500 database error (error opening!: 23) when saving a new document in app pause state

[HanzhiDou]

Hi,

• Version: 1.2.1 by Couchbase Lite Phonegap plugin
• Client OS: ios 9.3 (it happens also in earlier versions)

My ios cordova app uses the couchbase lite phonegap plugin, sometimes it can not save documents in app pause state(app is running in background), the restful save request get error response as below:

{ ... "status":500,"statusText":"Internal Server Error","responseText":"{\"status\":500,\"error\":\"Database error!\"}","responseXML":null,"responseBytes":null}

There is also one log:

error opening!: 23

However the save operation can succeed once app resumes from background mode, so just some documents are lost from user point of view. After further investigation and many tests, I observed the error occurred only when:

• app in background mode
• the database has never been read before the save document operation

Workaround: I add one query view operation just after the database ready in app startup phase, the error disappeared.

Though the workaround works, it's better to find the root cause and fix it.

Thanks!

[snej]

Are there any warnings written to the app's console log?

Can you explain how the app is running while in the background? Did you use a system API to get background time or to handle a notification?

The problem may be with the iOS file protection options — the default for CBL databases is NSFileProtectionCompleteUnlessOpen, which means that files can't be opened while the device is locked. This won't affect the main database file, which remains open, but would cause trouble for reading attachments, for example.

[HanzhiDou]

The error in console log:
error opening!: 23
The app uses background location updates, once new location available, it save the info to cbl.

background task is used to make the app running in background (beginBackgroundTaskWithExpirationHandler).

There is no attachment in this database, and the save operation is happened only after cbl ready and location updates are manual started.

[snej]

We don't have a REST API for changing the file protection settings of the database files. I think we'd need to add one, for this case. Then you can use a more lenient setting that allows you to access files while in the background.

[snej]

Note: We'd implement this along with the other proposed REST API extension to specify the db storage type, encryption key, etc.

[npomfret]

I'm also seeing thousands of these messages in the log

<Notice>: error opening!: 23

Is there a workaround?

[snej]

On Sep 27, 2016, at 1:47 AM, Nick Pomfret notifications@github.com wrote:

I'm also seeing thousands of these messages in the log

: error opening!: 23

Is there a workaround?

Yes, but it’s not available to PhoneGap apps unless you modify the native plugin code. You need to change the file protection mode of the CBLManager to one of the modes that allows file access after the app has been backgrounded. (Sorry, I don’t have the long names of those enums memorized!) We’re aware that this should be accessible from the REST API and have an issue open on that.

(It appears that iOS 10 is quicker to make files inaccessible after an app backgrounds; this problem has been coming up a lot more often.)

—Jens

[npomfret]

I'm using react-native so have access to the native code. I'll see what I can get working. Thanks for the advice. Can you point me at some docs?

[npomfret]

Does NSDataWritingFileProtectionCompleteUntilFirstUserAuthentication sound familiar?

I'm scratching around a bit here. My code was doing this:

CBLManager* dbmgr = [CBLManager sharedInstance]

And I've tried changing to this:

        NSString* dir = [CBLManager defaultDirectory];
        CBLManagerOptions options = {};
        options.fileProtection = NSDataWritingFileProtectionCompleteUntilFirstUserAuthentication;
        NSError* error;
        CBLManager* dbmgr =   [[CBLManager alloc] initWithDirectory: dir options: &options error: &error];

But its not worked. My databases aren't accessible over the rest api.

[snej]

dbmgr has to remain valid for the lifetime of the app, so you should make it a global variable, or an instance variable of the app delegate. Otherwise the reference will be released as soon as that method exits, which I believe will cause the manager to be dealloced. (Ah, the joys of using a language without full garbage collection!)

[npomfret]

Thank you! It's not live yet, but I hope this will improve the application responsiveness when backgrounded for long periods of time. At the moment my push notifications and background fetch operations only work for a while and eventually stop.

In case anyone out there is as incompetent as me, here's the change I made:

Instead of [CBLManager sharedInstance]...

        CBLManagerOptions options = {NO, NSDataWritingFileProtectionCompleteUntilFirstUserAuthentication};
        NSError* error;
        manager = [[CBLManager alloc] initWithDirectory: [CBLManager defaultDirectory]
                                                        options: &options error: &error];

And add this to my header file:

#import <CouchbaseLite/CouchbaseLite.h>

@interface ...
{
...
CBLManager *manager;
}
@end

I think owe you (and Jens) a beer!

[pasin]

I added couchbaselabs/Couchbase-Lite-PhoneGap-Plugin#89 for adding a configuration to set PhoneGap iOS file protection level. I will close this issue here.