Develop Reference

Implementing a custom error in global.asax

In my global.asax file, I have the following code:
void Application_Error(object sender, EventArgs e)
{
Exception TheError = Server.GetLastError();
if (TheError is HttpException && ((HttpException)TheError).GetHttpCode() == 404)
{
Response.Redirect("~/404.aspx");
}
else
{
Response.Redirect("~/500.aspx");
}
}
When I navigate to an non-existing page, I get the generic error page. I don't want anything pertaining to custom error in the web.config because my plan is to add code to the global.asax file to log the exceptions. Is there a way to handle custom error with just the global.asax file?

EDIT:
The answer is not obvious, but this seems to explain it: http://www.asp.net/web-forms/tutorials/deployment/deploying-web-site-projects/displaying-a-custom-error-page-cs
If you scroll down a ways, you'll find this lovely tidbit:
Note: The custom error page is only displayed when a request is made
to a resource handled by the ASP.NET engine. As we discussed in the
Core Differences Between IIS and the ASP.NET Development Server
tutorial , the web server may handle certain requests itself. By
default, the IIS web server processes requests for static content like
images and HTML files without invoking the ASP.NET engine.
Consequently, if the user requests a non-existent image file they will
get back IIS's default 404 error message rather than ASP.NET's
configured error page.
I've emphasized the first line. I tested this out in the default template, and sure enough, this URL:
http://localhost:49320/fkljflkfjelk
gets you the default IIS page, whereas simply appending a .aspx makes the Application_Error kick in. So, it sounds like you need to enable customErrors/httpErrors if you want to have all errors handled.
For IIS <= 6, add to <system.web>:
<customErrors mode="On" redirectMode="ResponseRewrite">
<error statusCode="404" redirect="/404.aspx"/>
<error statusCode="500" redirect="/500.aspx"/>
</customErrors>
For IIS7+, add to <system.webServer>:
<httpErrors errorMode="Custom">
<remove statusCode="404"/>
<error statusCode="404" path="/404.aspx" responseMode="ExecuteURL"/>
<remove statusCode="500"/>
<error statusCode="500" path="/500.aspx" responseMode="ExecuteURL"/>
</httpErrors>
I'll leave the original answer in case someone finds it useful.
I believe you need to clear the existing error code from the response, otherwise IIS ignores your redirect in favor of handling the error. There's also a Boolean flag, TrySkipIisCustomErrors, you can set for newer versions of IIS (7+).
So, something like this:
void Application_Error(object sender, EventArgs e)
{
Exception TheError = Server.GetLastError();
Server.ClearError();
// Avoid IIS7 getting in the middle
Response.TrySkipIisCustomErrors = true;
if (TheError is HttpException && ((HttpException)TheError).GetHttpCode() == 404)
{
Response.Redirect("~/404.aspx");
}
else
{
Response.Redirect("~/500.aspx");
}
}

Looks like IIS is looking for a page and did not find it.
Make sure:
404.aspx is created
customErrors tag from web.config is not present.

Redirect Loop for Custom Errors Page

For error handling, I have added the following code to Web.config:
<system.web>
<customErrors mode="On" defaultRedirect="~/Error.cshtml?">
</customErrors>
<system.web>
And in Global.asax.cs:
void Application_Error(object sender, EventArgs e)
{
// Code that runs when an unhandled error occurs
Response.Redirect("/Error.cshtml?");
}
However, when the redirect to /Error.cshtml? occurs, there is an error 'This page has a redirect loop'
I've searched through other similar questions (such as How to solve Redirect Loop). However, I have no other routes calling Error.cshtml -- so does anyone have any idea what is causing this loop and how I can work around it?
EDIT: There are multiple errors occurring, and therefore the error page redirect is involved in a redirect loop. Does anyone know of a way to only call Response.Redirect("~/Error.cshtml") once?
EDIT2: If I change the redirect url to a random url outside of the project (such as https://www.facebook.com/), the customError redirect works properly. Still looking for a way to redirect to project page without infinitely looping through the error

Try adding:
Server.ClearError();
first to clear the existing error before redirecting.

Add redirectMode="ResponseRewrite" to customErrors section.

