lnwire: add NodeAnnouncement interface

diff --git a/lnwire/interfaces.go b/lnwire/interfaces.go
index 3a8b7cb..975cd6c 100644
--- a/lnwire/interfaces.go
+++ b/lnwire/interfaces.go
@@ -91,6 +91,22 @@ type ChannelUpdate interface {
 	Message
 }
 
+// NodeAnnouncement is an interface that must be satisfied by any message used
+// to announce the existence of a node.
+type NodeAnnouncement interface {
+	// NodePub returns the identity public key of the node.
+	NodePub() [33]byte
+
+	// NodeFeatures returns the set of features supported by the node.
+	NodeFeatures() *FeatureVector
+
+	// TimestampDesc returns a human-readable description of the
+	// timestamp of the announcement.
+	TimestampDesc() string
+
+	Message
+}
+
 // ForwardingPolicy defines the set of forwarding constraints advertised in a
 // ChannelUpdate message.
 type ForwardingPolicy struct {
diff --git a/lnwire/node_announcement.go b/lnwire/node_announcement.go
index 0a7c605..384327f 100644
--- a/lnwire/node_announcement.go
+++ b/lnwire/node_announcement.go
@@ -104,6 +104,10 @@ type NodeAnnouncement1 struct {
 // lnwire.Message interface.
 var _ Message = (*NodeAnnouncement1)(nil)
 
+// A compile time check to ensure NodeAnnouncement1 implements the
+// lnwire.NodeAnnouncement interface.
+var _ NodeAnnouncement = (*NodeAnnouncement1)(nil)
+
 // A compile time check to ensure NodeAnnouncement1 implements the
 // lnwire.SizeableMessage interface.
 var _ SizeableMessage = (*NodeAnnouncement1)(nil)
@@ -217,3 +221,25 @@ func (a *NodeAnnouncement1) DataToSign() ([]byte, error) {
 func (a *NodeAnnouncement1) SerializedSize() (uint32, error) {
 	return MessageSerializedSize(a)
 }
+
+// NodePub returns the identity public key of the node.
+//
+// NOTE: part of the NodeAnnouncement interface.
+func (a *NodeAnnouncement1) NodePub() [33]byte {
+	return a.NodeID
+}
+
+// NodeFeatures returns the set of features supported by the node.
+//
+// NOTE: part of the NodeAnnouncement interface.
+func (a *NodeAnnouncement1) NodeFeatures() *FeatureVector {
+	return NewFeatureVector(a.Features, Features)
+}
+
+// TimestampDesc returns a human-readable description of the timestamp of the
+// announcement.
+//
+// NOTE: part of the NodeAnnouncement interface.
+func (a *NodeAnnouncement1) TimestampDesc() string {
+	return fmt.Sprintf("timestamp=%d", a.Timestamp)
+}
diff --git a/lnwire/node_announcement_2.go b/lnwire/node_announcement_2.go
index 23fcc50..0b7142d 100644
--- a/lnwire/node_announcement_2.go
+++ b/lnwire/node_announcement_2.go
@@ -199,10 +199,36 @@ func (n *NodeAnnouncement2) MsgType() MessageType {
 	return MsgNodeAnnouncement2
 }
 
+// NodePub returns the identity public key of the node.
+//
+// NOTE: part of the NodeAnnouncement interface.
+func (n *NodeAnnouncement2) NodePub() [33]byte {
+	return n.NodeID.Val
+}
+
+// NodeFeatures returns the set of features supported by the node.
+//
+// NOTE: part of the NodeAnnouncement interface.
+func (n *NodeAnnouncement2) NodeFeatures() *FeatureVector {
+	return NewFeatureVector(&n.Features.Val, Features)
+}
+
+// TimestampDesc returns a human-readable description of the timestamp of the
+// announcement.
+//
+// NOTE: part of the NodeAnnouncement interface.
+func (n *NodeAnnouncement2) TimestampDesc() string {
+	return fmt.Sprintf("block_height=%d", n.BlockHeight.Val)
+}
+
 // A compile-time check to ensure NodeAnnouncement2 implements the Message
 // interface.
 var _ Message = (*NodeAnnouncement2)(nil)
 
+// A compile time check to ensure NodeAnnouncement2 implements the
+// lnwire.NodeAnnouncement interface.
+var _ NodeAnnouncement = (*NodeAnnouncement2)(nil)
+
 // A compile-time check to ensure NodeAnnouncement2 implements the
 // PureTLVMessage interface.
 var _ PureTLVMessage = (*NodeAnnouncement2)(nil)