Remove and track perm failed nodes & channels
authorDuncan Dean <duncangleeddean@gmail.com>
Fri, 26 Aug 2022 10:54:16 +0000 (12:54 +0200)
committerDuncan Dean <duncangleeddean@gmail.com>
Fri, 7 Oct 2022 10:00:39 +0000 (12:00 +0200)
We never had the `NetworkGraph::node_failed` method implemented. The
scorer now handles non-permanent failures by downgrading nodes, so we
don't want that implemented.

The method is renamed to `node_failed_permanent` to explicitly indicate
that this is the only case it handles. We also add tracking in the form
of two maps as fields of `NetworkGraph`, namely, `removed_nodes` and
`removed_channels`. We track these removed graph entries to ensure we
don't just resync them right away from gossip soon after removing them.
We stop tracking these removed nodes whenever `remove_stale_channels_and_tracking()`
is called and the entries have been tracked for longer than
`REMOVED_ENTRIES_TRACKING_AGE_LIMIT_SECS` which is currently set to one
week.

lightning-background-processor/src/lib.rs
lightning/src/routing/gossip.rs

index 38f8fd40144ee18ef377594c8ebb9f0031937d90..938deee9bd7a0bc61f47387b18e77fa5a5b7c42b 100644 (file)
@@ -46,8 +46,8 @@ use futures::{select, future::FutureExt};
 ///   [`ChannelManager`] persistence should be done in the background.
 /// * Calling [`ChannelManager::timer_tick_occurred`] and [`PeerManager::timer_tick_occurred`]
 ///   at the appropriate intervals.
-/// * Calling [`NetworkGraph::remove_stale_channels`] (if a [`GossipSync`] with a [`NetworkGraph`]
-///   is provided to [`BackgroundProcessor::start`]).
+/// * Calling [`NetworkGraph::remove_stale_channels_and_tracking`] (if a [`GossipSync`] with a
+///   [`NetworkGraph`] is provided to [`BackgroundProcessor::start`]).
 ///
 /// It will also call [`PeerManager::process_events`] periodically though this shouldn't be relied
 /// upon as doing so may result in high latency.
@@ -312,7 +312,7 @@ macro_rules! define_run_body {
                                // The network graph must not be pruned while rapid sync completion is pending
                                log_trace!($logger, "Assessing prunability of network graph");
                                if let Some(network_graph) = $gossip_sync.prunable_network_graph() {
-                                       network_graph.remove_stale_channels();
+                                       network_graph.remove_stale_channels_and_tracking();
 
                                        if let Err(e) = $persister.persist_graph(network_graph) {
                                                log_error!($logger, "Error: Failed to persist network graph, check your disk and permissions {}", e)
index 60e3c94f3402339f840d7f3491301512bbcc000e..19f109f0cd5d2f8a041302d54becbe035acd4b3d 100644 (file)
@@ -50,6 +50,9 @@ use std::time::{SystemTime, UNIX_EPOCH};
 /// suggestion.
 const STALE_CHANNEL_UPDATE_AGE_LIMIT_SECS: u64 = 60 * 60 * 24 * 14;
 
+/// We stop tracking the removal of permanently failed nodes and channels one week after removal
+const REMOVED_ENTRIES_TRACKING_AGE_LIMIT_SECS: u64 = 60 * 60 * 24 * 7;
+
 /// The maximum number of extra bytes which we do not understand in a gossip message before we will
 /// refuse to relay the message.
 const MAX_EXCESS_BYTES_FOR_RELAY: usize = 1024;
@@ -130,6 +133,25 @@ pub struct NetworkGraph<L: Deref> where L::Target: Logger {
        // Lock order: channels -> nodes
        channels: RwLock<BTreeMap<u64, ChannelInfo>>,
        nodes: RwLock<BTreeMap<NodeId, NodeInfo>>,
+       // Lock order: removed_channels -> removed_nodes
+       //
+       // NOTE: In the following `removed_*` maps, we use seconds since UNIX epoch to track time instead
+       // of `std::time::Instant`s for a few reasons:
+       //   * We want it to be possible to do tracking in no-std environments where we can compare
+       //     a provided current UNIX timestamp with the time at which we started tracking.
+       //   * In the future, if we decide to persist these maps, they will already be serializable.
+       //   * Although we lose out on the platform's monotonic clock, the system clock in a std
+       //     environment should be practical over the time period we are considering (on the order of a
+       //     week).
+       //
+       /// Keeps track of short channel IDs for channels we have explicitly removed due to permanent
+       /// failure so that we don't resync them from gossip. Each SCID is mapped to the time (in seconds)
+       /// it was removed so that once some time passes, we can potentially resync it from gossip again.
+       removed_channels: Mutex<HashMap<u64, Option<u64>>>,
+       /// Keeps track of `NodeId`s we have explicitly removed due to permanent failure so that we don't
+       /// resync them from gossip. Each `NodeId` is mapped to the time (in seconds) it was removed so
+       /// that once some time passes, we can potentially resync it from gossip again.
+       removed_nodes: Mutex<HashMap<NodeId, Option<u64>>>,
 }
 
