Relocating localStorage in iOS 5.1 for PhoneGap Applications

See bug details here: https://issues.apache.org/jira/browse/CB-330

The general problem is that as of iOS update 5.1 (3/2012), Apple no longer considers data stored in localStorage or the SQL Lite DB to be persistent data. This means that any data stored using these HTML5 features is considered volatile across updates and process termination. To say the least, this is a problem for any developers replying on this data being available across app updates, backups, or crashes. It’s bad enough that we only get 5MB of storage (2.5MB if you’re storing 16bit text characters), now we can’t even persist the data when the app is run natively? That’s yucky.

Product groups like Sencha, Ext4.js, and  PohoneGap are working on work arounds for this new Apple specification but as of this entry, they aren’t all there yet. Until a fix exits for Sencha, I’ve taken the approach of changing the default location of localStorage and the SQL DB that resides within the app container on the device. This solution solves the problem entirely and has the added benefit of tons more storage capacity. The down side is that it requires modification of the native code-base and therefore requires apps for the iOS system to be built in xcode. Consequently, mobile app dev for iOS using this approach now requires a Mac. Lucky me, I have me some Macs.

The Fix

Copy and paste the following code into AppDelegate.m‘s method didFinishLaunchingWithOptions. The placement likely doesn’t matter but I add it as the first block of code.

You can read through the code to see that it won’t affect you older iOS devices and that it just relates where the localStorage mechanism point to on the device.

/* Fix problem with ios 5.0.1+ and Webkit databases described at the following urls:
     *   https://issues.apache.org/jira/browse/CB-347
     *   https://issues.apache.org/jira/browse/CB-330
     * My strategy is to move any existing database from default paths
     * to Documents/ and then changing app preferences accordingly
     */

    NSString* library = [NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES)objectAtIndex:0];
    NSString* documents = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];

    NSString *localStorageSubdir = (IsAtLeastiOSVersion(@"5.1")) ? @"Caches" : @"WebKit/LocalStorage";
    NSString *localStoragePath = [library stringByAppendingPathComponent:localStorageSubdir];
    NSString *localStorageDb = [localStoragePath stringByAppendingPathComponent:@"file__0.localstorage"];

    NSString *WebSQLSubdir = (IsAtLeastiOSVersion(@"5.1")) ? @"Caches" : @"WebKit/Databases";
    NSString *WebSQLPath = [library stringByAppendingPathComponent:WebSQLSubdir];
    NSString *WebSQLIndex = [WebSQLPath stringByAppendingPathComponent:@"Databases.db"];
    NSString *WebSQLDb = [WebSQLPath stringByAppendingPathComponent:@"file__0"];

    NSString *ourLocalStoragePath = [documents stringByAppendingPathComponent:@"LocalStorage"];;
    //NSString *ourLocalStorageDb = [documents stringByAppendingPathComponent:@"file__0.localstorage"];
    NSString *ourLocalStorageDb = [ourLocalStoragePath stringByAppendingPathComponent:@"file__0.localstorage"];

    NSString *ourWebSQLPath = [documents stringByAppendingPathComponent:@"Databases"];
    NSString *ourWebSQLIndex = [ourWebSQLPath stringByAppendingPathComponent:@"Databases.db"];
    NSString *ourWebSQLDb = [ourWebSQLPath stringByAppendingPathComponent:@"file__0"];

    NSFileManager* fileManager = [NSFileManager defaultManager];

    BOOL copy;
    NSError *err = nil; 
    copy = [fileManager fileExistsAtPath:localStorageDb] && ![fileManager fileExistsAtPath:ourLocalStorageDb];
    if (copy) {
        [fileManager createDirectoryAtPath:ourLocalStoragePath withIntermediateDirectories:YES attributes:nil error:&err];
        [fileManager copyItemAtPath:localStorageDb toPath:ourLocalStorageDb error:&err];
        if (err == nil)
            [fileManager removeItemAtPath:localStorageDb error:&err];
    }

    err = nil;
    copy = [fileManager fileExistsAtPath:WebSQLPath] && ![fileManager fileExistsAtPath:ourWebSQLPath];
    if (copy) {
        [fileManager createDirectoryAtPath:ourWebSQLPath withIntermediateDirectories:YES attributes:nil error:&err];
        [fileManager copyItemAtPath:WebSQLIndex toPath:ourWebSQLIndex error:&err];
        [fileManager copyItemAtPath:WebSQLDb toPath:ourWebSQLDb error:&err];
        if (err == nil)
            [fileManager removeItemAtPath:WebSQLPath error:&err];
    }

    NSUserDefaults* appPreferences = [NSUserDefaults standardUserDefaults];
    NSBundle* mainBundle = [NSBundle mainBundle];

    NSString *bundlePath = [[mainBundle bundlePath] stringByDeletingLastPathComponent];
    NSString *bundleIdentifier = [[mainBundle infoDictionary] objectForKey:@"CFBundleIdentifier"];
    NSString* libraryPreferences = @"Library/Preferences";

    NSString* appPlistPath = [[bundlePath stringByAppendingPathComponent:libraryPreferences]    stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.plist", bundleIdentifier]];
    NSMutableDictionary* appPlistDict = [NSMutableDictionary dictionaryWithContentsOfFile:appPlistPath];

    BOOL dirty = NO;

    NSString *value;
    NSString *key = @"WebKitLocalStorageDatabasePathPreferenceKey";
    value = [appPlistDict objectForKey: key];
    if (![value isEqual:ourLocalStoragePath]) {
        [appPlistDict setValue:ourLocalStoragePath forKey:key];
        dirty = YES;
    }

    key = @"WebDatabaseDirectory";
    value = [appPlistDict objectForKey: key];
    if (![value isEqual:ourWebSQLPath]) {
        [appPlistDict setValue:ourWebSQLPath forKey:key];
        dirty = YES;
    }

    if (dirty) 
    {
        BOOL ok = [appPlistDict writeToFile:appPlistPath atomically:YES];
        NSLog(@"Fix applied for database locations?: %@", ok? @"YES":@"NO");
        [appPreferences synchronize];
    }
    /* END Fix problem with ios 5.0.1+ and Webkit databases */

 

Next, copy and paste the following code in AppDelegate.h. Place it as the last line of code above @end

/* 
 * Returns YES if it is at least version specified as NSString(X)
 */
#define IsAtLeastiOSVersion(X) ([[[UIDevice currentDevice] systemVersion] compare:X options:NSNumericSearch] != NSOrderedAscending)