send warning when we receive a old commitment transaction

During a `channel_restablish` now we send a warning message when we we receive a old commitment transaction from the peer

Signed-off-by: Vincenzo Palazzo <[email protected]>

Author: vincenzopalazzo

lightning/src/ln/channel.rs

@@ -3679,6 +3679,20 @@ impl<Signer: Sign> Channel<Signer> {
 		}
 	}
 
+	/// Check if the we are trying to reestablish a connection with a peer with an old commitment
+	/// transaction that it is not possible recovered.
+	///
+	/// If the peer is not out of sync we return an empty result, otherwise just the channel error to sent.
+	fn try_reestablish_when_peer_is_late(&self, msg: &msgs::ChannelReestablish) -> Result<(), ChannelError> {
+		let _our_commitment_transaction = INITIAL_COMMITMENT_NUMBER - self.cur_holder_commitment_transaction_number - 1;
+		if  msg.next_remote_commitment_number + 1 < _our_commitment_transaction {
+			return Err(
+				ChannelError::Warn(format!("Peer attempted to reestablish channel with a very old local commitment transaction: {} (received) vs {} (expected)", msg.next_remote_commitment_number, _our_commitment_transaction))
+			);
+		}
+		Ok(())
+	}
+
 	/// May panic if some calls other than message-handling calls (which will all Err immediately)
 	/// have been called between remove_uncommitted_htlcs_and_mark_paused and this call.
 	pub fn channel_reestablish<L: Deref>(&mut self, msg: &msgs::ChannelReestablish, logger: &L,
@@ -3705,6 +3719,7 @@ impl<Signer: Sign> Channel<Signer> {
 					if expected_point != PublicKey::from_secret_key(&self.secp_ctx, &given_secret) {
 						return Err(ChannelError::Close("Peer sent a garbage channel_reestablish with secret key not matching the commitment height provided".to_owned()));
 					}
+
 					if msg.next_remote_commitment_number > INITIAL_COMMITMENT_NUMBER - self.cur_holder_commitment_transaction_number {
 						return Err(ChannelError::CloseDelayBroadcast(
 							"We have fallen behind - we have received proof that if we broadcast remote is going to claim our funds - we can't do any automated broadcasting".to_owned()
@@ -3715,6 +3730,12 @@ impl<Signer: Sign> Channel<Signer> {
 			}
 		}
 
+		// Before change the state of the channel we check if the peer is sending a very old
+		// commitment transaction number, if yes we send an error (warning message).
+		if let Err(err_msg) = self.try_reestablish_when_peer_is_late(msg) {
+			return Err(err_msg);
+		}
+
 		// Go ahead and unmark PeerDisconnected as various calls we may make check for it (and all
 		// remaining cases either succeed or ErrorMessage-fail).
 		self.channel_state &= !(ChannelState::PeerDisconnected as u32);