How do I use the _TypedDataEncoder hash function for EIP712?

[gperezalba]

Describe the bug
Trying to get the EIP712 structHash with ethers to call a contract function and disallow a previously approved offchain signature. After creating _TypedDataEncoder with types, I use hash function with domain, types and values but I get a TypeError:

TypeError: Cannot read property 'toHexString' of undefined

...I've checked and domain, types or values arent undefined.

Reproduction steps

`

        //sign
        const domain = {
            name: 'N21_FACTORY',
            version: '1',
            chainId: ethers.provider._network.chainId,
            verifyingContract: myFactory.address
        }

        const types = {
            Create: [
                { name: 'hashId', type: 'bytes32' },
                { name: 'account', type: 'address' },
                { name: 'value', type: 'uint256' },
                { name: 'currency', type: 'bytes32' },
                { name: 'startDate', type: 'uint256' },
                { name: 'endDate', type: 'uint256' },
                { name: 'uri', type: 'bytes32' },
                { name: 'deadline', type: 'uint256' }
            ]
        }

        const value = {
           hashId: HASH_ID,
            account: user,
            value: NFT1.value,
            currency: EUR,
            startDate: startDate,
            endDate: endDate,
            uri: utils.id(URI),
            deadline: deadline
        }

        let myWallet = await new ethers.Wallet.createRandom()
        myWallet = myWallet.connect(ethers.provider)
        await myManager.grantRole(AUTH_ROLE, myWallet.address)

        const signature = await myWallet._signTypedData(domain, types, value)

        const typedDataEncoder = new ethers.utils._TypedDataEncoder.from(types)
        const structHash = typedDataEncoder.hash(domain, types, value)`

Console output:

TypeError: Cannot read property 'toHexString' of undefined at isHexable (node_modules\ethers\node_modules\@ethersproject\bytes\src.ts\index.ts:55:21) at Object.arrayify (node_modules\ethers\node_modules\@ethersproject\bytes\src.ts\index.ts:111:9) at C:\Users\Guillermo\Documents\_nash21\repos\nash21-contracts\node_modules\ethers\node_modules\@ethersproject\hash\src.ts\typed-data.ts:117:31 at C:\Users\Guillermo\Documents\_nash21\repos\nash21-contracts\node_modules\ethers\node_modules\@ethersproject\hash\src.ts\typed-data.ts:293:57 at Array.map (<anonymous>) at C:\Users\Guillermo\Documents\_nash21\repos\nash21-contracts\node_modules\ethers\node_modules\@ethersproject\hash\src.ts\typed-data.ts:292:39 at TypedDataEncoder.encodeData (node_modules\ethers\node_modules\@ethersproject\hash\src.ts\typed-data.ts:314:37) at TypedDataEncoder.hashStruct (node_modules\ethers\node_modules\@ethersproject\hash\src.ts\typed-data.ts:318:31) at TypedDataEncoder.hash (node_modules\ethers\node_modules\@ethersproject\hash\src.ts\typed-data.ts:326:21) at Context.<anonymous> (test\Nash21Factory.test.js:615:49) at runMicrotasks (<anonymous>) at processTicksAndRejections (internal/process/task_queues.js:95:5)

Environment:
Using hardhat ^2.5.0 and "ethers": "5.0.18"

[zemse]

This problem can be reproduced with following script:

const domain = {
  name: 'N21_FACTORY',
  version: '1',
  chainId: 1,
  verifyingContract: ethers.constants.AddressZero
}

const types = {
  Create: [{
      name: 'hashId',
      type: 'bytes32'
    },
    {
      name: 'account',
      type: 'address'
    },
    {
      name: 'value',
      type: 'uint256'
    },
    {
      name: 'currency',
      type: 'bytes32'
    },
    {
      name: 'startDate',
      type: 'uint256'
    },
    {
      name: 'endDate',
      type: 'uint256'
    },
    {
      name: 'uri',
      type: 'bytes32'
    },
    {
      name: 'deadline',
      type: 'uint256'
    }
  ]
}

const value = {
  hashId: ethers.constants.HashZero,
  account: ethers.constants.AddressZero,
  value: 1,
  currency: ethers.constants.HashZero,
  startDate: 1,
  endDate: 1,
  uri: ethers.constants.HashZero,
  deadline: 1
}

const typedDataEncoder = new ethers.utils._TypedDataEncoder.from(types)
const structHash = typedDataEncoder.hash(domain, types, value) // this gives error

[ricmoo]

Thanks @zemse, I’ll look into this shortly.

[ricmoo]

I found the issue. There are two separate APIs, one that operates on an instance and one that is static. You are using the static API on an instance; passing too many parameters in (the instance method .hash only access one parameter, value), so it is trying to evaluate the domain as the value.

You likely want just this:

// Remove this line:
// const typedDataEncoder = ...

// And use the static method directly; no new, no instance
const structHash = ethers.utils._TypedDataEncoder.hash(domain, types, value)

The instance APIs are designed for more low-level modifications to the encoding process, for debugging and for reusing parts of the encoding.

Let me know if that helps. :)

[gperezalba]

Yesss, it works now!

Thanks @ricmoo @zemse ;)