script/dom/promise/
promise.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//! Native representation of JS Promise values.
6//!
7//! This implementation differs from the traditional Rust DOM object, because the reflector
8//! is provided by SpiderMonkey and has no knowledge of an associated native representation
9//! (ie. dom::Promise). This means that native instances use native reference counting (Rc)
10//! to ensure that no memory is leaked, which means that there can be multiple instances of
11//! native Promise values that refer to the same JS value yet are distinct native objects
12//! (ie. address equality for the native objects is meaningless).
13
14use std::cell::{Cell, RefCell};
15use std::ops::DerefMut;
16use std::ptr;
17use std::rc::Rc;
18
19use dom_struct::dom_struct;
20use js::context::JSContext;
21use js::conversions::{ConversionResult, FromJSValConvertibleRc};
22use js::jsapi::{
23    CallArgs, GetFunctionNativeReserved, Heap, JS_GetFunctionObject, JSContext as RawJSContext,
24    JSObject, PromiseState, PromiseUserInputEventHandlingState, RemoveRawValueRoot,
25    SetFunctionNativeReserved,
26};
27use js::jsval::{Int32Value, JSVal, NullValue, ObjectValue, UndefinedValue};
28use js::realm::CurrentRealm;
29use js::rust::wrappers2::{
30    AddPromiseReactions, AddRawValueRoot, CallOriginalPromiseReject, CallOriginalPromiseResolve,
31    GetPromiseIsHandled, GetPromiseState, IsPromiseObject, JS_ClearPendingException,
32    JS_NewFunction, NewFunctionWithReserved, NewPromiseObject, RejectPromise, ResolvePromise,
33    SetAnyPromiseIsHandled, SetPromiseUserInputEventHandlingState,
34};
35use js::rust::{HandleObject, HandleValue, MutableHandleObject, Runtime};
36use script_bindings::conversions::SafeToJSValConvertible;
37use script_bindings::reflector::{DomObject, MutDomObject, Reflector};
38use script_bindings::settings_stack::run_a_script;
39
40use crate::DomTypeHolder;
41use crate::dom::bindings::conversions::root_from_object;
42use crate::dom::bindings::error::{Error, ErrorToJsval};
43use crate::dom::bindings::reflector::DomGlobal;
44use crate::dom::bindings::root::{AsHandleValue, Dom};
45use crate::dom::globalscope::GlobalScope;
46use crate::dom::promisenativehandler::{Callback, PromiseNativeHandler};
47use crate::microtask::MicrotaskRunnable;
48use crate::realms::enter_auto_realm;
49use crate::script_thread::ScriptThread;
50
51#[dom_struct]
52#[cfg_attr(crown, crown::unrooted_must_root_lint::allow_unrooted_in_rc)]
53pub(crate) struct Promise {
54    reflector: Reflector,
55    /// Since Promise values are natively reference counted without the knowledge of
56    /// the SpiderMonkey GC, an explicit root for the reflector is stored while any
57    /// native instance exists. This ensures that the reflector will never be GCed
58    /// while native code could still interact with its native representation.
59    #[ignore_malloc_size_of = "SM handles JS values"]
60    permanent_js_root: Heap<JSVal>,
61}
62
63/// Private helper to enable adding new methods to `Rc<Promise>`.
64trait PromiseHelper {
65    fn initialize(&self, cx: &mut JSContext);
66}
67
68impl PromiseHelper for Rc<Promise> {
69    #[expect(unsafe_code)]
70    fn initialize(&self, cx: &mut JSContext) {
71        let obj = self.reflector().get_jsobject();
72        self.permanent_js_root.set(ObjectValue(*obj));
73        unsafe {
74            assert!(AddRawValueRoot(
75                cx,
76                self.permanent_js_root.get_unsafe(),
77                c"Promise::root".as_ptr(),
78            ));
79        }
80    }
81}
82
83// Promise objects are stored inside Rc values, so Drop is run when the last Rc is dropped,
84// rather than when SpiderMonkey runs a GC. This makes it safe to interact with the JS engine unlike
85// Drop implementations for other DOM types.
