file download link

I want to make sure that when the user clicks a link to a media file it shows the save file dialog

code:

Code:

---

<%@ Import Namespace="System.IO"%>
<script language="VB" runat="server">
Sub Page_Load(sender As Object, e As EventArgs)
 
  Dim root As String = "c:\dirname"
  Dim filepath As String = Request.Params("file")
  Response.Write(filePath)
  If Not filepath Is Nothing Then

    If File.Exists(filepath) And filepath.StartsWith(root) Then
      Dim filename As String = Path.GetFileName(filepath)
      Response.Clear()
      Response.ContentType = "application/octet-stream"
      Response.AddHeader("Content-Disposition", _
        "attachment; filename=""" & filename & """")
      Response.Flush()
      Response.WriteFile(filepath)
    End If
  End If

End Sub
</script>

---

but when the user gets the dialog it doesnt tell the user how big the file is.

How can i get it to show how big the file is?

Response.AddHeader "Content-Length", FileSize