Getting alias path of file in swift

Question

I'm having trouble resolving the alias link on mac. I'm checking if the file is an alias and then I would want to receive the original path. Instead I'm only getting a File-Id. Anly ideas?

func isFinderAlias(path:String) -> Bool? {

    var isAlias:Bool? = false // Initialize result var.

    // Create a CFURL instance for the given filesystem path.
    // This should never fail, because the existence isn't verified at this point.
    // Note: No need to call CFRelease(fUrl) later, because Swift auto-memory-manages CoreFoundation objects.
    print("path before \(path)");
    let fUrl = CFURLCreateWithFileSystemPath(nil, path, CFURLPathStyle.CFURLPOSIXPathStyle, false)
    print("path furl \(fUrl)");
    // Allocate void pointer - no need for initialization,
    // it will be assigned to by CFURLCopyResourcePropertyForKey() below.
    let ptrPropVal = UnsafeMutablePointer<Void>.alloc(1)

    // Call the CoreFoundation function that copies the desired information as
    // a CFBoolean to newly allocated memory that prt will point to on return.
    if CFURLCopyResourcePropertyForKey(fUrl, kCFURLIsAliasFileKey, ptrPropVal, nil) {

        // Extract the Bool value from the memory allocated.
        isAlias = UnsafePointer<CFBoolean>(ptrPropVal).memory as Bool


        // it will be assigned to by CFURLCopyResourcePropertyForKey() below.
        let ptrDarwin = UnsafeMutablePointer<DarwinBoolean>.alloc(1)

        if ((isAlias) == true){
            if let bookmark = CFURLCreateBookmarkDataFromFile(kCFAllocatorDefault, fUrl, nil){
                let url = CFURLCreateByResolvingBookmarkData(kCFAllocatorDefault, bookmark.takeRetainedValue(), CFURLBookmarkResolutionOptions.CFBookmarkResolutionWithoutMountingMask, nil, nil, ptrDarwin, nil)
                print("getting the path \(url)")
            }
        }

        // Since the CF*() call contains the word "Copy", WE are responsible
        // for destroying (freeing) the memory.
        ptrDarwin.destroy()
        ptrDarwin.dealloc(1)
        ptrPropVal.destroy()
    }

    // Deallocate the pointer
    ptrPropVal.dealloc(1)

    return isAlias
}

EDIT: Both Answers are correct! I would choose the answer of mklement0 due to the originally not stated requirement that the code run on 10.9 which makes it more flexible

Answer 1

This is a solution using NSURL.

It expects an NSURL object as parameter and returns either the original path if the url is an alias or nil.

func resolveFinderAlias(url:NSURL) -> String? {

  var isAlias : AnyObject?
  do {
    try url.getResourceValue(&isAlias, forKey: NSURLIsAliasFileKey)
    if isAlias as! Bool {
      do {
        let original = try NSURL(byResolvingAliasFileAtURL: url, options: NSURLBookmarkResolutionOptions())
        return original.path!
      } catch let error as NSError {
        print(error)
      }
    }
  } catch _ {}

  return nil
}

Swift 3:

func resolveFinderAlias(at url: URL) -> String? {
    do {
        let resourceValues = try url.resourceValues(forKeys: [.isAliasFileKey])
        if resourceValues.isAliasFile! {
            let original = try URL(resolvingAliasFileAt: url)
            return original.path
        }
    } catch  {
        print(error)
    }
    return nil
}

Be aware to provide appropriate entitlements if the function is called in a sandboxed environment.

Answer 2

vadian's answer works great on OS X 10.10+.

Here's an implementation that also works on OS X 10.9:

// OSX 10.9+
// Resolves a Finder alias to its full target path.
// If the given path is not a Finder alias, its *own* full path is returned.
// If the input path doesn't exist or any other error occurs, nil is returned.
func resolveFinderAlias(path: String) -> String? {
  let fUrl = NSURL(fileURLWithPath: path)
  var targetPath:String? = nil
  if (fUrl.fileReferenceURL() != nil) { // item exists
    do {
        // Get information about the file alias.
        // If the file is not an alias files, an exception is thrown
        // and execution continues in the catch clause.
        let data = try NSURL.bookmarkDataWithContentsOfURL(fUrl)
        // NSURLPathKey contains the target path.
        let rv = NSURL.resourceValuesForKeys([ NSURLPathKey ], fromBookmarkData: data) 
        targetPath = rv![NSURLPathKey] as! String?
    } catch {
        // We know that the input path exists, but treating it as an alias 
        // file failed, so we assume it's not an alias file and return its
        // *own* full path.
        targetPath = fUrl.path
    }
  }
  return targetPath
}

Note:

• Unlike vadian's solution, this will return a value even for non-alias files, namely that file's own full path, and takes a path string rather than a NSURL instance as input.

• vadian's solution requires appropriate entitlements in order to use the function in a sandboxed application/environment. It seems that this one at least doesn't need that to the same extent, as it will run in an Xcode Playground, unlike vadian's solution. ^{If someone can shed light on this, please help.}

  • Either solution, however, does run in a shell script with shebang line #!/usr/bin/env swift.

• If you want to explicitly test whether a given path is a Finder alias, see this answer, which is derived from vadian's, but due to its narrower focus also runs on 10.9.

Answer 3

Here's a Swift 3 implementation, based largely on vadian's approach. My idea is to return a file URL, so I effectively combine it with fileURLWithPath. It's an NSURL class extension because I need to be able to call into it from existing Objective-C code:

extension NSURL {
    class func fileURL(path:String, resolveAlias yn:Bool) -> URL {
        let url = URL(fileURLWithPath: path)
        if !yn {
            return url
        }
        do {
            let vals = try url.resourceValues(forKeys: [.isAliasFileKey])
            if let isAlias = vals.isAliasFile {
                if isAlias {
                    let original = try URL(resolvingAliasFileAt: url)
                    return original
                }
            }
        } catch {
            return url // give up
        }
        return url // really give up
    }
}

Answer 4

URL variant I need to return nil (not an alias or error) else original - Swift4

func resolvedFinderAlias() -> URL? {
    if (self.fileReferenceURL() != nil) { // item exists
        do {
            // Get information about the file alias.
            // If the file is not an alias files, an exception is thrown
            // and execution continues in the catch clause.
            let data = try NSURL.bookmarkData(withContentsOf: self as URL)
            // NSURLPathKey contains the target path.
            let rv = NSURL.resourceValues(forKeys: [ URLResourceKey.pathKey ], fromBookmarkData: data)
            var urlString = rv![URLResourceKey.pathKey] as! String
            if !urlString.hasPrefix("file://") {
                urlString = "file://" + urlString
            }
            return URL.init(string: urlString)
        } catch {
            // We know that the input path exists, but treating it as an alias
            // file failed, so we assume it's not an alias file so return nil.
            return nil
        }
    }
    return nil
}