can anyone tell me please, how SIGNALR manage consurrent user updates. What happened when user click "send" button at a same time. How SIGNALR identify which call is associated to which client.
Each single connection has a unique connectionId which is transmitted across server and clients usually at each call, so there is no issue with that. The server would receive 2 parallel calls but each one will be correctly associated to the right client through the exchanged connectionId. You should check the official documentation here.
Related
The SignalR server hub does not retain a list of groups so I assume that when I send out a broadcast message to a group it is sent to everyone connected to the hub and the clients filter out the message based on their participating groups. If I send a message to a specific group it seems that it is sent down the wire to everyone and can be intercepted by someone not in the specified group who knows how to use a browser debugger. If I want to have a secure broadcast (not even sent over the wire to some clients) I assume I need separate hubs or do I need separate sub domains?
Separate hubs do not sound like a good idea. While you probably can validate users on connect and refuse connections for non-authorized users what if you need a way to create isolated hubs dynamically. If however this functionality is enough for you you can use the Authorize attribute to secure either hubs or hub methods.
For cases where you do need to replicate the same functionality for different groups of users you can use SignalR groups but you need to verify that the user belongs to the group each time he connects. The SignalR documentation contains an example on how to do that verification. Note that everyone can try to connect to your groups and you should validate upon connection and not depend on the fact that you do not call the add method for a certain client.
SignalR only sends to the clients in the group. It's just a design issue that you can't retrieve a list of connections in a group. Groups, as pretty much everything else in SignalR, are subscription based, so the server knows which connections need to receive a message, but it's buried deep in the internals.
I would point you to the relevant server-side code, but don't have time to look it up right now.
It's easy to see in the client-side code though since it's not a lot of code - so you can verify there is no filtering going on there.
Groups also aren't separated per hub.
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.
Hy,
I'm using the signalR library on a project to handle an notification and chat modules. I've a table on an database to keep a track of online users.
The HUB for chat is inheriting IDisconnect where i disconnect the user. After disconnecting the user, i warm the users about that event. At this point, i check if the disconnect user is the client. If it's, then i call an method on HUB to reconnect the user (just update the table).
I do this because with the current implementation, once the user closes a tab on the browser it calls the Disconnect task but he could have another tab opened.
I've not tested (with larger requests) this module yet, but on my development server it could take a few seconds between the IDisconnect event, and the request from the user to connect again.
I'm concerned with my implementation to handle disconnected users from the chat but i can't see another way to improve this.
If possible, could someone give me a advice on this, or this is the only solution that i've?
Update: I ended up using a singleton class to store all the users and their connections id from signalr. This way i can get the id from user during the disconnect task (at this point you don't have any httpcontext to get the user information, but you can always get the user id with the connection id of signalr from the array in the singleton class).
20-02-2013 Although the above solution was doing the job, i had the need to scale my project. My solution was to use Redis to store all user connections, and take benefit of key expiration time on disconnect events. During the reconnect i check if the key is in pending state (gonna expire in a few minutes).
You can check out how JabbR, a multi-room chat application built on top of SignalR, solves this problem: https://github.com/JabbR/JabbR/blob/master/JabbR/Hubs/Chat.cs
It basically keeps a 1:N mapping of User<->ConnectionId, so when the last connection is disconnected the user can be marked as "offline".
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 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.