log.sol

pragma solidity >= 0.5.0;

contract Log {
    address public owner;
    
    event LogMsg(bytes message);
    
    constructor(address _owner) public {
        owner = _owner;    
    }
    
    function log(bytes memory message)
        public
    {
        require(msg.sender == owner, 'owner_only');
        
        emit LogMsg(message);
    }
}