ASP.net MVC ActionResult corrupts the excel file when returning from MemoryStream

Question

I have the following action inside my Controller

public ActionResult DownloadExcel()
        {
            //create and populate Excel file here
            C1XLBook testBook = new C1XLBook(); 
            //populate it here

            MemoryStream ms = new MemoryStream();
            testBook.Save(ms, FileFormat.Biff8);

            return File(ms, "application/ms-excel", "test-file.xls");           
        }

When opening the file, I get the Excel message saying that the file doesn't match the extension and the file opens up corrupted.

If I save the file on the hard drive and return it from there, everything is fine:

return base.File(@"C:\LOGS\test-file.xls", "application/ms-excel", "test-excel.xls");

I initially thought that the Save function corrupts it when saving it into the MemoryStream, so I saved and re-loaded it back and it was fine passing back to the user - when saved on the Hard Drive and returned from there, rather than from the MemoryStream

Any ideas? I am not too fond of saving the file on the Hard Drive....besides I should be able to save it into the MemoryStream and return it from there?

One hunch I have is that perhaps the MemoryStream should not be used to return files in MVC, since every request is isolated?

Answer 1

Perhaps you need to rewind the memory stream (set ms.Position = 0;) before passing it to the result? After the call to Save its position will be at the end, not the beginning.