refactor(script): auto ref-count `ServoJSPrincipals`

2 files changed, 86 insertions, 12 deletions

diff --git a/components/script/dom/bindings/interface.rs b/components/script/dom/bindings/interface.rs
index 2b4fcd67f3a..e22b897ac6e 100644
--- a/components/script/dom/bindings/interface.rs
+++ b/components/script/dom/bindings/interface.rs
@@ -155,7 +155,7 @@ pub unsafe fn create_global_object(
     rval.set(JS_NewGlobalObject(
         *cx,
         class,
-        principal.0,
+        principal.as_raw(),
         OnNewGlobalHookOption::DontFireOnNewGlobalHook,
         &*options,
     ));
diff --git a/components/script/dom/bindings/principals.rs b/components/script/dom/bindings/principals.rs
index 010fb28b39f..afaf02c74fe 100644
--- a/components/script/dom/bindings/principals.rs
+++ b/components/script/dom/bindings/principals.rs
@@ -1,23 +1,97 @@
-use js::glue::{
-    CreateRustJSPrincipals, DestroyRustJSPrincipals, GetRustJSPrincipalsPrivate,
-    JSPrincipalsCallbacks,
+use js::{
+    glue::{
+        CreateRustJSPrincipals, DestroyRustJSPrincipals, GetRustJSPrincipalsPrivate,
+        JSPrincipalsCallbacks,
+    },
+    jsapi::{JSPrincipals, JS_DropPrincipals, JS_HoldPrincipals},
+    rust::Runtime,
 };
-use js::jsapi::JSPrincipals;
 use servo_url::MutableOrigin;
+use std::{marker::PhantomData, ops::Deref, ptr::NonNull};
 
-// TODO: RAII ref-counting
-pub struct ServoJSPrincipals(pub *mut JSPrincipals);
+/// An owned reference to Servo's `JSPrincipals` instance.
+#[repr(transparent)]
+pub struct ServoJSPrincipals(NonNull<JSPrincipals>);
 
 impl ServoJSPrincipals {
     pub fn new(origin: &MutableOrigin) -> Self {
-        let private: Box<MutableOrigin> = Box::new(origin.clone());
-        Self(unsafe { CreateRustJSPrincipals(&PRINCIPALS_CALLBACKS, Box::into_raw(private) as _) })
+        unsafe {
+            let private: Box<MutableOrigin> = Box::new(origin.clone());
+            let raw = CreateRustJSPrincipals(&PRINCIPALS_CALLBACKS, Box::into_raw(private) as _);
+            // The created `JSPrincipals` object has an initial reference
+            // count of zero, so the following code will set it to one
+            Self::from_raw_nonnull(NonNull::new_unchecked(raw))
+        }
     }
 
+    /// Construct `Self` from a raw `*mut JSPrincipals`, incrementing its
+    /// reference count.
+    #[inline]
+    pub unsafe fn from_raw_nonnull(raw: NonNull<JSPrincipals>) -> Self {
+        JS_HoldPrincipals(raw.as_ptr());
+        Self(raw)
+    }
+
+    #[inline]
     pub unsafe fn origin(&self) -> MutableOrigin {
-        let origin = GetRustJSPrincipalsPrivate(self.0) as *mut MutableOrigin;
+        let origin = GetRustJSPrincipalsPrivate(self.0.as_ptr()) as *mut MutableOrigin;
         (*origin).clone()
     }
+
+    #[inline]
+    pub fn as_raw_nonnull(&self) -> NonNull<JSPrincipals> {
+        self.0
+    }
+
+    #[inline]
+    pub fn as_raw(&self) -> *mut JSPrincipals {
+        self.0.as_ptr()
+    }
+}
+
+impl Clone for ServoJSPrincipals {
+    #[inline]
+    fn clone(&self) -> Self {
+        unsafe { Self::from_raw_nonnull(self.as_raw_nonnull()) }
+    }
+}
+
+impl Drop for ServoJSPrincipals {
+    #[inline]
+    fn drop(&mut self) {
+        unsafe { JS_DropPrincipals(Runtime::get(), self.as_raw()) };
+    }
+}
+
+/// A borrowed reference to Servo's `JSPrincipals` instance.
+#[derive(Clone, Copy)]
+pub struct ServoJSPrincipalsRef<'a>(NonNull<JSPrincipals>, PhantomData<&'a ()>);
+
+impl ServoJSPrincipalsRef<'_> {
+    /// Construct `Self` from a raw `NonNull<JSPrincipals>`.
+    #[inline]
+    pub unsafe fn from_raw_nonnull(raw: NonNull<JSPrincipals>) -> Self {
+        Self(raw, PhantomData)
+    }
+
+    /// Construct `Self` from a raw `*mut JSPrincipals`.
+    ///
+    /// # Safety
+    ///
+    /// The behavior is undefined if `raw` is null.
+    #[inline]
+    pub unsafe fn from_raw_unchecked(raw: *mut JSPrincipals) -> Self {
+        Self::from_raw_nonnull(NonNull::new_unchecked(raw))
+    }
+}
+
+impl Deref for ServoJSPrincipalsRef<'_> {
+    type Target = ServoJSPrincipals;
+
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        unsafe { &*(&self.0 as *const NonNull<JSPrincipals> as *const ServoJSPrincipals) }
+    }
 }
 
 pub unsafe extern "C" fn destroy_servo_jsprincipal(principals: *mut JSPrincipals) {
@@ -36,8 +110,8 @@ unsafe extern "C" fn principals_is_system_or_addon_principal(_: *mut JSPrincipal
 
 //TODO is same_origin_domain equivalent to subsumes for our purposes
 pub unsafe extern "C" fn subsumes(obj: *mut JSPrincipals, other: *mut JSPrincipals) -> bool {
-    let obj = ServoJSPrincipals(obj);
-    let other = ServoJSPrincipals(other);
+    let obj = ServoJSPrincipalsRef::from_raw_unchecked(obj);
+    let other = ServoJSPrincipalsRef::from_raw_unchecked(other);
     let obj_origin = obj.origin();
     let other_origin = other.origin();
     obj_origin.same_origin_domain(&other_origin)