Is there a way to get an interface ID of a Solidity interface using ethersjs?

Question

Is there a way to get an interface ID of a Solidity interface using ethersjs? I'm using ethersjs in my test file and I want to test if the supportsInterface is returning a correct interface ID.

I could get the interface ID in Solidity with type(IMyContract).interfaceId but it doesn't seem like there is a straightforward way of achieving the same thing outside of Solidity.

How can I get the interface ID of a contract or interface in ethersjs?

Answer 1

Currently there is not. You have to xor all function selectors of IMyContract.

To make your life easier, you can use ethers.js interface and use its getSighash functions to not have to hash it and slice it ourself. But still you have to xor these selectors to get an interfaceId.

Answer 2

Here's how I solved it, Ethers v5 & Typescript with OpenZeppelin upgradeable contracts (will work with any type of contract).

import { Contract, ContractInterface, ethers } from "ethers";
import { IERC1155Upgradeable__factory } from "../typechain-types/factories/IERC1155Upgradeable__factory";
import { IERC165Upgradeable__factory } from "../typechain-types/factories/IERC165Upgradeable__factory";

    const IERC165UpgradeableInterface = IERC165Upgradeable__factory.createInterface();
    const IERC1155UpgradeableInterface = IERC1155Upgradeable__factory.createInterface();
    const IERC165InterfaceID = getInterfaceID(IERC165UpgradeableInterface)
    // interface ID does not include base contract(s) functions.
    const IERC11InterfaceID = getInterfaceID(IERC1155UpgradeableInterface).xor(IERC165InterfaceID);
    assert(await contract.supportsInterface(IERC11InterfaceID._hex), "Doesn't support IERC1155Upgradeable");

export function getInterfaceID(contractInterface: ethers.utils.Interface) {
  let interfaceID: ethers.BigNumber = ethers.constants.Zero;
  const functions: string[] = Object.keys(contractInterface.functions);
  for (let i=0; i< functions.length; i++) {
      interfaceID = interfaceID.xor(contractInterface.getSighash(functions[i]));
  }

  return interfaceID;
}

The tricky part is that you have to xor out any base contracts as I looked though the solc compiler and they do not include base contract functions.

Answer 3

If you do not mind to have a selector hardcoded, I would use the remix to get the selector. In particular, I would insert an interface of your contract into the remix and create another contract with a public variable with the type(IMyContract).interfaceId value assigned (see below). Then deploy the contract and get the value of the selector from the "DEPLOY & RUN TRANSACTIONS" panel.

Here is the workaround:

pragma solidity ^0.8.7;

interface IMyContract {
    function func1() external view returns (bytes32);
    function func2() external;
}

contract GetSelectorOfIMyContract {
    bytes4 public _interfaceId;
    constructor () {
        _interfaceId = type(IMyContract).interfaceId;
    }
}

Answer 4

I made a simple app to solve this problem(I had the same issue so i had to solve it). https://interfaceid.lucasgrasso.com.ar/ , You just have to paste the ABI of the Interface you want to have the ID to. Hope it´s useful.