Cocoa App that deletes itself - macos

Question

I'm writing a Mac OSX application using Cocoa that is designed to stop working after a specified date, to avoid the user simply changing their system clock and then re-running the app I would like the program to close and delete itself if it is loaded after the expiry date. Is this possible?
I am distributing the application directly not through the app store. Also, checking the date using the internet isn't really an option because the app needs to be useable offline.
Thanks,
Matthew

Answer 1

It's possible, but not reliably so. To delete your app, just get your main bundle's URL and tell NSFileManager to delete it. But your app bundle may not be writable — and thus not deletable either — and the user may have any number of backups even if you do manage to delete it. I would not write anything that depends on this being possible unless I had tight control over the systems the program will run on. (I mean, I probably wouldn't write something that does this anyway, because it's a little crazy. But if I were going to write something like this, it would have to be something that only runs on my own systems.)

Answer 2

You could perform some sanity checks in the system to get an idea whether the user manually set the clock back to the past.
Note that I still don't think the plan of (maliciously) deleting user files is a great idea in general and the following approach in particular will certainly break under Sandboxing..
..but out of curiosity: Here's a snippet that will check all files in /var/log and return whether some of them have been modified in the future (= the system is quite likely running "in the past")
- (bool)isFakeSystemTime
{
int futureFileCount = 0;
// let's check against 1 day from now in the future to be safe
NSTimeInterval secondsPerDay = 24 * 60 * 60;
NSDate *tomorrow = [[[NSDate alloc] initWithTimeIntervalSinceNow:secondsPerDay] autorelease];
NSString *directoryPath = #"/var/log";
NSArray *filesInDirectory = [[NSFileManager defaultManager] contentsOfDirectoryAtPath:directoryPath error:nil];
for (NSString* fileName in filesInDirectory)
{
NSDictionary *attributes = [[NSFileManager defaultManager] attributesOfItemAtPath:[directoryPath stringByAppendingPathComponent:fileName] error:nil];
NSDate *date = [attributes valueForKey:#"NSFileModificationDate"];
if (!date)
continue;
if ([date compare:tomorrow] == NSOrderedDescending)
{
NSLog(#"File '%#' modified >=1 day in the future", fileName);
futureFileCount++;
}
}
// again, some heuristic to be (more) on the safe side
return futureFileCount > 5;
}