Question

I’ve been struggling with a problem when downloading very big files (>2GB) on Silverlight. My application is an out-of-browser Download Manager running with elevated permissions.

When the file reaches a certain ammount of data (2GB), it throws the following exception:

System.ArgumentOutOfRangeException was caught
  Message=Specified argument was out of the range of valid values.
Parameter name: count
  StackTrace:
   in MS.Internal.InternalNetworkStream.BeginRead(Byte[] buffer, Int32 offset, Int32 count, AsyncCallback callback, Object state)
   in MS.Internal.InternalNetworkStream.Read(Byte[] buffer, Int32 offset, Int32 count)
   in MySolution.DM.Download.BeginResponseCallback(IAsyncResult ar)
  InnerException: 
Null

The only clue I have is this site, who shows the BeginCode implementation. This exception only occurs when count is < then 0.

My code

/* "Target" is a File object. "source" is a Stream object */

var buffer = new byte[64 * 1024];
int bytesRead;
Target.Seek(0, SeekOrigin.End); // The file might exists when resuming a download

/* The exception throws from inside "source.Read" */
while ((bytesRead = source.Read(buffer, 0, buffer.Length)) > 0)
{
    Target.Write(buffer, 0, bytesRead);
    _fileBytes = Target.Length;
    Deployment.Current.Dispatcher.BeginInvoke(() => { DownloadPercentual = Double.Parse(Math.Round((decimal)(_fileBytes / (_totalSize / 100)), 5).ToString()); });
}

Target.Close();
logFile.Close();

The error occurs with different kind of files, and they come from public buckets on Amazon S3. (with regular http requests).

Answer 1

I searched a bit and it looks like this is a known limitation in Silverlight. One possible workaround is to perform the download in multiple sections, each smaller than 2GB, using the Range header.