feature: add new feature pkg to manage feature sets

This commit introduces a feature.Manager, which derives feature vectors
for various contexts within the daemon. The sets can be described via a
staticly compiled format, which makes any runtime adjustments to the
feature sets when the manager is initialized.

feature/default_sets.go

@@ -0,0 +1,32 @@
+package feature
+
+import "github.com/lightningnetwork/lnd/lnwire"
+
+// setDesc describes which feature bits should be advertised in which feature
+// sets.
+type setDesc map[lnwire.FeatureBit]map[Set]struct{}
+
+// defaultSetDesc are the default set descriptors for generating feature
+// vectors. Each set is annotated with the corresponding identifier from BOLT 9
+// indicating where it should be advertised.
+var defaultSetDesc = setDesc{
+	lnwire.DataLossProtectRequired: {
+		SetInit:    {}, // I
+		SetNodeAnn: {}, // N
+	},
+	lnwire.GossipQueriesOptional: {
+		SetInit:    {}, // I
+		SetNodeAnn: {}, // N
+	},
+	lnwire.TLVOnionPayloadOptional: {
+		SetInit:         {}, // I
+		SetNodeAnn:      {}, // N
+		SetInvoice:      {}, // 9
+		SetLegacyGlobal: {},
+	},
+	lnwire.StaticRemoteKeyOptional: {
+		SetInit:         {}, // I
+		SetNodeAnn:      {}, // N
+		SetLegacyGlobal: {},
+	},
+}

feature/manager.go

@@ -0,0 +1,97 @@
+package feature
+
+import (
+	"fmt"
+
+	"github.com/lightningnetwork/lnd/lnwire"
+)
+
+// 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.
+type Config struct {
+	// NoTLVOnion unsets any optional or required TLVOnionPaylod bits from
+	// all feature sets.
+	NoTLVOnion bool
+
+	// NoStaticRemoteKey unsets any optional or required StaticRemoteKey
+	// bits from all feature sets.
+	NoStaticRemoteKey bool
+}
+
+// Manager is responsible for generating feature vectors for different requested
+// feature sets.
+type Manager struct {
+	// fsets is a static map of feature set to raw feature vectors. Requests
+	// are fulfilled by cloning these interal feature vectors.
+	fsets map[Set]*lnwire.RawFeatureVector
+}
+
+// NewManager creates a new feature Manager, applying any custom modifications
+// to its feature sets before returning.
+func NewManager(cfg Config) (*Manager, error) {
+	return newManager(cfg, defaultSetDesc)
+}
+
+// newManager creates a new feeature Manager, applying any custom modifications
+// to its feature sets before returning. This method accepts the setDesc as its
+// own parameter so that it can be unit tested.
+func newManager(cfg Config, desc setDesc) (*Manager, error) {
+	// First build the default feature vector for all known sets.
+	fsets := make(map[Set]*lnwire.RawFeatureVector)
+	for bit, sets := range desc {
+		for set := range sets {
+			// Fetch the feature vector for this set, allocating a
+			// new one if it doesn't exist.
+			fv, ok := fsets[set]
+			if !ok {
+				fv = lnwire.NewRawFeatureVector()
+			}
+
+			// Set the configured bit on the feature vector,
+			// ensuring that we don't set two feature bits for the
+			// same pair.
+			err := fv.SafeSet(bit)
+			if err != nil {
+				return nil, fmt.Errorf("unable to set "+
+					"%v in %v: %v", bit, set, err)
+			}
+
+			// Write the updated feature vector under its set.
+			fsets[set] = fv
+		}
+	}
+
+	// Now, remove any features as directed by the config.
+	for _, fv := range fsets {
+		if cfg.NoTLVOnion {
+			fv.Unset(lnwire.TLVOnionPayloadOptional)
+			fv.Unset(lnwire.TLVOnionPayloadRequired)
+		}
+		if cfg.NoStaticRemoteKey {
+			fv.Unset(lnwire.StaticRemoteKeyOptional)
+			fv.Unset(lnwire.StaticRemoteKeyRequired)
+		}
+	}
+
+	return &Manager{
+		fsets: fsets,
+	}, nil
+}
+
+// GetRaw returns a raw feature vector for the passed set. If no set is known,
+// an empty raw feature vector is returned.
+func (m *Manager) GetRaw(set Set) *lnwire.RawFeatureVector {
+	if fv, ok := m.fsets[set]; ok {
+		return fv.Clone()
+	}
+
+	return lnwire.NewRawFeatureVector()
+}
+
+// Get returns a feature vector for the passed set. If no set is known, an empty
+// feature vector is returned.
+func (m *Manager) Get(set Set) *lnwire.FeatureVector {
+	raw := m.GetRaw(set)
+	return lnwire.NewFeatureVector(raw, lnwire.Features)
+}

