js/ipc/WrapperAnswer.cpp
author Valentin Gosu <valentin.gosu@gmail.com>
Tue, 08 Nov 2016 00:42:27 +0100
changeset 323028 f87f327d7ef202c238ea6c5392150e416012c0ef
parent 318699 99bf3401b43f4f621c91facce91f729688941317
child 323303 50b7f70fbd5e724d2c3a2de0a4b5457f6fa1e721
permissions -rw-r--r--
Bug 1151899 - Add RustURL which implements nsIURI,nsIURL,nsIStandardURL,etc; r=bagder MozReview-Commit-ID: 2rVu4t66cfD

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=4 sw=4 et tw=80:
 *
 * 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/. */

#include "WrapperAnswer.h"
#include "JavaScriptLogging.h"
#include "mozilla/dom/ContentChild.h"
#include "mozilla/dom/BindingUtils.h"
#include "mozilla/dom/ScriptSettings.h"
#include "xpcprivate.h"
#include "js/Class.h"
#include "jsfriendapi.h"

using namespace JS;
using namespace mozilla;
using namespace mozilla::jsipc;

// Note - Using AutoJSAPI (rather than AutoEntryScript) for a trap means
// that we don't expect it to run script. For most of these traps that will only
// happen if the target is a scripted proxy, which is probably something that we
// don't want to support over CPOWs. When enough code is fixed up, the long-term
// plan is to have the JS engine throw if it encounters script when it isn't
// expecting it.
using mozilla::dom::AutoJSAPI;
using mozilla::dom::AutoEntryScript;

static void
MaybeForceDebugGC()
{
    static bool sEnvVarInitialized = false;
    static bool sDebugGCs = false;

    if (!sEnvVarInitialized)
        sDebugGCs = !!PR_GetEnv("MOZ_DEBUG_DEAD_CPOWS");

    if (sDebugGCs) {
        JSContext* cx = nsXPConnect::GetContextInstance()->Context();
        PrepareForFullGC(cx);
        GCForReason(cx, GC_NORMAL, gcreason::COMPONENT_UTILS);
    }
}

bool
WrapperAnswer::fail(AutoJSAPI& jsapi, ReturnStatus* rs)
{
    // By default, we set |undefined| unless we can get a more meaningful
    // exception.
    *rs = ReturnStatus(ReturnException(JSVariant(UndefinedVariant())));

    // Note we always return true from this function, since this propagates
    // to the IPC code, and we don't want a JS failure to cause the death
    // of the child process.

    JSContext* cx = jsapi.cx();
    RootedValue exn(cx);
    if (!jsapi.HasException())
        return true;

    if (!jsapi.StealException(&exn))
        return true;

    if (JS_IsStopIteration(exn)) {
        *rs = ReturnStatus(ReturnStopIteration());
        return true;
    }

    // If this fails, we still don't want to exit. Just return an invalid
    // exception.
    (void) toVariant(cx, exn, &rs->get_ReturnException().exn());
    return true;
}

bool
WrapperAnswer::ok(ReturnStatus* rs)
{
    *rs = ReturnStatus(ReturnSuccess());
    return true;
}

bool
WrapperAnswer::ok(ReturnStatus* rs, const JS::ObjectOpResult& result)
{
    *rs = result
          ? ReturnStatus(ReturnSuccess())
          : ReturnStatus(ReturnObjectOpResult(result.failureCode()));
    return true;
}

bool
WrapperAnswer::deadCPOW(AutoJSAPI& jsapi, ReturnStatus* rs)
{
    JSContext* cx = jsapi.cx();
    JS_ClearPendingException(cx);
    *rs = ReturnStatus(ReturnDeadCPOW());
    return true;
}

bool
WrapperAnswer::RecvPreventExtensions(const ObjectId& objId, ReturnStatus* rs)
{
    MaybeForceDebugGC();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    ObjectOpResult success;
    if (!JS_PreventExtensions(cx, obj, success))
        return fail(jsapi, rs);

