Friendly filename when public download Azure blob

Question

Is it possible to save a blob with a name of a GUID (or anything else) but when a user requests the files URI http://me.blob.core.windows.net/mycontainer/9BB34783-8F06-466D-AC20-37A03E504E3F the download comes down with a friendly name e.g. MyText.txt?

Answer 1

The answer is no. You would need to set the content-disposition header on the blob, and there's no way to set that header in blob storage.

Answer 2

Firstly you can use your own custom domain for blob URI: http://blogs.msdn.com/b/avkashchauhan/archive/2011/03/22/using-custom-domain-name-with-windows-azure-storage-instead-of-windows-stroage-name-blob-core-windows-net.aspx

Exemple of solution for you...

using Microsoft.WindowsAzure;
using Microsoft.WindowsAzure.StorageClient;

StorageCredentialsAccountAndKey credentials = new StorageCredentialsAccountAndKey(ConfigurationManager.AppSettings["WindowsAzureStorageAccountName"], ConfigurationManager.AppSettings["WindowsAzureStorageAccountKey"]);
CloudStorageAccount cloudStorageAccount = new CloudStorageAccount(credentials, true);

CloudBlobContainer blobContainer = blobClient.GetContainerReference("mycontainer");

// e.g. GUID of currently logged in user
string fileName = System.Web.Security.Membership.GetUser().ProviderUserKey.ToString();

CloudBlob blob = blobContainer.GetBlobReference(fileName);

byte[] blobArray = blob.DownloadByteArray();

Response.ContentType = "text/plain";
Response.AddHeader("content-disposition", "attachment; filename=" + "MyText.txt");
Response.BinaryWrite(blobArray);
Response.End();

Answer 3

Enabling users to download files (blobs) in Windows Azure can be done in 4 ways;

• Direct Download – Set the Access of the Container to Public Read Access or Full Public Read Access and expose the URL to the end user. The drawback of this method is obviously security – you have no way of controlling access when the URL is exposed. There is also no way of detecting downloads, and to execute code before/after the download.

• API Download – The user must run a Windows App, Silverlight etc. Also – the app must contain the storeaccount name and key – which might compromise security. Especially if you have several customers using the same account (they can still have their own containers of course).

• Proxy Download – Have the user access a URL on YOUR server – which then retrieves the file from Azure and sends it to the user. The advantage of this is that you have full control of downloads, you can execute code before/after downloading and you don’t have to expose any Azure URL’s / account info. In fact – the end user will not even see that the file is stored in Azure. You can also override the filename this way. A downside is that all traffic passes through your server – so you' might get a bottleneck here.

• Pass-through Download (Azure Shared Access Signature) - Creates a signature and inserts this signature in a URL where the user is redirected to Azure. The signature enables the user to access the file for a limited period of time. This is most likely your best option. It enables custom code to be executed before downloading, it will ensure max download speed for your users, and a good level of security is also ensured.

Here's a code snippet which streams files to user, and overrides the filename.

//Retrieve filenname from DB (based on fileid (Guid))
// *SNIP*
string filename = "some file name.txt"; 

//IE needs URL encoded filename. Important when there are spaces and other non-ansi chars in filename.
if (HttpContext.Current.Request.UserAgent != null &&     HttpContext.Current.Request.UserAgent.ToUpper().Contains("MSIE"))
filename = HttpUtility.UrlEncode(filename, System.Text.Encoding.UTF8).Replace("+", " ");

context.Response.Charset = "UTF-8";
//Important to set buffer to false. IIS will download entire blob before passing it on to user if this is not set to false
context.Response.Buffer = false;
context.Response.AddHeader("Content-Disposition", "attachment; filename=\"" + filename + "\"");
context.Response.AddHeader("Content-Length", "100122334"); //Set the length the file
context.Response.ContentType = "application/octet-stream";
context.Response.Flush();

//Use the Azure API to stream the blob to the user instantly.
// *SNIP*
fileBlob.DownloadToStream(context.Response.OutputStream);

See this blogpost for more: http://blog.degree.no/2012/04/downloading-blobs-from-windows-azure/

Answer 4

Now it is possible by setting the content-disposition header on generating the Shared Access Signature:

  string sasBlobToken = blob.GetSharedAccessSignature(sharedPolicy, new SharedAccessBlobHeaders()
            {
                ContentDisposition = "attachment; filename=" + friendlyFileName
            });
  string downloadLink = blob.Uri + sasBlobToken;

Answer 5

As of November 2013 there is now support for the content-disposition header in Windows Azure Blob Storage. You can assign the header either on blob creation or through a shared access signature.

I modified my save document method to take an optional parameter which is the friendly name to download.

public void SaveDocument(Stream documentToSave, string contentType, string containerName, string url, string friendlyName = null)
{
    var container = GetContainer(containerName);
    container.CreateIfNotExists();
    var blob = container.GetBlockBlobReference(url);
    blob.Properties.ContentType = contentType;
    if (friendlyName != null)
      blob.Properties.ContentDisposition = "attachment; filename=" + friendlyName;
    blob.UploadFromStream(documentToSave);
}

More about it: http://blog.simontimms.com/2013/12/02/content-disposition-comes-to-azure/