Azure Blob上传后PDF空白、Excel格式无效问题求助

你遇到的核心问题是二进制文件数据被错误地用文本编码处理，导致文件结构彻底损坏：

• 你拿到的data字符串是二进制文件的转义表示（比如开头的PK是Excel/ZIP文件的标识，\u0003是二进制字节0x03的转义写法），这类数据本质是二进制流，不是可编辑的文本内容。
• 用Encoding.UTF8.GetBytes(data)转换时，UTF-8会把非文本字节和转义序列当成普通文本字符处理，直接篡改原始二进制值，最终上传的Blob文件已经失去了正常的文件结构，所以下载后PDF显示空白、Excel提示格式错误。

1. 正确将转义字符串还原为二进制字节数组 #

先解析字符串中的转义序列（如\uXXXX），再用单字节编码提取原始字节，确保二进制数据不被篡改：

// 解析转义序列，还原成包含原始二进制字符的字符串
string unescapedData = System.Text.RegularExpressions.Regex.Unescape(data);
// 使用iso-8859-1单字节编码转换，保证每个字符对应原始字节
byte[] fileBytes = System.Text.Encoding.GetEncoding("iso-8859-1").GetBytes(unescapedData);
MemoryStream memoryStream = new MemoryStream(fileBytes);
memoryStream.Position = 0;

2. 修正Excel的Content-Type #

xlsx属于OpenXML格式，正确的Content-Type是application/vnd.openxmlformats-officedocument.spreadsheetml.sheet，旧的application/vnd.ms-excel对应xls格式，会导致文件类型识别错误：

// 替换else块中的ContentType设置
var file = new FormFile(memoryStream, 0, memoryStream.Length, null, companyId + ".xlsx")
{
    Headers = new HeaderDictionary(),
    ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"
};

3. 避免重复使用同一MemoryStream #

你同时用同一个MemoryStream创建FileStreamResult和FormFile，容易导致流位置偏移，建议创建独立的流或者复用前重置位置：

// 复制独立流用于上传
MemoryStream uploadStream = new MemoryStream(fileBytes);
uploadStream.Position = 0;
var file = new FormFile(uploadStream, 0, uploadStream.Length, null, companyId + ".pdf")
{
    // ...
};

// 处理原始转义字符串为二进制字节
string unescapedData = System.Text.RegularExpressions.Regex.Unescape(data);
byte[] fileBytes = System.Text.Encoding.GetEncoding("iso-8859-1").GetBytes(unescapedData);

var lastIndedOf = attachment.FileName.LastIndexOf(".");
var extension = attachment.FileName.Substring(lastIndedOf);

if (extension == ".pdf")
{
    MemoryStream uploadStream = new MemoryStream(fileBytes);
    uploadStream.Position = 0;
    
    var file = new FormFile(uploadStream, 0, uploadStream.Length, null, companyId + ".pdf")
    {
        Headers = new HeaderDictionary(),
        ContentType = "application/pdf"
    };
    var fileUploadData = await _azureBlobStorageService.SaveToFolderBlobStorage(file, companyId + ".pdf", companyId, companyId.ToString());
} 
else if (extension == ".xlsx")
{
    MemoryStream uploadStream = new MemoryStream(fileBytes);
    uploadStream.Position = 0;
    
    var file = new FormFile(uploadStream, 0, uploadStream.Length, null, companyId + "zoho" + ".xlsx")
    {
        Headers = new HeaderDictionary(),
        ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"
    };
    var fileUploadData = await _azureBlobStorageService.SaveToFolderBlobStorage(file, companyId + "zoho" + ".xlsx", companyId, companyId.ToString());
}

内容的提问来源于stack exchange，提问作者Sam