I would like to ask, if it is a good idea to use SinglR just for knowing if the current user now online or not?
For example I have an small website with log in system, and some where on the side i would like to show the logged in members.
Is this a good idea to use signalr for that?
And if it the case should I then on each page start the connection with hub? (In this case when user navigates on the pages, will be the ReConnected method called on hub, or OnDisconnected and OnConnected)?
I'm just starting with signalr, so curious what ppl think.
You could use SignalR though there might be better methods to do this. So when a user logs in, logs out or becomes inactive - you would have some sort of message being sent from the client to the server that indicates the change in status. You can store that information in a temporary database and whenever a value in the database changes you can use SignalR to relay that information to all the connected clients.
Signalr will get reconnected when the user moves from one page to another page. Whenever a user logs into a website the user security details will be persisted in a cookie assuming you are using Cookiebase authentication. So till the user logs out or session timesout the cookie will be active. So there is no real need for Signalr here.
I have been investigating the same thing. From my research, I would say that you COULD do this, but I'm on the fence of whether it's the best way to go about it. I would expect a LOT of disconnecting, connecting and reconnecting. If you're persisting this data in a database, you should anticipate a lot of database traffic. if you're only on a single server though, you could just persist this in memory.
Something to also note is that the ConnectionId changes with each page refresh. At first, I thought that was dumb because I wanted the connection id to be consistent so i could keep a handle on a user with it. However, if you open a link in a new tab and then close one of them, you have to still keep the other connection in storage. If the id was the same you would remove it on disconnect even though the other tab was open, so your user would incorrectly be marked as offline.
However, the other issue that i'm thinking about is that if you're just browsing around the site in a single tab, you will disconnect for a split second between each page load. So you might run into connection consistency issues with that.
I'd say online presence with signalr is more common to be used for a chat room or game lobby. So I'd say this is possible, but whether it's a good solution -- i'm unsure.
Related
Since I have noticed that once a user signs in with email and password, on reopening the application the session will not have expired and there is no need for a new authentication, I wish to avoid this.
I want to automatically .signOut() a user when .onDisconnect is triggered. How can I achieve this? I have tried with the following code, but unsuccessfully:
firebase.auth().onDisconnect().signOut();
When you say "onDisconnect", I'm assuming that you mean Realtime Database onDisconnect triggers.
The first thing to know about onDisconnect is that it triggers when the socket connection between Realtime Database and the client app is closed. This could happen for any number of reasons, and it can happen at any time, even if the app seemingly has a good internet connection. So, be careful about what you're trying to do here.
Also, onDisconnect triggers can only affect data in the database directly, and nothing else. So, this limits what you can effectively accomplish. You can't perform any action in the client app in response on an onDisconnect.
Between these two facts, what you're trying to do isn't really possible, and, I don't think it's desirable. You could end up logging out the user just because their train went underground momentarily, or if they simply switched out of the application for some time. This would be massively inconvenient to the user.
If you want to automatically log out the user, I strongly suggesting finding some other way to do this, such as writing some code to remember how long it's been since the user used your app, and forcing the logout on the on the client app based on your preferred logic.
The onDisconnect() is related to the database connection, and has little to do with your authenticated user. As in: onDisconnect() may fire when your user is signed in, simply because the connection to the database drops temporarily.
But more importantly: onDisconnect handlers run server-side, once the server detects that the client has disappeared. When this is because if a dirty disconnect (e.g. the app crashes), there is no way for the client to detect this anymore.
The most likely approach you'll want is to simply sign the user out when they close the app.
Alternative you might want to attach a listener to .info/connected in your client. This is a client-side listener that fires when the client detects that it is connected or disconnected.
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.
Im creating a chat app in ASP.NET MVC3.
im using long polling and AsyncController to do so
when a user posts a chat its saved in database , to retrieve should i constantly check database for change in record or after definite interval
or is there an better/ efficient way of doing it
i came across this question but could not get a usable answer.
You may take a look at SignalR for an efficient way. Contrary to the standard polling mechanism (in which you are sending requests at regular intervals to check for changes), SignalR uses a push mechanism in which the server sends notifications to connected clients to notify them about changes.
Since you're already using long polling and an asynccontrolller, why not create a message pool? Take a look at this solution.
