Transaction Decoder

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;
/* Library Imports */
import { AddressAliasHelper } from "../../standards/AddressAliasHelper.sol";
import { Lib_OVMCodec } from "../../libraries/codec/Lib_OVMCodec.sol";
import { Lib_AddressResolver } from "../../libraries/resolver/Lib_AddressResolver.sol";
/* Interface Imports */
import { ICanonicalTransactionChain } from "./ICanonicalTransactionChain.sol";
import { IChainStorageContainer } from "./IChainStorageContainer.sol";
/**
 * @title CanonicalTransactionChain
 * @dev The Canonical Transaction Chain (CTC) contract is an append-only log of transactions
 * which must be applied to the rollup state. It defines the ordering of rollup transactions by
 * writing them to the 'CTC:batches' instance of the Chain Storage Container.
 * The CTC also allows any account to 'enqueue' an L2 transaction, which will require that the
 * Sequencer will eventually append it to the rollup state.
 *
 * Runtime target: EVM
 */
contract CanonicalTransactionChain is ICanonicalTransactionChain, Lib_AddressResolver {
    /*************
     * Constants *
     *************/
    // L2 tx gas-related
    uint256 public constant MIN_ROLLUP_TX_GAS = 100000;
    uint256 public constant MAX_ROLLUP_TX_SIZE = 50000;
    // The approximate cost of calling the enqueue function
    uint256 public enqueueGasCost;
    // The ratio of the cost of L1 gas to the cost of L2 gas
    uint256 public l2GasDiscountDivisor;
    // The amount of L2 gas which can be forwarded to L2 without spam prevention via 'gas burn'.
    // Calculated as the product of l2GasDiscountDivisor * enqueueGasCost.
    // See comments in enqueue() for further detail.
    uint256 public enqueueL2GasPrepaid;
    // Encoding-related (all in bytes)
    uint256 internal constant BATCH_CONTEXT_SIZE = 16;
    uint256 internal constant BATCH_CONTEXT_LENGTH_POS = 12;
    uint256 internal constant BATCH_CONTEXT_START_POS = 15;
    uint256 internal constant TX_DATA_HEADER_SIZE = 3;
    uint256 internal constant BYTES_TILL_TX_DATA = 65;
    /*************
     * Variables *
     *************/
    uint256 public maxTransactionGasLimit;
    /***************
     * Queue State *
     ***************/
    uint40 private _nextQueueIndex; // index of the first queue element not yet included
    Lib_OVMCodec.QueueElement[] queueElements;
    /***************
     * Constructor *
     ***************/
    constructor(
        address _libAddressManager,
        uint256 _maxTransactionGasLimit,
        uint256 _l2GasDiscountDivisor,
        uint256 _enqueueGasCost
    ) Lib_AddressResolver(_libAddressManager) {
        maxTransactionGasLimit = _maxTransactionGasLimit;
        l2GasDiscountDivisor = _l2GasDiscountDivisor;
        enqueueGasCost = _enqueueGasCost;
        enqueueL2GasPrepaid = _l2GasDiscountDivisor * _enqueueGasCost;
    }
    /**********************
     * Function Modifiers *
     **********************/
    /**
     * Modifier to enforce that, if configured, only the Burn Admin may
     * successfully call a method.
     */
    modifier onlyBurnAdmin() {
        require(msg.sender == libAddressManager.owner(), "Only callable by the Burn Admin.");
        _;
    }
    /*******************************
     * Authorized Setter Functions *
     *******************************/
    /**
     * Allows the Burn Admin to update the parameters which determine the amount of gas to burn.
     * The value of enqueueL2GasPrepaid is immediately updated as well.
     */
    function setGasParams(uint256 _l2GasDiscountDivisor, uint256 _enqueueGasCost)
        external
        onlyBurnAdmin
    {
        enqueueGasCost = _enqueueGasCost;
        l2GasDiscountDivisor = _l2GasDiscountDivisor;
        // See the comment in enqueue() for the rationale behind this formula.
        enqueueL2GasPrepaid = _l2GasDiscountDivisor * _enqueueGasCost;
        emit L2GasParamsUpdated(l2GasDiscountDivisor, enqueueGasCost, enqueueL2GasPrepaid);
    }
    /********************
     * Public Functions *
     ********************/
    /**
     * Accesses the batch storage container.
     * @return Reference to the batch storage container.
     */
    function batches() public view returns (IChainStorageContainer) {
        return IChainStorageContainer(resolve("ChainStorageContainer-CTC-batches"));
    }
    /**
     * Retrieves the total number of elements submitted.
     * @return _totalElements Total submitted elements.
     */
    function getTotalElements() public view returns (uint256 _totalElements) {
        (uint40 totalElements, , , ) = _getBatchExtraData();
        return uint256(totalElements);
    }
    /**
     * Retrieves the total number of batches submitted.
     * @return _totalBatches Total submitted batches.
     */
    function getTotalBatches() public view returns (uint256 _totalBatches) {
        return batches().length();
    }
    /**
     * Returns the index of the next element to be enqueued.
     * @return Index for the next queue element.
     */
    function getNextQueueIndex() public view returns (uint40) {
        return _nextQueueIndex;
    }
    /**
     * Returns the timestamp of the last transaction.
     * @return Timestamp for the last transaction.
     */
    function getLastTimestamp() public view returns (uint40) {
        (, , uint40 lastTimestamp, ) = _getBatchExtraData();
        return lastTimestamp;
    }
    /**
     * Returns the blocknumber of the last transaction.
     * @return Blocknumber for the last transaction.
     */
    function getLastBlockNumber() public view returns (uint40) {
        (, , , uint40 lastBlockNumber) = _getBatchExtraData();
        return lastBlockNumber;
    }
    /**
     * Gets the queue element at a particular index.
     * @param _index Index of the queue element to access.
     * @return _element Queue element at the given index.
     */
    function getQueueElement(uint256 _index)
        public
        view
        returns (Lib_OVMCodec.QueueElement memory _element)
    {
        return queueElements[_index];
    }
    /**
     * Get the number of queue elements which have not yet been included.
     * @return Number of pending queue elements.
     */
    function getNumPendingQueueElements() public view returns (uint40) {
        return uint40(queueElements.length) - _nextQueueIndex;
    }
    /**
     * Retrieves the length of the queue, including
     * both pending and canonical transactions.
     * @return Length of the queue.
     */
    function getQueueLength() public view returns (uint40) {
        return uint40(queueElements.length);
    }
    /**
     * Adds a transaction to the queue.
     * @param _target Target L2 contract to send the transaction to.
     * @param _gasLimit Gas limit for the enqueued L2 transaction.
     * @param _data Transaction data.
     */
    function enqueue(
        address _target,
        uint256 _gasLimit,
        bytes memory _data
    ) external {
        require(
            _data.length <= MAX_ROLLUP_TX_SIZE,
            "Transaction data size exceeds maximum for rollup transaction."
        );
        require(
            _gasLimit <= maxTransactionGasLimit,
            "Transaction gas limit exceeds maximum for rollup transaction."
        );
        require(_gasLimit >= MIN_ROLLUP_TX_GAS, "Transaction gas limit too low to enqueue.");
        // Transactions submitted to the queue lack a method for paying gas fees to the Sequencer.
        // So we need to prevent spam attacks by ensuring that the cost of enqueueing a transaction
        // from L1 to L2 is not underpriced. For transaction with a high L2 gas limit, we do this by
        // burning some extra gas on L1. Of course there is also some intrinsic cost to enqueueing a
        // transaction, so we want to make sure not to over-charge (by burning too much L1 gas).
        // Therefore, we define 'enqueueL2GasPrepaid' as the L2 gas limit above which we must burn
        // additional gas on L1. This threshold is the product of two inputs:
        // 1. enqueueGasCost: the base cost of calling this function.
        // 2. l2GasDiscountDivisor: the ratio between the cost of gas on L1 and L2. This is a
        //    positive integer, meaning we assume L2 gas is always less costly.
        // The calculation below for gasToConsume can be seen as converting the difference (between
        // the specified L2 gas limit and the prepaid L2 gas limit) to an L1 gas amount.
        if (_gasLimit > enqueueL2GasPrepaid) {
            uint256 gasToConsume = (_gasLimit - enqueueL2GasPrepaid) / l2GasDiscountDivisor;
            uint256 startingGas = gasleft();
            // Although this check is not necessary (burn below will run out of gas if not true), it
            // gives the user an explicit reason as to why the enqueue attempt failed.
            require(startingGas > gasToConsume, "Insufficient gas for L2 rate limiting burn.");
            uint256 i;
            while (startingGas - gasleft() < gasToConsume) {
                i++;
            }
        }
        // Apply an aliasing unless msg.sender == tx.origin. This prevents an attack in which a
        // contract on L1 has the same address as a contract on L2 but doesn't have the same code.
