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Track pending stake requests balance #191

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Track pending stake requests balance #191

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142 changes: 141 additions & 1 deletion core/contracts/tbtc/TbtcDepositor.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,9 @@ contract TbtcDepositor is Ownable {
// tBTC token amount to stake after deducting tBTC minting fees and the
// Depositor fee.
uint256 amountToStake;
// Marks stake request that has already been deducted from the pending
// stakes balance.
bool excludedFromPendingStakesBalanceTracker;
}

/// @notice tBTC Bridge contract.
Expand Down Expand Up @@ -82,6 +85,21 @@ contract TbtcDepositor is Ownable {
/// `1/50 = 0.02 = 2%`.
uint64 public depositorFeeDivisor;

/// @notice Balance of stake requests that were initiated. The balance is
/// used to track asynchronous stake requests, before they are
/// finalized and included in the Acre contract max deposit cap.
/// @dev Value in the tBTC token precision (1e18).
/// A stake request amount is added to the pending stakes balance when
/// a stake request is initiated. It will be deducted once the request
/// is finalized. It may happen that a stake request is initialized with
/// invalid funding transaction details. In such case the balance is
/// reduced when this stake request is notified to be timed out.
uint256 public pendingStakesBalance;

// TODO: Confirm the value to include time needed for optimistic minting or sweeping
/// @notice A timeout duration to wait for the tBTC Bridge to initiate minting.
uint32 public tbtcBridgingInitializationTimeout = 3 days;

/// @notice Emitted when a stake request is initialized.
/// @dev Deposit details can be fetched from {{ Bridge.DepositRevealed }}
/// event emitted in the same transaction.
Expand All @@ -96,6 +114,10 @@ contract TbtcDepositor is Ownable {
uint16 referral
);

/// @notice Emitted when bridging timeout has been notified.
/// @param depositKey Deposit identifier.
event BridgingTimedOut(uint256 depositKey);

/// @notice Emitted when bridging completion has been notified.
/// @param depositKey Deposit identifier.
/// @param caller Address that notified about bridging completion.
Expand Down Expand Up @@ -131,6 +153,18 @@ contract TbtcDepositor is Ownable {
/// @dev Attempted to finalize a stake request that has not been initialized.
error StakeRequestNotInitialized();

/// @dev Attempted to notify bridging timeout, while bridging has not timed
/// out yet.
error StakeRequestNotTimedOut(uint256 timeoutTimestamp);

/// @dev Attempted to notify bridging timeout, while optimistic minting
/// was initiated.
error OptimisticMintingInProgress();

/// @dev Attempted to notify bridging timeout, while the deposit was already
/// swept.
error DepositAlreadySwept();

/// @dev Attempted to notify about completed bridging while the notification
/// was already submitted.
error BridgingAlreadyCompleted();
Expand Down Expand Up @@ -258,6 +292,62 @@ contract TbtcDepositor is Ownable {
// tBTC Vault supported by this contract.
if (bridgeDepositRequest.vault != address(tbtcVault))
revert UnexpectedTbtcVault(bridgeDepositRequest.vault);

// Increase pending stakes balance by the funds that stake request was
// initiated for.
pendingStakesBalance +=
bridgeDepositRequest.amount *
SATOSHI_MULTIPLIER;
}

/// @notice This function should be called for previously initialized stake
/// request, when tBTC Bridge cannot confirm validity of the funding
/// Bitcoin transaction, meaning the revealed deposit request is
/// most likely invalid.
/// @dev When a deposit is revealed to the tBTC Bridge contract, it is expected
/// that funding Bitcoin transaction is confirmed and optimistic minting
/// to be initiated. If optimistic minting is not initiated there is
/// a second path where tBTC nodes sweep the deposit to get tBTC minted.
/// If none of this happens within a bridging timeout duration it
/// means that most likely the revealed deposit was invalid and bridging
/// won't be completed.
/// @param depositKey Deposit key computed as
/// `keccak256(fundingTxHash | fundingOutputIndex)`.
function notifyBridgingTimeout(uint256 depositKey) external {
StakeRequest storage request = stakeRequests[depositKey];

if (request.requestedAt == 0) revert StakeRequestNotInitialized();
if (request.amountToStake > 0) revert BridgingAlreadyCompleted();

