Add weight annotation to pallet Ethereum's transact extrinsic (#202)

* Initial simple weight annotation for transact.

* Configureable gas to weight mapping

* refund unused weight

* Thought: gas weight conversion belongs in pallet evm

* Move GasToWeight to pallet_Evm

* Weight refund in pallet_evm

* indentation

* fix mocks

frame/ethereum/src/lib.rs

@@ -25,7 +25,8 @@
 
 use frame_support::{
 	decl_module, decl_storage, decl_error, decl_event,
-	traits::Get, traits::FindAuthor,
+	traits::Get, traits::FindAuthor, weights::Weight,
+	dispatch::DispatchResultWithPostInfo,
 };
 use sp_std::prelude::*;
 use frame_system::ensure_none;
@@ -38,7 +39,7 @@ use sp_runtime::{
 };
 use evm::ExitReason;
 use fp_evm::CallOrCreateInfo;
-use pallet_evm::Runner;
+use pallet_evm::{Runner, GasToWeight};
 use sha3::{Digest, Keccak256};
 use codec::Encode;
 use fp_consensus::{FRONTIER_ENGINE_ID, ConsensusLog};
@@ -112,8 +113,8 @@ decl_module! {
 		fn deposit_event() = default;
 
 		/// Transact an Ethereum transaction.
-		#[weight = 0]
-		fn transact(origin, transaction: ethereum::Transaction) {
+		#[weight = <T as pallet_evm::Trait>::GasToWeight::gas_to_weight(transaction.gas_limit.low_u32())]
+		fn transact(origin, transaction: ethereum::Transaction) -> DispatchResultWithPostInfo {
 			ensure_none(origin)?;
 
 			let source = Self::recover_signer(&transaction)
@@ -183,13 +184,14 @@ decl_module! {
 			Pending::append((transaction, status, receipt));
 
 			Self::deposit_event(Event::Executed(source, transaction_hash, reason));
+			Ok(Some(T::GasToWeight::gas_to_weight(used_gas.low_u32())).into())
 		}
 
 		fn on_finalize(n: T::BlockNumber) {
 			<Module<T>>::store_block();
 		}
 
-		fn on_initialize(n: T::BlockNumber) -> frame_support::weights::Weight {
+		fn on_initialize(n: T::BlockNumber) -> Weight {
 			Pending::kill();
 			0
 		}

frame/ethereum/src/mock.rs

@@ -138,6 +138,7 @@ impl AddressMapping<AccountId32> for HashedAddressMapping {
 
 impl pallet_evm::Trait for Test {
 	type FeeCalculator = FixedGasPrice;
+	type GasToWeight = ();
 	type CallOrigin = EnsureAddressTruncated;
 	type WithdrawOrigin = EnsureAddressTruncated;
 	type AddressMapping = HashedAddressMapping;

frame/evm/src/lib.rs

@@ -68,12 +68,12 @@ use codec::{Encode, Decode};
 #[cfg(feature = "std")]
 use serde::{Serialize, Deserialize};
 use frame_support::{decl_module, decl_storage, decl_event, decl_error};
-use frame_support::weights::{Weight, Pays};
+use frame_support::weights::{Weight, Pays, PostDispatchInfo};
 use frame_support::traits::{Currency, ExistenceRequirement, Get};
 use frame_support::dispatch::DispatchResultWithPostInfo;
 use frame_system::RawOrigin;
 use sp_core::{U256, H256, H160, Hasher};
-use sp_runtime::{AccountId32, traits::{UniqueSaturatedInto, SaturatedConversion, BadOrigin}};
+use sp_runtime::{AccountId32, traits::{UniqueSaturatedInto, BadOrigin}};
 use evm::Config;
 
 /// Type alias for currency balance.
@@ -207,6 +207,17 @@ impl<H: Hasher<Out=H256>> AddressMapping<AccountId32> for HashedAddressMapping<H
 	}
 }
 
+/// A mapping function that converts Ethereum gas to Substrate weight
+pub trait GasToWeight {
+	fn gas_to_weight(gas: u32) -> Weight;
+}
+
+impl GasToWeight for () {
+	fn gas_to_weight(gas: u32) -> Weight {
+		gas as Weight
+	}
+}
+
 /// Substrate system chain ID.
 pub struct SystemChainId;
 
@@ -223,6 +234,9 @@ pub trait Trait: frame_system::Trait + pallet_timestamp::Trait {
 	/// Calculator for current gas price.
 	type FeeCalculator: FeeCalculator;
 
+	/// Maps Ethereum gas to Substrate weight.
+	type GasToWeight: GasToWeight;
+
 	/// Allow the origin to call on behalf of given address.
 	type CallOrigin: EnsureAddressOrigin<Self::Origin>;
 	/// Allow the origin to withdraw on behalf of given address.
@@ -356,7 +370,7 @@ decl_module! {
 		}
 
