Fix default bridge byte fee to use TransactionByteFee of the bridged …

…chain (polkadot-fellows#174)

This PR does two things:
1) (tiny refactoring) adds `TRANSACTION_BYTE_FEE` constant to
`system-parachains-constants` crate. We are using the same value (`1 *
MILLICENTS`) across all chains, so it makes sense to move it there;
2) changes default value of governance-controlled
`XcmBridgeHubRouterByteFee` constant (which is used to cover the cost of
message delivery within the remote consensus) to use
`TRANSACTION_BYTE_FEE` of the bridged chain (also does 1:5/5:1
conversion). Since governance has not set value of this constant yet, we
are changing the default value here, in the code.

~The failing test is fixed by the polkadot-fellows#137, so it makes sense to merge this
PR only after polkadot-fellows#137~ Updated

---------

Co-authored-by: Branislav Kontur <bkontur@gmail.com>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

CHANGELOG.md

@@ -29,6 +29,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Removed the `SafeCallFilter` from the Relay Chain XCM config ([polkadot-fellows/runtimes#172](https://github.com/polkadot-fellows/runtimes/pull/172)).
 - Removed the `ImOnline` pallet ([polkadot-fellows/runtimes#178](https://github.com/polkadot-fellows/runtimes/pull/178))
 
+### Fixed
+
+- Fixed the cost of a single byte, sent over bridge to use the `TransactionByteFee` constant of the bridged chain [polkadot-fellows/runtimes#174](https://github.com/polkadot-fellows/runtimes/pull/174).
+
 ### Based on Polkadot-SDK
 
 - Upgrade dependencies to the [polkadot-sdk@1.5.0](https://github.com/paritytech/polkadot-sdk/releases/tag/polkadot-v1.5.0) release ([polkadot-fellows/runtimes#137](https://github.com/polkadot-fellows/runtimes/pull/137))

relay/kusama/constants/src/lib.rs

@@ -70,6 +70,9 @@ pub mod fee {
 	/// The block saturation level. Fees will be updates based on this value.
 	pub const TARGET_BLOCK_FULLNESS: Perbill = Perbill::from_percent(25);
 
+	/// Cost of every transaction byte at Kusama relay chain.
+	pub const TRANSACTION_BYTE_FEE: Balance = 10 * super::currency::MILLICENTS;
+
 	/// Handles converting a weight scalar to a fee value, based on the scale and granularity of the
 	/// node's balance type.
 	///

relay/kusama/src/lib.rs

@@ -413,7 +413,7 @@ impl pallet_beefy_mmr::Config for Runtime {
 }
 
 parameter_types! {
-	pub const TransactionByteFee: Balance = 10 * MILLICENTS;
+	pub const TransactionByteFee: Balance = kusama_runtime_constants::fee::TRANSACTION_BYTE_FEE;
 	/// This value increases the priority of `Operational` transactions by adding
 	/// a "virtual tip" that's equal to the `OperationalFeeMultiplier * final_fee`.
 	pub const OperationalFeeMultiplier: u8 = 5;

relay/polkadot/constants/src/lib.rs

@@ -72,6 +72,9 @@ pub mod fee {
 	/// The block saturation level. Fees will be updates based on this value.
 	pub const TARGET_BLOCK_FULLNESS: Perbill = Perbill::from_percent(25);
 
+	/// Cost of every transaction byte at Kusama relay chain.
+	pub const TRANSACTION_BYTE_FEE: Balance = 10 * super::currency::MILLICENTS;
+
 	/// Handles converting a weight scalar to a fee value, based on the scale and granularity of the
 	/// node's balance type.
 	///

relay/polkadot/src/lib.rs

@@ -400,7 +400,7 @@ impl pallet_beefy_mmr::Config for Runtime {
 }
 
 parameter_types! {
-	pub const TransactionByteFee: Balance = 10 * MILLICENTS;
+	pub const TransactionByteFee: Balance = polkadot_runtime_constants::fee::TRANSACTION_BYTE_FEE;
 	/// This value increases the priority of `Operational` transactions by adding
 	/// a "virtual tip" that's equal to the `OperationalFeeMultiplier * final_fee`.
 	pub const OperationalFeeMultiplier: u8 = 5;

