomRecords
+
+	// ExitHtlcCircuitKey is the circuit key that identifies the HTLC which
+	// is involved in the invoice settlement.
+	ExitHtlcCircuitKey CircuitKey
+
+	// ExitHtlcAmt is the amount of the HTLC which is involved in the
+	// invoice settlement.
+	ExitHtlcAmt lnwire.MilliSatoshi
+
+	// ExitHtlcExpiry is the absolute expiry height of the HTLC which is
+	// involved in the invoice settlement.
+	ExitHtlcExpiry uint32
+
+	// CurrentHeight is the current block height.
+	CurrentHeight uint32
+
+	// Invoice is the invoice that is being intercepted. The HTLCs within
+	// the invoice are only those previously accepted/settled for the same
+	// invoice.
+	Invoice Invoice
+}
+
+// HtlcModifyResponse is the response that the client should send back to the
+// interceptor after processing the HTLC modify request.
+type HtlcModifyResponse struct {
+	// AmountPaid is the amount that the client has decided the HTLC is
+	// actually worth. This might be different from the amount that the
+	// HTLC was originally sent with, in case additional value is carried
+	// along with it (which might be the case in custom channels).
+	AmountPaid lnwire.MilliSatoshi
+}
+
+// HtlcModifyCallback is a function that is called when an invoice is
+// intercepted by the invoice interceptor.
+type HtlcModifyCallback func(HtlcModifyRequest) (*HtlcModifyResponse, error)
+
+// HtlcModifier is an interface that allows an intercept client to register
+// itself as a modifier of HTLCs that are settling an invoice. The client can
+// then modify the HTLCs based on the invoice and the HTLC that is settling it.
+type HtlcModifier interface {
+	// RegisterInterceptor sets the client callback function that will be
+	// called when an invoice is intercepted. If a callback is already set,
+	// an error is returned. The returned function must be used to reset the
+	// callback to nil once the client is done or disconnects. The read-only
+	// channel closes when the server stops.
+	RegisterInterceptor(HtlcModifyCallback) (func(), <-chan struct{}, error)
+}
+
+// HtlcInterceptor is an interface that allows the invoice registry to let
+// clients intercept invoices before they are settled.
+type HtlcInterceptor interface {
+	// Intercept generates a new intercept session for the given invoice.
+	// The call blocks until the client has responded to the request or an
+	// error occurs. The response callback is only called if a session was
+	// created in the first place, which is only the case if a client is
+	// registered.
+	Intercept(HtlcModifyRequest, func(HtlcModifyResponse)) error
+}

invoices/invoiceregistry.go

@@ -74,6 +74,10 @@ type RegistryConfig struct {
 	// KeysendHoldTime indicates for how long we want to accept and hold
 	// spontaneous keysend payments.
 	KeysendHoldTime time.Duration
+
+	// HtlcInterceptor is an interface that allows the invoice registry to
+	// let clients intercept invoices before they are settled.
+	HtlcInterceptor HtlcInterceptor
 }
 
 // htlcReleaseEvent describes an htlc auto-release event. It is used to release
@@ -914,6 +918,7 @@ func (i *InvoiceRegistry) processAMP(ctx invoiceUpdateCtx) error {
 func (i *InvoiceRegistry) NotifyExitHopHtlc(rHash lntypes.Hash,
 	amtPaid lnwire.MilliSatoshi, expiry uint32, currentHeight int32,
 	circuitKey CircuitKey, hodlChan chan<- interface{},
+	wireCustomRecords lnwire.CustomRecords,
 	payload Payload) (HtlcResolution, error) {
 