// Check if timeout has passed.
uint64 expectedTimeoutAt = request.requestedAt +
tbtcBridgingInitializationTimeout;
// solhint-disable-next-line not-rely-on-time
if (expectedTimeoutAt > block.timestamp)
revert StakeRequestNotTimedOut(expectedTimeoutAt);

// Check if Optimistic Minting is in progress. If optimistic minting of
// the deposit was requested it's very likely the deposit request will be
// completed soon, as it is already being processed by tBTC Minters
// and Guardians.
ITBTCVault.OptimisticMintingRequest
memory optimisticMintingRequest = tbtcVault
.optimisticMintingRequests(depositKey);

if (optimisticMintingRequest.requestedAt > 0)
revert OptimisticMintingInProgress();

// Check if the Deposit was swept.
IBridge.DepositRequest memory bridgeDepositRequest = bridge.deposits(
depositKey
);
if (bridgeDepositRequest.sweptAt > 0) revert DepositAlreadySwept();

emit BridgingTimedOut(depositKey);

// Release the pending bridging amount, as it is unlikely the bridging
// will be completed.
reducePendingStakesBalance(depositKey);
}

/// @notice This function should be called for previously initialized stake
Expand Down Expand Up @@ -389,6 +479,10 @@ contract TbtcDepositor is Ownable {
// solhint-disable-next-line not-rely-on-time
request.finalizedAt = uint64(block.timestamp);

// Free pending stakes amount as the funds are being deposited to the Acre
// contract and will be included in Acre.maxDeposit limit.
reducePendingStakesBalance(depositKey);

// Get deposit details from tBTC Bridge.
IBridge.DepositRequest memory bridgeDepositRequest = bridge.deposits(
depositKey
Expand Down Expand Up @@ -424,6 +518,10 @@ contract TbtcDepositor is Ownable {
// solhint-disable-next-line not-rely-on-time
request.finalizedAt = uint64(block.timestamp);

// Free pending stakes amount as the funds are being withdraw from the
// Depositor contract and stake request will be marked as finalized.
reducePendingStakesBalance(depositKey);

// Get deposit details from tBTC Bridge and Vault contracts.
IBridge.DepositRequest memory bridgeDepositRequest = bridge.deposits(
depositKey
Expand Down Expand Up @@ -453,7 +551,21 @@ contract TbtcDepositor is Ownable {
emit DepositorFeeDivisorUpdated(newDepositorFeeDivisor);
}

// TODO: Handle minimum deposit amount in tBTC Bridge vs Acre.
/// @notice Maximum stake amount
/// @dev The value is returned in tBTC token precision (1e18).
/// This function should be called before Bitcoin transaction funding
/// is made.
/// @param receiver The address to which the stBTC shares will be minted.
/// @return Maximum allowed stake amount.
function maxStake(address receiver) external view returns (uint256) {
uint256 acreMaxDeposit = acre.maxDeposit(receiver);

if (acreMaxDeposit == type(uint256).max) {
return type(uint256).max;
}

return acreMaxDeposit - pendingStakesBalance;
}

/// @notice Calculates deposit key the same way as the Bridge contract.
/// @dev The deposit key is computed as
Expand Down Expand Up @@ -499,4 +611,32 @@ contract TbtcDepositor is Ownable {
// Next 2 bytes of extra data is referral info.
referral = uint16(bytes2(extraData << (8 * 20)));
}

/// @notice Deduct stake request's amount from the pending stakes balance
/// tracker.
/// @dev The function is intended to be called when stake request is finalized
/// or recalled, but also when the bridging request is timed out.
/// It makes sure it is called just once for a given stake request,
/// to avoid reducing the balance multiple times for the same stake
/// request. It may happen that bridging times out due to tBTC Bridge
/// related issues and timeout is notified to the stake request in this
/// contract. But when the deposit in tBTC Bridge is later minted
/// the finalize stake function may be called, so we don't want the balance
/// to be reduced twice.
/// @param depositKey Deposit key computed as
/// `keccak256(fundingTxHash | fundingOutputIndex)`.
function reducePendingStakesBalance(uint256 depositKey) internal {
StakeRequest storage request = stakeRequests[depositKey];

if (!request.excludedFromPendingStakesBalanceTracker) {
request.excludedFromPendingStakesBalanceTracker = true;

IBridge.DepositRequest memory bridgeDepositRequest = bridge
.deposits(depositKey);

pendingStakesBalance -=
bridgeDepositRequest.amount *
SATOSHI_MULTIPLIER;
}
}
}
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