I have a default.aspx page that sometimes will cause an exception that gets caught in the Global.asax file. How do I send data back to my default.aspx page to change the HTML output without doing a page refresh? Is that possible?
you will have to implement a try catch and then detect the error and take steps accordingly
so suppose you know in which line you have an error.
try
{
//error prone code
}
catch
{
reponse.write("error");
response.End()
}
doing this you will catch the error and it wont be caught in the global.asax file and the "error" string would be sent back as response to the user
*NOTE - this is just an example and th estructure of the code might differ widely depending upon the type of request GET OR POST or even if thats and AJAX based request
Related
When I call Response.Redirect(someUrl) I get the following HttpException:
Cannot redirect after HTTP headers have been sent.
Why do I get this? And how can I fix this issue?
According to the MSDN documentation for Response.Redirect(string url), it will throw an HttpException when "a redirection is attempted after the HTTP headers have been sent". Since Response.Redirect(string url) uses the Http "Location" response header (http://en.wikipedia.org/wiki/HTTP_headers#Responses), calling it will cause the headers to be sent to the client. This means that if you call it a second time, or if you call it after you've caused the headers to be sent in some other way, you'll get the HttpException.
One way to guard against calling Response.Redirect() multiple times is to check the Response.IsRequestBeingRedirected property (bool) before calling it.
// Causes headers to be sent to the client (Http "Location" response header)
Response.Redirect("http://www.stackoverflow.com");
if (!Response.IsRequestBeingRedirected)
// Will not be called
Response.Redirect("http://www.google.com");
Once you send any content at all to the client, the HTTP headers have already been sent. A Response.Redirect() call works by sending special information in the headers that make the browser ask for a different URL.
Since the headers were already sent, asp.net can't do what you want (modify the headers)
You can get around this by a) either doing the Redirect before you do anything else, or b) try using Response.Buffer = true before you do anything else, to make sure that no output is sent to the client until the whole page is done executing.
A Redirect can only happen if the first line in an HTTP message is "HTTP/1.x 3xx Redirect Reason".
If you already called Response.Write() or set some headers, it'll be too late for a redirect. You can try calling Response.Headers.Clear() before the Redirect to see if that helps.
Just check if you have set the buffering option to false (by default its true). For response.redirect to work,
Buffering should be true,
you should not have sent more data using response.write which exceeds the default buffer size (in which case it will flush itself causing the headers to be sent) therefore disallowing you to redirect.
Using
return RedirectPermanent(myUrl) worked for me
You can also use below mentioned code
Response.Write("<script type='text/javascript'>"); Response.Write("window.location = '" + redirect url + "'</script>");Response.Flush();
There is one simple answer for this:
You have been output something else, like text, or anything related to output from your page before you send your header. This affect why you get that error.
Just check your code for posible output or you can put the header on top of your method so it will be send first.
If you are trying to redirect after the headers have been sent (if, for instance, you are doing an error redirect from a partially-generated page), you can send some client Javascript (location.replace or location.href, etc.) to redirect to whatever URL you want. Of course, that depends on what HTML has already been sent down.
My Issue got resolved by adding the Exception Handler to handle
"Cannot redirect after HTTP headers have been sent". this Error as shown below code
catch (System.Threading.ThreadAbortException)
{
// To Handle HTTP Exception "Cannot redirect after HTTP headers have been sent".
}
catch (Exception e)
{//Here you can put your context.response.redirect("page.aspx");}
I solved the problem using:
Response.RedirectToRoute("CultureEnabled", RouteData.Values);
instead of Response.Redirect.
Be sure that you don't use Responses' methods like Response.Flush(); before your redirecting part.
Error
Cannot redirect after HTTP headers have been sent.
System.Web.HttpException (0x80004005): Cannot redirect after HTTP headers have been sent.
Suggestion
If we use asp.net mvc and working on same controller and redirect to different Action then you do not need to write.. Response.Redirect("ActionName","ControllerName"); its better to use only return RedirectToAction("ActionName"); or return View("ViewName");
The redirect function probably works by using the 'refresh' http header (and maybe using a 30X code as well). Once the headers have been sent to the client, there is not way for the server to append that redirect command, its too late.
If you get Cannot redirect after HTTP headers have been sent then try this below code.
HttpContext.Current.Server.ClearError();
// Response.Headers.Clear();
HttpContext.Current.Response.Redirect("/Home/Login",false);
There are 2 ways to fix this:
Just add a return statement after your Response.Redirect(someUrl);
( if the method signature is not "void", you will have to return that "type", of course )
as so:
Response.Redirect("Login.aspx");
return;
Note the return allows the server to perform the redirect...without it, the server wants to continue executing the rest of your code...
Make your Response.Redirect(someUrl) the LAST executed statement in the method that is throwing the exception. Replace your Response.Redirect(someUrl) with a string VARIABLE named "someUrl", and set it to the redirect location... as follows:
//......some code
string someUrl = String.Empty
.....some logic
if (x=y)
{
// comment (original location of Response.Redirect("Login.aspx");)
someUrl = "Login.aspx";
}
......more code
// MOVE your Response.Redirect to HERE (the end of the method):
Response.Redirect(someUrl);
return;
In my global.asax I have written code into the Application_Error event which catches all errors and shows a generic error page to the user as well as logging/emailing the error that occurred.
However, I have realised that the error page does not return the correct status code to the browser which has meant that, to a service like UptimeRobot, the site is still seen as functioning even when the page is broken.
