Data to different types ?

Found this which has been a little helpful but still no Date https://stackoverflow.com/questions/43241845/how-can-i-convert-data-into-types-like-doubles-ints-and-strings-in-swift

When you want to convert `Data` to some specific type, you need to know the data format of the Data.

When it is not a primitive type as in the linked article, things are not so easy.

And about the data format stored in extended attributes, there are very little information on the web.

Seems Apple would not like app programmers to access extended attributes explicitly, and they may be differ in versions of macOS.

As of "com.apple.lastuseddate#PS", I can get 16-byte Data, such as:

                    let lastUseddDateData = try url.extendedAttribute(forName: "com.apple.lastuseddate#PS")
                    print(lastUseddDateData as NSData)

-> <0430cb5c 00000000 4805492c 00000000>

It seems to be two 64-bit integers (little endian). I guess the first represents something like Unix time in seconds, and the other sub-seconds.

As far as I tested, the first seems to represent seconds from 1970-01-01 00:00:00 (UTC) (as well as Unix time), and the other for subseconds in nano-second.

                    let (seconds, subseconds) = lastUseddDateData.withUnsafeBytes {bytes in
                        return (bytes.load(as: Int64.self),
                                bytes.load(fromByteOffset: 8, as: Int64.self))
                    }
                    let NANO_SECONDS_IN_SECOND: TimeInterval = 1_000_000_000
                    let lastUsedData = Date(timeIntervalSince1970: TimeInterval(seconds)+TimeInterval(subseconds)/NANO_SECONDS_IN_SECOND)
                    print(lastUsedData, lastUsedData.timeIntervalSinceReferenceDate)

-> 2019-05-02 17:59:32 +0000 578512772.7429831

The result is nearly equivalent to the Date given by `NSMetadataItem(url: url)!.value(forAttribute: NSMetadataItemLastUsedDateKey) as! Date`, seems you have no need to access this extended attribute directly.

                    let date = NSMetadataItem(url: url)!.value(forAttribute: NSMetadataItemLastUsedDateKey) as! Date
                    print(date, date.timeIntervalSinceReferenceDate)

-> 2019-05-02 17:59:32 +0000 578512772.742983

OOPer wrote:

Seems Apple would not like app programmers to access extended attributes explicitly …

You should not depending on the name and format of extended attributes unless they are explicitly documented. So, it’s OK to do general things with extended attributes, like copy them, but you need to avoid poking around inside them unless they have a documented format. This is not the case here.

In most cases, these extended attributes act as the backing store for higher-level APIs, and that’s what you should be using. In this specific case, you should use

NSMetadataItemLastUsedDateKey

I guess the first represents something like Unix time in seconds, and the other sub-seconds.

FYI, this is a UNIX

timespec

timeval

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Apple Developer Relations, Developer Technical Support, Core OS/Hardware

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Thanks. I couldn't find anything and am assuming I can't write Spotlight data to a file, which is why I was looking at accessing the extra attributes. Any idea saving the date ?