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// SPDX-License-Identifier: MIT
pragma solidity 0.8.15;
import { Initializable } from "@openzeppelin/contracts/proxy/utils/Initializable.sol";
import { ISemver } from "src/universal/ISemver.sol";
import { Types } from "src/libraries/Types.sol";
import { Constants } from "src/libraries/Constants.sol";
/// @custom:proxied
/// @title L2OutputOracle
/// @notice The L2OutputOracle contains an array of L2 state outputs, where each output is a
/// commitment to the state of the L2 chain. Other contracts like the OptimismPortal use
/// these outputs to verify information about the state of L2.
contract L2OutputOracle is Initializable, ISemver {
/// @notice The number of the first L2 block recorded in this contract.
uint256 public startingBlockNumber;
/// @notice The timestamp of the first L2 block recorded in this contract.
uint256 public startingTimestamp;
/// @notice An array of L2 output proposals.
Types.OutputProposal[] internal l2Outputs;
/// @notice The interval in L2 blocks at which checkpoints must be submitted.
/// @custom:network-specific
uint256 public submissionInterval;
/// @notice The time between L2 blocks in seconds. Once set, this value MUST NOT be modified.
/// @custom:network-specific
uint256 public l2BlockTime;
/// @notice The address of the challenger. Can be updated via upgrade.
/// @custom:network-specific
address public challenger;
/// @notice The address of the proposer. Can be updated via upgrade.
/// @custom:network-specific
address public proposer;
/// @notice The minimum time (in seconds) that must elapse before a withdrawal can be finalized.
/// @custom:network-specific
uint256 public finalizationPeriodSeconds;
/// @notice Emitted when an output is proposed.
/// @param outputRoot The output root.
/// @param l2OutputIndex The index of the output in the l2Outputs array.
/// @param l2BlockNumber The L2 block number of the output root.
/// @param l1Timestamp The L1 timestamp when proposed.
event OutputProposed(
bytes32 indexed outputRoot, uint256 indexed l2OutputIndex, uint256 indexed l2BlockNumber, uint256 l1Timestamp
);
/// @notice Emitted when outputs are deleted.
/// @param prevNextOutputIndex Next L2 output index before the deletion.
/// @param newNextOutputIndex Next L2 output index after the deletion.
event OutputsDeleted(uint256 indexed prevNextOutputIndex, uint256 indexed newNextOutputIndex);
/// @notice Semantic version.
/// @custom:semver 1.8.0
string public constant version = "1.8.0";
/// @notice Constructs the L2OutputOracle contract. Initializes variables to the same values as
/// in the getting-started config.
constructor() {
initialize({
_submissionInterval: 1,
_l2BlockTime: 1,
_startingBlockNumber: 0,
_startingTimestamp: 0,
_proposer: address(0),
_challenger: address(0),
_finalizationPeriodSeconds: 0
});
}
/// @notice Initializer.
/// @param _submissionInterval Interval in blocks at which checkpoints must be submitted.
/// @param _l2BlockTime The time per L2 block, in seconds.
/// @param _startingBlockNumber The number of the first L2 block.
/// @param _startingTimestamp The timestamp of the first L2 block.
/// @param _proposer The address of the proposer.
/// @param _challenger The address of the challenger.
/// @param _finalizationPeriodSeconds The minimum time (in seconds) that must elapse before a withdrawal
/// can be finalized.
function initialize(
uint256 _submissionInterval,
uint256 _l2BlockTime,
uint256 _startingBlockNumber,
uint256 _startingTimestamp,
address _proposer,
address _challenger,
uint256 _finalizationPeriodSeconds
)
public
initializer
{
require(_submissionInterval > 0, "L2OutputOracle: submission interval must be greater than 0");
require(_l2BlockTime > 0, "L2OutputOracle: L2 block time must be greater than 0");
require(
_startingTimestamp <= block.timestamp,
"L2OutputOracle: starting L2 timestamp must be less than current time"
);
submissionInterval = _submissionInterval;
l2BlockTime = _l2BlockTime;
startingBlockNumber = _startingBlockNumber;
startingTimestamp = _startingTimestamp;
proposer = _proposer;
challenger = _challenger;
finalizationPeriodSeconds = _finalizationPeriodSeconds;
}
/// @notice Getter for the submissionInterval.
