OptimismPortal.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.15;

import { Initializable } from "@openzeppelin/contracts/proxy/utils/Initializable.sol";
import { SafeCall } from "../libraries/SafeCall.sol";
import { L2OutputOracle } from "./L2OutputOracle.sol";
import { SystemConfig } from "./SystemConfig.sol";
import { Constants } from "../libraries/Constants.sol";
import { Types } from "../libraries/Types.sol";
import { Hashing } from "../libraries/Hashing.sol";
import { SecureMerkleTrie } from "../libraries/trie/SecureMerkleTrie.sol";
import { AddressAliasHelper } from "../vendor/AddressAliasHelper.sol";
import { ResourceMetering } from "./ResourceMetering.sol";
import { Semver } from "../universal/Semver.sol";

/// @custom:proxied
/// @title OptimismPortal
/// @notice The OptimismPortal is a low-level contract responsible for passing messages between L1
///         and L2. Messages sent directly to the OptimismPortal have no form of replayability.
///         Users are encouraged to use the L1CrossDomainMessenger for a higher-level interface.
contract OptimismPortal is Initializable, ResourceMetering, Semver {
    /// @notice Represents a proven withdrawal.
    /// @custom:field outputRoot    Root of the L2 output this was proven against.
    /// @custom:field timestamp     Timestamp at whcih the withdrawal was proven.
    /// @custom:field l2OutputIndex Index of the output this was proven against.
    struct ProvenWithdrawal {
        bytes32 outputRoot;
        uint128 timestamp;
        uint128 l2OutputIndex;
    }

    /// @notice Version of the deposit event.
    uint256 internal constant DEPOSIT_VERSION = 0;

    /// @notice The L2 gas limit set when eth is deposited using the receive() function.
    uint64 internal constant RECEIVE_DEFAULT_GAS_LIMIT = 100_000;

    /// @notice Address of the L2OutputOracle contract.
    L2OutputOracle public immutable L2_ORACLE;

    /// @notice Address of the SystemConfig contract.
    SystemConfig public immutable SYSTEM_CONFIG;

    /// @notice Address that has the ability to pause and unpause withdrawals.
    address public immutable GUARDIAN;

    /// @notice Address of the L2 account which initiated a withdrawal in this transaction.
    ///         If the of this variable is the default L2 sender address, then we are NOT inside of
    ///         a call to finalizeWithdrawalTransaction.
    address public l2Sender;

    /// @notice A list of withdrawal hashes which have been successfully finalized.
    mapping(bytes32 => bool) public finalizedWithdrawals;

    /// @notice A mapping of withdrawal hashes to `ProvenWithdrawal` data.
    mapping(bytes32 => ProvenWithdrawal) public provenWithdrawals;

    /// @notice Determines if cross domain messaging is paused.
    ///         When set to true, withdrawals are paused.
    ///         This may be removed in the future.
    bool public paused;

    /// @notice Emitted when a transaction is deposited from L1 to L2.
    ///         The parameters of this event are read by the rollup node and used to derive deposit
    ///         transactions on L2.
    /// @param from       Address that triggered the deposit transaction.
    /// @param to         Address that the deposit transaction is directed to.
    /// @param version    Version of this deposit transaction event.
    /// @param opaqueData ABI encoded deposit data to be parsed off-chain.
    event TransactionDeposited(
        address indexed from,
        address indexed to,
        uint256 indexed version,
        bytes opaqueData
    );

    /// @notice Emitted when a withdrawal transaction is proven.
    /// @param withdrawalHash Hash of the withdrawal transaction.
    /// @param from           Address that triggered the withdrawal transaction.
    /// @param to             Address that the withdrawal transaction is directed to.
    event WithdrawalProven(
        bytes32 indexed withdrawalHash,
        address indexed from,
        address indexed to
    );

    /// @notice Emitted when a withdrawal transaction is finalized.
    /// @param withdrawalHash Hash of the withdrawal transaction.
    /// @param success        Whether the withdrawal transaction was successful.
    event WithdrawalFinalized(bytes32 indexed withdrawalHash, bool success);

    /// @notice Emitted when the pause is triggered.
    /// @param account Address of the account triggering the pause.
    event Paused(address account);

    /// @notice Emitted when the pause is lifted.
    /// @param account Address of the account triggering the unpause.
    event Unpaused(address account);

    /// @notice Reverts when paused.
    modifier whenNotPaused() {
        require(paused == false, "OptimismPortal: paused");
        _;
    }

