Check if calldata contains string

Question

I have a function that is called with some data - "SOMETHING".

function checker(address _from, uint _value, bytes calldata _data) external{
    //HOW to check if _data contains "SOMETHING"?
}

I have already tried:

if(string(_data) == ("SOMETHING")){...};
if(string(_data) == ("0x534f4d455448494e470a")){...}; // SOMETHING in hex
if(_data == 0x534f4d455448494e470a){...}
if(_data == hex"SOMETHING"){...}
if(_data == hex"534f4d455448494e470a"){...}

but it always says

Operator == not compatible with types string calldata and literal_string 

in some form or the other...

How can I compare the calldata with a String value? How to convert calldata to String correctly? How to check if the calldata contains some String value?

Answer 1

You cannot compare bytes or string using == in Solidity. You can however compare bytes32, so a simple solution is to hash the bytes first using keccak256 and compare the result of that.

For example:

function checker(bytes calldata _data) external pure returns (bool) {
  return keccak256(_data) == keccak256(abi.encodePacked("SOMETHING"));
}