Snowbridge - Zero relayer reward in Inbound Queue should not be registered for a reward

bridges/snowbridge/pallets/inbound-queue-v2/src/lib.rs

@@ -264,7 +264,13 @@ pub mod pallet {
 				})?;
 
 			// Pay relayer reward
-			T::RewardPayment::register_reward(&relayer, T::DefaultRewardKind::get(), relayer_fee);
+			if !relayer_fee.is_zero() {
+				T::RewardPayment::register_reward(
+					&relayer,
+					T::DefaultRewardKind::get(),
+					relayer_fee,
+				);
+			}
 
 			// Mark message as received
 			Nonce::<T>::set(nonce.into());

bridges/snowbridge/pallets/inbound-queue-v2/src/mock.rs

@@ -161,12 +161,22 @@ pub enum BridgeReward {
 	Snowbridge,
 }
 
+use std::cell::Cell;
+
+thread_local! {
+	pub static REWARD_ALLOCATED: Cell<u128> = Cell::new(0);
+}
+
 impl RewardLedger<<mock::Test as frame_system::Config>::AccountId, BridgeReward, u128> for () {
 	fn register_reward(
 		_relayer: &<mock::Test as frame_system::Config>::AccountId,
 		_reward: BridgeReward,
 		_reward_balance: u128,
 	) {
+		REWARD_ALLOCATED.with(|counter| {
+			let current = counter.get();
+			counter.set(current + 1);
+		});
 	}
 }
 

bridges/snowbridge/pallets/inbound-queue-v2/src/test.rs

@@ -5,7 +5,7 @@ use super::*;
 use crate::{mock::*, Error};
 use codec::Encode;
 use frame_support::{assert_noop, assert_ok};
-use snowbridge_inbound_queue_primitives::{EventProof, Proof};
+use snowbridge_inbound_queue_primitives::{v2::XcmPayload, EventProof, Proof};
 use snowbridge_test_utils::mock_xcm::{set_charge_fees_override, set_sender_override};
 use sp_keyring::sr25519::Keyring;
 use sp_runtime::DispatchError;
@@ -44,6 +44,9 @@ fn test_submit_happy_path() {
 			)),
 			"no fees paid event emitted."
 		);
+
+		let final_value = REWARD_ALLOCATED.with(|counter| counter.get());
+		assert_eq!(final_value, 1, "Relayer reward should have been registered");
 	});
 }
 
@@ -325,3 +328,28 @@ fn test_switch_operating_mode() {
 		assert_ok!(InboundQueue::submit(origin, Box::new(event)));
 	});
 }
+
+#[test]
+fn zero_reward_does_not_register_reward() {
+	new_tester().execute_with(|| {
+		let relayer: AccountId = Keyring::Bob.into();
+		let origin = H160::random();
+		assert_ok!(InboundQueue::process_message(
+			relayer,
+			Message {
+				nonce: 0,
+				assets: vec![],
+				xcm: XcmPayload::Raw(vec![]),
+				claimer: None,
+				execution_fee: 1_000_000_000,
+				relayer_fee: 0,
+				gateway: GatewayAddress::get(),
+				origin,
+				value: 3_000_000_000,
+			}
+		));
+
+		let final_value = REWARD_ALLOCATED.with(|counter| counter.get());
+		assert_eq!(final_value, 0, "Zero relayer reward should not be registered");
+	});
+}