    /// @custom:semver 1.7.2
    /// @notice Constructs the OptimismPortal contract.
    /// @param _l2Oracle Address of the L2OutputOracle contract.
    /// @param _guardian Address that can pause withdrawals.
    /// @param _paused Sets the contract's pausability state.
    /// @param _config Address of the SystemConfig contract.
    constructor(
        L2OutputOracle _l2Oracle,
        address _guardian,
        bool _paused,
        SystemConfig _config
    ) Semver(1, 7, 2) {
        L2_ORACLE = _l2Oracle;
        GUARDIAN = _guardian;
        SYSTEM_CONFIG = _config;
        initialize(_paused);
    }

    /// @notice Initializer.
    function initialize(bool _paused) public initializer {
        l2Sender = Constants.DEFAULT_L2_SENDER;
        paused = _paused;
        __ResourceMetering_init();
    }

    /// @notice Pauses withdrawals.
    function pause() external {
        require(msg.sender == GUARDIAN, "OptimismPortal: only guardian can pause");
        paused = true;
        emit Paused(msg.sender);
    }

    /// @notice Unpauses withdrawals.
    function unpause() external {
        require(msg.sender == GUARDIAN, "OptimismPortal: only guardian can unpause");
        paused = false;
        emit Unpaused(msg.sender);
    }

    /// @notice Computes the minimum gas limit for a deposit.
    ///         The minimum gas limit linearly increases based on the size of the calldata.
    ///         This is to prevent users from creating L2 resource usage without paying for it.
    ///         This function can be used when interacting with the portal to ensure forwards
    ///         compatibility.
    /// @param _byteCount Number of bytes in the calldata.
    /// @return The minimum gas limit for a deposit.
    function minimumGasLimit(uint64 _byteCount) public pure returns (uint64) {
        return _byteCount * 16 + 21000;
    }

    /// @notice Accepts value so that users can send ETH directly to this contract and have the
    ///         funds be deposited to their address on L2. This is intended as a convenience
    ///         function for EOAs. Contracts should call the depositTransaction() function directly
    ///         otherwise any deposited funds will be lost due to address aliasing.
    // solhint-disable-next-line ordering
    receive() external payable {
        depositTransaction(msg.sender, msg.value, RECEIVE_DEFAULT_GAS_LIMIT, false, bytes(""));
    }

    /// @notice Accepts ETH value without triggering a deposit to L2.
    ///         This function mainly exists for the sake of the migration between the legacy
    ///         Optimism system and Bedrock.
    function donateETH() external payable {
        // Intentionally empty.
    }

    /// @notice Getter for the resource config.
    ///         Used internally by the ResourceMetering contract.
    ///         The SystemConfig is the source of truth for the resource config.
    /// @return ResourceMetering ResourceConfig
    function _resourceConfig()
        internal
        view
        override
        returns (ResourceMetering.ResourceConfig memory)
    {
        return SYSTEM_CONFIG.resourceConfig();
    }

    /// @notice Proves a withdrawal transaction.
    /// @param _tx              Withdrawal transaction to finalize.
    /// @param _l2OutputIndex   L2 output index to prove against.
    /// @param _outputRootProof Inclusion proof of the L2ToL1MessagePasser contract's storage root.
    /// @param _withdrawalProof Inclusion proof of the withdrawal in L2ToL1MessagePasser contract.
    function proveWithdrawalTransaction(
        Types.WithdrawalTransaction memory _tx,
        uint256 _l2OutputIndex,
        Types.OutputRootProof calldata _outputRootProof,
        bytes[] calldata _withdrawalProof
    ) external whenNotPaused {
        // Prevent users from creating a deposit transaction where this address is the message
        // sender on L2. Because this is checked here, we do not need to check again in
        // `finalizeWithdrawalTransaction`.
        require(
            _tx.target != address(this),
            "OptimismPortal: you cannot send messages to the portal contract"
        );

        // Get the output root and load onto the stack to prevent multiple mloads. This will
        // revert if there is no output root for the given block number.
        bytes32 outputRoot = L2_ORACLE.getL2Output(_l2OutputIndex).outputRoot;

        // Verify that the output root can be generated with the elements in the proof.
        require(
            outputRoot == Hashing.hashOutputRootProof(_outputRootProof),
            "OptimismPortal: invalid output root proof"
        );

        // Load the ProvenWithdrawal into memory, using the withdrawal hash as a unique identifier.
        bytes32 withdrawalHash = Hashing.hashWithdrawal(_tx);
        ProvenWithdrawal memory provenWithdrawal = provenWithdrawals[withdrawalHash];

        // We generally want to prevent users from proving the same withdrawal multiple times
        // because each successive proof will update the timestamp. A malicious user can take
        // advantage of this to prevent other users from finalizing their withdrawal. However,
        // since withdrawals are proven before an output root is finalized, we need to allow users
        // to re-prove their withdrawal only in the case that the output root for their specified
        // output index has been updated.
        require(
            provenWithdrawal.timestamp == 0 ||
                L2_ORACLE.getL2Output(provenWithdrawal.l2OutputIndex).outputRoot !=
                provenWithdrawal.outputRoot,
            "OptimismPortal: withdrawal hash has already been proven"
        );