    LOG("%s.preventExtensions()", ReceiverObj(objId));
    return ok(rs, success);
}

static void
EmptyDesc(PPropertyDescriptor* desc)
{
    desc->obj() = LocalObject(0);
    desc->attrs() = 0;
    desc->value() = UndefinedVariant();
    desc->getter() = 0;
    desc->setter() = 0;
}

bool
WrapperAnswer::RecvGetPropertyDescriptor(const ObjectId& objId, const JSIDVariant& idVar,
                                         ReturnStatus* rs, PPropertyDescriptor* out)
{
    MaybeForceDebugGC();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();
    EmptyDesc(out);

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    LOG("%s.getPropertyDescriptor(%s)", ReceiverObj(objId), Identifier(idVar));

    RootedId id(cx);
    if (!fromJSIDVariant(cx, idVar, &id))
        return fail(jsapi, rs);

    Rooted<PropertyDescriptor> desc(cx);
    if (!JS_GetPropertyDescriptorById(cx, obj, id, &desc))
        return fail(jsapi, rs);

    if (!fromDescriptor(cx, desc, out))
        return fail(jsapi, rs);

    return ok(rs);
}

bool
WrapperAnswer::RecvGetOwnPropertyDescriptor(const ObjectId& objId, const JSIDVariant& idVar,
                                            ReturnStatus* rs, PPropertyDescriptor* out)
{
    MaybeForceDebugGC();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();
    EmptyDesc(out);

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    LOG("%s.getOwnPropertyDescriptor(%s)", ReceiverObj(objId), Identifier(idVar));

    RootedId id(cx);
    if (!fromJSIDVariant(cx, idVar, &id))
        return fail(jsapi, rs);

    Rooted<PropertyDescriptor> desc(cx);
    if (!JS_GetOwnPropertyDescriptorById(cx, obj, id, &desc))
        return fail(jsapi, rs);

    if (!fromDescriptor(cx, desc, out))
        return fail(jsapi, rs);

    return ok(rs);
}

bool
WrapperAnswer::RecvDefineProperty(const ObjectId& objId, const JSIDVariant& idVar,
                                  const PPropertyDescriptor& descriptor, ReturnStatus* rs)
{
    MaybeForceDebugGC();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    LOG("define %s[%s]", ReceiverObj(objId), Identifier(idVar));

    RootedId id(cx);
    if (!fromJSIDVariant(cx, idVar, &id))
        return fail(jsapi, rs);

    Rooted<PropertyDescriptor> desc(cx);
    if (!toDescriptor(cx, descriptor, &desc))
        return fail(jsapi, rs);

    ObjectOpResult success;
    if (!JS_DefinePropertyById(cx, obj, id, desc, success))
        return fail(jsapi, rs);
    return ok(rs, success);
}

bool
WrapperAnswer::RecvDelete(const ObjectId& objId, const JSIDVariant& idVar, ReturnStatus* rs)
{
    MaybeForceDebugGC();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    LOG("delete %s[%s]", ReceiverObj(objId), Identifier(idVar));

    RootedId id(cx);
    if (!fromJSIDVariant(cx, idVar, &id))
        return fail(jsapi, rs);

    ObjectOpResult success;
    if (!JS_DeletePropertyById(cx, obj, id, success))
        return fail(jsapi, rs);
    return ok(rs, success);
}

bool
WrapperAnswer::RecvHas(const ObjectId& objId, const JSIDVariant& idVar, ReturnStatus* rs,
                       bool* foundp)
{
    MaybeForceDebugGC();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();
    *foundp = false;

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    LOG("%s.has(%s)", ReceiverObj(objId), Identifier(idVar));

    RootedId id(cx);
    if (!fromJSIDVariant(cx, idVar, &id))
        return fail(jsapi, rs);

    if (!JS_HasPropertyById(cx, obj, id, foundp))
        return fail(jsapi, rs);
    return ok(rs);
}

bool
WrapperAnswer::RecvHasOwn(const ObjectId& objId, const JSIDVariant& idVar, ReturnStatus* rs,
                          bool* foundp)
{
    MaybeForceDebugGC();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();
    *foundp = false;

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    LOG("%s.hasOwn(%s)", ReceiverObj(objId), Identifier(idVar));

