Sparkles

Appearance

F16 — Clipboard + file drag-and-drop ​

Both are format negotiation between processes — the same machinery on Wayland/X11, two unrelated APIs elsewhere. The negotiation sequences, not the happy path, are the deliverable.

Requirements ​

  1. Copy: a key copies UTF-8 text (with a non-ASCII char — é漢🎈) to the clipboard; verify by pasting into another app (Tier C) and a companion CLI (Tier A: wl-paste/xclip; Win32: a second tiny D reader; macOS: pbpaste).
    • Wayland: wl_data_source offering text/plain;charset=utf-8 (+text/plain), serve the send fd; log cancelled (clipboard ownership loss).
    • X11: own CLIPBOARD, answer SelectionRequest with TARGETS + UTF8_STRING; implement INCR sending for a >256 KiB payload too.
    • Win32: OpenClipboard/SetClipboardData(CF_UNICODETEXT) plus delayed rendering (SetClipboardData(fmt, NULL) + WM_RENDERFORMAT) — log when rendering is demanded.
    • macOS: NSPasteboard setString:forType: + NSPasteboardItem lazy provider variant.
  2. Paste: a key reads the clipboard from another app, logging the offered formats/targets first, then the chosen one and byte count. X11: implement INCR receive (paste ≥1 MiB from another app; xclip can serve it).
  3. File drop: accept a file dragged from the system file manager (Tier C) and from a scripted source where possible; log the full negotiation: enter (offered MIME types/formats), position feedback, accept/reject signaling, drop, data transfer, finish:
    • Wayland: wl_data_device events, accept + set_actions/finish (dnd actions).
    • X11: XDND protocol messages (XdndEnter…XdndFinished) — implement by hand.
    • Win32: RegisterDragDrop + IDropTarget (COM) with CF_HDROP.
    • macOS: registerForDraggedTypes: + NSDraggingDestination with file-URL type.
  4. Clean ownership handling: copy, then another app copies — log the loss event per platform.

Instrumentation ​

clip_offer formats=[…], clip_request fmt=…, clip_send bytes=… incr=0|1, dnd_enter formats=[…], dnd_drop fmt=… bytes=…, ownership_lost.

Findings to record ​

  • The negotiation sequence diagrams (these feed event-sequences.md).
  • Lazy/delayed rendering support per platform and who pays when the source exits first.
  • INCR's design and its failure modes, observed first-hand.
  • Whether clipboard and DnD share machinery (and what that means for a framework's data API).

Verification ​

Wayland/X11: Tier A with companion CLI tools (wl-clipboard, xclip from nixpkgs) under headless weston/Xvfb. Win32: A[wine] within one prefix (two Wine processes can exchange clipboard); cross-app with real Windows apps is Tier C. macOS: A[ssh] via pbcopy/pbpaste; Finder drag is Tier C.