On my app (swift 2.3, xcode 7+, for iOS 9+) I'm write to a file, use the file, and then delete the file from a tmp directory created with NSTemporaryDirectory (on the app sandboxed). Although its a quick automated sequence, for a brief moment the file is written to the tmp directory in order to be used and then deleted.
My concern is: How secure, for that brief moment, is the file stored at tmp directory? Could an attacker get access to the file at the moment it's on the tmp directory?
If you're writing a file just to delete it, you should try to avoid storing the file on the system altogether. If you absolutely have to store the data on the device, you can use the .completeFileProtection option.
According to the documentation, .completeFileProtection will make it so the file is accessible only when the device is unlocked. This means that the only way that someone would have access to your data is if they have your phone's password, are somehow able to remotely unlock it using said password, and then execute code that has access to your app's sandboxed temporary file storage.
As far as I know, this would be very hard to achieve.
Related
Currently i was saving my application data (Media) to the CacheDirectory i.e
/var/mobile/Applications/BEAFC76C-C450-4A3A-9765-A0385A9580F3/Library/Caches
and things were going fine. But recently i got a bug report that the application data has been deleted. When i searched over it, i got this Apple Doc. According to it, DocumentsDirectory should be the ideal place to store the User/Application data.
Put user data in the /Documents/. User data is any
data that cannot be recreated by your app, such as user documents and
other user-generated content.
And Cache should not be used to store the User Data that could not be reproduced by the application.
Put data cache files in the /Library/Caches
directory. Examples of files you should put in this directory include
(but are not limited to) database cache files and downloadable
content, such as that used by magazine, newspaper, and map apps. Your
app should be able to gracefully handle situations where cached data
is deleted by the system to free up disk space.
What should be the ideal place to store it.
EDIT:
I have an application that allows user to store Videos and Photos in the application. For that i used CacheDirectory. But i am getting bug reports that the Data (Videos/Photos) is getting deleted. What conclusion i draw is that the data is being getting delete by the Device itself in order to provide space.
Secondly i also wanna give the iTunes sharing function. So only the particular files has to be stored in the DocumentsDirectory. Some files can never be exposed and some has has to be shared. What should be the ideal way to store the files.
Use Documents (NSDocumentDirectory) for files you wish to share via iTunes.
Use Application Support (NSApplicationSupportDirectory) for files you wish to hide from the user but still be backed up and never deleted by the OS.
Starting iOS 5, Apple says that it's no longer a good thing to save all kind of files in Documents Directory - if you do that, your app will be rejected for sure because this folder is backed up to iTunes & iCloud, unless otherwise specified.
It says that we should save files into Caches or Tmp Directory - these won't be backed up, but it's not a good thing to do because files from these directories can disappear if low memory happens.
So I think the best think to do is to save the important files that you need all the time in your app into Documents Directory and mark them not to be backed up, like this.
Library/Application Support Folder is the folder you should be using.
This directory doesn't always exist, and thus you may need to create it.
You can enable or disable whether you want to backup this data with iTunes or not.
This data is not accessible even if you enable file sharing. Only data that you put in Document directory would be shared with iTunes sharing, so you can still protect your data and get it backed up as well. Apple's documentation
I am implementing a resumable upload protocol that uploads in the background on iOS, which means I have to use an NSURLSessionUploadTask with a file. Since it's a resumable upload protocol, the file needs to be truncated based on the data that has already been received by the server, so I need to save a new temporary file to disk that has only the bytes to be uploaded within it.
If I can create that temporary upload file in the tmp/ or /Library/Caches/, can I trust that it will be kept as long as the NSURLSession is running?
EDIT: When an upload fails, the server will be saving the bytes it has already received and communicating that to the client. The client then should only send part of the file, which is why I need to create a smaller temporary file that must not be deleted mid-upload.
Huh? You provide the entire file, and the system takes care of managing the partial upload/download, and notifies you once the transfer is complete. In the case of a download, t hands you a temporary file once the download is complete and you have to save it to a permanent location.
You should not be mucking around with partial files at all.
