IFeeEscrow

The Fee Escrow interface provides a secure, on-chain escrow system for prepaid verification fees on Humanity Protocol.

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Contract address

Tesnet	0x1a247b7d7076e4c4D97D87c62947Ab5495C13423
Mainnet	0xe433f01131eAbD8060a1E34149eF0e79b2b86fEc

Overview

IFeeEscrow enables DApps to deposit native tokens to pre-fund verification requests. The Oracle reserves funds per request before processing, settles actual fees upon completion, and supports controlled withdrawals of unused balances.

Core Concepts

Concept	Description
Prepaid Model	DApps top up a balance in FeeEscrow. Funds are reserved per verification request before the Oracle processes it.
Per-Request Reservation	Each verification request (identified by requestUID) has an associated reserved amount, preventing double-spending of fees.
Settlement & Distribution	Upon successful verification, the Oracle finalizes the request and transfers the consumed fee to the designated receiver.

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Lifecycle Flow

1. DEPOSIT

DApp calls deposit(). Funds are added to the DApp's escrow balance.

2. CHECK BALANCE

Before verification, ensure getAvailable(dapp) >= verificationFee.

3. RESERVATION

Oracle calls reserveForRequest(dapp, requestUID, amount). Funds are locked for the specific verification request.

4a. SETTLEMENT (on success)

Oracle calls settleRequest(requestUID, consumedAmount). Fee is deducted and transferred to the recipient.

4b. RELEASE (on failure/cancellation)

Oracle calls releaseReservationForRequest(requestUID). Reserved funds are unlocked back to available balance.

5. WITHDRAWAL

DApp calls requestWithdrawal(recipient, amount). Admin approves, then funds are transferred to the recipient.

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Interface

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.29;

interface IFeeEscrow is IFeeEscrowErrors {
    // Core Functions
    function deposit(address dapp) external payable;
    function reserveForRequest(address dapp, bytes32 requestUID, uint256 amount) external;
    function settleRequest(bytes32 requestUID, uint256 consumedAmount) external;
    function releaseReservationForRequest(bytes32 requestUID) external;

    // Balance Queries
    function checkBalance(address dapp, uint256 requiredAmount) external view returns (bool);
    function getBalance(address dapp) external view returns (uint256);
    function getReserved(address dapp) external view returns (uint256);
    function getAvailable(address dapp) external view returns (uint256);
    function hasMinimumBalance(address dapp) external view returns (bool);
    function getBalanceInfo(address dapp) external view returns (uint256 total, uint256 reservedAmount, uint256 availableAmount);
    function canAffordFee(address dapp, uint256 fee) external view returns (bool canAfford, uint256 availableBalance);

    // Withdrawals
    function withdraw(uint256 amount) external;
    function requestWithdrawal(address recipient, uint256 amount) external returns (uint256 requestId);
    function cancelWithdrawalRequest(uint256 requestId) external;

    // Admin Functions
    function updateMinimumBalance(uint256 _newMinimumBalance) external;
    function updateMaxWithdrawalLimit(uint256 _newLimit) external;
    function updateVerificationOracle(address _newOracle) external;
    function pause() external;
    function unpause() external;
    function emergencyWithdraw(address dapp) external;

    // Contract Statistics
    function getContractStats() external view returns (uint256 _totalDeposited, uint256 _totalSettled, uint256 _currentHoldings);
    function getRequestReservation(bytes32 requestUID) external view returns (address dapp, uint256 amount);

    // State Variables
    function verificationOracle() external view returns (address);
    function minimumBalance() external view returns (uint256);
    function maxWithdrawalLimit() external view returns (uint256);
    function balances(address dapp) external view returns (uint256);
    function reserved(address dapp) external view returns (uint256);
    function totalDeposited() external view returns (uint256);
    function totalFeesSettled() external view returns (uint256);
}

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Functions

Funding

deposit()

DApp deposits native tokens to pre-fund dapp.

function deposit(address dapp) external payable;

Usage:

// DApp deposits 10 HP to their escrow balance
feeEscrow.deposit{value: 10 ether}(address(yourDApp));

Emits: Deposited(address indexed dapp, uint256 amount, uint256 newBalance)

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Reservation & Settlement

Note: These functions are restricted to the Verification Oracle via onlyOracle modifier.

reserveForRequest(address dapp, bytes32 requestUID, uint256 amount)

Lock funds for a specific verification request before processing.

function reserveForRequest(address dapp, bytes32 requestUID, uint256 amount) external;

Parameter	Type	Description
dapp	address	Address of the DApp
requestUID	bytes32	Unique identifier for the verification request
amount	uint256	Amount to reserve

Reverts:

• InsufficientAvailableBalance if DApp’s available balance is insufficient

Emits: ReservationCreated(bytes32 indexed requestUID, address indexed dapp, uint256 amount)

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settleRequest(bytes32 requestUID, uint256 consumedAmount)

Deduct actual consumed fee and transfer to the designated recipient.

function settleRequest(bytes32 requestUID, uint256 consumedAmount) external;

Parameter	Type	Description
requestUID	bytes32	Unique identifier for the verification request
consumedAmount	uint256	Actual fee amount consumed

Emits: ReservationSettled(bytes32 indexed requestUID, address indexed dapp, uint256 consumedAmount, uint256 reservedAmount)

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releaseReservationForRequest(bytes32 requestUID)

