Assume that I connected to the broker with "clean session=false" and started receiving events, in case of disconnection ideally my application will still receive data on connection. But if the application is crashed I want to have a fresh start and clear my session.
Can I clear my session on the MQTT broker and have a fresh start?
From the documentation I concluded that if I wanted to do that I would need to do the following:
application start
connect using "clean session=true" // this will cause any current session to be removed along with its data
every thing related to the session is purged from server
disconnect
connect using "clean session=false" and start getting the data.
I got the idea from
http://www.hivemq.com/blog/mqtt-essentials-part-3-client-broker-connection-establishment
"If clean session is set to true, the broker won’t store anything for
the client and will also purge all information from a previous
persistent session."
Is this the correct way to clear a previous session?
Yes, that is the only way to clear a session for a client.
Related
I have google'ed a lot on this question but haven't found an answer. I have a Guacamole server that connects to a local VNC session and I would like for it to disconnect the user session if it detects no activity for an hour.
What I've tried and attempted
used xprintidle to show idle time of the user, this works so will be put in a script that might be used later to terminate an idle session.
I have looked at Guacamole's api-session-timeout and set it for a minute, I had hoped it would not reconnect to the same session once the VNC server stops abruptly. It seems this did not work.
I have tried to use guacamole's user-mappings.xml to specify the parameter "autoretry" and set that to "1". Restarted and this did not work, I'm thinking its not used this way.
I have went to the guacamole postgres database and manually inserted the entry for autoretry into the parameter table. Restarted, but this did not work.
I have went to the VNC side (I use TurboVNC) and looked at the flag -idletimeout and configuration option max-idle-timeout. This terminates the TurboVNC service when there are no active connections. It is not what I am after, I'm trying to only disconnect the session when the user is idle.
I figured that the VNC side would not work because even if the VNC session is terminated Guacamole would keep on retying forever to reconnect to that session.
From some posts on the Guacamole mailing list it seems that disabling auto reconnect is not possible without a recompile from source.
Is there a way to disconnect an active session after an idle timeout period? or maybe a way to stop Guacamole from reconnecting?
I'm trying to connect to our push server via MQTT-Client-Framework.
There is no complication for connecting to server and with a few line of code i can connect to server and subscribe to topic.
but I have a few question that I could not find any direct answer for them.
1) How can I keep my client running at background?
2) What happen after device restart? how can I automatically connect to server after device restart?
3)Suppose I got an error during connecting to server. Will this library trying to connect in a loop? how many times it try? or I need to manage this myself?
4) The same 3 scenario for subscribing to topic?
Based on my experience on MQTT-client framework following are the answers to your questions/queries. I hope it clarifies your concerns and helps you to move ahead.
1) How can I keep my client running at background?
You can not keep your MQTT client running in background, as Apple doesn't allow any application to keep running for long time in background. Though if you override its not guaranteed your application will keep running in background. You can read more about background execution support in apple documentation.
Also refer issue posted on github for given framework.
2) What happen after device restart? how can I automatically connect to server after device restart?
Each time your app begin execution you need to connect to your server using MQTT client framework there is no auto connect mechanism available in MQTT-client framework. I suggest to write init your connection in specific controller which executes immediately after your app launch except same as AppDelegate
3) Suppose I got an error during connecting to server. Will this library trying to connect in a loop? how many times it try? or I need to manage this myself?
If your MQTT-client fails to connect your server, you need to handle it yourself, library doesn't try to auto connect as mentioned in previous answer. I have written sample code as below. Use NSTimer for auto connect to server.
[self.mqttSession connectToHost:MQTT_HOST port:MQTT_PORT usingSSL:NO connectHandler:^(NSError *error)
{
if(error)
{
// Application fail to connect to server, write your code to auto connect here
}
}];
4) The same 3 scenario for subscribing to topic?
If your broker server has configuration to track your existing subscription for individual users/client then you don't need to subscribe each time.
Otherwise each time you need to subscribe to same topic on successful connection. Use following MQTTSessionDelegate method to subscribe.
- (void)connected:(MQTTSession *)session
Happy coding :)
1)Project->Capabilities->Background Modes. There has some options for allowing your app to run at background.
2)Generally speaking, MQTT will not be disconnected to the server if your app is allowed to run at background, but i think you would better check up the connection and maybe re-connect MQTT to your server when the app become active again.
AppDelegate-> - (void)applicationDidBecomeActive:(UIApplication *)application;
3)Unfortunately, yes, it will. And you have to manage yourself.
4)I can't help.
For your first question:
Details on how to run in the background on iOS can be found here. This link also lists the actions that Apple allows to run in the background, if your app does not meet those criteria then it is likely to get thrown out of the app store by Apple.
The list also shows which UIBackgroundModes to place in your Info.plist to flag that your app needs background access.
The other 3 I can't help with
We all know that Apple doesn't allow app service to run in the background, so MQTT will be disconnected in the background mode.
Now do one thing use better frameworks for MQTT like this in this framework you will get auto-reconnect and callbacks and many things.
So When you receive a call back that the MQTT is connected, immediately subscribe to all the topics that you have.
And if you want to get all missed messages then you need to change the MQTT configuration to like 'clean = false'.
When NEVPNProtocol property is updated by the server such that the username & password isn't valid anymore, is there a way we can handle this?
Lets say if we turn on onDemandEnabled flag for NEVPNManager, and when the server invalidates the credential (since the user has been blacklisted), is there a way we can toggle this programmatically? From the end user's experience perspective, the user would wait for a long time to fail webpage loading. Background fetch using a timer might not work if the app is killed.
