MaxValues for OutboundLanes map (#1871)

bridges/modules/messages/src/lib.rs

@@ -583,8 +583,14 @@ pub mod pallet {
 
 	/// Map of lane id => outbound lane data.
 	#[pallet::storage]
-	pub type OutboundLanes<T: Config<I>, I: 'static = ()> =
-		StorageMap<_, Blake2_128Concat, LaneId, OutboundLaneData, ValueQuery>;
+	pub type OutboundLanes<T: Config<I>, I: 'static = ()> = StorageMap<
+		Hasher = Blake2_128Concat,
+		Key = LaneId,
+		Value = OutboundLaneData,
+		QueryKind = ValueQuery,
+		OnEmpty = GetDefault,
+		MaxValues = MaybeOutboundLanesCount<T, I>,
+	>;
 
 	/// All queued outbound messages.
 	#[pallet::storage]
@@ -648,6 +654,15 @@ pub mod pallet {
 			InboundLanes::<T, I>::get(lane).0
 		}
 	}
+
+	/// Get-parameter that returns number of active outbound lanes that the pallet maintains.
+	pub struct MaybeOutboundLanesCount<T, I>(PhantomData<(T, I)>);
+
+	impl<T: Config<I>, I: 'static> Get<Option<u32>> for MaybeOutboundLanesCount<T, I> {
+		fn get() -> Option<u32> {
+			Some(T::ActiveOutboundLanes::get().len() as u32)
+		}
+	}
 }
 
 impl<T, I> bp_messages::source_chain::MessagesBridge<T::RuntimeOrigin, T::OutboundPayload>
@@ -1962,4 +1977,12 @@ mod tests {
 		MessagesOperatingMode::Basic(BasicOperatingMode::Normal),
 		MessagesOperatingMode::Basic(BasicOperatingMode::Halted)
 	);
+
+	#[test]
+	fn maybe_outbound_lanes_count_returns_correct_value() {
+		assert_eq!(
+			MaybeOutboundLanesCount::<TestRuntime, ()>::get(),
+			Some(mock::ActiveOutboundLanes::get().len() as u32)
+		);
+	}
 }