Downloading file to browser from Azure Blob Storage using SAS

Question

In my DownloadFile page's Page_Load method, the filename a user wishes to download is retrieved from the query string. The file is hosted in an Azure Blob Storage account. I am attempting to download the file using shared access signatures (SAS) via this approach:

var containerName = "containerName";
var con = "connectionString";
CloudStorageAccount account = CloudStorageAccount.Parse(con);

var blobClient = account.CreateCloudBlobClient();
var container = blobClient.GetContainerReference(containerName);
var blob = container.GetBlockBlobReference("file.pdf");
var sasToken = blob.GetSharedAccessSignature(new SharedAccessBlobPolicy()
{
    Permissions = SharedAccessBlobPermissions.Read,
    SharedAccessExpiryTime = DateTime.UtcNow.AddMinutes(10),
}, new SharedAccessBlobHeaders()
{
    ContentDisposition = "attachment; filename=file.pdf"
});

var blobUrl = string.Format("{0}{1}", blob.Uri.AbsoluteUri, sasToken);
Response.Redirect(blobUrl);

However, this does not download the file. Instead, the browser just shows a garbled character stream of the file:

The blobUrl appears to be valid. But the Response.Redirect isn't working as expected. Am I doing something wrong?

Note: I am using WebForms (unfortunately), not MVC

Does this answer your question? Downloading Azure Blob files in MVC3 — Jazb
Is setting the ContentType property to application/pdf required? — Glenn
@Glenn I don't believe so because the url is to the actual file, which is hosted in Azure. The response does not contain the file. I did try that though without any luck. — JoshG
@404 unfortunately, no difference. Also, the file itself isn't included in the response. It's not being downloaded to the server first. Intead, a URL is generated using an Azure Storage SAS token, and the Response.Redirect is to redirect to that generated URL. — JoshG

JoshG JoshG · Accepted Answer · 2021-01-26T04:54:00

I was able to figure out a workaround by using an iframe. If I add an iframe to the page:

<iframe id="iframeFile" runat="server" style="display:none;"></iframe>

Then set the source in the codefile:

iframeFile.Src = blobUrl;

It downloads the file.

This may not be ideal, and I'm still not sure why Response.Redirect isn't working as expected. So I'm certainly open to other suggestions as well. But this workaround does resolve the issue of not being able to download the file.

Downloading file to browser from Azure Blob Storage using SAS

1 Answers