Race condition in _FileManagerImpl.currentDirectoryPath

[ahoppen]

Reading the following code, I noticed a race condition that causes us to return nil for the currentDirectoryPath even though there’s always a current directory path on Windows.

swift-foundation/Sources/FoundationEssentials/FileManager/FileManager+Directories.swift

Lines 467 to 476 in a0147ac

	var currentDirectoryPath: String? {
	#if os(Windows)
	let dwLength: DWORD = GetCurrentDirectoryW(0, nil)
	return withUnsafeTemporaryAllocation(of: WCHAR.self, capacity: Int(dwLength)) {
	if GetCurrentDirectoryW(dwLength, $0.baseAddress) == dwLength - 1 {
	return String(decodingCString: $0.baseAddress!, as: UTF16.self)
	}
	return nil
	}
	#else

Race:

• We execute let dwLength: DWORD = GetCurrentDirectoryW(0, nil) and allocate a buffer of the length dwLength
• The current directory path gets changed to be longer
• The temporary allocation is not sufficient to fit the new (longer) directory path
• The second GetCurrentDirectoryW call returns a non-zero value
• _Filemanager.currentDirectoryPath returns nil even though a current directory existed.