        // We can safely ignore this for EOAs because they're guaranteed to have the same "code"
        // (i.e. no code at all). This also makes it possible for users to interact with contracts
        // on L2 even when the Sequencer is down.
        address sender;
        if (msg.sender == tx.origin) {
            sender = msg.sender;
        } else {
            sender = AddressAliasHelper.applyL1ToL2Alias(msg.sender);
        }
        bytes32 transactionHash = keccak256(abi.encode(sender, _target, _gasLimit, _data));
        queueElements.push(
            Lib_OVMCodec.QueueElement({
                transactionHash: transactionHash,
                timestamp: uint40(block.timestamp),
                blockNumber: uint40(block.number)
            })
        );
        uint256 queueIndex = queueElements.length - 1;
        emit TransactionEnqueued(sender, _target, _gasLimit, _data, queueIndex, block.timestamp);
    }
    /**
     * Allows the sequencer to append a batch of transactions.
     * @dev This function uses a custom encoding scheme for efficiency reasons.
     * .param _shouldStartAtElement Specific batch we expect to start appending to.
     * .param _totalElementsToAppend Total number of batch elements we expect to append.
     * .param _contexts Array of batch contexts.
     * .param _transactionDataFields Array of raw transaction data.
     */
    function appendSequencerBatch() external {
        uint40 shouldStartAtElement;
        uint24 totalElementsToAppend;
        uint24 numContexts;
        assembly {
            shouldStartAtElement := shr(216, calldataload(4))
            totalElementsToAppend := shr(232, calldataload(9))
            numContexts := shr(232, calldataload(12))
        }
        require(
            shouldStartAtElement == getTotalElements(),
            "Actual batch start index does not match expected start index."
        );
        require(
            msg.sender == resolve("OVM_Sequencer"),
            "Function can only be called by the Sequencer."
        );
        uint40 nextTransactionPtr = uint40(
            BATCH_CONTEXT_START_POS + BATCH_CONTEXT_SIZE * numContexts
        );
        require(msg.data.length >= nextTransactionPtr, "Not enough BatchContexts provided.");
        // Counter for number of sequencer transactions appended so far.
        uint32 numSequencerTransactions = 0;
        // Cache the _nextQueueIndex storage variable to a temporary stack variable.
        // This is safe as long as nothing reads or writes to the storage variable
        // until it is updated by the temp variable.
        uint40 nextQueueIndex = _nextQueueIndex;
        BatchContext memory curContext;
        for (uint32 i = 0; i < numContexts; i++) {
            BatchContext memory nextContext = _getBatchContext(i);
            // Now we can update our current context.
            curContext = nextContext;
            // Process sequencer transactions first.
            numSequencerTransactions += uint32(curContext.numSequencedTransactions);
            // Now process any subsequent queue transactions.
            nextQueueIndex += uint40(curContext.numSubsequentQueueTransactions);
        }
        require(
            nextQueueIndex <= queueElements.length,
            "Attempted to append more elements than are available in the queue."
        );
        // Generate the required metadata that we need to append this batch
        uint40 numQueuedTransactions = totalElementsToAppend - numSequencerTransactions;
        uint40 blockTimestamp;
        uint40 blockNumber;
        if (curContext.numSubsequentQueueTransactions == 0) {
            // The last element is a sequencer tx, therefore pull timestamp and block number from
            // the last context.
            blockTimestamp = uint40(curContext.timestamp);
            blockNumber = uint40(curContext.blockNumber);
        } else {
            // The last element is a queue tx, therefore pull timestamp and block number from the
            // queue element.
            // curContext.numSubsequentQueueTransactions > 0 which means that we've processed at
            // least one queue element. We increment nextQueueIndex after processing each queue
            // element, so the index of the last element we processed is nextQueueIndex - 1.
            Lib_OVMCodec.QueueElement memory lastElement = queueElements[nextQueueIndex - 1];
            blockTimestamp = lastElement.timestamp;
            blockNumber = lastElement.blockNumber;
        }
        // Cache the previous blockhash to ensure all transaction data can be retrieved efficiently.
        _appendBatch(
            blockhash(block.number - 1),
            totalElementsToAppend,
            numQueuedTransactions,
            blockTimestamp,
            blockNumber
        );
        emit SequencerBatchAppended(
            nextQueueIndex - numQueuedTransactions,
            numQueuedTransactions,
            getTotalElements()
        );
        // Update the _nextQueueIndex storage variable.
        _nextQueueIndex = nextQueueIndex;
    }
    /**********************
     * Internal Functions *
     **********************/
    /**
     * Returns the BatchContext located at a particular index.
     * @param _index The index of the BatchContext
     * @return The BatchContext at the specified index.
     */
    function _getBatchContext(uint256 _index) internal pure returns (BatchContext memory) {
        uint256 contextPtr = 15 + _index * BATCH_CONTEXT_SIZE;
        uint256 numSequencedTransactions;
        uint256 numSubsequentQueueTransactions;
        uint256 ctxTimestamp;
        uint256 ctxBlockNumber;
        assembly {
            numSequencedTransactions := shr(232, calldataload(contextPtr))
            numSubsequentQueueTransactions := shr(232, calldataload(add(contextPtr, 3)))
            ctxTimestamp := shr(216, calldataload(add(contextPtr, 6)))
            ctxBlockNumber := shr(216, calldataload(add(contextPtr, 11)))
        }
        return
            BatchContext({
                numSequencedTransactions: numSequencedTransactions,
                numSubsequentQueueTransactions: numSubsequentQueueTransactions,
                timestamp: ctxTimestamp,
                blockNumber: ctxBlockNumber
            });
    }
    /**
     * Parses the batch context from the extra data.
     * @return Total number of elements submitted.
     * @return Index of the next queue element.
     */
    function _getBatchExtraData()
        internal
        view
        returns (
            uint40,
            uint40,
            uint40,
            uint40
        )
    {
        bytes27 extraData = batches().getGlobalMetadata();
        uint40 totalElements;
        uint40 nextQueueIndex;
        uint40 lastTimestamp;
        uint40 lastBlockNumber;
        // solhint-disable max-line-length
        assembly {
            extraData := shr(40, extraData)
            totalElements := and(
                extraData,
                0x000000000000000000000000000000000000000000000000000000FFFFFFFFFF
            )
            nextQueueIndex := shr(
                40,
                and(extraData, 0x00000000000000000000000000000000000000000000FFFFFFFFFF0000000000)
            )
            lastTimestamp := shr(
                80,
                and(extraData, 0x0000000000000000000000000000000000FFFFFFFFFF00000000000000000000)
            )
            lastBlockNumber := shr(
                120,
                and(extraData, 0x000000000000000000000000FFFFFFFFFF000000000000000000000000000000)
            )
        }
        // solhint-enable max-line-length
        return (totalElements, nextQueueIndex, lastTimestamp, lastBlockNumber);
    }
    /**
     * Encodes the batch context for the extra data.
     * @param _totalElements Total number of elements submitted.
     * @param _nextQueueIdx Index of the next queue element.
     * @param _timestamp Timestamp for the last batch.
     * @param _blockNumber Block number of the last batch.
     * @return Encoded batch context.
     */
    function _makeBatchExtraData(
        uint40 _totalElements,
        uint40 _nextQueueIdx,
        uint40 _timestamp,
        uint40 _blockNumber
    ) internal pure returns (bytes27) {
        bytes27 extraData;
        assembly {
            extraData := _totalElements
            extraData := or(extraData, shl(40, _nextQueueIdx))
            extraData := or(extraData, shl(80, _timestamp))
            extraData := or(extraData, shl(120, _blockNumber))
            extraData := shl(40, extraData)
        }
        return extraData;
    }
    /**
     * Inserts a batch into the chain of batches.
     * @param _transactionRoot Root of the transaction tree for this batch.
     * @param _batchSize Number of elements in the batch.
     * @param _numQueuedTransactions Number of queue transactions in the batch.
     * @param _timestamp The latest batch timestamp.
     * @param _blockNumber The latest batch blockNumber.
