NSURLSessionDownloadTask move temporary file - ios

I'm trying to reach the file which I was downloading earlier by NSURLSession. It seems I can't read the location of the file, even though I'm doing it before delegate method ends (as the file is temporary).
Still, I'm getting nil when trying to access the data under location returned from NSURLSession delegate and error 257.
The code goes as following:
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location {
NSError *movingError = nil;
NSData *fileData = [NSData dataWithContentsOfFile:location.path options:0 error:&movingError]; // is nil
NSLog(#"%#", movingError); // is error 257
}
What's wrong with this code..? I saw similar questions NSURLSessionDownloadTask - downloads but ends with error and iPhone - copying a file from resources to Documents gives an error but these completely doesn't apply to my case.
-- edit --
I've created a new project and pasted the very same code. It works... So:
1) In my project I'm receiving error 257, probably some configuration of the project is invalid or the fact I'm using backgroundTasks somewhere else in the app messes things up
2) Same as in 1 happens if I put the source files of this download to the external framework linked in by Carthage
3) On demo project I created (copy-pasted files used in 1 & 2) everything works corretly.
If someone has an idea what can cause the fact it isn't working - would be awesome.

Late to the discussion, but I've seen the same/similar issue and investigated.
With my investigation, what you are seeing is expected (should I say “it's observed”?).
But since I'm not 100% sure how you are using URL session, I put down below what I'm trying to do, followed by my observations (important ones only).
Also, I created a sample project and put it here as downLoader.zip. You can play and check how URL session background download works. But It's better to read thru below before trying to play, though this is fairly a long note.
A. what I'm trying to do
I'm developing kind a map app, where I need to download 1000+ of small size (0.5-150kB, mostly ~20kB) PNG files at a time. Total download size of them is ~50MB, and it takes a couple of minutes to download all of them. I think that keeping users to my app just waiting for download is bad design, so I made the app to use URL Session’s background download.
I have to admit, however, that Apple’s doc says that “Background sessions are optimized for transferring a small number of large resources that can be resumed as necessary.” So, the way I’m using background session is totally opposite. But, anyway...
B. what I've observed
Below, I’ve listed my observations and my guess of why. I should say guess since they are not documented.
(1) observation: sometimes, files that should come with didFinishDownlaodingTo don’t exist.
Temporary files are put at:
/var/mobile/Containers/Data/Application/randomHexString/Library/Caches/com.apple.nsurlsessiond/Downloads/yourName.yourApp. The randomHexString changes from app’s run to run. When the files don’t exist, the randomHexString that came with didFinishDownloadingTo is the one from the “previous” session. Now, “previous” here means the session at app’s previous run !, which clearly doesn't exist at the current session at current run.
There's another scenario for non-existent file, which is that the randomHexString is ok, but the files don't exist. This seems to happen after session cancel is requested (invalidateAndCancel) and before session becomes invalid (didBecomeInvalidWithError).
Guess: This happens especially on the development phase since we terminate the app while downloading, manually or by debugger or just by bug. It seems once the download requests are handed and accepted to the OS, the OS handles our requests even after the app quits. Note we can’t know if the OS has definitely accepted the requests or not. Even after the return from URLSessionDownloadTask:resume(), sometimes files don’t exit at the next launch and sometimes they do.
Workaround: If files don’t exist, just ignore them. In a while, “this time’s” files should come.
(2) observation: sometimes, the duplicated (same) files come with didFinishDownloadingTo.
My app converts downloaded PNG files to other format. W/in didFinishDownlaodingTo, I move temp files (== OS designated) to another my app’s directory, then spawn thread (GCD) to convert the format and delete downloaded temp files. So, the other thread (didFinishDownlaodingTo) to overwrite is an issue.
Workaround: I make list of URLSessionTask:taskIdentifier and w/in didFinishDownlaodingTo, check the duplication by retrieving the taskID list to ignore duplicated files.
(3) observation: even after the user terminated the app, OS relaunches the app again.
After the user terminated the app from task switcher, quite often, the OS relaunches the app w/ application:handleEventsForBackgroundURLSession:completionHandler.
Note the sequence of relaunch is that didFinishLaunchingWithOptions comes first as regular launch, then handleEventsForBackgroundURLSession comes next.
From user’s POV, when he/she terminated the app, that’s it, done! It looks strange even after they terminated the app, it relaunches in itself and notifies something to them. It's like a zombie.
