为什么我不能使用发布到Azure服务器的asp.net核心应用程序下载Azure Blob

Question

I am trying to download a Blob from an Azure storage account container. When I run the application locally, I get the correct "Download" folder C:\\Users\\xxxx\\Downloads. When I publish the application to Azure and try to download the file, I get an error. I have tried various "Knownfolders", and some return empty strings, others return the folders on the Azure server. I am able to upload files fine, list the files in a container, but am struggling with downloading a file.

string conn = 
configuration.GetValue<string>"AppSettings:AzureContainerConn");
CloudStorageAccount storageAcct = CloudStorageAccount.Parse(conn);
CloudBlobClient blobClient = storageAcct.CreateCloudBlobClient();
CloudBlobContainer container = 
blobClient.GetContainerReference(containerName);

 Uri uriObj = new Uri(uri);

string filename = Path.GetFileName(uriObj.LocalPath);

// get block blob reference  
CloudBlockBlob blockBlob = container.GetBlockBlobReference(filename);

Stream blobStream = await blockBlob.OpenReadAsync();

string _filepath = _knownfolder.Path + "\\projectfiles\\";
Directory.CreateDirectory(_filepath);

_filepath = _filepath + filename;
Stream _file = new MemoryStream();
try
{
 _file = File.Open(_filepath, FileMode.Create, FileAccess.Write);

 await blobStream.CopyToAsync(_file);
 }
finally
{
  _file.Dispose();
}

The expected end result is the file ends up in the folder within the users "Downloads" folder.

Answer 1

Since you're talking about publishing to Azure, the code is probably from a web application, right? And the code for the web application runs on the server . Which means the code is trying to download the blob to the server running the web application .

To present a downloadlink to the user to enable them to download the file, use the FileStreamResult which

Represents an ActionResult that when executed will write a file from a stream to the response.

A (pseudo code) example:

[HttpGet]
public FileStreamResult GetFile()
{
  var stream = new MemoryStream();
  CloudBlockBlob blockBlob = container.GetBlockBlobReference(filename);
  blockBlob.DownloadToStream(stream);
  blockBlob.Seek(0, SeekOrigin.Begin);
  return new FileStreamResult(stream, new MediaTypeHeaderValue("text/plain"))
  {
    FileDownloadName = "someFile.txt"
  };
}