ERC20 permit functión parametres v, r, s. Where do we get them from?

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1

In the new version v5 of ERC20 we have the function permit to allowance accounts without spending gas, that is to say, with signature of the account:

  function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) public virtual {
        if (block.timestamp > deadline) {
            revert ERC2612ExpiredSignature(deadline);
        }

        bytes32 structHash = keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, value, _useNonce(owner), deadline));

        bytes32 hash = _hashTypedDataV4(structHash);

        address signer = ECDSA.recover(hash, v, r, s);
        if (signer != owner) {
            revert ERC2612InvalidSigner(signer, owner);
        }

        _approve(owner, spender, value);
    }

But in the parameters I am asked for some values that are returned with the splitSignature signature in solidity:
https://solidity-by-example.org/signature/

How am I supposed to capture these values to pass them to you as a parameter?

The account signature will have to be done from the contract and not from a front end in order to call the splitSignature function and capture those values requested in the parameters?

2

Hey @Cainuriel. In fact, the signature is just the values r,s concatenated (and v depends on the chain), so you can either pick them up from the signature string, or use the ethers v6's Signature class:

const { Signature } = require('ethers');

const signature = Signature.from('0x96f68bacfedd996d40a3eb4db679314545ce3d24f07b7db007528f8507f1f8654dd988fba90bf798173fa6b28222c3afb402ff5bbeac5dcc24bd204ae0778b911c');

signature.r; // 0x96f68bacfedd996d40a3eb4db679314545ce3d24f07b7db007528f8507f1f865
signature.s; // 0x4dd988fba90bf798173fa6b28222c3afb402ff5bbeac5dcc24bd204ae0778b91
signature.v // 27 | 28
3

Thanks @ernestognw

Since I see that you know ethers.js version 6 well, would you be so kind to answer me this question?

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