Guess: The Apple’s document says “If the user terminates your app, the system cancels any pending tasks”. The definition of “pending tasks” is not clearly stated but I understand this is from iOS POV and not user’s or program developer’s. As guessed in (1), iOS seemed to have accepted the download requests, and they are not “pending tasks” anymore.
Workaround: I create a “flagFile” after all of download requests are handed to iOS w/ URLSessionDownloadTask:resume(), of which file means that “download is ongoing”. When users terminate the app, at UIApplicationDelegate:applicationWillTerminate, I delete the flag file. Or, if all of download requests not handed to iOS, there's no flag file. Then at app’s relaunch at UIApplicationDelegate:handleEventsForBackgroundURLSession, I check if we have the flag file. If missing, then I can assume that users terminated. Two choices here. Choice-1: I will not recreate URL session. What happens next is that iOS will terminate my app in about 20 seconds. I have no idea if this (== not creating the URL session) is a legal operation but it works. Users can launch w/in this 20 sec, so I put some more code to handle that scenario. Choice-2: I create URL session. What happens next is that iOS calls delegate methods didFinishDownlaodingTo/didCompleteWithError, followed by urlSessionDidFinishEvents. If I don't do anything here, the process (app) keeps alive indefinitely w/o any notification to users: nothing in task switcher. This is nothing more than waste of memory. The option here is to fire local notification and let users know of my app, so that they can go back to my app and can terminate (Again!), though my app clearly appears as a zombie. One issue for both choices: applicationWillTerminate may not be called in certain situation (though I've yet confirmed). At this case, flag file is left as regular ops and show zombie to users. So, the flag file method is just mitigation to the issue, but I think it works most of the time for my app.
Note the app is relaunched sometimes when it's killed by xcode debugger or killed by OS w/ bug (SEGFALUT).
(4) observation: after the app is terminated (by user, etc.) then relaunched by OS, the app is occasionally in active state (UIApplication.shared.applicationState is .active).
I want to notify the user on the download completion by local notification, but since it's active, local notification doesn't fire. So, I need to use UIAlertController instead. Therefore, I can't provide consistent user experience, and should look strange for users: most of the time local notification and very occasionally UIAlert. Note when app started in active state, it appears in task switcher.
Guess: totally no idea how this can happen. One good(?) thing is this happens only occasionally.
Workaround: seems none.
(5) observation: handleEventsForBackgroundURLSession/urlSessionDidFinishEvents is called just once.
I start the download after started background task (application.beginBackgroundTask). Then in expiration handler of beginBackgroundTask, I call endBackgroundTask. I don't know exactly why, but after endBackgroundTask, my process is still given lots of process time, so I can keep requesting download. This might be because download files keep coming w/ didFinishDownlaodingTo. To be a good citizen, I suspend to request further download, and fire local notification to user to put the app to foreground. Now, once I suspend the request, in 4-5 seconds, OS determines the URL session is over and handleEventsForBackgroundURLSession then urlSessionDidFinishEvents are called. This is one-off event. When the user put the app in foreground to resume download, then put it again in background, no handleEventsForBackgroundURLSession/urlSessionDidFinishEvents will come anymore. What's unclear to me is the definition of session's start and end. It seems the session starts at first URLSessionTask.resume(), then ends w/ timeout, which seems to be determined by URLSessionConfiguration.timeoutIntervalForRequest. However, setting large number here (1000 sec) doesn't affect anything, it's always 4-5 seconds.
Guess: no idea
Workaround: don't relay on urlSessionDidFinishEvents while the app is alive. Relay only when app relaunched by OS and at initial handleEventsForBackgroundURLSession/urlSessionDidFinishEvents.
===============
Below, I listed about the sample project (downLoader.zip). You can verify all of above with the sample.
The app has a list of download files. The number of files is 1921, and 56MB in total. They are 256x256 PNG map tile files that are located in a server managed by Geo Spatial Information Authority of Japan (GSI). After downloaded, they are moved to Library/Cache/download. If your device is jail-broken, you can view them w/ Filza.
crash itself to test relaunch
emulate background task expiration
logging to file since debugger doesn't work after relaunch by OS. The file is in Documents, can be moved to PC.
Do play with the real device. Simulator doesn't relaunch the app.
Project built w/ Xcode 8.3.3 and tested w/ iphone6+/9.3.3 and iphone7+/10.3.1
To see if app relaunched w/ xcode, go to Debug/Attach to Process menu and see if downLoader is listed.
===============
I think URL session background download behaves trickily, especially at relaunch. We need to consider at least the observations I listed above, or the app users will get confused.

