ERC-20 Permit Module

Manage ERC-2612 permit signatures and domain separators

Key Features

• Provides internal functions for ERC-2612 permit functionality.
• Manages unique domain separators to prevent replay attacks.
• Interacts with diamond storage for allowance updates.
• No external dependencies, promoting composability.

Module Usage

This module provides internal functions for use in your custom facets. Import it to access shared logic and storage.

Overview

This module manages ERC-2612 permit logic, including domain separators and signature validation for allowance approvals. Facets can use this module to implement the permit functionality, ensuring unique domain separators per contract and chain ID to prevent replay attacks. Changes to allowances made via permit are recorded in diamond storage and are visible to all facets.

Storage

ERC20MetadataStorage

storage-location: erc8042:erc20.metadata

Definition

struct ERC20MetadataStorage {
  string name;
}

---

ERC20Storage

storage-location: erc8042:erc20

Definition

struct ERC20Storage {
  mapping(address owner => uint256 balance) balanceOf;
  uint256 totalSupply;
  mapping(address owner => mapping(address spender => uint256 allowance)) allowance;
}

---

NoncesStorage

storage-location: erc8042:nonces

Definition

struct NoncesStorage {
  mapping(address owner => uint256) nonces;
}

State Variables

Property	Type	Description
ERC20_METADATA_STORAGE_POSITION	bytes32	Diamond storage slot position for this module (Value: keccak256("erc20.metadata"))
ERC20_STORAGE_POSITION	bytes32	Diamond storage slot position for this module (Value: keccak256("erc20"))
STORAGE_POSITION	bytes32	Diamond storage slot position for this module (Value: keccak256("nonces"))

Functions

DOMAIN_SEPARATOR

Returns the domain separator used in the encoding of the signature for {permit}. This value is unique to a contract and chain ID combination to prevent replay attacks.

function DOMAIN_SEPARATOR() view returns (bytes32);

Returns:

Property	Type	Description
-	bytes32	The domain separator.

---

getERC20MetadataStorage

function getERC20MetadataStorage() pure returns (ERC20MetadataStorage storage s);

---

getERC20Storage

function getERC20Storage() pure returns (ERC20Storage storage s);

---

getPermitStorage

function getPermitStorage() pure returns (NoncesStorage storage s);

---

permit

Validates a permit signature and sets allowance. Emits Approval event; must be emitted by the calling facet/contract.

function permit(address _owner, address _spender, uint256 _value, uint256 _deadline, uint8 _v, bytes32 _r, bytes32 _s) ;

Parameters:

Property	Type	Description
_owner	address	Token owner.
_spender	address	Token spender.
_value	uint256	Allowance value.
_deadline	uint256	Permit's time deadline.

Events

Emitted when an approval is made for a spender by an owner.

Signature:

event Approval(address indexed _owner, address indexed _spender, uint256 _value);

Parameters:

Property	Type	Description
_owner	address	The address granting the allowance.
_spender	address	The address receiving the allowance.
_value	uint256	The amount approved.

Errors

Thrown when the spender address is invalid (e.g., zero address).

Signature:

error ERC20InvalidSpender(address _spender);

Thrown when a permit signature is invalid or expired.

Signature:

error ERC2612InvalidSignature(
address _owner, address _spender, uint256 _value, uint256 _deadline, uint8 _v, bytes32 _r, bytes32 _s
);

Best Practices

Best Practice

• Ensure the calling facet correctly emits the Approval event after a successful permit call.
• Verify that the DOMAIN_SEPARATOR used by the module is correctly initialized and unique to the contract and chain ID.
• Handle the ERC2612InvalidSignature and ERC20InvalidSpender errors to provide appropriate feedback to users.

Integration Notes

Shared Storage

This module interacts with diamond storage to manage permit-related state, specifically related to allowances and nonces. The permit function updates allowance values directly in the shared diamond storage. The DOMAIN_SEPARATOR function is crucial for signature verification and ensures that permits are specific to the contract instance and chain. Changes made via the permit function are immediately visible to any other facet that reads the allowance state from the diamond storage.

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Last updated:March 13, 2026