     */
    function _appendBatch(
        bytes32 _transactionRoot,
        uint256 _batchSize,
        uint256 _numQueuedTransactions,
        uint40 _timestamp,
        uint40 _blockNumber
    ) internal {
        IChainStorageContainer batchesRef = batches();
        (uint40 totalElements, uint40 nextQueueIndex, , ) = _getBatchExtraData();
        Lib_OVMCodec.ChainBatchHeader memory header = Lib_OVMCodec.ChainBatchHeader({
            batchIndex: batchesRef.length(),
            batchRoot: _transactionRoot,
            batchSize: _batchSize,
            prevTotalElements: totalElements,
            extraData: hex""
        });
        emit TransactionBatchAppended(
            header.batchIndex,
            header.batchRoot,
            header.batchSize,
            header.prevTotalElements,
            header.extraData
        );
        bytes32 batchHeaderHash = Lib_OVMCodec.hashBatchHeader(header);
        bytes27 latestBatchContext = _makeBatchExtraData(
            totalElements + uint40(header.batchSize),
            nextQueueIndex + uint40(_numQueuedTransactions),
            _timestamp,
            _blockNumber
        );
        batchesRef.push(batchHeaderHash, latestBatchContext);
    }
}
// SPDX-License-Identifier: Apache-2.0
/*
 * Copyright 2019-2021, Offchain Labs, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
pragma solidity ^0.8.7;
library AddressAliasHelper {
    uint160 constant offset = uint160(0x1111000000000000000000000000000000001111);
    /// @notice Utility function that converts the address in the L1 that submitted a tx to
    /// the inbox to the msg.sender viewed in the L2
    /// @param l1Address the address in the L1 that triggered the tx to L2
    /// @return l2Address L2 address as viewed in msg.sender
    function applyL1ToL2Alias(address l1Address) internal pure returns (address l2Address) {
        unchecked {
            l2Address = address(uint160(l1Address) + offset);
        }
    }
    /// @notice Utility function that converts the msg.sender viewed in the L2 to the
    /// address in the L1 that submitted a tx to the inbox
    /// @param l2Address L2 address as viewed in msg.sender
    /// @return l1Address the address in the L1 that triggered the tx to L2
    function undoL1ToL2Alias(address l2Address) internal pure returns (address l1Address) {
        unchecked {
            l1Address = address(uint160(l2Address) - offset);
        }
    }
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;
/* Library Imports */
import { Lib_RLPReader } from "../rlp/Lib_RLPReader.sol";
import { Lib_RLPWriter } from "../rlp/Lib_RLPWriter.sol";
import { Lib_BytesUtils } from "../utils/Lib_BytesUtils.sol";
import { Lib_Bytes32Utils } from "../utils/Lib_Bytes32Utils.sol";
/**
 * @title Lib_OVMCodec
 */
library Lib_OVMCodec {
    /*********
     * Enums *
     *********/
    enum QueueOrigin {
        SEQUENCER_QUEUE,
        L1TOL2_QUEUE
    }
    /***********
     * Structs *
     ***********/
    struct EVMAccount {
        uint256 nonce;
        uint256 balance;
        bytes32 storageRoot;
        bytes32 codeHash;
    }
    struct ChainBatchHeader {
        uint256 batchIndex;
        bytes32 batchRoot;
        uint256 batchSize;
        uint256 prevTotalElements;
        bytes extraData;
    }
    struct ChainInclusionProof {
        uint256 index;
        bytes32[] siblings;
    }
    struct Transaction {
        uint256 timestamp;
        uint256 blockNumber;
        QueueOrigin l1QueueOrigin;
        address l1TxOrigin;
        address entrypoint;
        uint256 gasLimit;
        bytes data;
    }
    struct TransactionChainElement {
        bool isSequenced;
        uint256 queueIndex; // QUEUED TX ONLY
        uint256 timestamp; // SEQUENCER TX ONLY
        uint256 blockNumber; // SEQUENCER TX ONLY
        bytes txData; // SEQUENCER TX ONLY
    }
    struct QueueElement {
        bytes32 transactionHash;
        uint40 timestamp;
        uint40 blockNumber;
    }
    /**********************
     * Internal Functions *
     **********************/
    /**
     * Encodes a standard OVM transaction.
     * @param _transaction OVM transaction to encode.
     * @return Encoded transaction bytes.
     */
    function encodeTransaction(Transaction memory _transaction)
        internal
        pure
        returns (bytes memory)
    {
        return
            abi.encodePacked(
                _transaction.timestamp,
                _transaction.blockNumber,
                _transaction.l1QueueOrigin,
                _transaction.l1TxOrigin,
                _transaction.entrypoint,
                _transaction.gasLimit,
                _transaction.data
            );
    }
    /**
     * Hashes a standard OVM transaction.
     * @param _transaction OVM transaction to encode.
     * @return Hashed transaction
     */
    function hashTransaction(Transaction memory _transaction) internal pure returns (bytes32) {
        return keccak256(encodeTransaction(_transaction));
    }
    /**
     * @notice Decodes an RLP-encoded account state into a useful struct.
     * @param _encoded RLP-encoded account state.
     * @return Account state struct.
     */
    function decodeEVMAccount(bytes memory _encoded) internal pure returns (EVMAccount memory) {
        Lib_RLPReader.RLPItem[] memory accountState = Lib_RLPReader.readList(_encoded);
        return
            EVMAccount({
                nonce: Lib_RLPReader.readUint256(accountState[0]),
                balance: Lib_RLPReader.readUint256(accountState[1]),
                storageRoot: Lib_RLPReader.readBytes32(accountState[2]),
                codeHash: Lib_RLPReader.readBytes32(accountState[3])
            });
    }
    /**
     * Calculates a hash for a given batch header.
     * @param _batchHeader Header to hash.
     * @return Hash of the header.
     */
    function hashBatchHeader(Lib_OVMCodec.ChainBatchHeader memory _batchHeader)
        internal
        pure
        returns (bytes32)
    {
        return
            keccak256(
                abi.encode(
                    _batchHeader.batchRoot,
                    _batchHeader.batchSize,
                    _batchHeader.prevTotalElements,
                    _batchHeader.extraData
                )
            );
    }
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;
/* Library Imports */
import { Lib_AddressManager } from "./Lib_AddressManager.sol";
/**
 * @title Lib_AddressResolver
 */
abstract contract Lib_AddressResolver {
    /*************
     * Variables *
     *************/
    Lib_AddressManager public libAddressManager;
    /***************
     * Constructor *
     ***************/
    /**
     * @param _libAddressManager Address of the Lib_AddressManager.
     */
    constructor(address _libAddressManager) {
        libAddressManager = Lib_AddressManager(_libAddressManager);
    }
    /********************
     * Public Functions *
     ********************/
    /**
     * Resolves the address associated with a given name.
     * @param _name Name to resolve an address for.
     * @return Address associated with the given name.
     */
    function resolve(string memory _name) public view returns (address) {
        return libAddressManager.getAddress(_name);
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >0.5.0 <0.9.0;
/* Library Imports */
import { Lib_OVMCodec } from "../../libraries/codec/Lib_OVMCodec.sol";
/* Interface Imports */
import { IChainStorageContainer } from "./IChainStorageContainer.sol";
/**
 * @title ICanonicalTransactionChain
 */
interface ICanonicalTransactionChain {
    /**********
     * Events *
     **********/
    event L2GasParamsUpdated(
        uint256 l2GasDiscountDivisor,
        uint256 enqueueGasCost,
        uint256 enqueueL2GasPrepaid
    );
    event TransactionEnqueued(
        address indexed _l1TxOrigin,
        address indexed _target,
        uint256 _gasLimit,
        bytes _data,
        uint256 indexed _queueIndex,
        uint256 _timestamp
    );
    event QueueBatchAppended(
        uint256 _startingQueueIndex,
        uint256 _numQueueElements,
        uint256 _totalElements
    );
    event SequencerBatchAppended(
        uint256 _startingQueueIndex,
        uint256 _numQueueElements,
        uint256 _totalElements
    );
    event TransactionBatchAppended(
        uint256 indexed _batchIndex,
        bytes32 _batchRoot,
        uint256 _batchSize,
        uint256 _prevTotalElements,
        bytes _extraData
    );
    /***********
     * Structs *
     ***********/
    struct BatchContext {
        uint256 numSequencedTransactions;
        uint256 numSubsequentQueueTransactions;
        uint256 timestamp;
        uint256 blockNumber;
    }
    /*******************************
     * Authorized Setter Functions *
     *******************************/
    /**
     * Allows the Burn Admin to update the parameters which determine the amount of gas to burn.