86impl Drop for Promise {
87    #[expect(unsafe_code)]
88    fn drop(&mut self) {
89        unsafe {
90            let object = self.permanent_js_root.get().to_object();
91            assert!(!object.is_null());
92            if let Some(cx) = Runtime::get() {
93                RemoveRawValueRoot(cx.as_ptr(), self.permanent_js_root.get_unsafe());
94            }
95        }
96    }
97}
98
99impl Promise {
100    pub(crate) fn new(cx: &mut JSContext, global: &GlobalScope) -> Rc<Promise> {
101        let mut realm = enter_auto_realm(cx, global);
102        let cx = &mut realm.current_realm();
103        Promise::new_in_realm(cx)
104    }
105
106    pub(crate) fn new_in_realm(current_realm: &mut CurrentRealm) -> Rc<Promise> {
107        let cx = current_realm.deref_mut();
108        rooted!(&in(cx) let mut obj = ptr::null_mut::<JSObject>());
109        Promise::create_js_promise(cx, obj.handle_mut());
110        Promise::new_with_js_promise(cx, obj.handle())
111    }
112
113    pub(crate) fn duplicate(&self, cx: &mut JSContext) -> Rc<Promise> {
114        Promise::new_with_js_promise(cx, self.reflector().get_jsobject())
115    }
116
117    #[expect(unsafe_code)]
118    #[cfg_attr(crown, expect(crown::unrooted_must_root))]
119    pub(crate) fn new_with_js_promise(cx: &mut JSContext, obj: HandleObject) -> Rc<Promise> {
120        unsafe {
121            assert!(IsPromiseObject(obj));
122        }
123        let promise = Promise {
124            reflector: Reflector::new(),
125            permanent_js_root: Heap::default(),
126        };
127        let promise = Rc::new(promise);
128        unsafe {
129            promise.init_reflector_without_associated_memory(obj.get());
130        }
131        promise.initialize(cx);
132        promise
133    }
134
135    #[expect(unsafe_code)]
136    fn create_js_promise(cx: &mut JSContext, mut obj: MutableHandleObject) {
137        unsafe {
138            let do_nothing_func = JS_NewFunction(
139                cx,
140                Some(do_nothing_promise_executor),
141                /* nargs = */ 2,
142                /* flags = */ 0,
143                ptr::null(),
144            );
145            assert!(!do_nothing_func.is_null());
146            rooted!(&in(cx) let do_nothing_obj = JS_GetFunctionObject(do_nothing_func));
147            assert!(!do_nothing_obj.is_null());
148            obj.set(NewPromiseObject(cx, do_nothing_obj.handle()));
149            assert!(!obj.is_null());
150            let is_user_interacting = if ScriptThread::is_user_interacting() {
151                PromiseUserInputEventHandlingState::HadUserInteractionAtCreation
152            } else {
153                PromiseUserInputEventHandlingState::DidntHaveUserInteractionAtCreation
154            };
155            SetPromiseUserInputEventHandlingState(obj.handle(), is_user_interacting);
156        }
157    }
158
159    #[expect(unsafe_code)]
160    pub(crate) fn new_resolved(
161        cx: &mut JSContext,
162        global: &GlobalScope,
163        value: impl SafeToJSValConvertible,
164    ) -> Rc<Promise> {
165        let mut realm = enter_auto_realm(cx, global);
166        let cx = &mut realm.current_realm();
167        rooted!(&in(cx) let mut rval = UndefinedValue());
168        value.safe_to_jsval(cx, rval.handle_mut());
169        rooted!(&in(cx) let p = unsafe { CallOriginalPromiseResolve(cx, rval.handle()) });
170        assert!(!p.handle().is_null());
171        Promise::new_with_js_promise(cx, p.handle())
172    }
173
174    #[expect(unsafe_code)]
175    pub(crate) fn new_rejected(
176        cx: &mut JSContext,
177        global: &GlobalScope,
178        value: impl SafeToJSValConvertible,
179    ) -> Rc<Promise> {
180        let mut realm = enter_auto_realm(cx, global);
181        let cx = &mut realm.current_realm();
182        rooted!(&in(cx) let mut rval = UndefinedValue());
183        value.safe_to_jsval(cx, rval.handle_mut());
184        rooted!(&in(cx) let p = unsafe { CallOriginalPromiseReject(cx, rval.handle()) });
185        assert!(!p.handle().is_null());
186        Promise::new_with_js_promise(cx, p.handle())
187    }
188
189    pub(crate) fn resolve_native<T>(&self, cx: &mut JSContext, val: &T)
190    where
191        T: SafeToJSValConvertible,
192    {
193        let mut realm = enter_auto_realm(cx, self);
194        let cx = &mut realm.current_realm();
195        rooted!(&in(cx) let mut v = UndefinedValue());
196        val.safe_to_jsval(cx, v.handle_mut());
197        self.resolve(cx, v.handle());
198    }
