clone from: https://github.com/miquels/webdav-handler-rs

doc/APPLE-Finder-hints.md

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+# APPLE-FINDER-HINTS
+
+The Apple Finder (and other subsystems) seem to probe for a few
+files at the root of the filesystems to get a hint about the
+behaviour they should show processing this filesystem.
+
+It also looks for files with extra localization information in
+every directory, and for resource fork data (the `._` files).
+
+## FILES
+
+- `.metadata_never_index`
+  prevents the system from indexing all of the data
+- `.ql_disablethumbnails`
+  prevent the system from downloading all files that look like an
+  image or a video to create a thumbnail
+- `.ql_disablecache`
+  not really sure but it sounds useful
+
+The `.ql_` files are configuration for the "QuickLook" functionality
+of the Finder.
+
+The `.metadata_never_index` file appears to be a hint for the
+Spotlight indexing system.
+
+Additionally, the Finder probes for a `.localized` file in every
+directory it encounters, and it does a PROPSTAT for every file
+in the directory prefixed with `._`.
+
+## OPTIMIZATIONS
+
+For a macOS client we return the metadata for a zero-sized file if it
+does a PROPSTAT of `/.metadata_never_index` or `/.ql_disablethumbnails`.
+
+We always return a 404 Not Found for a PROPSTAT of any `.localized` file.
+
+Furthermore, we disallow moving, removing etc of those files. The files
+do not show up in a PROPSTAT of the rootdirectory.
+
+If a PROPFIND with `Depth: 1` is done on a directory, we add the
+directory pathname to an LRU cache, and the pathname of each file of
+which the name starts with `._`. Since we then know which `._` files
+exist, it is easy to return a fast 404 for PROPSTAT request for `._`
+files that do not exist. The cache is kept consistent by checking
+the timestamp on the parent directory, and a timeout.
+