Following the iPhone’s launch in 2007, as it was taking the world by storm, cloud services started to become popular. Apple released MobileMe in 2008 and followed it with iCloud in 2011; Microsoft OneDrive was initially released as SkyDrive in 2007, and Dropbox was launched in 2008. Since then cloud services have become increasingly important to mobile devices with their limited storage capacity, and have proved a good source of revenue for Apple and others.

For the first decade, each cloud service did its own thing, and integrated more or less with macOS. That started to change in 2019, and since 2021 Apple has encouraged the adoption of its new File Provider framework in macOS and its other OSes. iCloud Drive adopted it fully in macOS Sonoma in 2023, and most major cloud services have migrated to it now. This framework concerns itself with cloud-based file storage, branded by Apple as iCloud Drive, rather than shared databases such as Calendar and Contacts.

The File Provider framework brings consistency to the ways that users and their apps access files that are stored remotely in the cloud. All that is expected of the cloud service provider is to implement one or two extensions to interface between macOS and their servers. Apple describes these for developers in its documentation.

There are two models provided for this, depending on whether local copies are maintained of all files stored in the cloud:

• Replicated file providers are responsible for keeping local copies of all files that are also stored in the cloud, by syncing their contents. This requires them to upload any changes made locally, and to download all those changes made to the remote copy. In iCloud Drive, this applies when Optimise Mac Storage is turned off.
• Nonreplicated file providers have similar responsibilities, but full local copies of files aren’t required, allowing the user to remove some or all files from local storage. Those that are removed are then retained in local placeholders, whose management is also the file provider’s responsibility. In iCloud Drive, this is used when Optimise Mac Storage is turned on, and files can be evicted from local storage to leave just the placeholders.

Before iCloud Drive migrated to being a file provider, it used local stub files as placeholders when operating in nonreplicated mode. Those have since been replaced with dataless files and folders consisting only of file attributes and extended attributes, with no file extents containing the file’s data. The file provider is then responsible for downloading and restoring the data for those placeholders when required.

When a dataless placeholder file is to be used locally again, its data has to be downloaded from the cloud service, and the local dataless file is materialised by adding that back. Because that local file never lost its metadata, those remain intact, as should any locally stored versions. Although the APFS Reference details flags for dataless snapshots, it doesn’t contain any information about dataless files, which do have a flag to mark that state in their attributes, as explained here.

A file provider can offer additional features, including the ability to mark certain files and folders so they aren’t evicted from local storage, a feature commonly known as pinning, and originally offered by iCloud’s competitors.

iCloud Drive adopted the File Provider framework in 2023, and after initial trauma among some users who had come to rely on bugs in its previous implementation, it has brought general improvement. Third parties were reluctant at first, but once they had produced File Provider extensions and their bugs were ironed out, it has ensured better integration with apps and other services, as intended.