From 63ca72e5b06e3dc826935541aab7b69f34e3310d Mon Sep 17 00:00:00 2001
From: Matt Corallo <git@bluematt.me>
Date: Wed, 23 Mar 2022 22:10:15 +0000
Subject: [PATCH] Skip `channel_update` signature checks if we have a newer
 state

`channel_update` messages already have their signatures checked
with the network graph write lock held, so there's no reason to
check the signatures before doing other quicker checks first,
including checking if we're already aware of a newer update for the
channel.

This reduces common-case CPU usage as `channel_update`s are sent
rather liberally over the p2p network to gossip them.
---
 lightning/src/routing/network_graph.rs | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/lightning/src/routing/network_graph.rs b/lightning/src/routing/network_graph.rs
index 012357df3..13e6beedd 100644
--- a/lightning/src/routing/network_graph.rs
+++ b/lightning/src/routing/network_graph.rs
@@ -1376,8 +1376,8 @@ impl NetworkGraph {
 						}
 					}
 				}
-				macro_rules! maybe_update_channel_info {
-					( $target: expr, $src_node: expr) => {
+				macro_rules! check_update_latest {
+					($target: expr) => {
 						if let Some(existing_chan_info) = $target.as_ref() {
 							// The timestamp field is somewhat of a misnomer - the BOLTs use it to
 							// order updates to ensure you always have the latest one, only
@@ -1394,7 +1394,11 @@ impl NetworkGraph {
 						} else {
 							chan_was_enabled = false;
 						}
+					}
+				}
 
+				macro_rules! get_new_channel_info {
+					() => { {
 						let last_update_message = if msg.excess_data.len() <= MAX_EXCESS_BYTES_FOR_RELAY
 							{ full_msg.cloned() } else { None };
 
@@ -1410,29 +1414,31 @@ impl NetworkGraph {
 							},
 							last_update_message
 						};
-						$target = Some(updated_channel_update_info);
-					}
+						Some(updated_channel_update_info)
+					} }
 				}
 
 				let msg_hash = hash_to_message!(&Sha256dHash::hash(&msg.encode()[..])[..]);
 				if msg.flags & 1 == 1 {
 					dest_node_id = channel.node_one.clone();
+					check_update_latest!(channel.two_to_one);
 					if let Some((sig, ctx)) = sig_info {
 						secp_verify_sig!(ctx, &msg_hash, &sig, &PublicKey::from_slice(channel.node_two.as_slice()).map_err(|_| LightningError{
 							err: "Couldn't parse source node pubkey".to_owned(),
 							action: ErrorAction::IgnoreAndLog(Level::Debug)
 						})?, "channel_update");
 					}
-					maybe_update_channel_info!(channel.two_to_one, channel.node_two);
+					channel.two_to_one = get_new_channel_info!();
 				} else {
 					dest_node_id = channel.node_two.clone();
+					check_update_latest!(channel.one_to_two);
 					if let Some((sig, ctx)) = sig_info {
 						secp_verify_sig!(ctx, &msg_hash, &sig, &PublicKey::from_slice(channel.node_one.as_slice()).map_err(|_| LightningError{
 							err: "Couldn't parse destination node pubkey".to_owned(),
 							action: ErrorAction::IgnoreAndLog(Level::Debug)
 						})?, "channel_update");
 					}
-					maybe_update_channel_info!(channel.one_to_two, channel.node_one);
+					channel.one_to_two = get_new_channel_info!();
 				}
 			}
 		}
-- 
2.39.5