199
200    #[expect(unsafe_code)]
201    pub(crate) fn resolve(&self, cx: &mut JSContext, value: HandleValue) {
202        unsafe {
203            if !ResolvePromise(cx, self.promise_obj(), value) {
204                JS_ClearPendingException(cx);
205            }
206        }
207    }
208
209    pub(crate) fn reject_native<T>(&self, cx: &mut JSContext, val: &T)
210    where
211        T: SafeToJSValConvertible,
212    {
213        let mut realm = enter_auto_realm(cx, self);
214        let cx = &mut realm.current_realm();
215        rooted!(&in(cx) let mut v = UndefinedValue());
216        val.safe_to_jsval(cx, v.handle_mut());
217        self.reject(cx, v.handle());
218    }
219
220    pub(crate) fn reject_error(&self, cx: &mut JSContext, error: Error) {
221        let mut realm = enter_auto_realm(cx, self);
222        let cx = &mut realm.current_realm();
223        rooted!(&in(cx) let mut v = UndefinedValue());
224        error.to_jsval(cx, &self.global(), v.handle_mut());
225        self.reject(cx, v.handle());
226    }
227
228    #[expect(unsafe_code)]
229    pub(crate) fn reject(&self, cx: &mut JSContext, value: HandleValue) {
230        unsafe {
231            if !RejectPromise(cx, self.promise_obj(), value) {
232                JS_ClearPendingException(cx);
233            }
234        }
235    }
236
237    #[expect(unsafe_code)]
238    pub(crate) fn is_fulfilled(&self) -> bool {
239        let state = unsafe { GetPromiseState(self.promise_obj()) };
240        matches!(state, PromiseState::Rejected | PromiseState::Fulfilled)
241    }
242
243    #[expect(unsafe_code)]
244    pub(crate) fn is_rejected(&self) -> bool {
245        let state = unsafe { GetPromiseState(self.promise_obj()) };
246        matches!(state, PromiseState::Rejected)
247    }
248
249    #[expect(unsafe_code)]
250    pub(crate) fn is_pending(&self) -> bool {
251        let state = unsafe { GetPromiseState(self.promise_obj()) };
252        matches!(state, PromiseState::Pending)
253    }
254
255    #[expect(unsafe_code)]
256    pub(crate) fn promise_obj(&self) -> HandleObject<'_> {
257        let obj = self.reflector().get_jsobject();
258        unsafe {
259            assert!(IsPromiseObject(obj));
260        }
261        obj
262    }
263
264    #[expect(unsafe_code)]
265    pub(crate) fn append_native_handler(
266        &self,
267        cx: &mut CurrentRealm,
268        handler: &PromiseNativeHandler,
269    ) {
270        let global = GlobalScope::from_current_realm(cx);
271        run_a_script::<DomTypeHolder, _, _>(cx, &global, |cx| {
272            rooted!(&in(cx) let resolve_func =
273                create_native_handler_function(cx,
274                                               handler.reflector().get_jsobject(),
275                                               NativeHandlerTask::Resolve));
276
277            rooted!(&in(cx) let reject_func =
278                create_native_handler_function(cx,
279                                               handler.reflector().get_jsobject(),
280                                               NativeHandlerTask::Reject));
281
282            unsafe {
283                let ok = AddPromiseReactions(
284                    cx,
285                    self.promise_obj(),
286                    resolve_func.handle(),
287                    reject_func.handle(),
288                );
289                assert!(ok);
290            }
291        })
292    }
293
294    #[expect(unsafe_code)]
295    pub(crate) fn get_promise_is_handled(&self) -> bool {
296        unsafe { GetPromiseIsHandled(self.reflector().get_jsobject()) }
297    }
298
299    #[expect(unsafe_code)]
300    pub(crate) fn set_promise_is_handled(&self, cx: &mut JSContext) -> bool {
301        unsafe { SetAnyPromiseIsHandled(cx, self.reflector().get_jsobject()) }
302    }
303}
304
305#[expect(unsafe_code)]
306unsafe extern "C" fn do_nothing_promise_executor(
307    _cx: *mut RawJSContext,
308    argc: u32,
309    vp: *mut JSVal,
310) -> bool {
311    let args = unsafe { CallArgs::from_vp(vp, argc) };
312    args.rval().set(UndefinedValue());
313    true
314}
315
316const SLOT_NATIVEHANDLER: usize = 0;
317const SLOT_NATIVEHANDLER_TASK: usize = 1;
318
319#[derive(PartialEq)]
320enum NativeHandlerTask {
321    Resolve = 0,
322    Reject = 1,
323}
324
325#[expect(unsafe_code)]
326unsafe extern "C" fn native_handler_callback(
327    cx: *mut RawJSContext,
328    argc: u32,
329    vp: *mut JSVal,
330) -> bool {
331    // SAFETY: it is safe to construct a JSContext from engine hook.
