iTunes File Sharing app: realtime monitoring for incoming datas

Question

I'm working on iOS project that supports iTunes file sharing feature. The goal is realtime tracking incoming/changed data's.

I'm using (kinda modified) DirectoryWatcher class from Apple's sample code and also tried this source code.

The data is NSBundle (*.bundle) and some bundles are in 100-500 MB ranges, depends on its content, some video/audio stuff. The bundles has xml based descriptor file in it.

The problem is any of these codes above fires notification or whatever else when the data just started copying and but not when the copy/change/remove process finished completely.

Tried next:

checking file attributes:

NSDictionary *fileAttrs = [[NSFileManager defaultManager] attributesOfItemAtPath:[contURL path] error:nil];
BOOL fileBusy = [[fileAttrs objectForKey:NSFileBusy] boolValue];

looking for the fileSize changes:

dispatch_async(_checkQueue, ^{
    for (NSURL *contURL in tempBundleURLs) {
        NSInteger lastSize = 0;
        NSDictionary *fileAttrs = [[NSFileManager defaultManager] attributesOfItemAtPath:[contURL path] error:nil];
        NSInteger fileSize = [[fileAttrs objectForKey:NSFileSize] intValue];

        do {
            lastSize = fileSize;
            [NSThread sleepForTimeInterval:1];

            fileAttrs = [[NSFileManager defaultManager] attributesOfItemAtPath:[contURL path] error:nil];
            fileSize = [[fileAttrs objectForKey:NSFileSize] intValue];

            NSLog(@"doing job");
        } while (lastSize != fileSize);

        NSLog(@"next job");
    }
);

any other solutions?

The solution above works great for bin files, but not for .bundle (as .bundle files are directory actually). In order to make it work with .bundle, you should iterate each file inside .bundle

Answer 1

You can use GCD's dispatch sources mechanism - using it you can observe particular system events (in your case, this is vnode type events, since you're working with file system). To setup observer for particular directory, i used code like this:

- (dispatch_source_t) fileSystemDispatchSourceAtPath:(NSString*) path
{
    int fileDescr = open([path fileSystemRepresentation], O_EVTONLY);// observe file system events for particular path - you can pass here Documents directory path
    //observer queue is my private dispatch_queue_t object
    dispatch_source_t source = dispatch_source_create(DISPATCH_SOURCE_TYPE_VNODE, fileDescr, DISPATCH_VNODE_ATTRIB| DISPATCH_VNODE_WRITE|DISPATCH_VNODE_LINK|DISPATCH_VNODE_EXTEND, observerQueue);// create dispatch_source object to observe vnode events
    dispatch_source_set_registration_handler(source, ^{
        NSLog(@"registered for observation");
        //event handler is called each time file system event of selected type (DISPATCH_VNODE_*) has occurred
        dispatch_source_set_event_handler(source, ^{

            dispatch_source_vnode_flags_t flags = dispatch_source_get_data(source);//obtain flags
            NSLog(@"%lu",flags);

            if(flags & DISPATCH_VNODE_WRITE)//flag is set to DISPATCH_VNODE_WRITE every time data is appended to file
            {
                NSLog(@"DISPATCH_VNODE_WRITE");
                NSDictionary* dict = [[NSFileManager defaultManager] attributesOfItemAtPath:path error:nil];
                float size = [[dict valueForKey:NSFileSize] floatValue];
                NSLog(@"%f",size);
            }
            if(flags & DISPATCH_VNODE_ATTRIB)//this flag is passed when file is completely written.
            {
                NSLog(@"DISPATCH_VNODE_ATTRIB");
                dispatch_source_cancel(source);
            }
            if(flags & DISPATCH_VNODE_LINK)
            {
                NSLog(@"DISPATCH_VNODE_LINK");
            }
            if(flags & DISPATCH_VNODE_EXTEND)
            {
                NSLog(@"DISPATCH_VNODE_EXTEND");
            }
            NSLog(@"file = %@",path);
            NSLog(@"\n\n");
        });

        dispatch_source_set_cancel_handler(source, ^{
            close(fileDescr);
        });
    });

    //we have to resume dispatch_objects
    dispatch_resume(source);

    return source;
}

Answer 2

I found two rather reliable (i.e. not 100% reliable but reliable enough for my needs) approaches, which only work in conjunction with polling the contents of the directory:

1. Check NSURLContentModificationDateKey. While the file is being transferred, this value is set to the current date. After transfer has finished, it is set to the value the original file had: BOOL busy = (-1.0 * [modDate timeintervalSinceNow]) < pollInterval;
2. Check NSURLThumbnailDictionaryKey. While the file is being transferred, this value is nil, afterwards it cointains a thumbnail, but probably only for file types from which the system can produce a thumbnail. Not a problem for me cause I only care about images and videos, but maybe for you. While this is more reliable than solution 1, it hammers the CPU quite a bit and may even cause your app to get killed if you have a lot of files in the import directory.

Dispatch sources and polling can be combined, i.e. when a dispatch source detects a change, start polling until no busy files are left.