js/xpconnect/wrappers/XrayWrapper.cpp
author Boris Zbarsky <bzbarsky@mit.edu>
Fri, 28 Sep 2018 10:49:44 -0400
changeset 494475 8c9b27320d6e37b77631980d19607d5c58717896
parent 493598 fa86cfaf0db840ca0418c2b7d98ca2ed1a4a8b72
child 494496 59496d5915844c01b3aa71894e35cfedf347443f
permissions -rw-r--r--
Bug 1396482 part 2. Enumerate JS standard classes on Window Xrays, just like we enumerateWebIDL interfaces. r=bholley

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* vim: set ts=8 sts=4 et sw=4 tw=99: */
/* 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 "XrayWrapper.h"
#include "AccessCheck.h"
#include "WrapperFactory.h"

#include "nsDependentString.h"
#include "nsIScriptError.h"
#include "mozilla/dom/Element.h"
#include "mozilla/dom/ScriptSettings.h"

#include "XPCWrapper.h"
#include "xpcprivate.h"

#include "jsapi.h"
#include "nsJSUtils.h"
#include "nsPrintfCString.h"

#include "mozilla/dom/BindingUtils.h"
#include "mozilla/dom/WindowBinding.h"
#include "mozilla/dom/XrayExpandoClass.h"
#include "nsGlobalWindow.h"

using namespace mozilla::dom;
using namespace JS;
using namespace mozilla;

using js::Wrapper;
using js::BaseProxyHandler;
using js::IsCrossCompartmentWrapper;
using js::UncheckedUnwrap;
using js::CheckedUnwrap;

namespace xpc {

using namespace XrayUtils;

#define Between(x, a, b) (a <= x && x <= b)

static_assert(JSProto_URIError - JSProto_Error == 7, "New prototype added in error object range");
#define AssertErrorObjectKeyInBounds(key) \
    static_assert(Between(key, JSProto_Error, JSProto_URIError), "We depend on js/ProtoKey.h ordering here");
MOZ_FOR_EACH(AssertErrorObjectKeyInBounds, (),
             (JSProto_Error, JSProto_InternalError, JSProto_EvalError, JSProto_RangeError,
              JSProto_ReferenceError, JSProto_SyntaxError, JSProto_TypeError, JSProto_URIError));

static_assert(JSProto_Uint8ClampedArray - JSProto_Int8Array == 8, "New prototype added in typed array range");
#define AssertTypedArrayKeyInBounds(key) \
    static_assert(Between(key, JSProto_Int8Array, JSProto_Uint8ClampedArray), "We depend on js/ProtoKey.h ordering here");
MOZ_FOR_EACH(AssertTypedArrayKeyInBounds, (),
             (JSProto_Int8Array, JSProto_Uint8Array, JSProto_Int16Array, JSProto_Uint16Array,
              JSProto_Int32Array, JSProto_Uint32Array, JSProto_Float32Array, JSProto_Float64Array, JSProto_Uint8ClampedArray));

#undef Between

inline bool
IsErrorObjectKey(JSProtoKey key)
{
    return key >= JSProto_Error && key <= JSProto_URIError;
}

inline bool
IsTypedArrayKey(JSProtoKey key)
{
    return key >= JSProto_Int8Array && key <= JSProto_Uint8ClampedArray;
}

// Whitelist for the standard ES classes we can Xray to.
static bool
IsJSXraySupported(JSProtoKey key)
{
    if (IsTypedArrayKey(key)) {
        return true;
    }
    if (IsErrorObjectKey(key)) {
        return true;
    }
    switch (key) {
      case JSProto_Date:
      case JSProto_DataView:
      case JSProto_Object:
      case JSProto_Array:
      case JSProto_Function:
      case JSProto_TypedArray:
      case JSProto_SavedFrame:
      case JSProto_RegExp:
      case JSProto_Promise:
      case JSProto_ArrayBuffer:
      case JSProto_SharedArrayBuffer:
      case JSProto_Map:
      case JSProto_Set:
        return true;
      default:
        return false;
    }
}

XrayType
GetXrayType(JSObject* obj)
{
    obj = js::UncheckedUnwrap(obj, /* stopAtWindowProxy = */ false);
    if (mozilla::dom::UseDOMXray(obj)) {
        return XrayForDOMObject;
    }

    MOZ_ASSERT(!js::IsWindowProxy(obj));

    JSProtoKey standardProto = IdentifyStandardInstanceOrPrototype(obj);
    if (IsJSXraySupported(standardProto)) {
        return XrayForJSObject;
    }

    // Modulo a few exceptions, everything else counts as an XrayWrapper to an
    // opaque object, which means that more-privileged code sees nothing from
    // the underlying object. This is very important for security. In some cases
    // though, we need to make an exception for compatibility.
    if (IsSandbox(obj)) {
        return NotXray;
    }

    return XrayForOpaqueObject;
}

JSObject*
XrayAwareCalleeGlobal(JSObject* fun)
{
  MOZ_ASSERT(js::IsFunctionObject(fun));

  if (!js::FunctionHasNativeReserved(fun)) {
      // Just a normal function, no Xrays involved.
      return JS::GetNonCCWObjectGlobal(fun);
  }

  // The functions we expect here have the Xray wrapper they're associated with
  // in their XRAY_DOM_FUNCTION_PARENT_WRAPPER_SLOT and, in a debug build,
  // themselves in their XRAY_DOM_FUNCTION_NATIVE_SLOT_FOR_SELF.  Assert that
  // last bit.
  MOZ_ASSERT(&js::GetFunctionNativeReserved(fun, XRAY_DOM_FUNCTION_NATIVE_SLOT_FOR_SELF).toObject() ==
             fun);

  Value v =
      js::GetFunctionNativeReserved(fun, XRAY_DOM_FUNCTION_PARENT_WRAPPER_SLOT);
  MOZ_ASSERT(IsXrayWrapper(&v.toObject()));

  JSObject* xrayTarget = js::UncheckedUnwrap(&v.toObject());
  return JS::GetNonCCWObjectGlobal(xrayTarget);
}

JSObject*
XrayTraits::getExpandoChain(HandleObject obj)
{
    return ObjectScope(obj)->GetExpandoChain(obj);
}

JSObject*
XrayTraits::detachExpandoChain(HandleObject obj)
{
    return ObjectScope(obj)->DetachExpandoChain(obj);
}

bool
XrayTraits::setExpandoChain(JSContext* cx, HandleObject obj, HandleObject chain)
{
    return ObjectScope(obj)->SetExpandoChain(cx, obj, chain);
}

const JSClass XrayTraits::HolderClass = {
    "XrayHolder", JSCLASS_HAS_RESERVED_SLOTS(HOLDER_SHARED_SLOT_COUNT)
};

const JSClass JSXrayTraits::HolderClass = {
    "JSXrayHolder", JSCLASS_HAS_RESERVED_SLOTS(SLOT_COUNT)
};

bool
OpaqueXrayTraits::resolveOwnProperty(JSContext* cx, HandleObject wrapper, HandleObject target,
                                     HandleObject holder, HandleId id,
                                     MutableHandle<PropertyDescriptor> desc)
{
    bool ok = XrayTraits::resolveOwnProperty(cx, wrapper, target, holder, id, desc);
    if (!ok || desc.object()) {
        return ok;
    }

    return ReportWrapperDenial(cx, id, WrapperDenialForXray, "object is not safely Xrayable");
}

bool
ReportWrapperDenial(JSContext* cx, HandleId id, WrapperDenialType type, const char* reason)
{
    CompartmentPrivate* priv = CompartmentPrivate::Get(CurrentGlobalOrNull(cx));
    bool alreadyWarnedOnce = priv->wrapperDenialWarnings[type];
    priv->wrapperDenialWarnings[type] = true;

