The app I am building will be polling the server periodically to determine if the admin disabled the device on the server. When this happens, we abort all requests in progress and immediately “shutdown” the app.
Related
In my web app when the user logs in to the app, their browser opens a Websocket to the server so that updates can be pushed down to the browser.
It's an ASP.NET Core Web App (self-hosted) running in Azure App Services. I'd like to use Azure's deployment slot swapping feature to push code updates to production with zero downtime deployments.
In the limited testing I've done, it looks like after a slot swap the Websocket connection stays open to the original slot the browser was connected to. (So if the browser's Websocket was connected to slot A, and we swapped slot A and B so that new connections go to slot B, the Websocket would still be open to the app running on slot A.)
At some point the old slot will be taken offline, which will forcibly close any open Websockets. I would prefer to re-open the Websocket to the new slot as gracefully as possible and as soon as possible after the slot swap, so that if I update the Websocket-related code all clients will be running the new code as soon as possible.
A sketch of how this might work:
Slot swap takes place
A notification is sent to the code running on the old slot
Code running on the old slot pushes a Websocket message to reconnect
On receiving the message, the browser opens a new Websocket connection (which will go to the new slot)
When the connection succeeds, the browser closes the old Websocket
Is there a better way to do it?
How can the code running on the old slot know when it has been swapped?
Is handling this gracefully even possible? Or are there always going to be a bunch of race conditions?
The WebSockets do stay connected, because ARR can only direct new requests to the "new" application. You'd see the same behavior if you were downloading a large file in the middle of a swap, for example.
The way I've handled this is to have my deployment system (Octopus) do the swap, and then make a request to the "old" application that notifies all of the connected WebSocket clients that they need to disconnect and reconnect. The clients will immediately disconnect, pick a random delay (to prevent thousands of reconnects at once) and then reconnect after that delay.
Within the application the user can subscribe to notifications or unsubscribe. This events are handled by a Worklight adapter that register or delete in the database the users subscriptions.
But in case the app is uninstalled without unsubscribing, in the database will remain the user subscription.
How can this be handled?
Is there any way to notify Worklight of the application uninstall?
As explained in the Idan answer, the subscription will be removed by Worklight automatically after a not specific amount of time depending on the notification provider.
http://developer.android.com/google/gcm/adv.html#unreg
https://developer.apple.com/library/mac/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/Chapters/CommunicatingWIthAPS.html Look for "General Provider Requirements" and "The Feedback Service"
For Apple how proceeds Worklight? Does it check each day the feedback service and then removes the corresponding notifications?
I have tested with Android and a trace appears in the WL Server console saying that the subscription has been removed "because the notification was rejected by the server (NotRegistered)".
This was after two hours since I uninstalled the application and I sent 23 notifications with the application uninstalled.
Is it possible to add a custom handler for this "event"?
Reading the documentation, in the WL.Server.createEventSource method, the "onDeviceUnsubscribe" property of the "options" parameters says:
"The name of the JavaScript function that is called when the device subscription is removed by a client request or by the cleanup task"
What is a cleanup task? My first thought was that this callback would be invoked in the use case we are discussing but I have tried it and when the notification is automatically removed this callback is not called.
Currently I'm sending SMS to my customers, when the customer installs the application I will send notifications instead of SMS but in case the customer uninstalls the application I need to know it for starting to send SMS again.
The Worklight Server cannot be notified (by you) that the application has been uninstalled - this is a user action that you do not have any control over.
That said, you do not need to worry about this, because this exact scenario is being handled for you.
This is the flow:
In case a push-enabled application has been uninstalled, and you are sending a notification... this notification arrives to the APNS/GCM/MPNS server, which then send the notification to the device, to be displayed in the app.
Because the app is no longer installed, the device OS will provide feedback to the APNS/GCM/MPNS server that the notification failed to display.
Eventually, what that will happen is that the APNS/GCM/MPNS server will notify the Worklight Server that the token is no longer valid and the subscription will be removed from the database.
Worklight cannot control when will the APNS/GCM/MPNS server notify the above, though. For more information, consult with the respective service documentation.
The additions to your edited question are not totally clear, but here goes:
APNS token invalidation - only Apple can tell you about it. It could take minutes, hours, days, weeks... there are all sort of scenarios, so no specific time frame can be guaranteed.
The cleanup task is likely a task done by Worklight Server to remove stale subscriptions. It runs every 1 hour and connects to APNS feedback service to retrieve a list of inactive devices. On receiving the list of devices, it removes the device subscriptions from the database.
onDeviceUnsubscribe - Once the device is unsubscribed onDeviceUnsubscribe will be triggered. The idea of this callback is to allow the developer to notify the enterprise backend system that the device is no longer able to receive push notifications so that the backend will no longer try to send them. This is where you could tell your backend system to send SMS instead. But, did you actually implement it (the callback)?
