contractcourt+server: settle invoice for on-chain HTLC sweep

In this commit, we extend the htlcSuccessResolver to settle the invoice,
if any, of the corresponding on-chain HTLC sweep. This ensures that the
invoice state is consistent as when claiming the HTLC "off-chain".

contractcourt/chain_arbitrator.go

@@ -6,8 +6,6 @@ import (
 	"sync"
 	"sync/atomic"
 
-	"github.com/lightningnetwork/lnd/sweep"
-
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/btcsuite/btcutil"
@@ -15,6 +13,7 @@ import (
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/sweep"
 )
 
 // ErrChainArbExiting signals that the chain arbitrator is shutting down.
@@ -135,6 +134,11 @@ type ChainArbitratorConfig struct {
 
 	// Sweeper allows resolvers to sweep their final outputs.
 	Sweeper *sweep.UtxoSweeper
+
+	// SettleInvoice attempts to settle an existing invoice on-chain with
+	// the given payment hash. ErrInvoiceNotFound is returned if an invoice
+	// is not found.
+	SettleInvoice func(chainhash.Hash, lnwire.MilliSatoshi) error
 }
 
 // ChainArbitrator is a sub-system that oversees the on-chain resolution of all

contractcourt/channel_arbitrator_test.go

@@ -175,6 +175,9 @@ func createTestChannelArbitrator(log ArbitratorLog) (*ChannelArbitrator,
 			*lnwallet.IncomingHtlcResolution, uint32) error {
 			return nil
 		},
+		SettleInvoice: func(chainhash.Hash, lnwire.MilliSatoshi) error {
+			return nil
+		},
 	}
 
 	// We'll use the resolvedChan to synchronize on call to

contractcourt/htlc_success_resolver.go

@@ -3,9 +3,11 @@ package contractcourt
 import (
 	"encoding/binary"
 	"fmt"
-	"github.com/lightningnetwork/lnd/lnwire"
 	"io"
 
+	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/lnwire"
+
 	"github.com/btcsuite/btcd/wire"
 	"github.com/davecgh/go-spew/spew"
 	"github.com/lightningnetwork/lnd/lnwallet"
@@ -174,6 +176,14 @@ func (h *htlcSuccessResolver) Resolve() (ContractResolver, error) {
 			return nil, fmt.Errorf("quitting")
 		}
 
+		// With the HTLC claimed, we can attempt to settle its
+		// corresponding invoice if we were the original destination.
+		err = h.SettleInvoice(h.payHash, h.htlcAmt)
+		if err != nil && err != channeldb.ErrInvoiceNotFound {
+			log.Errorf("Unable to settle invoice with payment "+
+				"hash %x: %v", h.payHash, err)
+		}
+
 		// Once the transaction has received a sufficient number of
 		// confirmations, we'll mark ourselves as fully resolved and exit.
 		h.resolved = true
@@ -239,6 +249,14 @@ func (h *htlcSuccessResolver) Resolve() (ContractResolver, error) {
 		return nil, fmt.Errorf("quitting")
 	}
 
+	// With the HTLC claimed, we can attempt to settle its corresponding
+	// invoice if we were the original destination.
+	err = h.SettleInvoice(h.payHash, h.htlcAmt)
+	if err != nil && err != channeldb.ErrInvoiceNotFound {
+		log.Errorf("Unable to settle invoice with payment "+
+			"hash %x: %v", h.payHash, err)
+	}
+
 	h.resolved = true
 	return nil, h.Checkpoint(h)
 }

server.go

@@ -729,6 +729,7 @@ func newServer(listenAddrs []net.Addr, chanDB *channeldb.DB, cc *chainControl,
 			return s.announceChanStatus(op, true)
 		},
 		Sweeper:       s.sweeper,
+		SettleInvoice: s.invoices.SettleInvoice,
 	}, chanDB)
 
 	s.breachArbiter = newBreachArbiter(&BreachConfig{