In a nutshell, instead of just writing the updated chat to the database, you should also stick it in some sort of queue. Then each user's async thread is listening to that pool waiting for a message to appear. When one appears return the data to the user through your normal operation. When all listening threads have picked up the message it can be removed from the queue. This will prevent you from having several threads hammering your database looking for a new message.
You can give PServiceBus(http://pservicebus.codeplex.com/) a try and here is a sample web chat app(http://74.208.226.12/ChatApp/chat.html) running and does not need database in between to pass message between two web clients. If you want to persist data in the database for logging sake, you can always subscribe to the chat message and log it to database.
I'm considering updating an existing site to use SignalR. My site polls a third party service for data changes, does some magic on it, and clients poll it once every few minutes to refresh their view with any updates.
SignalR seems like a great way to eliminate the polling from the client, but I want to know how SignalR handles dropped & reconnected connections, especially with regards to mobile web apps which may have been suspended for some time. Will it automatically negotiate and queue up any updates that were missed in the meantime, or does the client need to resynch from scratch in these cases? I looked but couldn't find any docs on this so guidance would be appreciated.
All this is definitely possible since the client keeps track of the last message id it saw. If it happened to miss messages, it'll get those the next time it goes back to the server (asking for all messages since the last one it saw).
By default the server side of SignalR stores messages in memory (and it purges those every few seconds), but you can change it to persist to some persistent store (see IMessageStore) if you're thinking about clients going offline and catching up.
You could even persist messages yourself in your own app logic while SignalR stores stuff in memory. It really depends on the application.
We haven't added any special support for mobile clients, but you can persist the message id in whatever local storage you need to for your mobile client.
Those details aren't very specific but what you want to do is all possible with SignalR.
Read Understanding and Handling Connection Lifetime Events in SignalR, especially these sections:
How to continuously reconnect - required to recover from a disconnected state;
How to notify the user about disconnections - so your app can not only inform the user, but detect state changes (disconnected, reconnecting, reconnected) to refresh your app's state in other ways.
That document was written in 2014 and basically obsoletes many of the wrong or incomplete StackOverflow SignalR-related questions/answers from the 2011-2012 era.
I have a web application, where users will see notifications for their new messages, I want to push the notifications to the users who are already logged in.
I have seen that I can do it using Server Push of PokeIn, I have tried and understood the simple application using it, but I am not getting the ClientID thing.
The ClientId it saves in "OnClientConnected" is a simple integer, so how does it recognizes clients and calls functions on them ?
Also, it is written that it uses a hybrid long polling approach, can somebody please explain me what is this?
I will not be able to implement without having sufficient knowledge of it.
Does saving the ClientID in the database for logged in user and then pushing data using this will do ?
UPDATE:
Even from requests within the same
browser window or tab, the ClientId
received every time on every request
is different, so I had to include the
Handler in my master page and on every
request, I had to map the ClientId
received to the Logged In user, so
that I can send messages to him.
Can't I just map the (ClientId to
LoggedIn UserId) only once on LogIn
and then use that same ClientId to
send him messages ?
ClientID represents the identification key of the specific client view of your application and subject to change on each time.
It helps you to manage and target specific views by keys. On the other hand, you can still use ASP.NET session ids with PokeIn client ids.
The only difference is, if any user opens your application on the different tabs of same browser, each tab will have a unique client id. Actually, this is a great
functionality you may need. On the other hand, PokeIn also notifies you when a client is disconnected (almost instantly)..
You may reach session id by the client id;
CometWorker.GetSessionId(string ClientId)
or client ids for a session id by;
CometWorker.GetClientIdsBySessionId(string sessionId)
Additionally, if you don't want to use client id system (which is very useful), you may choose the "Joint" option. It helps you the send and receive messages from
the client with the name you have defined. (There is a sample for the "Joint" feature in here)
Because PokeIn provides various connection options, you don't have to think about the approach behind it when you work with PokeIn. It simply provides benefits
from the various solutions. More information can be accessible from : "FAQ" and "Advanced Tutorial" (http://www.pokein.com/Help/AdvancedTutorial.aspx)
At last, you don't have to save PokeIn client id to the database. PokeIn manages your server side objects per each client efficiently.
I suggest you to check the samples and tutorials.
As an answer for your update, you are free to use Joint feature of PokeIn when you need shared server side instances for the clients or consistent naming for the clients.