 		/// Issue an EVM call operation. This is similar to a message call transaction in Ethereum.
-		#[weight = (*gas_price).saturated_into::<Weight>().saturating_mul(*gas_limit as Weight)]
+		#[weight = T::GasToWeight::gas_to_weight(*gas_limit)]
 		fn call(
 			origin,
 			source: H160,
@@ -369,32 +383,34 @@ decl_module! {
 		) -> DispatchResultWithPostInfo {
 			T::CallOrigin::ensure_address_origin(&source, origin)?;
 
-			match T::Runner::call(
+			let info = T::Runner::call(
 				source,
 				target,
 				input,
 				value,
 				gas_limit,
 				Some(gas_price),
 				nonce,
-			)? {
-				CallInfo {
-					exit_reason: ExitReason::Succeed(_),
-					..
-				} => {
+			)?;
+
+			match info.exit_reason {
+				ExitReason::Succeed(_) => {
 					Module::<T>::deposit_event(Event::<T>::Executed(target));
 				},
 				_ => {
 					Module::<T>::deposit_event(Event::<T>::ExecutedFailed(target));
 				},
-			}
+			};
 
-			Ok(Pays::No.into())
+			Ok(PostDispatchInfo {
+				actual_weight: Some(T::GasToWeight::gas_to_weight(info.used_gas.low_u32())),
+				pays_fee: Pays::No,
+			})
 		}
 
 		/// Issue an EVM create operation. This is similar to a contract creation transaction in
 		/// Ethereum.
-		#[weight = (*gas_price).saturated_into::<Weight>().saturating_mul(*gas_limit as Weight)]
+		#[weight = T::GasToWeight::gas_to_weight(*gas_limit)]
 		fn create(
 			origin,
 			source: H160,
@@ -406,14 +422,16 @@ decl_module! {
 		) -> DispatchResultWithPostInfo {
 			T::CallOrigin::ensure_address_origin(&source, origin)?;
 
-			match T::Runner::create(
+			let info = T::Runner::create(
 				source,
 				init,
 				value,
 				gas_limit,
 				Some(gas_price),
 				nonce,
-			)? {
+			)?;
+
+			match info {
 				CreateInfo {
 					exit_reason: ExitReason::Succeed(_),
 					value: create_address,
@@ -430,11 +448,14 @@ decl_module! {
 				},
 			}
 
-			Ok(Pays::No.into())
+			Ok(PostDispatchInfo {
+				actual_weight: Some(T::GasToWeight::gas_to_weight(info.used_gas.low_u32())),
+				pays_fee: Pays::No,
+			})
 		}
 
 		/// Issue an EVM create2 operation.
-		#[weight = (*gas_price).saturated_into::<Weight>().saturating_mul(*gas_limit as Weight)]
+		#[weight = T::GasToWeight::gas_to_weight(*gas_limit)]
 		fn create2(
 			origin,
 			source: H160,
@@ -447,15 +468,17 @@ decl_module! {
 		) -> DispatchResultWithPostInfo {
 			T::CallOrigin::ensure_address_origin(&source, origin)?;
 
-			match T::Runner::create2(
+			let info = T::Runner::create2(
 				source,
 				init,
 				salt,
 				value,
 				gas_limit,
 				Some(gas_price),
 				nonce,
-			)? {
+			)?;
+
+			match info {
 				CreateInfo {
 					exit_reason: ExitReason::Succeed(_),
 					value: create_address,
@@ -472,7 +495,10 @@ decl_module! {
 				},
 			}
 
-			Ok(Pays::No.into())
+			Ok(PostDispatchInfo {
+				actual_weight: Some(T::GasToWeight::gas_to_weight(info.used_gas.low_u32())),
+				pays_fee: Pays::No,
+			})
 		}
 	}
 }

frame/evm/src/tests.rs

@@ -110,6 +110,7 @@ impl FeeCalculator for FixedGasPrice {
 
 impl Trait for Test {
 	type FeeCalculator = FixedGasPrice;
+	type GasToWeight = ();
 
 	type CallOrigin = EnsureAddressRoot<Self::AccountId>;
 	type WithdrawOrigin = EnsureAddressNever<Self::AccountId>;

template/runtime/src/lib.rs

@@ -284,6 +284,7 @@ parameter_types! {
 
 impl pallet_evm::Trait for Runtime {
 	type FeeCalculator = FixedGasPrice;
+	type GasToWeight = ();
 	type CallOrigin = EnsureAddressTruncated;
 	type WithdrawOrigin = EnsureAddressTruncated;
 	type AddressMapping = HashedAddressMapping<BlakeTwo256>;