File copy (clipboard)

Bidirectional Mac↔Windows file copy over MS-RDPECLIP — how each direction works and the two Windows-side limitations to know about.

Bidirectional via MS-RDPECLIP. Both directions support single files and folder trees.

Mac → Windows. Cmd-C a file or folder in Finder, Ctrl-V in Windows Explorer. The pasteboard walk recurses into directories (skipping symlinks, capped at 10 000 descriptors per copy) and emits the right relative_path so Explorer reconstructs the tree. Bytes stream on demand via FileContentsRequest chunks (4 MiB per chunk). Windows shows its native "Copying…" progress dialog.

Windows → Mac (lazy, default). Ctrl-C in Explorer, Cmd-V in Finder. The server pre-allocates an empty temp file per leaf at its declared size and registers each one with NSFileCoordinator via NSFilePresenter. Bytes only start streaming when Finder asks for them on Cmd-V, and macOS shows its native "Preparing to paste" progress dialog during the wait. Folder trees and multi-file selections both work. Lower chunk parallelism is used than the eager path so the RDP session stays responsive (mouse / keyboard / video) while a multi-hundred-MB paste is in flight. If you'd rather have files downloaded eagerly the moment Windows announces a copy (and Cmd-V auto-fired into Finder when ready, with an audible Glass-chime cue), pass --no-lazy-paste.

Known limitations

• Ctrl-C on a folder in Windows Explorer doesn't reach the Mac. Explorer puts only the Shell IDList format on the clipboard and delay-renders FileGroupDescriptorW, which mstsc doesn't request — so nothing is forwarded over the RDP clipboard channel and you'll hear a beep on Cmd-V. Windows + mstsc behavior, not fixable server-side. Workaround: open the folder in Explorer, Ctrl-A to select its contents, then Ctrl-C — that path uses FileGroupDescriptorW directly and folder structure is preserved.
• Some Windows shell extensions silently swallow specific files from the clipboard. Archive tools (7-Zip, WinRAR, built-in Compressed Folders) commonly hook extensions like .zip, .gz, .7z, .bz, .bz2, .rar, .tar and intercept Explorer's clipboard so Ctrl-C either sends no FileGroupDescriptorW to mstsc or sends none at all. The Mac side detects the clipboard transition and clears the pasteboard, so Cmd-V in Finder beeps clearly instead of silently re-pasting the previous file. Workaround: rename the file to a neutral extension (e.g. .bin) and Windows will publish it normally.