system-parachains/asset-hubs/asset-hub-kusama/src/lib.rs

@@ -235,7 +235,7 @@ impl pallet_balances::Config for Runtime {
 
 parameter_types! {
 	/// Relay Chain `TransactionByteFee` / 10
-	pub const TransactionByteFee: Balance = MILLICENTS;
+	pub const TransactionByteFee: Balance = system_parachains_constants::kusama::fee::TRANSACTION_BYTE_FEE;
 }
 
 impl pallet_transaction_payment::Config for Runtime {
@@ -1709,4 +1709,11 @@ mod tests {
 		let time_o_proof = time_fee.checked_div(proof_fee).unwrap_or_default();
 		assert!(time_o_proof <= 30, "{} should be at most 30", time_o_proof);
 	}
+
+	#[test]
+	fn test_transasction_byte_fee_is_one_tenth_of_relay() {
+		let relay_tbf = kusama_runtime_constants::fee::TRANSACTION_BYTE_FEE;
+		let parachain_tbf = TransactionByteFee::get();
+		assert_eq!(relay_tbf / 10, parachain_tbf);
+	}
 }

system-parachains/asset-hubs/asset-hub-kusama/src/xcm_config.rs

@@ -16,8 +16,8 @@
 use super::{
 	AccountId, AllPalletsWithSystem, Assets, Authorship, Balance, Balances, ParachainInfo,
 	ParachainSystem, PolkadotXcm, PoolAssets, PriceForParentDelivery, Runtime, RuntimeCall,
-	RuntimeEvent, RuntimeOrigin, ToPolkadotXcmRouter, TransactionByteFee,
-	TrustBackedAssetsInstance, WeightToFee, XcmpQueue,
+	RuntimeEvent, RuntimeOrigin, ToPolkadotXcmRouter, TrustBackedAssetsInstance, WeightToFee,
+	XcmpQueue,
 };
 use crate::{ForeignAssets, ForeignAssetsInstance};
 use assets_common::matching::{FromSiblingParachain, IsForeignConcreteAsset};
@@ -660,7 +660,7 @@ pub mod bridging {
 		);
 		/// Price of every byte of the Kusama -> Polkadot message. Can be adjusted via
 		/// governance `set_storage` call.
-		pub storage XcmBridgeHubRouterByteFee: Balance = TransactionByteFee::get();
+		pub storage XcmBridgeHubRouterByteFee: Balance = bp_bridge_hub_kusama::estimate_kusama_to_polkadot_byte_fee();
 
 		pub SiblingBridgeHubParaId: u32 = bp_bridge_hub_kusama::BRIDGE_HUB_KUSAMA_PARACHAIN_ID;
 		pub SiblingBridgeHub: MultiLocation = MultiLocation::new(1, X1(Parachain(SiblingBridgeHubParaId::get())));

system-parachains/asset-hubs/asset-hub-polkadot/src/lib.rs

@@ -248,7 +248,7 @@ impl pallet_balances::Config for Runtime {
 
 parameter_types! {
 	/// Relay Chain `TransactionByteFee` / 10
-	pub const TransactionByteFee: Balance = MILLICENTS;
+	pub const TransactionByteFee: Balance = system_parachains_constants::polkadot::fee::TRANSACTION_BYTE_FEE;
 }
 
 impl pallet_transaction_payment::Config for Runtime {
@@ -1537,4 +1537,11 @@ mod tests {
 		let time_o_proof = time_fee.checked_div(proof_fee).unwrap_or_default();
 		assert!(time_o_proof <= 30, "{} should be at most 30", time_o_proof);
 	}
+
+	#[test]
+	fn test_transasction_byte_fee_is_one_tenth_of_relay() {
+		let relay_tbf = polkadot_runtime_constants::fee::TRANSACTION_BYTE_FEE;
+		let parachain_tbf = TransactionByteFee::get();
+		assert_eq!(relay_tbf / 10, parachain_tbf);
+	}
 }