Live tiles are able to receive push notifications without the associated metro app needing to be running.
However I believe that the app must have run at least once in order for the app to acquire a notification channel and subscribe to a notification server, passing the channel to the server.
My question is -
What happens if the server cuts off the client? If the user turns off their computer I presume the server would start receiving delivery failure errors. The server might then cut off the client.
But what happens when the user turns their computer back on? Is the tile now disconnected until the user starts the app again and it resubscribes with the server for notifications?
Or is there a way for the tile to resubscribe automatically on start up without the app having to run?
The push notifications are not sent directly to the client; they're sent via the Windows Notification service in the cloud. This means your service will be able to just send them. The WNS service will do the right thing with notifications when the machine comes out of sleep / reconnects to the network.
http://msdn.microsoft.com/en-us/library/windows/apps/hh913756.aspx has a overview of the service side of notifications.
It's important to note that the tile channel expires after 30 days, and will need to be (programmatically) renewed. The guidance is that you should renew when the app runs to make sure it doesn't expire.
The only thing I can't seem to locate in the documentation is how many push notifications are queued on the client - I suspect that for a given tag notification, only one is kept.
Maybe another way to think about this is with the bad notification -- e.g a "new items" count. If you push this number while the device is disconnect from the network (off, driven over etc), then your service will succeed in sending the notification, and when that machine reconnects, it will seamlessly see the badge update.
You should handle that in your code that when your clients from the server went offline then you should remove them and disconnect them, the client side will only receive the cached values in the live tiles.
If they went back on, then you should also handle it in your server side to push the new notification data.
Just a quick tip: If you are using WCF as your service, you might want to check the Announcement Service Class there you can handle your clients online/offline scenarios.
I'm working on a messaging app (something like WhatsApp) and I have a dilemma about implementing it's main functionality - sending message from client1 to client2.
The thing is I'm using a centralized server design, where clients uses NSURLConnection to send messages to the server, the server doesn't keep and manage open sockets and can't send a message for one of the clients, so clients have a timer and query the server every 2 seconds to see if a new message is waiting for them.
The problem with this approach is that querying the server every 2 second seem to kill the battery very fast, so I thought maybe instead of client querying the server, to use APNS so when client1 send a message to the server, the server will send a push notification to client2, then client2 will fetch the data from the server.
Will this approach work with a massive messaging app requiring massive push notification uses?
Yes. I would say this approach is okay and will perform well.
You could also create a socket connection when your application is running in front. But the APNS-way (your preferred way) will also work when the user has quit your app.
APNS can handle huge load. There where only very few delays as far as i noticed.
The PUSH-System on iOS is just a HTTP Connection to apple which keeps the response-channel open for some hours (like loading a webpage for some hours).
It will use around +10% of your battery.
So best would be to not create another keep-alive HTTP/Socket connection and to re-use apples channel (APNS) to save the endusers battery.
In your app you will receive the Push-Notification and you can parse the JSON-Data and then pull/sync with your own server.
You should also take in mind what to do, when your app is not running in foreground (then you might display the received message as APNS messages as WhatsApp does).
Why can't the application server send messages directly to the application? Why do you need the C2DM service in the middle?
To send a message from the server side you have two possibilities:
The client polls for new messages in certain intervals. Downside: Not a real-time solution. If you poll too frequently it will drain battery, consume your quota (if you don't have an unlimited package). Generally you do a lot of unnecessary work and traffic as most polls will return no messages.
Stay connected all the time. Downside: hard to deliver technically as phones can close connections when going to sleep mode. (At least nothing guarantees that they won't). Also you are running a background application 24/7.
The current state of C2DM will give you:
The ability to get messages even when your application is not running as Android will start your application (the part of it you configured, not necessarily the whole UI) when a message arrives.
A central, shared channel to deliver such messages. If 10 applications need real-time notifications on your phone this is one single facility, not 10 applications running and polling in parallel.
The promise: As this is the sanctioned API by Google for push messaging you can expect it to be optimized in the future. One improvement can be carrier-level messaging to initiate a C2DM session. That would mean you can put 100% of the "smart" part of your phone asleep.
Because the application can't (or isn't supposed to) act as a server.
If you would like to send messages to your app directly, then your application would need to have some sort of server listening in some port. This is bad because:
connections are usually firewalled, you cant just listen in some port,
your device can be turned off or without connectivity (then you app sever would need to retry),
the app server would need to know the address of your device,
app would need to be running (at least the server module) all the time, this isn't battery friendly.