How to Download a PDF file from Azure in ASP.NET MVC via Save Dialog

Question

I have a file stored on Azure storage that I need to download from ASP.NET MVC controller. The code below actually works fine.

string fullPath =  ConfigurationManager.AppSettings["pdfStorage"].ToString() + fileName ;
Response.Redirect(fullPath);

However, the PDF opens in the same page. I want the file to be downloaded via a Save dialog box, so the user stays on the same page. Before moving to Azure, I could write

return File(fullPath, "application/pdf", file);

But with Azure that doesn't work.

Answer 1

Assuming you mean Azure Blob Storage when you say Azure Storage, there are two other ways without actually downloading the file from storage to your web server and both of them involve setting Content-Disposition property on your blob.

1. If you want the file to always download when accessed via a URL, you can set blob's content-disposition property.

   var account = new CloudStorageAccount(new StorageCredentials(accountName, accountKey), true);
   var blobClient = account.CreateCloudBlobClient();
   var container = blobClient.GetContainerReference("container-name");
   var blob = container.GetBlockBlobReference("somefile.pdf");
   blob.FetchAttributes();
   blob.Properties.ContentDisposition = "attachment; filename=\"somefile.pdf\"";
   blob.SetProperties();
   

2. However if you want the file to be downloaded sometimes and displayed in the browser other times, you can create a shared access signature and override the content-disposition property in the SAS and use that SAS URL for downloading.

       var account = new CloudStorageAccount(new StorageCredentials(accountName, accountKey), true);
       var blobClient = account.CreateCloudBlobClient();
       var container = blobClient.GetContainerReference("container-name");
       var blob = container.GetBlockBlobReference("somefile.pdf");
       var sasToken = blob.GetSharedAccessSignature(new SharedAccessBlobPolicy()
       {
           Permissions = SharedAccessBlobPermissions.Read,
           SharedAccessExpiryTime = DateTimeOffset.UtcNow.AddMinutes(15),
       }, new SharedAccessBlobHeaders()
       {
           ContentDisposition = "attachment; filename=\"somefile.pdf\"",
       });
       var downloadUrl = string.Format("{0}{1}", blob.Uri.AbsoluteUri, sasToken);//This URL will always do force download.
   

Answer 2

You could download the file and then push to the web browser so the user will be able to save.

var fileContent = new System.Net.WebClient().DownloadData(fullPath); //byte[]

return File(fileContent, "application/pdf", "my_file.pdf");

This particular overload takes a byte array, a content type and a destination file name.