ERC20PermitFacet

EIP-2612 permit functionality for ERC-20 tokens

Key Features

• Implements EIP-2612 permit function for off-chain approvals.
• Exposes nonces and DOMAIN_SEPARATOR for signature verification.
• Integrates with Compose diamond storage pattern.

Overview

This facet implements EIP-2612 permit functionality, enabling off-chain approvals for ERC-20 token transfers within a Compose diamond. It exposes the permit function to set allowances via signatures and provides nonces and DOMAIN_SEPARATOR for signature validation. Developers integrate this facet to allow users to grant token spending permissions without direct on-chain transactions.

---

Storage

ERC20Storage

Definition

struct ERC20Storage {
  mapping(address owner => uint256 balance) balanceOf;
  uint256 totalSupply;
  mapping(address owner => mapping(address spender => uint256 allowance)) allowance;
  uint8 decimals;
  string name;
}

---

ERC20PermitStorage

Definition

struct ERC20PermitStorage {
  mapping(address owner => uint256) nonces;
}

State Variables

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

Functions

nonces

Returns the current nonce for an owner. This value changes each time a permit is used.

function nonces(address _owner) external view returns (uint256);

Parameters:

Property	Type	Description
_owner	address	The address of the owner.

Returns:

Property	Type	Description
-	uint256	The current nonce.

---

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() external view returns (bytes32);

Returns:

Property	Type	Description
-	bytes32	The domain separator.

---

permit

Sets the allowance for a spender via a signature. This function implements EIP-2612 permit functionality.

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

Parameters:

Property	Type	Description
_owner	address	The address of the token owner.
_spender	address	The address of the spender.
_value	uint256	The amount of tokens to approve.
_deadline	uint256	The deadline for the permit (timestamp).
_v	uint8	The recovery byte of the signature.
_r	bytes32	The r value of the signature.
_s	bytes32	The s value of the signature.

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 a permit signature is invalid or expired.

Signature:

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

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

Signature:

error ERC20InvalidSpender(address _spender);

Best Practices

Best Practice

• Integrate the ERC20PermitFacet during diamond initialization.
• Ensure DOMAIN_SEPARATOR is correctly configured for the specific chain and diamond.
• Validate signature parameters (_v, _r, _s) before relaying them to the permit function.

Security Considerations

Security

The permit function allows setting allowances via signatures. Ensure correct implementation of signature verification logic by consumers of this facet. Reentrancy is not applicable as permit only modifies storage. Input validation for spender and value is handled internally. Follow standard Solidity security practices.

Related Documentation

📦

ERC20PermitMod

Module used by ERC20PermitFacet

Was this helpful?

Last updated:December 30, 2025