        // Compute the storage slot of the withdrawal hash in the L2ToL1MessagePasser contract.
        // Refer to the Solidity documentation for more information on how storage layouts are
        // computed for mappings.
        bytes32 storageKey = keccak256(
            abi.encode(
                withdrawalHash,
                uint256(0) // The withdrawals mapping is at the first slot in the layout.
            )
        );

        // Verify that the hash of this withdrawal was stored in the L2toL1MessagePasser contract
        // on L2. If this is true, under the assumption that the SecureMerkleTrie does not have
        // bugs, then we know that this withdrawal was actually triggered on L2 and can therefore
        // be relayed on L1.
        require(
            SecureMerkleTrie.verifyInclusionProof(
                abi.encode(storageKey),
                hex"01",
                _withdrawalProof,
                _outputRootProof.messagePasserStorageRoot
            ),
            "OptimismPortal: invalid withdrawal inclusion proof"
        );

        // Designate the withdrawalHash as proven by storing the `outputRoot`, `timestamp`, and
        // `l2BlockNumber` in the `provenWithdrawals` mapping. A `withdrawalHash` can only be
        // proven once unless it is submitted again with a different outputRoot.
        provenWithdrawals[withdrawalHash] = ProvenWithdrawal({
            outputRoot: outputRoot,
            timestamp: uint128(block.timestamp),
            l2OutputIndex: uint128(_l2OutputIndex)
        });

        // Emit a `WithdrawalProven` event.
        emit WithdrawalProven(withdrawalHash, _tx.sender, _tx.target);
    }

    /// @notice Finalizes a withdrawal transaction.
    /// @param _tx Withdrawal transaction to finalize.
    function finalizeWithdrawalTransaction(Types.WithdrawalTransaction memory _tx)
        external
        whenNotPaused
    {
        // Make sure that the l2Sender has not yet been set. The l2Sender is set to a value other
        // than the default value when a withdrawal transaction is being finalized. This check is
        // a defacto reentrancy guard.
        require(
            l2Sender == Constants.DEFAULT_L2_SENDER,
            "OptimismPortal: can only trigger one withdrawal per transaction"
        );

        // Grab the proven withdrawal from the `provenWithdrawals` map.
        bytes32 withdrawalHash = Hashing.hashWithdrawal(_tx);
        ProvenWithdrawal memory provenWithdrawal = provenWithdrawals[withdrawalHash];

        // A withdrawal can only be finalized if it has been proven. We know that a withdrawal has
        // been proven at least once when its timestamp is non-zero. Unproven withdrawals will have
        // a timestamp of zero.
        require(
            provenWithdrawal.timestamp != 0,
            "OptimismPortal: withdrawal has not been proven yet"
        );

        // As a sanity check, we make sure that the proven withdrawal's timestamp is greater than
        // starting timestamp inside the L2OutputOracle. Not strictly necessary but extra layer of
        // safety against weird bugs in the proving step.
        require(
            provenWithdrawal.timestamp >= L2_ORACLE.startingTimestamp(),
            "OptimismPortal: withdrawal timestamp less than L2 Oracle starting timestamp"
        );

        // A proven withdrawal must wait at least the finalization period before it can be
        // finalized. This waiting period can elapse in parallel with the waiting period for the
        // output the withdrawal was proven against. In effect, this means that the minimum
        // withdrawal time is proposal submission time + finalization period.
        require(
            _isFinalizationPeriodElapsed(provenWithdrawal.timestamp),
            "OptimismPortal: proven withdrawal finalization period has not elapsed"
        );

        // Grab the OutputProposal from the L2OutputOracle, will revert if the output that
        // corresponds to the given index has not been proposed yet.
        Types.OutputProposal memory proposal = L2_ORACLE.getL2Output(
            provenWithdrawal.l2OutputIndex
        );

        // Check that the output root that was used to prove the withdrawal is the same as the
        // current output root for the given output index. An output root may change if it is
        // deleted by the challenger address and then re-proposed.
        require(
            proposal.outputRoot == provenWithdrawal.outputRoot,
            "OptimismPortal: output root proven is not the same as current output root"
        );

        // Check that the output proposal has also been finalized.
        require(
            _isFinalizationPeriodElapsed(proposal.timestamp),
            "OptimismPortal: output proposal finalization period has not elapsed"
        );

        // Check that this withdrawal has not already been finalized, this is replay protection.
        require(
            finalizedWithdrawals[withdrawalHash] == false,
            "OptimismPortal: withdrawal has already been finalized"
        );

