Why do I have a million null characters at the end of my CSV file

Question

I am generating a CSV export of data on the fly. I do this by getting a hashset of items, then transforming them row for row and writing them to a MemoryStream, which in turn gets sent to the client as a FileResult. Problem is there is about a million NULL characters at the end of the file, I would guess the number of these characters is equal to the number of items in the hashset. But they're at the end of the file, not the end of each line.

Anyways, the code is like such:

The Controller method:

public ActionResult ExportList(ListExportModel model)
{
  System.IO.MemoryStream ms = ls.ExportListToCsv(model,Server.MapPath("~/uploads"));
  return File(ms.GetBuffer(),"text/csv",model.MailingList.ListName + ".csv");
}

The ExportListToCsv method

public MemoryStream ExportListToCsv(ListExportModel model, string folderpath)
{
    MemoryStream stream = new MemoryStream();
    StreamWriter writer = new StreamWriter(stream);

    writer.WriteLine(string.Join(",", model.Columns));
    var data = GetListItemsFromCsv(model.ListId, folderpath);

    XmlDocument doc = new XmlDocument();
    // Parallel.ForEach(data, (li) =>
    foreach (var li in data)
    {
        string line = "";
        foreach (var field in model.Columns)
        {
            doc.LoadXml(li.CustomFields);
            switch (field)
            {
                //our standard fields
                    case "email":
                        line += li.Email + ",";
                        break;
                    case "tel":
                        line += li.Tel + ",";
                        break;

                    default:
                        line += (doc.SelectNodes("//" + field))[0].Value + ",";
                        break;
                }
            }

            writer.WriteLine(line.TrimEnd(','));
        }
        writer.Flush();
        stream.Position = 0;
        return stream;
    }

And the file (all dummy data, no actual persons were harmed during the making of the screenshot):

Note: I get the same results regardless of whether I use

writer.Flush()

and

stream.Position = 0

or not

Answer 1

You are calling GetBuffer() instead of ToArray().

See: http://msdn.microsoft.com/en-us/library/system.io.memorystream.toarray

This method omits unused bytes in MemoryStream from the array. To get the entire buffer, use the GetBuffer method.

This method returns a copy of the contents of the MemoryStream as a byte array. If the current instance was constructed on a provided byte array, a copy of the section of the array to which this instance has access is returned. See the MemoryStream constructor for details.

Answer 2

It looks like there could be a lot of blank lines at the end of your .csv file. This would cause the default: case to be executed numerous times at the end of processing.