    // The browser console warning is only emitted for the first violation,
    // whereas the (debug-only) NS_WARNING is emitted for each violation.
#ifndef DEBUG
    if (alreadyWarnedOnce) {
        return true;
    }
#endif

    nsAutoJSString propertyName;
    RootedValue idval(cx);
    if (!JS_IdToValue(cx, id, &idval)) {
        return false;
    }
    JSString* str = JS_ValueToSource(cx, idval);
    if (!str) {
        return false;
    }
    if (!propertyName.init(cx, str)) {
        return false;
    }
    AutoFilename filename;
    unsigned line = 0, column = 0;
    DescribeScriptedCaller(cx, &filename, &line, &column);

    // Warn to the terminal for the logs.
    NS_WARNING(nsPrintfCString("Silently denied access to property %s: %s (@%s:%u:%u)",
                               NS_LossyConvertUTF16toASCII(propertyName).get(), reason,
                               filename.get(), line, column).get());

    // If this isn't the first warning on this topic for this global, we've
    // already bailed out in opt builds. Now that the NS_WARNING is done, bail
    // out in debug builds as well.
    if (alreadyWarnedOnce) {
        return true;
    }

    //
    // Log a message to the console service.
    //

    // Grab the pieces.
    nsCOMPtr<nsIConsoleService> consoleService = do_GetService(NS_CONSOLESERVICE_CONTRACTID);
    NS_ENSURE_TRUE(consoleService, true);
    nsCOMPtr<nsIScriptError> errorObject = do_CreateInstance(NS_SCRIPTERROR_CONTRACTID);
    NS_ENSURE_TRUE(errorObject, true);

    // Compute the current window id if any.
    uint64_t windowId = 0;
    if (nsGlobalWindowInner* win = CurrentWindowOrNull(cx)) {
      windowId = win->WindowID();
    }


    Maybe<nsPrintfCString> errorMessage;
    if (type == WrapperDenialForXray) {
        errorMessage.emplace("XrayWrapper denied access to property %s (reason: %s). "
                             "See https://developer.mozilla.org/en-US/docs/Xray_vision "
                             "for more information. Note that only the first denied "
                             "property access from a given global object will be reported.",
                             NS_LossyConvertUTF16toASCII(propertyName).get(),
                             reason);
    } else {
        MOZ_ASSERT(type == WrapperDenialForCOW);
        errorMessage.emplace("Security wrapper denied access to property %s on privileged "
                             "Javascript object. Support for exposing privileged objects "
                             "to untrusted content via __exposedProps__ has been "
                             "removed - use WebIDL bindings or Components.utils.cloneInto "
                             "instead. Note that only the first denied property access from a "
                             "given global object will be reported.",
                             NS_LossyConvertUTF16toASCII(propertyName).get());
    }
    nsString filenameStr(NS_ConvertASCIItoUTF16(filename.get()));
    nsresult rv = errorObject->InitWithWindowID(NS_ConvertASCIItoUTF16(errorMessage.ref()),
                                                filenameStr,
                                                EmptyString(),
                                                line, column,
                                                nsIScriptError::warningFlag,
                                                "XPConnect",
                                                windowId);
    NS_ENSURE_SUCCESS(rv, true);
    rv = consoleService->LogMessage(errorObject);
    NS_ENSURE_SUCCESS(rv, true);

    return true;
}

bool JSXrayTraits::getOwnPropertyFromWrapperIfSafe(JSContext* cx,
                                                   HandleObject wrapper,
                                                   HandleId id,
                                                   MutableHandle<PropertyDescriptor> outDesc)
{
    MOZ_ASSERT(js::IsObjectInContextCompartment(wrapper, cx));
    RootedObject target(cx, getTargetObject(wrapper));
    RootedObject wrapperGlobal(cx, JS::CurrentGlobalOrNull(cx));
    {
        JSAutoRealm ar(cx, target);
        JS_MarkCrossZoneId(cx, id);
        if (!getOwnPropertyFromTargetIfSafe(cx, target, wrapper, wrapperGlobal, id, outDesc)) {
            return false;
        }
    }
    return JS_WrapPropertyDescriptor(cx, outDesc);
}

bool JSXrayTraits::getOwnPropertyFromTargetIfSafe(JSContext* cx,
                                                  HandleObject target,
                                                  HandleObject wrapper,
                                                  HandleObject wrapperGlobal,
                                                  HandleId id,
                                                  MutableHandle<PropertyDescriptor> outDesc)
{
    // Note - This function operates in the target compartment, because it
    // avoids a bunch of back-and-forth wrapping in enumerateNames.
    MOZ_ASSERT(getTargetObject(wrapper) == target);
    MOZ_ASSERT(js::IsObjectInContextCompartment(target, cx));
    MOZ_ASSERT(WrapperFactory::IsXrayWrapper(wrapper));
    MOZ_ASSERT(JS_IsGlobalObject(wrapperGlobal));
    js::AssertSameCompartment(wrapper, wrapperGlobal);
    MOZ_ASSERT(outDesc.object() == nullptr);

    Rooted<PropertyDescriptor> desc(cx);
    if (!JS_GetOwnPropertyDescriptorById(cx, target, id, &desc)) {
        return false;
    }

    // If the property doesn't exist at all, we're done.
    if (!desc.object()) {
        return true;
    }

    // Disallow accessor properties.
    if (desc.hasGetterOrSetter()) {
        JSAutoRealm ar(cx, wrapperGlobal);
        JS_MarkCrossZoneId(cx, id);
        return ReportWrapperDenial(cx, id, WrapperDenialForXray, "property has accessor");
    }

    // Apply extra scrutiny to objects.
    if (desc.value().isObject()) {
        RootedObject propObj(cx, js::UncheckedUnwrap(&desc.value().toObject()));
        JSAutoRealm ar(cx, propObj);

        // Disallow non-subsumed objects.
        if (!AccessCheck::subsumes(target, propObj)) {
            JSAutoRealm ar(cx, wrapperGlobal);
            JS_MarkCrossZoneId(cx, id);
            return ReportWrapperDenial(cx, id, WrapperDenialForXray, "value not same-origin with target");
        }

        // Disallow non-Xrayable objects.
        XrayType xrayType = GetXrayType(propObj);
        if (xrayType == NotXray || xrayType == XrayForOpaqueObject) {
            JSAutoRealm ar(cx, wrapperGlobal);
            JS_MarkCrossZoneId(cx, id);
            return ReportWrapperDenial(cx, id, WrapperDenialForXray, "value not Xrayable");
        }

        // Disallow callables.
        if (JS::IsCallable(propObj)) {
            JSAutoRealm ar(cx, wrapperGlobal);
            JS_MarkCrossZoneId(cx, id);
            return ReportWrapperDenial(cx, id, WrapperDenialForXray, "value is callable");
        }
    }

