Compact a BlindedPath's introduction node

[rust-lightning] / lightning / src / blinded_path / mod.rs

diff --git a/lightning/src/blinded_path/mod.rs b/lightning/src/blinded_path/mod.rs
index 5abf53ec166561b351c17255eeaf7424cf2677fb..2d3d085bddf35d51a5276c5c9c048506527ac45b 100644 (file)
--- a/lightning/src/blinded_path/mod.rs
+++ b/lightning/src/blinded_path/mod.rs
@@ -21,6 +21,7 @@ use crate::offers::invoice::BlindedPayInfo;
 use crate::routing::gossip::{NodeId, ReadOnlyNetworkGraph};
 use crate::sign::EntropySource;
 use crate::util::ser::{Readable, Writeable, Writer};
+use crate::util::scid_utils;
 
 use crate::io;
 use crate::prelude::*;
@@ -217,6 +218,35 @@ 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 {