How to parse the contents of a foreign file created with NSKeyedArchiver

I need to be able to compare two versions of a plist file created with NSKeyedArchiver. In particular, it's the "elements" file created in Xcode for a .xcdatamodeld file.

Since I have not created this file myself I can not recreate its object model. Instead, I need to understand which classes and keyed properties the archive contains.

Ideally, I want to create a tree containing strings representing the names of classes along with their property names and values. I assume that all this information is stored in the archive, so it should be possible to generically parse this archive, right?

I've read about NSKeyedUnarchiver and its delegate. I've only gotten as as as this:

Unarchive the file data:

NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
unarchiver.delegate = self;
id graph = [unarchiver decodeObjectForKey:@"root"];

Here's the delegate method that gets called when an unknown class is requested. I return a proxy class here in which I hope to collect its values:

- (Class)unarchiver:(NSKeyedUnarchiver *)unarchiver cannotDecodeObjectOfClassName:(NSString *)name originalClasses:(NSArray *)classNames
{
    NSLog(@"wants: %@", name);
    return [ObjProxy class];
}
开发者_开发问答

The proxy class implements

- (id)initWithCoder:(NSCoder *)aDecoder

in which I do not know how to proceed, not knowing the actual properties of the classes. NSCoder doesn't seem to provide any function to learn of the available keys. Is there a trick to get to them, maybe by overriding some of the lower level objc methods?

So far, with this little code shown above, when parsing the "elements" file, I only get the request for one class, "XDPMModel", and then it's done.

Any ideas how to get this working, i.e. traverse the tree deeper?

You can use PlistExplorer, it's a Cocoa Tool to inspect files written by NSKeyedArchiver.

I've done exactly this before, to decode objects stored in the preferences file for Panic's Coda. What I did was to use class-dump on the app (in your case Xcode and its related frameworks), which allows you to see the properties of the real objects, and use these to create proxy objects that match those properties. You can then use NSKeyedUnarchiver successfully and query the proxy objects for their values.

It's a fairly laborious process but it works perfectly. In my case I was working with a user defaults plist so I only had to define a couple of these proxy classes for the objects I was interested in, but I would imagine that you'll have to define quite a few for Xcode.

I'd also be very interested to know if there's a way to do this without having to go the class-dump route (possibly, as you say, via some of the lower-level Objective-C functions) because it would greatly simplify this type of reverse engineering.