I am developing a matrimonial web application in asp.net. In that I want to display number of users in online (logged in).
I am planning to maintain a "login-status table" in dB. And will maintain the table every time the user have logged in and out. But there is problem if the user have closed the browser directly without logging out.
Is there any other easy way to achieve this. Pleas provide sample code.
And I want to know how can I update the table that if the user click the browser's close button.
I recently implemented something similar. The challenge I had is what defines "online". What if the user walks away from the computer, closes the browser, network is disconnected?
In the end I went with online means visited a page in the last 15 minutes. It avoids the issues with trying to detect when they walk away from the browser, or close it.
I did consider binding to the browsers onclose event and hitting a /user/closed/browser url. I have used that before in a call center website to unlock the call. But really the 15 minute rule was "good enough".
I coded it by keeping an in memory dictionary that I persisted to db every 5 minutes. Sorry I have no code to provide.
Related
I am working on an asp.net application. "Online Examination".
my application will uses the concept of session to maintain the state of user who is giving the exam. , since in case browser shut down, system crash i do not want my user should start from the 1st question.
Infact, i want my user should start from where he left. Now i am not able to think on this.
How to test this. Is there any easy way so that i can simply test my concept.
CASE1: USER WANT TO QUIT FROM EXAM. SO HE/SHE CAN INTENTIONALLY CLOSE THE BROWSER.
CASE2: BY MISTAKE USER CLOSE THE BROWSER, SO WHEN HE RETURN BACK HE/SHE WILL START THE EXAM FROM WHERE HE/SHE LEFT.
he just have to enter the url> enter his exam id> continue the exam.
Plssss help me in this respect. give me some idea how to apply session management.
You cannot distinguish between Case1 and Case2. Typically in these scenarios there is a button on the web page like Logout or Finish that would mark the exam as completed. Simply closing the browser would mean that the exam is still in progress.
Also note that you cannot use standard Session state management - that lasts only while the browser is open. You have to store the exam progress data in a database based on the user's ID.
Use application variables so that we can easily remove this when the user suddenly closes the browser or tab.
How to restrict the page by accessing only one user at a time. Using asp.net can i use global.asax, is there any other way to restrict, if one user accessing the page, another user not able to access that page. we have to give message that one user is accessing the page. is it possible. can you help me or give some reference.
Although there are probably many better ways of dealing with this sort of problem, I'm going to assume that you do actually need this.
What I would do:
Make your application so that when the page is loaded(when it isn't "locked"), it logs to a database that the page was loaded and "lock" it. In the actual page, I'd have some kind of AJAX to constantly poll the web server every 5-15 seconds to tell your application the user is still on the page. And then make it so that the page becomes unlocked after 5-15 seconds from the time saved to the database by the last AJAX call.
Again, I really suspect that there is a better way around an issue like this, but this is a direct answer to your question
Based on this:
yeah sure, jupaol, it is depend on accounts, in my web application, one report has to approve only one user, but the approve authority having two users. if both of them accessing the same page and approve at a time, it will big mess. here i an not using database.
The problem is related with concurrency, there are several ways to face an issue like this, for example the easiest one is to use optimistic concurrency. Even when you are not using a database for this, you can emulate it.
You should be storing the result of the approvers somewhere, in order to mark the report as approved, with this in mind you should be able to do something like this:
Before render the page get the latest report status
If the report has not been approved, render normally
If the report was approved seconds before, render it in read-only mode reporting who approved it (or similar approach)
Add a validation to your ChangeStatus method, in this method do the following:
Get the latest status of the current report
If the report is still not validated, then block the thread (you could use a Mutex or similar) and mark the report as validate it
If the report was already validate it, raise a domain exception and handle it in your page correctly (perhaps render the page in read-only mode explaining that the report was already validate it)
If you want a more responsive application, (RIA), you might want to consider the following approaches:
Perhaps this would be the worst approach but it's still an option, you could keep a log tracking when a user request your page, then in subsequent requests check if the log is still valid, if it is not, then redirect to another page indicating the page is in use, otherwise allow access to the page. I believe this is an error-prone approach because you would be relying on this simple validation in order to prevent an inconsistency in your system, besides you would have the polling problem described in the following approach
Using AJAX to poll data from a service checking if the report has been approved. Perhaps this is the easiest way to accomplish this but it is not recommended it, because you would be polling your server constantly, and eventually you would have scalability problems
You could use Comet to get notified to the browser (client) whenever a server event has occurred, in this case when your report has been approved. The problem with this approach is that you have to keep an opened connection with the server in order to get notified.
The last approach and the most recommended these days is to use Web Sockets, this is the technology used in StackOverflow to get notifications in real time.
How do I disable offline caching for firefox in ASP.NET or in IIS? I found this post:
Disabling browser caching for all browsers from ASP.NET
This doesn't address the issue completely. It just disables caching from the back button (when not in off-line mode).
Here is a simple scenario:
If user A logs on to his bank. User A is doing transactions and he even goes to update some personal data. Finally user A is done and logs off from his bank website. User A leaves the browser on, because he has another tab open downloading a file that is a few gigs. User B would like to go on to his email to send out some emails, so user A doesn't close the browser. He knows the security risks, because he has read what must be done once you log off of the site, but he doesn't want to stop the download. For user A, to have to redownload is too much time for him and well he is just your typical user and doesn't think user B (being a good friend of his) will do anything malicious. So then user B uses the browser. The first thing user B does is "work offline". User B now has all data from user A. The page has an off-line cache for user B to see. User B is now able to open the history to view those cached pages, or just simply click back if the page was left open (either way works). User B now has all the pages that user A has browsed to. So any sensitive data is now his.
