Allow to verify channel updates without applying them

We introduce a new `NetworkGraph::verify_channel_update` method that
allows to check whether an update would be applied by `update_channel`.

diff --git a/lightning/src/routing/gossip.rs b/lightning/src/routing/gossip.rs
index edb6226041d2e694b31842a7149cda25ed28ebe8..d13fe9a2b76e8230c279880698539387ca23c45e 100644 (file)
--- a/lightning/src/routing/gossip.rs
+++ b/lightning/src/routing/gossip.rs
@@ -1845,14 +1845,14 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
        /// For an already known (from announcement) channel, update info about one of the directions
        /// of the channel.
        ///
-       /// You probably don't want to call this directly, instead relying on a P2PGossipSync's
-       /// RoutingMessageHandler implementation to call it indirectly. This may be useful to accept
+       /// You probably don't want to call this directly, instead relying on a [`P2PGossipSync`]'s
+       /// [`RoutingMessageHandler`] implementation to call it indirectly. This may be useful to accept
        /// routing messages from a source using a protocol other than the lightning P2P protocol.
        ///
        /// If built with `no-std`, any updates with a timestamp more than two weeks in the past or
        /// materially in the future will be rejected.
        pub fn update_channel(&self, msg: &msgs::ChannelUpdate) -> Result<(), LightningError> {
-               self.update_channel_intern(&msg.contents, Some(&msg), Some(&msg.signature))
+               self.update_channel_internal(&msg.contents, Some(&msg), Some(&msg.signature), false)
        }
 
        /// For an already known (from announcement) channel, update info about one of the directions
@@ -1862,10 +1862,23 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
        /// If built with `no-std`, any updates with a timestamp more than two weeks in the past or
        /// materially in the future will be rejected.
        pub fn update_channel_unsigned(&self, msg: &msgs::UnsignedChannelUpdate) -> Result<(), LightningError> {
-               self.update_channel_intern(msg, None, None)
+               self.update_channel_internal(msg, None, None, false)
        }
 
-       fn update_channel_intern(&self, msg: &msgs::UnsignedChannelUpdate, full_msg: Option<&msgs::ChannelUpdate>, sig: Option<&secp256k1::ecdsa::Signature>) -> Result<(), LightningError> {
+       /// For an already known (from announcement) channel, verify the given [`ChannelUpdate`].
+       ///
+       /// This checks whether the update currently is applicable by [`Self::update_channel`].
+       ///
+       /// If built with `no-std`, any updates with a timestamp more than two weeks in the past or
+       /// materially in the future will be rejected.
+       pub fn verify_channel_update(&self, msg: &msgs::ChannelUpdate) -> Result<(), LightningError> {
+               self.update_channel_internal(&msg.contents, Some(&msg), Some(&msg.signature), true)
+       }
+
+       fn update_channel_internal(&self, msg: &msgs::UnsignedChannelUpdate,
+               full_msg: Option<&msgs::ChannelUpdate>, sig: Option<&secp256k1::ecdsa::Signature>,
+               only_verify: bool) -> Result<(), LightningError>
+       {
                let chan_enabled = msg.flags & (1 << 1) != (1 << 1);
 
                if msg.chain_hash != self.chain_hash {
@@ -1961,7 +1974,9 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
                                                        action: ErrorAction::IgnoreAndLog(Level::Debug)
                                                })?, "channel_update");
                                        }
-                                       channel.two_to_one = get_new_channel_info!();
+                                       if !only_verify {
+                                               channel.two_to_one = get_new_channel_info!();
+                                       }
                                } else {
                                        check_update_latest!(channel.one_to_two);
                                        if let Some(sig) = sig {
@@ -1970,7 +1985,9 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
                                                        action: ErrorAction::IgnoreAndLog(Level::Debug)
                                                })?, "channel_update");
                                        }
-                                       channel.one_to_two = get_new_channel_info!();
+                                       if !only_verify {
+                                               channel.one_to_two = get_new_channel_info!();
+                                       }
                                }
                        }
                }
@@ -2411,6 +2428,7 @@ pub(crate) mod tests {
                }
 
                let valid_channel_update = get_signed_channel_update(|_| {}, node_1_privkey, &secp_ctx);
+               network_graph.verify_channel_update(&valid_channel_update).unwrap();
                match gossip_sync.handle_channel_update(&valid_channel_update) {
                        Ok(res) => assert!(res),
                        _ => panic!(),