经典智能合约之智能拍卖

实现一个简易的拍卖合约

角色分析：4类角色（拍卖师actioneer，委托人seller，竞买人bidder，买受人buyer）

功能分析：拍卖的基本原则是价高者得，在设定的拍卖时限内，出价最高者最终获得拍卖得标物（提示：在数据结构上，不用太复杂的设计，只需能记录当前最高价的竞买人及其金额、拍卖结束时间即可。）

竞拍功能：竞买人可以多次出价，价格必须高于当前记录的最高价，并将最高价和竞买人替换。
竞拍结束：竞拍结束时，宣布胜利者。

状态变量定义和初始化

定义变量：委托人、拍卖师、买受人、竞拍结束标志、时间限制、竞拍最高金额。(提示：合约调用者为拍卖师，如果涉及到转账的角色需要用address
payable，构造函数可以初始化拍卖师[即msg.sender]、拍卖时限、竞拍结束标志，竞买人在程序中选择不同account，根据account和msg.value更新买受人和最高金额)

竞拍功能

只要竞拍未结束都可以发起竞拍（提示：从调用信息窗口选择买家，输入竞拍价格，用msg.sender和msg.value获得买家和价格信息）

但需要满足以下条件：竞拍未结束；竞拍时的价格一定要比之前的价格高；竞拍在时限内；

当竞拍被允许时，需要退钱给上一个买家，并替换原有的最高价格和买受人。

结束竞拍

判断是否超过时限，并且是第一次执行本操作，确认通过后，转账给委托人。

合约代码

pragma solidity ^0.8.4;
contract auction {
    uint auctionEndTime;
    address public auctioneer;
    address public buyer;
    address payable public seller;
    uint public auctionAmount;

    // Allowed withdrawals of previous bids
    mapping(address => uint) pendingReturns;

    // A sign to judge whether the auction is over
    // Set to true at the end, disallows any change.
    bool ended;

    // Events that will be emitted on changes.
    event auctionAmountIncreased(address bidder, uint amount);
    event AuctionEnded(address winner, uint amount);

    // Errors that describe failures.
    /// The auction has already ended.
    error AuctionAlreadyEnded();
    /// There is already a higher or equal bid.
    error BidNotHighEnough(uint auctionAmount);
    /// The auction has not ended yet.
    error AuctionNotYetEnded();
    /// The function auctionEnd has already been called.
    error AuctionEndAlreadyCalled();

    constructor(
        uint biddingTime,
        address payable sellerAddress
    ) {
        seller = sellerAddress;
        auctionEndTime = block.timestamp + biddingTime;
        auctioneer = msg.sender;
    }

    /// Bid function
    function bid() external payable {
        // Revert the call if the bidding period is over.
        if (block.timestamp > auctionEndTime)
            revert AuctionAlreadyEnded();

        // Return money if the bid is not high enough
        if (msg.value <= auctionAmount)
            revert BidNotHighEnough(auctionAmount);

        if (auctionAmount != 0) {
            pendingReturns[buyer] += auctionAmount;
        }
        buyer = msg.sender;
        auctionAmount = msg.value;
        emit auctionAmountIncreased(msg.sender, msg.value);
    }

    /// End the auction and send the highest bid to the seller.
    function auctionEnd() external payable {

        // Analyzing conditions
        if (block.timestamp < auctionEndTime)
            revert AuctionNotYetEnded();
        if (ended)
            revert AuctionEndAlreadyCalled();
        ended = true;
        emit AuctionEnded(buyer, auctionAmount);
        // transfer
        seller.transfer(auctionAmount);
    }
}

首先，按照要求deploy拍卖合约，按照要求设置相关参数，其中seller的地址是 0x78731D3Ca6b7E34aC0F824c42a7cC18A495cabaB ，竞拍的时间是 120。

如下所示：