Open Radar

 
Summary:

The FileManager url(for:in:appropriateFor:create:) method, when configured to create a temporary directory, fails after 1000 calls with: Error Domain=NSCocoaErrorDomain Code=512 "The file couldn’t be saved."

Steps to Reproduce:

	func test_FileManager_url_for() {
		
		for num in 1...10000 {
			do {
				let relativeURL = FileManager.default.temporaryDirectory.appendingPathComponent(UUID().uuidString)
				print("\(num): \(relativeURL)")
				let tempDirURL = try FileManager.default.url(for: .itemReplacementDirectory, in: .userDomainMask, appropriateFor: relativeURL, create: true)
				print(tempDirURL)
			}
			catch {
				XCTFail("\(error)")
				return
			}
		}
	}


Expected Results:

There should be no (reasonable) limit to the number of temporary directories which can be created.

Actual Results:

Only 1000 directories can be created and then an error is generated: Error Domain=NSCocoaErrorDomain Code=512 "The file couldn’t be saved."

Test Case '-[test_FileManager_url_for]' started.
1: file:///Users/levi/Library/Developer/CoreSimulator/Devices/B36B631A-CA93-4155-A676-345CCBC5DBF4/data/tmp/4C04A494-A861-4DAD-9DCF-1F9175214345
file:///Users/levi/Library/Developer/CoreSimulator/Devices/B36B631A-CA93-4155-A676-345CCBC5DBF4/data/tmp/(A%20Document%20Being%20Saved%20By%20xctest)/
2: file:///Users/levi/Library/Developer/CoreSimulator/Devices/B36B631A-CA93-4155-A676-345CCBC5DBF4/data/tmp/2CCD122D-ABAD-465C-89BB-810F3CDE9090
file:///Users/levi/Library/Developer/CoreSimulator/Devices/B36B631A-CA93-4155-A676-345CCBC5DBF4/data/tmp/(A%20Document%20Being%20Saved%20By%20xctest%202)/
...
1000: file:///Users/levi/Library/Developer/CoreSimulator/Devices/B36B631A-CA93-4155-A676-345CCBC5DBF4/data/tmp/0B5973DC-C1BC-4F46-BBE3-4DB574DBFAD6
file:///Users/levi/Library/Developer/CoreSimulator/Devices/B36B631A-CA93-4155-A676-345CCBC5DBF4/data/tmp/(A%20Document%20Being%20Saved%20By%20xctest%201000)/
1001: file:///Users/levi/Library/Developer/CoreSimulator/Devices/B36B631A-CA93-4155-A676-345CCBC5DBF4/data/tmp/23203909-2CD8-4B91-982C-51849A5F1851
error: -[test_FileManager_url_for] : failed - Error Domain=NSCocoaErrorDomain Code=512 "The file couldn’t be saved."

Version/Build:

Xcode 10.2.1, Swift 5

Speculation:

The FileManager code which attempts to create a uniquely named temporary directory only attempts a unique name 1000 times, then fails.

"(A Document Being Saved By xctest #NUM#)"

My concerns are:

1) The number of attempts to create a unique name is undoubtably hardcoded to the arbitrarily small value of 1000.

2) The code is apparently trying to create a unique directory, starting with "(A Document Being Saved By xctest)" as the name and then making sequential attempts ( "(A Document Being Saved By xctest 2)", (A Document Being Saved By xctest 3)", etc.) until it finds one which is available, which is a performance issue since it will have to repeat these attempts each call, going over every possibility every time.