routing: return full htlc attempt from router

lnrpc/routerrpc/router_server.go

@@ -318,25 +318,30 @@ func (s *Server) SendToRoute(ctx context.Context,
 		return nil, err
 	}
 
-	preimage, err := s.cfg.Router.SendToRoute(hash, route)
+	// Pass route to the router. This call returns the full htlc attempt
+	// information as it is stored in the database. It is possible that both
+	// the attempt return value and err are non-nil. This can happen when
+	// the attempt was already initiated before the error happened. In that
+	// case, we give precedence to the attempt information as stored in the
+	// db.
+	attempt, err := s.cfg.Router.SendToRoute(hash, route)
+	if attempt != nil {
+		rpcAttempt, err := s.cfg.RouterBackend.MarshalHTLCAttempt(
+			*attempt,
+		)
+		if err != nil {
+			return nil, err
+		}
 
-	// In the success case, return the preimage.
-	if err == nil {
-		return &SendToRouteResponse{
-			Preimage: preimage[:],
-		}, nil
+		resp := &SendToRouteResponse{
+			Preimage: rpcAttempt.Preimage,
+			Failure:  rpcAttempt.Failure,
+		}
+
+		return resp, nil
 	}
 
-	// In the failure case, marshall the failure message to the rpc format
-	// before returning it to the caller.
-	rpcErr, err := marshallError(err)
-	if err != nil {
-		return nil, err
-	}
-
-	return &SendToRouteResponse{
-		Failure: rpcErr,
-	}, nil
+	return nil, err
 }
 
 // ResetMissionControl clears all mission control state and starts with a clean

routing/router.go

@@ -1741,10 +1741,12 @@ func (r *ChannelRouter) preparePayment(payment *LightningPayment) (
 }
 
 // SendToRoute attempts to send a payment with the given hash through the
-// provided route. This function is blocking and will return the obtained
-// preimage if the payment is successful or the full error in case of a failure.
+// provided route. This function is blocking and will return the attempt
+// information as it is stored in the database. For a successful htlc, this
+// information will contain the preimage. If an error occurs after the attempt
+// was initiated, both return values will be non-nil.
 func (r *ChannelRouter) SendToRoute(hash lntypes.Hash, rt *route.Route) (
-	lntypes.Preimage, error) {
+	*channeldb.HTLCAttempt, error) {
 
 	// Calculate amount paid to receiver.
 	amt := rt.ReceiverAmt()
@@ -1774,7 +1776,7 @@ func (r *ChannelRouter) SendToRoute(hash lntypes.Hash, rt *route.Route) (
 
 	// Any other error is not tolerated.
 	case err != nil:
-		return [32]byte{}, err
+		return nil, err
 	}
 
 	log.Tracef("Dispatching SendToRoute for hash %v: %v",
@@ -1804,34 +1806,37 @@ func (r *ChannelRouter) SendToRoute(hash lntypes.Hash, rt *route.Route) (
 			hash, channeldb.FailureReasonError,
 		)
 		if controlErr != nil {
-			return [32]byte{}, controlErr
+			return nil, controlErr
 		}
 	}
 
 	// In any case, don't continue if there is an error.
 	if err != nil {
-		return lntypes.Preimage{}, err
+		return nil, err
 	}
 
+	var htlcAttempt *channeldb.HTLCAttempt
 	switch {
 	// Failed to launch shard.
 	case outcome.err != nil:
 		shardError = outcome.err
+		htlcAttempt = outcome.attempt
 
 	// Shard successfully launched, wait for the result to be available.
 	default:
 		result, err := sh.collectResult(attempt)
 		if err != nil {
-			return lntypes.Preimage{}, err
+			return nil, err
 		}
 
 		// We got a successful result.
 		if result.err == nil {
-			return result.attempt.Settle.Preimage, nil
+			return result.attempt, nil
 		}
 
 		// The shard failed, break switch to handle it.
 		shardError = result.err
+		htlcAttempt = result.attempt
 	}
 
 	// Since for SendToRoute we won't retry in case the shard fails, we'll
@@ -1848,10 +1853,10 @@ func (r *ChannelRouter) SendToRoute(hash lntypes.Hash, rt *route.Route) (
 
 	err = r.cfg.Control.Fail(hash, *reason)
 	if err != nil {
-		return lntypes.Preimage{}, err
+		return nil, err
 	}
 
-	return lntypes.Preimage{}, shardError
+	return htlcAttempt, shardError
 }
 
 // sendPayment attempts to send a payment to the passed payment hash. This

routing/router_test.go

@@ -2809,13 +2809,13 @@ func TestSendToRouteMultiShardSend(t *testing.T) {
 
 	for i := 0; i < numShards; i++ {
 		go func() {
-			preimg, err := ctx.router.SendToRoute(payment, rt)
+			attempt, err := ctx.router.SendToRoute(payment, rt)
 			if err != nil {
 				errChan <- err
 				return
 			}
 
-			successes <- preimg
+			successes <- attempt.Settle.Preimage
 		}()
 	}
 

rpcserver.go

@@ -3978,10 +3978,15 @@ func (r *rpcServer) dispatchPaymentIntent(
 			payment,
 		)
 	} else {
-		preImage, routerErr = r.server.chanRouter.SendToRoute(
+		var attempt *channeldb.HTLCAttempt
+		attempt, routerErr = r.server.chanRouter.SendToRoute(
 			payIntent.rHash, payIntent.route,
 		)
 
+		if routerErr == nil {
+			preImage = attempt.Settle.Preimage
+		}
+
 		route = payIntent.route
 	}