     * The value of enqueueL2GasPrepaid is immediately updated as well.
     */
    function setGasParams(uint256 _l2GasDiscountDivisor, uint256 _enqueueGasCost) external;
    /********************
     * Public Functions *
     ********************/
    /**
     * Accesses the batch storage container.
     * @return Reference to the batch storage container.
     */
    function batches() external view returns (IChainStorageContainer);
    /**
     * Retrieves the total number of elements submitted.
     * @return _totalElements Total submitted elements.
     */
    function getTotalElements() external view returns (uint256 _totalElements);
    /**
     * Retrieves the total number of batches submitted.
     * @return _totalBatches Total submitted batches.
     */
    function getTotalBatches() external view returns (uint256 _totalBatches);
    /**
     * Returns the index of the next element to be enqueued.
     * @return Index for the next queue element.
     */
    function getNextQueueIndex() external view returns (uint40);
    /**
     * Gets the queue element at a particular index.
     * @param _index Index of the queue element to access.
     * @return _element Queue element at the given index.
     */
    function getQueueElement(uint256 _index)
        external
        view
        returns (Lib_OVMCodec.QueueElement memory _element);
    /**
     * Returns the timestamp of the last transaction.
     * @return Timestamp for the last transaction.
     */
    function getLastTimestamp() external view returns (uint40);
    /**
     * Returns the blocknumber of the last transaction.
     * @return Blocknumber for the last transaction.
     */
    function getLastBlockNumber() external view returns (uint40);
    /**
     * Get the number of queue elements which have not yet been included.
     * @return Number of pending queue elements.
     */
    function getNumPendingQueueElements() external view returns (uint40);
    /**
     * Retrieves the length of the queue, including
     * both pending and canonical transactions.
     * @return Length of the queue.
     */
    function getQueueLength() external view returns (uint40);
    /**
     * Adds a transaction to the queue.
     * @param _target Target contract to send the transaction to.
     * @param _gasLimit Gas limit for the given transaction.
     * @param _data Transaction data.
     */
    function enqueue(
        address _target,
        uint256 _gasLimit,
        bytes memory _data
    ) external;
    /**
     * Allows the sequencer to append a batch of transactions.
     * @dev This function uses a custom encoding scheme for efficiency reasons.
     * .param _shouldStartAtElement Specific batch we expect to start appending to.
     * .param _totalElementsToAppend Total number of batch elements we expect to append.
     * .param _contexts Array of batch contexts.
     * .param _transactionDataFields Array of raw transaction data.
     */
    function appendSequencerBatch(
        // uint40 _shouldStartAtElement,
        // uint24 _totalElementsToAppend,
        // BatchContext[] _contexts,
        // bytes[] _transactionDataFields
    ) external;
}
// SPDX-License-Identifier: MIT
pragma solidity >0.5.0 <0.9.0;
/**
 * @title IChainStorageContainer
 */
interface IChainStorageContainer {
    /********************
     * Public Functions *
     ********************/
    /**
     * Sets the container's global metadata field. We're using `bytes27` here because we use five
     * bytes to maintain the length of the underlying data structure, meaning we have an extra
     * 27 bytes to store arbitrary data.
     * @param _globalMetadata New global metadata to set.
     */
    function setGlobalMetadata(bytes27 _globalMetadata) external;
    /**
     * Retrieves the container's global metadata field.
     * @return Container global metadata field.
     */
    function getGlobalMetadata() external view returns (bytes27);
    /**
     * Retrieves the number of objects stored in the container.
     * @return Number of objects in the container.
     */
    function length() external view returns (uint256);
    /**
     * Pushes an object into the container.
     * @param _object A 32 byte value to insert into the container.
     */
    function push(bytes32 _object) external;
    /**
     * Pushes an object into the container. Function allows setting the global metadata since
     * we'll need to touch the "length" storage slot anyway, which also contains the global
     * metadata (it's an optimization).
     * @param _object A 32 byte value to insert into the container.
     * @param _globalMetadata New global metadata for the container.
     */
    function push(bytes32 _object, bytes27 _globalMetadata) external;
    /**
     * Retrieves an object from the container.
     * @param _index Index of the particular object to access.
     * @return 32 byte object value.
     */
    function get(uint256 _index) external view returns (bytes32);
    /**
     * Removes all objects after and including a given index.
     * @param _index Object index to delete from.
     */
    function deleteElementsAfterInclusive(uint256 _index) external;
    /**
     * Removes all objects after and including a given index. Also allows setting the global
     * metadata field.
     * @param _index Object index to delete from.
     * @param _globalMetadata New global metadata for the container.
     */
    function deleteElementsAfterInclusive(uint256 _index, bytes27 _globalMetadata) external;
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;
/**
 * @title Lib_RLPReader
 * @dev Adapted from "RLPReader" by Hamdi Allam ([email protected]).
 */
library Lib_RLPReader {
    /*************
     * Constants *
     *************/
    uint256 internal constant MAX_LIST_LENGTH = 32;
    /*********
     * Enums *
     *********/
    enum RLPItemType {
        DATA_ITEM,
        LIST_ITEM
    }
    /***********
     * Structs *
     ***********/
    struct RLPItem {
        uint256 length;
        uint256 ptr;
    }
    /**********************
     * Internal Functions *
     **********************/
    /**
     * Converts bytes to a reference to memory position and length.
     * @param _in Input bytes to convert.
     * @return Output memory reference.
     */
    function toRLPItem(bytes memory _in) internal pure returns (RLPItem memory) {
        uint256 ptr;
        assembly {
            ptr := add(_in, 32)
        }
        return RLPItem({ length: _in.length, ptr: ptr });
    }
    /**
     * Reads an RLP list value into a list of RLP items.
     * @param _in RLP list value.
     * @return Decoded RLP list items.
     */
    function readList(RLPItem memory _in) internal pure returns (RLPItem[] memory) {
        (uint256 listOffset, , RLPItemType itemType) = _decodeLength(_in);
        require(itemType == RLPItemType.LIST_ITEM, "Invalid RLP list value.");
        // Solidity in-memory arrays can't be increased in size, but *can* be decreased in size by
        // writing to the length. Since we can't know the number of RLP items without looping over
        // the entire input, we'd have to loop twice to accurately size this array. It's easier to
        // simply set a reasonable maximum list length and decrease the size before we finish.
        RLPItem[] memory out = new RLPItem[](MAX_LIST_LENGTH);
        uint256 itemCount = 0;
        uint256 offset = listOffset;
        while (offset < _in.length) {
            require(itemCount < MAX_LIST_LENGTH, "Provided RLP list exceeds max list length.");
            (uint256 itemOffset, uint256 itemLength, ) = _decodeLength(
                RLPItem({ length: _in.length - offset, ptr: _in.ptr + offset })
            );
            out[itemCount] = RLPItem({ length: itemLength + itemOffset, ptr: _in.ptr + offset });
            itemCount += 1;
            offset += itemOffset + itemLength;
        }
        // Decrease the array size to match the actual item count.
        assembly {
            mstore(out, itemCount)
        }
        return out;
    }
    /**
     * Reads an RLP list value into a list of RLP items.
     * @param _in RLP list value.
     * @return Decoded RLP list items.
     */
    function readList(bytes memory _in) internal pure returns (RLPItem[] memory) {
        return readList(toRLPItem(_in));
    }
    /**
     * Reads an RLP bytes value into bytes.
     * @param _in RLP bytes value.
     * @return Decoded bytes.
     */
    function readBytes(RLPItem memory _in) internal pure returns (bytes memory) {
        (uint256 itemOffset, uint256 itemLength, RLPItemType itemType) = _decodeLength(_in);
        require(itemType == RLPItemType.DATA_ITEM, "Invalid RLP bytes value.");
        return _copy(_in.ptr, itemOffset, itemLength);
    }
    /**
     * Reads an RLP bytes value into bytes.
     * @param _in RLP bytes value.
     * @return Decoded bytes.
     */
    function readBytes(bytes memory _in) internal pure returns (bytes memory) {
        return readBytes(toRLPItem(_in));
    }
    /**
     * Reads an RLP string value into a string.
     * @param _in RLP string value.
     * @return Decoded string.
     */
    function readString(RLPItem memory _in) internal pure returns (string memory) {
        return string(readBytes(_in));
    }
    /**
     * Reads an RLP string value into a string.