Server.Transfer causing Session exception

In my global I have the following code to handle when an error occurs
//[..] code goes here
Server.Transfer("~/Error.aspx?ErrorID=" + errorId);
It used to be a Response.Redirect which worked perfectly except that it changed the url (which is why I want to use Server.Transfer)
Unfortunately, now when it tries to load the Error page, it crashes on the Masterpage when it tries to refer to the Session
HttpException:
Session state can only be used when enableSessionState is set to true,
either in a configuration file or in the Page directive. Please also
make sure that System.Web.SessionStateModule or a custom session state
module is included in the \\
section in the application configuration.
I do have enableSessionState in both my config and my page.
I also found some links which suggest using Context.RewritePath - that just causes a blank page to load for me.
Using Response.Redirect works perfectly and as expected, so I assume Server.Transfer is the issue here. What is it?
EDIT Code:
protected void Application_Error(object sender, EventArgs e)
{
lock (_lockMe)
{
Exception ex = Server.GetLastError();
if (ex != null)
{
if (ex.InnerException != null)
ex = ex.InnerException;
ErrorLoggingManager.AddError(ex, new MembershipData(), ...); //etc
}
Server.ClearError();
//Some other database code for cleaning up some stuff when an error happens
}
try
{
if (Response != null)
{
//Get the last error logged
MyDataContext db = new MyDataContext();
int errorId = db.LoggedErrors.OrderByDescending(le => le.ErrorId).Select(le => le.ErrorId).FirstOrDefault();
Server.Transfer("~/Error.aspx?ErrorID=" + errorId);
}
}
catch (Exception)
{
}
}

As you have not posted much code. So without seeing the actual implementation you have done. I could suggest you below points.
Point 1. First of all, you need to check if SessionState is enabled for pages. You could set them globally in web.config file. Try the snippet given below in web.config
<configuration>
<system.web>
<pages enableSessionState="true" />
</system.web>
</configuration>
Point 2. And put your Redirection in Application_Error in Global.asax.
public void Application_Error(object sender, EventArgs e)
{
HttpApplication app = (HttpApplication)sender;
app.Server.Transfer("~/Error.aspx?ErrorID=" + errorId,true);
}
Point 3. Also check if your SessionStateis set properly in IIS too.
Details are on MSDN to enable sessionstate
Hope this helps..!!!

From what I understand, Server.Transfer sends the content of another page to the client rather than the requested content. If that is the case, then I am wondering if it does not have something to do with applying a master page to the error page? I had a similar error years ago with earlier technology and it turned out that the master page did not like what I was trying to do.
I hope this helps at least point to a solution.

Here's what the problem is:
If there is a page render exception (ex. "File Not Found") then Server.Transfer screws up the session. This has something to do with it being called during the page render.
As long as you are not appending headers before the error occurs, Response.Redirect will work just fine; if you are, however, using Response.AppendHeader then Response.Redirect will not work during a page render.
Try using HttpContext.Current.RewritePath instead. That should fix all these problems. For whatever reason, RewritePath() does not care that the page hasn't finished rendering.

why not just use customErrors in web.config to do the redirect?
<customErrors mode="Off" defaultRedirect="~/Common/Error.aspx">
<error statusCode="403" redirect="~/SM_AccessDenied.aspx" />
<error statusCode="404" redirect="~/Common/FileNotFound.aspx" />
</customErrors>

I had the same problem in a different context a while ago. I don't know if it is your case, but if you're using IIS7 on Windows 2008, in addition to setting enableSessionState=true in your web.config, you have to put your modules inside the <system.webServer> section, instead of <system.web>. Changing this little thing solved it for me.

Why don't you try like this:
The Server.Transfer method also has a second parameter—"preserveForm". If you set this to True, using a statement such as Server.Transfer("WebForm2.aspx", True), the existing query string and any form variables will still be available to the page you are transferring to.
So I think doing like this your session will not expire.
Server.Transfer("~/Error.aspx?ErrorID=" + errorId,True);

The error you are encountering is because you are using a query string parameter. Per the msdn docs
However, the path parameter must not contain a query string, or ASP returns an error.
http://msdn.microsoft.com/en-us/library/ms525800%28v=vs.90%29.aspx
Its about 3/4 of the way down the page just above Requirements.
Even though the docs here are mentioning asp. and not asp.net, keep in mind the session state is a feature of IIS and is handled before asp.net is ever called.

