discovery+switch: apply zero forwarding policy updates in-memory as w…

…ell as on disk

In this commit, we fix a bug where if a user updates a forwarding policy to be
zero, the update will be applied to the policy correctly on-disk, but not
in-memory.

We solve this issue by having the gossiper return the list of on-disk updated
policies and passing these policies to the switch, so the switch can assume
that zero-valued fields are intentional and not just uninitialized.

discovery/gossiper.go

@@ -93,7 +93,7 @@ type chanPolicyUpdateRequest struct {
 	targetChans []wire.OutPoint
 	newSchema   routing.ChannelPolicy
 
-	errResp chan error
+	chanPolicies chan updatedChanPolicies
 }
 
 // Config defines the configuration for the service. ALL elements within the
@@ -338,27 +338,40 @@ func New(cfg Config, selfKey *btcec.PublicKey) *AuthenticatedGossiper {
 	return gossiper
 }
 
+// updatedChanPolicies is a set of channel policies that have been successfully
+// updated and written to disk, or an error if the policy update failed. This
+// struct's map field is intended to be used for updating channel policies on
+// the link layer.
+type updatedChanPolicies struct {
+	chanPolicies map[wire.OutPoint]*channeldb.ChannelEdgePolicy
+	err          error
+}
+
 // PropagateChanPolicyUpdate signals the AuthenticatedGossiper to update the
 // channel forwarding policies for the specified channels. If no channels are
 // specified, then the update will be applied to all outgoing channels from the
 // source node. Policy updates are done in two stages: first, the
 // AuthenticatedGossiper ensures the update has been committed by dependent
-// sub-systems, then it signs and broadcasts new updates to the network.
+// sub-systems, then it signs and broadcasts new updates to the network. A
+// mapping between outpoints and updated channel policies is returned, which is
+// used to update the forwarding policies of the underlying links.
 func (d *AuthenticatedGossiper) PropagateChanPolicyUpdate(
-	newSchema routing.ChannelPolicy, chanPoints ...wire.OutPoint) error {
+	newSchema routing.ChannelPolicy, chanPoints ...wire.OutPoint) (
+	map[wire.OutPoint]*channeldb.ChannelEdgePolicy, error) {
 
-	errChan := make(chan error, 1)
+	chanPolicyChan := make(chan updatedChanPolicies, 1)
 	policyUpdate := &chanPolicyUpdateRequest{
-		targetChans: chanPoints,
-		newSchema:   newSchema,
-		errResp:     errChan,
+		targetChans:  chanPoints,
+		newSchema:    newSchema,
+		chanPolicies: chanPolicyChan,
 	}
 
 	select {
 	case d.chanPolicyUpdates <- policyUpdate:
-		return <-errChan
+		updatedPolicies := <-chanPolicyChan
+		return updatedPolicies.chanPolicies, updatedPolicies.err
 	case <-d.quit:
-		return fmt.Errorf("AuthenticatedGossiper shutting down")
+		return nil, fmt.Errorf("AuthenticatedGossiper shutting down")
 	}
 }
 
@@ -895,13 +908,17 @@ func (d *AuthenticatedGossiper) networkHandler() {
 			// First, we'll now create new fully signed updates for
 			// the affected channels and also update the underlying
 			// graph with the new state.
-			newChanUpdates, err := d.processChanPolicyUpdate(
+			chanPolicies, newChanUpdates, err := d.processChanPolicyUpdate(
 				policyUpdate,
 			)
+			update := updatedChanPolicies{
+				chanPolicies,
+				err,
+			}
+			policyUpdate.chanPolicies <- update
 			if err != nil {
 				log.Errorf("Unable to craft policy updates: %v",
 					err)
-				policyUpdate.errResp <- err
 				continue
 			}
 
@@ -910,8 +927,6 @@ func (d *AuthenticatedGossiper) networkHandler() {
 			// start of the next epoch.
 			announcements.AddMsgs(newChanUpdates...)
 