 /// A read-only view of [`NetworkGraph`].
@@ -160,7 +182,7 @@ pub enum NetworkUpdate {
                is_permanent: bool,
        },
        /// An error indicating that a node failed to route a payment, which should be applied via
-       /// [`NetworkGraph::node_failed`].
+       /// [`NetworkGraph::node_failed_permanent`] if permanent.
        NodeFailure {
                /// The node id of the failed node.
                node_id: PublicKey,
@@ -269,9 +291,11 @@ impl<L: Deref> EventHandler for NetworkGraph<L> where L::Target: Logger {
                                                self.channel_failed(short_channel_id, is_permanent);
                                        },
                                        NetworkUpdate::NodeFailure { ref node_id, is_permanent } => {
-                                               let action = if is_permanent { "Removing" } else { "Disabling" };
-                                               log_debug!(self.logger, "{} node graph entry for {} due to a payment failure.", action, node_id);
-                                               self.node_failed(node_id, is_permanent);
+                                               if is_permanent {
+                                                       log_debug!(self.logger,
+                                                               "Removed node graph entry for {} due to a payment failure.", log_pubkey!(node_id));
+                                                       self.node_failed_permanent(node_id);
+                                               };
                                        },
                                }
                        }
@@ -1203,6 +1227,8 @@ impl<L: Deref> ReadableArgs<L> for NetworkGraph<L> where L::Target: Logger {
                        channels: RwLock::new(channels),
                        nodes: RwLock::new(nodes),
                        last_rapid_gossip_sync_timestamp: Mutex::new(last_rapid_gossip_sync_timestamp),
+                       removed_nodes: Mutex::new(HashMap::new()),
+                       removed_channels: Mutex::new(HashMap::new()),
                })
        }
 }
@@ -1239,6 +1265,8 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
                        channels: RwLock::new(BTreeMap::new()),
                        nodes: RwLock::new(BTreeMap::new()),
                        last_rapid_gossip_sync_timestamp: Mutex::new(None),
+                       removed_channels: Mutex::new(HashMap::new()),
+                       removed_nodes: Mutex::new(HashMap::new()),
                }
        }
 
@@ -1450,6 +1478,9 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
                        return Err(LightningError{err: "Channel announcement node had a channel with itself".to_owned(), action: ErrorAction::IgnoreError});
                }
 
+               let node_one = NodeId::from_pubkey(&msg.node_id_1);
+               let node_two = NodeId::from_pubkey(&msg.node_id_2);
+
                {
                        let channels = self.channels.read().unwrap();
 
@@ -1466,7 +1497,7 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
                                        // We use the Node IDs rather than the bitcoin_keys to check for "equivalence"
                                        // as we didn't (necessarily) store the bitcoin keys, and we only really care
                                        // if the peers on the channel changed anyway.
-                                       if NodeId::from_pubkey(&msg.node_id_1) == chan.node_one && NodeId::from_pubkey(&msg.node_id_2) == chan.node_two {
+                                       if node_one == chan.node_one && node_two == chan.node_two {
                                                return Err(LightningError {
                                                        err: "Already have chain-validated channel".to_owned(),
                                                        action: ErrorAction::IgnoreDuplicateGossip
@@ -1483,6 +1514,18 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
                        }
                }
 