EDIT:
You don't have access to tmp or /Library/Caches/, except through the sandbox. You can get access to the caches directory with the call
[NSSearchPathForDirectoriesInDomains(
NSCachesDirectory,
NSUserDomainMask, YES) lastObject];
It's my understanding that the caches directory only gets purged on restart, or if the device gets critically low on space, but I seem to remember that the docs are vague on when, exactly, the caches directory gets cleared.
You would probably be better off saving your file to the documents directory, then deleting it once you're done with it.
The answer to your question is no. NSURLSessionUploadTask's description appears to support keeping the source file around but it's misleading:
"In iOS, when you create an upload task for a file in a background session, the system copies that file to a temporary location and streams data from there"
But it says nothing about whether it will keep the original source file in the tmp directory. Specifically for your case where your server supports uploading partial files and you need to restart them after failures. Or in the more common situation where you need to manually restart an entire failed upload, for example from a retry-able server error, or if user killed your app and then restarted it (iOS doesn't continue uploads for user killed apps).
In these cases you can't count on the file still being around if you create it in the apps tmp directory. The file system programming guide tells us this.
https://developer.apple.com/library/archive/documentation/FileManagement/Conceptual/FileSystemProgrammingGuide/FileSystemOverview/FileSystemOverview.html
"Use this directory to write temporary files that do not need to persist between launches of your app. Your app should remove files from this directory when they are no longer needed; however, the system may purge this directory when your app is not running. The contents of this directory are not backed up by iTunes or iCloud."
So any tmp directory files can be deleted by iOS when your app stops running, and I can confirm I've seen this in production releases of our app. If you think you may need the source file for the upload again, you must store it in your own app directory, and manage deleting it yourself when done with it. Sorry, extra work, but I don't know of any way around it.
I developed an Ipad app which download different kind of files, but after a week or some days the downloaded files are removed and the app that open the file can find it anymore.
Could anybody help me, Where should I save downloaded files in my app to avoid that the file came automatically deleted?. IOS usually remove downloaded files after certain time?.
I already read this apple documentation
I know that maybe is not something complicated but I can't figure out why the file is removed If anybody can help me I'll appreciate that.
Put data cache files in the /Library/Caches
directory. Examples of files you should put in this directory include
(but are not limited to) database cache files and downloadable
content, such as that used by magazine, newspaper, and map apps. Your
app should be able to gracefully handle situations where cached data
is deleted by the system to free up disk space.
Most probably you are using caches/temp directory which the system can clear contents of in case of low space. To avoid deletion use Documents Directory.
If you are already storing in documents directory, then the file can appear missing if you are storing its hardcoded path , which can change during app update. Try storing relative path and log the contents of your documents directory to see what files exist.
save the files in your local sqlite db, data core or if you can serialize them with the standard user defaults
We have a requirement to implement files protection in the app. Even though apple provides file protection attributes, we are doubtful about the behavior when iPhone is jail broken or device is not password protected.
In order to implement this one idea is to encrypt all the files, file names, and such like. This is a long route. I m thinking instead of encrypting everything if possible add protection only at the top level. Say I have a folder named 'Top Folder' in documents folder where I store all the apps folders and files. With a password key can I add lock to only the top folder? How will it work?
No, you can't. A folder is only a part of file path, it cannot change (encrypt) data in files.
On Mac, it would be possible to mount an encrypted filesystem to a folder, but no such functionality is possible on iOS.
For encryption on iOS you have to encrypt/decrypt each file separately. Make sure the encryption keys are saved into the keychain and you encrypt/decrypt the files on the fly. Don't leave temporary decrypted files anywhere.
I need to be sure I am doing the right thing:
In my app the user can download audio files from the server. I don't want those big file to be backed up as he can re download them when ever he needs to.
My app is addressed for iOS 4.0 and above.
So as I understand I need to store the files is the documents directory and set a flag for the directory to not back up ?
Am I correct ?
Instead of putting them into the "Documents" directory (which gets backed up to the cloud), why not put your audio files into a "Cache" directory (specifically "/Library/Cache", which does not get backed up)?
Here's another question here on Stackoverflow that may help give a further answer to your question.
You can also prevent files to backed up:
https://developer.apple.com/library/ios/qa/qa1719/_index.html