-			policyUpdate.errResp <- nil
-
 		case announcement := <-d.networkMsgs:
 			// We should only broadcast this message forward if it
 			// originated from us or it wasn't received as part of
@@ -1244,14 +1259,20 @@ func (d *AuthenticatedGossiper) retransmitStaleChannels() error {
 //
 // TODO(roasbeef): generalize into generic for any channel update
 func (d *AuthenticatedGossiper) processChanPolicyUpdate(
-	policyUpdate *chanPolicyUpdateRequest) ([]networkMsg, error) {
+	policyUpdate *chanPolicyUpdateRequest) (
+	map[wire.OutPoint]*channeldb.ChannelEdgePolicy, []networkMsg, error) {
+
 	// First, we'll construct a set of all the channels that need to be
 	// updated.
 	chansToUpdate := make(map[wire.OutPoint]struct{})
 	for _, chanPoint := range policyUpdate.targetChans {
 		chansToUpdate[chanPoint] = struct{}{}
 	}
 
+	// Next, we'll create a mapping from outpoint to edge policy that will
+	// be used by each edge's underlying link to update its policy.
+	chanPolicies := make(map[wire.OutPoint]*channeldb.ChannelEdgePolicy)
+
 	haveChanFilter := len(chansToUpdate) != 0
 	if haveChanFilter {
 		log.Infof("Updating routing policies for chan_points=%v",
@@ -1295,7 +1316,7 @@ func (d *AuthenticatedGossiper) processChanPolicyUpdate(
 		return nil
 	})
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 
 	// With the set of edges we need to update retrieved, we'll now re-sign
@@ -1309,9 +1330,13 @@ func (d *AuthenticatedGossiper) processChanPolicyUpdate(
 			edgeInfo.info, edgeInfo.edge,
 		)
 		if err != nil {
-			return nil, err
+			return nil, nil, err
 		}
 
+		// Since the update succeeded, add the edge to our policy
+		// mapping.
+		chanPolicies[edgeInfo.info.ChannelPoint] = edgeInfo.edge
+
 		// We'll avoid broadcasting any updates for private channels to
 		// avoid directly giving away their existence. Instead, we'll
 		// send the update directly to the remote party.
@@ -1340,7 +1365,7 @@ func (d *AuthenticatedGossiper) processChanPolicyUpdate(
 		})
 	}
 
-	return chanUpdates, nil
+	return chanPolicies, chanUpdates, nil
 }
 
 // processRejectedEdge examines a rejected edge to see if we can extract any

discovery/gossiper_test.go

@@ -3391,8 +3391,14 @@ func TestPropagateChanPolicyUpdate(t *testing.T) {
 	// the channel ann proof from the first channel in order to have it be
 	// marked as private channel.
 	firstChanID := channelsToAnnounce[0].localChanAnn.ShortChannelID
-	for _, batch := range channelsToAnnounce {
-		sendLocalMsg(t, ctx, batch.localChanAnn, localKey)
+	for i, batch := range channelsToAnnounce {
+		// channelPoint ensures that each channel policy in the map
+		// returned by PropagateChanPolicyUpdate has a unique key. Since
+		// the map is keyed by wire.OutPoint, we want to ensure that
+		// each channel has a unique channel point.
+		channelPoint := ChannelPoint(wire.OutPoint{Index: uint32(i)})
+
+		sendLocalMsg(t, ctx, batch.localChanAnn, localKey, channelPoint)
 		sendLocalMsg(t, ctx, batch.chanUpdAnn1, localKey)
 		sendLocalMsg(t, ctx, batch.nodeAnn1, localKey)
 
@@ -3430,11 +3436,19 @@ out:
 	newPolicy := routing.ChannelPolicy{
 		TimeLockDelta: newTimeLockDelta,
 	}
-	err = ctx.gossiper.PropagateChanPolicyUpdate(newPolicy)
+	newChanPolicies, err := ctx.gossiper.PropagateChanPolicyUpdate(newPolicy)
 	if err != nil {
 		t.Fatalf("unable to chan policies: %v", err)
 	}
 