Other than using push notifications, is there a better way to solve this issue?
I didn't try it myself, but what you should do is when you configure your VPN and set the onDemandEnabled, you need to define the onDemandRules.
There you have NEOnDemandRuleDisconnect, which will prevent your VPN from starting, and will disconnect it if it's already active.
https://developer.apple.com/library/ios/documentation/NetworkExtension/Reference/NEOnDemandRuleDisconnectClassRef/index.html#//apple_ref/occ/cl/NEOnDemandRuleDisconnect
This way even if your VPN is active, you will use it only when the rules still applies.
Edit: you can also use onDemandRule - probeURL . With this, before any activation of your VPN, it will send a request to a server of your choice. The server will return an answer if you should use your VPN or not.
I have an app that tracks wildlife where the user enters data based on their observations (eg. user enters they see 3 moose). The data is then uploaded to a server. However, because this app will be used out in the field where there is often no internet connection, I want to save data if there is no connection, and upload the data as soon as the network is available
I know about Reachability, but it looks like I can only check if the internet connection is available at that moment, and doesn't check in the background for internet connectivity
So to summarize:
If there is an internet connection when users submits data, then that's fine.
If there is no internet connection, when user submits data, I want to save this data. As soon as there is an internet connection, I want the data to be uploaded, without needing the user to open up the app again. I can't rely on the user to open the app again causing the data to be submitted, because they will likely only use this app out of the range of cell towers, and will likely NEVER run the app in a location with a network connection, so it would have to automatically submit this data for them.
Looking around, I can't find an answer so I'm beginning to wonder...is this even possible?
No, Apple don't allow applications to run indefinitely in the background for this purpose, and they don't allow applications to be triggered remotely or anything of that nature. At best you could have your application run in the background to get notifications about major location changes, but you'd have to have it as a proper feature rather than a hack to get around this limitation, otherwise your application won't get approved by Apple.
I know it's possible to utilize the network in the background but only for a limited time after the user closes the app. You could create a timer which checks for a network connection (using Reachability or by pinging Google) and set the timer to fire every minute after the app closes. It's not a very efficient solution but it may work. You should look into how long you can maintain a connection after the app close though, I think it is 5-10 minutes.
I have to add e-mail notifications to a client server application.
Notifications happen as the user do some particular action on the client UI.
If I had a middle tier or a service running at server I can imagine how to do it:
1) I simply create a DB tables with "pending notifications"
2) as a user does an action that generates a notification I add a record to the table
3) serverside I would continuously try to send those mails and removing them from the table once sending is succesful
Now I cannot do this now, I have a plan to add a service later on, but for now I must go the quick and dirty way.
So somehow what I was thinking to is to implement something like this:
1) as a notify-worth event occurs at client, the same client (my exe) tries to send the notification, upon failure it will log the notification in the "pending notifications" table (failure can be becuase lack of internet connection or any other problem)
2) I add a Timer that will work from any client machine to check for pending notifications. If there are any the client will try to send the e-mail (using a transaction: I will mark a field as "TryngToSendFromClientX" and in case of failure I will reset that field to NULL)
I think this approach would work, it has obvious limitations (if after failure no one logs into the system, no notification will be sent - same would be if service goes "down"). But can you comment on this approach and suggest a better one?
Additional notes (to better understand the scenario):
a) Note: all notifications are sent from the same e-mail account.
b) I don't need to keep track of who sent the e-mail.
c) the problem of creating the service now is that it will basically complicate significantly deployment and I need to create tools for monitoring the status of the service. Something that I will do in future but not now, in future I have plan to add more functionality (not only sending notifications) to the service, so in that case it makes more sense to create it.
d) I will send e-mails by using Indy components and SMTP server.
If you are not willing to create the service now, I think you are stuck with the scenario you describe. There are some things though you could do to circumvent the problem of no user firing up the client anymore while there are still pending messages.
You could add a commandline utility (or commandline parameter as bepe4711 suggested) that will only check for pending messages and try to send them.
Add this commandline utility to the StartUp folder or Run key in the registry. This way messages will at least get sent when the computer restarts, even if the user does not fire up the your app.
Add a scheduled task to run this utility at least once every day. The scheduled task can be added by code or by your installer.
If you do both, you will only have to worry about pending messages of users that never start their computer again.
Perhaps you can add a parameter to your client which causes it to just look at the pending notifications and send them. After this it can terminate itself. It will just act like some kind of service.
Then you install the client on the server and start it every x minutes.
I do something very similar to the approach you describe. Instead of sending emails I need to call a web service. My application is installed on several laptops and they are commonly not connected to any network.
When my application raises an exception I collect various bits of information including user comments and screen shots. Then I attempt to send this to our web service. If by chance the web service is not available. (i.e. not connected to the internet or web service is down) I write the results to an XML file on disk in the User Profile (App_Data) directory.
The one major difference is I don't poll to check to see if the server is up. I attempt to send them again on the startup of the application.
If both Systems are running on Windows, have a look at MS Message Queue. It is designed to send notifications to systems, which are not allways online. I did it in .Net, there are already easy to use classes implemented. Not sure about Delphi.
Latest version of Windows uses much more the Windows Task Scheduler, and now task can be fired on event (i.e. when a network card gets connected...). You could write a separate utility that tries to send pending notification, even if noone is logged in.