     * @param _in RLP string value.
     * @return Decoded string.
     */
    function readString(bytes memory _in) internal pure returns (string memory) {
        return readString(toRLPItem(_in));
    }
    /**
     * Reads an RLP bytes32 value into a bytes32.
     * @param _in RLP bytes32 value.
     * @return Decoded bytes32.
     */
    function readBytes32(RLPItem memory _in) internal pure returns (bytes32) {
        require(_in.length <= 33, "Invalid RLP bytes32 value.");
        (uint256 itemOffset, uint256 itemLength, RLPItemType itemType) = _decodeLength(_in);
        require(itemType == RLPItemType.DATA_ITEM, "Invalid RLP bytes32 value.");
        uint256 ptr = _in.ptr + itemOffset;
        bytes32 out;
        assembly {
            out := mload(ptr)
            // Shift the bytes over to match the item size.
            if lt(itemLength, 32) {
                out := div(out, exp(256, sub(32, itemLength)))
            }
        }
        return out;
    }
    /**
     * Reads an RLP bytes32 value into a bytes32.
     * @param _in RLP bytes32 value.
     * @return Decoded bytes32.
     */
    function readBytes32(bytes memory _in) internal pure returns (bytes32) {
        return readBytes32(toRLPItem(_in));
    }
    /**
     * Reads an RLP uint256 value into a uint256.
     * @param _in RLP uint256 value.
     * @return Decoded uint256.
     */
    function readUint256(RLPItem memory _in) internal pure returns (uint256) {
        return uint256(readBytes32(_in));
    }
    /**
     * Reads an RLP uint256 value into a uint256.
     * @param _in RLP uint256 value.
     * @return Decoded uint256.
     */
    function readUint256(bytes memory _in) internal pure returns (uint256) {
        return readUint256(toRLPItem(_in));
    }
    /**
     * Reads an RLP bool value into a bool.
     * @param _in RLP bool value.
     * @return Decoded bool.
     */
    function readBool(RLPItem memory _in) internal pure returns (bool) {
        require(_in.length == 1, "Invalid RLP boolean value.");
        uint256 ptr = _in.ptr;
        uint256 out;
        assembly {
            out := byte(0, mload(ptr))
        }
        require(out == 0 || out == 1, "Lib_RLPReader: Invalid RLP boolean value, must be 0 or 1");
        return out != 0;
    }
    /**
     * Reads an RLP bool value into a bool.
     * @param _in RLP bool value.
     * @return Decoded bool.
     */
    function readBool(bytes memory _in) internal pure returns (bool) {
        return readBool(toRLPItem(_in));
    }
    /**
     * Reads an RLP address value into a address.
     * @param _in RLP address value.
     * @return Decoded address.
     */
    function readAddress(RLPItem memory _in) internal pure returns (address) {
        if (_in.length == 1) {
            return address(0);
        }
        require(_in.length == 21, "Invalid RLP address value.");
        return address(uint160(readUint256(_in)));
    }
    /**
     * Reads an RLP address value into a address.
     * @param _in RLP address value.
     * @return Decoded address.
     */
    function readAddress(bytes memory _in) internal pure returns (address) {
        return readAddress(toRLPItem(_in));
    }
    /**
     * Reads the raw bytes of an RLP item.
     * @param _in RLP item to read.
     * @return Raw RLP bytes.
     */
    function readRawBytes(RLPItem memory _in) internal pure returns (bytes memory) {
        return _copy(_in);
    }
    /*********************
     * Private Functions *
     *********************/
    /**
     * Decodes the length of an RLP item.
     * @param _in RLP item to decode.
     * @return Offset of the encoded data.
     * @return Length of the encoded data.
     * @return RLP item type (LIST_ITEM or DATA_ITEM).
     */
    function _decodeLength(RLPItem memory _in)
        private
        pure
        returns (
            uint256,
            uint256,
            RLPItemType
        )
    {
        require(_in.length > 0, "RLP item cannot be null.");
        uint256 ptr = _in.ptr;
        uint256 prefix;
        assembly {
            prefix := byte(0, mload(ptr))
        }
        if (prefix <= 0x7f) {
            // Single byte.
            return (0, 1, RLPItemType.DATA_ITEM);
        } else if (prefix <= 0xb7) {
            // Short string.
            uint256 strLen = prefix - 0x80;
            require(_in.length > strLen, "Invalid RLP short string.");
            return (1, strLen, RLPItemType.DATA_ITEM);
        } else if (prefix <= 0xbf) {
            // Long string.
            uint256 lenOfStrLen = prefix - 0xb7;
            require(_in.length > lenOfStrLen, "Invalid RLP long string length.");
            uint256 strLen;
            assembly {
                // Pick out the string length.
                strLen := div(mload(add(ptr, 1)), exp(256, sub(32, lenOfStrLen)))
            }
            require(_in.length > lenOfStrLen + strLen, "Invalid RLP long string.");
            return (1 + lenOfStrLen, strLen, RLPItemType.DATA_ITEM);
        } else if (prefix <= 0xf7) {
            // Short list.
            uint256 listLen = prefix - 0xc0;
            require(_in.length > listLen, "Invalid RLP short list.");
            return (1, listLen, RLPItemType.LIST_ITEM);
        } else {
            // Long list.
            uint256 lenOfListLen = prefix - 0xf7;
            require(_in.length > lenOfListLen, "Invalid RLP long list length.");
            uint256 listLen;
            assembly {
                // Pick out the list length.
                listLen := div(mload(add(ptr, 1)), exp(256, sub(32, lenOfListLen)))
            }
            require(_in.length > lenOfListLen + listLen, "Invalid RLP long list.");
            return (1 + lenOfListLen, listLen, RLPItemType.LIST_ITEM);
        }
    }
    /**
     * Copies the bytes from a memory location.
     * @param _src Pointer to the location to read from.
     * @param _offset Offset to start reading from.
     * @param _length Number of bytes to read.
     * @return Copied bytes.
     */
    function _copy(
        uint256 _src,
        uint256 _offset,
        uint256 _length
    ) private pure returns (bytes memory) {
        bytes memory out = new bytes(_length);
        if (out.length == 0) {
            return out;
        }
        uint256 src = _src + _offset;
        uint256 dest;
        assembly {
            dest := add(out, 32)
        }
        // Copy over as many complete words as we can.
        for (uint256 i = 0; i < _length / 32; i++) {
            assembly {
                mstore(dest, mload(src))
            }
            src += 32;
            dest += 32;
        }
        // Pick out the remaining bytes.
        uint256 mask;
        unchecked {
            mask = 256**(32 - (_length % 32)) - 1;
        }
        assembly {
            mstore(dest, or(and(mload(src), not(mask)), and(mload(dest), mask)))
        }
        return out;
    }
    /**
     * Copies an RLP item into bytes.
     * @param _in RLP item to copy.
     * @return Copied bytes.
     */
    function _copy(RLPItem memory _in) private pure returns (bytes memory) {
        return _copy(_in.ptr, 0, _in.length);
    }
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;
/**
 * @title Lib_RLPWriter
 * @author Bakaoh (with modifications)
 */
library Lib_RLPWriter {
    /**********************
     * Internal Functions *
     **********************/
    /**
     * RLP encodes a byte string.
     * @param _in The byte string to encode.
     * @return The RLP encoded string in bytes.
     */
    function writeBytes(bytes memory _in) internal pure returns (bytes memory) {
        bytes memory encoded;
        if (_in.length == 1 && uint8(_in[0]) < 128) {
            encoded = _in;
        } else {
            encoded = abi.encodePacked(_writeLength(_in.length, 128), _in);
        }
        return encoded;
    }
    /**
     * RLP encodes a list of RLP encoded byte byte strings.
     * @param _in The list of RLP encoded byte strings.
     * @return The RLP encoded list of items in bytes.
     */
    function writeList(bytes[] memory _in) internal pure returns (bytes memory) {
        bytes memory list = _flatten(_in);
        return abi.encodePacked(_writeLength(list.length, 192), list);
    }
    /**
     * RLP encodes a string.
     * @param _in The string to encode.
     * @return The RLP encoded string in bytes.
     */
    function writeString(string memory _in) internal pure returns (bytes memory) {
        return writeBytes(bytes(_in));
    }
    /**
     * RLP encodes an address.
     * @param _in The address to encode.
     * @return The RLP encoded address in bytes.