332    let mut cx = unsafe { JSContext::from_ptr(ptr::NonNull::new(cx).unwrap()) };
333    let mut cx = CurrentRealm::assert(&mut cx);
334    let cx = &mut cx;
335
336    let args = unsafe { CallArgs::from_vp(vp, argc) };
337    let native_handler_value =
338        unsafe { *GetFunctionNativeReserved(args.callee(), SLOT_NATIVEHANDLER) };
339    rooted!(&in(cx) let native_handler_value = native_handler_value);
340    assert!(native_handler_value.get().is_object());
341
342    let handler =
343        unsafe { root_from_object::<PromiseNativeHandler>(cx, native_handler_value.to_object()) }
344            .expect("unexpected value for native handler in promise native handler callback");
345
346    let native_handler_task_value =
347        unsafe { *GetFunctionNativeReserved(args.callee(), SLOT_NATIVEHANDLER_TASK) };
348    rooted!(&in(cx) let native_handler_task_value = native_handler_task_value);
349    match native_handler_task_value.to_int32() {
350        native_handler_task_value
351            if native_handler_task_value == NativeHandlerTask::Resolve as i32 =>
352        {
353            handler.resolved_callback(cx, unsafe { HandleValue::from_raw(args.get(0)) })
354        },
355        native_handler_task_value
356            if native_handler_task_value == NativeHandlerTask::Reject as i32 =>
357        {
358            handler.rejected_callback(cx, unsafe { HandleValue::from_raw(args.get(0)) })
359        },
360        _ => panic!("unexpected native handler task value"),
361    };
362
363    true
364}
365
366#[expect(unsafe_code)]
367fn create_native_handler_function(
368    cx: &mut JSContext,
369    holder: HandleObject,
370    task: NativeHandlerTask,
371) -> *mut JSObject {
372    unsafe {
373        let func = NewFunctionWithReserved(cx, Some(native_handler_callback), 1, 0, ptr::null());
374        assert!(!func.is_null());
375
376        rooted!(&in(cx) let obj = JS_GetFunctionObject(func));
377        assert!(!obj.is_null());
378        SetFunctionNativeReserved(obj.get(), SLOT_NATIVEHANDLER, &ObjectValue(*holder));
379        SetFunctionNativeReserved(obj.get(), SLOT_NATIVEHANDLER_TASK, &Int32Value(task as i32));
380        obj.get()
381    }
382}
383
384impl FromJSValConvertibleRc for Promise {
385    fn safe_from_jsval(
386        cx: &mut JSContext,
387        value: HandleValue,
388    ) -> Result<ConversionResult<Rc<Promise>>, ()> {
389        if value.get().is_null() {
390            return Ok(ConversionResult::Failure(c"null not allowed".into()));
391        }
392
393        let mut realm = CurrentRealm::assert(cx);
394        let global_scope = GlobalScope::from_current_realm(&mut realm);
395
396        let promise = Promise::new_resolved(cx, &global_scope, value);
397        Ok(ConversionResult::Success(promise))
398    }
399}
400
401/// The success steps of <https://webidl.spec.whatwg.org/#wait-for-all>
402type WaitForAllSuccessSteps = Rc<dyn Fn(&mut JSContext, Vec<HandleValue>)>;
403
404/// The failure steps of <https://webidl.spec.whatwg.org/#wait-for-all>
405type WaitForAllFailureSteps = Rc<dyn Fn(&mut JSContext, HandleValue)>;
406
407/// The fulfillment handler for the list of promises in
408/// <https://webidl.spec.whatwg.org/#wait-for-all>.