 	// Create the update context containing the relevant details of the
@@ -925,6 +930,7 @@ func (i *InvoiceRegistry) NotifyExitHopHtlc(rHash lntypes.Hash,
 		expiry:               expiry,
 		currentHeight:        currentHeight,
 		finalCltvRejectDelta: i.cfg.FinalCltvRejectDelta,
+		wireCustomRecords:    wireCustomRecords,
 		customRecords:        payload.CustomRecords(),
 		mpp:                  payload.MultiPath(),
 		amp:                  payload.AMPRecord(),
@@ -1019,13 +1025,62 @@ func (i *InvoiceRegistry) notifyExitHopHtlcLocked(
 	ctx *invoiceUpdateCtx, hodlChan chan<- interface{}) (
 	HtlcResolution, invoiceExpiry, error) {
 
+	invoiceRef := ctx.invoiceRef()
+	setID := (*SetID)(ctx.setID())
+
+	// We need to look up the current state of the invoice in order to send
+	// the previously accepted/settled HTLCs to the interceptor.
+	existingInvoice, err := i.idb.LookupInvoice(
+		context.Background(), invoiceRef,
+	)
+	switch {
+	case errors.Is(err, ErrInvoiceNotFound) ||
+		errors.Is(err, ErrNoInvoicesCreated):
+
+		// If the invoice was not found, return a failure resolution
+		// with an invoice not found result.
+		return NewFailResolution(
+			ctx.circuitKey, ctx.currentHeight,
+			ResultInvoiceNotFound,
+		), nil, nil
+
+	case err != nil:
+		ctx.log(err.Error())
+		return nil, nil, err
+	}
+
+	// Provide the invoice to the settlement interceptor to allow
+	// the interceptor's client an opportunity to manipulate the
+	// settlement process.
+	err = i.cfg.HtlcInterceptor.Intercept(HtlcModifyRequest{
+		WireCustomRecords:  ctx.wireCustomRecords,
+		ExitHtlcCircuitKey: ctx.circuitKey,
+		ExitHtlcAmt:        ctx.amtPaid,
+		ExitHtlcExpiry:     ctx.expiry,
+		CurrentHeight:      uint32(ctx.currentHeight),
+		Invoice:            existingInvoice,
+	}, func(resp HtlcModifyResponse) {
+		log.Debugf("Received invoice HTLC interceptor response: %v",
+			resp)
+
+		if resp.AmountPaid != 0 {
+			ctx.amtPaid = resp.AmountPaid
+		}
+	})
+	if err != nil {
+		err := fmt.Errorf("error during invoice HTLC interception: %w",
+			err)
+		ctx.log(err.Error())
+
+		return nil, nil, err
+	}
+
 	// We'll attempt to settle an invoice matching this rHash on disk (if
 	// one exists). The callback will update the invoice state and/or htlcs.
 	var (
 		resolution        HtlcResolution
 		updateSubscribers bool
 	)
-
 	callback := func(inv *Invoice) (*InvoiceUpdateDesc, error) {
 		updateDesc, res, err := updateInvoice(ctx, inv)
 		if err != nil {
@@ -1042,8 +1097,6 @@ func (i *InvoiceRegistry) notifyExitHopHtlcLocked(
 		return updateDesc, nil
 	}
 
-	invoiceRef := ctx.invoiceRef()
-	setID := (*SetID)(ctx.setID())
 	invoice, err := i.idb.UpdateInvoice(
 		context.Background(), invoiceRef, setID, callback,
 	)
@@ -1080,6 +1133,8 @@ func (i *InvoiceRegistry) notifyExitHopHtlcLocked(
 
 	var invoiceToExpire invoiceExpiry
 
+	log.Tracef("Settlement resolution: %T %v", resolution, resolution)
+
 	switch res := resolution.(type) {
 	case *HtlcFailResolution:
 		// Inspect latest htlc state on the invoice. If it is found,
@@ -1212,7 +1267,7 @@ func (i *InvoiceRegistry) notifyExitHopHtlcLocked(
 	}
 
 	// Now that the links have been notified of any state changes to their
-	// HTLCs, we'll go ahead and notify any clients wiaiting on the invoice
+	// HTLCs, we'll go ahead and notify any clients waiting on the invoice
 	// state changes.
 	if updateSubscribers {
 		// We'll add a setID onto the notification, but only if this is