send warning when we have a old commitment transaction

During a `channel_restablish` now we send a warning message when we have a old commitment transaction.

Signed-off-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

lightning/src/ln/channel.rs

@@ -3679,6 +3679,21 @@ impl<Signer: Sign> Channel<Signer> {
 		}
 	}
 
+	/// Check if the we are trying to reestablish a connection when we have a
+	/// very old local commitment transaction.
+	///
+	/// If we are out of sync we return an empty result, otherwise just the channel error tu sent.
+	fn try_reestablish_when_we_are_late(&mut self,  msg: &msgs::ChannelReestablish) -> Result<(), ChannelError> {
+		//FIXME(vincenzopalazzo) We receive the next commitment transaction to one to sent, so to be in sync we should
+		// be equal at list to the `next - 1`?
+		if self.next_remote_commitment_number < msg.next_remote_commitment_number - 1 {
+			return Err(
+				ChannelError::Warn("we have a very old commitment transaction".to_owned())
+			);
+		}
+		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,
@@ -3715,6 +3730,13 @@ impl<Signer: Sign> Channel<Signer> {
 			}
 		}
 
+		// Before change the state of the channel, we check if
+		// we have a very old local commitment transaction.
+		// this is more a sanity check!
+		if let Err(err_msg) = self.try_reestablish_when_we_are_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);