support meta transactions for grantOperatorPermissions

[iavl]

Imagine this scenario: a new user sets up an operator. All subsequent interactions, such as follow, like, and post note, will be initiated by the operator on behalf of the user. In other words, the user only needs to interact with the blockchain once during the entire process, which is when calling grantOperatorPermissions to set the operator. To do this, they need to add the Crossbell RPC network through MetaMask, sign the transaction, send the transaction to the blockchain network through the RPC node, and pay the gas fees. If their wallet does not have CSB, they will also need to claim it from the faucet.

The above process would be tedious, especially for a new user.

If we can make the grantOperatorPermissionsWithSig method support meta transactions, users would only need to sign a signature indicating that they want to set up an operator. The relayer would then package this signature into a transaction and send it to the blockchain network to help users set up the operator. This would shield users from the underlying blockchain, making them unaware of RPC and gas fees. Although the transaction gas fee would be paid by the relayer, I believe that DApp developers would be willing to do this for their users at the moment.

The grantOperatorPermissionsWithSig interface looks like:

function grantOperatorPermissionsWithSig(
        uint256 characterId,
        address operator,
        uint256 permissionBitMap,
        EIP712Signature calldata sig
    ) external

#106

[iavl]

The following methods should be implemented:

function nonces(address owner) external view returns (uint256)
function DOMAIN_SEPARATOR() external view returns (bytes32)

function grantOperatorPermissionsWithSig(
        uint256 characterId,
        address operator,
        uint256 permissionBitMap,
        EIP712Signature calldata sig
    ) external

with the EIP712Signature struct:

struct EIP712Signature {
        uint8 v;
        bytes32 r;
        bytes32 s;
        uint256 deadline;
    }

The semantics of which are as follows:

For all uint256 characterId, addressoperator, uint256 permissionBitMap, EIP712Signature sig, a call to grantOperatorPermissionsWithSig(characterId, operator, permissionBitMap, sig) will set operator for characterId with permissionBitMap, increment nonces[owner] by 1, and emit a corresponding GrantOperatorPermissions event, if and only if the following conditions are met:

• The current blocktime is less than or equal to deadline.
• nonces[owner] (before the state update) is equal to nonce.
• r, s and v is a valid secp256k1 signature from owner of the message:

keccak256(abi.encodePacked(
   hex"1901",
   DOMAIN_SEPARATOR,
   keccak256(abi.encode(
            keccak256("grantOperatorPermissions(uint256 characterId,address operator,uint256 permissionBitMap,uint256 nonce,uint256 deadline)"),
            characterId,
            operator,
            permissionBitMap,
            nonce,
            deadline))
))

where DOMAIN_SEPARATOR is defined according to EIP-712. The DOMAIN_SEPARATOR
 should be unique to the contract and chain to prevent replay attacks from other domains, and satisfy the requirements of EIP-712. The DOMAIN_SEPARATOR looks like:

DOMAIN_SEPARATOR = keccak256(
    abi.encode(
        keccak256('EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)'),
        keccak256(bytes("Web3 Entry Character")),
        keccak256('1'),
        3737,
        address(0xa6f969045641Cf486a747A2688F3a5A6d43cd0D8)
));

the message is the EIP-712 typed structure:

{
  "types": {
    "EIP712Domain": [
      {
        "name": "name",
        "type": "string"
      },
      {
        "name": "version",
        "type": "string"
      },
      {
        "name": "chainId",
        "type": "uint256"
      },
      {
        "name": "verifyingContract",
        "type": "address"
      }
    ],
    "grantOperatorPermissions": [{
      "name": "characterId",
      "type": "uint256"
      },
      {
        "name": "operator",
        "type": "address"
      },
      {
        "name": "permissionBitMap",
        "type": "uint256"
      },
      {
        "name": "nonce",
        "type": "uint256"
      },
      {
        "name": "deadline",
        "type": "uint256"
      }
    ],
    "primaryType": "grantOperatorPermissions",
    "domain": {
      "name": "Web3 Entry Character",
      "version": 1,
      "chainId": 3737,
      "verifyingContract": "0xa6f969045641Cf486a747A2688F3a5A6d43cd0D8"
  },
  "message": {
    "characterId": characterId,
    "operator": operator,
    "permissionBitMap": permissionBitMap,
    "nonce": nonce,
    "deadline": deadline
  }
}}