UIDocumentPickerViewController returns url to a file that does not exist

Question

I'm using UIDocumentPickerViewController to let the user select a file from iCloud Drive for uploading to the backend.

Most of the time, it works correctly. However, sometimes (especially when the internet connection is spotty)documentPicker:didPickDocumentAtURL: gives a url that does not actually exist on the filesystem, and any attempt to use it returns a NSError "No such file or directory".

What is the correct way to handle this? I'm thinking about using NSFileManager fileExistsAtPath: and tell the user to try again if it doesn't exist. But that doesn't sound very user friendly. Is there a way to get the real error reason from iCloud Drive and perhaps tell iCloud Drive to try again?

The relevant parts of the code:

@IBAction func add(sender: UIBarButtonItem) {
    let documentMenu = UIDocumentMenuViewController(
        documentTypes: [kUTTypeImage as String],
        inMode: .Import)

    documentMenu.delegate = self
    documentMenu.popoverPresentationController?.barButtonItem = sender
    presentViewController(documentMenu, animated: true, completion: nil)
}

func documentMenu(documentMenu: UIDocumentMenuViewController, didPickDocumentPicker documentPicker: UIDocumentPickerViewController) {
    documentPicker.delegate = self
    documentPicker.popoverPresentationController?.sourceView = self.view
    presentViewController(documentPicker, animated: true, completion: nil)
}

func documentPicker(controller: UIDocumentPickerViewController, didPickDocumentAtURL url: NSURL) {
    print("original URL", url)

    url.startAccessingSecurityScopedResource()

    var error: NSError?
    NSFileCoordinator().coordinateReadingItemAtURL(
    url, options: .ForUploading, error: &error) { url in
        print("coordinated URL", url)
    }

    if let error = error {
        print(error)
    }

    url.stopAccessingSecurityScopedResource()
}

I reproduced this by adding two large images (~5MiB each) to iCloud Drive on OS X and opening only one of them (a synced file.bmp) on an iPhone and not opening the other (an unsynced file.bmp). And then turned off WiFi. Then I tried to select them in my application:

The synced file:

original URL file:///private/var/mobile/Containers/Data/Application/CE70EE57-B906-4BF8-B351-A57110BE2B01/tmp/example.com.demo-Inbox/a%20synced%20file.bmp
coordinated URL file:///private/var/mobile/Containers/Data/Application/CE70EE57-B906-4BF8-B351-A57110BE2B01/tmp/CoordinatedZipFileDR7e5I/a%20synced%20file.bmp

The unsynced file:

original URL file:///private/var/mobile/Containers/Data/Application/CE70EE57-B906-4BF8-B351-A57110BE2B01/tmp/example.com.demo-Inbox/an%20unsynced%20file.bmp
Error Domain=NSCocoaErrorDomain Code=260 "The file “an unsynced file.bmp” couldn’t be opened because there is no such file." UserInfo={NSURL=file:///private/var/mobile/Containers/Data/Application/CE70EE57-B906-4BF8-B351-A57110BE2B01/tmp/example.com.demo-Inbox/an%20unsynced%20file.bmp, NSFilePath=/private/var/mobile/Containers/Data/Application/CE70EE57-B906-4BF8-B351-A57110BE2B01/tmp/example.com.demo-Inbox/an unsynced file.bmp, NSUnderlyingError=0x15fee1210 {Error Domain=NSPOSIXErrorDomain Code=2 "No such file or directory"}}

Answer 1

Description

Similar problem occurred to me. I have document picker initialized like this:

var documentPicker: UIDocumentPickerViewController = UIDocumentPickerViewController(documentTypes: ["public.data"], in: .import)

Which means that files are copied to app_id-Inbox directory after they are selected in documentPicker. When delegate method documentPicker(_:didPickDocumentsAt:) gets called it gives URLs which are pointing to files that are located in app_id-Inbox directory.

Problem

After some time (without closing app) those URLs were pointing to files that are not existing. That happened because app_id-Inbox in tmp/ folder was cleared meanwhile. For example I pick documents, show them in table view and leave iPhone on that screen for like a minute, then when I try to click on specific documents which opens file in QLPreviewController using URL provided from documentPicker it returns file not existing.

This seems like a bug because Apple's documentation states following here

UIDocumentPickerModeImport

The URLs refer to a copy of the selected documents. These documents are temporary files. They remain available only until your application terminates. To keep a permanent copy, move these files to a permanent location inside your sandbox.

It clearly says until application terminates, but in my case that was around minute of not opening that URL.

Workaround

Move files from app_id-Inbox folder to tmp/ or any other directory then use URLs that are pointing to new location.

Swift 4

func documentPicker(_ controller: UIDocumentPickerViewController, didPickDocumentsAt urls: [URL]) {
    let newUrls = urls.compactMap { (url: URL) -> URL? in
        // Create file URL to temporary folder
        var tempURL = URL(fileURLWithPath: NSTemporaryDirectory())
        // Apend filename (name+extension) to URL
        tempURL.appendPathComponent(url.lastPathComponent)
        do {
            // If file with same name exists remove it (replace file with new one)
            if FileManager.default.fileExists(atPath: tempURL.path) {
                try FileManager.default.removeItem(atPath: tempURL.path)
            }
            // Move file from app_id-Inbox to tmp/filename
            try FileManager.default.moveItem(atPath: url.path, toPath: tempURL.path)
            return tempURL
        } catch {
            print(error.localizedDescription)
            return nil
        }
    }
    // ... do something with URLs
}

---

Although system will take care of /tmp directory it's recommended to clear its content when it's not needed anymore.