removed MintReward and added PayLaneRewardFromAccount (#1693)

* removed MintReward and added PayLaneRewardFromAccount

* clippy

* added issue ref to TODO

bin/millau/runtime/src/lib.rs

@@ -379,7 +379,8 @@ impl pallet_session::Config for Runtime {
 impl pallet_bridge_relayers::Config for Runtime {
 	type RuntimeEvent = RuntimeEvent;
 	type Reward = Balance;
-	type PaymentProcedure = bp_relayers::MintReward<pallet_balances::Pallet<Runtime>, AccountId>;
+	type PaymentProcedure =
+		bp_relayers::PayLaneRewardFromAccount<pallet_balances::Pallet<Runtime>, AccountId>;
 	type WeightInfo = ();
 }
 

bin/rialto-parachain/runtime/src/lib.rs

@@ -511,7 +511,8 @@ impl pallet_aura::Config for Runtime {
 impl pallet_bridge_relayers::Config for Runtime {
 	type RuntimeEvent = RuntimeEvent;
 	type Reward = Balance;
-	type PaymentProcedure = bp_relayers::MintReward<pallet_balances::Pallet<Runtime>, AccountId>;
+	type PaymentProcedure =
+		bp_relayers::PayLaneRewardFromAccount<pallet_balances::Pallet<Runtime>, AccountId>;
 	type WeightInfo = ();
 }
 

bin/rialto/runtime/src/lib.rs

@@ -396,7 +396,8 @@ impl pallet_authority_discovery::Config for Runtime {
 impl pallet_bridge_relayers::Config for Runtime {
 	type RuntimeEvent = RuntimeEvent;
 	type Reward = Balance;
-	type PaymentProcedure = bp_relayers::MintReward<pallet_balances::Pallet<Runtime>, AccountId>;
+	type PaymentProcedure =
+		bp_relayers::PayLaneRewardFromAccount<pallet_balances::Pallet<Runtime>, AccountId>;
 	type WeightInfo = ();
 }
 

modules/relayers/src/lib.rs

@@ -157,7 +157,10 @@ mod tests {
 	use mock::{RuntimeEvent as TestEvent, *};
 
 	use crate::Event::RewardPaid;
-	use frame_support::{assert_noop, assert_ok, traits::fungible::Inspect};
+	use frame_support::{
+		assert_noop, assert_ok,
+		traits::fungible::{Inspect, Mutate},
+	};
 	use frame_system::{EventRecord, Pallet as System, Phase};
 	use sp_runtime::DispatchError;
 
@@ -232,16 +235,31 @@ mod tests {
 	}
 
 	#[test]
-	fn mint_reward_payment_procedure_actually_mints_tokens() {
+	fn pay_lane_reward_from_account_actually_pays_reward() {
 		type Balances = pallet_balances::Pallet<TestRuntime>;
+		type PayLaneRewardFromAccount = bp_relayers::PayLaneRewardFromAccount<Balances, AccountId>;
 
 		run_test(|| {
+			let lane0_rewards_account =
+				PayLaneRewardFromAccount::lane_rewards_account([0, 0, 0, 0]);
+			let lane1_rewards_account =
+				PayLaneRewardFromAccount::lane_rewards_account([0, 0, 0, 1]);
+
+			Balances::mint_into(&lane0_rewards_account, 100).unwrap();
+			Balances::mint_into(&lane1_rewards_account, 100).unwrap();
+			assert_eq!(Balances::balance(&lane0_rewards_account), 100);
+			assert_eq!(Balances::balance(&lane1_rewards_account), 100);
 			assert_eq!(Balances::balance(&1), 0);
-			assert_eq!(Balances::total_issuance(), 0);
-			bp_relayers::MintReward::<Balances, AccountId>::pay_reward(&1, TEST_LANE_ID, 100)
-				.unwrap();
+
+			PayLaneRewardFromAccount::pay_reward(&1, [0, 0, 0, 0], 100).unwrap();
+			assert_eq!(Balances::balance(&lane0_rewards_account), 0);
+			assert_eq!(Balances::balance(&lane1_rewards_account), 100);
 			assert_eq!(Balances::balance(&1), 100);
-			assert_eq!(Balances::total_issuance(), 100);
+
+			PayLaneRewardFromAccount::pay_reward(&1, [0, 0, 0, 1], 100).unwrap();
+			assert_eq!(Balances::balance(&lane0_rewards_account), 0);
+			assert_eq!(Balances::balance(&lane1_rewards_account), 0);
+			assert_eq!(Balances::balance(&1), 200);
 		});
 	}
 }

primitives/messages/src/lib.rs

@@ -24,6 +24,7 @@ use bp_runtime::{BasicOperatingMode, OperatingMode};
 use codec::{Decode, Encode, MaxEncodedLen};
 use frame_support::RuntimeDebug;
 use scale_info::TypeInfo;
+use sp_core::TypeId;
 use sp_std::{collections::vec_deque::VecDeque, prelude::*};
 
 pub mod source_chain;
@@ -68,6 +69,16 @@ impl OperatingMode for MessagesOperatingMode {
 /// Lane identifier.
 pub type LaneId = [u8; 4];
 
