script_bindings/
callback.rs

1/* This Source Code Form is subject to the terms of the Mozilla Public
2 * License, v. 2.0. If a copy of the MPL was not distributed with this
3 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
4
5//! Base classes to work with IDL callbacks.
6
7use std::default::Default;
8use std::ffi::CStr;
9use std::rc::Rc;
10
11use js::context::JSContext;
12use js::jsapi::{Heap, IsCallable, JSObject, RemoveRawValueRoot};
13use js::jsval::{JSVal, NullValue, ObjectValue, UndefinedValue};
14use js::rust::wrappers2::{AddRawValueRoot, EnterRealm, JS_GetProperty, JS_WrapObject, LeaveRealm};
15use js::rust::{HandleObject, MutableHandleValue, Runtime};
16
17use crate::codegen::GenericBindings::WindowBinding::Window_Binding::WindowMethods;
18use crate::error::{Error, Fallible};
19use crate::inheritance::Castable;
20use crate::interfaces::{DocumentHelpers, DomHelpers, GlobalScopeHelpers};
21use crate::realms::enter_auto_realm;
22use crate::reflector::DomObject;
23use crate::root::Dom;
24use crate::settings_stack::{run_a_callback, run_a_script};
25use crate::{DomTypes, cformat};
26
27pub trait ThisReflector {
28    fn jsobject(&self) -> *mut JSObject;
29}
30
31impl<T: DomObject> ThisReflector for T {
32    fn jsobject(&self) -> *mut JSObject {
33        self.reflector().get_jsobject().get()
34    }
35}
36
37impl ThisReflector for HandleObject<'_> {
38    fn jsobject(&self) -> *mut JSObject {
39        self.get()
40    }
41}
42
43/// The exception handling used for a call.
44#[derive(Clone, Copy, PartialEq)]
45pub enum ExceptionHandling {
46    /// Report any exception and don't throw it to the caller code.
47    Report,
48    /// Throw any exception to the caller code.
49    Rethrow,
50}
51
52/// A common base class for representing IDL callback function and
53/// callback interface types.
54#[derive(JSTraceable, MallocSizeOf)]
55#[cfg_attr(crown, crown::unrooted_must_root_lint::must_root)]
56pub struct CallbackObject<D: DomTypes> {
57    /// The underlying `JSObject`.
58    #[ignore_malloc_size_of = "measured by mozjs"]
59    callback: Heap<*mut JSObject>,
60    #[ignore_malloc_size_of = "measured by mozjs"]
61    permanent_js_root: Heap<JSVal>,
62
63    /// The ["callback context"], that is, the global to use as incumbent
64    /// global when calling the callback.
65    ///
66    /// Looking at the WebIDL standard, it appears as though there would always
67    /// be a value here, but [sometimes] callback functions are created by
68    /// hand-waving without defining the value of the callback context, and
69    /// without any JavaScript code on the stack to grab an incumbent global
70    /// from.
71    ///
72    /// ["callback context"]: https://heycam.github.io/webidl/#dfn-callback-context
73    /// [sometimes]: https://github.com/whatwg/html/issues/2248
74    incumbent: Option<Dom<D::GlobalScope>>,
75}
76
77impl<D: DomTypes> CallbackObject<D> {
78    // These are used by the bindings and do not need `default()` functions.
79    #[allow(clippy::new_without_default)]
80    fn new() -> Self {
81        Self {
82            callback: Heap::default(),
83            permanent_js_root: Heap::default(),
84            incumbent: D::GlobalScope::incumbent().map(|i| Dom::from_ref(&*i)),
85        }
86    }
87
88    pub fn get(&self) -> *mut JSObject {
89        self.callback.get()
90    }
91
92    #[expect(unsafe_code)]
93    unsafe fn init(&mut self, cx: &JSContext, callback: *mut JSObject) {
94        self.callback.set(callback);
95        self.permanent_js_root.set(ObjectValue(callback));
96        unsafe {
97            assert!(AddRawValueRoot(
98                cx,
99                self.permanent_js_root.get_unsafe(),
100                c"CallbackObject::root".as_ptr()
101            ));
102        }
103    }
104}
105
106impl<D: DomTypes> Drop for CallbackObject<D> {
107    #[expect(unsafe_code)]
108    fn drop(&mut self) {
109        unsafe {
110            if let Some(cx) = Runtime::get() {
111                RemoveRawValueRoot(cx.as_ptr(), self.permanent_js_root.get_unsafe());
112            }
113        }
114    }
115}
116
117impl<D: DomTypes> PartialEq for CallbackObject<D> {
118    fn eq(&self, other: &CallbackObject<D>) -> bool {
119        self.callback.get() == other.callback.get()
120    }
121}
122
123/// A trait to be implemented by concrete IDL callback function and
124/// callback interface types.
125pub trait CallbackContainer<D: DomTypes> {
126    /// Create a new CallbackContainer object for the given `JSObject`.
127    ///
128    /// # Safety
129    /// `callback` must point to a valid, non-null JSObject.
130    unsafe fn new(cx: &JSContext, callback: *mut JSObject) -> Rc<Self>;
131    /// Returns the underlying `CallbackObject`.
132    fn callback_holder(&self) -> &CallbackObject<D>;
133    /// Returns the underlying `JSObject`.
134    fn callback(&self) -> *mut JSObject {
135        self.callback_holder().get()
136    }
137    /// Returns the ["callback context"], that is, the global to use as
138    /// incumbent global when calling the callback.
139    ///
140    /// ["callback context"]: https://heycam.github.io/webidl/#dfn-callback-context
141    fn incumbent(&self) -> Option<&D::GlobalScope> {
142        self.callback_holder().incumbent.as_deref()
143    }
144}
145
146/// A common base class for representing IDL callback function types.
