f more comments

Author: TheBlueMatt

fuzz/src/chanmon_consistency.rs

@@ -142,9 +142,20 @@ impl Writer for VecWriter {
 	}
 }
 
+/// The LDK API requires that any time we tell it we're done persisting a `ChannelMonitor[Update]`
+/// we never pass it in as the "latest" `ChannelMonitor` on startup. However, we can pass
+/// out-of-date monitors as long as we never told LDK we finished persisting them, which we do by
+/// storing both old `ChannelMonitor`s and ones that are "being persisted" here.
+///
+/// Note that such "being persisted" `ChannelMonitor`s are stored in `ChannelManager` and will
+/// simply be replayed on startup.
 struct LatestMonitorState {
+	/// The latest monitor id which we told LDK we've persisted
 	persisted_monitor_id: u64,
+	/// The latest serialized `ChannelMonitor` that we told LDK we persisted.
 	persisted_monitor: Vec<u8>,
+	/// A set of (monitor id, serialized `ChannelMonitor`)s which we're currently "persisting",
+	/// from LDK's perspective.
 	pending_monitor_updates: Vec<(u64, Vec<u8>)>,
 }
 
@@ -153,14 +164,6 @@ struct TestChainMonitor {
 	pub keys: Arc<KeyProvider>,
 	pub persister: Arc<TestPersister>,
 	pub chain_monitor: Arc<chainmonitor::ChainMonitor<TestChannelSigner, Arc<dyn chain::Filter>, Arc<TestBroadcaster>, Arc<FuzzEstimator>, Arc<dyn Logger>, Arc<TestPersister>>>,
-	// If we reload a node with an old copy of ChannelMonitors, the ChannelManager deserialization
-	// logic will automatically force-close our channels for us (as we don't have an up-to-date
-	// monitor implying we are not able to punish misbehaving counterparties). Because this test
-	// "fails" if we ever force-close a channel, we avoid doing so, always saving the latest
-	// fully-serialized monitor state here, as well as the corresponding update_id.
-	//
-	// Note that this doesn't apply to monitors which are pending persistence, so we store the
-	// latest pending monitor separately.
 	pub latest_monitors: Mutex<HashMap<OutPoint, LatestMonitorState>>,
 }
 impl TestChainMonitor {
@@ -549,6 +552,9 @@ pub fn do_test<Out: Output>(data: &[u8], underlying_out: Out, anchors: bool) {
 				monitors.insert(outpoint, <(BlockHash, ChannelMonitor<TestChannelSigner>)>::read(
 					&mut Cursor::new(&prev_state.persisted_monitor), (&*$keys_manager, &*$keys_manager)
 				).expect("Failed to read monitor").1);
+				// Wipe any `ChannelMonitor`s which we never told LDK we finished persisting,
+				// considering them discarded. LDK should replay these for us as they're stored in
+				// the `ChannelManager`.
 				prev_state.pending_monitor_updates.clear();
 				chain_monitor.latest_monitors.lock().unwrap().insert(outpoint, prev_state);
 			}