Write structs to serialise-deserialise Channels inside Peer-storage

'PeerStorageMonitorHolder' is used to wrap a single ChannelMonitor, here we are
adding some fields separetly so that we do not need to read the whole ChannelMonitor
to identify if we have lost some states.

`PeerStorageMonitorHolderList` is used to keep the list of all the channels which would
be sent over the wire inside Peer Storage.

Author: adi2011

lightning/src/ln/our_peer_storage.rs

@@ -13,7 +13,9 @@
 
 use bitcoin::hashes::sha256::Hash as Sha256;
 use bitcoin::hashes::{Hash, HashEngine, Hmac, HmacEngine};
+use bitcoin::secp256k1::PublicKey;
 
+use crate::ln::types::ChannelId;
 use crate::sign::PeerStorageKey;
 
 use crate::crypto::chacha20poly1305rfc::ChaCha20Poly1305RFC;
@@ -146,6 +148,34 @@ fn derive_nonce(key: &PeerStorageKey, random_bytes: &[u8]) -> [u8; 12] {
 	nonce
 }
 
+/// [`PeerStorageMonitorHolder`] represents a single channel sent over the wire.
+/// This would be used inside [`ChannelManager`] to determine
+/// if the user has lost channel states so that we can do something about it.
+///
+/// The main idea here is to just enable node to figure out that it has lost some data
+/// using peer storage backups.
+///
+/// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
+///
+/// TODO(aditya): Write FundRecoverer to use `monitor_bytes` to drop onchain.
+pub(crate) struct PeerStorageMonitorHolder {
+	/// Channel Id of the channel.
+	pub(crate) channel_id: ChannelId,
+	/// Node Id of the channel partner.
+	pub(crate) counterparty_node_id: PublicKey,
+	/// Minimum seen secret to determine if we have lost state.
+	pub(crate) min_seen_secret: u64,
+	/// Whole serialised ChannelMonitor to recover funds.
+	pub(crate) monitor_bytes: Vec<u8>,
+}
+
+impl_writeable_tlv_based!(PeerStorageMonitorHolder, {
+	(0, channel_id, required),
+	(2, counterparty_node_id, required),
+	(4, min_seen_secret, required),
+	(6, monitor_bytes, required_vec),
+});
+
 #[cfg(test)]
 mod tests {
 	use crate::ln::our_peer_storage::{derive_nonce, DecryptedOurPeerStorage};

lightning/src/util/ser.rs

@@ -1084,6 +1084,7 @@ impl_for_vec!((A, B), A, B);
 impl_for_vec!(SerialId);
 impl_for_vec!(NegotiatedTxInput);
 impl_for_vec!(InteractiveTxOutput);
+impl_for_vec!(crate::ln::our_peer_storage::PeerStorageMonitorHolder);
 impl_writeable_for_vec!(&crate::routing::router::BlindedTail);
 impl_readable_for_vec!(crate::routing::router::BlindedTail);
 impl_for_vec!(crate::routing::router::TrampolineHop);