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我的智能合约中有这个功能：

  function getBackgroundColor(uint256 tokenId) public pure returns (string memory) {
    uint256 rand = random(string(abi.encodePacked(toString(tokenId))));
    bytes32 val = bytes32(rand);
    bytes memory hx = "0123456789ABCDEF";
    bytes memory str = new bytes(26);

    for (uint i = 17; i < 20; i++) {
      str[i*2] = hx[uint(uint8(val[i + 12] >> 4))];
      str[1+i*2] = hx[uint(uint8(val[i + 12] & 0x0f))];
    }

    return string(str);
  }

我像这样使用它：

function tokenURI(uint256 tokenId) override public pure returns (string memory) {
    string[17] memory parts;
    string memory backgroundColor = getBackgroundColor(tokenId);

    parts[0] = '<svg xmlns="http://www.w3.org/2000/svg" preserveAspectRatio="xMinYMin meet" viewBox="0 0 512 512"><rect width="100%" height="100%" fill="#';
    parts[1] = backgroundColor;
    parts[2] = '"/><path d="M256 372.057L378 203.686L331.4 140H180.6L134 203.686L256 372.057Z" fill="hsl(';
...
    string memory output = string(abi.encodePacked(parts[0], parts[1], parts[2], parts[3], parts[4], parts[5], parts[6], parts[7], parts[8]));
    output = string(abi.encodePacked(output, parts[9], parts[10], parts[11], parts[12], parts[13], parts[14], parts[15], parts[16]));

    string memory json = Base64.encode(bytes(string(abi.encodePacked('{"name": "Fweb3 NFT", "description": "This NFT represents participation in Fweb3.", "image": "data:image/svg+xml;base64,', Base64.encode(bytes(output)), '"}'))));
    output = string(abi.encodePacked('data:application/json;base64,', json));

    return output;

不幸的是，它在渲染的 SVG 中显示如下：

...<rect width="100%" height="100%" fill="#����������������������������������000001�����������&quot;>...

我如何将它更干净地包含在结果字符串中？

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