rpcserver: add SettleDate to rpcserver invoice response

lnd_test.go

@@ -2262,10 +2262,14 @@ func testInvoiceSubscriptions(net *networkHarness, t *harnessTest) {
 		}
 
 		// The invoice update should exactly match the invoice created
-		// above, but should now be settled.
+		// above, but should now be settled and have SettleDate
 		if !invoiceUpdate.Settled {
 			t.Fatalf("invoice not settled but shoudl be")
 		}
+		if invoiceUpdate.SettleDate == 0 {
+			t.Fatalf("invoice should have non zero settle date, but doesn't")
+		}
+
 		if !bytes.Equal(invoiceUpdate.RPreimage, invoice.RPreimage) {
 			t.Fatalf("payment preimages don't match: expected %v, got %v",
 				invoice.RPreimage, invoiceUpdate.RPreimage)

rpcserver.go

@@ -2123,6 +2123,11 @@ func createRPCInvoice(invoice *channeldb.Invoice) (*lnrpc.Invoice, error) {
 		fallbackAddr = decoded.FallbackAddr.String()
 	}
 
+	settleDate := int64(0)
+	if !invoice.SettleDate.IsZero() {
+		settleDate = invoice.SettleDate.Unix()
+	}
+
 	// Expiry time will default to 3600 seconds if not specified
 	// explicitly.
 	expiry := int64(decoded.Expiry().Seconds())
@@ -2140,6 +2145,7 @@ func createRPCInvoice(invoice *channeldb.Invoice) (*lnrpc.Invoice, error) {
 		RPreimage:       preimage[:],
 		Value:           int64(satAmt),
 		CreationDate:    invoice.CreationDate.Unix(),
+		SettleDate:      settleDate,
 		Settled:         invoice.Terms.Settled,
 		PaymentRequest:  paymentRequest,
 		DescriptionHash: descHash,