409#[derive(JSTraceable, MallocSizeOf)]
410#[cfg_attr(crown, crown::unrooted_must_root_lint::must_root)]
411struct WaitForAllFulfillmentHandler {
412    /// The steps to call when all promises are resolved.
413    #[ignore_malloc_size_of = "callbacks are hard"]
414    #[no_trace]
415    success_steps: WaitForAllSuccessSteps,
416
417    /// The results of the promises.
418    #[ignore_malloc_size_of = "mozjs"]
419    #[expect(clippy::vec_box)]
420    result: Rc<RefCell<Vec<Box<Heap<JSVal>>>>>,
421
422    /// The index identifying which promise this handler is attached to.
423    promise_index: usize,
424
425    /// A count of fulfilled promises.
426    #[conditional_malloc_size_of]
427    fulfilled_count: Rc<Cell<usize>>,
428}
429
430impl Callback for WaitForAllFulfillmentHandler {
431    fn callback(&self, cx: &mut CurrentRealm, v: HandleValue) {
432        // Let fulfillmentHandler be the following steps given arg:
433
434        let equals_total = {
435            // Set result[promiseIndex] to arg.
436            let result = self.result.borrow_mut();
437            result[self.promise_index].set(v.get());
438
439            // Set fulfilledCount to fulfilledCount + 1.
440            let mut fulfilled_count = self.fulfilled_count.get();
441            fulfilled_count += 1;
442            self.fulfilled_count.set(fulfilled_count);
443
444            fulfilled_count == result.len()
445        };
446
447        // If fulfilledCount equals total, then perform successSteps given result.
448        if equals_total {
449            let result_ref = self.result.borrow();
450            let result_handles: Vec<HandleValue> =
451                result_ref.iter().map(|v| v.as_handle_value()).collect();
452
453            (self.success_steps)(cx, result_handles);
454        }
455    }
456}
457
458/// The rejection handler for the list of promises in
459/// <https://webidl.spec.whatwg.org/#wait-for-all>.
460#[derive(Clone, JSTraceable, MallocSizeOf)]
461struct WaitForAllRejectionHandler {
462    /// The steps to call if any promise rejects.
463    #[ignore_malloc_size_of = "callbacks are hard"]
464    #[no_trace]
465    failure_steps: WaitForAllFailureSteps,
466
467    /// Whether any promises have been rejected already.
468    rejected: Cell<bool>,
469}
470
471impl Callback for WaitForAllRejectionHandler {
472    fn callback(&self, cx: &mut CurrentRealm, v: HandleValue) {
473        // Let rejectionHandlerSteps be the following steps given arg:
474
475        if self.rejected.replace(true) {
476            // If rejected is true, abort these steps.
477            return;
478        }
479
480        // Set rejected to true.
481        // Done above with `replace`.
482        (self.failure_steps)(cx, v);
483    }
484}
485
486/// The microtask for performing successSteps given « » in
487/// <https://webidl.spec.whatwg.org/#wait-for-all>.
488#[derive(JSTraceable, MallocSizeOf)]
489#[cfg_attr(crown, crown::unrooted_must_root_lint::must_root)]
490pub(crate) struct WaitForAllSuccessStepsMicrotask {
491    global: Dom<GlobalScope>,
492
493    #[ignore_malloc_size_of = "Closure is hard"]
494    #[no_trace]
495    success_steps: WaitForAllSuccessSteps,
496}
497
498impl MicrotaskRunnable for WaitForAllSuccessStepsMicrotask {
499    fn handler(&self, cx: &mut JSContext) {
500        let mut realm = enter_auto_realm(cx, &*self.global);
501        (self.success_steps)(&mut realm, vec![]);
502    }
503}
504
505/// <https://webidl.spec.whatwg.org/#wait-for-all>
506#[cfg_attr(crown, expect(crown::unrooted_must_root))]
507fn wait_for_all(
508    cx: &mut CurrentRealm,
509    global: &GlobalScope,
510    promises: Vec<Rc<Promise>>,
511    success_steps: WaitForAllSuccessSteps,
512    failure_steps: WaitForAllFailureSteps,
513) {
514    // Let fulfilledCount be 0.