+               {
+                       let removed_channels = self.removed_channels.lock().unwrap();
+                       let removed_nodes = self.removed_nodes.lock().unwrap();
+                       if removed_channels.contains_key(&msg.short_channel_id) ||
+                               removed_nodes.contains_key(&node_one) ||
+                               removed_nodes.contains_key(&node_two) {
+                               return Err(LightningError{
+                                       err: format!("Channel with SCID {} or one of its nodes was removed from our network graph recently", &msg.short_channel_id),
+                                       action: ErrorAction::IgnoreAndLog(Level::Gossip)});
+                       }
+               }
+
                let utxo_value = match &chain_access {
                        &None => {
                                // Tentatively accept, potentially exposing us to DoS attacks
@@ -1519,9 +1562,9 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
 
                let chan_info = ChannelInfo {
                        features: msg.features.clone(),
-                       node_one: NodeId::from_pubkey(&msg.node_id_1),
+                       node_one,
                        one_to_two: None,
-                       node_two: NodeId::from_pubkey(&msg.node_id_2),
+                       node_two,
                        two_to_one: None,
                        capacity_sats: utxo_value,
                        announcement_message: if msg.excess_data.len() <= MAX_EXCESS_BYTES_FOR_RELAY
@@ -1537,10 +1580,16 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
        /// May cause the removal of nodes too, if this was their last channel.
        /// If not permanent, makes channels unavailable for routing.
        pub fn channel_failed(&self, short_channel_id: u64, is_permanent: bool) {
+               #[cfg(feature = "std")]
+               let current_time_unix = Some(SystemTime::now().duration_since(UNIX_EPOCH).expect("Time must be > 1970").as_secs());
+               #[cfg(not(feature = "std"))]
+               let current_time_unix = None;
+
                let mut channels = self.channels.write().unwrap();
                if is_permanent {
                        if let Some(chan) = channels.remove(&short_channel_id) {
                                let mut nodes = self.nodes.write().unwrap();
+                               self.removed_channels.lock().unwrap().insert(short_channel_id, current_time_unix);
                                Self::remove_channel_in_nodes(&mut nodes, &chan, short_channel_id);
                        }
                } else {
@@ -1555,12 +1604,36 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
                }
        }
 
-       /// Marks a node in the graph as failed.
-       pub fn node_failed(&self, _node_id: &PublicKey, is_permanent: bool) {
-               if is_permanent {
-                       // TODO: Wholly remove the node
-               } else {
-                       // TODO: downgrade the node
+       /// Marks a node in the graph as permanently failed, effectively removing it and its channels
+       /// from local storage.
+       pub fn node_failed_permanent(&self, node_id: &PublicKey) {
+               #[cfg(feature = "std")]
+               let current_time_unix = Some(SystemTime::now().duration_since(UNIX_EPOCH).expect("Time must be > 1970").as_secs());
+               #[cfg(not(feature = "std"))]
+               let current_time_unix = None;
+
+               let node_id = NodeId::from_pubkey(node_id);
+               let mut channels = self.channels.write().unwrap();
+               let mut nodes = self.nodes.write().unwrap();
+               let mut removed_channels = self.removed_channels.lock().unwrap();
+               let mut removed_nodes = self.removed_nodes.lock().unwrap();
+
+               if let Some(node) = nodes.remove(&node_id) {
+                       for scid in node.channels.iter() {
+                               if let Some(chan_info) = channels.remove(scid) {
+                                       let other_node_id = if node_id == chan_info.node_one { chan_info.node_two } else { chan_info.node_one };
+                                       if let BtreeEntry::Occupied(mut other_node_entry) = nodes.entry(other_node_id) {
+                                               other_node_entry.get_mut().channels.retain(|chan_id| {
+                                                       *scid != *chan_id
+                                               });
+                                               if other_node_entry.get().channels.is_empty() {
+                                                       other_node_entry.remove_entry();
+                                               }
+                                       }
+                                       removed_channels.insert(*scid, current_time_unix);
+                               }
+                       }
+                       removed_nodes.insert(node_id, current_time_unix);
                }
        }
 
@@ -1576,11 +1649,14 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
        /// Note that for users of the `lightning-background-processor` crate this method may be
        /// automatically called regularly for you.
        ///
+       /// This method will also cause us to stop tracking removed nodes and channels if they have been
+       /// in the map for a while so that these can be resynced from gossip in the future.
+       ///
        /// This method is only available with the `std` feature. See
-       /// [`NetworkGraph::remove_stale_channels_with_time`] for `no-std` use.
-       pub fn remove_stale_channels(&self) {
+       /// [`NetworkGraph::remove_stale_channels_and_tracking_with_time`] for `no-std` use.
+       pub fn remove_stale_channels_and_tracking(&self) {
                let time = SystemTime::now().duration_since(UNIX_EPOCH).expect("Time must be > 1970").as_secs();
-               self.remove_stale_channels_with_time(time);
+               self.remove_stale_channels_and_tracking_with_time(time);
        }
 
