Running Two SkyScript Plugins

Two SkyScript-based plugins in one copy of X-Plane need one packaging step, or the second one loaded will quietly serve the first one's apps.

The problem

Every consumer ships its own copy of the SkyScript library, and every copy carries the same identity:

Platform	Identity	Set by
macOS	@rpath/libSkyScriptLib.dylib	LC_ID_DYLIB install name
Linux	libSkyScriptLib.so	SONAME
Windows	SkyScriptLib.dll	module base name

Dynamic loaders key loaded images by that identity, not by path. So when X-Plane loads a second SkyScript plugin, the loader sees a library it already has and hands over the existing image rather than mapping a new one.

Both plugins then share one set of globals: the Path singleton holding the plugin directory, the app registry, the Dataref bindings. The second plugin scans the first plugin's apps/ folder, adopts its windows, and never reads its own manifest.

It does not look like a crash. It looks like a plugin that works, and shows the wrong window:

[zoal-charts] Started (version 0.0.0-dev)
[zoal-charts]: Dataref is not owned by you - you cannot unregister.
[zoal-charts]: XPLMWindowCallbackRecord at 0x... is being deleted by a different plugin.
- 0x... previously created by zoal-atc v0.1.0 (ai.zoal.atc) at 0.00000
[zoal-atc skyscript] Discovered app: zoal-atc (id: app-zoal-atc, default: no)
[zoal-charts] Loaded 1 app(s)

The tell is the prefix: those [zoal-atc skyscript] lines were written during zoal-charts' own skyscript_load_apps_from_directory() call.

Since this release, skyscript_initialize() detects a second consumer in the same image and says so in Log.txt rather than leaving you to work it out.

The fix

Give each plugin's copy an identity of its own, as the last step before zipping a release:

scripts/unique-library-identity.sh dist/my-plugin my-plugin

dist/my-plugin is the folder that goes into Resources/plugins — the one holding mac_x64/, win_x64/ and lin_x64/. Platforms that are not there are skipped, so packaging on one machine works.

What it does per platform:

• macOS — renames to libSkyScriptLib-<plugin>.dylib, rewrites the install name with install_name_tool -id, points each .xpl at it with -change, then re-signs both ad-hoc. The re-signing is required, not cosmetic: editing a Mach-O invalidates its signature and arm64 refuses to load a modified binary whose signature no longer matches.
• Linux — renames to libSkyScriptLib-<plugin>.so, sets the SONAME with patchelf --set-soname, and repoints each .xpl with patchelf --replace-needed. Needs patchelf installed.
• Windows — PE has no install_name_tool, and the DLL name lives in the import descriptor as a plain string, so it is patched in place. In place means same length: SkyScriptLib.dll is 16 characters and so is SkyS + 8 hex + .dll, so the name is derived from a hash of the plugin name. The file size is unchanged and the PE structure is untouched.

What is still shared

Renaming stops plugins from sharing an image. X-Plane's command namespace is still global, and this release namespaces what SkyScript owns in it:

• skyscript/<plugin>/toggle — every plugin gets one only it owns.
• skyscript/toggle — kept for anyone who already bound it, but claimed only by the first plugin to ask. A second plugin logs that it was taken and uses its namespaced command instead.

Per-app commands and datarefs were already safe: the app id comes from its folder name, so skyscript/app-charts/* and skyscript/app-zoal-atc/* never collided.