download a SQL back up file in asp.net-CodePudding

I am trying to download sql back up file but getting error : "Unable to evaluate expression because the code is optimized or a native frame is on top of the call stack" near respone.end()

protected void btnDownload_Click(object sender, EventArgs e)
    {
        try
        {
            string backupDestination = backupPath;
            string dbNAme = dbName;
            string dateStamp = DateTime.Now.ToString("yy-MM-dd@HHmm");
            string backupfile = backupDestination   '\\'   dbNAme   " of "   dateStamp   ".bak";

            DataTable dt = blu.queryFunction("BACKUP database "   dbNAme   " to disk='"   backupDestination   "\\"   dbNAme   " of "   dateStamp   ".Bak'");

            WebClient req = new WebClient();
            HttpResponse response = HttpContext.Current.Response;

            response.Clear();
            response.ClearContent();
            response.ClearHeaders();
            response.Buffer = true;

            response.AddHeader("content-disposition", "attachment; filename= "   dbNAme   ".bak");
            
            byte[] data = req.DownloadData(backupfile);
            response.ContentType = "application/sql";
            response.BinaryWrite(data);
            response.End();
        }
        catch (Exception ex)
        {
            ScriptManager.RegisterStartupScript(this, this.GetType(), "alertscipt", "swal('Error!','Database Backup Failed."   ex.ToString()   "','warning')", true);
        }
    }

CodePudding user response：

If the backup file is present on the server running the application, you shouldn't be using a WebClient. Something that reads the file from local disk, e.g. TransmitFile(), would then be sufficient - like this:

string backupDestination = backupPath;
string dbNAme = dbName;
string dateStamp = DateTime.Now.ToString("yy-MM-dd@HHmm");
string backupfile = backupDestination   '\\'   dbNAme   " of "   dateStamp   ".bak";

DataTable dt = blu.queryFunction("BACKUP database "   dbNAme   " to disk='"   backupDestination   "\\"   dbNAme   " of "   dateStamp   ".Bak'");

HttpResponse response = HttpContext.Current.Response;

response.Clear();
response.ClearContent();
response.ClearHeaders();
response.Buffer = true;

response.AddHeader("content-disposition", "attachment; filename= "   dbNAme   ".bak");

response.ContentType = "application/octet-stream";
response.TransmitFile(backupfile);
response.Flush();

CodePudding user response：

One issue that I see is the buffer - change the response.Buffer = true; to false

response.Buffer = false;

for big files this is wrong because its put it on a buffer but you want to send it direct to the user...

also remove the catch (Exception ex) to see other problems on your code - the ScriptManager.RegisterStartupScript is not run from the moment you have change the headers. So the issue is hidden from you.

One other better and more correct way is to create a handler and download the file from there.