Add LinkToken on Optimism [bridge v2]

CHANGELOG.md

@@ -4,11 +4,12 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased] - Apr 2021
+## [Unreleased] - Jun 2021
 
 ### Added
 
 - Access controlled mintable & burnable LinkToken, for use on sidechains and L2 networks.
+- Documentation and token implementation for the Optimism bridge v2.
 - Added versioning to v0.6 & v0.7 contracts
 
 ### Changed

contracts/v0.7/bridge/README.md

@@ -23,3 +23,5 @@ NOTICE: Current implementation of LinkTokenChild contract requires some addition
   gets defined, and once online transfer the ownership (bridge gateway role) to the new bridge.
 
 TODO: Potentially create an upgradeable `LinkTokenChild.sol` and limit gateway support to only one (owner)!
+
+- `./token/optimism/`: Documentation and token implementation for the Optimism bridge v2.

contracts/v0.7/bridge/token/optimism/IERC20Optimism.sol

@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: MIT
+pragma solidity >0.6.0 <0.8.0;
+
+/* Interface Imports */
+import { IERC20 } from "../../../../../vendor/OpenZeppelin/openzeppelin-contracts/contracts/token/ERC20/IERC20.sol";
+import { IERC165 } from "../../../../../vendor/OpenZeppelin/openzeppelin-contracts/contracts/introspection/IERC165.sol";
+
+/// @dev Interface for the bridged ERC20 token expected by the Optimism standard bridge L2 gateway.
+interface IERC20Optimism is IERC20, IERC165 {
+  /// @dev Returns the address of an L1 token contract linked to this L2 token contract
+  function l1Token()
+    external
+    returns (address);
+
+  /**
+   * @dev Creates `_amount` tokens `_to` account.
+   * @notice Called by L2 gateway to deposit tokens.
+   * @param _to Address of the recipient.
+   * @param _amount Number of tokens to mint.
+   */
+  function mint(
+    address _to,
+    uint256 _amount
+  )
+    external;
+
+  /**
+   * @dev Destroys `_amount` tokens `_from` account.
+   * @notice Called by L2 gateway to withdraw tokens.
+   * @param _from Address of the account holding the tokens to be burnt.
+   * @param _amount Number of tokens to burn.
+   */
+  function burn(
+    address _from,
+    uint256 _amount
+  )
+    external;
+
+  /// @dev Emitted when `_amount` tokens are deposited from L1 to L2.
+  event Mint(
+    address indexed _account,
+    uint256 _amount
+  );
+
+  /// @dev Emitted when `_amount` tokens are withdrawn from L2 to L1.
+  event Burn(
+    address indexed _account,
+    uint256 _amount
+  );
+}

