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

Question

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);
}
}

Answer 1

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.

Answer 2

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();

Answer 3

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();
}
}