130 lines
4.3 KiB
Go
130 lines
4.3 KiB
Go
package feature
|
|
|
|
import (
|
|
"fmt"
|
|
|
|
"github.com/lightningnetwork/lnd/lnwire"
|
|
)
|
|
|
|
type (
|
|
// featureSet contains a set of feature bits.
|
|
featureSet map[lnwire.FeatureBit]struct{}
|
|
|
|
// supportedFeatures maps the feature bit from a feature vector to a
|
|
// boolean indicating if this features dependencies have already been
|
|
// verified. This allows us to short circuit verification if multiple
|
|
// features have common dependencies, or map traversal starts verifying
|
|
// from the bottom up.
|
|
supportedFeatures map[lnwire.FeatureBit]bool
|
|
|
|
// depDesc maps a features to its set of dependent features, which must
|
|
// also be present for the vector to be valid. This can be used to
|
|
// recursively check the dependency chain for features in a feature
|
|
// vector.
|
|
depDesc map[lnwire.FeatureBit]featureSet
|
|
)
|
|
|
|
// ErrMissingFeatureDep is an error signaling that a transitive dependency in a
|
|
// feature vector is not set properly.
|
|
type ErrMissingFeatureDep struct {
|
|
dep lnwire.FeatureBit
|
|
}
|
|
|
|
// NewErrMissingFeatureDep creates a new ErrMissingFeatureDep error.
|
|
func NewErrMissingFeatureDep(dep lnwire.FeatureBit) ErrMissingFeatureDep {
|
|
return ErrMissingFeatureDep{dep: dep}
|
|
}
|
|
|
|
// Error returns a human-readable description of the missing dep error.
|
|
func (e ErrMissingFeatureDep) Error() string {
|
|
return fmt.Sprintf("missing feature dependency: %v", e.dep)
|
|
}
|
|
|
|
// deps is the default set of dependencies for assigned feature bits. If a
|
|
// feature is not present in the depDesc it is assumed to have no dependencies.
|
|
//
|
|
// NOTE: For proper functioning, only the optional variant of feature bits
|
|
// should be used in the following descriptor. In the future it may be necessary
|
|
// to distinguish the dependencies for optional and required bits, but for now
|
|
// the validation code maps required bits to optional ones since it simplifies
|
|
// the number of constraints.
|
|
var deps = depDesc{
|
|
lnwire.PaymentAddrOptional: {
|
|
lnwire.TLVOnionPayloadOptional: {},
|
|
},
|
|
lnwire.MPPOptional: {
|
|
lnwire.PaymentAddrOptional: {},
|
|
},
|
|
}
|
|
|
|
// ValidateDeps asserts that a feature vector sets all features and their
|
|
// transitive dependencies properly. It assumes that the dependencies between
|
|
// optional and required features are identical, e.g. if a feature is required
|
|
// but its dependency is optional, that is sufficient.
|
|
func ValidateDeps(fv *lnwire.FeatureVector) error {
|
|
features := fv.Features()
|
|
supported := initSupported(features)
|
|
|
|
return validateDeps(features, supported)
|
|
}
|
|
|
|
// validateDeps is a subroutine that recursively checks that the passed features
|
|
// have all of their associated dependencies in the supported map.
|
|
func validateDeps(features featureSet, supported supportedFeatures) error {
|
|
for bit := range features {
|
|
// Convert any required bits to optional.
|
|
bit = mapToOptional(bit)
|
|
|
|
// If the supported features doesn't contain the dependency, this
|
|
// vector is invalid.
|
|
checked, ok := supported[bit]
|
|
if !ok {
|
|
return NewErrMissingFeatureDep(bit)
|
|
}
|
|
|
|
// Alternatively, if we know that this depdendency is valid, we
|
|
// can short circuit and continue verifying other bits.
|
|
if checked {
|
|
continue
|
|
}
|
|
|
|
// Recursively validate dependencies, since this method ranges
|
|
// over the subDeps. This method will return true even if
|
|
// subDeps is nil.
|
|
subDeps := deps[bit]
|
|
if err := validateDeps(subDeps, supported); err != nil {
|
|
return err
|
|
}
|
|
|
|
// Once we've confirmed that this feature's dependencies, if
|
|
// any, are sound, we record this so other paths taken through
|
|
// `bit` return early when inspecting the supported map.
|
|
supported[bit] = true
|
|
}
|
|
|
|
return nil
|
|
}
|
|
|
|
// initSupported sets all bits from the feature vector as supported but not
|
|
// checked. This signals that the validity of their dependencies has not been
|
|
// verified. All required bits are mapped to optional to simplify the DAG.
|
|
func initSupported(features featureSet) supportedFeatures {
|
|
supported := make(supportedFeatures)
|
|
for bit := range features {
|
|
bit = mapToOptional(bit)
|
|
supported[bit] = false
|
|
}
|
|
|
|
return supported
|
|
}
|
|
|
|
// mapToOptional returns the optional variant of a given feature bit pair. Our
|
|
// dependendency graph is described using only optional feature bits, which
|
|
// reduces the number of constraints we need to express in the descriptor.
|
|
func mapToOptional(bit lnwire.FeatureBit) lnwire.FeatureBit {
|
|
if bit.IsRequired() {
|
|
bit ^= 0x01
|
|
}
|
|
return bit
|
|
}
|