    RootedId id(cx);
    if (!fromJSIDVariant(cx, idVar, &id))
        return fail(jsapi, rs);

    if (!JS_HasOwnPropertyById(cx, obj, id, foundp))
        return fail(jsapi, rs);
    return ok(rs);
}

bool
WrapperAnswer::RecvGet(const ObjectId& objId, const JSVariant& receiverVar,
                       const JSIDVariant& idVar, ReturnStatus* rs, JSVariant* result)
{
    MaybeForceDebugGC();

    // We may run scripted getters.
    AutoEntryScript aes(scopeForTargetObjects(),
                        "Cross-Process Object Wrapper 'get'");
    JSContext* cx = aes.cx();

    // The outparam will be written to the buffer, so it must be set even if
    // the parent won't read it.
    *result = UndefinedVariant();

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(aes, rs);

    RootedValue receiver(cx);
    if (!fromVariant(cx, receiverVar, &receiver))
        return fail(aes, rs);

    RootedId id(cx);
    if (!fromJSIDVariant(cx, idVar, &id))
        return fail(aes, rs);

    JS::RootedValue val(cx);
    if (!JS_ForwardGetPropertyTo(cx, obj, id, receiver, &val))
        return fail(aes, rs);

    if (!toVariant(cx, val, result))
        return fail(aes, rs);

    LOG("get %s.%s = %s", ReceiverObj(objId), Identifier(idVar), OutVariant(*result));

    return ok(rs);
}

bool
WrapperAnswer::RecvSet(const ObjectId& objId, const JSIDVariant& idVar, const JSVariant& value,
                       const JSVariant& receiverVar, ReturnStatus* rs)
{
    MaybeForceDebugGC();

    // We may run scripted setters.
    AutoEntryScript aes(scopeForTargetObjects(),
                        "Cross-Process Object Wrapper 'set'");
    JSContext* cx = aes.cx();

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(aes, rs);

    LOG("set %s[%s] = %s", ReceiverObj(objId), Identifier(idVar), InVariant(value));

    RootedId id(cx);
    if (!fromJSIDVariant(cx, idVar, &id))
        return fail(aes, rs);

    RootedValue val(cx);
    if (!fromVariant(cx, value, &val))
        return fail(aes, rs);

    RootedValue receiver(cx);
    if (!fromVariant(cx, receiverVar, &receiver))
        return fail(aes, rs);

    ObjectOpResult result;
    if (!JS_ForwardSetPropertyTo(cx, obj, id, val, receiver, result))
        return fail(aes, rs);

    return ok(rs, result);
}

bool
WrapperAnswer::RecvIsExtensible(const ObjectId& objId, ReturnStatus* rs, bool* result)
{
    MaybeForceDebugGC();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();
    *result = false;

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    LOG("%s.isExtensible()", ReceiverObj(objId));

    bool extensible;
    if (!JS_IsExtensible(cx, obj, &extensible))
        return fail(jsapi, rs);

    *result = !!extensible;
    return ok(rs);
}

bool
WrapperAnswer::RecvCallOrConstruct(const ObjectId& objId,
                                   InfallibleTArray<JSParam>&& argv,
                                   const bool& construct,
                                   ReturnStatus* rs,
                                   JSVariant* result,
                                   nsTArray<JSParam>* outparams)
{
    MaybeForceDebugGC();

    AutoEntryScript aes(scopeForTargetObjects(),
                        "Cross-Process Object Wrapper call/construct");
    JSContext* cx = aes.cx();

    // The outparam will be written to the buffer, so it must be set even if
    // the parent won't read it.
    *result = UndefinedVariant();

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(aes, rs);

    MOZ_ASSERT(argv.Length() >= 2);

    RootedValue objv(cx);
    if (!fromVariant(cx, argv[0], &objv))
        return fail(aes, rs);

    *result = JSVariant(UndefinedVariant());

    AutoValueVector vals(cx);
    AutoValueVector outobjects(cx);
    for (size_t i = 0; i < argv.Length(); i++) {
        if (argv[i].type() == JSParam::Tvoid_t) {
            // This is an outparam.
            RootedObject obj(cx, xpc::NewOutObject(cx));
            if (!obj)
                return fail(aes, rs);
            if (!outobjects.append(ObjectValue(*obj)))
                return fail(aes, rs);
            if (!vals.append(ObjectValue(*obj)))
                return fail(aes, rs);
        } else {
            RootedValue v(cx);
            if (!fromVariant(cx, argv[i].get_JSVariant(), &v))
                return fail(aes, rs);
            if (!vals.append(v))
                return fail(aes, rs);
        }
    }

