Move compact blinded path util to message paths only.

It's only used for message paths, so let's move it there to help make the
BlindedPath struct private.

Author: valentinewallace

lightning/src/blinded_path/message.rs

@@ -16,7 +16,7 @@ use crate::prelude::*;
 
 use bitcoin::hashes::hmac::Hmac;
 use bitcoin::hashes::sha256::Hash as Sha256;
-use crate::blinded_path::{BlindedHop, BlindedPath, IntroductionNode, NextMessageHop, NodeIdLookUp};
+use crate::blinded_path::{BlindedHop, BlindedPath, Direction, IntroductionNode, NextMessageHop, NodeIdLookUp};
 use crate::blinded_path::utils;
 use crate::io;
 use crate::io::Cursor;
@@ -25,8 +25,10 @@ use crate::ln::msgs::DecodeError;
 use crate::ln::{PaymentHash, onion_utils};
 use crate::offers::nonce::Nonce;
 use crate::onion_message::packet::ControlTlvs;
+use crate::routing::gossip::{NodeId, ReadOnlyNetworkGraph};
 use crate::sign::{EntropySource, NodeSigner, Recipient};
 use crate::crypto::streams::ChaChaPolyReadAdapter;
+use crate::util::scid_utils;
 use crate::util::ser::{FixedLengthReader, LengthReadableArgs, Readable, Writeable, Writer};
 
 use core::mem;
@@ -81,6 +83,35 @@ impl BlindedMessagePath {
 			).map_err(|_| ())?,
 		}))
 	}
+
+	/// Attempts to a use a compact representation for the [`IntroductionNode`] by using a directed
+	/// short channel id from a channel in `network_graph` leading to the introduction node.
+	///
+	/// While this may result in a smaller encoding, there is a trade off in that the path may
+	/// become invalid if the channel is closed or hasn't been propagated via gossip. Therefore,
+	/// calling this may not be suitable for long-lived blinded paths.
+	pub fn use_compact_introduction_node(&mut self, network_graph: &ReadOnlyNetworkGraph) {
+		if let IntroductionNode::NodeId(pubkey) = &self.0.introduction_node {
+			let node_id = NodeId::from_pubkey(pubkey);
+			if let Some(node_info) = network_graph.node(&node_id) {
+				if let Some((scid, channel_info)) = node_info
+					.channels
+						.iter()
+						.filter_map(|scid| network_graph.channel(*scid).map(|info| (*scid, info)))
+						.min_by_key(|(scid, _)| scid_utils::block_from_scid(*scid))
+				{
+					let direction = if node_id == channel_info.node_one {
+						Direction::NodeOne
+					} else {
+						debug_assert_eq!(node_id, channel_info.node_two);
+						Direction::NodeTwo
+					};
+					self.0.introduction_node =
+						IntroductionNode::DirectedShortChannelId(direction, scid);
+				}
+			}
+		}
+	}
 }
 
 /// An intermediate node, and possibly a short channel id leading to the next node.

lightning/src/blinded_path/mod.rs

@@ -19,7 +19,6 @@ use core::ops::Deref;
 use crate::ln::msgs::DecodeError;
 use crate::routing::gossip::{NodeId, ReadOnlyNetworkGraph};
 use crate::util::ser::{Readable, Writeable, Writer};
-use crate::util::scid_utils;
 
 use crate::io;
 use crate::prelude::*;
@@ -139,35 +138,6 @@ impl BlindedPath {
 			},
 		}
 	}
-
-	/// Attempts to a use a compact representation for the [`IntroductionNode`] by using a directed
-	/// short channel id from a channel in `network_graph` leading to the introduction node.
-	///
-	/// While this may result in a smaller encoding, there is a trade off in that the path may
-	/// become invalid if the channel is closed or hasn't been propagated via gossip. Therefore,
-	/// calling this may not be suitable for long-lived blinded paths.
-	pub fn use_compact_introduction_node(&mut self, network_graph: &ReadOnlyNetworkGraph) {
-		if let IntroductionNode::NodeId(pubkey) = &self.introduction_node {
-			let node_id = NodeId::from_pubkey(pubkey);
-			if let Some(node_info) = network_graph.node(&node_id) {
-				if let Some((scid, channel_info)) = node_info
-					.channels
-					.iter()
-					.filter_map(|scid| network_graph.channel(*scid).map(|info| (*scid, info)))
-					.min_by_key(|(scid, _)| scid_utils::block_from_scid(*scid))
-				{
-					let direction = if node_id == channel_info.node_one {
-						Direction::NodeOne
-					} else {
-						debug_assert_eq!(node_id, channel_info.node_two);
-						Direction::NodeTwo
-					};
-					self.introduction_node =
-						IntroductionNode::DirectedShortChannelId(direction, scid);
-				}
-			}
-		}
-	}
 }
 
 impl Writeable for BlindedPath {

lightning/src/onion_message/messenger.rs

@@ -457,7 +457,7 @@ pub trait MessageRouter {
 	///
 	/// Implementations using additional intermediate nodes are responsible for using a
 	/// [`ForwardNode`] with `Some` short channel id, if possible. Similarly, implementations should
-	/// call [`BlindedPath::use_compact_introduction_node`].
+	/// call [`BlindedMessagePath::use_compact_introduction_node`].
 	///
 	/// The provided implementation simply delegates to [`MessageRouter::create_blinded_paths`],
 	/// ignoring the short channel ids.
@@ -565,7 +565,7 @@ where
 
 		if compact_paths {
 			for path in &mut paths {
-				path.0.use_compact_introduction_node(&network_graph);
+				path.use_compact_introduction_node(&network_graph);
 			}
 		}