+ pub blinded_hops: Vec<BlindedHop>,
+}
+
+/// The unblinded node in a [`BlindedPath`].
+#[derive(Clone, Debug, Hash, PartialEq, Eq)]
+pub enum IntroductionNode {
+ /// The node id of the introduction node.
+ NodeId(PublicKey),
+ /// The short channel id of the channel leading to the introduction node. The [`Direction`]
+ /// identifies which side of the channel is the introduction node.
+ DirectedShortChannelId(Direction, u64),
+}
+
+/// The side of a channel that is the [`IntroductionNode`] in a [`BlindedPath`]. [BOLT 7] defines
+/// which nodes is which in the [`ChannelAnnouncement`] message.
+///
+/// [BOLT 7]: https://github.com/lightning/bolts/blob/master/07-routing-gossip.md#the-channel_announcement-message
+/// [`ChannelAnnouncement`]: crate::ln::msgs::ChannelAnnouncement
+#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
+pub enum Direction {
+ /// The lesser node id when compared lexicographically in ascending order.
+ NodeOne,
+ /// The greater node id when compared lexicographically in ascending order.
+ NodeTwo,
+}
+
+/// An interface for looking up the node id of a channel counterparty for the purpose of forwarding
+/// an [`OnionMessage`].
+///
+/// [`OnionMessage`]: crate::ln::msgs::OnionMessage
+pub trait NodeIdLookUp {
+ /// Returns the node id of the forwarding node's channel counterparty with `short_channel_id`.
+ ///
+ /// Here, the forwarding node is referring to the node of the [`OnionMessenger`] parameterized
+ /// by the [`NodeIdLookUp`] and the counterparty to one of that node's peers.
+ ///
+ /// [`OnionMessenger`]: crate::onion_message::messenger::OnionMessenger
+ fn next_node_id(&self, short_channel_id: u64) -> Option<PublicKey>;
+}
+
+/// A [`NodeIdLookUp`] that always returns `None`.
+pub struct EmptyNodeIdLookUp {}
+
+impl NodeIdLookUp for EmptyNodeIdLookUp {
+ fn next_node_id(&self, _short_channel_id: u64) -> Option<PublicKey> {
+ None
+ }
+}
+
+impl Deref for EmptyNodeIdLookUp {
+ type Target = EmptyNodeIdLookUp;
+ fn deref(&self) -> &Self { self }