/// Public getter is legacy and will be removed in the future. Use `submissionInterval` instead.
/// @return Submission interval.
/// @custom:legacy
function SUBMISSION_INTERVAL() external view returns (uint256) {
return submissionInterval;
}
/// @notice Getter for the l2BlockTime.
/// Public getter is legacy and will be removed in the future. Use `l2BlockTime` instead.
/// @return L2 block time.
/// @custom:legacy
function L2_BLOCK_TIME() external view returns (uint256) {
return l2BlockTime;
}
/// @notice Getter for the challenger address.
/// Public getter is legacy and will be removed in the future. Use `challenger` instead.
/// @return Address of the challenger.
/// @custom:legacy
function CHALLENGER() external view returns (address) {
return challenger;
}
/// @notice Getter for the proposer address.
/// Public getter is legacy and will be removed in the future. Use `proposer` instead.
/// @return Address of the proposer.
/// @custom:legacy
function PROPOSER() external view returns (address) {
return proposer;
}
/// @notice Getter for the finalizationPeriodSeconds.
/// Public getter is legacy and will be removed in the future. Use `finalizationPeriodSeconds` instead.
/// @return Finalization period in seconds.
/// @custom:legacy
function FINALIZATION_PERIOD_SECONDS() external view returns (uint256) {
return finalizationPeriodSeconds;
}
/// @notice Deletes all output proposals after and including the proposal that corresponds to
/// the given output index. Only the challenger address can delete outputs.
/// @param _l2OutputIndex Index of the first L2 output to be deleted.
/// All outputs after this output will also be deleted.
function deleteL2Outputs(uint256 _l2OutputIndex) external {
require(msg.sender == challenger, "L2OutputOracle: only the challenger address can delete outputs");
// Make sure we're not *increasing* the length of the array.
require(
_l2OutputIndex < l2Outputs.length, "L2OutputOracle: cannot delete outputs after the latest output index"
);
// Do not allow deleting any outputs that have already been finalized.
require(
block.timestamp - l2Outputs[_l2OutputIndex].timestamp < finalizationPeriodSeconds,
"L2OutputOracle: cannot delete outputs that have already been finalized"
);
uint256 prevNextL2OutputIndex = nextOutputIndex();
// Use assembly to delete the array elements because Solidity doesn't allow it.
assembly {
sstore(l2Outputs.slot, _l2OutputIndex)
}
emit OutputsDeleted(prevNextL2OutputIndex, _l2OutputIndex);
}
/// @notice Accepts an outputRoot and the timestamp of the corresponding L2 block.
/// The timestamp must be equal to the current value returned by `nextTimestamp()` in
/// order to be accepted. This function may only be called by the Proposer.
/// @param _outputRoot The L2 output of the checkpoint block.
/// @param _l2BlockNumber The L2 block number that resulted in _outputRoot.
/// @param _l1BlockHash A block hash which must be included in the current chain.
/// @param _l1BlockNumber The block number with the specified block hash.
function proposeL2Output(
bytes32 _outputRoot,
uint256 _l2BlockNumber,
bytes32 _l1BlockHash,
uint256 _l1BlockNumber
)
external
payable
{
require(msg.sender == proposer, "L2OutputOracle: only the proposer address can propose new outputs");
require(
_l2BlockNumber == nextBlockNumber(),
"L2OutputOracle: block number must be equal to next expected block number"
);
require(
computeL2Timestamp(_l2BlockNumber) < block.timestamp,
"L2OutputOracle: cannot propose L2 output in the future"
);
require(_outputRoot != bytes32(0), "L2OutputOracle: L2 output proposal cannot be the zero hash");
if (_l1BlockHash != bytes32(0)) {
// This check allows the proposer to propose an output based on a given L1 block,
// without fear that it will be reorged out.
