I am trying to "log" forcefully when a user has been inactive and or the session has ended (either by inactivity or more importantly, when the browser has closed).
I dont want to use any silly AJAX solution to perform a post every few minutes for "im alive" or call when the browser is closed.
I was under the impression that if you store an object in Session, and you reach the Session_End event, then you will not be able to gain access to anything stored in Session as its ended.
But from some testing I have done, it appears that this is probably the last chance you can obtain access to the object.
Could this be true? is it reliable?
using ASP.NET 4.0 here.
Typically there are two things done.
The first is that a javascript timer is added to the client, not as a heartbeat, but rather as a reminder. If they are close to the session ending, then it simply says "session is about to end. Are you still there?" If so, then it does the "silly" post to ensure the server keeps the session going. This is purely to be nice to your users.
The second (and point of your question) is that you put something in session_end in order to clean up the session. Reliable? well.. most of the time.
Session_End won't run if the app pool is recycled. However, assuming the app pool is ok then yes it will execute when the session expires. The app pool can be recycled for a LOT of reasons ranging from the app crashing to exceeded memory usage to simply because it's been a while since the last reset. This is configurable in IIS.
Would I trust session_end? No. Not 100%. Of course, I wouldn't put anything inside of a session object that would require me to trust it 100% anyway.
For logging the timeout You can use the Global events to log at timeout. See this link for order of events http://www.techrepublic.com/article/working-with-the-aspnet-globalasax-file/5771721
Related
I have a simple scenario. in one page of asp.net, I store a some values in session like
session("var") = "some string"
or
session("var1") = object of generic list of string
and then use response.redirect to goto another page.
on other page it shows things fine, but when we press a button to do an action on it, session gets null.
Remember, it doesn't always happen. Just sometimes it does so and other times it works fine. We do this practice a lot to move some values from page to page (by storing them into session and goto other page). We have very big application and all works fine, but from some days, have been having this issue on some sites with some users. Once again, it doesn't always happen. 99% it works fine but few times, we have this issue where session variable is no longer available.
Is there any way to know what is going wrong and where? We do store some other variables in the session as well, they seems fine at that time. only some of the session variables lose their values.
From my research, it seems people blames on the IIS worker process restart or Application Pool recycle. But I believe in such case all the session variables in the application must be voided, not selected few. Right?
also, is there any way to know in code if the pool or worker process was restarted?
thanks
Sameers
Perhaps you're passing domain boundaries. Session is identified by a client cookie, which are usually stored on a per-domain basis. So, for example, a redirect from www.whatever.com to client.whatever.com will cause you to lose the session ID, which will appear to you as "voiding the session". So, be careful about sub-domains too. Going from whatever.com to www.whatever.com is fine, but the other way round, nope.
And yes, unless you're on a web farm IIS, restarting the worker process will kill all the sessions. Unless you store them in a database or something.
Everytime my page is reloaded, I reset the session time out to 1 day.
Is this a good idea in the shared hosting environment?
No, it's a very bad idea, and even rude, as every new session created will consume more and more resources and enough sessions will bring your and every other hosted app to its knees.
Are you just trying to avoid having to log in repeatedly? Because you can use alternative methods of authentication with cookies once you pass the initial test.
That is decidedly odd, you'd keep in RAM every single session object with all their object handles that you create throughout each day.
If you're just trying to prevent timeouts during use, why not just use an ajax call every 30sec-2min to a heart-beat page so the server refreshes the timeout for your application. This way, a 10min timeout will be more than sufficient.
Is there a way to do a Session.Abandon() when the user just kills the session by X'ing out with the little red X box in the upper right corner? I am seeing situations where after an "X out", the user comes back in and it seems like session variables are still present? I guess explorer keeps them intact? (I am unsure of this).
You can try doing an AJAX type callback in the OnUnload event - however, as someone else mentioned you'd have to be aware of other tabs being open (not easy), and it still won't guarantee you get that event.
There's a combination of things to do to get a similar type of effect.
Session Cookie should have a null/empty expiry time. This ensures the browser deletes the session from it's end after the browser is closed.
The ASP Session can be set with a short SessionState timeout value. This means if there's no client activity within that period, the Session will expire.
The side effect of this is that if a user is just looking at the site, and not performing activity (regardless of whether the browser is still open) - the session can expire.