147#[derive(JSTraceable, MallocSizeOf, PartialEq)]
148#[cfg_attr(crown, crown::unrooted_must_root_lint::must_root)]
149pub struct CallbackFunction<D: DomTypes> {
150    object: CallbackObject<D>,
151}
152
153impl<D: DomTypes> CallbackFunction<D> {
154    /// Create a new `CallbackFunction` for this object.
155    // These are used by the bindings and do not need `default()` functions.
156    #[expect(clippy::new_without_default)]
157    pub fn new() -> Self {
158        Self {
159            object: CallbackObject::new(),
160        }
161    }
162
163    /// Returns the underlying `CallbackObject`.
164    pub fn callback_holder(&self) -> &CallbackObject<D> {
165        &self.object
166    }
167
168    /// Initialize the callback function with a value.
169    /// Should be called once this object is done moving.
170    ///
171    /// # Safety
172    /// `callback` must point to a valid, non-null JSObject.
173    pub unsafe fn init(&mut self, cx: &JSContext, callback: *mut JSObject) {
174        unsafe { self.object.init(cx, callback) };
175    }
176}
177
178/// A common base class for representing IDL callback interface types.
179#[derive(JSTraceable, MallocSizeOf, PartialEq)]
180#[cfg_attr(crown, crown::unrooted_must_root_lint::must_root)]
181pub struct CallbackInterface<D: DomTypes> {
182    object: CallbackObject<D>,
183}
184
185impl<D: DomTypes> CallbackInterface<D> {
186    /// Create a new CallbackInterface object for the given `JSObject`.
187    // These are used by the bindings and do not need `default()` functions.
188    #[expect(clippy::new_without_default)]
189    pub fn new() -> Self {
190        Self {
191            object: CallbackObject::new(),
192        }
193    }
194
195    /// Returns the underlying `CallbackObject`.
196    pub fn callback_holder(&self) -> &CallbackObject<D> {
197        &self.object
198    }
199
200    /// Initialize the callback function with a value.
201    /// Should be called once this object is done moving.
202    ///
203    /// # Safety
204    /// `callback` must point to a valid, non-null JSObject.
205    pub unsafe fn init(&mut self, cx: &JSContext, callback: *mut JSObject) {
206        unsafe { self.object.init(cx, callback) };
207    }
208
209    /// Returns the property with the given `name`, if it is a callable object,
210    /// or an error otherwise.
211    pub fn get_callable_property(&self, cx: &mut JSContext, name: &CStr) -> Fallible<JSVal> {
212        rooted!(&in(cx) let mut callable = UndefinedValue());
213        rooted!(&in(cx) let obj = self.callback_holder().get());
214        unsafe {
215            if !JS_GetProperty(cx, obj.handle(), name.as_ptr(), callable.handle_mut()) {
216                return Err(Error::JSFailed);
217            }
218
219            if !callable.is_object() || !IsCallable(callable.to_object()) {
220                return Err(Error::Type(cformat!(
221                    "The value of the {} property is not callable",
222                    name.to_string_lossy()
223                )));
224            }
225        }
226        Ok(callable.get())
227    }
228}
229
230/// Wraps the reflector for `p` into the realm of `cx`.
231pub(crate) fn wrap_call_this_value<T: ThisReflector>(
232    cx: &mut JSContext,
233    p: &T,
234    mut rval: MutableHandleValue,
235) -> bool {
236    rooted!(&in(cx) let mut obj = p.jsobject());
237
238    if obj.is_null() {
239        rval.set(NullValue());
240        return true;
241    }
242
243    unsafe {
244        if !JS_WrapObject(cx, obj.handle_mut()) {
245            return false;
246        }
247    }
248
249    rval.set(ObjectValue(*obj));
250    true
251}
252
253/// A function wrapper that performs whatever setup we need to safely make a call.
254///
255/// <https://webidl.spec.whatwg.org/#es-invoking-callback-functions>
256pub fn call_setup<D: DomTypes, T: CallbackContainer<D>, R>(
257    cx: &mut JSContext,
258    callback: &T,
259    handling: ExceptionHandling,
260    f: impl FnOnce(&mut JSContext) -> R,
261) -> R {
262    // The global for reporting exceptions. This is the global object of the
263    // (possibly wrapped) callback object.
264    let global = unsafe { D::GlobalScope::from_object(callback.callback()) };
265    if let Some(window) = global.downcast::<D::Window>() {
266        window.Document().ensure_safe_to_run_script_or_layout();
267    }
268
269    let global = &global;
270
271    // Step 8: Prepare to run script with relevant settings.
272    run_a_script::<D, R, _>(cx, global, move |cx| {
273        let actual_callback = || {
274            let old_realm = unsafe { EnterRealm(cx, callback.callback()) };
275            let result = f(cx);
276            unsafe {
277                LeaveRealm(cx, old_realm);
278            }
279            if handling == ExceptionHandling::Report {
280                let mut realm = enter_auto_realm::<D>(cx, &**global);
281                let cx = &mut realm.current_realm();
282                <D as DomHelpers<D>>::report_pending_exception(cx);
283            }
284            result
285        };
286        if let Some(incumbent_global) = callback.incumbent() {
287            // Step 9: Prepare to run a callback with stored settings.
288            run_a_callback::<D, R>(incumbent_global, actual_callback)
289        } else {
290            actual_callback()
291        }
292    }) // Step 14.2: Clean up after running script with relevant settings.
293}
script_bindings/callback.rs

script_bindings/
callback.rs