     */
    function writeAddress(address _in) internal pure returns (bytes memory) {
        return writeBytes(abi.encodePacked(_in));
    }
    /**
     * RLP encodes a uint.
     * @param _in The uint256 to encode.
     * @return The RLP encoded uint256 in bytes.
     */
    function writeUint(uint256 _in) internal pure returns (bytes memory) {
        return writeBytes(_toBinary(_in));
    }
    /**
     * RLP encodes a bool.
     * @param _in The bool to encode.
     * @return The RLP encoded bool in bytes.
     */
    function writeBool(bool _in) internal pure returns (bytes memory) {
        bytes memory encoded = new bytes(1);
        encoded[0] = (_in ? bytes1(0x01) : bytes1(0x80));
        return encoded;
    }
    /*********************
     * Private Functions *
     *********************/
    /**
     * Encode the first byte, followed by the `len` in binary form if `length` is more than 55.
     * @param _len The length of the string or the payload.
     * @param _offset 128 if item is string, 192 if item is list.
     * @return RLP encoded bytes.
     */
    function _writeLength(uint256 _len, uint256 _offset) private pure returns (bytes memory) {
        bytes memory encoded;
        if (_len < 56) {
            encoded = new bytes(1);
            encoded[0] = bytes1(uint8(_len) + uint8(_offset));
        } else {
            uint256 lenLen;
            uint256 i = 1;
            while (_len / i != 0) {
                lenLen++;
                i *= 256;
            }
            encoded = new bytes(lenLen + 1);
            encoded[0] = bytes1(uint8(lenLen) + uint8(_offset) + 55);
            for (i = 1; i <= lenLen; i++) {
                encoded[i] = bytes1(uint8((_len / (256**(lenLen - i))) % 256));
            }
        }
        return encoded;
    }
    /**
     * Encode integer in big endian binary form with no leading zeroes.
     * @notice TODO: This should be optimized with assembly to save gas costs.
     * @param _x The integer to encode.
     * @return RLP encoded bytes.
     */
    function _toBinary(uint256 _x) private pure returns (bytes memory) {
        bytes memory b = abi.encodePacked(_x);
        uint256 i = 0;
        for (; i < 32; i++) {
            if (b[i] != 0) {
                break;
            }
        }
        bytes memory res = new bytes(32 - i);
        for (uint256 j = 0; j < res.length; j++) {
            res[j] = b[i++];
        }
        return res;
    }
    /**
     * Copies a piece of memory to another location.
     * @notice From: https://github.com/Arachnid/solidity-stringutils/blob/master/src/strings.sol.
     * @param _dest Destination location.
     * @param _src Source location.
     * @param _len Length of memory to copy.
     */
    function _memcpy(
        uint256 _dest,
        uint256 _src,
        uint256 _len
    ) private pure {
        uint256 dest = _dest;
        uint256 src = _src;
        uint256 len = _len;
        for (; len >= 32; len -= 32) {
            assembly {
                mstore(dest, mload(src))
            }
            dest += 32;
            src += 32;
        }
        uint256 mask;
        unchecked {
            mask = 256**(32 - len) - 1;
        }
        assembly {
            let srcpart := and(mload(src), not(mask))
            let destpart := and(mload(dest), mask)
            mstore(dest, or(destpart, srcpart))
        }
    }
    /**
     * Flattens a list of byte strings into one byte string.
     * @notice From: https://github.com/sammayo/solidity-rlp-encoder/blob/master/RLPEncode.sol.
     * @param _list List of byte strings to flatten.
     * @return The flattened byte string.
     */
    function _flatten(bytes[] memory _list) private pure returns (bytes memory) {
        if (_list.length == 0) {
            return new bytes(0);
        }
        uint256 len;
        uint256 i = 0;
        for (; i < _list.length; i++) {
            len += _list[i].length;
        }
        bytes memory flattened = new bytes(len);
        uint256 flattenedPtr;
        assembly {
            flattenedPtr := add(flattened, 0x20)
        }
        for (i = 0; i < _list.length; i++) {
            bytes memory item = _list[i];
            uint256 listPtr;
            assembly {
                listPtr := add(item, 0x20)
            }
            _memcpy(flattenedPtr, listPtr, item.length);
            flattenedPtr += _list[i].length;
        }
        return flattened;
    }
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;
/**
 * @title Lib_BytesUtils
 */
library Lib_BytesUtils {
    /**********************
     * Internal Functions *
     **********************/
    function slice(
        bytes memory _bytes,
        uint256 _start,
        uint256 _length
    ) internal pure returns (bytes memory) {
        require(_length + 31 >= _length, "slice_overflow");
        require(_start + _length >= _start, "slice_overflow");
        require(_bytes.length >= _start + _length, "slice_outOfBounds");
        bytes memory tempBytes;
        assembly {
            switch iszero(_length)
            case 0 {
                // Get a location of some free memory and store it in tempBytes as
                // Solidity does for memory variables.
                tempBytes := mload(0x40)
                // The first word of the slice result is potentially a partial
                // word read from the original array. To read it, we calculate
                // the length of that partial word and start copying that many
                // bytes into the array. The first word we copy will start with
                // data we don't care about, but the last `lengthmod` bytes will
                // land at the beginning of the contents of the new array. When
                // we're done copying, we overwrite the full first word with
                // the actual length of the slice.
                let lengthmod := and(_length, 31)
                // The multiplication in the next line is necessary
                // because when slicing multiples of 32 bytes (lengthmod == 0)
                // the following copy loop was copying the origin's length
                // and then ending prematurely not copying everything it should.
                let mc := add(add(tempBytes, lengthmod), mul(0x20, iszero(lengthmod)))
                let end := add(mc, _length)
                for {
                    // The multiplication in the next line has the same exact purpose
                    // as the one above.
                    let cc := add(add(add(_bytes, lengthmod), mul(0x20, iszero(lengthmod))), _start)
                } lt(mc, end) {
                    mc := add(mc, 0x20)
                    cc := add(cc, 0x20)
                } {
                    mstore(mc, mload(cc))
                }
                mstore(tempBytes, _length)
                //update free-memory pointer
                //allocating the array padded to 32 bytes like the compiler does now
                mstore(0x40, and(add(mc, 31), not(31)))
            }
            //if we want a zero-length slice let's just return a zero-length array
            default {
                tempBytes := mload(0x40)
                //zero out the 32 bytes slice we are about to return
                //we need to do it because Solidity does not garbage collect
                mstore(tempBytes, 0)
                mstore(0x40, add(tempBytes, 0x20))
            }
        }
        return tempBytes;
    }
    function slice(bytes memory _bytes, uint256 _start) internal pure returns (bytes memory) {
        if (_start >= _bytes.length) {
            return bytes("");
        }
        return slice(_bytes, _start, _bytes.length - _start);
    }
    function toBytes32(bytes memory _bytes) internal pure returns (bytes32) {
        if (_bytes.length < 32) {
            bytes32 ret;
            assembly {
                ret := mload(add(_bytes, 32))
            }
            return ret;
        }
        return abi.decode(_bytes, (bytes32)); // will truncate if input length > 32 bytes
    }
    function toUint256(bytes memory _bytes) internal pure returns (uint256) {
        return uint256(toBytes32(_bytes));
    }
    function toNibbles(bytes memory _bytes) internal pure returns (bytes memory) {
        bytes memory nibbles = new bytes(_bytes.length * 2);
        for (uint256 i = 0; i < _bytes.length; i++) {
            nibbles[i * 2] = _bytes[i] >> 4;
            nibbles[i * 2 + 1] = bytes1(uint8(_bytes[i]) % 16);
        }
        return nibbles;
    }
    function fromNibbles(bytes memory _bytes) internal pure returns (bytes memory) {
        bytes memory ret = new bytes(_bytes.length / 2);
        for (uint256 i = 0; i < ret.length; i++) {
            ret[i] = (_bytes[i * 2] << 4) | (_bytes[i * 2 + 1]);
        }
        return ret;
    }
    function equal(bytes memory _bytes, bytes memory _other) internal pure returns (bool) {
        return keccak256(_bytes) == keccak256(_other);
    }
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;
/**
 * @title Lib_Byte32Utils
 */
library Lib_Bytes32Utils {
    /**********************
     * Internal Functions *
     **********************/
    /**
     * Converts a bytes32 value to a boolean. Anything non-zero will be converted to "true."
     * @param _in Input bytes32 value.
     * @return Bytes32 as a boolean.
