XCM: Properly set the pricing for the DMP router

runtime/kusama/Cargo.toml

@@ -24,7 +24,7 @@ sp-api = { git = "https://github.com/paritytech/substrate", branch = "master", d
 inherents = { package = "sp-inherents", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 offchain-primitives = { package = "sp-offchain", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-std = { package = "sp-std", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
-sp-arithmetic = { package = "sp-arithmetic", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+sp-arithmetic = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-io = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-mmr-primitives = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-runtime = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
@@ -128,6 +128,7 @@ std = [
 	"parity-scale-codec/std",
 	"scale-info/std",
 	"inherents/std",
+	"sp-arithmetic/std",
 	"sp-core/std",
 	"sp-api/std",
 	"tx-pool-api/std",

runtime/kusama/src/lib.rs

@@ -1416,7 +1416,7 @@ construct_runtime! {
 		ParaScheduler: parachains_scheduler::{Pallet, Storage} = 55,
 		Paras: parachains_paras::{Pallet, Call, Storage, Event, Config, ValidateUnsigned} = 56,
 		Initializer: parachains_initializer::{Pallet, Call, Storage} = 57,
-		Dmp: parachains_dmp::{Pallet, Call, Storage} = 58,
+		Dmp: parachains_dmp::{Pallet, Storage} = 58,
 		Ump: parachains_ump::{Pallet, Call, Storage, Event} = 59,
 		Hrmp: parachains_hrmp::{Pallet, Call, Storage, Event<T>, Config} = 60,
 		ParaSessionInfo: parachains_session_info::{Pallet, Storage} = 61,

runtime/kusama/src/xcm_config.rs

@@ -17,16 +17,22 @@
 //! XCM configurations for the Kusama runtime.
 
 use super::{
-	parachains_origin, AccountId, AllPalletsWithSystem, Balances, CouncilCollective, Fellows,
-	ParaId, Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin, StakingAdmin, WeightToFee,
-	XcmPallet,
+	parachains_dmp, parachains_origin, AccountId, AllPalletsWithSystem, Balances,
+	CouncilCollective, Dmp, Fellows, ParaId, Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin,
+	StakingAdmin, TransactionByteFee, WeightToFee, XcmPallet,
 };
 use frame_support::{
 	match_types, parameter_types,
 	traits::{Contains, Everything, Nothing},
 	weights::Weight,
 };
-use runtime_common::{paras_registrar, xcm_sender, ToAuthor};
+use kusama_runtime_constants::currency::CENTS;
+use runtime_common::{
+	paras_registrar,
+	xcm_sender::{ChildParachainRouter, PriceForParachainDelivery},
+	ToAuthor,
+};
+use sp_arithmetic::FixedPointNumber;
 use sp_core::ConstU32;
 use xcm::latest::prelude::*;
 use xcm_builder::{
@@ -103,11 +109,30 @@ parameter_types! {
 	pub const MaxInstructions: u32 = 100;
 }
 
+pub struct ExponentialKsmPrice;
+impl PriceForParachainDelivery for ExponentialKsmPrice {
+	fn price_for_parachain_delivery(para: ParaId, msg: &Xcm<()>) -> MultiAssets {
+		let base = CENTS.saturating_mul(3);
+		let msg_fee = (msg.len() as u128).saturating_mul(TransactionByteFee::get());
+
+		let excess_msgs =
+			Dmp::dmq_length(para).saturating_sub(parachains_dmp::MAX_MESSAGE_QUEUE_SIZE) as usize;
+		let factor = if excess_msgs != 0 {
+			Dmp::raise_fee_factor(excess_msgs)
+		} else {
+			Dmp::reduce_fee_factor(1)
+		};
+
+		let amount = factor.saturating_mul_int(base + msg_fee);
+		(Here, amount).into()
+	}
+}
+
 /// The XCM router. When we want to send an XCM message, we use this type. It amalgamates all of our
 /// individual routers.
 pub type XcmRouter = (
 	// Only one router so far - use DMP to communicate with child parachains.
-	xcm_sender::ChildParachainRouter<Runtime, XcmPallet, ()>,
+	ChildParachainRouter<Runtime, XcmPallet, ExponentialKsmPrice>,
 );
 
 parameter_types! {

runtime/parachains/src/dmp.rs

@@ -20,7 +20,10 @@ use crate::{
 };
 use frame_support::pallet_prelude::*;
 use primitives::{DownwardMessage, Hash, Id as ParaId, InboundDownwardMessage};
-use sp_runtime::traits::{BlakeTwo256, Hash as HashT, SaturatedConversion};
+use sp_runtime::{
+	traits::{BlakeTwo256, Hash as HashT, SaturatedConversion},
+	FixedU128, Saturating,
+};
 use sp_std::{fmt, prelude::*};
 use xcm::latest::SendError;
 