system-parachains/asset-hubs/asset-hub-polkadot/src/xcm_config.rs

@@ -16,8 +16,8 @@
 use super::{
 	AccountId, AllPalletsWithSystem, Assets, Authorship, Balance, Balances, ForeignAssets,
 	ParachainInfo, ParachainSystem, PolkadotXcm, PriceForParentDelivery, Runtime, RuntimeCall,
-	RuntimeEvent, RuntimeOrigin, ToKusamaXcmRouter, TransactionByteFee, TrustBackedAssetsInstance,
-	WeightToFee, XcmpQueue,
+	RuntimeEvent, RuntimeOrigin, ToKusamaXcmRouter, TrustBackedAssetsInstance, WeightToFee,
+	XcmpQueue,
 };
 use crate::ForeignAssetsInstance;
 use assets_common::matching::{FromSiblingParachain, IsForeignConcreteAsset};
@@ -604,7 +604,7 @@ pub mod bridging {
 		);
 		/// Price of every byte of the Polkadot -> Kusama message. Can be adjusted via
 		/// governance `set_storage` call.
-		pub storage XcmBridgeHubRouterByteFee: Balance = TransactionByteFee::get();
+		pub storage XcmBridgeHubRouterByteFee: Balance = bp_bridge_hub_polkadot::estimate_polkadot_to_kusama_byte_fee();
 
 		pub SiblingBridgeHubParaId: u32 = bp_bridge_hub_polkadot::BRIDGE_HUB_POLKADOT_PARACHAIN_ID;
 		pub SiblingBridgeHub: MultiLocation = MultiLocation::new(1, X1(Parachain(SiblingBridgeHubParaId::get())));

system-parachains/bridge-hubs/bridge-hub-kusama/primitives/Cargo.toml

@@ -10,8 +10,9 @@ license.workspace = true
 [dependencies]
 
 # Local
-kusama-runtime-constants = { path = "../../../../relay/kusama/constants", default-features = false}
-polkadot-runtime-constants = { path = "../../../../relay/polkadot/constants", default-features = false}
+kusama-runtime-constants = { path = "../../../../relay/kusama/constants", default-features = false }
+polkadot-runtime-constants = { path = "../../../../relay/polkadot/constants", default-features = false }
+system-parachains-constants = { path = "../../../constants", default-features = false }
 
 # Bridge Dependencies
 bp-bridge-hub-cumulus = { default-features = false , version = "0.7.0" }
@@ -36,4 +37,5 @@ std = [
 	"sp-api/std",
 	"sp-runtime/std",
 	"sp-std/std",
+	"system-parachains-constants/std",
 ]

system-parachains/bridge-hubs/bridge-hub-kusama/primitives/src/lib.rs

@@ -118,6 +118,18 @@ pub fn estimate_kusama_to_polkadot_message_fee(
 		.saturating_add(BridgeHubKusamaBaseConfirmationFeeInKsms::get())
 }
 
+/// Compute the per-byte fee that needs to be paid in KSMs by the sender when sending
+/// message from Kusama Bridge Hub to Polkadot Bridge Hub.
+pub fn estimate_kusama_to_polkadot_byte_fee() -> Balance {
+	// the sender pays for the same byte twice:
+	// 1) the first part comes from the HRMP, when message travels from Kusama Asset Hub to Kusama
+	//    Bridge Hub;
+	// 2) the second part is the payment for bytes of the message delivery transaction, which is
+	//    "mined" at Polkadot Bridge Hub. Hence, we need to use byte fees from that chain and
+	//    convert it to KSMs here.
+	convert_from_udot_to_uksm(system_parachains_constants::polkadot::fee::TRANSACTION_BYTE_FEE)
+}
+
 /// Convert from uDOTs to uKSMs.
 fn convert_from_udot_to_uksm(price_in_udot: Balance) -> Balance {
 	// assuming exchange rate is 5 DOTs for 1 KSM

system-parachains/bridge-hubs/bridge-hub-kusama/src/lib.rs

@@ -274,7 +274,7 @@ impl pallet_balances::Config for Runtime {
 
 parameter_types! {
 	/// Relay Chain `TransactionByteFee` / 10
-	pub const TransactionByteFee: Balance = MILLICENTS;
+	pub const TransactionByteFee: Balance = system_parachains_constants::kusama::fee::TRANSACTION_BYTE_FEE;
 }
 
 impl pallet_transaction_payment::Config for Runtime {
@@ -1116,3 +1116,15 @@ cumulus_pallet_parachain_system::register_validate_block! {
 	Runtime = Runtime,
 	BlockExecutor = cumulus_pallet_aura_ext::BlockExecutor::<Runtime, Executive>,
 }
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn test_transasction_byte_fee_is_one_tenth_of_relay() {
+		let relay_tbf = kusama_runtime_constants::fee::TRANSACTION_BYTE_FEE;
+		let parachain_tbf = TransactionByteFee::get();
+		assert_eq!(relay_tbf / 10, parachain_tbf);
+	}
+}

system-parachains/bridge-hubs/bridge-hub-polkadot/primitives/Cargo.toml

@@ -10,8 +10,9 @@ license.workspace = true
 [dependencies]
 