This can be worked-around by having a Javascript timer periodically ping back to the server with an AJAX call or similar. The side effect of THIS is that it generates more site traffic.
The server is typically not aware of such events on the client. The only way the server can be notified about anything is if there is a request sent back to it. I guess you could create such a notification in a JavaScript, but then you should also keep in mind that the session in mind that the session is not per-page but (usually) per user, which means that you would need to keep track of how many tabs/windows the user has opened so that you don't kill the session when you should not.
Personally, I usually try to design the web apps so that they live well with the default handling of sessions, either providing a specific "Logout" command that will kill the session, or simply let it hit the timeout and die.
THE CODE:
Session["foo"] = "bar";
Response.Redirect("foo.aspx");
THE PROBLEM:
When foo.aspx reads "foo" from the session, it's not there. The session is there, but there's no value for "foo".
I've observed this intermittently in our production environment. But I don't mean here to ask a question about Response.Redirect().
THE EXPLANATION:
Bertrand Le Roy explains (the bolding is mine):
Now, what Redirect does is to send a
special header to the client so that
it asks the server for a different
page than the one it was waiting for.
Server-side, after sending this
header, Redirect ends the response.
This is a very violent thing to do.
Response.End actually stops the
execution of the page wherever it is
using a ThreadAbortException. What
happens really here is that the
session token gets lost in the battle.
My takeaway there is that Response.Redirect() can be heavy-handed with ending threads. And that can threaten my session writes if they occur too near that heavy-handedness.
THE QUESTION:
What about ASP.NET session management makes it so vulnerable to this? The Response.Redirect() line of code doesn't begin its execution until the session write line is "finished" -- how can it be such a threat to my session write?
What about the session write doesn't "finish" before the next line of code executes? Are there other scenarios in which session writes are similarly (as though they never occurred) lost?
I'm not familiar enough with the internals of session writing, but I imagine it has some complexities, as it relies on translating the browser session cookies into a server identification. Additionally, ThreadAbortExceptions do have special considerations in the runtime, which may play in here, I'm not sure.
In any case, Response.Redirect() has an overload that takes a boolean parameter that lets you specify whether you want to end the thread or not.
Response.Redirect(string url, bool endResponse);
If you call it with endResponse set to "false", it will gracefully finish, rather than calling Thread.Abort() internally. However, this means it will also execute any code left in the page lifecycle before finishing up.
A good compromise is to call Response.Redirect(url, false) followed by Application.CompleteRequest(). This will allow your redirect to happen but also gracefully shut down the current execution context with a minimal amount of additional lifecycle processing.
After testing several alternatives (Response.Redirect(..., false), Server.Transfer(), and other "solutions" I can't now recall), we've found only one reliable answer to this problem.
Moving our session state from InProc to SqlServer effectively eradicated this behavior from our systems, leaving Response.Redirect(...) completely reliable. If further testing shows otherwise, I'll report here, but I say, to make this stop happening in your environment: move your session state into SqlServer (or is "out of InProc" good enough? I'm not sure).
Application pool recycle can cause your session to go away. You can configure the app pool to recycle at fixed times (recommended, and at night or during low-usage periods) or increase the timeout period of your app pool recycle.
By default the session expiry seems to be 20 minutes.
Update: I do not want the session to expire until the browser is closed.
Update2: This is my scenario. User logs into site. Plays around the site. Leaves computer to go for a shower (>20 mins ;)). Comes back to computer and should be able to play around. He closes browser, which deletes session cookie. The next time he comes to the site from a new browser instance, he would need to login again.
In PHP I can set session.cookie_lifetime in php.ini to zero to achieve this.
If you want to extend the session beyond 20 minutes, you change the default using the IIS admin or you can set it in the web.config file. For example, to set the timeout to 60 minutes in web.config:
<configuration>
<system.web>
<sessionState timeout="60" />
... other elements omitted ...
</system.web>
... other elements omitted ....
</configuration>
You can do the same for a particular user in code with:
Session.Timeout = 60
Whichever method you choose, you can change the timeout to whatever value you think is reasonable to allow your users to do other things and still maintain their session.
