Excel file corrupt in Windows 8

A while ago, I made something in Asp.Net with CarlosAg Excel XML Writer Library. This is a free component to generate Excel (.xls) documents (xml). It does not require an installation of Office on your IIS server.

Here is a code sample to show how easy it works.

using CarlosAg.ExcelXmlWriter;

class TestApp {
    static void Main(string[] args) {
        Workbook book = new Workbook();
        Worksheet sheet = book.Worksheets.Add("Sample");
        WorksheetRow row =  sheet.Table.Rows.Add();
        row.Cells.Add("Hello World");
        book.Save(@"c:\test.xls");
    }
}

The downside is that it is a library dated from 2005 and it has no xlsx support (office 2010, office 365). But it works!

So I made an generic handler (.ashx) which gives this popup to download the Excel workbook. [more]

public void ProcessRequest (HttpContext context) {
    context.Response.ContentType = "application/vnd.ms-excel";
    context.Response.AddHeader("Content-Disposition", 
        "attachment; filename=Report-" + DateTime.Now.ToString("yyyy-MM-dd") + ".xls");

    GenerateMyExcel gme = new GenerateMyExcel ();
    Workbook book = gme.GetExcelReport();
    
    book.Save(context.Response.OutputStream);
}

And I also made a method which takes this workbook and attaches it and mails it.

MailMessage msg = new MailMessage("from@mydomain.com", 
    "to@mydomain.com", "Report", "look at attachment");
GenerateMyExcel gme = new GenerateMyExcel();
Workbook book = gme.GetExcelReport();
MemoryStream ms = new MemoryStream();
book.Save(ms);
Byte[] byteArray = ms.ToArray();
ms.Close();
MemoryStream StreamToAttach = new MemoryStream(byteArray);
msg.Attachments.Add(new Attachment(StreamToAttach, "report.xls"));

SmtpClient sc = new SmtpClient();
try
{
    sc.Send(msg);
}
catch (Exception ex)
{
    System.Diagnostics.Debug.WriteLine(ex.Message + " " + ex.StackTrace);
}
StreamToAttach.Close();

But When I opened the file, my excel in Office 365 Home Premium Preview on Windows 8, I get this “File is corrupt” message.

Was this information helpful? Seriously?

Hours debugging later, I found out that it was a security issue. When you open the properties of the file (and have a Dutch Windows):

There is this security message: “This file came from another computer and might be blocked…” So When I hit ‘unblock’ and ‘ok’, I can open the file normally!

This took me a day, because I thought that there was some thing with the CarlosAg library which made my file corrupt. Like setting a cell to number when there is a string inside.

The next time that I want to generate an Excel file, I will use EPPlus.