feature/manager_internal_test.go

@@ -0,0 +1,128 @@
+package feature
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/lightningnetwork/lnd/lnwire"
+)
+
+type managerTest struct {
+	name string
+	cfg  Config
+}
+
+const unknownFeature lnwire.FeatureBit = 30
+
+var testSetDesc = setDesc{
+	lnwire.DataLossProtectRequired: {
+		SetNodeAnn: {}, // I
+	},
+	lnwire.TLVOnionPayloadOptional: {
+		SetInit:    {}, // I
+		SetNodeAnn: {}, // N
+	},
+	lnwire.StaticRemoteKeyOptional: {
+		SetInit:    {}, // I
+		SetNodeAnn: {}, // N
+	},
+}
+
+var managerTests = []managerTest{
+	{
+		name: "default",
+		cfg:  Config{},
+	},
+	{
+		name: "no tlv",
+		cfg: Config{
+			NoTLVOnion: true,
+		},
+	},
+	{
+		name: "no static remote key",
+		cfg: Config{
+			NoStaticRemoteKey: true,
+		},
+	},
+	{
+		name: "no tlv or static remote key",
+		cfg: Config{
+			NoTLVOnion:        true,
+			NoStaticRemoteKey: true,
+		},
+	},
+}
+
+// TestManager asserts basic initialazation and operation of a feature manager,
+// including that the proper features are removed in response to config changes.
+func TestManager(t *testing.T) {
+	for _, test := range managerTests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			testManager(t, test)
+		})
+	}
+}
+
+func testManager(t *testing.T, test managerTest) {
+	m, err := newManager(test.cfg, testSetDesc)
+	if err != nil {
+		t.Fatalf("unable to create feature manager: %v", err)
+	}
+
+	sets := []Set{
+		SetInit,
+		SetLegacyGlobal,
+		SetNodeAnn,
+		SetInvoice,
+	}
+
+	for _, set := range sets {
+		raw := m.GetRaw(set)
+		fv := m.Get(set)
+
+		fv2 := lnwire.NewFeatureVector(raw, lnwire.Features)
+
+		if !reflect.DeepEqual(fv, fv2) {
+			t.Fatalf("mismatch Get vs GetRaw, raw: %v vs fv: %v",
+				fv2, fv)
+		}
+
+		assertUnset := func(bit lnwire.FeatureBit) {
+			hasBit := fv.HasFeature(bit) || fv.HasFeature(bit^1)
+			if hasBit {
+				t.Fatalf("bit %v or %v is set", bit, bit^1)
+			}
+		}
+
+		// Assert that the manager properly unset the configured feature
+		// bits from all sets.
+		if test.cfg.NoTLVOnion {
+			assertUnset(lnwire.TLVOnionPayloadOptional)
+		}
+		if test.cfg.NoStaticRemoteKey {
+			assertUnset(lnwire.StaticRemoteKeyOptional)
+		}
+
+		assertUnset(unknownFeature)
+	}
+
+	// Do same basic sanity checks on features that are always present.
+	nodeFeatures := m.Get(SetNodeAnn)
+
+	assertSet := func(bit lnwire.FeatureBit) {
+		has := nodeFeatures.HasFeature(bit)
+		if !has {
+			t.Fatalf("node features don't advertised %v", bit)
+		}
+	}
+
+	assertSet(lnwire.DataLossProtectOptional)
+	if !test.cfg.NoTLVOnion {
+		assertSet(lnwire.TLVOnionPayloadRequired)
+	}
+	if !test.cfg.NoStaticRemoteKey {
+		assertSet(lnwire.StaticRemoteKeyOptional)
+	}
+}

feature/set.go

@@ -0,0 +1,41 @@
+package feature
+
+// Set is an enum identifying various feature sets, which separates the single
+// feature namespace into distinct categories depending what context a feature
+// vector is being used.
+type Set uint8
+
+const (
+	// SetInit identifies features that should be sent in an Init message to
+	// a remote peer.
+	SetInit Set = iota
+
+	// SetLegacyGlobal identifies features that should be set in the legacy
+	// GlobalFeatures field of an Init message, which maintains backwards
+	// compatibility with nodes that haven't implemented flat features.
+	SetLegacyGlobal
+
+	// SetNodeAnn identifies features that should be advertised on node
+	// announcements.
+	SetNodeAnn
+
+	// SetInvoice identifies features that should be advertised on invoices
+	// generated by the daemon.
+	SetInvoice
+)
+
+// String returns a human-readable description of a Set.
+func (s Set) String() string {
+	switch s {
+	case SetInit:
+		return "SetInit"
+	case SetLegacyGlobal:
+		return "SetLegacyGlobal"
+	case SetNodeAnn:
+		return "SetNodeAnn"
+	case SetInvoice:
+		return "SetInvoice"
+	default:
+		return "SetUnknown"
+	}
+}

lnwire/features.go

@@ -2,10 +2,17 @@ package lnwire
 
 import (
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"io"
 )
 
+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")
+)
+
 // FeatureBit represents a feature that can be enabled in either a local or
 // global feature vector at a specific bit position. Feature bits follow the
 // "it's OK to be odd" rule, where features at even bit positions must be known
@@ -136,6 +143,15 @@ func NewRawFeatureVector(bits ...FeatureBit) *RawFeatureVector {
 	return fv
 }
 
+// Clone makes a copy of a feature vector.
+func (fv *RawFeatureVector) Clone() *RawFeatureVector {
+	newFeatures := NewRawFeatureVector()
+	for bit := range fv.features {
+		newFeatures.Set(bit)
+	}
+	return newFeatures
+}
+
 // IsSet returns whether a particular feature bit is enabled in the vector.
 func (fv *RawFeatureVector) IsSet(feature FeatureBit) bool {
 	return fv.features[feature]
@@ -146,6 +162,20 @@ func (fv *RawFeatureVector) Set(feature FeatureBit) {
 	fv.features[feature] = true
 }
 
+// SafeSet sets the chosen feature bit in the feature vector, but returns an
+// error if the opposing feature bit is already set. This ensures both that we
+// are creating properly structured feature vectors, and in some cases, that
+// peers are sending properly encoded ones, i.e. it can't be both optional and
+// required.
+func (fv *RawFeatureVector) SafeSet(feature FeatureBit) error {
+	if _, ok := fv.features[feature^1]; ok {
+		return ErrFeaturePairExists
+	}
+
+	fv.Set(feature)
+	return nil
+}
+
 // Unset marks a feature as disabled in the vector.
 func (fv *RawFeatureVector) Unset(feature FeatureBit) {
 	delete(fv.features, feature)