Find a matching ABI function by selector.

[novaknole]

So, I have 4 byte signature and I also have the abi of the contract.

Is there any easy way to figure out to get the abi of the function that my 4 byte signature matches in the abi of the contract ?

One way to do would be to loop through the abi of the contract, hash each one of function, and compare its 4 byte signature to my signature, but if the ethers already has this functionality, it would be great.

[zemse]

I don't see an explicit method, but contractInst.interface.decodeFunctionData method throws a useful error which can help you to achieve that.

function doesFunctionExist(contractInst: ethers.Contract, functionSig: string) {
  try {
    // this method needs 2 args and if second one is undefined, it throws error anyway
    contractInst.interface.decodeFunctionData('0x208b3804')
  } catch (err) {
    return !err.message.includes('no matching function');
  }
}

[ricmoo]

Either of those will work, but you can also just pass a sighash (or any allowed fragment specifier) into the interface.getFunction method, and it will find it for you. :)

It will throw though, if it isn't available in the Interface, so you will still need the try...catch.

e.g.

homestead> iface = new ethers.utils.Interface([ "function foo()" ])
homestead> iface.getFunction("foo")
FunctionFragment {
  type: 'function',
  name: 'foo',
  constant: false,
  inputs: [],
  outputs: [],
  payable: false,
  stateMutability: 'nonpayable',
  gas: null,
  _isFragment: true
}
homestead> id("foo()")
'0xc2985578b8f3b75f7dc66a767be2a4ef7d7c2224896a1c86e92ccf30bae678b7'
homestead> iface.getFunction("0xc2985578")
FunctionFragment {
  type: 'function',
  name: 'foo',
  constant: false,
  inputs: [],
  outputs: [],
  payable: false,
  stateMutability: 'nonpayable',
  gas: null,
  _isFragment: true
}

Let me know if that works for you. :)

[ricmoo]

(moving to discussions)