    RootedValue rval(cx);
    {
        HandleValueArray args = HandleValueArray::subarray(vals, 2, vals.length() - 2);
        if (construct) {
            RootedObject obj(cx);
            if (!JS::Construct(cx, vals[0], args, &obj))
                return fail(aes, rs);
            rval.setObject(*obj);
        } else {
            if(!JS::Call(cx, vals[1], vals[0], args, &rval))
                return fail(aes, rs);
        }
    }

    if (!toVariant(cx, rval, result))
        return fail(aes, rs);

    // Prefill everything with a dummy jsval.
    for (size_t i = 0; i < outobjects.length(); i++)
        outparams->AppendElement(JSParam(void_t()));

    // Go through each argument that was an outparam, retrieve the "value"
    // field, and add it to a temporary list. We need to do this separately
    // because the outparams vector is not rooted.
    vals.clear();
    for (size_t i = 0; i < outobjects.length(); i++) {
        RootedObject obj(cx, &outobjects[i].toObject());

        RootedValue v(cx);
        bool found;
        if (JS_HasProperty(cx, obj, "value", &found)) {
            if (!JS_GetProperty(cx, obj, "value", &v))
                return fail(aes, rs);
        } else {
            v = UndefinedValue();
        }
        if (!vals.append(v))
            return fail(aes, rs);
    }

    // Copy the outparams. If any outparam is already set to a void_t, we
    // treat this as the outparam never having been set.
    for (size_t i = 0; i < vals.length(); i++) {
        JSVariant variant;
        if (!toVariant(cx, vals[i], &variant))
            return fail(aes, rs);
        outparams->ReplaceElementAt(i, JSParam(variant));
    }

    LOG("%s.call(%s) = %s", ReceiverObj(objId), argv, OutVariant(*result));

    return ok(rs);
}

bool
WrapperAnswer::RecvHasInstance(const ObjectId& objId, const JSVariant& vVar, ReturnStatus* rs, bool* bp)
{
    MaybeForceDebugGC();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    LOG("%s.hasInstance(%s)", ReceiverObj(objId), InVariant(vVar));

    RootedValue val(cx);
    if (!fromVariant(cx, vVar, &val))
        return fail(jsapi, rs);

    if (!JS_HasInstance(cx, obj, val, bp))
        return fail(jsapi, rs);

    return ok(rs);
}

bool
WrapperAnswer::RecvGetBuiltinClass(const ObjectId& objId, ReturnStatus* rs,
                                   uint32_t* classValue)
{
    MaybeForceDebugGC();

    *classValue = uint32_t(js::ESClass::Other);

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    LOG("%s.getBuiltinClass()", ReceiverObj(objId));

    js::ESClass cls;
    if (!js::GetBuiltinClass(cx, obj, &cls))
        return fail(jsapi, rs);

    *classValue = uint32_t(cls);
    return ok(rs);
}

bool
WrapperAnswer::RecvIsArray(const ObjectId& objId, ReturnStatus* rs,
                           uint32_t* ans)
{
    MaybeForceDebugGC();

    *ans = uint32_t(IsArrayAnswer::NotArray);

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    LOG("%s.isArray()", ReceiverObj(objId));

    IsArrayAnswer answer;
    if (!JS::IsArray(cx, obj, &answer))
        return fail(jsapi, rs);

    *ans = uint32_t(answer);
    return ok(rs);
}

bool
WrapperAnswer::RecvClassName(const ObjectId& objId, nsCString* name)
{
    MaybeForceDebugGC();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj) {
        // This is very unfortunate, but we have no choice.
        *name = "<dead CPOW>";
        return true;
    }

    LOG("%s.className()", ReceiverObj(objId));

    *name = js::ObjectClassName(cx, obj);
    return true;
}

bool
WrapperAnswer::RecvGetPrototype(const ObjectId& objId, ReturnStatus* rs, ObjectOrNullVariant* result)
{
    MaybeForceDebugGC();

