Stop services when AppKit terminates the app on macOS

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "local-dev-proxy"
-version = "0.0.17"
+version = "0.0.18"
 edition = "2024"
 description = "Local development process orchestration with a built-in reverse proxy"
 authors = ["Andrew Chen <hello@andrewtheguy.com>"]
@@ -37,6 +37,8 @@ windows-sys = { version = "0.61", features = ["Win32_Foundation", "Win32_System_
 [target.'cfg(target_os = "macos")'.dependencies]
 objc2 = "0.6.4"
 objc2-app-kit = { version = "0.3.2", default-features = false, features = ["std", "NSApplication", "NSResponder"] }
+objc2-foundation = { version = "0.3.2", default-features = false, features = ["std", "block2", "NSNotification", "NSOperation", "NSString"] }
+block2 = "0.6.2"
 
 [dev-dependencies]
 futures-util = { version = "0.3.34", default-features = false, features = ["sink", "std"] }

README.md

@@ -164,8 +164,9 @@ similar locations resolve even when the binary is started outside a terminal.
   it from the tray icon's **Open Manager** (or by launching the application again). On
   macOS the Dock icon is shown only while the window is open. Without a tray icon,
   closing the window quits.
-- **Quit** (the window's button, the tray menu, or Ctrl/Cmd-Q) → stops the proxy, stops
-  every managed service together with its child processes, and exits.
+- **Quit** (the window's button, the tray menu, or Ctrl/Cmd-Q; on macOS also the app
+  menu, the Dock, and logging out) → stops the proxy, stops every managed service
+  together with its child processes, and exits.
 - **SIGTERM, SIGINT (Ctrl-C), or SIGHUP** (Ctrl-C, Ctrl-Break, or closing the console
   window on Windows) → the same as Quit.
 - **A managed service exits on its own** → it is reported as `crashed` with its exit

src/desktop.rs

@@ -53,10 +53,16 @@ pub struct Desktop;
 impl Frontend for Desktop {
     fn run(self: Box<Self>, manager: Manager, events: Receiver<AppEvent>) -> ExitCode {
         let manager = Arc::new(Mutex::new(manager));
+        // AppKit's own quit paths (the app menu's Quit and its Cmd-Q, the
+        // Dock's Quit, logging out) exit the process from inside the event
+        // loop, so this never regains control after them.
+        let _terminate = app_exit::on_terminate({
+            let manager = Arc::clone(&manager);
+            move || shut_down(&manager)
+        });
         let result = run_event_loop(Arc::clone(&manager), events);
         // However the event loop ended, the window is gone; stop everything.
-        tracing::info!("Shutting down");
-        lock(&manager).stop();
+        shut_down(&manager);
         match result {
             Ok(()) => ExitCode::SUCCESS,
             Err(err) => {
@@ -115,6 +121,11 @@ fn forward_app_events(
     Ok(())
 }
 
+fn shut_down(manager: &Mutex<Manager>) {
+    tracing::info!("Shutting down");
+    lock(manager).stop();
+}
+
 fn lock(manager: &Mutex<Manager>) -> MutexGuard<'_, Manager> {
     manager.lock().unwrap_or_else(PoisonError::into_inner)
 }
@@ -770,6 +781,56 @@ mod dock {
     pub fn set_icon_visible(_visible: bool) {}
 }
 
+mod app_exit {
+    /// Keeps the terminate handler registered while alive.
+    pub struct Registration {
+        #[cfg(target_os = "macos")]
+        token: objc2::rc::Retained<
+            objc2::runtime::ProtocolObject<dyn objc2::runtime::NSObjectProtocol>,
+        >,
+    }
+
+    /// Run `handler` when AppKit is about to exit the process (`terminate:`),
+    /// which it does without returning from the event loop.
+    #[cfg(target_os = "macos")]
+    pub fn on_terminate(handler: impl Fn() + Send + 'static) -> Registration {
+        use std::ptr::NonNull;
+
+        use block2::RcBlock;
+        use objc2_app_kit::NSApplicationWillTerminateNotification;
+        use objc2_foundation::{NSNotification, NSNotificationCenter};
+
+        let block = RcBlock::new(move |_: NonNull<NSNotification>| handler());
+        let center = NSNotificationCenter::defaultCenter();
+        // SAFETY: the name is an AppKit constant; with no queue the block
+        // runs synchronously on the posting (main) thread, and it is `Send`.
+        let token = unsafe {
+            center.addObserverForName_object_queue_usingBlock(
+                Some(NSApplicationWillTerminateNotification),
+                None,
+                None,
+                &block,
+            )
+        };
+        Registration { token }
+    }
+
+    #[cfg(not(target_os = "macos"))]
+    pub fn on_terminate(_handler: impl Fn() + Send + 'static) -> Registration {
+        Registration {}
+    }
+
+    #[cfg(target_os = "macos")]
+    impl Drop for Registration {
+        fn drop(&mut self) {
+            use objc2_foundation::NSNotificationCenter;
+
+            // SAFETY: `token` came from this center's `addObserverForName`.
+            unsafe { NSNotificationCenter::defaultCenter().removeObserver(self.token.as_ref()) };
+        }
+    }
+}
+
 fn install_toml_syntax(window: &ManagerWindow) {
     let syntax = window.global::<TomlSyntax>();
     syntax.on_tokenize(|text| {