Extract util for HTLCIntercepted event creation
What the developer wrote
Authored by Valentine Wallace
Extract util for HTLCIntercepted event creation
We have an overarching goal of (mostly) getting rid of ChannelManager
persistence and rebuilding the ChannelManager's state from existing
ChannelMonitors, due to issues when the two structs are out-of-sync on restart.
The main issue that can arise is channel force closure.
As part of rebuilding ChannelManager forward HTLCs maps, we will also add
a fix that will regenerate HTLCIntercepted events for HTLC intercepts that
are present but have no corresponding event in the queue. That fix will use
this new method.
What changed, and why it matters
This commit is a small internal code cleanup in the Lightning Dev Kit's channel manager. It pulls out duplicated code for creating an 'HTLC intercepted' event into a shared helper function. The change does not fix a security bug and does not alter user-facing behavior; it is preparation for a future reliability improvement around restarting the channel manager without losing track of intercepted payments.
No security action required. Treat as normal maintenance/refactoring. Review the follow-up commit that regenerates HTLCIntercepted events from rebuilt ChannelManager state when it lands, as that is where any actual security or reliability implications would reside.
Security signals we found
No security-relevant behavior change: pure refactor/DRY extraction
New helper returns `Result<Event, ()>` instead of unwrapping, adding defensive checks for missing fields
Failure path now fails the intercepted HTLC rather than panicking
Commit message mentions future fix for ChannelManager/ChannelMonitor state resynchronization after restart
Evidence from the diff
The patch extracts a new private utility create_htlc_intercepted_event in lightning/src/ln/channelmanager.rs. The helper builds an Event::HTLCIntercepted from a PendingAddHTLCInfo, returning Err(()) if the required forward-routing variant or inbound amount is missing. The existing call site that previously constructed the event inline now uses this helper and, on failure, calls fail_intercepted_htlc(pending_add) with a debug_assert!(false). The commit message frames this as groundwork for later rebuilding ChannelManager state from ChannelMonitors and regenerating lost HTLCIntercepted events after restart.
Changed components
lightning/src/ln/channelmanager.rsHTLC interception event generationPendingAddHTLCInfo handlingInspect captured patch +28 / −16
diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs
index 72585d6..aa78710 100644
--- a/lightning/src/ln/channelmanager.rs
+++ b/lightning/src/ln/channelmanager.rs
@@ -3911,6 +3911,25 @@ macro_rules! process_events_body {
}
}
+/// Creates an [`Event::HTLCIntercepted`] from a [`PendingAddHTLCInfo`]. We generate this event in a
+/// few places so this DRYs the code.
+fn create_htlc_intercepted_event(
+ intercept_id: InterceptId, pending_add: &PendingAddHTLCInfo,
+) -> Result<Event, ()> {
+ let inbound_amount_msat = pending_add.forward_info.incoming_amt_msat.ok_or(())?;
+ let requested_next_hop_scid = match pending_add.forward_info.routing {
+ PendingHTLCRouting::Forward { short_channel_id, .. } => short_channel_id,
+ _ => return Err(()),
+ };
+ Ok(Event::HTLCIntercepted {
+ requested_next_hop_scid,
+ payment_hash: pending_add.forward_info.payment_hash,
+ inbound_amount_msat,
+ expected_outbound_amount_msat: pending_add.forward_info.outgoing_amt_msat,
+ intercept_id,
+ })
+}
+
impl<
M: Deref,
T: Deref,
@@ -11486,22 +11505,15 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
let mut pending_intercepts = self.pending_intercepted_htlcs.lock().unwrap();
match pending_intercepts.entry(intercept_id) {
hash_map::Entry::Vacant(entry) => {
- new_intercept_events.push_back((
- events::Event::HTLCIntercepted {
- requested_next_hop_scid: scid,
- payment_hash,
- inbound_amount_msat: pending_add
- .forward_info
- .incoming_amt_msat
- .unwrap(),
- expected_outbound_amount_msat: pending_add
- .forward_info
- .outgoing_amt_msat,
- intercept_id,
- },
- None,
- ));
- entry.insert(pending_add);
+ if let Ok(intercept_ev) =
+ create_htlc_intercepted_event(intercept_id, &pending_add)
+ {
+ new_intercept_events.push_back((intercept_ev, None));
+ entry.insert(pending_add);
+ } else {
+ debug_assert!(false);
+ fail_intercepted_htlc(pending_add);
+ }
},
hash_map::Entry::Occupied(_) => {
log_info!(
Why this scored 12/100
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