    *result = NullVariant();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    JS::RootedObject proto(cx);
    if (!JS_GetPrototype(cx, obj, &proto))
        return fail(jsapi, rs);

    if (!toObjectOrNullVariant(cx, proto, result))
        return fail(jsapi, rs);

    LOG("getPrototype(%s)", ReceiverObj(objId));

    return ok(rs);
}

bool
WrapperAnswer::RecvGetPrototypeIfOrdinary(const ObjectId& objId, ReturnStatus* rs, bool* isOrdinary,
                                          ObjectOrNullVariant* result)
{
    MaybeForceDebugGC();

    *result = NullVariant();
    *isOrdinary = false;

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    JS::RootedObject proto(cx);
    if (!JS_GetPrototypeIfOrdinary(cx, obj, isOrdinary, &proto))
        return fail(jsapi, rs);

    if (!toObjectOrNullVariant(cx, proto, result))
        return fail(jsapi, rs);

    LOG("getPrototypeIfOrdinary(%s)", ReceiverObj(objId));

    return ok(rs);
}

bool
WrapperAnswer::RecvRegExpToShared(const ObjectId& objId, ReturnStatus* rs,
                                  nsString* source, uint32_t* flags)
{
    MaybeForceDebugGC();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    RootedString sourceJSStr(cx, JS_GetRegExpSource(cx, obj));
    if (!sourceJSStr)
        return fail(jsapi, rs);
    nsAutoJSString sourceStr;
    if (!sourceStr.init(cx, sourceJSStr))
        return fail(jsapi, rs);
    source->Assign(sourceStr);

    *flags = JS_GetRegExpFlags(cx, obj);

    return ok(rs);
}

bool
WrapperAnswer::RecvGetPropertyKeys(const ObjectId& objId, const uint32_t& flags,
                                   ReturnStatus* rs, nsTArray<JSIDVariant>* ids)
{
    MaybeForceDebugGC();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    LOG("%s.getPropertyKeys()", ReceiverObj(objId));

    AutoIdVector props(cx);
    if (!js::GetPropertyKeys(cx, obj, flags, &props))
        return fail(jsapi, rs);

    for (size_t i = 0; i < props.length(); i++) {
        JSIDVariant id;
        if (!toJSIDVariant(cx, props[i], &id))
            return fail(jsapi, rs);

        ids->AppendElement(id);
    }

    return ok(rs);
}

bool
WrapperAnswer::RecvInstanceOf(const ObjectId& objId, const JSIID& iid, ReturnStatus* rs,
                              bool* instanceof)
{
    MaybeForceDebugGC();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();

    *instanceof = false;

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    LOG("%s.instanceOf()", ReceiverObj(objId));

    nsID nsiid;
    ConvertID(iid, &nsiid);

    nsresult rv = xpc::HasInstance(cx, obj, &nsiid, instanceof);
    if (rv != NS_OK)
        return fail(jsapi, rs);

    return ok(rs);
}

bool
WrapperAnswer::RecvDOMInstanceOf(const ObjectId& objId, const int& prototypeID,
                                 const int& depth, ReturnStatus* rs, bool* instanceof)
{
    MaybeForceDebugGC();

    AutoJSAPI jsapi;
    if (NS_WARN_IF(!jsapi.Init(scopeForTargetObjects())))
        return false;
    JSContext* cx = jsapi.cx();
    *instanceof = false;

    RootedObject obj(cx, findObjectById(cx, objId));
    if (!obj)
        return deadCPOW(jsapi, rs);

    LOG("%s.domInstanceOf()", ReceiverObj(objId));

    bool tmp;
    if (!mozilla::dom::InterfaceHasInstance(cx, prototypeID, depth, obj, &tmp))
        return fail(jsapi, rs);
    *instanceof = tmp;

    return ok(rs);
}

bool
WrapperAnswer::RecvDropObject(const ObjectId& objId)
{
    JSObject* obj = objects_.find(objId);
    if (obj) {
        objectIdMap(objId.hasXrayWaiver()).remove(obj);
        objects_.remove(objId);
    }
    return true;
}