c# - 使用 API 从 Azure blob 下载

Question

我需要使用 API 将 PDF 或 Excel 文件从 azure blob 存储传输到前端。我正在使用download to byte array of blob storage然后将其转换为内存流以将其发送回用户。

这是我的 Controller

[AllowAnonymous]
[HttpGet]
[Route("GetFiles")]
public HttpResponseMessage GetFiles()
{
        const string StorageAccountName = "nameofAccount";
        const string StorageAccountKey = "TheKey";
        try
        {
          var storageAccount = new CloudStorageAccount(new StorageCredentials(StorageAccountName, StorageAccountKey), true);// login to azure and storage Account
          
          var bloblClinet = storageAccount.CreateCloudBlobClient();// get blob client refernce

          var container = bloblClinet.GetContainerReference("crmtestblob");// get container refernce 

          var blob = container.GetBlockBlobReference("test.xlsx");
          long fileByteLength = blob.Properties.Length;// this return -1 
          byte[] fileContent = new byte[100000];

          var MyArray = blob.DownloadToByteArray(fileContent, 0);
            
          HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK);


          var stream = new MemoryStream(MyArray);//application/octet-stream
            result.Content = new StreamContent(stream);//application/vnd.ms-excel
          result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
          result.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
          {
              FileName = "test.xlsx"
          };
          return result;

        }
        catch (Exception ex)
        {
           

            
            return new HttpResponseMessage(HttpStatusCode.InternalServerError);
        }

    }

我收到回复 200 但没有发送文件，或者文件已损坏 任何帮助都会很棒

Answer 1

您错误地使用了 DownloadToByteArray 函数导致了您的问题。

根据官方API引用CloudBlob.DownloadToByteArray(Byte\[\], Int32, AccessCondition, BlobRequestOptions, OperationContext) Method ，函数的返回结果是读入缓冲区的总字节数，而不是blob内容。

下面有两个 SO 线程，我认为它们的答案足以帮助您修复它。

1. Downloading a file from Azure Storage to client using Angular2 with .NET Web Api 2

   使用CloudBlob.OpenReadAsync Method打开一个可读流作为响应流内容。

   var stream = await blob.OpenReadAsync();
   result.Content = new StreamContent(stream);
   

2. HttpResponseMessage Redirect to Private Azure Blob Storage

   使用 sas token 将请求重定向到 blob url。

   var sasToken = blob.GetSharedAccessSignature(new SharedAccessBlobPolicy()
   {
       Permissions = SharedAccessBlobPermissions.Read,
       SharedAccessExpiryTime = DateTime.UtcNow.AddHours(1)//Assuming you want the link to expire after 1 hour
   });
   var blobUrl = string.Format("{0}{1}", blob.Uri.AbsoluteUri, sasToken);
   var response = Request.CreateResponse(HttpStatusCode.Moved);
   response.Headers.Location = new Uri(bloburl);