htlcswitch: modify the InvoiceDatabase interface to allow specifying final payment amt

In this commit, we modify the InvoiceDatabase slightly to allow the link
to record what the final payment about for an invoice was. It may be the
case that the invoice actually had no specified value, or that the payer
paid more than necessary. As a result, it's important that our on-disk
records properly reflect this.

To fix this issue, the SettleInvoice method now also accepts the final
amount paid.

Fixes #856.

htlcswitch/interfaces.go

@@ -18,7 +18,7 @@ type InvoiceDatabase interface {
 
 	// SettleInvoice attempts to mark an invoice corresponding to the
 	// passed payment hash as fully settled.
-	SettleInvoice(chainhash.Hash) error
+	SettleInvoice(payHash chainhash.Hash, paidAmount lnwire.MilliSatoshi) error
 }
 
 // ChannelLink is an interface which represents the subsystem for managing the

htlcswitch/link.go

@@ -2298,8 +2298,9 @@ func (l *channelLink) processRemoteAdds(fwdPkg *channeldb.FwdPkg,
 			}
 
 			preimage := invoice.Terms.PaymentPreimage
-			err = l.channel.SettleHTLC(preimage,
+			err = l.channel.SettleHTLC(
-				pd.HtlcIndex, pd.SourceRef, nil, nil)
+				preimage, pd.HtlcIndex, pd.SourceRef, nil, nil,
+			)
 			if err != nil {
 				l.fail(LinkFailureError{code: ErrInternalError},
 					"unable to settle htlc: %v", err)
@@ -2307,8 +2308,11 @@ func (l *channelLink) processRemoteAdds(fwdPkg *channeldb.FwdPkg,
 			}
 
 			// Notify the invoiceRegistry of the invoices we just
-			// settled with this latest commitment update.
+			// settled (with the amount accepted at settle time)
-			err = l.cfg.Registry.SettleInvoice(invoiceHash)
+			// with this latest commitment update.
+			err = l.cfg.Registry.SettleInvoice(
+				invoiceHash, pd.Amount,
+			)
 			if err != nil {
 				l.fail(LinkFailureError{code: ErrInternalError},
 					"unable to settle invoice: %v", err)

htlcswitch/link_test.go

@@ -3657,6 +3657,13 @@ func TestChannelLinkAcceptOverpay(t *testing.T) {
 		t.Fatalf("channel bandwidth incorrect: expected %v, got %v",
 			expectedCarolBandwidth, n.carolChannelLink.Bandwidth())
 	}
+
+	// Finally, we'll ensure that the amount we paid is properly reflected
+	// in the stored invoice.
+	if invoice.AmtPaid != amount {
+		t.Fatalf("expected amt paid to be %v, is instead %v", amount,
+			invoice.AmtPaid)
+	}
 }
 
 // chanRestoreFunc is a method signature for functions that can reload both

htlcswitch/mock.go

@@ -673,7 +673,9 @@ func (i *mockInvoiceRegistry) LookupInvoice(rHash chainhash.Hash) (channeldb.Inv
 	return invoice, i.finalDelta, nil
 }
 
-func (i *mockInvoiceRegistry) SettleInvoice(rhash chainhash.Hash) error {
+func (i *mockInvoiceRegistry) SettleInvoice(rhash chainhash.Hash,
+	amt lnwire.MilliSatoshi) error {
+
 	i.Lock()
 	defer i.Unlock()
 
@@ -687,6 +689,7 @@ func (i *mockInvoiceRegistry) SettleInvoice(rhash chainhash.Hash) error {
 	}
 
 	invoice.Terms.Settled = true
+	invoice.AmtPaid = amt
 	i.invoices[rhash] = invoice
 
 	return nil