Release reserved funds if the request is cancelled or fails.

function releaseReservationForRequest(bytes32 requestUID) external;

Parameter	Type	Description
requestUID	bytes32	Unique identifier for the verification request

Emits: ReservationReleasedForRequest(bytes32 indexed requestUID, address indexed dapp, uint256 amount)

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Balance Queries

getBalance(address dapp)

Get current total balance of a DApp (reserved + available).

function getBalance(address dapp) external view returns (uint256);

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getReserved(address dapp)

Get amount currently reserved for pending verification requests.

function getReserved(address dapp) external view returns (uint256);

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getAvailable(address dapp)

Get available balance (total - reserved) that can be used for new requests or withdrawals.

function getAvailable(address dapp) external view returns (uint256);

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getBalanceInfo(address dapp)

Get comprehensive balance information in a single call.

function getBalanceInfo(address dapp) external view returns (
    uint256 total,
    uint256 reservedAmount,
    uint256 availableAmount
);

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checkBalance(address dapp, uint256 requiredAmount)

Check if DApp has sufficient available balance.

function checkBalance(address dapp, uint256 requiredAmount) external view returns (bool);

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canAffordFee(address dapp, uint256 fee)

Check if a DApp can afford a specific verification fee.

function canAffordFee(address dapp, uint256 fee) external view returns (
    bool canAfford,
    uint256 availableBalance
);

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Withdrawals

requestWithdrawal(address recipient, uint256 amount)

DApp initiates withdrawal from available funds (not reserved).

function requestWithdrawal(address recipient, uint256 amount) external returns (uint256 requestId);

Parameter	Type	Description
recipient	address	Wallet address to receive the withdrawn funds
amount	uint256	Amount to withdraw

Returns: requestId - The ID of the created withdrawal request

Reverts:

• NoBalanceToWithdraw if no available funds

• WithdrawalLimitExceeded if amount exceeds configured cap

• PendingWithdrawalExists if a withdrawal is already pending

Emits: WithdrawalRequested(uint256 indexed requestId, address indexed dapp, address indexed recipient, uint256 amount, uint256 timestamp)

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cancelWithdrawalRequest(uint256 requestId)

Cancel a pending withdrawal request.

function cancelWithdrawalRequest(uint256 requestId) external;

Reverts:

• WithdrawalRequestNotFound if request doesn’t exist

• UnauthorizedWithdrawalCancellation if caller is not authorized

Emits: WithdrawalCancelled(uint256 indexed requestId, address indexed dapp, uint256 amount)

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Admin Functions

updateMinimumBalance(uint256 _newMinimumBalance)

Update minimum balance requirement for DApps.

function updateMinimumBalance(uint256 _newMinimumBalance) external;

Emits: MinimumBalanceUpdated(uint256 oldValue, uint256 newValue)

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updateMaxWithdrawalLimit(uint256 _newLimit)

Update maximum withdrawal limit per request.

function updateMaxWithdrawalLimit(uint256 _newLimit) external;

Emits: MaxWithdrawalLimitUpdated(uint256 oldValue, uint256 newValue)

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updateVerificationOracle(address _newOracle)

Update the authorized Verification Oracle address.

function updateVerificationOracle(address _newOracle) external;

Emits: VerificationOracleUpdated(address oldOracle, address newOracle)

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pause() / unpause()

Pause or unpause contract operations.

function pause() external;
function unpause() external;

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emergencyWithdraw(address dapp)

Emergency withdrawal function for DApps (only available when contract is paused).

function emergencyWithdraw(address dapp) external;

Emits: EmergencyWithdrawal(address indexed dapp, uint256 amount)

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Integration Example

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.29;

import "./interfaces/feeEscrow/IFeeEscrow.sol";

contract MyDApp {
    IFeeEscrow public feeEscrow;

    constructor(address _feeEscrow) {
        feeEscrow = IFeeEscrow(_feeEscrow);
    }

    // Fund the escrow for verification fees
    function fundEscrow() external payable {
        feeEscrow.deposit{value: msg.value}();
    }

    // Check balance before requesting verification
    function canRequestVerification(uint256 verificationFee) external view returns (bool) {
        return feeEscrow.getAvailable(address(this)) >= verificationFee;
    }

    // Get detailed balance info
    function getEscrowBalance() external view returns (
        uint256 total,
        uint256 reserved,
        uint256 available
    ) {
        return feeEscrow.getBalanceInfo(address(this));
    }

    // Withdraw unused funds
    function withdrawFunds(address recipient, uint256 amount) external returns (uint256) {
        return feeEscrow.requestWithdrawal(recipient, amount);
    }
}

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Integration Tips

1. Configure Oracle Address: Ensure the escrow’s verificationOracle is set to the actual Oracle contract address. Otherwise, reserveForRequest and settleRequest will revert with UnauthorizedCaller.

2. Pre-fund Before Requests: Always check getAvailable(dapp) >= verificationFee before initiating verification requests to avoid InsufficientAvailableBalance errors.

3. Monitor Available Balance: The available balance (not total) determines what can be used for new requests or withdrawals. Reserved funds are locked until settlement or release.

4. Handle Withdrawal Limits: Be aware of maxWithdrawalLimit when requesting withdrawals. Large withdrawals may need to be split into multiple requests.

5. Upgrades (UUPS): Do not increase __gap size on upgrade. Only append new state variables and decrement __gap accordingly.