        /// Removes information about channels that we haven't heard any updates about in some time.
@@ -1591,9 +1667,12 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
        /// updates every two weeks, the non-normative section of BOLT 7 currently suggests that
        /// pruning occur for updates which are at least two weeks old, which we implement here.
        ///
+       /// This method will also cause us to stop tracking removed nodes and channels if they have been
+       /// in the map for a while so that these can be resynced from gossip in the future.
+       ///
        /// This function takes the current unix time as an argument. For users with the `std` feature
-       /// enabled, [`NetworkGraph::remove_stale_channels`] may be preferable.
-       pub fn remove_stale_channels_with_time(&self, current_time_unix: u64) {
+       /// enabled, [`NetworkGraph::remove_stale_channels_and_tracking`] may be preferable.
+       pub fn remove_stale_channels_and_tracking_with_time(&self, current_time_unix: u64) {
                let mut channels = self.channels.write().unwrap();
                // Time out if we haven't received an update in at least 14 days.
                if current_time_unix > u32::max_value() as u64 { return; } // Remove by 2106
@@ -1625,6 +1704,26 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
                                Self::remove_channel_in_nodes(&mut nodes, &info, scid);
                        }
                }
+
+               let should_keep_tracking = |time: &mut Option<u64>| {
+                       if let Some(time) = time {
+                               current_time_unix.saturating_sub(*time) < REMOVED_ENTRIES_TRACKING_AGE_LIMIT_SECS
+                       } else {
+                               // NOTE: In the case of no-std, we won't have access to the current UNIX time at the time of removal,
+                               // so we'll just set the removal time here to the current UNIX time on the very next invocation
+                               // of this function.
+                               #[cfg(feature = "no-std")]
+                               {
+                                       let mut tracked_time = Some(current_time_unix);
+                                       core::mem::swap(time, &mut tracked_time);
+                                       return true;
+                               }
+                               #[allow(unreachable_code)]
+                               false
+                       }};
+
+               self.removed_channels.lock().unwrap().retain(|_, time| should_keep_tracking(time));
+               self.removed_nodes.lock().unwrap().retain(|_, time| should_keep_tracking(time));
        }
 
        /// For an already known (from announcement) channel, update info about one of the directions
@@ -1882,6 +1981,7 @@ mod tests {
        use util::events::{Event, EventHandler, MessageSendEvent, MessageSendEventsProvider};
        use util::scid_utils::scid_from_parts;
 
+       use crate::routing::gossip::REMOVED_ENTRIES_TRACKING_AGE_LIMIT_SECS;
        use super::STALE_CHANNEL_UPDATE_AGE_LIMIT_SECS;
 
        use bitcoin::hashes::sha256d::Hash as Sha256dHash;
@@ -2140,9 +2240,35 @@ mod tests {
                        Err(e) => assert_eq!(e.err, "Already have chain-validated channel")
                };
 
+               #[cfg(feature = "std")]
+               {
+                       use std::time::{SystemTime, UNIX_EPOCH};
+
+                       let tracking_time = SystemTime::now().duration_since(UNIX_EPOCH).expect("Time must be > 1970").as_secs();
+                       // Mark a node as permanently failed so it's tracked as removed.
+                       gossip_sync.network_graph().node_failed_permanent(&PublicKey::from_secret_key(&secp_ctx, node_1_privkey));
+
+                       // Return error and ignore valid channel announcement if one of the nodes has been tracked as removed.
+                       let valid_announcement = get_signed_channel_announcement(|unsigned_announcement| {
+                               unsigned_announcement.short_channel_id += 3;
+                       }, node_1_privkey, node_2_privkey, &secp_ctx);
+                       match gossip_sync.handle_channel_announcement(&valid_announcement) {
+                               Ok(_) => panic!(),
+                               Err(e) => assert_eq!(e.err, "Channel with SCID 3 or one of its nodes was removed from our network graph recently")
+                       }
+
+                       gossip_sync.network_graph().remove_stale_channels_and_tracking_with_time(tracking_time + REMOVED_ENTRIES_TRACKING_AGE_LIMIT_SECS);
+
+                       // The above channel announcement should be handled as per normal now.
+                       match gossip_sync.handle_channel_announcement(&valid_announcement) {
+                               Ok(res) => assert!(res),
+                               _ => panic!()
+                       }
+               }
+
                // Don't relay valid channels with excess data
                let valid_announcement = get_signed_channel_announcement(|unsigned_announcement| {
-                       unsigned_announcement.short_channel_id += 3;
+                       unsigned_announcement.short_channel_id += 4;
                        unsigned_announcement.excess_data.resize(MAX_EXCESS_BYTES_FOR_RELAY + 1, 0);
                }, node_1_privkey, node_2_privkey, &secp_ctx);
                match gossip_sync.handle_channel_announcement(&valid_announcement) {
@@ -2277,6 +2403,7 @@ mod tests {
 
                let node_1_privkey = &SecretKey::from_slice(&[42; 32]).unwrap();
                let node_2_privkey = &SecretKey::from_slice(&[41; 32]).unwrap();
+               let node_2_id = PublicKey::from_secret_key(&secp_ctx, node_2_privkey);
 
