f - resolve intro node with NodeIdLookUp

Author: jkczyz

lightning/src/blinded_path/mod.rs

@@ -58,7 +58,7 @@ pub enum IntroductionNode {
 ///
 /// [BOLT 7]: https://github.com/lightning/bolts/blob/master/07-routing-gossip.md#the-channel_announcement-message
 /// [`ChannelAnnouncement`]: crate::ln::msgs::ChannelAnnouncement
-#[derive(Clone, Debug, Hash, PartialEq, Eq)]
+#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
 pub enum Direction {
 	/// The lesser node id when compared lexicographically in ascending order.
 	NodeOne,
@@ -255,4 +255,17 @@ impl Direction {
 			Direction::NodeTwo => core::cmp::max(node_a, node_b)
 		}
 	}
+
+	/// Returns the [`PublicKey`] from the inputs corresponding to the direction.
+	pub fn select_pubkey<'a>(&self, node_a: &'a PublicKey, node_b: &'a PublicKey) -> &'a PublicKey {
+		let (node_one, node_two) = if node_a < node_b {
+			(node_a, node_b)
+		} else {
+			(node_b, node_a)
+		};
+		match self {
+			Direction::NodeOne => node_one,
+			Direction::NodeTwo => node_two,
+		}
+	}
 }

lightning/src/onion_message/messenger.rs

@@ -610,14 +610,17 @@ where
 	// advance the blinded path by 1 hop so the second hop is the new introduction node.
 	if intermediate_nodes.len() == 0 {
 		if let Destination::BlindedPath(ref mut blinded_path) = destination {
+			let our_node_id = node_signer.get_node_id(Recipient::Node)
+				.map_err(|()| SendError::GetNodeIdFailed)?;
 			let introduction_node_id = match blinded_path.introduction_node {
 				IntroductionNode::NodeId(pubkey) => pubkey,
-				IntroductionNode::DirectedShortChannelId(..) => {
-					return Err(SendError::UnresolvedIntroductionNode);
+				IntroductionNode::DirectedShortChannelId(direction, scid) => {
+					match node_id_lookup.next_node_id(scid) {
+						Some(next_node_id) => *direction.select_pubkey(&our_node_id, &next_node_id),
+						None => return Err(SendError::UnresolvedIntroductionNode),
+					}
 				},
 			};
-			let our_node_id = node_signer.get_node_id(Recipient::Node)
-				.map_err(|()| SendError::GetNodeIdFailed)?;
 			if introduction_node_id == our_node_id {
 				advance_path_by_one(blinded_path, node_signer, node_id_lookup, &secp_ctx)
 					.map_err(|()| SendError::BlindedPathAdvanceFailed)?;