SampleUpdater.sol for Talking to Ethereum Smart Contracts by Tim Cotten

SampleUpdater.sol

pragma solidity ^0.4.0;
contract SampleUpdater {

    address authorized_service_provider;
    uint nonce;
    
    function getNonce() public view returns(uint) {
        return nonce;
    }
    
    function update() public {
        require(msg.sender == authorized_service_provider, 'Not the authorized service provider.');
        
        nonce += 1;
    }
    
    constructor() public {
        authorized_service_provider = msg.sender;
        nonce = 0;
    }
}