Question 88222 in ASP.NET Question posted in
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download a SQL back up file in asp.net

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);
        }
    }
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3

Answers


  1. Chosen as BEST ANSWER
    0

    ok so after 72 hours i have found the error. the download button was inside update panel so i was getting "Unable to evaluate expression because the code is optimized or a native frame is on top of the call stack"

    protected void btnDownload_Click(object sender, EventArgs e)
    {
        try
        {
            string dbNAme = dbName;
            string backupDestination = Server.MapPath("~/BackUp");
            string dateStamp = DateTime.Now.ToString("yyyy-MM-dd@HH_mm");
            string fileName = dbName + " of " + dateStamp + ".Bak";

            if (!Directory.Exists(backupDestination))
            {
                Directory.CreateDirectory(backupDestination);
            }

            DataTable dt = blu.queryFunction("BACKUP database " + dbNAme + " to disk='" + backupDestination + "\" + fileName + "'");


            byte[] bytes = File.ReadAllBytes(Path.Combine(backupDestination, fileName));
            // Delete .bak file from server folder.
            if (Directory.Exists(backupDestination))
            {
                Directory.Delete(backupDestination, true);
            }
            Response.Clear();
            Response.Buffer = false;
            Response.Charset = "";
            Response.Cache.SetCacheability(HttpCacheability.NoCache);
            Response.ContentType = "application/octet-stream";
            Response.AppendHeader("Content-Disposition", "attachment; filename=" + fileName);
            Response.BinaryWrite(bytes);
            Response.Flush();
            Response.End();
        }
        catch(Exception ex)
        {
            string exception = ex.ToString();
        }            
    }

  2. 0

    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();
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  3. 0

    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.

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