itest: set error codes for failed lnd payments

itest/lntest/lnd_node.go

@@ -639,7 +639,28 @@ func (n *LndNode) PayViaRoute(amountMsat uint64, paymentHash []byte, paymentSecr
 	}
 
 	if resp.PaymentRoute == nil {
-		n.harness.T.Fatal(fmt.Errorf("missing payment route after pay"))
+		payments, err := n.runtime.rpc.ListPayments(n.harness.Ctx, &lnd.ListPaymentsRequest{
+			IncludeIncomplete: true,
+		})
+		CheckError(n.harness.T, err)
+
+		paymentHashStr := hex.EncodeToString(paymentHash)
+		for _, payment := range payments.Payments {
+			if payment.PaymentHash != paymentHashStr {
+				continue
+			}
+
+			switch payment.Htlcs[0].Failure.Code {
+			case lnd.Failure_TEMPORARY_CHANNEL_FAILURE:
+				return nil, fmt.Errorf("WIRE_TEMPORARY_CHANNEL_FAILURE")
+			case lnd.Failure_UNKNOWN_NEXT_PEER:
+				return nil, fmt.Errorf("WIRE_UNKNOWN_NEXT_PEER")
+			case lnd.Failure_UNKNOWN_FAILURE:
+				return nil, fmt.Errorf("WIRE_TEMPORARY_CHANNEL_FAILURE")
+			}
+		}
+
+		return nil, fmt.Errorf("missing payment route after pay")
 	}
 
 	lastHop := resp.PaymentRoute.Hops[len(resp.PaymentRoute.Hops)-1]