Solidity – How to Get Interface ID of Solidity Interface Using Ethers.js?

eip-165ethers.jsinterfacessolidity

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?

Best Answer

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.

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The equivalent in ethers.js involves first creating an "interface" object and calling a method on that:

> let ABI = [ "function transfer(address to, uint amount)" ];
> let iface = new ethers.utils.Interface(ABI);
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Taken from here

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As @0xSanson mentioned in the comment above it should be abi.encodePackaged(r, s, v). In the same order in which the data is read:

assembly {
    r := mload(add(signature, 0x20))
    s := mload(add(signature, 0x40))
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