File Size Goes to Zero when Returning FileStreamResult from MVC Controller

Question

I am attempting to download a file from Azure Storage in the form of an CloudBlockBlob. I want to allow the user to select where to put the downloaded file, so I have written the following code to do this

[AllowAnonymous]
public async Task<ActionResult> DownloadFile(string displayName)
{
    ApplicationUser user = null;
    if (ModelState.IsValid)
    {
        user = await UserManager.FindByIdAsync(User.Identity.GetUserId());

        // Retrieve storage account and blob client.
        CloudStorageAccount storageAccount = CloudStorageAccount.Parse(
            ConfigurationManager.AppSettings["StorageConnectionString"]);
        CloudBlobClient blobClient = storageAccount.CreateCloudBlobClient();
        CloudBlobContainer container = blobClient.GetContainerReference(
            VisasysNET.Utilities.Constants.ContainerName);

        // If the container does not exist, return error.
        if (container.Exists())
        {
            foreach (IListBlobItem item in container.ListBlobs(null, false))
            {
                if (item.GetType() == typeof(CloudBlockBlob))
                {
                    CloudBlockBlob blob = (CloudBlockBlob)item;
                    if (blob.Name.CompareNoCase(displayName))
                    {
                        string contentType = String.Format(
                            "application/{0}", 
                            Path.GetExtension(displayName).TrimStart('.'));

                        // No need to dispose, FileStreamResult will do this for us.
                        Stream stream = new MemoryStream();
                        await blob.DownloadRangeToStreamAsync(stream, null, null);
                        return File(stream, contentType, displayName);
                    }
                }
            }
            return RedirectToAction("Index", "Tools");
        }
    }
    return new HttpStatusCodeResult(HttpStatusCode.ServiceUnavailable);
}

This downloads the file from the blob storage fine, but when the controller returns to the view using FileStreamResult, the browser is launching the save file dialog as expected but the file size is 0 bytes. The Stream shows that the correct file size, but when I do

 return File(stream, contentType, displayName);

the data does not seem to be passed to the save dialog.

How can I get the file to save properly?

Thanks for your time.

Answer 1

Your memorystream position after DownloadRangeToStreamAsync will be on the last byte. Set it back to the begining before you return it.

stream.Seek(0,0)