Determine if we have lost data

Deserialise the ChannelMonitors and compare the data to determine if we have
lost some states.

Author: adi2011

lightning/src/ln/channelmanager.rs

@@ -58,6 +58,7 @@ use crate::events::{
 use crate::events::{FundingInfo, PaidBolt12Invoice};
 // Since this struct is returned in `list_channels` methods, expose it here in case users want to
 // construct one themselves.
+use crate::io;
 use crate::ln::channel::PendingV2Channel;
 use crate::ln::channel::{
 	self, Channel, ChannelError, ChannelUpdateStatus, FundedChannel, InboundV1Channel,
@@ -78,7 +79,7 @@ use crate::ln::onion_payment::{
 };
 use crate::ln::onion_utils::{self};
 use crate::ln::onion_utils::{HTLCFailReason, LocalHTLCFailureReason};
-use crate::ln::our_peer_storage::EncryptedOurPeerStorage;
+use crate::ln::our_peer_storage::{EncryptedOurPeerStorage, PeerStorageMonitorHolderList};
 #[cfg(test)]
 use crate::ln::outbound_payment;
 use crate::ln::outbound_payment::{
@@ -174,7 +175,6 @@ use lightning_invoice::{
 
 use alloc::collections::{btree_map, BTreeMap};
 
-use crate::io;
 use crate::io::Read;
 use crate::prelude::*;
 use crate::sync::{Arc, FairRwLock, LockHeldState, LockTestExt, Mutex, RwLock, RwLockReadGuard};
@@ -8807,6 +8807,7 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 		&self, peer_node_id: PublicKey, msg: msgs::PeerStorageRetrieval,
 	) -> Result<(), MsgHandleErrInternal> {
 		// TODO: Check if have any stale or missing ChannelMonitor.
+		let per_peer_state = self.per_peer_state.read().unwrap();
 		let logger = WithContext::from(&self.logger, Some(peer_node_id), None, None);
 		let err = || {
 			MsgHandleErrInternal::from_chan_no_close(
@@ -8833,6 +8834,55 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 
 		log_trace!(logger, "Got valid {}-byte peer backup from {}", decrypted.len(), peer_node_id);
 
+		let mut cursor = io::Cursor::new(decrypted);
+		match <PeerStorageMonitorHolderList as Readable>::read(&mut cursor) {
+			Ok(mon_list) => {
+				for mon_holder in mon_list.monitors.iter() {
+					let peer_state_mutex =
+						match per_peer_state.get(&mon_holder.counterparty_node_id) {
+							Some(mutex) => mutex,
+							None => {
+								log_debug!(
+									logger,
+									"Not able to find peer_state for the counterparty {}, channelId {}",
+									log_pubkey!(mon_holder.counterparty_node_id),
+									mon_holder.channel_id
+								);
+								continue;
+							},
+						};
+
+					let peer_state_lock = peer_state_mutex.lock().unwrap();
+					let peer_state = &*peer_state_lock;
+
+					match peer_state.channel_by_id.get(&mon_holder.channel_id) {
+						Some(chan) => {
+							if let Some(funded_chan) = chan.as_funded() {
+								if funded_chan
+									.get_revoked_counterparty_commitment_transaction_number()
+									> mon_holder.min_seen_secret
+								{
+									panic!(
+										"Lost channel state for channel {}.
+										Received peer storage with a more recent state than what our node had.
+										Use the FundRecoverer to initiate a force close and sweep the funds.",
+										&mon_holder.channel_id
+									);
+								}
+							}
+						},
+						None => {
+							// TODO: Figure out if this channel is so old that we have forgotten about it.
+							panic!("Lost a channel {}", &mon_holder.channel_id);
+						},
+					}
+				}
+			},
+
+			Err(e) => {
+				panic!("Wrong serialisation of PeerStorageMonitorHolderList: {}", e);
+			},
+		}
 		Ok(())
 	}
 
@@ -8858,6 +8908,7 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 			), ChannelId([0; 32])));
 		}
 
+		#[cfg(not(test))]
 		if msg.data.len() > MAX_PEER_STORAGE_SIZE {
 			log_debug!(logger, "Sending warning to peer and ignoring peer storage request from {} as its over 1KiB", log_pubkey!(counterparty_node_id));