                {
                        // There is no nodes in the table at the beginning.
@@ -2366,12 +2493,64 @@ mod tests {
                assert_eq!(network_graph.read_only().channels().len(), 0);
                // Nodes are also deleted because there are no associated channels anymore
                assert_eq!(network_graph.read_only().nodes().len(), 0);
-               // TODO: Test NetworkUpdate::NodeFailure, which is not implemented yet.
+
+               {
+                       // Get a new network graph since we don't want to track removed nodes in this test with "std"
+                       let network_graph = NetworkGraph::new(genesis_hash, &logger);
+
+                       // Announce a channel to test permanent node failure
+                       let valid_channel_announcement = get_signed_channel_announcement(|_| {}, node_1_privkey, node_2_privkey, &secp_ctx);
+                       let short_channel_id = valid_channel_announcement.contents.short_channel_id;
+                       let chain_source: Option<&test_utils::TestChainSource> = None;
+                       assert!(network_graph.update_channel_from_announcement(&valid_channel_announcement, &chain_source).is_ok());
+                       assert!(network_graph.read_only().channels().get(&short_channel_id).is_some());
+
+                       // Non-permanent node failure does not delete any nodes or channels
+                       network_graph.handle_event(&Event::PaymentPathFailed {
+                               payment_id: None,
+                               payment_hash: PaymentHash([0; 32]),
+                               payment_failed_permanently: false,
+                               all_paths_failed: true,
+                               path: vec![],
+                               network_update: Some(NetworkUpdate::NodeFailure {
+                                       node_id: node_2_id,
+                                       is_permanent: false,
+                               }),
+                               short_channel_id: None,
+                               retry: None,
+                               error_code: None,
+                               error_data: None,
+                       });
+
+                       assert!(network_graph.read_only().channels().get(&short_channel_id).is_some());
+                       assert!(network_graph.read_only().nodes().get(&NodeId::from_pubkey(&node_2_id)).is_some());
+
+                       // Permanent node failure deletes node and its channels
+                       network_graph.handle_event(&Event::PaymentPathFailed {
+                               payment_id: None,
+                               payment_hash: PaymentHash([0; 32]),
+                               payment_failed_permanently: false,
+                               all_paths_failed: true,
+                               path: vec![],
+                               network_update: Some(NetworkUpdate::NodeFailure {
+                                       node_id: node_2_id,
+                                       is_permanent: true,
+                               }),
+                               short_channel_id: None,
+                               retry: None,
+                               error_code: None,
+                               error_data: None,
+                       });
+
+                       assert_eq!(network_graph.read_only().nodes().len(), 0);
+                       // Channels are also deleted because the associated node has been deleted
+                       assert_eq!(network_graph.read_only().channels().len(), 0);
+               }
        }
 
        #[test]
        fn test_channel_timeouts() {
-               // Test the removal of channels with `remove_stale_channels`.
+               // Test the removal of channels with `remove_stale_channels_and_tracking`.
                let logger = test_utils::TestLogger::new();
                let chain_source = test_utils::TestChainSource::new(Network::Testnet);
                let genesis_hash = genesis_block(Network::Testnet).header.block_hash();
@@ -2392,11 +2571,11 @@ mod tests {
                assert!(gossip_sync.handle_channel_update(&valid_channel_update).is_ok());
                assert!(network_graph.read_only().channels().get(&short_channel_id).unwrap().one_to_two.is_some());
 
-               network_graph.remove_stale_channels_with_time(100 + STALE_CHANNEL_UPDATE_AGE_LIMIT_SECS);
+               network_graph.remove_stale_channels_and_tracking_with_time(100 + STALE_CHANNEL_UPDATE_AGE_LIMIT_SECS);
                assert_eq!(network_graph.read_only().channels().len(), 1);
                assert_eq!(network_graph.read_only().nodes().len(), 2);
 