// It will also revert if the blockheight provided is more than 256 blocks behind the
// chain tip (as the hash will return as zero). This does open the door to a griefing
// attack in which the proposer's submission is censored until the block is no longer
// retrievable, if the proposer is experiencing this attack it can simply leave out the
// blockhash value, and delay submission until it is confident that the L1 block is
// finalized.
require(
blockhash(_l1BlockNumber) == _l1BlockHash,
"L2OutputOracle: block hash does not match the hash at the expected height"
);
}
emit OutputProposed(_outputRoot, nextOutputIndex(), _l2BlockNumber, block.timestamp);
l2Outputs.push(
Types.OutputProposal({
outputRoot: _outputRoot,
timestamp: uint128(block.timestamp),
l2BlockNumber: uint128(_l2BlockNumber)
})
);
}
/// @notice Returns an output by index. Needed to return a struct instead of a tuple.
/// @param _l2OutputIndex Index of the output to return.
/// @return The output at the given index.
function getL2Output(uint256 _l2OutputIndex) external view returns (Types.OutputProposal memory) {
return l2Outputs[_l2OutputIndex];
}
/// @notice Returns the index of the L2 output that checkpoints a given L2 block number.
/// Uses a binary search to find the first output greater than or equal to the given
/// block.
/// @param _l2BlockNumber L2 block number to find a checkpoint for.
/// @return Index of the first checkpoint that commits to the given L2 block number.
function getL2OutputIndexAfter(uint256 _l2BlockNumber) public view returns (uint256) {
// Make sure an output for this block number has actually been proposed.
require(
_l2BlockNumber <= latestBlockNumber(),
"L2OutputOracle: cannot get output for a block that has not been proposed"
);
// Make sure there's at least one output proposed.
require(l2Outputs.length > 0, "L2OutputOracle: cannot get output as no outputs have been proposed yet");
// Find the output via binary search, guaranteed to exist.
uint256 lo = 0;
uint256 hi = l2Outputs.length;
while (lo < hi) {
uint256 mid = (lo + hi) / 2;
if (l2Outputs[mid].l2BlockNumber < _l2BlockNumber) {
lo = mid + 1;
} else {
hi = mid;
}
}
return lo;
}
/// @notice Returns the L2 output proposal that checkpoints a given L2 block number.
/// Uses a binary search to find the first output greater than or equal to the given
/// block.
/// @param _l2BlockNumber L2 block number to find a checkpoint for.
/// @return First checkpoint that commits to the given L2 block number.
function getL2OutputAfter(uint256 _l2BlockNumber) external view returns (Types.OutputProposal memory) {
return l2Outputs[getL2OutputIndexAfter(_l2BlockNumber)];
}
/// @notice Returns the number of outputs that have been proposed.
/// Will revert if no outputs have been proposed yet.
/// @return The number of outputs that have been proposed.
function latestOutputIndex() external view returns (uint256) {
return l2Outputs.length - 1;
}
/// @notice Returns the index of the next output to be proposed.
/// @return The index of the next output to be proposed.
function nextOutputIndex() public view returns (uint256) {
return l2Outputs.length;
}
/// @notice Returns the block number of the latest submitted L2 output proposal.
/// If no proposals been submitted yet then this function will return the starting
/// block number.
/// @return Latest submitted L2 block number.
function latestBlockNumber() public view returns (uint256) {
return l2Outputs.length == 0 ? startingBlockNumber : l2Outputs[l2Outputs.length - 1].l2BlockNumber;
}
/// @notice Computes the block number of the next L2 block that needs to be checkpointed.
/// @return Next L2 block number.
function nextBlockNumber() public view returns (uint256) {
return latestBlockNumber() + submissionInterval;
}
/// @notice Returns the L2 timestamp corresponding to a given L2 block number.
/// @param _l2BlockNumber The L2 block number of the target block.
/// @return L2 timestamp of the given block.
function computeL2Timestamp(uint256 _l2BlockNumber) public view returns (uint256) {
return startingTimestamp + ((_l2BlockNumber - startingBlockNumber) * l2BlockTime);
}
}