     */
    function toBool(bytes32 _in) internal pure returns (bool) {
        return _in != 0;
    }
    /**
     * Converts a boolean to a bytes32 value.
     * @param _in Input boolean value.
     * @return Boolean as a bytes32.
     */
    function fromBool(bool _in) internal pure returns (bytes32) {
        return bytes32(uint256(_in ? 1 : 0));
    }
    /**
     * Converts a bytes32 value to an address. Takes the *last* 20 bytes.
     * @param _in Input bytes32 value.
     * @return Bytes32 as an address.
     */
    function toAddress(bytes32 _in) internal pure returns (address) {
        return address(uint160(uint256(_in)));
    }
    /**
     * Converts an address to a bytes32.
     * @param _in Input address value.
     * @return Address as a bytes32.
     */
    function fromAddress(address _in) internal pure returns (bytes32) {
        return bytes32(uint256(uint160(_in)));
    }
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;
/* External Imports */
import { Ownable } from "@openzeppelin/contracts/access/Ownable.sol";
/**
 * @title Lib_AddressManager
 */
contract Lib_AddressManager is Ownable {
    /**********
     * Events *
     **********/
    event AddressSet(string indexed _name, address _newAddress, address _oldAddress);
    /*************
     * Variables *
     *************/
    mapping(bytes32 => address) private addresses;
    /********************
     * Public Functions *
     ********************/
    /**
     * Changes the address associated with a particular name.
     * @param _name String name to associate an address with.
     * @param _address Address to associate with the name.
     */
    function setAddress(string memory _name, address _address) external onlyOwner {
        bytes32 nameHash = _getNameHash(_name);
        address oldAddress = addresses[nameHash];
        addresses[nameHash] = _address;
        emit AddressSet(_name, _address, oldAddress);
    }
    /**
     * Retrieves the address associated with a given name.
     * @param _name Name to retrieve an address for.
     * @return Address associated with the given name.
     */
    function getAddress(string memory _name) external view returns (address) {
        return addresses[_getNameHash(_name)];
    }
    /**********************
     * Internal Functions *
     **********************/
    /**
     * Computes the hash of a name.
     * @param _name Name to compute a hash for.
     * @return Hash of the given name.
     */
    function _getNameHash(string memory _name) internal pure returns (bytes32) {
        return keccak256(abi.encodePacked(_name));
    }
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "../utils/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;
    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _setOwner(_msgSender());
    }
    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }
    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }
    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        _setOwner(address(0));
    }
    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        _setOwner(newOwner);
    }
    function _setOwner(address newOwner) private {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }
    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}

// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
import "../utils/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;
    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }
    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }
    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }
    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }
    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }
    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >0.5.0 <0.8.0;
/* External Imports */
import { Ownable } from "@openzeppelin/contracts/access/Ownable.sol";
/**
 * @title Lib_AddressManager
 */
contract Lib_AddressManager is Ownable {
    /**********
     * Events *
     **********/
    event AddressSet(
        string indexed _name,
        address _newAddress,
        address _oldAddress
    );
    /*************
     * Variables *
     *************/
    mapping (bytes32 => address) private addresses;
    /********************
     * Public Functions *
     ********************/
    /**
     * Changes the address associated with a particular name.
     * @param _name String name to associate an address with.
     * @param _address Address to associate with the name.
     */
    function setAddress(
        string memory _name,
        address _address
    )
        external
        onlyOwner
    {
        bytes32 nameHash = _getNameHash(_name);
        address oldAddress = addresses[nameHash];
        addresses[nameHash] = _address;
        emit AddressSet(
            _name,
            _address,
            oldAddress
        );
    }
    /**
     * Retrieves the address associated with a given name.
     * @param _name Name to retrieve an address for.
     * @return Address associated with the given name.
     */
    function getAddress(
        string memory _name
    )
        external
        view
        returns (
            address
        )
    {
        return addresses[_getNameHash(_name)];
    }
    /**********************
     * Internal Functions *
     **********************/
    /**
     * Computes the hash of a name.
     * @param _name Name to compute a hash for.
     * @return Hash of the given name.
     */
    function _getNameHash(
        string memory _name
    )
        internal
        pure
        returns (
            bytes32
        )
    {
        return keccak256(abi.encodePacked(_name));
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;
/* Library Imports */
import { Lib_Buffer } from "../../libraries/utils/Lib_Buffer.sol";
import { Lib_AddressResolver } from "../../libraries/resolver/Lib_AddressResolver.sol";
/* Interface Imports */
import { IChainStorageContainer } from "./IChainStorageContainer.sol";
/**
 * @title ChainStorageContainer
 * @dev The Chain Storage Container provides its owner contract with read, write and delete
 * functionality. This provides gas efficiency gains by enabling it to overwrite storage slots which
 * can no longer be used in a fraud proof due to the fraud window having passed, and the associated
 * chain state or transactions being finalized.
 * Three distinct Chain Storage Containers will be deployed on Layer 1:
 * 1. Stores transaction batches for the Canonical Transaction Chain
 * 2. Stores queued transactions for the Canonical Transaction Chain
 * 3. Stores chain state batches for the State Commitment Chain
 *
 * Runtime target: EVM
 */
contract ChainStorageContainer is IChainStorageContainer, Lib_AddressResolver {
    /*************
     * Libraries *
     *************/
    using Lib_Buffer for Lib_Buffer.Buffer;
    /*************
     * Variables *
     *************/
    string public owner;
    Lib_Buffer.Buffer internal buffer;
    /***************
     * Constructor *
     ***************/
    /**
     * @param _libAddressManager Address of the Address Manager.
     * @param _owner Name of the contract that owns this container (will be resolved later).
     */
    constructor(address _libAddressManager, string memory _owner)
        Lib_AddressResolver(_libAddressManager)
    {
        owner = _owner;
    }
    /**********************
     * Function Modifiers *
     **********************/
    modifier onlyOwner() {
        require(
            msg.sender == resolve(owner),
            "ChainStorageContainer: Function can only be called by the owner."
        );
        _;
    }
    /********************
     * Public Functions *
     ********************/
    /**
     * @inheritdoc IChainStorageContainer
     */
    function setGlobalMetadata(bytes27 _globalMetadata) public onlyOwner {
        return buffer.setExtraData(_globalMetadata);
    }
    /**
     * @inheritdoc IChainStorageContainer
     */
    function getGlobalMetadata() public view returns (bytes27) {
        return buffer.getExtraData();
    }
    /**
     * @inheritdoc IChainStorageContainer
     */
    function length() public view returns (uint256) {
        return uint256(buffer.getLength());
    }
    /**
     * @inheritdoc IChainStorageContainer
     */
    function push(bytes32 _object) public onlyOwner {
        buffer.push(_object);
    }
    /**
     * @inheritdoc IChainStorageContainer
     */
    function push(bytes32 _object, bytes27 _globalMetadata) public onlyOwner {
        buffer.push(_object, _globalMetadata);
    }
    /**
     * @inheritdoc IChainStorageContainer
     */
    function get(uint256 _index) public view returns (bytes32) {
        return buffer.get(uint40(_index));
    }
    /**
     * @inheritdoc IChainStorageContainer
     */
    function deleteElementsAfterInclusive(uint256 _index) public onlyOwner {
        buffer.deleteElementsAfterInclusive(uint40(_index));
    }
    /**
     * @inheritdoc IChainStorageContainer
     */
    function deleteElementsAfterInclusive(uint256 _index, bytes27 _globalMetadata)
        public
        onlyOwner
    {
        buffer.deleteElementsAfterInclusive(uint40(_index), _globalMetadata);
    }
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;
/**
 * @title Lib_Buffer
 * @dev This library implements a bytes32 storage array with some additional gas-optimized
 * functionality. In particular, it encodes its length as a uint40, and tightly packs this with an
 * overwritable "extra data" field so we can store more information with a single SSTORE.
 */
library Lib_Buffer {
    /*************
     * Libraries *
     *************/
    using Lib_Buffer for Buffer;
    /***********
     * Structs *
     ***********/
    struct Buffer {
        bytes32 context;
        mapping(uint256 => bytes32) buf;
    }
    struct BufferContext {
        // Stores the length of the array. Uint40 is way more elements than we'll ever reasonably
        // need in an array and we get an extra 27 bytes of extra data to play with.
        uint40 length;
        // Arbitrary extra data that can be modified whenever the length is updated. Useful for
        // squeezing out some gas optimizations.
        bytes27 extraData;
    }
    /**********************
     * Internal Functions *
     **********************/
    /**
     * Pushes a single element to the buffer.
