This contract implements EIP2612 (an ERC20 Permit extension).Its approval can be signed offline, and the signature information can be submitted to the chain when the transfer transaction is received, and the authorization and transfer are completed in one transaction. At the same time, the transfer transaction can also be submitted by the recipient (or a third party), avoiding the need for users to rely on FIL.

Compliant contracts must implement 3 new functions in addition to EIP-20:

permit(address owner, address spender, uint256 value, uint256 deadline, uint8 v, bytes32 r, bytes32 s)

Sets value as the allowance of spender over owner’s tokens, given owner’s signed approval.

IMPORTANT: The same issues {IERC20-approve} has related to transaction ordering also apply here.

Emits an {Approval} event.

Requirements:

• owner cannot be address(0).

• spender cannot be address(0).

• deadline must be a timestamp in the future.

• v, r and s must be a valid secp256k1 signature from owner over the EIP712-formatted function arguments.

• the signature must use owner’s current nonce (see {nonces}).

For more information on the signature format, see the https://eips.ethereum.org/EIPS/eip-2612

function permit(address owner, address spender, uint256 value, uint256 deadline, uint8 v, bytes32 r, bytes32 s) external;

nonces(address owner)

Returns the current ERC2612 nonce for owner. This value must be ncluded whenever a signature is generated for {permit}.

Every successful call to {permit} increases owner’s nonce by one. This prevents a signature from being used multiple times.

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

DOMAIN_SEPARATOR()

Returns the domain separator used in the encoding of the signature for {permit}, as defined by EIP712.

function DOMAIN_SEPARATOR() external view returns (bytes32);