question

Testing. This editor doesn't seem to be working. It's rejected anything I've tried to add. Testing.

I've found how the Excel spreadsheet is created, so sort of solved one problem, but came up with another one. Here's the code as it was:

 Private Sub MakeExcel(ByVal withReport As ReportClass)
    
  Dim ps As WicReportBasics.ReportParameters = Session.Item("Parameters")
    
  'Dim tempDir As String = "c:\temp\"
  Dim tempDir As String = Common.GetTempDir()
    
  ' Write the xls file to a local directory temporarily
  Dim Fname As String = tempDir & Session.SessionID.ToString & ".xls"
  Dim DiskOptions As DiskFileDestinationOptions = New DiskFileDestinationOptions
  DiskOptions.DiskFileName = Fname
    
  Dim ExportOptions As ExportOptions = withReport.ExportOptions
  With ExportOptions
  .DestinationOptions = DiskOptions
  .ExportDestinationType = ExportDestinationType.DiskFile
  .ExportFormatType = ExportFormatType.Excel
  End With
  withReport.Export()
    
  ' The following code writes the excel file 
  ' to the Client’s browser.
  Response.ClearContent()
  Response.ClearHeaders()
  Response.ContentType = "application/vnd.ms-excel"  'This needed to be updated https://stackoverflow.com/questions/974079/setting-mime-type-for-excel-document
  Response.AddHeader("Content-Disposition", "attachment; filename=" & ps.OutputFileName & ".xls")
  WriteFile(Fname)
  Response.Close()
    
  ' delete the exported file from disk
  System.IO.File.Delete(Fname)
    
 End Sub

The assigning of tempDir to Common.GetTempDir() was something I put in, some time back.

Please note that I had made a mistake with the Response.AddHeader call. ps.OutputFileName returned "Temp". But as you can see, I'd created a different filename, so it couldn't find Temp.xls. I fixed that then tested it. It worked fine on my dev box. So, I published it to the web server. There it failed, again with a network error. I'm thinking the problem is with the System.IO.File.Delete(Fname) call that was put there by the original developer. That it was going too fast and deleting the .xls file before the browser had a chance to download it to the user's machine. So I changed it like so:

 Private Sub MakeExcel(ByVal withReport As ReportClass)
    
  Dim ps As WicReportBasics.ReportParameters = Session.Item("Parameters")
    
  'Dim tempDir As String = "c:\temp\"
  Dim tempDir As String = Common.GetTempDir()
    
  ' Write the xls file to a local directory temporarily
  Dim Fname As String = tempDir & Session.SessionID.ToString & ".xls"
  Dim DiskOptions As DiskFileDestinationOptions = New DiskFileDestinationOptions
  DiskOptions.DiskFileName = Fname
    
  Dim ExportOptions As ExportOptions = withReport.ExportOptions
  With ExportOptions
  .DestinationOptions = DiskOptions
  .ExportDestinationType = ExportDestinationType.DiskFile
  .ExportFormatType = ExportFormatType.Excel
  End With
  withReport.Export()
    
  ' The following code writes the excel file 
  ' to the Client’s browser.
  Response.ClearContent()
  Response.ClearHeaders()
  Response.ContentType = "application/vnd.ms-excel"  'This needed to be updated https://stackoverflow.com/questions/974079/setting-mime-type-for-excel-document
  'Response.AddHeader("Content-Disposition", "attachment; filename=" & ps.OutputFileName & ".xls")    'old way of handling the file
  Response.AddHeader("Content-Disposition", "attachment; filename=" & Fname)
  WriteFile(Fname)
  Response.Close()
    
  DeleteTemporaryExportFileAsync(Fname)
 End Sub
    
 Private Shared Async Sub DeleteTemporaryExportFileAsync(Fname As String)
  Await Task.Delay(5000)   'give the browser time to download the Excel spreadsheet
    
  Try
  ' delete the exported file from disk
  System.IO.File.Delete(Fname)
  Catch ex As Exception
  ' if the deletion fails, ignore it and move on
  End Try
 End Sub

This gives a weird filename that looks something like this:

C_Windows_Temp_hsnceshdnntdiul.xls

Why has it changed the backslash character ("\") to an underscore, when run from the web server?

