Track the full list of outpoints a chanmon wants monitoring for.

Upon deserialization/reload we need to be able to register each
outpoint which spends the commitment txo which a channelmonitor
believes to be on chain. While our other internal tracking is
likely sufficient to regenerate these, its much easier to simply
track all outpouts we've ever generated, so we do that here.

Author: TheBlueMatt

lightning/src/ln/channelmonitor.rs

@@ -117,9 +117,16 @@ pub struct HTLCUpdate {
 pub trait ManyChannelMonitor<ChanSigner: ChannelKeys>: Send + Sync {
 	/// Adds or updates a monitor for the given `funding_txo`.
 	///
-	/// Implementor must also ensure that the funding_txo outpoint is registered with any relevant
-	/// ChainWatchInterfaces such that the provided monitor receives block_connected callbacks with
-	/// any spends of it.
+	/// Implementer must also ensure that the funding_txo txid *and* outpoint are registered with
+	/// any relevant ChainWatchInterfaces such that the provided monitor receives block_connected
+	/// callbacks with the funding transaction, or any spends of it.
+	///
+	/// Further, the implementer must also ensure that each output returned in
+	/// monitor.get_outputs_to_watch() is registered to ensure that the provided monitor learns about
+	/// any spends of any of the outputs.
+	///
+	/// Any spends of outputs which should have been registered which aren't passed to
+	/// ChannelMonitors via block_connected may result in funds loss.
 	fn add_update_monitor(&self, funding_txo: OutPoint, monitor: ChannelMonitor<ChanSigner>) -> Result<(), ChannelMonitorUpdateErr>;
 
 	/// Used by ChannelManager to get list of HTLC resolved onchain and which needed to be updated
@@ -259,6 +266,11 @@ impl<Key : Send + cmp::Eq + hash::Hash + 'static, ChanSigner: ChannelKeys> Simpl
 				self.chain_monitor.watch_all_txn();
 			}
 		}
+		for (txid, outputs) in monitor.get_outputs_to_watch().iter() {
+			for (idx, script) in outputs.iter().enumerate() {
+				self.chain_monitor.install_watch_outpoint((*txid, idx as u32), script);
+			}
+		}
 		monitors.insert(key, monitor);
 		Ok(())
 	}
@@ -666,6 +678,12 @@ pub struct ChannelMonitor<ChanSigner: ChannelKeys> {
 	// actions when we receive a block with given height. Actions depend on OnchainEvent type.
 	onchain_events_waiting_threshold_conf: HashMap<u32, Vec<OnchainEvent>>,
 
+	// If we get serialized out and re-read, we need to make sure that the chain monitoring
+	// interface knows about the TXOs that we want to be notified of spends of. We could probably
+	// be smart and derive them from the above storage fields, but its much simpler and more
+	// Obviously Correct (tm) if we just keep track of them explicitly.
+	outputs_to_watch: HashMap<Sha256dHash, Vec<Script>>,
+
 	// We simply modify last_block_hash in Channel's block_connected so that serialization is
 	// consistent but hopefully the users' copy handles block_connected in a consistent way.
 	// (we do *not*, however, update them in insert_combine to ensure any local user copies keep
@@ -736,7 +754,8 @@ impl<ChanSigner: ChannelKeys> PartialEq for ChannelMonitor<ChanSigner> {
 			self.to_remote_rescue != other.to_remote_rescue ||
 			self.pending_claim_requests != other.pending_claim_requests ||
 			self.claimable_outpoints != other.claimable_outpoints ||
-			self.onchain_events_waiting_threshold_conf != other.onchain_events_waiting_threshold_conf
+			self.onchain_events_waiting_threshold_conf != other.onchain_events_waiting_threshold_conf ||
+			self.outputs_to_watch != other.outputs_to_watch
 		{
 			false
 		} else {
@@ -966,6 +985,15 @@ impl<ChanSigner: ChannelKeys + Writeable> ChannelMonitor<ChanSigner> {
 			}
 		}
 
+		(self.outputs_to_watch.len() as u64).write(writer)?;
+		for (txid, output_scripts) in self.outputs_to_watch.iter() {
+			txid.write(writer)?;
+			(output_scripts.len() as u64).write(writer)?;
+			for script in output_scripts.iter() {
+				script.write(writer)?;
+			}
+		}
+
 		Ok(())
 	}
 
@@ -1036,6 +1064,7 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 			claimable_outpoints: HashMap::new(),
 
 			onchain_events_waiting_threshold_conf: HashMap::new(),
+			outputs_to_watch: HashMap::new(),
 
 			last_block_hash: Default::default(),
 			secp_ctx: Secp256k1::new(),
@@ -1370,6 +1399,12 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 		}
 	}
 
+	/// Gets a list of txids, with their output scripts (in the order they appear in the
+	/// transaction), which we must learn about spends of via block_connected().
+	pub fn get_outputs_to_watch(&self) -> &HashMap<Sha256dHash, Vec<Script>> {
+		&self.outputs_to_watch
+	}
+
 	/// Gets the sets of all outpoints which this ChannelMonitor expects to hear about spends of.
 	/// Generally useful when deserializing as during normal operation the return values of
 	/// block_connected are sufficient to ensure all relevant outpoints are being monitored (note
@@ -2589,6 +2624,9 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 			}
 		}
 		self.last_block_hash = block_hash.clone();
+		for &(ref txid, ref output_scripts) in watch_outputs.iter() {
+			self.outputs_to_watch.insert(txid.clone(), output_scripts.iter().map(|o| o.script_pubkey.clone()).collect());
+		}
 		(watch_outputs, spendable_outputs, htlc_updated)
 	}
 
@@ -3241,6 +3279,20 @@ impl<R: ::std::io::Read, ChanSigner: ChannelKeys + Readable<R>> ReadableArgs<R,
 			onchain_events_waiting_threshold_conf.insert(height_target, events);
 		}
 
+		let outputs_to_watch_len: u64 = Readable::read(reader)?;
+		let mut outputs_to_watch = HashMap::with_capacity(cmp::min(outputs_to_watch_len as usize, MAX_ALLOC_SIZE / (mem::size_of::<Sha256dHash>() + mem::size_of::<Vec<Script>>())));
+		for _ in 0..outputs_to_watch_len {
+			let txid = Readable::read(reader)?;
+			let outputs_len: u64 = Readable::read(reader)?;
+			let mut outputs = Vec::with_capacity(cmp::min(outputs_len as usize, MAX_ALLOC_SIZE / mem::size_of::<Script>()));
+			for _ in 0..outputs_len {
+				outputs.push(Readable::read(reader)?);
+			}
+			if let Some(_) = outputs_to_watch.insert(txid, outputs) {
+				return Err(DecodeError::InvalidValue);
+			}
+		}
+
 		Ok((last_block_hash.clone(), ChannelMonitor {
 			commitment_transaction_number_obscure_factor,
 
@@ -3273,6 +3325,7 @@ impl<R: ::std::io::Read, ChanSigner: ChannelKeys + Readable<R>> ReadableArgs<R,
 			claimable_outpoints,
 
 			onchain_events_waiting_threshold_conf,
+			outputs_to_watch,
 
 			last_block_hash,
 			secp_ctx,