+	// Ensure that the updated channel policies are as expected.
+	for _, dbPolicy := range newChanPolicies {
+		if dbPolicy.TimeLockDelta != uint16(newPolicy.TimeLockDelta) {
+			t.Fatalf("wrong delta: expected %v, got %v",
+				newPolicy.TimeLockDelta, dbPolicy.TimeLockDelta)
+		}
+	}
+
 	// Two channel updates should now be broadcast, with neither of them
 	// being the channel our first private channel.
 	for i := 0; i < numChannels-1; i++ {

htlcswitch/link.go

@@ -2156,31 +2156,16 @@ func (l *channelLink) AttachMailBox(mailbox MailBox) {
 
 // UpdateForwardingPolicy updates the forwarding policy for the target
 // ChannelLink. Once updated, the link will use the new forwarding policy to
-// govern if it an incoming HTLC should be forwarded or not. Note that this
-// processing of the new policy will ensure that uninitialized fields in the
-// passed policy won't override already initialized fields in the current
-// policy.
+// govern if it an incoming HTLC should be forwarded or not. We assume that
+// fields that are zero are intentionally set to zero, so we'll use newPolicy to
+// update all of the link's FwrdingPolicy's values.
 //
 // NOTE: Part of the ChannelLink interface.
 func (l *channelLink) UpdateForwardingPolicy(newPolicy ForwardingPolicy) {
 	l.Lock()
 	defer l.Unlock()
 
-	// In order to avoid overriding a valid policy with a "null" field in
-	// the new policy, we'll only update to the set sub policy if the new
-	// value isn't uninitialized.
-	if newPolicy.BaseFee != 0 {
-		l.cfg.FwrdingPolicy.BaseFee = newPolicy.BaseFee
-	}
-	if newPolicy.FeeRate != 0 {
-		l.cfg.FwrdingPolicy.FeeRate = newPolicy.FeeRate
-	}
-	if newPolicy.TimeLockDelta != 0 {
-		l.cfg.FwrdingPolicy.TimeLockDelta = newPolicy.TimeLockDelta
-	}
-	if newPolicy.MinHTLC != 0 {
-		l.cfg.FwrdingPolicy.MinHTLC = newPolicy.MinHTLC
-	}
+	l.cfg.FwrdingPolicy = newPolicy
 }
 
 // HtlcSatifiesPolicy should return a nil error if the passed HTLC details

htlcswitch/link_test.go

@@ -5530,9 +5530,9 @@ func TestForwardingAsymmetricTimeLockPolicies(t *testing.T) {
 	// Now that each of the links are up, we'll modify the link from Alice
 	// -> Bob to have a greater time lock delta than that of the link of
 	// Bob -> Carol.
-	n.firstBobChannelLink.UpdateForwardingPolicy(ForwardingPolicy{
-		TimeLockDelta: 7,
-	})
+	newPolicy := n.firstBobChannelLink.cfg.FwrdingPolicy
+	newPolicy.TimeLockDelta = 7
+	n.firstBobChannelLink.UpdateForwardingPolicy(newPolicy)
 
 	// Now that the Alice -> Bob link has been updated, we'll craft and
 	// send a payment from Alice -> Carol. This should succeed as normal,

htlcswitch/switch.go

@@ -439,60 +439,51 @@ func (s *Switch) SendHTLC(firstHop lnwire.ShortChannelID, paymentID uint64,
 }
 
 // UpdateForwardingPolicies sends a message to the switch to update the
-// forwarding policies for the set of target channels. If the set of targeted
-// channels is nil, then the forwarding policies for all active channels with
-// be updated.
+// forwarding policies for the set of target channels, keyed in chanPolicies.
 //
 // NOTE: This function is synchronous and will block until either the
 // forwarding policies for all links have been updated, or the switch shuts
 // down.
-func (s *Switch) UpdateForwardingPolicies(newPolicy ForwardingPolicy,
-	targetChans ...wire.OutPoint) error {
+func (s *Switch) UpdateForwardingPolicies(
+	chanPolicies map[wire.OutPoint]*channeldb.ChannelEdgePolicy) {
 
-	log.Debugf("Updating link policies: %v", newLogClosure(func() string {
-		return spew.Sdump(newPolicy)
+	log.Tracef("Updating link policies: %v", newLogClosure(func() string {
+		return spew.Sdump(chanPolicies)
 	}))
 
-	var linksToUpdate []ChannelLink
-
 	s.indexMtx.RLock()
 