I found same error code 257 from online users feedback.In the error scene, the location always refers to a strange bundle identifier:com.sdyd.SDMobileMixSmart. And I guess this's an apple system bug.

Related

No "kCFBundleVersionKey" sometimes: all possible scenarios?

I have a code like this in my app:
NSString* version = [[NSBundle mainBundle] objectForInfoDictionaryKey:(NSString *)kCFBundleVersionKey];
In most cases it works, and returns the Bundle version, but sometimes (let's say in 2% of cases) it returns nil.
The code is called within the function [AppDelegate application:didFinishLaunchingWithOptions:], in Main thread, an app is in foreground.
I could imagine this being an Apple's bug with some file reading error, but the percentage is quite high as for a rare Apple bug.
Also I know a one could mess with versions/bundles/Info.plist - but the percentage is too small for such case.
So, the first question: what can be the reason of [[NSBundle mainBundle] objectForInfoDictionaryKey:(NSString *)kCFBundleVersionKey] returning nil in this case?
The second question: do you know if these hypotheses make sense / are easy to check:
The user launches an app the first time after update, and [NSBundle mainBundle] becomes fully configured after application:didFinishLaunchingWithOptions ?
The app is in the process of an auto-update (from AppStore), the user opens it, and the system is currently writing a new data to Info.plist.
Some background thread in my app is also reading the [NSBundle mainBundle], the system uses some weird lock, so the read from a Main thread fails.
UPD: I've seen this question, but it's not related.
By default all files of the application, on a device that uses content protection, are encrypted. If you try to read them before they are decrypted(by the OS) you will get nil. The files are decrypted and they are available shortly after the user unlocks her phone, this might change and be more strict if you set a different value for the data protection entitlement. So the data might not be available when the application launches because they are not yet decrypted. This might be one reason that you get nil some times, the solution would be to wait to be notified in the app delegate that they data are ready before you read them.
The answers to all parts of the second questions are NO. There is no documented configuration that the app needs to do after an update that might affect the main Bundle. The user can not open an application if it is in the process of updating. The access to the main Bundle is thread-safe.

iOS - How long does NSManagedObject stay allocated without saving

Here is the scenario in my app: I download data from a JSON File which I stock in Coredata WITHOUT saving it. If the users wants to keep the data, he clicks on a button, and I save the context.
My question is: if the user doesn't click on the button and I don't save the data, how long will the Context stay the way it is? Until the user closes the app? Or even goes to background?
I'm looking for the best way to manage it.
Assuming that you do nothing to change it and that the app receives no memory warnings, doesn't crash and doesn't go to the background - indefinitely. If the app goes to the background it may be killed at any time if the OS requires it, so you can rely on nothing.
Really you should save the context as soon as possible. If you need to, save to a different store file on disk, then if the user discards you can delete that file and if they save you can move it to replace the original file (or just update a config which says where the current valid file is located on disk).

iOS Newsstand download failed when shut down the app

I'm having difficulty in the download using NewsstandKit when the app shut down.
My newsstand app download does starts in Background Mode, and exit to the background or push a download notification, the download issue everything is OK, but i shut down the app then the task is downloading,the downloading task failed.
Does it has to do some thing with the Server? or others?
You need to resume your downloads when the App Launches again.
Something to the tune of this would work
// Inside App Delegate Did Finish Launching
NKLibrary *nkLib = [NKLibrary sharedLibrary];
for(NKAssetDownload *asset in [nkLib downloadingAssets]){
[asset downloadWithDelegate:newsstandDownloadDelegate];
}
If you read the documentation you will find the following paragraph detailing how you should handle app termination:
While assets are being downloaded, the application could be suspended
or even terminated entirely if, for instance, there is insufficient
memory or the user force-quits the application. The application
(assuming it has the newsstand-content property) is later relaunched
into the background to handle the completion of the download or any
authentication challenges or errors related to it. The procedure in
this case is the following:
When the application is launched, it can use the
UIApplicationLaunchOptionsNewsstandDownloadsKey key to access an array
in the launchOptions dictionary passed into the
application:didFinishLaunchingWithOptions:. If there is an array, it
contains the identifiers that caused the launch; these could be
identifiers for downloads that have finished downloading that or could
not complete downloading. It iterates through the array of
NKAssetDownload objects from the downloadingAssets property of the
NKLibrary object and calls downloadWithDelegate: on each of them. If
it wants, the application can use the asset identifiers obtained in
the previous step to check which asset downloads caused the relaunch.
The NSURLConnectionDownloadDelegate object handles the asset downloads
as it does normally. The Newsstand Kit framework expects all calls of
its methods to be made on the main thread; the NSURLConnectionDelegate
Protocol methods are also invoked on the main thread.

