Dynamic fee pallet for evm's FeeCalculator (#278)

Cargo.toml

@@ -1,5 +1,6 @@
 [workspace]
 members = [
+	"frame/dynamic-fee",
 	"frame/ethereum",
 	"frame/evm",
 	"frame/evm/precompile/simple",

frame/dynamic-fee/Cargo.toml

@@ -0,0 +1,30 @@
+[package]
+name = "pallet-dynamic-fee"
+version = "0.1.0"
+authors = ["Parity Technologies <[email protected]>"]
+edition = "2018"
+description = "Dynamic fee handling for EVM."
+license = "Apache-2.0"
+
+[dependencies]
+codec = { package = "parity-scale-codec", version = "1.0.0", default-features = false }
+serde = { version = "1.0.101", optional = true }
+sp-std = { version = "2.0.0-dev", git = "https://github.com/paritytech/substrate.git", branch = "frontier" }
+sp-core = { version = "2.0.0-dev", git = "https://github.com/paritytech/substrate.git", branch = "frontier" }
+sp-runtime = { version = "2.0.0-dev", git = "https://github.com/paritytech/substrate.git", branch = "frontier" }
+sp-inherents = { version = "2.0.0-dev", git = "https://github.com/paritytech/substrate.git", branch = "frontier" }
+frame-system = { version = "2.0.0-dev", default-features = false, git = "https://github.com/paritytech/substrate.git", branch = "frontier" }
+frame-support = { version = "2.0.0-dev", default-features = false, git = "https://github.com/paritytech/substrate.git", branch = "frontier" }
+
+[features]
+default = ["std"]
+std = [
+	"codec/std",
+	"serde",
+	"sp-std/std",
+	"sp-core/std",
+	"sp-runtime/std",
+	"sp-inherents/std",
+	"frame-system/std",
+	"frame-support/std",
+]

frame/dynamic-fee/src/lib.rs

@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: Apache-2.0
+// This file is part of Frontier.
+//
+// Copyright (c) 2021 Parity Technologies (UK) Ltd.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Ensure we're `no_std` when compiling for Wasm.
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use codec::{Encode, Decode};
+use sp_std::{result, cmp::{min, max}};
+use sp_runtime::RuntimeDebug;
+use sp_core::U256;
+use sp_inherents::{InherentIdentifier, InherentData, ProvideInherent, IsFatalError};
+#[cfg(feature = "std")]
+use sp_inherents::ProvideInherentData;
+use frame_support::{
+	decl_module, decl_storage, decl_event,
+	traits::Get,
+};
+use frame_system::ensure_none;
+
+pub trait Config: frame_system::Config {
+	/// The overarching event type.
+	type Event: From<Event> + Into<<Self as frame_system::Config>::Event>;
+	/// Bound divisor for min gas price.
+	type MinGasPriceBoundDivisor: Get<U256>;
+}
+
+decl_storage! {
+	trait Store for Module<T: Config> as DynamicFee {
+		MinGasPrice get(fn min_gas_price) config(): U256;
+		TargetMinGasPrice: Option<U256>;
+	}
+}
+
+decl_event!(
+	pub enum Event {
+		TargetMinGasPriceSet(U256),
+	}
+);
+
+decl_module! {
+	pub struct Module<T: Config> for enum Call where origin: T::Origin {
+		fn deposit_event() = default;
+
+		fn on_finalize(n: T::BlockNumber) {
+			if let Some(target) = TargetMinGasPrice::get() {
+				let bound = MinGasPrice::get() / T::MinGasPriceBoundDivisor::get() + U256::one();
+
+				let upper_limit = MinGasPrice::get().saturating_add(bound);
+				let lower_limit = MinGasPrice::get().saturating_sub(bound);
+
+				MinGasPrice::set(min(upper_limit, max(lower_limit, target)));
+			}
+
+			TargetMinGasPrice::kill();
+		}
+
+		#[weight = 0]
+		fn note_min_gas_price_target(
+			origin,
+			target: U256,
+		) {
+			ensure_none(origin)?;
+
+			TargetMinGasPrice::set(Some(target));
+			Self::deposit_event(Event::TargetMinGasPriceSet(target));
+		}
+	}
+}
+
+#[derive(Encode, Decode, RuntimeDebug)]
+pub enum InherentError { }
+
+impl IsFatalError for InherentError {
+	fn is_fatal_error(&self) -> bool {
+		match *self { }
+	}
+}
+
+pub const INHERENT_IDENTIFIER: InherentIdentifier = *b"dynfee0_";
+
+pub type InherentType = U256;
+
+#[cfg(feature = "std")]
+pub struct InherentDataProvider(pub InherentType);
+
+#[cfg(feature = "std")]
+impl ProvideInherentData for InherentDataProvider {
+	fn inherent_identifier(&self) -> &'static InherentIdentifier {
+		&INHERENT_IDENTIFIER
+	}
+
+	fn provide_inherent_data(
+		&self,
+		inherent_data: &mut InherentData
+	) -> Result<(), sp_inherents::Error> {
+		inherent_data.put_data(INHERENT_IDENTIFIER, &self.0)
+	}
+
+	fn error_to_string(&self, _: &[u8]) -> Option<String> {
+		None
+	}
+}
+
+impl<T: Config> ProvideInherent for Module<T> {
+	type Call = Call<T>;
+	type Error = InherentError;
+	const INHERENT_IDENTIFIER: InherentIdentifier = INHERENT_IDENTIFIER;
+
+	fn create_inherent(data: &InherentData) -> Option<Self::Call> {
+		let target = data.get_data::<InherentType>(&INHERENT_IDENTIFIER).ok()??;
+
+		Some(Call::note_min_gas_price_target(target))
+	}
+
+	fn check_inherent(_call: &Self::Call, _data: &InherentData) -> result::Result<(), Self::Error> {
+		Ok(())
+	}
+}