There are downsides of course: for the user, there is the possible security issue of leaving their browser unattended and having it still logged in when someone else starts to use it. For you there is the issue of memory usage on the server - the longer sessions last, the more memory you'll be using at any one time. Whether or not that matters depends on the load on your server.
If you don't want to guesstimate a reasonable extended timeout, you'll need to use one of the other techniques already suggested, requiring some JavaScript running in the browser to ping the server periodically and/or abandon the session when a page is unloaded (provided the user isn't going to another page on your site, of course).
You could set a short session timeout (eg 5 mins) and then get the page to poll the server periodically, either by using Javascript to fire an XmlHttpRequest every 2 minutes, or by having a hidden iframe which points to a page which refreshes itself every 2 minutes.
Once the browser closes, the session would timeout pretty quickly afterwards as there would be nothing to keep it alive.
This is not a new problem, there are several scenarios that must be handled if you want to catch all the ways a session can end, here are general examples of some of them:
The browser instance or tab is closed.
User navigates away from your website using the same browser instance or tab.
The users loses their connection to the internet (this could include power loss to user's computer or any other means).
User walks away from the computer (or in some other way stops interacting with your site).
The server loses power/reboots.
The first two items must be handled by the client sending information to the server, generally you would use javascript to navigate to a logout page that quickly expires the session.
The third and fourth items are normally handled by setting the session state timeout (it can be any amount of time). The amount of time you use is based on finding a value that allows the users to use your site without overwhelming the server. A very rough rule of thumb could be 30 minutes plus or minus 10 minutes. However the appropriate value would probably have to be the subject of another post.
The fifth item is handled based on how you are storing your sessions. Sessions stored in-state will not survive a reboot since they are in the computer's ram. Sessions stored in a db or cookie would survive the reboot. You could handle this as you see fit.
In my limited experience when this issue has come up before, it's been determined that just setting the session timeout to an acceptable value is all that's needed. However it can be done.
This is default. When you have a session, it stores the session in a "Session Cookie", which is automatically deleted when the browser is closed.
If you want to have the session between 2 browser session, you have to set the Cookie.Expired to a date in the feature.
Because the session you talk about is stored by the server, and not the client you can't do what you want.
But consider not using ASP.NET server side session, and instead only rely on cookies.
Unfortunately due to the explicit nature of the web and the fact there is no permanent link between a website server and a users browser it is impossible to tell when a user has closed their browser. There are events and JavaScript which you can implement (e.g. onunload) which you can use to place calls back to the server which in turn could 'kill' a session - Session.Abandon();
You can set the timeout length of a session within the web.config, remember this timeout is based on the time since the last call to the server was placed by the users browser.
Browser timedout did not added.
There's no way to explicitly clear the session if you don't communicate in some way between the client and the server at the point of window closing, so I would expect sending a special URI request to clear the session at the point of receiving a window close message.
My Javascript is not good enough to give you the actual instructions to do that; sorry :(
You cant, as you can't control how the html client response.
Actually why you need to do so? As long as no one can pick up the session to use again, it would expire after that 20 minutes. If resources does matter, set a more aggressive session expiry (most hosting companies did that, which is horribly annoying) or use less objects in session. Try to avoid any kind of object, instead just store the keys for retrieving them, that is a very important design as it helps you to scale your session to a state server when you get big.
Correct me if I am misreading the intent of your question, but the underlying question seems to be less about how to force the session to end when a user closes the browser and more about how to prevent a session from ending until the browser is closed.
I think the real answer to this is to re-evaluate what you are using sessions to do. If you are using them to maintain state, I agree with the other responses that you may be out of luck.
However, a preferred approach is to use a persistent state mechanism with the same scope as the browser session such as a cookie that expires when the browser is closed. That cookie could contain just enough information to re-initiate the session on the server if it has expired since the last request. Combined with a relatively short (5-10 min) session timeout, I think this gives you the best balance between server resource usage and not making the user continually "re-boot" the site.
Oh you have rewritten the question.
That one is absolutely feasible, as long as javascript is alive. Use any timed ajax will do. Check with prototype library http://www.prototypejs.org PeriodicalExecutor or jQuery with the ajax + timer plugin. Setup a dummy page which your executor will call from time to time, so your session is always alive unless if he logouts (kill the ajax timer in the same time) or close browser (which means the executor is killed anyway)