servo/components/script/dom/bindings/proxyhandler.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

//! Utilities for the implementation of JSAPI proxy handlers.

#![deny(missing_docs)]

use dom::bindings::conversions::is_dom_proxy;
use dom::bindings::utils::delete_property_by_id;
use js::glue::GetProxyExtra;
use js::glue::InvokeGetOwnPropertyDescriptor;
use js::glue::{GetProxyHandler, SetProxyExtra};
use js::jsapi::GetObjectProto;
use js::jsapi::JS_GetPropertyDescriptorById;
use js::jsapi::{Handle, HandleId, HandleObject, MutableHandle, ObjectOpResult, RootedObject};
use js::jsapi::{JSContext, JSObject, JSPropertyDescriptor};
use js::jsapi::{JSErrNum, JS_StrictPropertyStub};
use js::jsapi::{JS_DefinePropertyById6, JS_NewObjectWithGivenProto};
use js::jsval::ObjectValue;
use js::{JSPROP_ENUMERATE, JSPROP_GETTER, JSPROP_READONLY};
use libc;
use std::{mem, ptr};

static JSPROXYSLOT_EXPANDO: u32 = 0;

/// Invoke the [[GetOwnProperty]] trap (`getOwnPropertyDescriptor`) on `proxy`,
/// with argument `id` and return the result, if it is not `undefined`.
/// Otherwise, walk along the prototype chain to find a property with that
/// name.
pub unsafe extern "C" fn get_property_descriptor(cx: *mut JSContext,
                                                 proxy: HandleObject,
                                                 id: HandleId,
                                                 desc: MutableHandle<JSPropertyDescriptor>)
                                                 -> bool {
    let handler = GetProxyHandler(proxy.get());
    if !InvokeGetOwnPropertyDescriptor(handler, cx, proxy, id, desc) {
        return false;
    }
    if !desc.get().obj.is_null() {
        return true;
    }

    let mut proto = RootedObject::new(cx, ptr::null_mut());
    if !GetObjectProto(cx, proxy, proto.handle_mut()) {
        desc.get().obj = ptr::null_mut();
        return true;
    }

    JS_GetPropertyDescriptorById(cx, proto.handle(), id, desc)
}

/// Defines an expando on the given `proxy`.
pub unsafe extern "C" fn define_property(cx: *mut JSContext,
                                         proxy: HandleObject,
                                         id: HandleId,
                                         desc: Handle<JSPropertyDescriptor>,
                                         result: *mut ObjectOpResult)
                                         -> bool {
    // FIXME: Workaround for https://github.com/mozilla/rust/issues/13385
    let setter: *const libc::c_void = mem::transmute(desc.get().setter);
    let setter_stub: *const libc::c_void = mem::transmute(JS_StrictPropertyStub);
    if (desc.get().attrs & JSPROP_GETTER) != 0 && setter == setter_stub {
        (*result).code_ = JSErrNum::JSMSG_GETTER_ONLY as ::libc::uintptr_t;
        return true;
    }

    let expando = RootedObject::new(cx, ensure_expando_object(cx, proxy));
    JS_DefinePropertyById6(cx, expando.handle(), id, desc, result)
}

/// Deletes an expando off the given `proxy`.
pub unsafe extern "C" fn delete(cx: *mut JSContext,
                                proxy: HandleObject,
                                id: HandleId,
                                bp: *mut ObjectOpResult)
                                -> bool {
    let expando = RootedObject::new(cx, get_expando_object(proxy));
    if expando.ptr.is_null() {
        (*bp).code_ = 0 /* OkCode */;
        return true;
    }

    delete_property_by_id(cx, expando.handle(), id, bp)
}

/// Controls whether the Extensible bit can be changed
pub unsafe extern "C" fn prevent_extensions(_cx: *mut JSContext,
                                            _proxy: HandleObject,
                                            result: *mut ObjectOpResult)
                                            -> bool {
    (*result).code_ = JSErrNum::JSMSG_CANT_PREVENT_EXTENSIONS as ::libc::uintptr_t;
    true
}

/// Reports whether the object is Extensible
pub unsafe extern "C" fn is_extensible(_cx: *mut JSContext,
                                       _proxy: HandleObject,
                                       succeeded: *mut bool)
                                       -> bool {
    *succeeded = true;
    true
}

/// Get the expando object, or null if there is none.
pub fn get_expando_object(obj: HandleObject) -> *mut JSObject {
    unsafe {
        assert!(is_dom_proxy(obj.get()));
        let val = GetProxyExtra(obj.get(), JSPROXYSLOT_EXPANDO);
        if val.is_undefined() {
            ptr::null_mut()
        } else {
            val.to_object()
        }
    }
}

/// Get the expando object, or create it if it doesn't exist yet.
/// Fails on JSAPI failure.
pub fn ensure_expando_object(cx: *mut JSContext, obj: HandleObject) -> *mut JSObject {
    unsafe {
        assert!(is_dom_proxy(obj.get()));
        let mut expando = get_expando_object(obj);
        if expando.is_null() {
            expando = JS_NewObjectWithGivenProto(cx, ptr::null_mut(), HandleObject::null());
            assert!(!expando.is_null());

            SetProxyExtra(obj.get(), JSPROXYSLOT_EXPANDO, ObjectValue(&*expando));
        }
        expando
    }
}

/// Set the property descriptor's object to `obj` and set it to enumerable,
/// and writable if `readonly` is true.
pub fn fill_property_descriptor(desc: &mut JSPropertyDescriptor,
                                obj: *mut JSObject,
                                readonly: bool) {
    desc.obj = obj;
    desc.attrs = if readonly { JSPROP_READONLY } else { 0 } | JSPROP_ENUMERATE;
    desc.getter = None;
    desc.setter = None;
}