    // Disallow any property that shadows something on its (Xrayed)
    // prototype chain.
    JSAutoRealm ar2(cx, wrapperGlobal);
    JS_MarkCrossZoneId(cx, id);
    RootedObject proto(cx);
    bool foundOnProto = false;
    if (!JS_GetPrototype(cx, wrapper, &proto) ||
        (proto && !JS_HasPropertyById(cx, proto, id, &foundOnProto)))
    {
        return false;
    }
    if (foundOnProto) {
        return ReportWrapperDenial(cx, id, WrapperDenialForXray, "value shadows a property on the standard prototype");
    }

    // We made it! Assign over the descriptor, and don't forget to wrap.
    outDesc.assign(desc.get());
    return true;
}

// Returns true on success (in the JSAPI sense), false on failure.  If true is
// returned, desc.object() will indicate whether we actually resolved
// the property.
//
// id is the property id we're looking for.
// holder is the object to define the property on.
// fs is the relevant JSFunctionSpec*.
// ps is the relevant JSPropertySpec*.
// desc is the descriptor we're resolving into.
static bool
TryResolvePropertyFromSpecs(JSContext* cx, HandleId id, HandleObject holder,
                            const JSFunctionSpec* fs,
                            const JSPropertySpec* ps,
                            MutableHandle<PropertyDescriptor> desc)
{
    // Scan through the functions.
    const JSFunctionSpec* fsMatch = nullptr;
    for ( ; fs && fs->name; ++fs) {
        if (PropertySpecNameEqualsId(fs->name, id)) {
            fsMatch = fs;
            break;
        }
    }
    if (fsMatch) {
        // Generate an Xrayed version of the method.
        RootedFunction fun(cx, JS::NewFunctionFromSpec(cx, fsMatch, id));
        if (!fun) {
            return false;
        }

        // The generic Xray machinery only defines non-own properties of the target on
        // the holder. This is broken, and will be fixed at some point, but for now we
        // need to cache the value explicitly. See the corresponding call to
        // JS_GetOwnPropertyDescriptorById at the top of
        // JSXrayTraits::resolveOwnProperty.
        RootedObject funObj(cx, JS_GetFunctionObject(fun));
        return JS_DefinePropertyById(cx, holder, id, funObj, 0) &&
               JS_GetOwnPropertyDescriptorById(cx, holder, id, desc);
    }

    // Scan through the properties.
    const JSPropertySpec* psMatch = nullptr;
    for ( ; ps && ps->name; ++ps) {
        if (PropertySpecNameEqualsId(ps->name, id)) {
            psMatch = ps;
            break;
        }
    }
    if (psMatch) {
        // The generic Xray machinery only defines non-own properties on the holder.
        // This is broken, and will be fixed at some point, but for now we need to
        // cache the value explicitly. See the corresponding call to
        // JS_GetPropertyById at the top of JSXrayTraits::resolveOwnProperty.
        //
        // Note also that the public-facing API here doesn't give us a way to
        // pass along JITInfo. It's probably ok though, since Xrays are already
        // pretty slow.
        desc.value().setUndefined();
        unsigned flags = psMatch->flags;
        if (psMatch->isAccessor()) {
            if (psMatch->isSelfHosted()) {
                JSFunction* getterFun = JS::GetSelfHostedFunction(cx, psMatch->accessors.getter.selfHosted.funname, id, 0);
                if (!getterFun) {
                    return false;
                }
                RootedObject getterObj(cx, JS_GetFunctionObject(getterFun));
                RootedObject setterObj(cx);
                if (psMatch->accessors.setter.selfHosted.funname) {
                    MOZ_ASSERT(flags & JSPROP_SETTER);
                    JSFunction* setterFun = JS::GetSelfHostedFunction(cx, psMatch->accessors.setter.selfHosted.funname, id, 0);
                    if (!setterFun) {
                        return false;
                    }
                    setterObj = JS_GetFunctionObject(setterFun);
                }
                if (!JS_DefinePropertyById(cx, holder, id, getterObj, setterObj, flags)) {
                    return false;
                }
            } else {
                if (!JS_DefinePropertyById(cx, holder, id,
                                           psMatch->accessors.getter.native.op,
                                           psMatch->accessors.setter.native.op,
                                           flags))
                {
                    return false;
                }
            }
        } else {
            RootedValue v(cx);
            if (!psMatch->getValue(cx, &v)) {
                return false;
            }
            if (!JS_DefinePropertyById(cx, holder, id, v, flags & ~JSPROP_INTERNAL_USE_BIT)) {
                return false;
            }
        }

        return JS_GetOwnPropertyDescriptorById(cx, holder, id, desc);
    }

    return true;
}

static bool
ShouldResolveStaticProperties(JSProtoKey key)
{
    // Don't try to resolve static properties on RegExp, because they
    // have issues.  In particular, some of them grab state off the
    // global of the RegExp constructor that describes the last regexp
    // evaluation in that global, which is not a useful thing to do
    // over Xrays.
    return key != JSProto_RegExp;
}

bool
JSXrayTraits::resolveOwnProperty(JSContext* cx, HandleObject wrapper,
                                 HandleObject target, HandleObject holder,
                                 HandleId id,
                                 MutableHandle<PropertyDescriptor> desc)
{
    // Call the common code.
    bool ok = XrayTraits::resolveOwnProperty(cx, wrapper, target, holder,
                                             id, desc);
    if (!ok || desc.object()) {
        return ok;
    }

    // The non-HasPrototypes semantics implemented by traditional Xrays are kind
    // of broken with respect to |own|-ness and the holder. The common code
    // muddles through by only checking the holder for non-|own| lookups, but
    // that doesn't work for us. So we do an explicit holder check here, and hope
    // that this mess gets fixed up soon.
    if (!JS_GetOwnPropertyDescriptorById(cx, holder, id, desc)) {
        return false;
    }
    if (desc.object()) {
        desc.object().set(wrapper);
        return true;
    }

