Handle duplicate payment claims during initialization

In the next commit we'll start using (much of) the normal HTLC
claim pipeline to replay payment claims on startup. In order to do
so, however, we have to properly handle cases where we get a
`DuplicateClaim` back from the channel for an inbound-payment HTLC.

Here we do so, handling the `MonitorUpdateCompletionAction` and
allowing an already-completed RAA blocker.

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -6964,7 +6964,16 @@ where
 							UpdateFulfillCommitFetch::DuplicateClaim {} => {
 								let (action_opt, raa_blocker_opt) = completion_action(None, true);
 								if let Some(raa_blocker) = raa_blocker_opt {
-									debug_assert!(peer_state.actions_blocking_raa_monitor_updates.get(&chan_id).unwrap().contains(&raa_blocker));
+									// If we're making a claim during startup, its a replay of a
+									// payment claim from a `ChannelMonitor`. In some cases (MPP or
+									// if the HTLC was only recently removed) we make such claims
+									// after an HTLC has been removed from a channel entirely, and
+									// thus the RAA blocker has long since completed.
+									//
+									// In any other case, the RAA blocker must still be present and
+									// blocking RAAs.
+									debug_assert!(during_init ||
+										peer_state.actions_blocking_raa_monitor_updates.get(&chan_id).unwrap().contains(&raa_blocker));
 								}
 								let action = if let Some(action) = action_opt {
 									action
@@ -6976,38 +6985,41 @@ where
 
 								log_trace!(logger, "Completing monitor update completion action for channel {} as claim was redundant: {:?}",
 									chan_id, action);
-								let (node_id, _funding_outpoint, channel_id, blocker) =
 								if let MonitorUpdateCompletionAction::FreeOtherChannelImmediately {
 									downstream_counterparty_node_id: node_id,
-									downstream_funding_outpoint: funding_outpoint,
+									downstream_funding_outpoint: _,
 									blocking_action: blocker, downstream_channel_id: channel_id,
 								} = action {
-									(node_id, funding_outpoint, channel_id, blocker)
+									if let Some(peer_state_mtx) = per_peer_state.get(&node_id) {
+										let mut peer_state = peer_state_mtx.lock().unwrap();
+										if let Some(blockers) = peer_state
+											.actions_blocking_raa_monitor_updates
+											.get_mut(&channel_id)
+										{
+											let mut found_blocker = false;
+											blockers.retain(|iter| {
+												// Note that we could actually be blocked, in
+												// which case we need to only remove the one
+												// blocker which was added duplicatively.
+												let first_blocker = !found_blocker;
+												if *iter == blocker { found_blocker = true; }
+												*iter != blocker || !first_blocker
+											});
+											debug_assert!(found_blocker);
+										}
+									} else {
+										debug_assert!(false);
+									}
+								} else if matches!(action, MonitorUpdateCompletionAction::PaymentClaimed { .. }) {
+									debug_assert!(during_init,
+										"Duplicate claims should always either be for forwarded payments(freeing another channel immediately) or during init (for claim replay)");
+									mem::drop(per_peer_state);
+									self.handle_monitor_update_completion_actions([action]);
 								} else {
 									debug_assert!(false,
-										"Duplicate claims should always free another channel immediately");
+										"Duplicate claims should always either be for forwarded payments(freeing another channel immediately) or during init (for claim replay)");
 									return;
 								};
-								if let Some(peer_state_mtx) = per_peer_state.get(&node_id) {
-									let mut peer_state = peer_state_mtx.lock().unwrap();
-									if let Some(blockers) = peer_state
-										.actions_blocking_raa_monitor_updates
-										.get_mut(&channel_id)
-									{
-										let mut found_blocker = false;
-										blockers.retain(|iter| {
-											// Note that we could actually be blocked, in
-											// which case we need to only remove the one
-											// blocker which was added duplicatively.
-											let first_blocker = !found_blocker;
-											if *iter == blocker { found_blocker = true; }
-											*iter != blocker || !first_blocker
-										});
-										debug_assert!(found_blocker);
-									}
-								} else {
-									debug_assert!(false);
-								}
 							}
 						}
 					}