@@ -29,7 +32,8 @@ pub use pallet::*;
 #[cfg(test)]
 mod tests;
 
-pub const MAX_MESSAGE_QUEUE_SIZE: usize = 1024;
+pub const MAX_MESSAGE_QUEUE_SIZE: u32 = 1024;
+pub const MULTIPLICATIVE_FEE_FACTOR: FixedU128 = FixedU128::from_rational(101, 100); // 1.01
 
 /// An error sending a downward message.
 #[cfg_attr(test, derive(Debug))]
@@ -103,8 +107,14 @@ pub mod pallet {
 	pub(crate) type DownwardMessageQueueHeads<T: Config> =
 		StorageMap<_, Twox64Concat, ParaId, Hash, ValueQuery>;
 
-	#[pallet::call]
-	impl<T: Config> Pallet<T> {}
+	frame_support::parameter_types! {
+		pub InitialFactor: FixedU128 = FixedU128::from_u32(1);
+	}
+
+	/// The number to multiply the base delivery fee by.
+	#[pallet::storage]
+	pub(crate) type DeliveryFeeFactor<T: Config> =
+		StorageValue<_, FixedU128, ValueQuery, InitialFactor>;
 }
 
 /// Routines and getters related to downward message passing.
@@ -144,20 +154,14 @@ impl<T: Config> Pallet<T> {
 	/// `queue_downward_message` with the same parameters will be successful.
 	pub fn can_queue_downward_message(
 		config: &HostConfiguration<T::BlockNumber>,
-		para: &ParaId,
+		_: &ParaId,
 		msg: &DownwardMessage,
 	) -> Result<(), QueueDownwardMessageError> {
 		let serialized_len = msg.len() as u32;
 		if serialized_len > config.max_downward_message_size {
 			return Err(QueueDownwardMessageError::ExceedsMaxMessageSize)
 		}
 
-		if <Self as Store>::DownwardMessageQueues::decode_len(para).unwrap_or(0) >
-			MAX_MESSAGE_QUEUE_SIZE
-		{
-			return Err(QueueDownwardMessageError::ExceedsMaxMessageSize)
-		}
-
 		Ok(())
 	}
 
@@ -179,12 +183,6 @@ impl<T: Config> Pallet<T> {
 			return Err(QueueDownwardMessageError::ExceedsMaxMessageSize)
 		}
 
-		if <Self as Store>::DownwardMessageQueues::decode_len(para).unwrap_or(0) >
-			MAX_MESSAGE_QUEUE_SIZE
-		{
-			return Err(QueueDownwardMessageError::ExceedsMaxMessageSize)
-		}
-
 		let inbound =
 			InboundDownwardMessage { msg, sent_at: <frame_system::Pallet<T>>::block_number() };
 
@@ -247,7 +245,7 @@ impl<T: Config> Pallet<T> {
 	/// Returns the number of pending downward messages addressed to the given para.
 	///
 	/// Returns 0 if the para doesn't have an associated downward message queue.
-	pub(crate) fn dmq_length(para: ParaId) -> u32 {
+	pub fn dmq_length(para: ParaId) -> u32 {
 		<Self as Store>::DownwardMessageQueues::decode_len(&para)
 			.unwrap_or(0)
 			.saturated_into::<u32>()
@@ -259,4 +257,30 @@ impl<T: Config> Pallet<T> {
 	pub(crate) fn dmq_contents(recipient: ParaId) -> Vec<InboundDownwardMessage<T::BlockNumber>> {
 		<Self as Store>::DownwardMessageQueues::get(&recipient)
 	}
+
+	/// Raise the delivery fee factor by a multiplicative factor to the power of `n`, and stores
+	/// the resulting value.
+	///
+	/// Returns the new delivery fee factor after the raise.
+	pub fn raise_fee_factor(n: usize) -> FixedU128 {
+		<DeliveryFeeFactor<T>>::mutate(|f| {
+			let factor = MULTIPLICATIVE_FEE_FACTOR.saturating_pow(n);
+			*f = f.saturating_mul(factor);
+			*f
+		})
+	}
+
+	/// Reduce the delivery fee factor by a multiplicative factor to the power of `n`, and stores
+	/// the resulting value.
+	///
+	/// Does not reduce the fee factor below the initial value, which is currently set as 1.
+	///
+	/// Returns the new delivery fee factor after the reduction.
+	pub fn reduce_fee_factor(n: usize) -> FixedU128 {
+		<DeliveryFeeFactor<T>>::mutate(|f| {
+			let factor = MULTIPLICATIVE_FEE_FACTOR.saturating_pow(n);
+			*f = InitialFactor::get().min(*f / factor);
+			*f
+		})
+	}
 }