#user2110845 : I had faced similar problem few months ago. the problem was with having an underscore in the website name. We were deploying a website in IIS with two different host names(adding two entries through the 'Edit Bindings' option on the website). The host names provided were abc_ts, abc_is. When the underscore was removed then the session problem got resolved.
It seems there are certain characters not allowed in a website host name. Check if that is your problem.
I found the answer here : link (check 'update 2' in the article)

You don't mention what version of ASP.NET you are using, but there were some changes between 2.0 and 3.5 in how unhandled exceptions bubbled their way up through an ASP.NET web app and then IIS.
Among some other possibles, while you are clearing the error you are not setting Context.Response.TrySkipIisCustomErrors = true; While this particular flag could have nothing to do with your issue (and is only available for 3.5+), it also could help deal with what is potentially two error pages behind the scenes that are obscuring the real issue. Regardless, it'll save you a lot of grief (at least if you are running 3.5+) with other potential issues. Check out two posts I wrote several years back that may be helpful: while they don't cover session handling, they do cover the multiple song-and-dance routines I had to follow to get proper 500 and 404 handling in various versions of ASP.NET. It's possible you will run into something that will get you further ahead, if not all the way there.
http://www.andornot.com/blog/post/Errors-Sending-the-Right-Message-(Redux-Covering-ASPNET-3540).aspx
http://www.andornot.com/blog/post/Errors-Sending-the-Right-Message.aspx

Application_Error doesn't triggers at Server

I have the following code in my Global.asax file:
protected void Application_Error()
{
var exception = Server.GetLastError();
Response.Clear();
Server.ClearError();
//processing
Response.RedirectPermanent("url processed"));
}
At localhost this works fine, doing something like this:
I access to "www.somesite.com/uk/en-GB", and because this route isn't registered the Application_Error "catch" the error, process it and redirect to the correct route "www.somesite.com/en-GB". (As shown in the code above at Global.asax)
But at the server, I try to access to "www.somesite.com/uk/en-GB", and it don't goes to Application_Error, instead of that show me this error:
Anyone know how to solve this?

You didn't get an error. You got a 404 response code. You'll need to handle that scenario differently. The Application_Error only catches uncaught exceptions.

I'm running IIS 6 and I found that this problem was easily fixed with adding this to my Web.Config file under system.web:
<customErrors mode="Off">
</customErrors>
This will allow the code in Application_Error to execute.

Passing Exceptions to an error screen in ASP.net/C#

Coming from a desktop background I'm not sure exactly how to pass the exceptions I have caught to an Error page in order to avoid the standard exception screen being seen by my users.
My general question is how do I pass the exception from page X to my Error page in ASP.net?

I suggest using the customErrors section in the web.config:
<customErrors mode="RemoteOnly" defaultRedirect="/error.html">
<error statusCode="403" redirect="/accessdenied.html" />
<error statusCode="404" redirect="/pagenotfound.html" />
</customErrors>
And then using ELMAH to email and/or log the error.

The pattern I use is to log the error in a try/catch block (using log4net), then do a response.redirect to a simple error page. This assumes you don't need to show any error details.
If you need the exception details on a separate page, you might want to look at Server.GetLastError. I use that in global.asax (in the Application_Error event) to log unhandled exceptions and redirect to an error page.

We've had good luck capturing exceptions in the Global.asax Application_Error event, storing them in session, and redirecting to our error page. Alternately you could encode the error message and pass it to the error page in the querystring.

You can also get the exception from
Server.GetLastError();

Use the custom error pages in asp.net, you can find it in the customError section in the web.config

We capture the exception in the Global.asax file, store it in Session, the user is then redirected to the Error Page where we grab the exception for our Session variable and display the Message information to the user.
protected void Application_Error(object sender, EventArgs e)
{
Exception ex = Server.GetLastError();
this.Session[CacheProvider.ToCacheKey(CacheKeys.LastError)] = ex;
}
We do log the error message prior to displaying it the user.

I think you can use the global.asax -- Application_Exception handler to catch the exception and then store it for displaying in an error page.
But actually, your error page shouldn't contains code that might cause just another error. It should be simple "Oops! something went wrong" page.
If you want details on the error, use Windows' events viewer or ELMAH or employ some logging mechanism.