lndclient: add preimage to invoice subscription

lndclient/invoices_client.go

@@ -30,6 +30,10 @@ type InvoicesClient interface {
 type InvoiceUpdate struct {
 	State   channeldb.ContractState
 	AmtPaid btcutil.Amount
+
+	// Preimage is the preimage for the invoice that has just been
+	// paid. This field will be nil for updates that are not settles.
+	Preimage *lntypes.Preimage
 }
 
 type invoicesClient struct {
@@ -111,11 +115,26 @@ func (s *invoicesClient) SubscribeSingleInvoice(ctx context.Context,
 				return
 			}
 
-			select {
-			case updateChan <- InvoiceUpdate{
+			update := InvoiceUpdate{
 				State:   state,
 				AmtPaid: btcutil.Amount(invoice.AmtPaidSat),
-			}:
+			}
+
+			// If the invoice is settled, we expect the preimage
+			// to be present so we include it.
+			if state == channeldb.ContractSettled {
+				preimage, err := lntypes.MakePreimage(
+					invoice.RPreimage,
+				)
+				if err != nil {
+					errChan <- err
+					return
+				}
+				update.Preimage = &preimage
+			}
+
+			select {
+			case updateChan <- update:
 			case <-ctx.Done():
 				return
 			}

loopin_test.go

@@ -10,6 +10,7 @@ import (
 	"github.com/lightninglabs/loop/test"
 	"github.com/lightningnetwork/lnd/chainntnfs"
 	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/lntypes"
 
 	"github.com/btcsuite/btcd/wire"
 	"github.com/btcsuite/btcutil"
@@ -82,11 +83,17 @@ func TestLoopInSuccess(t *testing.T) {
 		t.Fatal("client subscribing to wrong invoice")
 	}
 
+	typedPreimage, err := lntypes.MakePreimage(testPreimage[:])
+	if err != nil {
+		t.Fatalf("could not make preimage: %v", err)
+	}
+
 	// Server has already paid invoice before spending the htlc. Signal
 	// settled.
 	subscription.Update <- lndclient.InvoiceUpdate{
-		State:   channeldb.ContractSettled,
-		AmtPaid: 49000,
+		State:    channeldb.ContractSettled,
+		AmtPaid:  49000,
+		Preimage: &typedPreimage,
 	}
 
 	// Swap is expected to move to the state InvoiceSettled
@@ -393,11 +400,17 @@ func testLoopInResume(t *testing.T, state loopdb.SwapState, expired bool) {
 		t.Fatal("client subscribing to wrong invoice")
 	}
 
+	typedPreimage, err := lntypes.MakePreimage(testPreimage[:])
+	if err != nil {
+		t.Fatalf("could not make preimage: %v", err)
+	}
+
 	// Server has already paid invoice before spending the htlc. Signal
 	// settled.
 	subscription.Update <- lndclient.InvoiceUpdate{
-		State:   channeldb.ContractSettled,
-		AmtPaid: 49000,
+		State:    channeldb.ContractSettled,
+		AmtPaid:  49000,
+		Preimage: &typedPreimage,
 	}
 
 	// Swap is expected to move to the state InvoiceSettled