runtime/polkadot/Cargo.toml

@@ -23,6 +23,7 @@ block-builder-api = { package = "sp-block-builder", git = "https://github.com/pa
 inherents = { package = "sp-inherents", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 offchain-primitives = { package = "sp-offchain", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 tx-pool-api = { package = "sp-transaction-pool", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+sp-arithmetic = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-api = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-std = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-io = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
@@ -120,6 +121,7 @@ std = [
 	"parity-scale-codec/std",
 	"scale-info/std",
 	"inherents/std",
+	"sp-arithmetic/std",
 	"sp-core/std",
 	"sp-api/std",
 	"tx-pool-api/std",

runtime/polkadot/src/lib.rs

@@ -1536,7 +1536,7 @@ construct_runtime! {
 		ParaScheduler: parachains_scheduler::{Pallet, Storage} = 55,
 		Paras: parachains_paras::{Pallet, Call, Storage, Event, Config, ValidateUnsigned} = 56,
 		Initializer: parachains_initializer::{Pallet, Call, Storage} = 57,
-		Dmp: parachains_dmp::{Pallet, Call, Storage} = 58,
+		Dmp: parachains_dmp::{Pallet, Storage} = 58,
 		Ump: parachains_ump::{Pallet, Call, Storage, Event} = 59,
 		Hrmp: parachains_hrmp::{Pallet, Call, Storage, Event<T>, Config} = 60,
 		ParaSessionInfo: parachains_session_info::{Pallet, Storage} = 61,

runtime/polkadot/src/xcm_config.rs

@@ -17,15 +17,22 @@
 //! XCM configuration for Polkadot.
 
 use super::{
-	parachains_origin, AccountId, AllPalletsWithSystem, Balances, CouncilCollective, ParaId,
-	Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin, WeightToFee, XcmPallet,
+	parachains_dmp, parachains_origin, AccountId, AllPalletsWithSystem, Balances,
+	CouncilCollective, Dmp, ParaId, Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin,
+	TransactionByteFee, WeightToFee, XcmPallet,
 };
 use frame_support::{
 	match_types, parameter_types,
 	traits::{Contains, Everything, Nothing},
 	weights::Weight,
 };
-use runtime_common::{paras_registrar, xcm_sender, ToAuthor};
+use polkadot_runtime_constants::currency::CENTS;
+use runtime_common::{
+	paras_registrar,
+	xcm_sender::{ChildParachainRouter, PriceForParachainDelivery},
+	ToAuthor,
+};
+use sp_arithmetic::FixedPointNumber;
 use sp_core::ConstU32;
 use xcm::latest::prelude::*;
 use xcm_builder::{
@@ -101,11 +108,30 @@ parameter_types! {
 	pub const MaxInstructions: u32 = 100;
 }
 
+pub struct ExponentialDotPrice;
+impl PriceForParachainDelivery for ExponentialDotPrice {
+	fn price_for_parachain_delivery(para: ParaId, msg: &Xcm<()>) -> MultiAssets {
+		let base = CENTS.saturating_mul(3);
+		let msg_fee = (msg.len() as u128).saturating_mul(TransactionByteFee::get());
+
+		let excess_msgs =
+			Dmp::dmq_length(para).saturating_sub(parachains_dmp::MAX_MESSAGE_QUEUE_SIZE) as usize;
+		let factor = if excess_msgs != 0 {
+			Dmp::raise_fee_factor(excess_msgs)
+		} else {
+			Dmp::reduce_fee_factor(1)
+		};
+
+		let amount = factor.saturating_mul_int(base + msg_fee);
+		(Here, amount).into()
+	}
+}
+
 /// The XCM router. When we want to send an XCM message, we use this type. It amalgamates all of our
 /// individual routers.
 pub type XcmRouter = (
 	// Only one router so far - use DMP to communicate with child parachains.
-	xcm_sender::ChildParachainRouter<Runtime, XcmPallet, ()>,
+	ChildParachainRouter<Runtime, XcmPallet, ExponentialDotPrice>,
 );
 
