auction.sol

pragma solidity ^0.4.15;

contract auction {
    address highestBidder;
    uint highestBid;
    mapping(address => uint) refunds;

    function bid() payable external {
        if (msg.value < highestBid) revert();

        if (highestBidder != 0) {
            refunds[highestBidder] += highestBid; // record the refund that this user can claim
        }

        highestBidder = msg.sender;
        highestBid = msg.value;
    }

    function getHighestBidder() constant returns (address hghstBidder) {
       return highestBidder;
    } 

    function getHighestBid() constant returns (uint hghstBid) {
       return highestBid;
    }    

    function withdrawRefund() external {
        uint refund = refunds[msg.sender];
        refunds[msg.sender] = 0;
        if (!msg.sender.send(refund)) {
            refunds[msg.sender] = refund; // reverting state because send failed
        }
    }
}