f avoid excess write space

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -7180,9 +7180,19 @@ where
 		}
 
 		let events = self.pending_events.lock().unwrap();
-		(events.len() as u64).write(writer)?;
-		for (event, _) in events.iter() {
-			event.write(writer)?;
+		// LDK versions prior to 0.0.115 don't support post-event actions, thus if there's no
+		// actions at all, skip writing the required TLV. Otherwise, pre-0.0.114 versions will
+		// refuse to read the new ChannelManager.
+		let events_not_backwards_compatible = events.iter().any(|(_, action)| action.is_some());
+		if events_not_backwards_compatible {
+			// If we're gonna write a even TLV that will overwrite our events anyway we might as
+			// well save the space and not write any events here.
+			0u64.write(writer)?;
+		} else {
+			(events.len() as u64).write(writer)?;
+			for (event, _) in events.iter() {
+				event.write(writer)?;
+			}
 		}
 
 		let background_events = self.pending_background_events.lock().unwrap();
@@ -7263,10 +7273,7 @@ where
 			(5, self.our_network_pubkey, required),
 			(6, monitor_update_blocked_actions_per_peer, option),
 			(7, self.fake_scid_rand_bytes, required),
-			// LDK versions prior to 0.0.115 don't support post-event actions, thus if there's no
-			// actions at all, skip writing the required TLV. Otherwise, pre-0.0.114 versions will
-			// refuse to read the new ChannelManager.
-			(8, if events.iter().any(|(_, action)| action.is_some()) { Some(&*events) } else { None }, option),
+			(8, if events_not_backwards_compatible { Some(&*events) } else { None }, option),
 			(9, htlc_purposes, vec_type),
 			(11, self.probing_cookie_secret, required),
 		});