 # Local
-kusama-runtime-constants = { path = "../../../../relay/kusama/constants", default-features = false}
-polkadot-runtime-constants = { path = "../../../../relay/polkadot/constants", default-features = false}
+kusama-runtime-constants = { path = "../../../../relay/kusama/constants", default-features = false }
+polkadot-runtime-constants = { path = "../../../../relay/polkadot/constants", default-features = false }
+system-parachains-constants = { path = "../../../constants", default-features = false }
 
 # Bridge Dependencies
 bp-bridge-hub-cumulus = { default-features = false , version = "0.7.0" }
@@ -36,4 +37,5 @@ std = [
 	"sp-api/std",
 	"sp-runtime/std",
 	"sp-std/std",
+	"system-parachains-constants/std",
 ]

system-parachains/bridge-hubs/bridge-hub-polkadot/primitives/src/lib.rs

@@ -109,6 +109,18 @@ pub fn estimate_polkadot_to_kusama_message_fee(
 		.saturating_add(BridgeHubPolkadotBaseConfirmationFeeInDots::get())
 }
 
+/// Compute the per-byte fee that needs to be paid in DOTs by the sender when sending
+/// message from Polkadot Bridge Hub to Kusama Bridge Hub.
+pub fn estimate_polkadot_to_kusama_byte_fee() -> Balance {
+	// the sender pays for the same byte twice:
+	// 1) the first part comes from the HRMP, when message travels from Polkadot Asset Hub to
+	//    Polkadot Bridge Hub;
+	// 2) the second part is the payment for bytes of the message delivery transaction, which is
+	//    "mined" at Kusama Bridge Hub. Hence, we need to use byte fees from that chain and convert
+	//    it to DOTs here.
+	convert_from_uksm_to_udot(system_parachains_constants::kusama::fee::TRANSACTION_BYTE_FEE)
+}
+
 /// Convert from uKSMs to uDOTs.
 fn convert_from_uksm_to_udot(price_in_uksm: Balance) -> Balance {
 	// assuming exchange rate is 5 DOTs for 1 KSM

system-parachains/bridge-hubs/bridge-hub-polkadot/src/lib.rs

@@ -274,7 +274,7 @@ impl pallet_balances::Config for Runtime {
 
 parameter_types! {
 	/// Relay Chain `TransactionByteFee` / 10
-	pub const TransactionByteFee: Balance = MILLICENTS;
+	pub const TransactionByteFee: Balance = system_parachains_constants::polkadot::fee::TRANSACTION_BYTE_FEE;
 }
 
 impl pallet_transaction_payment::Config for Runtime {
@@ -1116,3 +1116,15 @@ cumulus_pallet_parachain_system::register_validate_block! {
 	Runtime = Runtime,
 	BlockExecutor = cumulus_pallet_aura_ext::BlockExecutor::<Runtime, Executive>,
 }
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn test_transasction_byte_fee_is_one_tenth_of_relay() {
+		let relay_tbf = polkadot_runtime_constants::fee::TRANSACTION_BYTE_FEE;
+		let parachain_tbf = TransactionByteFee::get();
+		assert_eq!(relay_tbf / 10, parachain_tbf);
+	}
+}

system-parachains/collectives/collectives-polkadot/src/lib.rs

@@ -222,7 +222,7 @@ impl pallet_balances::Config for Runtime {
 
 parameter_types! {
 	/// Relay Chain `TransactionByteFee` / 10
-	pub const TransactionByteFee: Balance = MILLICENTS;
+	pub const TransactionByteFee: Balance = system_parachains_constants::polkadot::fee::TRANSACTION_BYTE_FEE;
 }
 