+/// Lane id which implements `TypeId`.
+// TODO (https://github.com/paritytech/parity-bridges-common/issues/1694):
+// `LaneId` shall be replaced with this across all codebase (codec-compatible)
+#[derive(Decode, Encode, RuntimeDebug)]
+pub struct TypedLaneId(pub [u8; 4]);
+
+impl TypeId for TypedLaneId {
+	const TYPE_ID: [u8; 4] = *b"blan";
+}
+
 /// Message nonce. Valid messages will never have 0 nonce.
 pub type MessageNonce = u64;
 

primitives/relayers/Cargo.toml

@@ -19,6 +19,7 @@ sp-runtime = { git = "https://github.com/paritytech/substrate", branch = "master
 sp-std = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 
 [dev-dependencies]
+bp-rialto = { path = "../chain-rialto" }
 hex = "0.4"
 hex-literal = "0.3"
 

primitives/relayers/src/lib.rs

@@ -19,7 +19,11 @@
 #![warn(missing_docs)]
 #![cfg_attr(not(feature = "std"), no_std)]
 
-use bp_messages::LaneId;
+use bp_messages::{LaneId, TypedLaneId};
+use sp_runtime::{
+	codec::{Decode, Encode},
+	traits::AccountIdConversion,
+};
 use sp_std::{fmt::Debug, marker::PhantomData};
 
 /// Reward payment procedure.
@@ -31,20 +35,56 @@ pub trait PaymentProcedure<Relayer, Reward> {
 	fn pay_reward(relayer: &Relayer, lane_id: LaneId, reward: Reward) -> Result<(), Self::Error>;
 }
 
-/// Reward payment procedure that is simply minting given amount of tokens.
-pub struct MintReward<T, Relayer>(PhantomData<(T, Relayer)>);
+/// Reward payment procedure that does `balances::transfer` call from the account, derived from
+/// given lane.
+pub struct PayLaneRewardFromAccount<T, Relayer>(PhantomData<(T, Relayer)>);
 
-impl<T, Relayer> PaymentProcedure<Relayer, T::Balance> for MintReward<T, Relayer>
+impl<T, Relayer> PayLaneRewardFromAccount<T, Relayer>
 where
-	T: frame_support::traits::fungible::Mutate<Relayer>,
+	Relayer: Decode + Encode,
+{
+	/// Return account that pay rewards for serving given lane.
+	pub fn lane_rewards_account(lane_id: LaneId) -> Relayer {
+		TypedLaneId(lane_id).into_sub_account_truncating(b"bridge-lane")
+	}
+}
+
+impl<T, Relayer> PaymentProcedure<Relayer, T::Balance> for PayLaneRewardFromAccount<T, Relayer>
+where
+	T: frame_support::traits::fungible::Transfer<Relayer>,
+	Relayer: Decode + Encode,
 {
 	type Error = sp_runtime::DispatchError;
 
 	fn pay_reward(
 		relayer: &Relayer,
-		_lane_id: LaneId,
+		lane_id: LaneId,
 		reward: T::Balance,
 	) -> Result<(), Self::Error> {
-		T::mint_into(relayer, reward)
+		T::transfer(&Self::lane_rewards_account(lane_id), relayer, reward, false).map(drop)
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn lanes_are_using_different_accounts() {
+		assert_eq!(
+			PayLaneRewardFromAccount::<(), bp_rialto::AccountId>::lane_rewards_account([
+				0, 0, 0, 0
+			]),
+			hex_literal::hex!("626c616e000000006272696467652d6c616e6500000000000000000000000000")
+				.into(),
+		);
+
+		assert_eq!(
+			PayLaneRewardFromAccount::<(), bp_rialto::AccountId>::lane_rewards_account([
+				0, 0, 0, 1
+			]),
+			hex_literal::hex!("626c616e000000016272696467652d6c616e6500000000000000000000000000")
+				.into(),
+		);
 	}
 }