Keep track of the Init Features for every connected/channel'd peer

Since we want to keep track of the Init-context features for every
peer we have channels with, we have to keep them for as long as the
peer is connected (since we may open a channel with them at any
point).

We go ahead and take this opportunity to create a new per-peer-state
struct which has two levels of mutexes which is appropriate for
moving channel storage to.

Since we can't process messages from a given peer in parallel, the
inner lock is a regular mutex, but the outer lock is RW so that we
can process for different peers at the same time with an outer read
lock.

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -275,6 +275,12 @@ pub(super) struct ChannelHolder<ChanSigner: ChannelKeys> {
 	pub(super) pending_msg_events: Vec<events::MessageSendEvent>,
 }
 
+/// State we hold per-peer. In the future we should put channels in here, but for now we only hold
+/// the latest Init features we heard from the peer.
+struct PeerState {
+	latest_features: InitFeatures,
+}
+
 #[cfg(not(any(target_pointer_width = "32", target_pointer_width = "64")))]
 const ERR: () = "You need at least 32 bit pointers (well, usize, but we'll assume they're the same) for ChannelManager::latest_block_height";
 
@@ -328,6 +334,14 @@ pub struct ChannelManager<ChanSigner: ChannelKeys> {
 	channel_state: Mutex<ChannelHolder<ChanSigner>>,
 	our_network_key: SecretKey,
 
+	/// The bulk of our storage will eventually be here (channels and message queues and the like).
+	/// If we are connected to a peer we always at least have an entry here, even if no channels
+	/// are currently open with that peer.
+	/// Because adding or removing an entry is rare, we usually take an outer read lock and then
+	/// operate on the inner value freely. Sadly, this prevents parallel operation when opening a
+	/// new channel.
+	per_peer_state: RwLock<HashMap<PublicKey, Mutex<PeerState>>>,
+
 	pending_events: Mutex<Vec<events::Event>>,
 	/// Used when we have to take a BIG lock to make sure everything is self-consistent.
 	/// Essentially just when we're serializing ourselves out.
@@ -610,6 +624,8 @@ impl<ChanSigner: ChannelKeys> ChannelManager<ChanSigner> {
 			}),
 			our_network_key: keys_manager.get_node_secret(),
 
+			per_peer_state: RwLock::new(HashMap::new()),
+
 			pending_events: Mutex::new(Vec::new()),
 			total_consistency_lock: RwLock::new(()),
 
@@ -2780,6 +2796,7 @@ impl<ChanSigner: ChannelKeys> ChannelMessageHandler for ChannelManager<ChanSigne
 		let _ = self.total_consistency_lock.read().unwrap();
 		let mut failed_channels = Vec::new();
 		let mut failed_payments = Vec::new();
+		let mut no_channels_remain = true;
 		{
 			let mut channel_state_lock = self.channel_state.lock().unwrap();
 			let channel_state = &mut *channel_state_lock;
@@ -2818,6 +2835,8 @@ impl<ChanSigner: ChannelKeys> ChannelMessageHandler for ChannelManager<ChanSigne
 								short_to_id.remove(&short_id);
 							}
 							return false;
+						} else {
+							no_channels_remain = false;
 						}
 					}
 					true
@@ -2843,6 +2862,10 @@ impl<ChanSigner: ChannelKeys> ChannelMessageHandler for ChannelManager<ChanSigne
 				}
 			});
 		}
+		if no_channels_remain {
+			self.per_peer_state.write().unwrap().remove(their_node_id);
+		}
+
 		for failure in failed_channels.drain(..) {
 			self.finish_force_close_channel(failure);
 		}
@@ -2853,10 +2876,25 @@ impl<ChanSigner: ChannelKeys> ChannelMessageHandler for ChannelManager<ChanSigne
 		}
 	}
 
-	fn peer_connected(&self, their_node_id: &PublicKey, _init_msg: &msgs::Init) {
+	fn peer_connected(&self, their_node_id: &PublicKey, init_msg: &msgs::Init) {
 		log_debug!(self, "Generating channel_reestablish events for {}", log_pubkey!(their_node_id));
 
 		let _ = self.total_consistency_lock.read().unwrap();
+
+		{
+			let mut peer_state_lock = self.per_peer_state.write().unwrap();
+			match peer_state_lock.entry(their_node_id.clone()) {
+				hash_map::Entry::Vacant(e) => {
+					e.insert(Mutex::new(PeerState {
+						latest_features: init_msg.features.clone(),
+					}));
+				},
+				hash_map::Entry::Occupied(e) => {
+					e.get().lock().unwrap().latest_features = init_msg.features.clone();
+				},
+			}
+		}
+
 		let mut channel_state_lock = self.channel_state.lock().unwrap();
 		let channel_state = &mut *channel_state_lock;
 		let pending_msg_events = &mut channel_state.pending_msg_events;
@@ -3123,6 +3161,14 @@ impl<ChanSigner: ChannelKeys + Writeable> Writeable for ChannelManager<ChanSigne
 			}
 		}
 
+		let per_peer_state = self.per_peer_state.write().unwrap();
+		(per_peer_state.len() as u64).write(writer)?;
+		for (peer_pubkey, peer_state_mutex) in per_peer_state.iter() {
+			peer_pubkey.write(writer)?;
+			let peer_state = peer_state_mutex.lock().unwrap();
+			peer_state.latest_features.write(writer)?;
+		}
+
 		Ok(())
 	}
 }
@@ -3256,6 +3302,16 @@ impl<'a, R : ::std::io::Read, ChanSigner: ChannelKeys + Readable<R>> ReadableArg
 			claimable_htlcs.insert(payment_hash, previous_hops);
 		}
 
+		let peer_count: u64 = Readable::read(reader)?;
+		let mut per_peer_state = HashMap::with_capacity(cmp::min(peer_count as usize, 128));
+		for _ in 0..peer_count {
+			let peer_pubkey = Readable::read(reader)?;
+			let peer_state = PeerState {
+				latest_features: Readable::read(reader)?,
+			};
+			per_peer_state.insert(peer_pubkey, Mutex::new(peer_state));
+		}
+
 		let channel_manager = ChannelManager {
 			genesis_hash,
 			fee_estimator: args.fee_estimator,
@@ -3275,6 +3331,8 @@ impl<'a, R : ::std::io::Read, ChanSigner: ChannelKeys + Readable<R>> ReadableArg
 			}),
 			our_network_key: args.keys_manager.get_node_secret(),
 
+			per_peer_state: RwLock::new(per_peer_state),
+
 			pending_events: Mutex::new(Vec::new()),
 			total_consistency_lock: RwLock::new(()),
 			keys_manager: args.keys_manager,