Adjust MUP to read only old monitor height instead of deserializing whole monitor

Author: domZippilli

lightning/src/util/persist.rs

@@ -14,7 +14,7 @@ use core::ops::Deref;
 use bitcoin::hashes::hex::{FromHex, ToHex};
 use bitcoin::{BlockHash, Txid};
 
-use crate::{io, log_error};
+use crate::{io, io::Read, log_error};
 use crate::alloc::string::ToString;
 use crate::prelude::*;
 
@@ -538,6 +538,34 @@ where
 		}
 	}
 
+	/// Read a channel monitor's height only.
+	fn read_monitor_height(
+		&self, monitor_name: &MonitorName,
+	) -> Result<u64, io::Error> {
+		let mut monitor_cursor = io::Cursor::new(self.kv_store.read(
+			CHANNEL_MONITOR_PERSISTENCE_PRIMARY_NAMESPACE,
+			CHANNEL_MONITOR_PERSISTENCE_SECONDARY_NAMESPACE,
+			monitor_name.as_str(),
+		)?);
+		// Discard the sentinel bytes if found.
+		if monitor_cursor.get_ref().starts_with(MONITOR_UPDATING_PERSISTER_PREPEND_SENTINEL) {
+			monitor_cursor.set_position(MONITOR_UPDATING_PERSISTER_PREPEND_SENTINEL.len() as u64);
+		}
+
+		// This doesn't compile because of an error type mismatch
+		// let height = 0u64;
+		// decode_tlv_stream!(monitor_cursor, {
+		// 	     (0, height, required),
+		// 	 });
+
+		// Skip T, L, and get to V
+		monitor_cursor.set_position(monitor_cursor.position() + 2);
+		let mut buf = [0; 8];
+		monitor_cursor.read_exact(&mut buf)?;
+		let height: u64 = u64::from_ne_bytes(buf);
+		Ok(height)
+	}
+
 	/// Read a channel monitor update.
 	fn read_monitor_update(
 		&self, monitor_name: &MonitorName, update_name: &UpdateName,
@@ -610,24 +638,28 @@ where
 	) -> chain::ChannelMonitorUpdateStatus {
 		// Determine the proper key for this monitor
 		let monitor_name = MonitorName::from(funding_txo);
-		let maybe_old_monitor = self.read_monitor(&monitor_name);
-		match maybe_old_monitor {
-			Ok((_, ref old_monitor)) => {
-				// Check that this key isn't already storing a monitor with a higher update_id
-				// (collision)
-				if old_monitor.get_latest_update_id() > monitor.get_latest_update_id() {
-					log_error!(
-						self.logger,
-						"Tried to write a monitor at the same outpoint {} with a higher update_id!",
-						monitor_name.as_str()
-					);
-					return chain::ChannelMonitorUpdateStatus::UnrecoverableError;
-				}
-			}
-			// This means the channel monitor is new.
-			Err(ref e) if e.kind() == io::ErrorKind::NotFound => {}
-			_ => return chain::ChannelMonitorUpdateStatus::UnrecoverableError,
-		}
+		let maybe_old_monitor_height = self.read_monitor_height(&monitor_name);
+
+		// // Can this check be sacrificed?
+		// let maybe_old_monitor = self.read_monitor(&monitor_name);
+		// match maybe_old_monitor {
+		// 	Ok((_, ref old_monitor)) => {
+		// 		// Check that this key isn't already storing a monitor with a higher update_id
+		// 		// (collision)
+		// 		if old_monitor.get_latest_update_id() > monitor.get_latest_update_id() {
+		// 			log_error!(
+		// 				self.logger,
+		// 				"Tried to write a monitor at the same outpoint {} with a higher update_id!",
+		// 				monitor_name.as_str()
+		// 			);
+		// 			return chain::ChannelMonitorUpdateStatus::UnrecoverableError;
+		// 		}
+		// 	}
+		// 	// This means the channel monitor is new.
+		// 	Err(ref e) if e.kind() == io::ErrorKind::NotFound => {}
+		// 	_ => return chain::ChannelMonitorUpdateStatus::UnrecoverableError,
+		// }
+
 		// Serialize and write the new monitor
 		let mut monitor_bytes = Vec::with_capacity(
 			MONITOR_UPDATING_PERSISTER_PREPEND_SENTINEL.len() + monitor.serialized_length(),
@@ -643,8 +675,8 @@ where
 			Ok(_) => {
 				// Assess cleanup. Typically, we'll clean up only between the last two known full
 				// monitors.
-				if let Ok((_, old_monitor)) = maybe_old_monitor {
-					let start = old_monitor.get_latest_update_id();
+				if let Ok(old_monitor_height) = maybe_old_monitor_height {
+					let start = old_monitor_height;
 					let end = if monitor.get_latest_update_id() == CLOSED_CHANNEL_UPDATE_ID {
 						// We don't want to clean the rest of u64, so just do possible pending
 						// updates. Note that we never write updates at