Add a new monitor update result handling macro

Over the next few commits, this macro will replace the
`handle_monitor_update_res` macro. It takes a different approach -
instead of receiving the message(s) that need to be re-sent after
the monitor update completes and pushing them back into the
channel, we'll not get the messages from the channel at all until
we're ready for them.

This will unify our message sending into only actually fetching +
sending messages in the common monitor-update-completed code,
rather than both there *and* in the functions that call `Channel`
when new messages are originated.

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -1476,6 +1476,81 @@ macro_rules! emit_channel_ready_event {
 	}
 }
 
+macro_rules! handle_new_monitor_update {
+	($self: ident, $update_res: expr, $update_id: expr, $peer_state_lock: expr, $peer_state: expr, $chan: expr, MANUALLY_REMOVING, $remove: expr) => { {
+		// update_maps_on_chan_removal needs to be able to take id_to_peer, so make sure we can in
+		// any case so that it won't deadlock.
+		debug_assert!($self.id_to_peer.try_lock().is_ok());
+		match $update_res {
+			ChannelMonitorUpdateStatus::InProgress => {
+				log_debug!($self.logger, "ChannelMonitor update for {} in flight, holding messages until the update completes.",
+					log_bytes!($chan.channel_id()[..]));
+				Ok(())
+			},
+			ChannelMonitorUpdateStatus::PermanentFailure => {
+				log_error!($self.logger, "Closing channel {} due to monitor update ChannelMonitorUpdateStatus::PermanentFailure",
+					log_bytes!($chan.channel_id()[..]));
+				update_maps_on_chan_removal!($self, $chan);
+				let res: Result<(), _> = Err(MsgHandleErrInternal::from_finish_shutdown(
+					"ChannelMonitor storage failure".to_owned(), $chan.channel_id(),
+					$chan.get_user_id(), $chan.force_shutdown(false),
+					$self.get_channel_update_for_broadcast(&$chan).ok()));
+				$remove;
+				res
+			},
+			ChannelMonitorUpdateStatus::Completed => {
+				if ($update_id == 0 || $chan.get_next_monitor_update()
+					.expect("We can't be processing a monitor update if it isn't queued")
+					.update_id == $update_id) &&
+					$chan.get_latest_monitor_update_id() == $update_id
+				{
+					let mut updates = $chan.monitor_updating_restored(&$self.logger,
+						&$self.node_signer, $self.genesis_hash, &$self.default_configuration,
+						$self.best_block.read().unwrap().height());
+					let counterparty_node_id = $chan.get_counterparty_node_id();
+					let channel_update = if updates.channel_ready.is_some() && $chan.is_usable() {
+						// We only send a channel_update in the case where we are just now sending a
+						// channel_ready and the channel is in a usable state. We may re-send a
+						// channel_update later through the announcement_signatures process for public
+						// channels, but there's no reason not to just inform our counterparty of our fees
+						// now.
+						if let Ok(msg) = $self.get_channel_update_for_unicast($chan) {
+							Some(events::MessageSendEvent::SendChannelUpdate {
+								node_id: counterparty_node_id,
+								msg,
+							})
+						} else { None }
+					} else { None };
+					let htlc_forwards = $self.handle_channel_resumption(
+						&mut $peer_state.pending_msg_events, $chan, updates.raa,
+						updates.commitment_update, updates.order, updates.accepted_htlcs,
+						updates.funding_broadcastable, updates.channel_ready,
+						updates.announcement_sigs);
+					if let Some(upd) = channel_update {
+						$peer_state.pending_msg_events.push(upd);
+					}
+
+					let channel_id = $chan.channel_id();
+					core::mem::drop($peer_state_lock);
+
+					if let Some(forwards) = htlc_forwards {
+						$self.forward_htlcs(&mut [forwards][..]);
+					}
+					$self.finalize_claims(updates.finalized_claimed_htlcs);
+					for failure in updates.failed_htlcs.drain(..) {
+						let receiver = HTLCDestination::NextHopChannel { node_id: Some(counterparty_node_id), channel_id };
+						$self.fail_htlc_backwards_internal(&failure.0, &failure.1, &failure.2, receiver);
+					}
+				}
+				Ok(())
+			},
+		}
+	} };
+	($self: ident, $update_res: expr, $update_id: expr, $peer_state_lock: expr, $peer_state: expr, $chan_entry: expr) => {
+		handle_new_monitor_update!($self, $update_res, $update_id, $peer_state_lock, $peer_state, $chan_entry.get_mut(), MANUALLY_REMOVING, $chan_entry.remove_entry())
+	}
+}
+
 impl<M: Deref, T: Deref, ES: Deref, NS: Deref, SP: Deref, F: Deref, R: Deref, L: Deref> ChannelManager<M, T, ES, NS, SP, F, R, L>
 where
 	M::Target: chain::Watch<<SP::Target as SignerProvider>::Signer>,