    JSProtoKey key = getProtoKey(holder);
    if (!isPrototype(holder)) {
        // For Object and Array instances, we expose some properties from the
        // underlying object, but only after filtering them carefully.
        //
        // Note that, as far as JS observables go, Arrays are just Objects with
        // a different prototype and a magic (own, non-configurable) |.length| that
        // serves as a non-tight upper bound on |own| indexed properties. So while
        // it's tempting to try to impose some sort of structure on what Arrays
        // "should" look like over Xrays, the underlying object is squishy enough
        // that it makes sense to just treat them like Objects for Xray purposes.
        if (key == JSProto_Object || key == JSProto_Array) {
            return getOwnPropertyFromWrapperIfSafe(cx, wrapper, id, desc);
        }
        if (IsTypedArrayKey(key)) {
            if (IsArrayIndex(GetArrayIndexFromId(cx, id))) {
                // WebExtensions can't use cloneInto(), so we just let them do
                // the slow thing to maximize compatibility.
                if (CompartmentPrivate::Get(CurrentGlobalOrNull(cx))->isWebExtensionContentScript) {
                    Rooted<PropertyDescriptor> innerDesc(cx);
                    {
                        JSAutoRealm ar(cx, target);
                        JS_MarkCrossZoneId(cx, id);
                        if (!JS_GetOwnPropertyDescriptorById(cx, target, id, &innerDesc)) {
                            return false;
                        }
                    }
                    if (innerDesc.isDataDescriptor() && innerDesc.value().isNumber()) {
                        desc.setValue(innerDesc.value());
                        desc.object().set(wrapper);
                    }
                    return true;
                }
                JS_ReportErrorASCII(cx, "Accessing TypedArray data over Xrays is slow, and forbidden "
                                    "in order to encourage performant code. To copy TypedArrays "
                                    "across origin boundaries, consider using Components.utils.cloneInto().");
                return false;
            }
        } else if (key == JSProto_Function) {
            if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_LENGTH)) {
                uint16_t length;
                RootedFunction fun(cx, JS_GetObjectFunction(target));
                {
                    JSAutoRealm ar(cx, target);
                    if (!JS_GetFunctionLength(cx, fun, &length)) {
                        return false;
                    }
                }
                FillPropertyDescriptor(desc, wrapper, JSPROP_PERMANENT | JSPROP_READONLY,
                                       NumberValue(length));
                return true;
            }
            if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_NAME)) {
                RootedString fname(cx, JS_GetFunctionId(JS_GetObjectFunction(target)));
                if (fname) {
                    JS_MarkCrossZoneIdValue(cx, StringValue(fname));
                }
                FillPropertyDescriptor(desc, wrapper, JSPROP_PERMANENT | JSPROP_READONLY,
                                       fname ? StringValue(fname) : JS_GetEmptyStringValue(cx));
            } else {
                // Look for various static properties/methods and the
                // 'prototype' property.
                JSProtoKey standardConstructor = constructorFor(holder);
                if (standardConstructor != JSProto_Null) {
                    // Handle the 'prototype' property to make
                    // xrayedGlobal.StandardClass.prototype work.
                    if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_PROTOTYPE)) {
                        RootedObject standardProto(cx);
                        {
                            JSAutoRealm ar(cx, target);
                            if (!JS_GetClassPrototype(cx, standardConstructor, &standardProto)) {
                                return false;
                            }
                            MOZ_ASSERT(standardProto);
                        }

                        if (!JS_WrapObject(cx, &standardProto)) {
                            return false;
                        }
                        FillPropertyDescriptor(desc, wrapper, JSPROP_PERMANENT | JSPROP_READONLY,
                                               ObjectValue(*standardProto));
                        return true;
                    }

                    if (ShouldResolveStaticProperties(standardConstructor)) {
                        const js::Class* clasp = js::ProtoKeyToClass(standardConstructor);
                        MOZ_ASSERT(clasp->specDefined());

                        if (!TryResolvePropertyFromSpecs(cx, id, holder,
                               clasp->specConstructorFunctions(),
                               clasp->specConstructorProperties(), desc)) {
                            return false;
                        }

                        if (desc.object()) {
                            desc.object().set(wrapper);
                            return true;
                        }
                    }
                }
            }
        } else if (IsErrorObjectKey(key)) {
            // The useful state of error objects (except for .stack) is
            // (unfortunately) represented as own data properties per-spec. This
            // means that we can't have a a clean representation of the data
            // (free from tampering) without doubling the slots of Error
            // objects, which isn't great. So we forward these properties to the
            // underlying object and then just censor any values with the wrong
            // type. This limits the ability of content to do anything all that
            // confusing.
            bool isErrorIntProperty =
                id == GetJSIDByIndex(cx, XPCJSContext::IDX_LINENUMBER) ||
                id == GetJSIDByIndex(cx, XPCJSContext::IDX_COLUMNNUMBER);
            bool isErrorStringProperty =
                id == GetJSIDByIndex(cx, XPCJSContext::IDX_FILENAME) ||
                id == GetJSIDByIndex(cx, XPCJSContext::IDX_MESSAGE);
            if (isErrorIntProperty || isErrorStringProperty) {
                RootedObject waiver(cx, wrapper);
                if (!WrapperFactory::WaiveXrayAndWrap(cx, &waiver)) {
                    return false;
                }
                if (!JS_GetOwnPropertyDescriptorById(cx, waiver, id, desc)) {
                    return false;
                }
                bool valueMatchesType = (isErrorIntProperty && desc.value().isInt32()) ||
                                        (isErrorStringProperty && desc.value().isString());
                if (desc.hasGetterOrSetter() || !valueMatchesType) {
                    FillPropertyDescriptor(desc, nullptr, 0, UndefinedValue());
                }
                return true;
            }
        } else if (key == JSProto_RegExp) {
            if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_LASTINDEX)) {
                return getOwnPropertyFromWrapperIfSafe(cx, wrapper, id, desc);
            }
        }

        // The rest of this function applies only to prototypes.
        return true;
    }

    // Handle the 'constructor' property.
    if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_CONSTRUCTOR)) {
        RootedObject constructor(cx);
        {
            JSAutoRealm ar(cx, target);
            if (!JS_GetClassObject(cx, key, &constructor)) {
                return false;
            }
        }
        if (!JS_WrapObject(cx, &constructor)) {
            return false;
        }
        desc.object().set(wrapper);
        desc.setAttributes(0);
        desc.setGetter(nullptr);
        desc.setSetter(nullptr);
        desc.value().setObject(*constructor);
        return true;
    }

    // Grab the JSClass. We require all Xrayable classes to have a ClassSpec.
    const js::Class* clasp = js::GetObjectClass(target);
    MOZ_ASSERT(clasp->specDefined());

    // Indexed array properties are handled above, so we can just work with the
    // class spec here.
    if (!TryResolvePropertyFromSpecs(cx, id, holder,
                                     clasp->specPrototypeFunctions(),
                                     clasp->specPrototypeProperties(),
                                     desc)) {
        return false;
    }

    if (desc.object()) {
        desc.object().set(wrapper);
    }

    return true;
}

bool
JSXrayTraits::delete_(JSContext* cx, HandleObject wrapper, HandleId id, ObjectOpResult& result)
{
    MOZ_ASSERT(js::IsObjectInContextCompartment(wrapper, cx));

    RootedObject holder(cx, ensureHolder(cx, wrapper));
    if (!holder) {
        return false;
    }

    // If we're using Object Xrays, we allow callers to attempt to delete any
    // property from the underlying object that they are able to resolve. Note
    // that this deleting may fail if the property is non-configurable.
    JSProtoKey key = getProtoKey(holder);
    bool isObjectOrArrayInstance = (key == JSProto_Object || key == JSProto_Array) &&
                                   !isPrototype(holder);
    if (isObjectOrArrayInstance) {
        RootedObject wrapperGlobal(cx, JS::CurrentGlobalOrNull(cx));
        RootedObject target(cx, getTargetObject(wrapper));
        JSAutoRealm ar(cx, target);
        JS_MarkCrossZoneId(cx, id);
        Rooted<PropertyDescriptor> desc(cx);
        if (!getOwnPropertyFromTargetIfSafe(cx, target, wrapper, wrapperGlobal, id, &desc)) {
            return false;
        }
        if (desc.object()) {
            return JS_DeletePropertyById(cx, target, id, result);
        }
    }
    return result.succeed();
}

bool
JSXrayTraits::defineProperty(JSContext* cx, HandleObject wrapper, HandleId id,
                             Handle<PropertyDescriptor> desc,
                             Handle<PropertyDescriptor> existingDesc,
                             ObjectOpResult& result,
                             bool* defined)
{
    *defined = false;
    RootedObject holder(cx, ensureHolder(cx, wrapper));
    if (!holder) {
        return false;
    }