-	// If no channels have been targeted, then we'll collect all inks to
-	// update their policies.
-	if len(targetChans) == 0 {
-		for _, link := range s.linkIndex {
-			linksToUpdate = append(linksToUpdate, link)
-		}
-	} else {
-		// Otherwise, we'll only attempt to update the forwarding
-		// policies for the set of targeted links.
-		for _, targetLink := range targetChans {
-			cid := lnwire.NewChanIDFromOutPoint(&targetLink)
-
-			// If we can't locate a link by its converted channel
-			// ID, then we'll return an error back to the caller.
-			link, ok := s.linkIndex[cid]
-			if !ok {
-				s.indexMtx.RUnlock()
-
-				return fmt.Errorf("unable to find "+
-					"ChannelPoint(%v) to update link "+
-					"policy", targetLink)
-			}
+	// Update each link in chanPolicies.
+	for targetLink := range chanPolicies {
+		cid := lnwire.NewChanIDFromOutPoint(&targetLink)
 
-			linksToUpdate = append(linksToUpdate, link)
+		link, ok := s.linkIndex[cid]
+		if !ok {
+			log.Debugf("Unable to find ChannelPoint(%v) to update "+
+				"link policy", targetLink)
+			continue
 		}
+
+		newPolicy := dbPolicyToFwdingPolicy(
+			chanPolicies[*link.ChannelPoint()],
+		)
+		link.UpdateForwardingPolicy(newPolicy)
 	}
 
 	s.indexMtx.RUnlock()
+}
 
-	// With all the links we need to update collected, we can release the
-	// mutex then update each link directly.
-	for _, link := range linksToUpdate {
-		link.UpdateForwardingPolicy(newPolicy)
+// dbPolicyToFwdingPolicy is a helper function that converts a channeldb
+// ChannelEdgePolicy into a ForwardingPolicy struct for the purpose of updating
+// the forwarding policy of a link.
+func dbPolicyToFwdingPolicy(policy *channeldb.ChannelEdgePolicy) ForwardingPolicy {
+	return ForwardingPolicy{
+		BaseFee:       policy.FeeBaseMSat,
+		FeeRate:       policy.FeeProportionalMillionths,
+		TimeLockDelta: uint32(policy.TimeLockDelta),
+		MinHTLC:       policy.MinHTLC,
+		MaxHTLC:       policy.MaxHTLC,
 	}
-
-	return nil
 }
 
 // forward is used in order to find next channel link and apply htlc update.

rpcserver.go

@@ -4550,6 +4550,12 @@ func (r *rpcServer) FeeReport(ctx context.Context,
 // 0.000001, or 0.0001%.
 const minFeeRate = 1e-6
 
+// policyUpdateLock ensures that the database and the link do not fall out of
+// sync if there are concurrent fee update calls. Without it, there is a chance
+// that policy A updates the database, then policy B updates the database, then
+// policy B updates the link, then policy A updates the link.
+var policyUpdateLock sync.Mutex
+
 // UpdateChannelPolicy allows the caller to update the channel forwarding policy
 // for all channels globally, or a particular channel.
 func (r *rpcServer) UpdateChannelPolicy(ctx context.Context,
@@ -4617,30 +4623,18 @@ func (r *rpcServer) UpdateChannelPolicy(ctx context.Context,
 	// With the scope resolved, we'll now send this to the
 	// AuthenticatedGossiper so it can propagate the new policy for our
 	// target channel(s).
-	err := r.server.authGossiper.PropagateChanPolicyUpdate(
+	policyUpdateLock.Lock()
+	defer policyUpdateLock.Unlock()
+	chanPolicies, err := r.server.authGossiper.PropagateChanPolicyUpdate(
 		chanPolicy, targetChans...,
 	)
 	if err != nil {
 		return nil, err
 	}
 
-	// Finally, we'll apply the set of active links amongst the target
-	// channels.
-	//
-	// We create a partially policy as the logic won't overwrite a valid
-	// sub-policy with a "nil" one.
-	p := htlcswitch.ForwardingPolicy{
-		BaseFee:       baseFeeMsat,
-		FeeRate:       lnwire.MilliSatoshi(feeRateFixed),
-		TimeLockDelta: req.TimeLockDelta,
-	}
-	err = r.server.htlcSwitch.UpdateForwardingPolicies(p, targetChans...)
-	if err != nil {
-		// If we're unable update the fees due to the links not being
-		// online, then we don't need to fail the call. We'll simply
-		// log the failure.
-		rpcsLog.Warnf("Unable to update link fees: %v", err)
-	}
+	// Finally, we'll apply the set of channel policies to the target
+	// channels' links.
+	r.server.htlcSwitch.UpdateForwardingPolicies(chanPolicies)
 
 	return &lnrpc.PolicyUpdateResponse{}, nil
 }