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