LazyMinting是如何实现的？

业务场景

我们lazyMinting使用场景主要是针对nft的竞拍业务来做的。 creator可以在上架nft时，不需要真正的mint nft，而是等有合适的bidder来购买后，才去mint nft。这样可以减少nft mint的成本，从而鼓励creator来创建更多的nft；

LazyMinting的实现思路：

核心思路是通过EIP-712的TypeDataSign来验证签名：

用户在链下用privateKey进行签名，链上通过合约验证确认签名消息的合法性以及业务逻辑的合理性。一但验证通过，立刻执行合约里的方法，mint nft，transfer给真正的买家。

我们项目里具体实现方案是什么？

定义了auction合约, 记录竞拍信息ActionData、NFT 购买者凭证信息Voucher；

solidity 复制代码

{
  // 竞拍信息
	struct AuctionDetails {
      address seller; // 卖家地址
      string uri; // nft信息
      uint256 startPrice;
      uint256 duration;
      // 最终竞拍人
      address bidder;
      uint256 bidPrice;
      bool isActive;
      bool isEnd;
      uint256 tokenId;
  }
  // 购买者的凭证
	struct NFTVoucher {
        string auctionId;
        uint256 bidPrice;
        bytes signature;
  }
  
  // 记录action信息
	 mapping(string => AuctionDetails))  public auctionIdToAuction;

  // 记录voucher
	mapping(string => NFTVoucher)) public auctionIdToVoucher;
}

当creator上架一个nft action的时候，传入auctionId，minPrice、duration这些信息，保存在map里；注意此时bidder/tokenId这些信息都是不存在的；

当用户出价购买时，组装数据，通过_signTypedData方法，调用钱包签名，生成一个Voucher，并且记录到链下；

ts 复制代码

  /**
   * Creates a new NFTVoucher object and signs it using this LazyMinter's signing key.

   * @returns {NFTVoucher}
   */
  async createVoucher(auctionId, bidPrice) {
    const voucher = { auctionId, bidPrice };
    const domain = await this._signingDomain();

    const types = {
      NFTVoucher: [
        { name: "auctionId", type: "string" },
        { name: "bidPrice", type: "uint256" },
      ],
    };
    const signature = await this.signer._signTypedData(domain, types, voucher);

    // const recoveredAddress = ethers.utils.verifyTypedData(domain, types, voucher, signature);
    // const expectedSignerAddress = this.signer.address;
    // assert(recoveredAddress === expectedSignerAddress); 单纯验证下代码逻辑
    // console.log("recoveredAddress = " + recoveredAddress);

    return {
      ...voucher,
      signature,
    };
  }

当竞拍结束，或者creator提前结束时，选择一个出价高的bidder作为获胜者。构造一个Winner凭证: WinnerVoucher

ts 复制代码

{
  auctionId: "auction123",
  bidder: "0x中标者地址",
  bidPrice: 1000000000000000000,
  nftAddress: "0xNFT合约地址",
  signature: "卖家的签名"
}

中标的bidder去链上进行redeem，提交两个voucher: 自身出价的voucher，卖家选择的voucher。

合约会验证的两个voucher的合法性，检查数据一致等等

address和Voucher里签名的用户是否是同一个，并且验证调用redeem的msg.value > Voucher.bidderPrice

solidity 复制代码

// 新增结构体
struct WinnerVoucher {
    string auctionId;
    address bidder;
    uint256 bidPrice;
    bytes signature;
}

// 计算哈希
function _hashWinner(WinnerVoucher calldata voucher)
    internal
    view
    returns (bytes32)
{
    bytes32 WINNER_VOUCHER_TYPE_HASH = keccak256(
        "WinnerVoucher(string auctionId,address bidder,uint256 bidPrice)"
    );
    bytes32 structHash = keccak256(
        abi.encode(
            WINNER_VOUCHER_TYPE_HASH,
            keccak256(bytes(voucher.auctionId)),
            voucher.bidder,
            voucher.bidPrice
        )
    );
    return _hashTypedDataV4(structHash);
}

// 新增验证函数
function _verifyWinner(WinnerVoucher calldata voucher)
    internal
    view
    returns (address)
{
    bytes32 digest = _hashWinner(voucher);
    return ECDSA.recover(digest, voucher.signature);
}

// 修改后的 redeem 函数
function redeemWithWinnerVoucher(
    address _nftAddress,
    string memory _auctionId,
    NFTVoucher calldata nftVoucher,
    WinnerVoucher calldata winnerVoucher
) public payable returns (uint256) {
    // 1. 验证 NFT voucher 是中标者签的
    address nftSigner = _verify(nftVoucher);
    require(msg.sender == nftSigner, "Invalid NFT signature");
    
    // 2. 验证 winner voucher 是卖家签的
    AuctionDetails storage auction = auctionIdToAuction[_auctionId];
    address winnerSigner = _verifyWinner(winnerVoucher);
    require(winnerSigner == auction.seller, "Invalid seller signature");
    
    // 3. 验证 winner voucher 指定的 bidder 就是调用者
    require(msg.sender == winnerVoucher.bidder, "NOT the winner");
    
    // 4. 验证出价金额
    require(msg.value >= winnerVoucher.bidPrice, "Insufficient funds");
    
    // 5. mint 并转移 NFT
    uint256 tokenId = nftContract.mint(_auctionId, auction.uri);
    nftContract.safeTransferFrom(address(this), msg.sender, tokenId);
    
    // 5. 将付款转账给卖家，这里假设是用 native token付款的
    (bool success, ) = auction.seller.call{value: winnerVoucher.bidPrice}("");
    require(success);
    
    // 7. 更新拍卖状态
    auction.bidder = winnerVoucher.bidder;
    auction.bidPrice = winnerVoucher.bidPrice;
    auction.isEnd = true;
    auction.tokenId = tokenId;
    
    return tokenId;
}

repo: github.com/6gunner/sca...