OPStackHook.sol

// SPDX-License-Identifier: MIT OR Apache-2.0
pragma solidity >=0.8.0;

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// ============ Internal Imports ============
import {AbstractMessageIdAuthHook} from "./libs/AbstractMessageIdAuthHook.sol";
import {StandardHookMetadata} from "./libs/StandardHookMetadata.sol";
import {TypeCasts} from "../libs/TypeCasts.sol";
import {Message} from "../libs/Message.sol";
import {IPostDispatchHook} from "../interfaces/hooks/IPostDispatchHook.sol";

// ============ External Imports ============
import {ICrossDomainMessenger} from "../interfaces/optimism/ICrossDomainMessenger.sol";
import {Address} from "@openzeppelin/contracts/utils/Address.sol";

/**
 * @title OPStackHook
 * @notice Message hook to inform the OPStackIsm of messages published through
 * the native OPStack bridge.
 * @notice This works only for L1 -> L2 messages.
 */
contract OPStackHook is AbstractMessageIdAuthHook {
    using StandardHookMetadata for bytes;

    // ============ Constants ============

    /// @notice messenger contract specified by the rollup
    ICrossDomainMessenger public immutable l1Messenger;

    // Gas limit for sending messages to L2
    // First 1.92e6 gas is provided by Optimism, see more here:
    // https://community.optimism.io/docs/developers/bridge/messaging/#for-l1-%E2%87%92-l2-transactions
    uint32 internal constant GAS_LIMIT = 1_920_000;

    // ============ Constructor ============

    constructor(
        address _mailbox,
        uint32 _destinationDomain,
        bytes32 _ism,
        address _l1Messenger
    ) AbstractMessageIdAuthHook(_mailbox, _destinationDomain, _ism) {
        require(
            Address.isContract(_l1Messenger),
            "OPStackHook: invalid messenger"
        );
        l1Messenger = ICrossDomainMessenger(_l1Messenger);
    }

    // ============ Internal functions ============
    function _quoteDispatch(
        bytes calldata,
        bytes calldata
    ) internal pure override returns (uint256) {
        return 0; // gas subsidized by the L2
    }

    /// @inheritdoc AbstractMessageIdAuthHook
    function _sendMessageId(
        bytes calldata metadata,
        bytes memory payload
    ) internal override {
        require(
            metadata.msgValue(0) < 2 ** 255,
            "OPStackHook: msgValue must be less than 2 ** 255"
        );
        l1Messenger.sendMessage{value: metadata.msgValue(0)}(
            TypeCasts.bytes32ToAddress(ism),
            payload,
            GAS_LIMIT
        );
    }
}