Descargar archivos Blob de Azure en MVC3

Aquí hay una versión resumible (útil para archivos grandes o para permitir la búsqueda en la reproducción de video o audio) del acceso privado a blob:

public class AzureBlobStream : ActionResult
{
    private string filename, containerName;

    public AzureBlobStream(string containerName, string filename)
    {
        this.containerName = containerName;
        this.filename = filename;
        this.contentType = contentType;
    }

    public override void ExecuteResult(ControllerContext context)
    {
        var response = context.HttpContext.Response;
        var request = context.HttpContext.Request;

        var connectionString = ConfigurationManager.ConnectionStrings["Storage"].ConnectionString;
        var account = CloudStorageAccount.Parse(connectionString);
        var client = account.CreateCloudBlobClient();
        var container = client.GetContainerReference(containerName);
        var blob = container.GetBlockBlobReference(filename);

        blob.FetchAttributes();
        var fileLength = blob.Properties.Length;
        var fileExists = fileLength > 0;
        var etag = blob.Properties.ETag;

        var responseLength = fileLength;
        var buffer = new byte[4096];
        var startIndex = 0;

        //if the "If-Match" exists and is different to etag (or is equal to any "*" with no resource) then return 412 precondition failed
        if (request.Headers["If-Match"] == "*" && !fileExists ||
            request.Headers["If-Match"] != null && request.Headers["If-Match"] != "*" && request.Headers["If-Match"] != etag)
        {
            response.StatusCode = (int)HttpStatusCode.PreconditionFailed;
            return;
        }

        if (!fileExists)
        {
            response.StatusCode = (int)HttpStatusCode.NotFound;
            return;
        }

        if (request.Headers["If-None-Match"] == etag)
        {
            response.StatusCode = (int)HttpStatusCode.NotModified;
            return;
        }

        if (request.Headers["Range"] != null && (request.Headers["If-Range"] == null || request.Headers["IF-Range"] == etag))
        {
            var match = Regex.Match(request.Headers["Range"], @"bytes=(\d*)-(\d*)");
            startIndex = Util.Parse<int>(match.Groups[1].Value);
            responseLength = (Util.Parse<int?>(match.Groups[2].Value) + 1 ?? fileLength) - startIndex;
            response.StatusCode = (int)HttpStatusCode.PartialContent;
            response.Headers["Content-Range"] = "bytes " + startIndex + "-" + (startIndex + responseLength - 1) + "/" + fileLength;
        }

        response.Headers["Accept-Ranges"] = "bytes";
        response.Headers["Content-Length"] = responseLength.ToString();
        response.Cache.SetCacheability(HttpCacheability.Public); //required for etag output
        response.Cache.SetETag(etag); //required for IE9 resumable downloads
        response.ContentType = blob.Properties.ContentType;

        blob.DownloadRangeToStream(response.OutputStream, startIndex, responseLength);
    }
}

Ejemplo:

Response.AddHeader("Content-Disposition", "attachment; filename=" + filename); // force download
return new AzureBlobStream(blobContainerName, filename);

Me di cuenta de que escribir en el flujo de respuesta desde el método action estropea las cabeceras HTTP. Faltan algunas cabeceras esperadas y otras no están configuradas correctamente.

Así que en lugar de escribir en el flujo de respuesta, obtengo el contenido del blob como un flujo y lo paso al Controlador.Método File ().

CloudBlockBlob blob = container.GetBlockBlobReference(blobName);
Stream blobStream = blob.OpenRead();
return File(blobStream, blob.Properties.ContentType, "FileName.txt");