lnwire: add feature vector update validation helpers

lnwire/features.go

@@ -3,6 +3,7 @@ package lnwire
 import (
 	"encoding/binary"
 	"errors"
+	"fmt"
 	"io"
 )
 
@@ -10,6 +11,11 @@ var (
 	// ErrFeaturePairExists signals an error in feature vector construction
 	// where the opposing bit in a feature pair has already been set.
 	ErrFeaturePairExists = errors.New("feature pair exists")
+
+	// ErrFeatureStandard is returned when attempts to modify LND's known
+	// set of features are made.
+	ErrFeatureStandard = errors.New("feature is used in standard " +
+		"protocol set")
 )
 
 // FeatureBit represents a feature that can be enabled in either a local or
@@ -344,6 +350,57 @@ func (fv *RawFeatureVector) Merge(other *RawFeatureVector) error {
 	return nil
 }
 
+// ValidateUpdate checks whether a feature vector can safely be updated to the
+// new feature vector provided, checking that it does not alter any of the
+// "standard" features that are defined by LND. The new feature vector should
+// be inclusive of all features in the original vector that it still wants to
+// advertise, setting and unsetting updates as desired.
+func (fv *RawFeatureVector) ValidateUpdate(other *RawFeatureVector) error {
+	// Run through the new set of features and check that we're not adding
+	// any feature bits that are defined but not set in LND.
+	for feature := range other.features {
+		if fv.IsSet(feature) {
+			continue
+		}
+
+		if name, known := Features[feature]; known {
+			return fmt.Errorf("can't set feature "+
+				"bit %d (%v): %w", feature, name,
+				ErrFeatureStandard)
+		}
+	}
+
+	// Check that the new feature vector for this set does not unset any
+	// features that are standard in LND by comparing the features in our
+	// current set to the omitted values in the new set.
+	for feature := range fv.features {
+		if other.IsSet(feature) {
+			continue
+		}
+
+		if name, known := Features[feature]; known {
+			return fmt.Errorf("can't unset feature "+
+				"bit %d (%v): %w", feature, name,
+				ErrFeatureStandard)
+		}
+	}
+
+	return nil
+}
+
+// ValidatePairs checks each feature bit in a raw vector to ensure that the
+// opposing bit is not set, validating that the vector has either the optional
+// or required bit set, not both.
+func (fv *RawFeatureVector) ValidatePairs() error {
+	for feature := range fv.features {
+		if _, ok := fv.features[feature^1]; ok {
+			return ErrFeaturePairExists
+		}
+	}
+
+	return nil
+}
+
 // Clone makes a copy of a feature vector.
 func (fv *RawFeatureVector) Clone() *RawFeatureVector {
 	newFeatures := NewRawFeatureVector()