     * @param _self Buffer to access.
     * @param _value Value to push to the buffer.
     * @param _extraData Global extra data.
     */
    function push(
        Buffer storage _self,
        bytes32 _value,
        bytes27 _extraData
    ) internal {
        BufferContext memory ctx = _self.getContext();
        _self.buf[ctx.length] = _value;
        // Bump the global index and insert our extra data, then save the context.
        ctx.length++;
        ctx.extraData = _extraData;
        _self.setContext(ctx);
    }
    /**
     * Pushes a single element to the buffer.
     * @param _self Buffer to access.
     * @param _value Value to push to the buffer.
     */
    function push(Buffer storage _self, bytes32 _value) internal {
        BufferContext memory ctx = _self.getContext();
        _self.push(_value, ctx.extraData);
    }
    /**
     * Retrieves an element from the buffer.
     * @param _self Buffer to access.
     * @param _index Element index to retrieve.
     * @return Value of the element at the given index.
     */
    function get(Buffer storage _self, uint256 _index) internal view returns (bytes32) {
        BufferContext memory ctx = _self.getContext();
        require(_index < ctx.length, "Index out of bounds.");
        return _self.buf[_index];
    }
    /**
     * Deletes all elements after (and including) a given index.
     * @param _self Buffer to access.
     * @param _index Index of the element to delete from (inclusive).
     * @param _extraData Optional global extra data.
     */
    function deleteElementsAfterInclusive(
        Buffer storage _self,
        uint40 _index,
        bytes27 _extraData
    ) internal {
        BufferContext memory ctx = _self.getContext();
        require(_index < ctx.length, "Index out of bounds.");
        // Set our length and extra data, save the context.
        ctx.length = _index;
        ctx.extraData = _extraData;
        _self.setContext(ctx);
    }
    /**
     * Deletes all elements after (and including) a given index.
     * @param _self Buffer to access.
     * @param _index Index of the element to delete from (inclusive).
     */
    function deleteElementsAfterInclusive(Buffer storage _self, uint40 _index) internal {
        BufferContext memory ctx = _self.getContext();
        _self.deleteElementsAfterInclusive(_index, ctx.extraData);
    }
    /**
     * Retrieves the current global index.
     * @param _self Buffer to access.
     * @return Current global index.
     */
    function getLength(Buffer storage _self) internal view returns (uint40) {
        BufferContext memory ctx = _self.getContext();
        return ctx.length;
    }
    /**
     * Changes current global extra data.
     * @param _self Buffer to access.
     * @param _extraData New global extra data.
     */
    function setExtraData(Buffer storage _self, bytes27 _extraData) internal {
        BufferContext memory ctx = _self.getContext();
        ctx.extraData = _extraData;
        _self.setContext(ctx);
    }
    /**
     * Retrieves the current global extra data.
     * @param _self Buffer to access.
     * @return Current global extra data.
     */
    function getExtraData(Buffer storage _self) internal view returns (bytes27) {
        BufferContext memory ctx = _self.getContext();
        return ctx.extraData;
    }
    /**
     * Sets the current buffer context.
     * @param _self Buffer to access.
     * @param _ctx Current buffer context.
     */
    function setContext(Buffer storage _self, BufferContext memory _ctx) internal {
        bytes32 context;
        uint40 length = _ctx.length;
        bytes27 extraData = _ctx.extraData;
        assembly {
            context := length
            context := or(context, extraData)
        }
        if (_self.context != context) {
            _self.context = context;
        }
    }
    /**
     * Retrieves the current buffer context.
     * @param _self Buffer to access.
     * @return Current buffer context.
     */
    function getContext(Buffer storage _self) internal view returns (BufferContext memory) {
        bytes32 context = _self.context;
        uint40 length;
        bytes27 extraData;
        assembly {
            length := and(
                context,
                0x000000000000000000000000000000000000000000000000000000FFFFFFFFFF
            )
            extraData := and(
                context,
                0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF0000000000
            )
        }
        return BufferContext({ length: length, extraData: extraData });
    }
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;
/* Library Imports */
import { Lib_AddressManager } from "./Lib_AddressManager.sol";
/**
 * @title Lib_AddressResolver
 */
abstract contract Lib_AddressResolver {
    /*************
     * Variables *
     *************/
    Lib_AddressManager public libAddressManager;
    /***************
     * Constructor *
     ***************/
    /**
     * @param _libAddressManager Address of the Lib_AddressManager.
     */
    constructor(address _libAddressManager) {
        libAddressManager = Lib_AddressManager(_libAddressManager);
    }
    /********************
     * Public Functions *
     ********************/
    /**
     * Resolves the address associated with a given name.
     * @param _name Name to resolve an address for.
     * @return Address associated with the given name.
     */
    function resolve(string memory _name) public view returns (address) {
        return libAddressManager.getAddress(_name);
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >0.5.0 <0.9.0;
/**
 * @title IChainStorageContainer
 */
interface IChainStorageContainer {
    /********************
     * Public Functions *
     ********************/
    /**
     * Sets the container's global metadata field. We're using `bytes27` here because we use five
     * bytes to maintain the length of the underlying data structure, meaning we have an extra
     * 27 bytes to store arbitrary data.
     * @param _globalMetadata New global metadata to set.
     */
    function setGlobalMetadata(bytes27 _globalMetadata) external;
    /**
     * Retrieves the container's global metadata field.
     * @return Container global metadata field.
     */
    function getGlobalMetadata() external view returns (bytes27);
    /**
     * Retrieves the number of objects stored in the container.
     * @return Number of objects in the container.
     */
    function length() external view returns (uint256);
    /**
     * Pushes an object into the container.
     * @param _object A 32 byte value to insert into the container.
     */
    function push(bytes32 _object) external;
    /**
     * Pushes an object into the container. Function allows setting the global metadata since
     * we'll need to touch the "length" storage slot anyway, which also contains the global
     * metadata (it's an optimization).
     * @param _object A 32 byte value to insert into the container.
     * @param _globalMetadata New global metadata for the container.
     */
    function push(bytes32 _object, bytes27 _globalMetadata) external;
    /**
     * Retrieves an object from the container.
     * @param _index Index of the particular object to access.
     * @return 32 byte object value.
     */
    function get(uint256 _index) external view returns (bytes32);
    /**
     * Removes all objects after and including a given index.
     * @param _index Object index to delete from.
     */
    function deleteElementsAfterInclusive(uint256 _index) external;
    /**
     * Removes all objects after and including a given index. Also allows setting the global
     * metadata field.
     * @param _index Object index to delete from.
     * @param _globalMetadata New global metadata for the container.
     */
    function deleteElementsAfterInclusive(uint256 _index, bytes27 _globalMetadata) external;
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;
/* External Imports */
import { Ownable } from "@openzeppelin/contracts/access/Ownable.sol";
/**
 * @title Lib_AddressManager
 */
contract Lib_AddressManager is Ownable {
    /**********
     * Events *
     **********/
    event AddressSet(string indexed _name, address _newAddress, address _oldAddress);
    /*************
     * Variables *
     *************/
    mapping(bytes32 => address) private addresses;
    /********************
     * Public Functions *
     ********************/
    /**
     * Changes the address associated with a particular name.
     * @param _name String name to associate an address with.
     * @param _address Address to associate with the name.
     */
    function setAddress(string memory _name, address _address) external onlyOwner {
        bytes32 nameHash = _getNameHash(_name);
        address oldAddress = addresses[nameHash];
        addresses[nameHash] = _address;
        emit AddressSet(_name, _address, oldAddress);
    }
    /**
     * Retrieves the address associated with a given name.
     * @param _name Name to retrieve an address for.
     * @return Address associated with the given name.
     */
    function getAddress(string memory _name) external view returns (address) {
        return addresses[_getNameHash(_name)];
    }
    /**********************
     * Internal Functions *
     **********************/
    /**
     * Computes the hash of a name.
     * @param _name Name to compute a hash for.
     * @return Hash of the given name.
     */
    function _getNameHash(string memory _name) internal pure returns (bytes32) {
        return keccak256(abi.encodePacked(_name));
    }
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "../utils/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;
    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _setOwner(_msgSender());
    }
    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }
    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }
    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        _setOwner(address(0));
    }
    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        _setOwner(newOwner);
    }
    function _setOwner(address newOwner) private {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }
    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}