    // Object and Array instances are special. For those cases, we forward property
    // definitions to the underlying object if the following conditions are met:
    // * The property being defined is a value-prop.
    // * The property being defined is either a primitive or subsumed by the target.
    // * As seen from the Xray, any existing property that we would overwrite is an
    //   |own| value-prop.
    //
    // To avoid confusion, we disallow expandos on Object and Array instances, and
    // therefore raise an exception here if the above conditions aren't met.
    JSProtoKey key = getProtoKey(holder);
    bool isInstance = !isPrototype(holder);
    bool isObjectOrArray = (key == JSProto_Object || key == JSProto_Array);
    if (isObjectOrArray && isInstance) {
        RootedObject target(cx, getTargetObject(wrapper));
        if (desc.hasGetterOrSetter()) {
            JS_ReportErrorASCII(cx, "Not allowed to define accessor property on [Object] or [Array] XrayWrapper");
            return false;
        }
        if (desc.value().isObject() &&
            !AccessCheck::subsumes(target, js::UncheckedUnwrap(&desc.value().toObject())))
        {
            JS_ReportErrorASCII(cx, "Not allowed to define cross-origin object as property on [Object] or [Array] XrayWrapper");
            return false;
        }
        if (existingDesc.hasGetterOrSetter()) {
            JS_ReportErrorASCII(cx, "Not allowed to overwrite accessor property on [Object] or [Array] XrayWrapper");
            return false;
        }
        if (existingDesc.object() && existingDesc.object() != wrapper) {
            JS_ReportErrorASCII(cx, "Not allowed to shadow non-own Xray-resolved property on [Object] or [Array] XrayWrapper");
            return false;
        }

        Rooted<PropertyDescriptor> wrappedDesc(cx, desc);
        JSAutoRealm ar(cx, target);
        JS_MarkCrossZoneId(cx, id);
        if (!JS_WrapPropertyDescriptor(cx, &wrappedDesc) ||
            !JS_DefinePropertyById(cx, target, id, wrappedDesc, result))
        {
            return false;
        }
        *defined = true;
        return true;
    }

    // For WebExtensions content scripts, we forward the definition of indexed properties. By
    // validating that the key and value are both numbers, we can avoid doing any wrapping.
    if (isInstance && IsTypedArrayKey(key) &&
        CompartmentPrivate::Get(JS::CurrentGlobalOrNull(cx))->isWebExtensionContentScript &&
        desc.isDataDescriptor() && (desc.value().isNumber() || desc.value().isUndefined()) &&
        IsArrayIndex(GetArrayIndexFromId(cx, id)))
    {
        RootedObject target(cx, getTargetObject(wrapper));
        JSAutoRealm ar(cx, target);
        JS_MarkCrossZoneId(cx, id);
        if (!JS_DefinePropertyById(cx, target, id, desc, result)) {
            return false;
        }
        *defined = true;
        return true;
    }

    return true;
}

static bool
MaybeAppend(jsid id, unsigned flags, AutoIdVector& props)
{
    MOZ_ASSERT(!(flags & JSITER_SYMBOLSONLY));
    if (!(flags & JSITER_SYMBOLS) && JSID_IS_SYMBOL(id)) {
        return true;
    }
    return props.append(id);
}

// Append the names from the given function and property specs to props.
static bool
AppendNamesFromFunctionAndPropertySpecs(JSContext* cx,
                                        const JSFunctionSpec* fs,
                                        const JSPropertySpec* ps,
                                        unsigned flags,
                                        AutoIdVector& props)
{
    // Convert the method and property names to jsids and pass them to the caller.
    for ( ; fs && fs->name; ++fs) {
        jsid id;
        if (!PropertySpecNameToPermanentId(cx, fs->name, &id)) {
            return false;
        }
        if (!MaybeAppend(id, flags, props)) {
            return false;
        }
    }
    for ( ; ps && ps->name; ++ps) {
        jsid id;
        if (!PropertySpecNameToPermanentId(cx, ps->name, &id)) {
            return false;
        }
        if (!MaybeAppend(id, flags, props)) {
            return false;
        }
    }

    return true;
}

bool
JSXrayTraits::enumerateNames(JSContext* cx, HandleObject wrapper, unsigned flags,
                             AutoIdVector& props)
{
    MOZ_ASSERT(js::IsObjectInContextCompartment(wrapper, cx));

    RootedObject target(cx, getTargetObject(wrapper));
    RootedObject holder(cx, ensureHolder(cx, wrapper));
    if (!holder) {
        return false;
    }

    JSProtoKey key = getProtoKey(holder);
    if (!isPrototype(holder)) {
        // For Object and Array instances, we expose some properties from the underlying
        // object, but only after filtering them carefully.
        if (key == JSProto_Object || key == JSProto_Array) {
            MOZ_ASSERT(props.empty());
            RootedObject wrapperGlobal(cx, JS::CurrentGlobalOrNull(cx));
            {
                JSAutoRealm ar(cx, target);
                AutoIdVector targetProps(cx);
                if (!js::GetPropertyKeys(cx, target, flags | JSITER_OWNONLY, &targetProps)) {
                    return false;
                }
                // Loop over the properties, and only pass along the ones that
                // we determine to be safe.
                if (!props.reserve(targetProps.length())) {
                    return false;
                }
                for (size_t i = 0; i < targetProps.length(); ++i) {
                    Rooted<PropertyDescriptor> desc(cx);
                    RootedId id(cx, targetProps[i]);
                    if (!getOwnPropertyFromTargetIfSafe(cx, target, wrapper, wrapperGlobal, id,
                                                        &desc))
                    {
                        return false;
                    }
                    if (desc.object()) {
                        props.infallibleAppend(id);
                    }
                }
            }
            for (size_t i = 0; i < props.length(); ++i) {
                JS_MarkCrossZoneId(cx, props[i]);
            }
            return true;
        }
        if (IsTypedArrayKey(key)) {
            uint32_t length = JS_GetTypedArrayLength(target);
            // TypedArrays enumerate every indexed property in range, but
            // |length| is a getter that lives on the proto, like it should be.
            if (!props.reserve(length)) {
                return false;
            }
            for (int32_t i = 0; i <= int32_t(length - 1); ++i) {
                props.infallibleAppend(INT_TO_JSID(i));
            }
        } else if (key == JSProto_Function) {
            if (!props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_LENGTH))) {
                return false;
            }
            if (!props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_NAME))) {
                return false;
            }
            // Handle the .prototype property and static properties on standard
            // constructors.
            JSProtoKey standardConstructor = constructorFor(holder);
            if (standardConstructor != JSProto_Null) {
                if (!props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_PROTOTYPE))) {
                    return false;
                }

                if (ShouldResolveStaticProperties(standardConstructor)) {
                    const js::Class* clasp = js::ProtoKeyToClass(standardConstructor);
                    MOZ_ASSERT(clasp->specDefined());

                    if (!AppendNamesFromFunctionAndPropertySpecs(
                           cx, clasp->specConstructorFunctions(),
                           clasp->specConstructorProperties(), flags, props)) {
                        return false;
                    }
                }
            }
        } else if (IsErrorObjectKey(key)) {
            if (!props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_FILENAME)) ||
                !props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_LINENUMBER)) ||
                !props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_COLUMNNUMBER)) ||
                !props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_STACK)) ||
                !props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_MESSAGE)))
            {
                return false;
            }
        } else if (key == JSProto_RegExp) {
            if (!props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_LASTINDEX))) {
                return false;
            }
        }