Hi @RodAtWork ,

I will continue to discuss with you in this thread. There are three points that I think you need to confirm.

1. Check MIME types on IIS. Make sure that .xls application/vdn.ms-excel exist in MIME types at the server and site level. This ensures that IIS allows such file transfers.
   

2. Use Response.End() to replace Response.Close(). Response.Close sends a reset packet to the client and using it in anything other than error condition will lead to all sorts of problems - eg, if you are talking to a client with enough latency, the reset packet can cause any other response data buffered on the server, client or somewhere in between to be dropped.
   

3. Use other browsers and try to download. Sometime network issue only report in chrome but other browsers can work well. IE, Edge and firefox are also great choices.
   

4. When you removed the line that deletes the .xls file, does the file exist in folder?

For some reason your other thread redirects here so my response is lost.

Your code uses the file path on the server as the file name. You want the actual file name. Use the Path.GetFileName() method to grab the file name from the path.

 Response.AddHeader("Content-Disposition", "attachment; filename=" & Path.GetFileName(Fname))

Response.Close() can cause problems. The reference documentation recommends Response.End() or HttpContext.Current.ApplicationInstance.CompleteRequest()

 Response.ClearContent()
 Response.ClearHeaders()
 Response.ContentType = "application/vnd.ms-excel"
 Response.AddHeader("Content-Disposition", "attachment; filename=" & Path.GetFileName(Fname))
 WriteFile(Fname)
 Response.End()

I'm pretty sure you not using ascyn methods correctly but it does not matter because execution never reaches DeleteTemporaryExportFileAsync() due to the Response.Close(). Secondly, there is no logical reason to implement an async method because the code is synchronous. Just delete the file once the WriteFile completes.

 Response.ClearContent()
 Response.ClearHeaders()
 Response.ContentType = "application/vnd.ms-excel"
 Response.AddHeader("Content-Disposition", "attachment; filename=" & Path.GetFileName(Fname))
 WriteFile(Fname)
 File.Delete(Fname)
 Response.End()

If you really want to implement an async delete then replace Response.End() with HttpContext.Current.ApplicationInstance.CompleteRequest()

Lastly, I tested the WriteFile() method with a 350,000 KB using the updated code above and logic worked as expected. WriteFile() methods writes to the response stream in 300,000 byte blocks. Once the WriteFile() finished the file is deleted. Below is my test code.

 Public Class _Default11
     Inherits System.Web.UI.Page
    
     Dim Fname As String = "C:\Temp\largefile.xls"
     Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    
     End Sub
    
     Protected Sub Button1_Click(sender As Object, e As EventArgs)
         Response.ClearContent()
         Response.ClearHeaders()
         Response.ContentType = "application/vnd.ms-excel"
         Response.AddHeader("Content-Disposition", "attachment; filename=" & Path.GetFileName(Fname))
         WriteFile(Fname)
         File.Delete(Fname)
         Response.End()
     End Sub
    
     Private Sub WriteFile(ByVal Fname As String)
    
         Dim MyFileInfo As FileInfo
         Dim StartPos As Long = 0
         Dim FileSize, ThisWrite, LeftToWrite As Long
    
         MyFileInfo = New FileInfo(Fname)
         FileSize = MyFileInfo.Length
         LeftToWrite = FileSize
    
         While LeftToWrite > 0
             ThisWrite = IIf(LeftToWrite > 300000, 300000, LeftToWrite)
             Response.WriteFile(Fname, StartPos, ThisWrite)
             Response.Flush()
             StartPos += ThisWrite
             LeftToWrite -= ThisWrite
         End While
    
     End Sub
    
    
 End Class

It would be very helpful if you can revert back to a code base that worked as expected. It's not clear if this bug is due to your updates or is an existing bug.

 Response.AddHeader("Content-Disposition", "attachment; filename=C:\Temp\" & Path.GetFileName(Fname))

I think Access permission is for application pool. I saw website where mention these details. This might be works

https://www.thedummyprogrammer.com/asp-net/configure-access-permission-to-a-folder-for-an-iis-application-pool

For you.