+/// 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
+ }
+}
+