contracts/v0.7/bridge/token/optimism/LinkTokenOptimism.sol

@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: MIT
+pragma solidity >0.6.0 <0.8.0;
+
+/* Interface Imports */
+import { IERC165 } from "../../../../../vendor/OpenZeppelin/openzeppelin-contracts/contracts/introspection/IERC165.sol";
+import { ITypeAndVersion } from "../../../../v0.6/ITypeAndVersion.sol";
+import { IERC20Optimism } from "./IERC20Optimism.sol";
+
+/* Contract Imports */
+import { ERC20 } from "../../../../../vendor/OpenZeppelin/openzeppelin-contracts/contracts/token/ERC20/ERC20.sol";
+import { LinkToken } from "../../../../v0.6/LinkToken.sol";
+
+/// @dev Access controlled mintable & burnable LinkToken, for use on Optimism L2 network.
+contract LinkTokenOptimism is ITypeAndVersion, IERC20Optimism, LinkToken {
+  /// @dev Returns the address of an L2 bridge contract that has access to mint & burn
+  address public immutable l2Bridge;
+  /// @inheritdoc IERC20Optimism
+  address public immutable override l1Token;
+
+  /**
+   * @dev Creates an L2 token connected to a specific L2 bridge gateway & L1 token
+   * @param l2BridgeAddr Address of the corresponding L2 bridge gateway.
+   * @param l1TokenAddr Address of the corresponding L1 token.
+   */
+  constructor(
+    address l2BridgeAddr,
+    address l1TokenAddr
+  ) {
+    l2Bridge = l2BridgeAddr;
+    l1Token = l1TokenAddr;
+  }
+
+  /**
+   * @notice versions:
+   *
+   * - LinkTokenOptimism 0.0.1: initial release
+   *
+   * @inheritdoc ITypeAndVersion
+   */
+  function typeAndVersion()
+    external
+    pure
+    override(ITypeAndVersion, LinkToken)
+    virtual
+    returns (string memory)
+  {
+    return "LinkTokenOptimism 0.0.1";
+  }
+
+  /// @dev Checks that message sender is the L2 bridge contract (locked access to mint & burn)
+  modifier onlyL2Bridge {
+    require(msg.sender == l2Bridge, "Only L2 Bridge can mint and burn");
+    _;
+  }
+
+  /**
+   * @dev Optimism standard bridge L2 gateway uses ERC165 to confirm the required interface
+   * @inheritdoc IERC165
+   */
+  function supportsInterface(
+    bytes4 interfaceId
+  )
+    public
+    override
+    pure
+    returns (bool)
+  {
+    bytes4 firstSupportedInterface = bytes4(keccak256("supportsInterface(bytes4)")); // ERC165
+    bytes4 secondSupportedInterface = IERC20Optimism.l1Token.selector
+      ^ IERC20Optimism.mint.selector
+      ^ IERC20Optimism.burn.selector;
+    return interfaceId == firstSupportedInterface || interfaceId == secondSupportedInterface;
+  }
+
+  /// @inheritdoc IERC20Optimism
+  function mint(
+    address _to,
+    uint256 _amount
+  )
+    public
+    override
+    onlyL2Bridge()
+  {
+    _mint(_to, _amount);
+    emit Mint(_to, _amount);
+  }
+
+  /// @inheritdoc IERC20Optimism
+  function burn(
+    address _from,
+    uint256 _amount
+  )
+    public
+    override
+    onlyL2Bridge()
+  {
+    _burn(_from, _amount);
+    emit Burn(_from, _amount);
+  }
+
+  /**
+   * @dev Overrides parent contract so no tokens are minted on deployment.
+   * @inheritdoc LinkToken
+   */
+  function _onCreate()
+    internal
+    override
+  {}
+}

contracts/v0.7/bridge/token/optimism/README.md

@@ -0,0 +1,13 @@
+# LINK Token on Optimism
+
+- `./token/IERC20Optimism.sol`: Interface for the bridged ERC20 token expected by the Optimism standard bridge L2 gateway.
+- `./token/LinkTokenOptimism.sol`: Access controlled mintable & burnable LinkToken, for use on Optimism L2 network.
+
+`LinkTokenOptimism.sol` is a slightly modified version of Optimism's [`L2StandardERC20.sol`](https://github.com/ethereum-optimism/optimism/blob/master/packages/contracts/contracts/optimistic-ethereum/libraries/standards/L2StandardERC20.sol) and will be connected to the [`OVM_L2StandardBridge.sol`](https://github.com/ethereum-optimism/optimism/blob/master/packages/contracts/contracts/optimistic-ethereum/OVM/bridge/tokens/OVM_L2StandardBridge.sol). Modifications include:
+
+- Contract versioning via `ITypeAndVersion` interface
+- ERC677 support by extending the `LinkToken` contract
+- Transfers & approves to the contract itself blocked (provided by `LinkToken` contract)
+- `l2Bridge` & `l1Token` were changed from storage vars to immutable vars, which provides some gas savings
+
+The [Optimism Gateway](https://gateway.optimism.io) bridge UI can be used to move the tokens between networks.