 impl pallet_transaction_payment::Config for Runtime {
@@ -1061,3 +1061,10 @@ fn test_ed_is_one_tenth_of_relay() {
 	let collectives_ed = ExistentialDeposit::get();
 	assert_eq!(relay_ed / 10, collectives_ed);
 }
+
+#[test]
+fn test_transasction_byte_fee_is_one_tenth_of_relay() {
+	let relay_tbf = polkadot_runtime_constants::fee::TRANSACTION_BYTE_FEE;
+	let parachain_tbf = TransactionByteFee::get();
+	assert_eq!(relay_tbf / 10, parachain_tbf);
+}

system-parachains/constants/src/kusama.rs

@@ -64,6 +64,11 @@ pub mod fee {
 	/// The block saturation level. Fees will be updates based on this value.
 	pub const TARGET_BLOCK_FULLNESS: Perbill = Perbill::from_percent(25);
 
+	/// Cost of every transaction byte at Kusama system parachains.
+	///
+	/// It is the Relay Chain (Kusama) `TransactionByteFee` / 10.
+	pub const TRANSACTION_BYTE_FEE: Balance = super::currency::MILLICENTS;
+
 	/// Handles converting a weight scalar to a fee value, based on the scale and granularity of the
 	/// node's balance type.
 	///

system-parachains/constants/src/polkadot.rs

@@ -86,6 +86,11 @@ pub mod fee {
 	/// The block saturation level. Fees will be updates based on this value.
 	pub const TARGET_BLOCK_FULLNESS: Perbill = Perbill::from_percent(25);
 
+	/// Cost of every transaction byte at Polkadot system parachains.
+	///
+	/// It is the Relay Chain (Polkadot) `TransactionByteFee` / 10.
+	pub const TRANSACTION_BYTE_FEE: Balance = super::currency::MILLICENTS;
+
 	/// Handles converting a weight scalar to a fee value, based on the scale and granularity of the
 	/// node's balance type.
 	///

system-parachains/encointer/src/lib.rs

@@ -316,7 +316,7 @@ impl pallet_balances::Config for Runtime {
 
 parameter_types! {
 	/// Relay Chain `TransactionByteFee` / 10, same as statemine
-	pub const TransactionByteFee: Balance = MILLICENTS;
+	pub const TransactionByteFee: Balance = system_parachains_constants::kusama::fee::TRANSACTION_BYTE_FEE;
 	pub const OperationalFeeMultiplier: u8 = 5;
 }
 
@@ -1116,6 +1116,10 @@ fn test_constants_compatiblity() {
 		::system_parachains_constants::kusama::currency::system_para_deposit(5, 3),
 		system_parachains_constants::kusama::currency::system_para_deposit(5, 3)
 	);
+	assert_eq!(
+		::system_parachains_constants::kusama::fee::TRANSACTION_BYTE_FEE,
+		system_parachains_constants::kusama::fee::TRANSACTION_BYTE_FEE
+	);
 	assert_eq!(
 		::system_parachains_constants::kusama::fee::calculate_weight_to_fee(
 			&::system_parachains_constants::MAXIMUM_BLOCK_WEIGHT
@@ -1126,6 +1130,13 @@ fn test_constants_compatiblity() {
 	);
 }
 
+#[test]
+fn test_transasction_byte_fee_is_one_tenth_of_relay() {
+	let relay_tbf = ::kusama_runtime_constants::fee::TRANSACTION_BYTE_FEE;
+	let parachain_tbf = TransactionByteFee::get();
+	assert_eq!(relay_tbf / 10, parachain_tbf);
+}
+
 // The Encointer pallets do not have compatible versions with `polkadot-sdk`, making it difficult
 // for us to reuse the `system-parachains-constants` module. Therefore, we have copies of it here
 // with `test_constants_compatiblity`.
@@ -1209,6 +1220,11 @@ mod system_parachains_constants {
 			use smallvec::smallvec;
 			pub use sp_runtime::Perbill;
 
+			/// Cost of every transaction byte at Kusama system parachains.
+			///
+			/// It is the Relay Chain (Kusama) `TransactionByteFee` / 10.
+			pub const TRANSACTION_BYTE_FEE: Balance = super::currency::MILLICENTS;
+
 			/// Handles converting a weight scalar to a fee value, based on the scale and
 			/// granularity of the node's balance type.
 			///