How to detect OneDrive online-only files

Question

Starting from Windows 10 Fall Creators Update (version 16299.15) and OneDrive build 17.3.7064.1005 the On-Demand Files are available for users (https://support.office.com/en-us/article/learn-about-onedrive-files-on-demand-0e6860d3-d9f3-4971-b321-7092438fb38e)

Any OneDrive file now can have one of the following type: online-only, locally available, and always available.

Using WinAPI how can I know that the file (e.g. "C:\Users\Username\OneDrive\Getting started with OneDrive.pdf") is online-only file?

Answer 1

To check for "online only" all you need is to call GetFileAttributes() and see if the FILE_ATTRIBUTE_OFFLINE attribute is set.

In fact this isn't new for OneDrive, that attribute has existed for a long time.

There are other OneDrive attributes available via the shell (although the property you need is PKEY_StorageProviderState rather than PKEY_FilePlaceholderStatus) but "online only" is easy to check for.

Edit: Another filesystem attribute, FILE_ATTRIBUTE_PINNED is new for Windows 10, and is used by OneDrive to indicate a file that's "always available".

Edit: As of 2019 it appears that OneDrive now uses FILE_ATTRIBUTE_RECALL_ON_DATA_ACCESS rather than FILE_ATTRIBUTE_OFFLINE, as suggested below.

Edit: PKEY_StorageProviderState was broken in Windows 10 1903, and still not fixed in 1909. It returns 4 ("uploading") for all files in any apps other than Explorer.