"Bad Realm file header (#1)" Exception when opening Realm file in iOS

Question

I am using REALM version 0.98.1 (For Objective C), and sometimes getting "Bad Realm file header" exception while compressing DB size on app launch.

Below is the method calling sequence in AppDelegate application didFinishLaunch....

[self setDefaultConfigrutaionForRealm];
[self vacuumRealm];

Below is the code to Configure Realm:

+(void)setDefaultConfigrutaionForRealm{
    RLMRealmConfiguration * defCongfig = [RLMRealmConfiguration defaultConfiguration];
    defCongfig.path = REALM_PATH(REALM_FILE_NAME);
    defCongfig.schemaVersion = SCHEMA_VERSION; 
    [RLMRealmConfiguration setDefaultConfiguration:defCongfig];
}

And below is the code to VacuumRealm (Compress DB size):

+ (void)vacuumRealm {
@try{
    @autoreleasepool {
        RLMRealm *realm = [RLMRealm defaultRealm];
        NSString *realmPath = [realm path];
        NSLog(@"vacuumRealm realmPath = %@", realmPath);

        long long fileSize = [[[NSFileManager defaultManager] attributesOfItemAtPath:realmPath error:nil][NSFileSize] longLongValue];
        NSLog(@"vacuumRealm ENTER filesize = %llu", fileSize);

        //
        NSError *err;
        BOOL success;
        NSDate *startDate = [NSDate date];
        NSString *copyPath = [realmPath stringByAppendingString:@".copy"];

        [[NSFileManager defaultManager] removeItemAtPath:copyPath error:&err];
        success = [realm writeCopyToPath:copyPath error:&err];

        if (success) {
            success = [[NSFileManager defaultManager] removeItemAtPath:realmPath error:&err];
            if (success) {
                success = [[NSFileManager defaultManager] copyItemAtPath:copyPath toPath:realmPath error:&err];
                if (success) {
                    [[NSFileManager defaultManager] removeItemAtPath:copyPath error:&err];

                    NSDate *endDate = [NSDate date];
                    NSTimeInterval executionTime = [endDate timeIntervalSinceDate:startDate];
                    NSLog(@"vacuumRealm cleanup took %f ms", executionTime);
                }
            }
        }
        //

        fileSize = [[[NSFileManager defaultManager] attributesOfItemAtPath:realmPath error:nil][NSFileSize] longLongValue];
        NSLog(@"vacuumRealm EXIT filesize = %llu", fileSize);
    }
}
@catch (NSException *exception) {
    NSLog(@"Inside vacuumRealm exception = %@",exception.description);
}
@finally {
  }
 }

While debugging I observed realm path has been configured properly in "setDefaultConfigrutaionForRealm" method (Attached Screen shot for reference), but once "vacuumRealm" method is called there I am getting "Bad Realm file header (#1)" on below line :

RLMRealm *realm = [RLMRealm defaultRealm];

any help to resolve this Exception will really be helpful.

Thanks in advance.

Answer 1

You're creating a Realm instance (RLMRealm *realm = [RLMRealm defaultRealm];) and deleting the file from under it without releasing the instance. This will cause problems like the corruption you're seeing because you're modifying the file while Realm is still accessing it.

Here's an updated version of your method (omitting the debug logs and err since it wasn't being used):

__block BOOL copySuccess = NO;
NSString *realmPath = [[RLMRealmConfiguration defaultConfiguration] path];
NSString *copyPath = [realmPath stringByAppendingString:@".copy"];
@autoreleasepool {
    [[NSFileManager defaultManager] removeItemAtPath:copyPath error:nil];
    copySuccess = [[RLMRealm defaultRealm] writeCopyToPath:copyPath error:nil];
}
if (copySuccess && [[NSFileManager defaultManager] removeItemAtPath:realmPath error:nil]) {
    [[NSFileManager defaultManager] moveItemAtPath:copyPath toPath:realmPath error:nil];
}

Also, whatever exceptions are being thrown in this process are not designed to be recoverable. So the only safe thing to do in the @catch block is to abort. Or not have a @try/@catch clause at all.