 parameter_types! {

runtime/rococo/Cargo.toml

@@ -27,6 +27,7 @@ sp-io = { git = "https://github.com/paritytech/substrate", branch = "master", de
 sp-mmr-primitives = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-runtime = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-staking = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+sp-arithmetic = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-core = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-session = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-version = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
@@ -112,6 +113,7 @@ std = [
 	"parity-scale-codec/std",
 	"scale-info/std",
 	"inherents/std",
+	"sp-arithmetic/std",
 	"sp-core/std",
 	"sp-api/std",
 	"tx-pool-api/std",

runtime/rococo/src/lib.rs

@@ -1424,7 +1424,7 @@ construct_runtime! {
 		ParaScheduler: parachains_scheduler::{Pallet, Storage} = 55,
 		Paras: parachains_paras::{Pallet, Call, Storage, Event, Config, ValidateUnsigned} = 56,
 		Initializer: parachains_initializer::{Pallet, Call, Storage} = 57,
-		Dmp: parachains_dmp::{Pallet, Call, Storage} = 58,
+		Dmp: parachains_dmp::{Pallet, Storage} = 58,
 		Ump: parachains_ump::{Pallet, Call, Storage, Event} = 59,
 		Hrmp: parachains_hrmp::{Pallet, Call, Storage, Event<T>, Config} = 60,
 		ParaSessionInfo: parachains_session_info::{Pallet, Storage} = 61,

runtime/rococo/src/xcm_config.rs

@@ -17,15 +17,22 @@
 //! XCM configuration for Rococo.
 
 use super::{
-	parachains_origin, AccountId, AllPalletsWithSystem, Balances, CouncilCollective, ParaId,
-	Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin, WeightToFee, XcmPallet,
+	parachains_dmp, parachains_origin, AccountId, AllPalletsWithSystem, Balances,
+	CouncilCollective, Dmp, ParaId, Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin,
+	TransactionByteFee, WeightToFee, XcmPallet,
 };
 use frame_support::{
 	match_types, parameter_types,
 	traits::{Contains, Everything, Nothing},
 	weights::Weight,
 };
-use runtime_common::{paras_registrar, xcm_sender, ToAuthor};
+use rococo_runtime_constants::currency::CENTS;
+use runtime_common::{
+	paras_registrar,
+	xcm_sender::{ChildParachainRouter, PriceForParachainDelivery},
+	ToAuthor,
+};
+use sp_arithmetic::FixedPointNumber;
 use sp_core::ConstU32;
 use xcm::latest::prelude::*;
 use xcm_builder::{
@@ -82,11 +89,31 @@ parameter_types! {
 	/// The amount of weight an XCM operation takes. This is a safe overestimate.
 	pub const BaseXcmWeight: Weight = Weight::from_parts(1_000_000_000, 64 * 1024);
 }
+
+pub struct ExponentialRocPrice;
+impl PriceForParachainDelivery for ExponentialRocPrice {
+	fn price_for_parachain_delivery(para: ParaId, msg: &Xcm<()>) -> MultiAssets {
+		let base = CENTS.saturating_mul(3);
+		let msg_fee = (msg.len() as u128).saturating_mul(TransactionByteFee::get());
+
+		let excess_msgs =
+			Dmp::dmq_length(para).saturating_sub(parachains_dmp::MAX_MESSAGE_QUEUE_SIZE) as usize;
+		let factor = if excess_msgs != 0 {
+			Dmp::raise_fee_factor(excess_msgs)
+		} else {
+			Dmp::reduce_fee_factor(1)
+		};
+
+		let amount = factor.saturating_mul_int(base + msg_fee);
+		(Here, amount).into()
+	}
+}
+
 /// The XCM router. When we want to send an XCM message, we use this type. It amalgamates all of our
 /// individual routers.
 pub type XcmRouter = (
 	// Only one router so far - use DMP to communicate with child parachains.
-	xcm_sender::ChildParachainRouter<Runtime, XcmPallet, ()>,
+	ChildParachainRouter<Runtime, XcmPallet, ExponentialRocPrice>,
 );
 
 parameter_types! {

runtime/test-runtime/src/lib.rs

@@ -667,7 +667,7 @@ construct_runtime! {
 		ParaSessionInfo: parachains_session_info::{Pallet, Storage},
 		Hrmp: parachains_hrmp::{Pallet, Call, Storage, Event<T>},
 		Ump: parachains_ump::{Pallet, Call, Storage, Event},
-		Dmp: parachains_dmp::{Pallet, Call, Storage},
+		Dmp: parachains_dmp::{Pallet, Storage},
 		Xcm: pallet_xcm::{Pallet, Call, Event<T>, Origin},
 		ParasDisputes: parachains_disputes::{Pallet, Storage, Event<T>},