Does anyone know if this is possible to control at the server level. I know in firefox you go to about:config, but that is not an option for the server to tweak. Even so this can be told to the user, but not every user is going to be able to do this (being too complicated for some users) or some users will just ignore the warnings out of laziness or just not reading what the page says. I know there will be that one person that will say, "oh well that's their own fault and they deserve that". I honestly think ignorance in this sense is not the user's fault. Consider an older person in their 80s who is not technology-centric (like my father who I constantly give him the do's and don't's about online, but he still doesn't really understand the risks completely).
So I reiterate again, is it possible to disable this kind of off-line caching at the server level? I also found this post:
http://forums.asp.net/post/1386380.aspx
Would this help at all? Any help please. Please be constructive and not start a debate. I think I have been very clear, and I have done a lot of research on this with no luck. Please note that only the off-line caching on firefox is what is giving the problem, on every other browser (or on firefox onlinle) the caching has been disabled as expected.
Update:
I actually already have what the last link suggests (http://forums.asp.net/post/1386380.aspx) and it still doesn't prevent the problem.
Disabling cache from server side is kind of impossible because server can only request the browser to not store in cache. Rest is up to the browser to follow it or not.
The best option is not to send the data to browser , so it is never cached, instead fetch it on demand using json/Xml or any thing you are comfortable with.
The only trick that worked for me was to remove all sensitive information from loading via regular page methods, and load it via ajax/jquery on window.ready event. Once I implemented callback and ajax the back button and 'work offline' problem got solved but rolling out that with ajax callback was really a big task.
I want to execute a action on the event of browser crash in asp.net. I want to destroy the item added in the cart and revert back to the original state of the application and database if the browser crashes.
How can I do this?
Sadly, not possible, due to several factors.
1) the net is stateless, that is to say that the web server has no idea about the web browser, other than that it requested something. After it's serviced the request, it has no way of communicating with the browser.
2) the browser has the same issue. Once it's asked the server for the content and got it, that's it. If the user closes their browser, or lets their session time out, or if the browser crashes, the server doesn't know about it, and the browser doesn't tell it.
3) if the browser crashes, it's crashed, so it can't send any information anywhere, on account of the fact that it isn't working any more.
You can hook into the session_end event, which will fire when a user's session ends (a session ends when the user hasn't asked for anything for a certain period of time, 20 minutes is the default for this), however there's no way to tell WHY the session ended. the users browser may have crashed, they may have closed their browser, or they may have got bored and gone to another site.
Normally I wouldn't update the application state until after a user checks out, so the basket would be the only thing I'd need to delete. To do that I set a datetime column on my cart table, and update it every time the cart is updated. I then run a scheduled task on the database every day that deletes all baskets that are older than the amount of time I keep the baskets for.
Here's the question scenario:
Suppose you have a multiple-page ASP.NET web site with the following
requirements:
User-specific data for the currently logged in user is loaded and is required on each individual page of the application during a user's session.
The application itself only allows a certain number of users to be logged in at one time.
The next time a specific user logs in, the user should be returned to the last page visited.
Given this information, briefly describe how you would use ASP.NET to manage the state of the application to meet these needs?
Here's my thoughts and reasons. Please provide yours.
User-specific data for the currently
logged in user is loaded and is
required on each individual page of
the application during a user's
session.
This is suggesting to me that the interviewer is looking to see if I would suggest using Master pages as a way to provide a common approach to displaying the same thing on every page.
The application itself only allows a
certain number of users to be logged
in at one time.
Could the sought response be that, because scaling isn't an issue due to the limited number of users, that it is OK to put this information in the Session object for performance reasons or is this a trap and some of approach is better?
The next time a specific user logs in,
the user should be returned to the
last page visited
A cookie seems the best approach to track the last page access, since this doesn't seem to be critical information.
Please tell me how you would handle these question if you wanted to make the best impression
Feel free to provide input or comment an any line item.
Thanks!
As far as (3) is concerned, consider a shared PC. User A logs into a website using their site based user name/password. Does a whole load of work and shuts down the browser. USer B then comes along and on the same PC logs into the same site using their details. However, they will get the cookie from User A and be redirected to the last page they saw. This happens because Cookies are tied to the browser / OS user, where as you are potentially applying the site security separately in the application.
In this situation you would either need to put the user name into the cookie (encrypted) or use a server side method to store the location
Here are my thoughts:
They might be looking for Master Pages, but my first thought here was whether you're going to cache this user data, so you're not making a database query every time they hit a new page. To really impress them, you might mention partial caching techniques so that the repetitive portions of the page don't even need to be re-rendered with each page load.
I think you're right: they're helping you to conclude that the session state is an appropriate place to cache the user data. Just be sure you ask the appropriate questions, like "How many users?", and "How much data per user?"
The cached data could be used to keep track of the last-requested page, and when the user's session expires, you could save this data into a database table to be retrieved next time they log in.
That third item is awfully tricky. What if the user was last looking at an object that has since been deleted? What would be the intended behavior if a user logged in from one computer, did some work, and then logged in simultaneously from another computer or browser? I'd be sure to ask these kinds of questions, not least to show that I understand the implications of a requirement like this. If their responses lead you to believe that they're looking for a simple solution, go with the simple solution. Otherwise, tweak your response to be only as complicated as necessary.
Just a small thought.. If the system are running in a "Farmed" environment the Session data can be cleared and need to be handled some way.
http://www.beansoftware.com/ASP.NET-Tutorials/Store-Session-State-Server.aspx