        // The rest of this function applies only to prototypes.
        return true;
    }

    // Add the 'constructor' property.
    if (!props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_CONSTRUCTOR))) {
        return false;
    }

    // Grab the JSClass. We require all Xrayable classes to have a ClassSpec.
    const js::Class* clasp = js::GetObjectClass(target);
    MOZ_ASSERT(clasp->specDefined());

    return AppendNamesFromFunctionAndPropertySpecs(
        cx, clasp->specPrototypeFunctions(),
        clasp->specPrototypeProperties(), flags, props);
}

bool
JSXrayTraits::construct(JSContext* cx, HandleObject wrapper,
                        const JS::CallArgs& args, const js::Wrapper& baseInstance)
{
    JSXrayTraits& self = JSXrayTraits::singleton;
    JS::RootedObject holder(cx, self.ensureHolder(cx, wrapper));
    if (!holder) {
        return false;
    }

    if (xpc::JSXrayTraits::getProtoKey(holder) == JSProto_Function) {
        JSProtoKey standardConstructor = constructorFor(holder);
        if (standardConstructor == JSProto_Null) {
            return baseInstance.construct(cx, wrapper, args);
        }

        const js::Class* clasp = js::ProtoKeyToClass(standardConstructor);
        MOZ_ASSERT(clasp);
        if (!(clasp->flags & JSCLASS_HAS_XRAYED_CONSTRUCTOR)) {
            return baseInstance.construct(cx, wrapper, args);
        }

        // If the JSCLASS_HAS_XRAYED_CONSTRUCTOR flag is set on the Class,
        // we don't use the constructor at hand. Instead, we retrieve the
        // equivalent standard constructor in the xray compartment and run
        // it in that compartment. The newTarget isn't unwrapped, and the
        // constructor has to be able to detect and handle this situation.
        // See the comments in js/public/Class.h and PromiseConstructor for
        // details and an example.
        RootedObject ctor(cx);
        if (!JS_GetClassObject(cx, standardConstructor, &ctor)) {
            return false;
        }

        RootedValue ctorVal(cx, ObjectValue(*ctor));
        HandleValueArray vals(args);
        RootedObject result(cx);
        if (!JS::Construct(cx, ctorVal, wrapper, vals, &result)) {
            return false;
        }
        AssertSameCompartment(cx, result);
        args.rval().setObject(*result);
        return true;
    }

    JS::RootedValue v(cx, JS::ObjectValue(*wrapper));
    js::ReportIsNotFunction(cx, v);
    return false;
}

JSObject*
JSXrayTraits::createHolder(JSContext* cx, JSObject* wrapper)
{
    RootedObject target(cx, getTargetObject(wrapper));
    RootedObject holder(cx, JS_NewObjectWithGivenProto(cx, &HolderClass,
                                                       nullptr));
    if (!holder) {
        return nullptr;
    }

    // Compute information about the target.
    bool isPrototype = false;
    JSProtoKey key = IdentifyStandardInstance(target);
    if (key == JSProto_Null) {
        isPrototype = true;
        key = IdentifyStandardPrototype(target);
    }
    MOZ_ASSERT(key != JSProto_Null);

    // Special case: pretend Arguments objects are arrays for Xrays.
    //
    // Arguments objects are strange beasts - they inherit Object.prototype,
    // and implement iteration by defining an |own| property for
    // Symbol.iterator. Since this value is callable, Array/Object Xrays will
    // filter it out, causing the Xray view to be non-iterable, which in turn
    // breaks consumers.
    //
    // We can't trust the iterator value from the content compartment,
    // but the generic one on Array.prototype works well enough. So we force
    // the Xray view of Arguments objects to inherit Array.prototype, which
    // in turn allows iteration via the inherited Array.prototype[Symbol.iterator].
    // This doesn't emulate any of the weird semantics of Arguments iterators,
    // but is probably good enough.
    //
    // Note that there are various Xray traps that do other special behavior for
    // JSProto_Array, but they also provide that special behavior for
    // JSProto_Object, and since Arguments would otherwise get JSProto_Object,
    // this does not cause any behavior change at those sites.
    if (key == JSProto_Object && js::IsArgumentsObject(target)) {
        key = JSProto_Array;
    }

    // Store it on the holder.
    RootedValue v(cx);
    v.setNumber(static_cast<uint32_t>(key));
    js::SetReservedSlot(holder, SLOT_PROTOKEY, v);
    v.setBoolean(isPrototype);
    js::SetReservedSlot(holder, SLOT_ISPROTOTYPE, v);

    // If this is a function, also compute whether it serves as a constructor
    // for a standard class.
    if (key == JSProto_Function) {
        v.setNumber(static_cast<uint32_t>(IdentifyStandardConstructor(target)));
        js::SetReservedSlot(holder, SLOT_CONSTRUCTOR_FOR, v);
    }

    return holder;
}

DOMXrayTraits DOMXrayTraits::singleton;
JSXrayTraits JSXrayTraits::singleton;
OpaqueXrayTraits OpaqueXrayTraits::singleton;

XrayTraits*
GetXrayTraits(JSObject* obj)
{
    switch (GetXrayType(obj)) {
      case XrayForDOMObject:
        return &DOMXrayTraits::singleton;
      case XrayForJSObject:
        return &JSXrayTraits::singleton;
      case XrayForOpaqueObject:
        return &OpaqueXrayTraits::singleton;
      default:
        return nullptr;
    }
}

/*
 * Xray expando handling.
 *
 * We hang expandos for Xray wrappers off a reserved slot on the target object
 * so that same-origin compartments can share expandos for a given object. We
 * have a linked list of expando objects, one per origin. The properties on these
 * objects are generally wrappers pointing back to the compartment that applied
 * them.
 *
 * The expando objects should _never_ be exposed to script. The fact that they
 * live in the target compartment is a detail of the implementation, and does
 * not imply that code in the target compartment should be allowed to inspect
 * them. They are private to the origin that placed them.
 */

