UIBridge.bundle

A standalone, autoloaded GNUstep AppKit user bundle that vends the UIBridge introspection / UI-automation service over Distributed Objects (DO).

Because it loads into every app via the GSAppKitUserBundles default, it works under any GSTheme — including the base theme — and no application needs modifying. The service was originally embedded in the Eau theme; it was extracted here so introspection is theme-independent and so a class of object-lifetime / concurrency bugs could be fixed at the root.

What it provides

A per-PID DO service named org.gershwin.Gershwin.Theme.UIBridge.<pid>, registered on the main run loop, implementing UIBridgeProtocol:

• Widget tree — rootObjects, detailsForObject:, fullTreeForObject:
• Action — invokeSelector:onObject:withArgs:
• Menus — listMenus, invokeMenuItem:
• JSON-string variants of each (for clients that prefer strings over DO bycopy)

Objects are addressed by stable ids (objc:<n>) issued from a real id↔object registry. The wire protocol (UIBridgeProtocol.h) and the per-PID name are unchanged from the original in-theme service, so an existing UIBridgeServer client talks to it unmodified.

Status

• Service fully extracted into this bundle; builds warning-free (ARC).
• The Eau theme no longer ships its own UIBridge — it was removed entirely and the theme now assumes this bundle. (In the Eau fork that "strip" change is the first patch in the upstreaming order; the theme depends on the bundle being present for introspection.)
• Validated in-harness (the goldstep specimen harness) under both the base GSTheme and Eau: the bundle walks the live AppKit tree correctly (e.g. 24 buttons in the Buttons specimen) and get_details round-trips resolve. Also exercised across the full specimen suite during the theme's upstreaming dry-run — introspection via the bundle was correct throughout.
• Not yet validated on a production /System desktop install (the install.sh path). On the dev harness the bundle is autoloaded per-sandbox via GSAppKitUserBundles.

Hardening vs the original in-theme service

This is not a verbatim copy — four deliberate changes, all fixing real bugs the embedded version had:

1. id↔object registry, not pointer casting. A weak NSMapTable (objc:<n> ↔ object). A weak value auto-nils when its object is deallocated, so looking up a stale id returns nil instead of dereferencing a freed pointer. Fixes a use-after-free (the original cast a raw hex pointer back to id).
2. Type-correct argument marshalling. invokeSelector: decodes each argument according to the method's real parameter type (NSNumber→primitive; struct / pointer / SEL args refused), instead of writing every argument as an id. Fixes a type-confusion — e.g. setTag:[7] now sets the integer 7, where the original shoved an object pointer into the primitive slot.
3. Single-threaded. No -enableMultipleThreads and no connection delegate; the receive port is added to the main run loop, so DO requests are serviced on the main thread alongside AppKit and never race the app's drawing. This removes the cross-thread DO hazard that came from coupling an automation server to the drawing theme. (Note: a separate teardown stack-overflow once suspected to come from enableMultipleThreads was later traced to an unrelated base NSAutoreleasePool bug — this bundle does not claim to fix that.)
4. Theme-independent menus. Menu methods are reimplemented against [NSApp mainMenu] / each window's -menu and performActionForItemAtIndex:, dropping the theme's private window→menu cache. The service depends only on NSApp, never on the active theme.

Requirements

• GNUstep (-base / Foundation + -gui / AppKit) with the GNUstep make system.
• libobjc2 (non-fragile ABI v2, ARC), clang.
• Portable across Linux and FreeBSD — no OS-specific code.

Build & install

. /System/Library/Makefiles/GNUstep.sh
gmake
sudo -E gmake install        # installs UIBridge.bundle to $(GNUSTEP_LIBRARY)/Bundles

Or run ./install.sh, which builds, installs, and enables autoload per-user. For a debug build of the service: gmake ADDITIONAL_OBJCFLAGS+=-DUIBRIDGE_DEBUG.

Enable (autoload)

AppKit instantiates the principal class of every bundle named in GSAppKitUserBundles:

# per-user
defaults write NSGlobalDomain GSAppKitUserBundles '(UIBridge)'

System-wide (e.g. on Gershwin), add UIBridge to GSAppKitUserBundles in /System/Library/Preferences/GlobalDefaults/NSGlobalDomain.plist so every app picks it up. No application needs modifying.

Tip: if a theme that also self-registers the same per-PID name runs alongside this bundle, the two collide. The theme must stand down when the bundle is present (the Eau theme removes its in-theme service entirely for exactly this reason).

Layout

File	Role
UIBridgeLoader.{h,m}	principal class: autoload hook + single-threaded per-PID DO registration on the main run loop
UIBridgeService.{h,m}	UIBridgeProtocol implementation: id registry, live-tree walk, typed invokeSelector:, menus
UIBridgeProtocol.h	DO wire contract
GNUmakefile, install.sh	bundle build + install/enable
validate.py	in-harness validation against the goldstep specimen suite

License

BSD-2-Clause.