Add deposit/withdraw wETH functions to balances ERC20 precompile

precompiles/balances-erc20/ERC20.sol

@@ -83,6 +83,21 @@ interface IERC20 {
   function transferFrom(address from, address to, uint256 value)
     external returns (bool);
 
+  /**
+   * @dev Provide compatibility for contracts that expect wETH design.
+   * Returns funds to sender as this precompile tokens and the native tokens are the same.
+   * Selector: d0e30db0
+   */
+  function deposit() external payable;
+
+  /**
+   * @dev Provide compatibility for contracts that expect wETH design.
+   * Does nothing.
+   * Selector: 2e1a7d4d
+   * @param Amount to withdraw/unwrap.
+   */
+  function withdraw(uint256 value) external;
+
   /**
    * @dev Event emited when a transfer has been performed.
    * Selector: ddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef
@@ -108,4 +123,26 @@ interface IERC20 {
     address indexed spender,
     uint256 value
   );
+
+  /**
+   * @dev Event emited when deposit() has been called.
+   * Selector: e1fffcc4923d04b559f4d29a8bfc6cda04eb5b0d3c460751c2402c5c5cc9109c
+   * @param owner address Owner of the tokens
+   * @param value uint256 The amount of tokens "wrapped".
+   */
+  event Deposit(
+    address indexed owner,
+    uint value
+  );
+
+    /**
+   * @dev Event emited when withdraw(uint256) has been called.
+   * Selector: 7fcf532c15f0a6db0bd6d0e038bea71d30d808c7d98cb3bf7268a95bf5081b65
+   * @param owner address Owner of the tokens
+   * @param value uint256 The amount of tokens "unwrapped".
+   */
+  event Withdrawal(
+    address indexed owner,
+    uint value
+  );
 }

precompiles/balances-erc20/src/lib.rs

@@ -54,6 +54,12 @@ pub const SELECTOR_LOG_TRANSFER: [u8; 32] = keccak256!("Transfer(address,address
 /// Solidity selector of the Approval log, which is the Keccak of the Log signature.
 pub const SELECTOR_LOG_APPROVAL: [u8; 32] = keccak256!("Approval(address,address,uint256)");
 
+/// Solidity selector of the Deposit log, which is the Keccak of the Log signature.
+pub const SELECTOR_LOG_DEPOSIT: [u8; 32] = keccak256!("Deposit(address,uint256)");
+
+/// Solidity selector of the Withdraw log, which is the Keccak of the Log signature.
+pub const SELECTOR_LOG_WITHDRAWAL: [u8; 32] = keccak256!("Withdrawal(address,uint256)");
+
 /// Associates pallet Instance to a prefix used for the Approves storage.
 /// This trait is implemented for () and the 16 substrate Instance.
 pub trait InstanceToPrefix {
@@ -126,6 +132,8 @@ pub enum Action {
 	Name = "name()",
 	Symbol = "symbol()",
 	Decimals = "decimals()",
+	Deposit = "deposit()",
+	Withdraw = "withdraw(uint256)",
 }
 
 /// Metadata of an ERC20 token.
@@ -167,7 +175,8 @@ where
 		let mut gasometer = Gasometer::new(target_gas);
 		let gasometer = &mut gasometer;
 
-		let (mut input, selector) = EvmDataReader::new_with_selector(gasometer, input)?;
+		let (mut input, selector) = EvmDataReader::new_with_selector(gasometer, input)
+			.unwrap_or_else(|_| (EvmDataReader::new(input), Action::Deposit));
 		let input = &mut input;
 
 		match selector {
@@ -180,6 +189,8 @@ where
 			Action::Name => Self::name(input, gasometer, context),
 			Action::Symbol => Self::symbol(input, gasometer, context),
 			Action::Decimals => Self::decimals(input, gasometer, context),
+			Action::Deposit => Self::deposit(input, gasometer, context),
+			Action::Withdraw => Self::withdraw(input, gasometer, context),
 		}
 	}
 }
@@ -472,6 +483,78 @@ where
 		})
 	}
 
+	fn deposit(
+		_: &mut EvmDataReader,
+		gasometer: &mut Gasometer,
+		context: &Context,
+	) -> EvmResult<PrecompileOutput> {
+		let caller: Runtime::AccountId = Runtime::AddressMapping::into_account_id(context.caller);
+		let precompile = Runtime::AddressMapping::into_account_id(context.address);
+		let amount = Self::u256_to_amount(gasometer, context.apparent_value)?;
+
+		if amount.into() == U256::from(0u32) {
+			return Err(gasometer.revert("deposited amount must be non-zero"));
+		}
+
+		gasometer.record_log_costs_manual(2, 32)?;
+
+		// Send back funds received by the precompile.
+		RuntimeHelper::<Runtime>::try_dispatch(
+			Some(precompile).into(),
+			pallet_balances::Call::<Runtime, Instance>::transfer {
+				dest: Runtime::Lookup::unlookup(caller),
+				value: amount,
+			},
+			gasometer,
+		)?;
+
+		Ok(PrecompileOutput {
+			exit_status: ExitSucceed::Returned,
+			cost: gasometer.used_gas(),
+			output: Default::default(),
+			logs: LogsBuilder::new(context.address)
+				.log2(
+					SELECTOR_LOG_DEPOSIT,
+					context.caller,
+					EvmDataWriter::new().write(context.apparent_value).build(),
+				)
+				.build(),
+		})
+	}
+
+	fn withdraw(
+		input: &mut EvmDataReader,
+		gasometer: &mut Gasometer,
+		context: &Context,
+	) -> EvmResult<PrecompileOutput> {
+		gasometer.record_log_costs_manual(2, 32)?;
+
+		let withdrawn_amount: U256 = input.read(gasometer)?;
+
+		let account_amount: U256 = {
+			let owner: Runtime::AccountId =
+				Runtime::AddressMapping::into_account_id(context.caller);
+			pallet_balances::Pallet::<Runtime, Instance>::usable_balance(&owner).into()
+		};
+
+		if withdrawn_amount > account_amount {
+			return Err(gasometer.revert("trying to withdraw more than owned"));
+		}
+
+		Ok(PrecompileOutput {
+			exit_status: ExitSucceed::Returned,
+			cost: gasometer.used_gas(),
+			output: Default::default(),
+			logs: LogsBuilder::new(context.address)
+				.log2(
+					SELECTOR_LOG_WITHDRAWAL,
+					context.caller,
+					EvmDataWriter::new().write(withdrawn_amount).build(),
+				)
+				.build(),
+		})
+	}
+
 	fn u256_to_amount(
 		gasometer: &mut Gasometer,
 		value: U256,

precompiles/balances-erc20/src/mock.rs

@@ -284,3 +284,10 @@ impl ExtBuilder {
 		ext
 	}
 }
+
+pub(crate) fn events() -> Vec<Event> {
+	System::events()
+		.into_iter()
+		.map(|r| r.event)
+		.collect::<Vec<_>>()
+}