        // Mark the withdrawal as finalized so it can't be replayed.
        finalizedWithdrawals[withdrawalHash] = true;

        // Set the l2Sender so contracts know who triggered this withdrawal on L2.
        l2Sender = _tx.sender;

        // Trigger the call to the target contract. We use a custom low level method
        // SafeCall.callWithMinGas to ensure two key properties
        //   1. Target contracts cannot force this call to run out of gas by returning a very large
        //      amount of data (and this is OK because we don't care about the returndata here).
        //   2. The amount of gas provided to the execution context of the target is at least the
        //      gas limit specified by the user. If there is not enough gas in the current context
        //      to accomplish this, `callWithMinGas` will revert.
        bool success = SafeCall.callWithMinGas(_tx.target, _tx.gasLimit, _tx.value, _tx.data);

        // Reset the l2Sender back to the default value.
        l2Sender = Constants.DEFAULT_L2_SENDER;

        // All withdrawals are immediately finalized. Replayability can
        // be achieved through contracts built on top of this contract
        emit WithdrawalFinalized(withdrawalHash, success);

        // Reverting here is useful for determining the exact gas cost to successfully execute the
        // sub call to the target contract if the minimum gas limit specified by the user would not
        // be sufficient to execute the sub call.
        if (success == false && tx.origin == Constants.ESTIMATION_ADDRESS) {
            revert("OptimismPortal: withdrawal failed");
        }
    }

    /// @notice Accepts deposits of ETH and data, and emits a TransactionDeposited event for use in
    ///         deriving deposit transactions. Note that if a deposit is made by a contract, its
    ///         address will be aliased when retrieved using `tx.origin` or `msg.sender`. Consider
    ///         using the CrossDomainMessenger contracts for a simpler developer experience.
    /// @param _to         Target address on L2.
    /// @param _value      ETH value to send to the recipient.
    /// @param _gasLimit   Amount of L2 gas to purchase by burning gas on L1.
    /// @param _isCreation Whether or not the transaction is a contract creation.
    /// @param _data       Data to trigger the recipient with.
    function depositTransaction(
        address _to,
        uint256 _value,
        uint64 _gasLimit,
        bool _isCreation,
        bytes memory _data
    ) public payable metered(_gasLimit) {
        // Just to be safe, make sure that people specify address(0) as the target when doing
        // contract creations.
        if (_isCreation) {
            require(
                _to == address(0),
                "OptimismPortal: must send to address(0) when creating a contract"
            );
        }

        // Prevent depositing transactions that have too small of a gas limit. Users should pay
        // more for more resource usage.
        require(
            _gasLimit >= minimumGasLimit(uint64(_data.length)),
            "OptimismPortal: gas limit too small"
        );

        // Prevent the creation of deposit transactions that have too much calldata. This gives an
        // upper limit on the size of unsafe blocks over the p2p network. 120kb is chosen to ensure
        // that the transaction can fit into the p2p network policy of 128kb even though deposit
        // transactions are not gossipped over the p2p network.
        require(_data.length <= 120_000, "OptimismPortal: data too large");

        // Transform the from-address to its alias if the caller is a contract.
        address from = msg.sender;
        if (msg.sender != tx.origin) {
            from = AddressAliasHelper.applyL1ToL2Alias(msg.sender);
        }

        // Compute the opaque data that will be emitted as part of the TransactionDeposited event.
        // We use opaque data so that we can update the TransactionDeposited event in the future
        // without breaking the current interface.
        bytes memory opaqueData = abi.encodePacked(
            msg.value,
            _value,
            _gasLimit,
            _isCreation,
            _data
        );

        // Emit a TransactionDeposited event so that the rollup node can derive a deposit
        // transaction for this deposit.
        emit TransactionDeposited(from, _to, DEPOSIT_VERSION, opaqueData);
    }

    /// @notice Determine if a given output is finalized.
    ///         Reverts if the call to L2_ORACLE.getL2Output reverts.
    ///         Returns a boolean otherwise.
    /// @param _l2OutputIndex Index of the L2 output to check.
    /// @return Whether or not the output is finalized.
    function isOutputFinalized(uint256 _l2OutputIndex) external view returns (bool) {
        return _isFinalizationPeriodElapsed(L2_ORACLE.getL2Output(_l2OutputIndex).timestamp);
    }

    /// @notice Determines whether the finalization period has elapsed with respect to
    ///         the provided block timestamp.
    /// @param _timestamp Timestamp to check.
    /// @return Whether or not the finalization period has elapsed.
    function _isFinalizationPeriodElapsed(uint256 _timestamp) internal view returns (bool) {
        return block.timestamp > _timestamp + L2_ORACLE.FINALIZATION_PERIOD_SECONDS();
    }
}