Getting error in using ECDSA

Question

We have a function:

function _validSignature(bytes memory signature, bytes32 msgHash) internal view returns (bool) {
        return msgHash.toEthSignedMessageHash().recover(signature) == _signerAddress;
    }

As i know toEthSignedMessageHash() takes messageHash as argument and recover() takes messageHash and signature as argument. But i did not understand how writing code like this:msgHash.toEthSignedMessageHash().recover(signature) working. Can you explain me this? When i tried same thing like this:

function recoverAddress(bytes32 _hash) public returns(address recovered){
        bytes32 signature = ECDSA.toEthSignedMessageHash(_hash);
        recovered = ECDSA.recover(_hash, signature);
        return recovered;
    }

its giving error for ECDSA.recover().

Error:

Member "recover" not found or not visible after argument-dependent lookup in type(library ECDSA).

Why? Why my approach giving error?

Answer 1

msgHash.toEthSignedMessageHash().recover(signature) works because you're attaching the ECDSA library's functions to bytes32.

This line:

using ECDSA for bytes32

will make it so everytime you have bytes32var.someFunction(otherArgs), the compiler will interpret it like ECDSA.someFunction(bytes32var, otherArgs).

---

This function:

    function recoverAddress(bytes32 _hash) public returns(address recovered){
        bytes32 signature = ECDSA.toEthSignedMessageHash(_hash);
        recovered = ECDSA.recover(_hash, signature);
        return recovered;
    }

is giving you error cause there's no recover function that takes (bytes32, bytes32) as arguments. You probably meant to write something like:

    function recoverAddress(bytes memory signature, bytes32 msgHash) public returns(address recovered){
        bytes32 _message = ECDSA.toEthSignedMessageHash(msgHash);
        recovered = ECDSA.recover(_message, signature);
        return recovered;
    }