-               network_graph.remove_stale_channels_with_time(101 + STALE_CHANNEL_UPDATE_AGE_LIMIT_SECS);
+               network_graph.remove_stale_channels_and_tracking_with_time(101 + STALE_CHANNEL_UPDATE_AGE_LIMIT_SECS);
                #[cfg(feature = "std")]
                {
                        // In std mode, a further check is performed before fully removing the channel -
@@ -2409,11 +2588,74 @@ mod tests {
 
                        use std::time::{SystemTime, UNIX_EPOCH};
                        let announcement_time = SystemTime::now().duration_since(UNIX_EPOCH).expect("Time must be > 1970").as_secs();
-                       network_graph.remove_stale_channels_with_time(announcement_time + 1 + STALE_CHANNEL_UPDATE_AGE_LIMIT_SECS);
+                       network_graph.remove_stale_channels_and_tracking_with_time(announcement_time + 1 + STALE_CHANNEL_UPDATE_AGE_LIMIT_SECS);
                }
 
                assert_eq!(network_graph.read_only().channels().len(), 0);
                assert_eq!(network_graph.read_only().nodes().len(), 0);
+
+               #[cfg(feature = "std")]
+               {
+                       use std::time::{SystemTime, UNIX_EPOCH};
+
+                       let tracking_time = SystemTime::now().duration_since(UNIX_EPOCH).expect("Time must be > 1970").as_secs();
+
+                       // Clear tracked nodes and channels for clean slate
+                       network_graph.removed_channels.lock().unwrap().clear();
+                       network_graph.removed_nodes.lock().unwrap().clear();
+
+                       // Add a channel and nodes from channel announcement. So our network graph will
+                       // now only consist of two nodes and one channel between them.
+                       assert!(network_graph.update_channel_from_announcement(
+                               &valid_channel_announcement, &chain_source).is_ok());
+
+                       // Mark the channel as permanently failed. This will also remove the two nodes
+                       // and all of the entries will be tracked as removed.
+                       network_graph.channel_failed(short_channel_id, true);
+
+                       // Should not remove from tracking if insufficient time has passed
+                       network_graph.remove_stale_channels_and_tracking_with_time(
+                               tracking_time + REMOVED_ENTRIES_TRACKING_AGE_LIMIT_SECS - 1);
+                       assert_eq!(network_graph.removed_channels.lock().unwrap().len(), 1);
+
+                       // Provide a later time so that sufficient time has passed
+                       network_graph.remove_stale_channels_and_tracking_with_time(
+                               tracking_time + REMOVED_ENTRIES_TRACKING_AGE_LIMIT_SECS);
+                       assert!(network_graph.removed_channels.lock().unwrap().is_empty());
+                       assert!(network_graph.removed_nodes.lock().unwrap().is_empty());
+               }
+
+               #[cfg(not(feature = "std"))]
+               {
+                       // When we don't have access to the system clock, the time we started tracking removal will only
+                       // be that provided by the first call to `remove_stale_channels_and_tracking_with_time`. Hence,
+                       // only if sufficient time has passed after that first call, will the next call remove it from
+                       // tracking.
+                       let removal_time = 1664619654;
+
+                       // Clear removed nodes and channels for clean slate
+                       network_graph.removed_channels.lock().unwrap().clear();
+                       network_graph.removed_nodes.lock().unwrap().clear();
+
+                       // Add a channel and nodes from channel announcement. So our network graph will
+                       // now only consist of two nodes and one channel between them.
+                       assert!(network_graph.update_channel_from_announcement(
+                               &valid_channel_announcement, &chain_source).is_ok());
+
+                       // Mark the channel as permanently failed. This will also remove the two nodes
+                       // and all of the entries will be tracked as removed.
+                       network_graph.channel_failed(short_channel_id, true);
+
+                       // The first time we call the following, the channel will have a removal time assigned.
+                       network_graph.remove_stale_channels_and_tracking_with_time(removal_time);
+                       assert_eq!(network_graph.removed_channels.lock().unwrap().len(), 1);
+
+                       // Provide a later time so that sufficient time has passed
+                       network_graph.remove_stale_channels_and_tracking_with_time(
+                               removal_time + REMOVED_ENTRIES_TRACKING_AGE_LIMIT_SECS);
+                       assert!(network_graph.removed_channels.lock().unwrap().is_empty());
+                       assert!(network_graph.removed_nodes.lock().unwrap().is_empty());
+               }
        }
 
        #[test]