background audio recording in iOS

I have searched far and wide for documentation on how to record audio in the background and have come to the conclusion that specifying 'audio' in the plist file might work. But, because iOS 4 will terminate background apps when it runs low on memory, we must also take some steps to reduce our memory usage when we transition to the background. How do we reduce our memory usage?
Also, does anybody know a sure shot way of recording audio in the background on iOS??
I unchecked the box in the Info.plist file that says "Application does not run in background" and also added the
<key> UIBackgroundModes </ key> < array> < string> audio</ string></ array>
in Info.plist. But, the recording stops as soon as I press the "HOME" button.
What callbacks do we implement to know that application has gone to background?
Please advise.
Just in case anyone else is looking for an answer here, I got mine working by adding the UIBackgroundModes array to the plist, adding 'audio' as Item 0.
I free up all memory/controllers on exit as you would by quitting the app anyhow so all that is left are the buffers the app uses (I've allocated around 1Mb though which makes me a little nervous however it seems to have worked!) I guess reducing the fidelity would help too but it seems to work as is.
In my core Audio setup I had to either change the buffer size from 1024 to 4096 or explicitly set the buffer size... I opted for the latter as latency was an issue.
NSTimeInterval iobuffersize = (float)1024.0f/SAMPLE_RATE);
sizeofdata = sizeof(iobuffersize);
AudioSessionSetProperty(kAudioSessionProperty_PreferredHardwareIOBufferDuration, &sizeofdata, &iobuffersize);
I also had to make sure that it didn't kill the app on exit via not enabling the 'Does not run in background' option however this should be off by default anyhow.
So guess I'm answering this for peace of mind for anyone else that it does work with not much setup after all.
I am however experiencing problems with Bluetooth setup, I guess that's because the buffer sizes change again but can't figure this one out... just get -50 = invalid property warning when rendering the data via the recordingCallback. I'm guessing it's the freq/sample size but who knows... will look later but seems like background now works.
Apart from specifying background recording in the plist file, we can implement applicationDidEnterBackground wihch will tell us when the application enters background. Here, we should stop any updates to the UI because that consumes memory for eg, updating a timer and an equalizer.
The call applicationWillEnterForeground will be called just before the app returns to foreground so we can resume whatever we stopped.
The recording then takes place in the background. It would also help to implement an interruption listener(this would work in the backgroud as well) so that you don't lose your recordings.

