Thanks for that, Charles!
I wasn't sure because of the existence of the clonefile() call in
<sys/clonefile.h>, implying that operation was different from copyfile(), but
looking more closely at the sample code, I see that you can call copyfile()
with COPYFILE_CLONE, which seems like it will clone if possible and copy if not.
But there didn't seem to be equivalent calls in NSFileManager, hence my
question.
> On Jun 27, 2017, at 13:55 , Charles Srstka <cocoa...@charlessoft.com> wrote:
>
>> On Jun 27, 2017, at 12:28 AM, Jens Alfke <j...@mooseyard.com> wrote:
>>
>>> On Jun 26, 2017, at 7:38 PM, Rick Mann <rm...@latencyzero.com> wrote:
>>>
>>> But there's actually a POSIX "clone" API, and so I wonder if a copy is
>>> different from a clone.
>>
>> The low level file copying API that I’m aware of is <copyfiles.h>, which is
>> Apple specific. It has options for doing copy-on-write.
>> I don’t know if NSFileManager’s copy method clones files. I would assume
>> that it does, on APFS.
>
> Well, I mean, you could always *try* it ;-)
>
> import Foundation
>
> func unclonedSize(of url: URL) throws -> off_t {
> var list = attrlist(bitmapcount: UInt16(ATTR_BIT_MAP_COUNT),
> reserved: 0,
> commonattr: 0,
> volattr: 0,
> dirattr: 0,
> fileattr: 0,
> forkattr: attrgroup_t(ATTR_CMNEXT_PRIVATESIZE))
>
> let bufsize = 4 + MemoryLayout<off_t>.size
> let buf = UnsafeMutablePointer<UInt8>.allocate(capacity: bufsize)
> defer { buf.deallocate(capacity: bufsize) }
>
> let err = url.withUnsafeFileSystemRepresentation { getattrlist($0,
> &list, buf, bufsize, UInt32(FSOPT_ATTR_CMN_EXTENDED)) }
>
> if err != 0 { throw POSIXError.Code(rawValue: errno).map {
> POSIXError($0) } ?? CocoaError(.fileReadUnknown) }
>
> let attrsize = buf.withMemoryRebound(to: UInt32.self, capacity: 1) {
> $0.pointee }
>
> if attrsize < bufsize { throw CocoaError(.fileReadUnknown) }
>
> var unclonedSize: off_t = 0
>
> _ = withUnsafeMutableBytes(of: &unclonedSize) { memcpy($0.baseAddress!,
> buf + 4, MemoryLayout<off_t>.size) }
>
> return unclonedSize
> }
>
> do {
> let sourceURL = URL(fileURLWithPath: "/tmp/tempfile1")
> let destURL = URL(fileURLWithPath: "/tmp/tempfile2")
>
> let sortaRandomData = Data(bytes: (0..<100 * 1024).map {
> UInt8(extendingOrTruncating: $0) })
>
> try sortaRandomData.write(to: sourceURL)
>
> print("Uncloned size of source file: \(try unclonedSize(of:
> sourceURL))")
>
> try FileManager.default.copyItem(at: sourceURL, to: destURL)
>
> print("Uncloned size of dest file: \(try unclonedSize(of: destURL))")
> } catch {
> print("Error occurred: \(error.localizedDescription)")
> }
>
> - - - - - - - - -
>
> outputs:
>
> Uncloned size of source file: 102400
> Uncloned size of dest file: 0
>
> So, it seems quite clear that (NS)FileManager does, in fact, clone the files
> you tell it to copy. :-)
>
> Charles
>
--
Rick Mann
rm...@latencyzero.com
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