// Certain compartments do not share expandos with other compartments. Xrays in
// these compartments cache expandos on the wrapper's holder, as there is only
// one such wrapper which can create or access the expando. This allows for
// faster access to the expando, including through JIT inline caches.
static inline bool
CompartmentHasExclusiveExpandos(JSObject* obj)
{
    return IsInSandboxCompartment(obj);
}

static inline JSObject*
GetCachedXrayExpando(JSObject* wrapper);

static inline void
SetCachedXrayExpando(JSObject* holder, JSObject* expandoWrapper);

static nsIPrincipal*
WrapperPrincipal(JSObject* obj)
{
    // Use the principal stored in CompartmentOriginInfo. That works because
    // consumers are only interested in the origin-ignoring-document.domain.
    // See expandoObjectMatchesConsumer.
    MOZ_ASSERT(IsXrayWrapper(obj));
    JS::Compartment* comp = js::GetObjectCompartment(obj);
    CompartmentPrivate* priv = CompartmentPrivate::Get(comp);
    return priv->originInfo.GetPrincipalIgnoringDocumentDomain();
}

static nsIPrincipal*
GetExpandoObjectPrincipal(JSObject* expandoObject)
{
    Value v = JS_GetReservedSlot(expandoObject, JSSLOT_EXPANDO_ORIGIN);
    return static_cast<nsIPrincipal*>(v.toPrivate());
}

static void
ExpandoObjectFinalize(JSFreeOp* fop, JSObject* obj)
{
    // Release the principal.
    nsIPrincipal* principal = GetExpandoObjectPrincipal(obj);
    NS_RELEASE(principal);
}

const JSClassOps XrayExpandoObjectClassOps = {
    nullptr, nullptr, nullptr, nullptr,
    nullptr, nullptr,
    ExpandoObjectFinalize
};

bool
XrayTraits::expandoObjectMatchesConsumer(JSContext* cx,
                                         HandleObject expandoObject,
                                         nsIPrincipal* consumerOrigin)
{
    MOZ_ASSERT(js::IsObjectInContextCompartment(expandoObject, cx));

    // First, compare the principals.
    nsIPrincipal* o = GetExpandoObjectPrincipal(expandoObject);
    // Note that it's very important here to ignore document.domain. We
    // pull the principal for the expando object off of the first consumer
    // for a given origin, and freely share the expandos amongst multiple
    // same-origin consumers afterwards. However, this means that we have
    // no way to know whether _all_ consumers have opted in to collaboration
    // by explicitly setting document.domain. So we just mandate that expando
    // sharing is unaffected by it.
    if (!consumerOrigin->Equals(o)) {
      return false;
    }

    // Certain globals exclusively own the associated expandos, in which case
    // the caller should have used the cached expando on the wrapper instead.
    JSObject* owner = JS_GetReservedSlot(expandoObject,
                                         JSSLOT_EXPANDO_EXCLUSIVE_WRAPPER_HOLDER)
                                        .toObjectOrNull();
    return owner == nullptr;
}

bool
XrayTraits::getExpandoObjectInternal(JSContext* cx, JSObject* expandoChain,
                                     HandleObject exclusiveWrapper,
                                     nsIPrincipal* origin,
                                     MutableHandleObject expandoObject)
{
    MOZ_ASSERT(!JS_IsExceptionPending(cx));
    expandoObject.set(nullptr);

    // Use the cached expando if this wrapper has exclusive access to it.
    if (exclusiveWrapper) {
        JSObject* expandoWrapper = GetCachedXrayExpando(exclusiveWrapper);
        expandoObject.set(expandoWrapper ? UncheckedUnwrap(expandoWrapper) : nullptr);
#ifdef DEBUG
        // Make sure the expando we found is on the target's chain. While we
        // don't use this chain to look up expandos for the wrapper,
        // the expando still needs to be on the chain to keep the wrapper and
        // expando alive.
        if (expandoObject) {
            JSObject* head = expandoChain;
            while (head && head != expandoObject) {
                head = JS_GetReservedSlot(head, JSSLOT_EXPANDO_NEXT).toObjectOrNull();
            }
            MOZ_ASSERT(head == expandoObject);
        }
#endif
        return true;
    }

    // The expando object lives in the compartment of the target, so all our
    // work needs to happen there.
    RootedObject head(cx, expandoChain);
    JSAutoRealm ar(cx, head);

    // Iterate through the chain, looking for a same-origin object.
    while (head) {
        if (expandoObjectMatchesConsumer(cx, head, origin)) {
            expandoObject.set(head);
            return true;
        }
        head = JS_GetReservedSlot(head, JSSLOT_EXPANDO_NEXT).toObjectOrNull();
    }

    // Not found.
    return true;
}

bool
XrayTraits::getExpandoObject(JSContext* cx, HandleObject target, HandleObject consumer,
                             MutableHandleObject expandoObject)
{
    // Return early if no expando object has ever been attached, which is
    // usually the case.
    JSObject* chain = getExpandoChain(target);
    if (!chain) {
        return true;
    }

    bool isExclusive = CompartmentHasExclusiveExpandos(consumer);
    return getExpandoObjectInternal(cx, chain, isExclusive ? consumer : nullptr,
                                    WrapperPrincipal(consumer), expandoObject);
}

// Wrappers which have exclusive access to the expando on their target object
// need to be kept alive as long as the target object exists. This is done by
// keeping the expando in the expando chain on the target (even though it will
// not be used while looking up the expando for the wrapper), and keeping a
// strong reference from that expando to the wrapper itself, via the
// JSSLOT_EXPANDO_EXCLUSIVE_WRAPPER_HOLDER reserved slot. This slot does not
// point to the wrapper itself, because it is a cross compartment edge and we
// can't create a wrapper for a wrapper. Instead, the slot points to an
// instance of the holder class below in the wrapper's compartment, and the
// wrapper is held via this holder object's reserved slot.
static const JSClass gWrapperHolderClass = {
    "XrayExpandoWrapperHolder",
    JSCLASS_HAS_RESERVED_SLOTS(1)
};
static const size_t JSSLOT_WRAPPER_HOLDER_CONTENTS = 0;

JSObject*
XrayTraits::attachExpandoObject(JSContext* cx, HandleObject target,
                                HandleObject exclusiveWrapper,
                                HandleObject exclusiveWrapperGlobal,
                                nsIPrincipal* origin)
{
    // Make sure the compartments are sane.
    MOZ_ASSERT(js::IsObjectInContextCompartment(target, cx));
    if (exclusiveWrapper) {
        MOZ_ASSERT(!js::IsObjectInContextCompartment(exclusiveWrapper, cx));
        MOZ_ASSERT(JS_IsGlobalObject(exclusiveWrapperGlobal));
        js::AssertSameCompartment(exclusiveWrapper, exclusiveWrapperGlobal);
    }

    // No duplicates allowed.
#ifdef DEBUG
    {
        JSObject* chain = getExpandoChain(target);
        if (chain) {
            RootedObject existingExpandoObject(cx);
            if (getExpandoObjectInternal(cx, chain, exclusiveWrapper, origin, &existingExpandoObject)) {
                MOZ_ASSERT(!existingExpandoObject);
            } else {
                JS_ClearPendingException(cx);
            }
        }
    }
#endif

    // Create the expando object.
    const JSClass* expandoClass = getExpandoClass(cx, target);
    MOZ_ASSERT(!strcmp(expandoClass->name, "XrayExpandoObject"));
    RootedObject expandoObject(cx,
      JS_NewObjectWithGivenProto(cx, expandoClass, nullptr));
    if (!expandoObject) {
        return nullptr;
    }

    // AddRef and store the principal.
    NS_ADDREF(origin);
    JS_SetReservedSlot(expandoObject, JSSLOT_EXPANDO_ORIGIN, JS::PrivateValue(origin));