Firebase Analytics events from iOS not showing up

I am testing the new Google-powered Firebase, and have implemented remote notifications and crash reporting. I am, however, having massive problems with getting Analytics to work.
I track events with FIRAnalytics.logEventWithName(...) and save user pproperties with FIRAnalytics.setUserPropertyString(...). However, no matter what I do, no data shows up in the Firebase Analytics Console.
Well, I do receive some events, but those are not sent by me (like first_open and session_start). Also, this data seems to drop in after a very long time.
Furthermore, when I track events and save user data, I receive the following:
Upload task scheduled to be executed in approx. (s): 3102.294599890709
This seems really strange - Firebase waiting almost an hour before trying to send the next batch of data must be a bug, or is it configurable? When I waited that extremely long delay out, data was sent...but does not show up.
Firebase events are batched together and uploaded once every hour in order to prevent excessive battery drain on the devices. On iOS when you background the app before the 1h upload target the events will be dispatched at this time in the background.
You can enable debug logging for iOS (https://firebase.google.com/docs/analytics/ios/events#view_events_in_the_xcode_debug_console) to see when events are uploaded in debug console.
Once the events are uploaded there is delay at about 3h before the data will show up in the Firebase Analytics dashboard. Also the default day range excludes "today" so you only see events from yesterday. You can switch the date picker to include Today if you like to see the latest events.
The main reason to delay/batch data uploading is to save battery. Each time the network is used the device mobile network modem is put in hi power mode and stay in this mode for a while. If network is used regularly it has sever impact on the battery life. By batching the uploads together and delaying the upload the impact on the battery is significantly reduced.
In Swift it should be like:
FIRAnalytics.logEvent(withName: "SignUp", parameters: ["user_id": userid, "user_name": username])
To view this event in Firebase:
Go to Firebase console → Analytics tab
Click on DebugView tab; your Events are shown there
To view this event in Xcode:
In Xcode, select Product → Scheme → EditScheme
Select Run from left Menu
Select Arguments tab
In the Arguments Passed on Launch, add -FIRAnalyticsDebugEnabled
One dash only!!
Note that -FIRAnalyticsDebugEnabled has only ONE dash in front of it.
If you are not receiving events in console, it may be because you are not following naming convention, as I experienced if there is a space in event name it will never show up in the console like following:
mFirebaseAnalytics.logEvent("Add Camera", bundle);
But when you remove the space like following:
mFirebaseAnalytics.logEvent("Add_Camera", bundle);
Now you will see events in console, after approximately 3 hours.
Application will dispatch the data to console in following cases:
1- Data is more than an hours old
2- App goes into the background
You can watch this tutorial for more information:
Getting Started with Firebase Analytics on iOS: Events - Firecasts
Another thing to check is making sure your logging entries in the Arguments Passed on Launch are correct. They should start with a - e.g
-FIRAnalyticsDebugEnabled
and not
FIRAnalyticsDebugEnabled
I wasted an hour the other day wondering why nothing gets logged.
React-Native App (IOS/Android)
I had the same problem, debugView wasn't working, and streamView glitches a few times, the best way ive found to test my events was to logEvents with my createPageEvent() and then
the important thing is to put the app into background after logging the events, they will show up almost in realtime on firebase events or in streamView (check this article to see when events are sent to firebase)
events are only sent after 1 hour since they have been logged or immediately if you put your app in background.
import firebase, { RNFirebase } from 'react-native-firebase';
export default class AnalyticsService {
static async initialize() {
firebase.analytics().setAnalyticsCollectionEnabled(true);
}
static async createPageEvent(screen: string) {
firebase.analytics().setCurrentScreen(screen)
firebase.analytics().logEvent(`open_${screen}`)
}
}
the result is this in streamView almost realtime ->
Now you can start building funnels and stuff
first_open, session_start are listed by Firebase as Automatically collected events.
I can not help you with the extreme upload task delay you encounter on your custom events.. but Firebase Analytics is less than a week old and it may be just a bug on their side.
I found this StackOverflow question which mention the same debug lines but related to Google App Measurement or old Google Mobile Analytics SDK.
Also, be aware that Firebase Console won't show events in real-time (source):
You can view aggregrated statistics about your events in the Firebase console dashboards. These dashboards update periodically throughout the day. For immediate testing, use the logcat output as described in the previous section.
Just a simple note here: according to this little video https://www.youtube.com/watch?v=5pYdTgSkW5E after playing with your simulator you must press the home button on the Xcode, otherwise the data will not be sent to the server.
The most common problem most of the people are facing is the firebase is not logging events even though everything is working perfectly fine
This is what i found in there docs
If you need to deactivate Analytics collection permanently in a version of your app, set FIREBASE_ANALYTICS_COLLECTION_DEACTIVATED to YES in your app's Info.plist file. Setting FIREBASE_ANALYTICS_COLLECTION_DEACTIVATED to YES takes priority over any values for FIREBASE_ANALYTICS_COLLECTION_ENABLED in your app's Info.plist as well as any values set with setAnalyticsCollectionEnabled.
To re-enable collection, remove FIREBASE_ANALYTICS_COLLECTION_DEACTIVATED from your Info.plist. Setting FIREBASE_ANALYTICS_COLLECTION_DEACTIVATED to NO has no effect and results in the same behavior as not having FIREBASE_ANALYTICS_COLLECTION_DEACTIVATED set in your Info.plist file.
So you have to remove FIREBASE_ANALYTICS_COLLECTION_DEACTIVATED from your google-servicesinfo.plist file to make analytics work
Make sure your device is not set to battery save mode. In this mode events may be accumulated and sent only once in a while, even if you run firebase in debug mode as explained by others.
It takes too much time to update events in Firebase. Probably it is done once a day. See iOS or Android logging of Firebase events.
You can enable verbose logging to monitor logging of events by the SDK
to help verify that events are being logged properly. This includes
both automatically and manually logged events.
You can enable verbose logging as follows:
In Xcode, select Product > Scheme > Edit scheme...
Select Run from the left menu.
Select the Arguments tab.
In the Arguments Passed On Launch section, add
-FIRAnalyticsDebugEnabled.
The next time you run your app, your events will display in the Xcode
debug console, helping you immediately verify that events are being
sent.

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