Creating a PList using the value of a key of type data

[nyg]

Hello,

First of all, thanks a lot for this library, it looks very good and is very intuitive.

However, I'm not able to do something, probably because I'm missing something. I wrote a Swift program to execute the command defaults export -app Transmission - and create a PList object using the output of that command. This works fine, I'm able to read all the keys and values.

But if I print the values that have the "data" type using String.init(data: val, encoding: String.Encoding.ascii) I can see something like: Optional("bplist00Ô\u{01}\u{02}\u{03}\....

So I was wondering if some keys of type "data" store their value as another Plist (in binary format) and therefore tried to create a second PList object using that data but it didn't work:

let plist = try PList(data: data) // works
for (key, value) in plist.root.value {
    switch value {
        // …
        case let val as Data:
            guard let sublist = try? PList(data: val) else {
                // fails with
                // Fatal error: Error raised at top level: PListKit.PList.LoadError.formatNotExpected
                print("Could not create list for key \(key)")
                print("Value is: \(String.init(data: val, encoding: String.Encoding.ascii))")
                print("---")
                continue
            }
            print(sublist)
            break
    }
}

Is it possible to do that? Am I correct assuming that the "bplist" is a binary plist and can be parsed?

Thanks again,
nyg

[nyg]

Ok, I looked at the code a bit and think it could be related to this:

public convenience
init(data: Data) throws {
    self.init()
    
    // load as raw NS objects
    
    // just a default, will be replaced...
    var getFormat: PropertyListSerialization.PropertyListFormat = .xml // any way to have .binary?

[orchetect]

That's a confusing code comment - it's not determining the format. It's just initializing the variable so it can be mutated by the call to PropertyListSerialization. Old Objective-C bridged to Swift. The property gets set to the data's actual format afterwards.

[orchetect]

The data blobs may be correctly encoded binary plists but they do not have a dictionary as the top-level element. PList in PListKit 1.x.x relies on the top element being a dictionary and when it isn't, it will fail to load. This is a known issue and it's been on my to-do list to refactor the code so the top-level element can be any PList value type, not just a dictionary.

By plist spec, the top level object can by any PList type:

Since it's been on my to-do list for a while, I spent the day refactoring the library to fully accommodate plists that use a top-level (root) element other than Dictionary. It's pushed to main now as release 2.0.0.

This may solve your issue since my best guess is that those binary plist chunks are plists with non-dictionary roots (could be an Array, or even a single value like String, Int, etc.)

If you like, check out the 2.0.0 branch and try that.

The API has changed a bit.

There is now an AnyPList object that you can instance when you don't know a plist's root element ahead of time. You can then unwrap it to produce a strongly typed specialized PList<> class that behaves almost identically to the old PList class.

The old vanilla PList class now takes the form of PList<PListDictionary> (typealias DictionaryPList) and behaves much the same as before.

So if you know what a plist's root type is ahead of time, before reading the file, then just use the specialized PList<> class for it which lets you skip the unwrapping step of having to use AnyPList first. For example: if it's a plist file you created, or if it's a standard plist file that is known to always be dictionary-rooted like various system plists.

The new documentation further explains this.

So a revised version of your code snippet may look like this:

let plist = try DictionaryPList(data: data) // < -- 💡 use dictionary-specialized plist here
for (key, value) in plist.root.value {
    switch value {
        // …
        case let val as Data:
            guard let sublist = try? AnyPList(data: val) else {  // < -- 💡 use AnyPList here
                print("Could not create list for key \(key)")
                continue
            }

            // 💡 unwrap the AnyPList instance to its root element form here
            switch sublist.plist {
                case .arrayRoot(let arrayPList):
                    print(arrayPList.storage) // prints the array

                // ... can try remaining root type cases here ...
            }
            break
    }
}

At the very least this will allow you to introspect what the data blobs are. If you find out that there is reasonable expectation for them to be of a certain root type (like maybe some are always arrays) then you can replace AnyPList with ArrayPList for example.

[nyg]

Hey, thanks a lot! Unfortunately I can't try the 2.0.0 branch because it requires Swift 5.5 (correct?) and I'm still on Catalina and therefore can't upgrade Xcode :). Actually I was planning to do the upgrade but just need to find the time.

[orchetect]

There is a chance the min. requirement could be dropped but 5.5 is what allows the documentation to be generated with Xcode. If you want to try, grab the 2.0.0 release and then change the toolchain version in the Package.swift file back to 5.4 or 5.3.