Find whether a directory contains a URL, following symlinks - swift

Question

I have two directories as follows:
Directory A contains file X.
Directory B contains an alias to directory A named C.
So there are two possible absolute URLs for file X: /A/X and /B/C/X. (A and B can be anywhere in my filesystem.)
What I need to do is, given the file URL for directory B (file:///B/) and either file URL for file X, determine whether or not file X is within directory B.
Here's what I came up with:
extension URL {
func isIdenticalFile(to other: URL) -> Bool {
return resolvingSymlinksInPath() == other.resolvingSymlinksInPath()
}
func contains(_ other: URL) -> Bool {
guard isFileURL, other.isFileURL, let enumerator = FileManager.default.enumerator(atPath: path) else {
return false
}
for subURL in enumerator.map({ appendingPathComponent($0 as! String) }) {
if subURL.isIdenticalFile(to: other) || subURL.contains(other) {
return true
}
}
return false
}
}
let b = URL(string: "file:///B/")!
let ax = URL(string: "file:///A/X")!
let bcx = URL(string: "file:///B/C/X")!
// Both b.contains(ax) and b.contains(bcx) are true
Is there a simpler/more efficient way to do this?

Answer 1

A better method to determine if two URLs refer to the same
file is to compare their fileResourceIdentifier. From the documentation:
An identifier which can be used to compare two file system objects for equality using isEqual.
Two object identifiers are equal if they have the same file system path or if the paths are linked to same inode on the same file system. This identifier is not persistent across system restarts.
Determining the resource identifier should be faster than fully
resolving the file path. In addition this detects also hard links to
the same file.
More remarks:
The recursion in your code is not necessary because the enumerator
already does a "deep" enumeration.
With enumerator(at: self, ...) you get an enumerator for URLs
instead of paths, so that you don't have to build the subURL.
The code then could look like this:
extension URL {
// Helper property get the resource identifier:
private var identifier: NSObjectProtocol? {
return (try? resourceValues(forKeys: [.fileResourceIdentifierKey]))?.fileResourceIdentifier
}
func contains(_ other: URL) -> Bool {
guard isFileURL, other.isFileURL else {
return false
}
guard let otherId = other.identifier else {
return false
}
guard let enumerator = FileManager.default.enumerator(at: self, includingPropertiesForKeys: [.fileResourceIdentifierKey]) else {
return false
}
for case let subURL as URL in enumerator {
if let fileId = subURL.identifier, fileId.isEqual(otherId) {
return true
}
}
return false
}
}