Add prune_stale_channel_monitors to ChainMonitor

lightning/src/chain/chainmonitor.rs

@@ -656,6 +656,19 @@ where C::Target: chain::Filter,
 			}
 		}
 	}
+
+	pub fn prune_stale_channel_monitors(&self) {
+		let mut monitors = self.monitors.write().unwrap();
+		let mut to_remove = Vec::new();
+		for (funding_outpoint, monitor_holder) in monitors.iter() {
+			if monitor_holder.monitor.is_stale() {
+				to_remove.push(*funding_outpoint);
+			}
+		}
+		for funding_outpoint in to_remove {
+			monitors.remove(&funding_outpoint);
+		}
+	}
 }
 
 impl<ChannelSigner: WriteableEcdsaChannelSigner, C: Deref, T: Deref, F: Deref, L: Deref, P: Deref>
@@ -1108,4 +1121,17 @@ mod tests {
 			core::mem::drop(nodes);
 		}).is_err());
 	}
+
+	#[test]
+	fn prune_stale_channel_monitor() {
+		// Test that we can prune a ChannelMonitor that has no active channel.
+		let chanmon_cfgs = create_chanmon_cfgs(2);
+		let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
+		let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None]);
+		let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+		let push_msat = 0;
+		let channel_id = exchange_open_accept_chan(&nodes[0], &nodes[1], 10000, push_msat);
+		nodes[0].node.close_channel(&channel_id, &nodes[1].node.get_our_node_id()).unwrap();
+		// try to prune stale channel monitor
+	}
 }

lightning/src/chain/channelmonitor.rs

@@ -1855,6 +1855,16 @@ impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitor<Signer> {
 		spendable_outputs
 	}
 
+	pub(crate) fn is_stale(&self) -> bool {
+		let _inner = self.inner.lock().unwrap();
+		// Access channel data to check if:
+		// 1) No push_msat is set
+		// 2) Inbound channel
+		// 3) No commitment tx updates occured
+		// 4) Channel is closed
+		false
+	}
+
 	#[cfg(test)]
 	pub fn get_counterparty_payment_script(&self) -> ScriptBuf {
 		self.inner.lock().unwrap().counterparty_payment_script.clone()