It’s a common scenario: user needs to download a file from the server by clicking link or a button in your ASPX page. The server-side code for this is pretty straightforward and looks something like this:

Sub DownloadFile(ByVal i_sServerPath As String, ByVal i_sDisplayName As String)
   Dim oFile As FileInfo = New FileInfo(i_sServerPath)

   With Response
      .Clear()
      .ClearHeaders()
      .AddHeader("Content-Length", oFile.Length.ToString())
      .ContentType = ReturnContentType(oFile.Extension.ToLower())
      .AddHeader("Content-Disposition", "attachment; filename=" & i_sDisplayName)
      .TransmitFile(oFile.FullName)
      .End()
   End With

End Sub

The code accepts 2 parameters: i_sServerPath – full path to the file on the server and i_sDisplayName – file name that will be displayed to the user in the “Save As” dialog. Code also populates response headers based on file information. I use this handy function to populate ContentType based on file extention:

Function ReturnContentType(ByVal i_sfileExtension As String) As String
   Select Case i_sfileExtension
      Case ".htm", ".html", ".log" : Return "text/HTML"
      Case ".txt" : Return "text/plain"
      Case ".doc" : Return "application/ms-word"
      Case ".tiff", ".tif" : Return "image/tiff"
      Case ".asf" : Return "video/x-ms-asf"
      Case ".avi" : Return "video/avi"
      Case ".zip" : Return "application/zip"
      Case ".xls", ".csv" : Return "application/vnd.ms-excel"
      Case ".gif" : Return "image/gif"
      Case ".jpg", "jpeg" : Return "image/jpeg"
      Case ".bmp" : Return "image/bmp"
      Case ".wav" : Return "audio/wav"
      Case ".mp3" : Return "audio/mpeg3"
      Case ".mpg", "mpeg" : Return "video/mpeg"
      Case ".rtf" : Return "application/rtf"
      Case ".asp" : Return "text/asp"
      Case ".pdf" : Return "application/pdf"
      Case ".fdf" : Return "application/vnd.fdf"
      Case ".ppt" : Return "application/mspowerpoint"
      Case ".dwg" : Return "image/vnd.dwg"
      Case ".msg" : Return "application/msoutlook"
      Case ".xml", ".sdxl" : Return "application/xml"
      Case ".xdp" : Return "application/vnd.adobe.xdp+xml"
      Case Else : Return "application/octet-stream"
   End Select
End Function

It’s all good, but what if you need to delete the file from the server immediately after user downloaded it? For example it was a report, generated by user’s request and saved into temporary file, and that file needs to be deleted after user downloads it.

We have to user Response.End() after Response.TransmitFile() otherwise download won’t work. But any server-side command after Response.End() doesn’t work either. The solution is to flush data, delete file and then call Response.End(). Here is the modified version of DownloadFile:

Sub DownloadFile(ByVal i_sServerPath As String, ByVal i_sDisplayName As String)
   Dim oFile As FileInfo = New FileInfo(i_sServerPath)

   With Response
      .Clear()
      .ClearHeaders()
      .AddHeader("Content-Length", oFile.Length.ToString())
      .ContentType = ReturnContentType(oFile.Extension.ToLower())
      .AddHeader("Content-Disposition", "attachment; filename=" & i_sDisplayName)
      .TransmitFile(oFile.FullName)
      .Flush()
      oFile.Delete()
      .End()
   End With

End Sub

Take a look at Lines 11 and 12 – the code flushes the data and then deletes the file. If you call this function in a server-side code (e.g. as a response to a button click) user gets a prompt to download file and then, after file is downloaded – it is deleted from the server.