feature: add update function for safe feature update

Disallow update of any features that are defined by LND (since
just updating the feature, but not the functionality will result in
strange behavior). All known feature bits should be toggled using
protocol config options.

feature/manager.go

@@ -1,11 +1,16 @@
 package feature
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/lightningnetwork/lnd/lnwire"
 )
 
+// ErrUnknownSet is returned if a proposed feature vector contains a set that
+// is unknown to LND.
+var ErrUnknownSet = errors.New("unknown feature bit set")
+
 // Config houses any runtime modifications to the default set descriptors. For
 // our purposes, this typically means disabling certain features to test legacy
 // protocol interoperability or functionality.
@@ -198,3 +203,40 @@ func (m *Manager) ListSets() []Set {
 
 	return sets
 }
+
+// UpdateFeatureSets accepts a map of new feature vectors for each of the
+// manager's known sets, validates that the update can be applied and modifies
+// the feature manager's internal state. If a set is not included in the update
+// map, it is left unchanged. The feature vectors provided are expected to
+// include the current set of features, updated with desired bits added/removed.
+func (m *Manager) UpdateFeatureSets(
+	updates map[Set]*lnwire.RawFeatureVector) error {
+
+	for set, newFeatures := range updates {
+		if !set.valid() {
+			return fmt.Errorf("%w: set: %d", ErrUnknownSet, set)
+		}
+
+		if err := newFeatures.ValidatePairs(); err != nil {
+			return err
+		}
+
+		if err := m.Get(set).ValidateUpdate(newFeatures); err != nil {
+			return err
+		}
+
+		fv := lnwire.NewFeatureVector(newFeatures, lnwire.Features)
+		if err := ValidateDeps(fv); err != nil {
+			return err
+		}
+	}
+
+	// Only update the current feature sets once every proposed set has
+	// passed validation so that we don't partially update any sets then
+	// fail out on a later set's validation.
+	for set, features := range updates {
+		m.SetRaw(set, features.Clone())
+	}
+
+	return nil
+}