Is it possible to derive the correct status code from an error and return it to the browser?
By default IIS intercepts the status code and sends either the debug info or a custom error page. You can deactivate this default behavior and manually set the error code through the Response object:
Context.Response.TrySkipIisCustomErrors = true;
Context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
Context.Response.ContentType = "text/plain";
Context.Response.Write("Your error message");
We have a C# AJAX server that handles database requests we want to return a 400/403/500 status code on an exception so that we can understand what went on at the client side. However, all we get back is "Bad Request" in the response body.
For example, if the ADO.Net driver returns this message:
Invalid length parameter passed to the LEFT or SUBSTRING function.
Cannot insert the value NULL into column '--COLUMN--', table
'--DATABASE.SCHEMA.TABLE--'; column does not allow nulls. INSERT
fails. The statement has been terminated.
Then our AJAX Server simply returns this text:
Bad Request
I have looked at the full response headers in Chrome and there is nothing even remotely resembling this error message in there. This is the code we're using to send the error back:
catch (Exception ex)
{
//Response.TrySkipIisCustomErrors = true;
Response.StatusCode = (int)HttpStatusCode.SC_BAD_REQUEST;
Response.Write(ex.Message);
Response.Flush();
}
In the Java/JSP equivalent to this server we are getting the correct behavior with this code:
} catch (Exception e) {
response.sendError(response.SC_BAD_REQUEST, e.getClass() + " : " + e.getMessage());
}
There's a few things that could be going wrong, but I'd be prepared to bet that you're running on IIS7 and its defaults are causing it to rewrite the error. Try the TrySkipIisCustomErrors property and the existingResponse attribute on the httpErrors configuration setting.
The server is encapsulating the error message into a bad request to prevent secure details from reaching the client. You can modify this behavior by setting the customErrors to off, e.g.
<system.web>
<customErrors mode="Off">
</customErrors>
</system.web>
I have a button that when clicked, will generate a PDF and write it out to the response.
This is the basic structure of the code:
try
{
using(Stream stream = generatePdf())
{
var file = createFile(stream);
file.Transmit(HttpContext.Current.Response);
}
}
catch (Exception ex)
{
// Handle exception
// Display Error Message
}
The transmit method contains the following code:
response.AddHeader("Content-Disposition", String.Format("attachment; filename={0}", filename));
response.AddHeader("Content-Length", bytes.Length.ToString());
response.ContentType = "application/octet-stream";
response.BinaryWrite(bytes);
Downloading the file works fine, except that it doesn't complete the postback.
If I were to throw an exception above file.Transmit, the error handling would work properly and I would see the message get displayed in my browser. However, if there is an exception after the file.Transmit then nothing happens. The user saves/opens the pdf and the page does not reload.
How can I make it so that the postback always completes, that way I can display an appropriate message to the user?
It sounds like you're trying to make the response contain two parts: the page and the PDF. You can't do that. Typically download pages start a download as a separate request when you've gone to them (via JavaScript, I believe), with a direct link just in case the JavaScript doesn't work.
Any one HTTP request can only have one response.
Response.End() literally ends the entire response.
There are two methods that I employ when I use it:
1) Always make sure it's the final required point in the postback.
2) (and the only way to use AJAX for file calls) Make a small page in an iframe solely for the purpose of sending files and call a refresh on the frame... the response.end will just end the response from that frame, not the entire postback.
EDIT: Here's my question thread on the same topic
Using Response.TransmitFile for physical file not working
How can I get the Compiler Error Message if I have the pageUrl?
I tried using the HttpWebRequest class, but I haven't gotten the result yet.
I have collection of pages, that must execute automatically, and if the page fails, I need it to create a log.
Thank you
You can catch all application errors in application global class (global.asax) in Application_Error handler.
Other way. You can catch exceptions in custom error module as well, just register you module in <httpModules> section and implement following function there:
void context_Error(object sender, EventArgs e)
{
HttpApplication application = (HttpApplication)sender;
HttpContext context = application.Context;
Exception ex = context.Server.GetLastError();
//... here goes some code
}
Thus you have to ways to catch any error. Other task is to request all pages. As I can see from your post, you've already have such solution.
string pagetext = (new System.Net.WebClient()).DownLoadString(<url>);
//Add a better control here
if(pagetext.Contains("Server Error"))
{
`enter code here`
}
You can write a program to visit the pages, if the response of the request is a HTTP error than you can investigate further.
If you do not want to write your own program to detect errors originating from HTTP requests, you can use a testing framework like selenium.
Disclaimer: I do very little with ASP.NET type stuff.
ELMAH might help you a bit. It's an error logger for ASP.NET projects.
Where are you trying to catch these exceptions? In your website, or in an external application that is crawling a site?
In an external application, using an HttpWebRequest you'd do something like this:
string urlToTry = "http://www.example.com/ServerErrorPage.htm";
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(urlToTry);
try
{
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
// Process your success response.
}
catch (WebException we)
{
HttpWebResponse error = (HttpWebResponse)we.Response;
// If you want to log multiple codes, prefer a switch statement.
if (error.StatusCode == HttpStatusCode.InternalServerError)
{
// This is your 500 internal server error, perform logging.
}
}
The WebException class will give you messages like:
The remote server returned an error: (500) Internal Server Error.
Once you cast them to an HttpWebResponse, you can get at the StatusCode and perform whatever logging you require.