While looking into https://github.com/nextcloud/talk-ios/issues/946 I noticed 2 areas where performance can be improved: One is date handling and one is UTI handling.

This PR adds caching in places where it made sense, after the PR the profiling looks like this:

I did run several tests to determine what makes sense. My test folder consists of 1021 files, 2 folders and around 1,4 GB of files ("/Talk"). Tests were done like this (so just the converting, no network activity):

diff --git a/NextcloudKit/WebDAV/NextcloudKit+WebDAV.swift b/NextcloudKit/WebDAV/NextcloudKit+WebDAV.swift
index ce5e65c..53b6588 100644
--- a/NextcloudKit/WebDAV/NextcloudKit+WebDAV.swift
+++ b/NextcloudKit/WebDAV/NextcloudKit+WebDAV.swift
@@ -239,8 +239,11 @@ extension NextcloudKit {
                 options.queue.async { completion(account, files, nil, error) }
             case .success( _):
                 if let xmlData = response.data {
+                    let startTime = CFAbsoluteTimeGetCurrent()
                     files = NKDataFileXML().convertDataFile(xmlData: xmlData, dav: dav, urlBase: urlBase, user: user, userId: userId, showHiddenFiles: showHiddenFiles)
                     options.queue.async { completion(account, files, xmlData, .success) }
+                    let timeElapsed = CFAbsoluteTimeGetCurrent() - startTime
+                    print("Elapsed: \(timeElapsed) s")
                 } else {
                     options.queue.async { completion(account, files, nil, .xmlError) }
                 }

Results:

Original
Elapsed: 20.474599957466125 s
Elapsed: 21.04942297935486 s
Elapsed: 21.118688941001892 s

Cached DateFormatter:
Elapsed: 19.68568205833435 s
Elapsed: 20.38596498966217 s
Elapsed: 20.67156493663788 s

Lazy Date:
Elapsed: 18.591894030570984 s
Elapsed: 18.96753704547882 s
Elapsed: 18.888224005699158 s

Cached UTI
Elapsed: 13.251657962799072 s
Elapsed: 13.313650012016296 s
Elapsed: 13.511384010314941 s

Cached MimeType
Elapsed: 13.352138042449951 s
Elapsed: 12.624964952468872 s
Elapsed: 12.715412020683289 s

Cached FileProperties
Elapsed: 5.698162078857422 s
Elapsed: 5.549528002738953 s
Elapsed: 5.532379984855652 s

If I also add the changes in https://github.com/nextcloud/talk-ios/issues/946 (because we don't need most of the properties) I'm now down to:

With talk changes
Elapsed: 2.637057065963745 s
Elapsed: 2.553444027900696 s
Elapsed: 2.5751129388809204 s

Fix the concurrency issue introduced in #7 (as swift dictionaries are not thread safe...). This one uses NSCache now, according to the docs:

You can add, remove, and query items in the cache from different threads without having to lock the cache yourself.

This one also adds NKFileProperty, because we need a class to store in NSCache. As swifts String is not supported by NSCache, we now bridge to NSString where needed.

https://github.com/nextcloud/NextcloudKit/blob/e6650c7c5c40b2ac6f87571cb793cfe16279d6d0/NextcloudKit/NKModel.swift#L609

should be

<lock-owner-type xmlns=\"http://nextcloud.org/ns\"/> 

I think?

There are a few small errors when trying to use NCKit on a macOS project due to imports of iOS frameworks

This PR fixes them by preventing their inclusion in a macOS build. It also adds normal macOS (non Catalyst/Designed for iPad) as a supported destination