515    let fulfilled_count: Rc<Cell<usize>> = Default::default();
516
517    // Let rejected be false.
518    // Note: done below when constructing a rejection handler.
519
520    // Let rejectionHandlerSteps be the following steps given arg:
521    // Note: implemented with the `WaitForAllRejectionHandler`.
522
523    // Let rejectionHandler be CreateBuiltinFunction(rejectionHandlerSteps, « »):
524    // Note: done as part of attaching the `WaitForAllRejectionHandler` as native rejection handler.
525    let rejection_handler = WaitForAllRejectionHandler {
526        failure_steps,
527        rejected: Default::default(),
528    };
529
530    // Let total be promises’s size.
531    // Note: done using the len of result.
532
533    // If total is 0, then:
534    if promises.is_empty() {
535        // Queue a microtask to perform successSteps given « ».
536        global.enqueue_microtask(
537            cx,
538            Box::new(WaitForAllSuccessStepsMicrotask {
539                global: Dom::from_ref(global),
540                success_steps,
541            }),
542        );
543
544        // Return.
545        return;
546    }
547
548    // Let index be 0.
549    // Note: done with `enumerate` below.
550
551    // Let result be a list containing total null values.
552    let result: Rc<RefCell<Vec<Box<Heap<JSVal>>>>> = Default::default();
553
554    // For each promise of promises:
555    for (promise_index, promise) in promises.into_iter().enumerate() {
556        let result = result.clone();
557
558        {
559            // Note: adding a null value for this promise result.
560            let mut result_list = result.borrow_mut();
561            rooted!(&in(cx) let null_value = NullValue());
562            result_list.push(Heap::boxed(null_value.get()));
563        }
564
565        // Let promiseIndex be index.
566        // Note: done with `enumerate` above.
567
568        // Let fulfillmentHandler be the following steps given arg:
569        // Note: implemented with the `WaitForAllFulFillmentHandler`.
570
571        // Let fulfillmentHandler be CreateBuiltinFunction(fulfillmentHandler, « »):
572        // Note: passed below to avoid the need to root it.
573
574        // Perform PerformPromiseThen(promise, fulfillmentHandler, rejectionHandler).
575        let handler = PromiseNativeHandler::new(
576            cx,
577            global,
578            Some(Box::new(WaitForAllFulfillmentHandler {
579                success_steps: success_steps.clone(),
580                result,
581                promise_index,
582                fulfilled_count: fulfilled_count.clone(),
583            })),
584            Some(Box::new(rejection_handler.clone())),
585        );
586        promise.append_native_handler(cx, &handler);
587
588        // Set index to index + 1.
589        // Note: done above with `enumerate`.
590    }
591}
592
593/// <https://webidl.spec.whatwg.org/#waiting-for-all-promise>
594pub(crate) fn wait_for_all_promise(
595    cx: &mut CurrentRealm,
596    global: &GlobalScope,
597    promises: Vec<Rc<Promise>>,
598) -> Rc<Promise> {
599    // Let promise be a new promise of type Promise<sequence<T>> in realm.
600    let promise = Promise::new(cx, global);
601    let success_promise = promise.clone();
602    let failure_promise = promise.clone();
603
604    // Let successSteps be the following steps, given results:
605    let success_steps = Rc::new(move |cx: &mut JSContext, results: Vec<HandleValue>| {
606        // Resolve promise with results.
607        success_promise.resolve_native(cx, &results);
608    });
609
610    // Let failureSteps be the following steps, given reason:
611    let failure_steps = Rc::new(move |cx: &mut JSContext, reason: HandleValue| {
612        // Reject promise with reason.
613        failure_promise.reject_native(cx, &reason);
614    });
615
616    // Wait for all with promises, given successSteps and failureSteps.
617    wait_for_all(cx, global, promises, success_steps, failure_steps);
618
619    // Return promise.
620    promise
621}
script/dom/promise/promise.rs

script/dom/promise/
promise.rs
