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Overview

EtherspotPaymaster is a smart contract that allows an external signer to sign a UserOperation and pay for the gas costs of executing that UserOperation. The paymaster signs to agree to pay for gas, and the wallet signs to prove identity and account ownership.

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Version

Solidity pragma version ^0.8.12.

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Global Variables

  • VALID_TIMESTAMP_OFFSET: A constant of type uint256 that represents a 20 second time offset used to validate timestamps.
  • SIGNATURE_OFFSET: A constant of type uint256 that represents an 84-byte signature offset.
  • COST_OF_POST: The pre-calculated cost of calling _postOp (required for gas calculation).

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Imports

  • ECDSA: A contract from the OpenZeppelin library used for signature verification.
  • IERC20: A contract from the OpenZeppelin library used for interacting with ERC20 tokens.
  • SafeERC20: A contract from the OpenZeppelin library used for safe ERC20 token transfers.
  • Whitelist: Whitelist.sol smart contract used for whitelisting addresses.

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Mappings

  • sponsorFunds: A mapping of type mapping(address => uint256) used to store the amount of sponsor funds transferred to the paymaster contract.
  • senderNonce: A mapping of type mapping(address => uint256) used to store the nonce of the sender.

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Events

  • SponsorSuccessful: An event emitted when a sponsor successfully sponsors a user operation.
  • SponsorUnsuccessful: An event emitted when a sponsor is unsuccessful in sponsoring a user operation.

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Constructor

  • constructor(IEntryPoint _entryPoint): A constructor that accepts an IEntryPoint parameter _entryPoint.

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Public/External Functions

  • depositFunds() external payable: A function used to deposit funds to the paymaster.
    • Error EtherspotPaymaster:: Not enough balance: Checks that the sponsor has enough funds to deposit into paymaster contract.
  • withdrawFunds() address payable _sponsor, uint256 _amount) external: A function used to withdraw sponsor funds from paymaster.
    • Error EtherspotPaymaster:: can only withdraw own funds: Checks msg.sender matches the sponsor address provided.
    • Error EtherspotPaymaster:: not enough deposited funds: Checks amount is >= deposited funds for the given sponsor.
  • checkSponsorFunds(address _sponsor) public view returns (uint256): A function used to check the amount of sponsor funds transferred to the paymaster contract for a given sponsor.
  • function getHash(UserOperation calldata userOp, uint48 validUntil, uint48 validAfter) public view returns (bytes32): A function to return the hash to be sign off-chain (and validate on-chain) by a sponsor.
  • function parsePaymasterAndData(bytes calldata paymasterAndData) public pure returns (uint48 validUntil, uint48 validAfter, bytes calldata signature): Extracts validUntil, validAfter and signature from paymasterAndData passed in as input.

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Internal Functions

  • _debitSponsor(address _sponsor, uint256 _amount) internal: A function used to debit a sponsor’s fund amount for gas costs once a transaction has been processed.
  • _creditSponsor: A function used to credit a sponsor’s deposited amount.
  • _pack(UserOperation calldata userOp): A function used to pack the user operation.
  • _validatePaymasterUserOp(UserOperation calldata userOp, bytes32 userOpHash, uint256 requiredPreFund): A function used to verify the external signer (sponsor) that signed the request. Debits the sponsor’s deposited balance by full requiredPreFund amount (credits back in _postOp).
    • Error EtherspotPaymaster:: invalid signature length in paymasterAndData: Triggered on incorrect signature length.
    • Error EtherspotPaymaster:: Sponsor paymaster funds too low: Checks sponsor has enough funds to pay the gas costs for a sponsored UserOperation.
  • _postOp(PostOpMode mode, bytes calldata context, uint256 actualGasCost) internal override: A function that overrides the _postOp function from BasePaymaster.sol that checks for a validated UserOperation and credits back any remaining funds after the gas cost for the UserOperation execution plus _postOp call.
    • Emits SponsorSuccessful(paymaster, sender, userOpHash) on successfully sponsored UserOperation.
    • Emits SponsorUnsuccessful(paymaster, sender, userOpHash) on unsuccessfully sponsored UserOperation.

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License

This contract is licensed under the MIT license.