    // Note the exclusive wrapper, if there is one.
    RootedObject wrapperHolder(cx);
    if (exclusiveWrapper) {
        JSAutoRealm ar(cx, exclusiveWrapperGlobal);
        wrapperHolder = JS_NewObjectWithGivenProto(cx, &gWrapperHolderClass, nullptr);
        if (!wrapperHolder) {
            return nullptr;
        }
        JS_SetReservedSlot(wrapperHolder, JSSLOT_WRAPPER_HOLDER_CONTENTS, ObjectValue(*exclusiveWrapper));
    }
    if (!JS_WrapObject(cx, &wrapperHolder)) {
        return nullptr;
    }
    JS_SetReservedSlot(expandoObject, JSSLOT_EXPANDO_EXCLUSIVE_WRAPPER_HOLDER,
                       ObjectOrNullValue(wrapperHolder));

    // Store it on the exclusive wrapper, if there is one.
    if (exclusiveWrapper) {
        RootedObject cachedExpandoObject(cx, expandoObject);
        JSAutoRealm ar(cx, exclusiveWrapperGlobal);
        if (!JS_WrapObject(cx, &cachedExpandoObject)) {
            return nullptr;
        }
        JSObject* holder = ensureHolder(cx, exclusiveWrapper);
        if (!holder) {
            return nullptr;
        }
        SetCachedXrayExpando(holder, cachedExpandoObject);
    }

    // If this is our first expando object, take the opportunity to preserve
    // the wrapper. This keeps our expandos alive even if the Xray wrapper gets
    // collected.
    RootedObject chain(cx, getExpandoChain(target));
    if (!chain) {
        preserveWrapper(target);
    }

    // Insert it at the front of the chain.
    JS_SetReservedSlot(expandoObject, JSSLOT_EXPANDO_NEXT, ObjectOrNullValue(chain));
    setExpandoChain(cx, target, expandoObject);

    return expandoObject;
}

JSObject*
XrayTraits::ensureExpandoObject(JSContext* cx, HandleObject wrapper,
                                HandleObject target)
{
    MOZ_ASSERT(js::IsObjectInContextCompartment(wrapper, cx));
    RootedObject wrapperGlobal(cx, JS::CurrentGlobalOrNull(cx));

    // Expando objects live in the target compartment.
    JSAutoRealm ar(cx, target);
    RootedObject expandoObject(cx);
    if (!getExpandoObject(cx, target, wrapper, &expandoObject)) {
        return nullptr;
    }
    if (!expandoObject) {
        bool isExclusive = CompartmentHasExclusiveExpandos(wrapper);
        expandoObject = attachExpandoObject(cx, target, isExclusive ? wrapper : nullptr,
                                            wrapperGlobal,
                                            WrapperPrincipal(wrapper));
    }
    return expandoObject;
}

bool
XrayTraits::cloneExpandoChain(JSContext* cx, HandleObject dst, HandleObject srcChain)
{
    MOZ_ASSERT(js::IsObjectInContextCompartment(dst, cx));
    MOZ_ASSERT(getExpandoChain(dst) == nullptr);

    RootedObject oldHead(cx, srcChain);
    while (oldHead) {
        // If movingIntoXrayCompartment is true, then our new reflector is in a
        // compartment that used to have an Xray-with-expandos to the old reflector
        // and we should copy the expandos to the new reflector directly.
        bool movingIntoXrayCompartment;

        // exclusiveWrapper is only used if movingIntoXrayCompartment ends up true.
        RootedObject exclusiveWrapper(cx);
        RootedObject exclusiveWrapperGlobal(cx);
        RootedObject wrapperHolder(cx, JS_GetReservedSlot(oldHead,
                                                          JSSLOT_EXPANDO_EXCLUSIVE_WRAPPER_HOLDER)
                                                         .toObjectOrNull());
        if (wrapperHolder) {
            RootedObject unwrappedHolder(cx, UncheckedUnwrap(wrapperHolder));
            // unwrappedHolder is the compartment of the relevant Xray, so check
            // whether that matches the compartment of cx (which matches the
            // compartment of dst).
            movingIntoXrayCompartment =
                js::IsObjectInContextCompartment(unwrappedHolder, cx);

            if (!movingIntoXrayCompartment) {
                // The global containing this wrapper holder has an xray for |src|
                // with expandos. Create an xray in the global for |dst| which
                // will be associated with a clone of |src|'s expando object.
                JSAutoRealm ar(cx, unwrappedHolder);
                exclusiveWrapper = dst;
                if (!JS_WrapObject(cx, &exclusiveWrapper)) {
                    return false;
                }
                exclusiveWrapperGlobal = JS::CurrentGlobalOrNull(cx);
            }
        } else {
            JSAutoRealm ar(cx, oldHead);
            movingIntoXrayCompartment =
                expandoObjectMatchesConsumer(cx, oldHead, GetObjectPrincipal(dst));
        }

        if (movingIntoXrayCompartment) {
            // Just copy properties directly onto dst.
            if (!JS_CopyPropertiesFrom(cx, dst, oldHead)) {
                return false;
            }
        } else {
            // Create a new expando object in the compartment of dst to replace
            // oldHead.
            RootedObject newHead(cx, attachExpandoObject(cx, dst, exclusiveWrapper,
                                                         exclusiveWrapperGlobal,
                                                         GetExpandoObjectPrincipal(oldHead)));
            if (!JS_CopyPropertiesFrom(cx, newHead, oldHead)) {
                return false;
            }
        }
        oldHead = JS_GetReservedSlot(oldHead, JSSLOT_EXPANDO_NEXT).toObjectOrNull();
    }
    return true;
}

void
ClearXrayExpandoSlots(JSObject* target, size_t slotIndex)
{
    if (!NS_IsMainThread()) {
        // No Xrays
        return;
    }

    MOZ_ASSERT(slotIndex != JSSLOT_EXPANDO_NEXT);
    MOZ_ASSERT(slotIndex != JSSLOT_EXPANDO_EXCLUSIVE_WRAPPER_HOLDER);
    MOZ_ASSERT(GetXrayTraits(target) == &DOMXrayTraits::singleton);
    RootingContext* rootingCx = RootingCx();
    RootedObject rootedTarget(rootingCx, target);
    RootedObject head(rootingCx,
                      DOMXrayTraits::singleton.getExpandoChain(rootedTarget));
    while (head) {
        MOZ_ASSERT(JSCLASS_RESERVED_SLOTS(js::GetObjectClass(head)) > slotIndex);
        js::SetReservedSlot(head, slotIndex, UndefinedValue());
        head = js::GetReservedSlot(head, JSSLOT_EXPANDO_NEXT).toObjectOrNull();
    }
}

JSObject*
EnsureXrayExpandoObject(JSContext* cx, JS::HandleObject wrapper)
{
    MOZ_ASSERT(NS_IsMainThread());
    MOZ_ASSERT(GetXrayTraits(wrapper) == &DOMXrayTraits::singleton);
    MOZ_ASSERT(IsXrayWrapper(wrapper));

    RootedObject target(cx, DOMXrayTraits::getTargetObject(wrapper));
    return DOMXrayTraits::singleton.ensureExpandoObject(cx, wrapper, target);
}

const JSClass*
XrayTraits::getExpandoClass(JSContext* cx, HandleObject target) const
{
    return &DefaultXrayExpandoObjectClass;
}

static const size_t JSSLOT_XRAY_HOLDER = 0;

/* static */ JSObject*
XrayTraits::getHolder(JSObject* wrapper)
{
    MOZ_ASSERT(WrapperFactory::IsXrayWrapper(wrapper));
    js::Value v = js::GetProxyReservedSlot(wrapper, JSSLOT_XRAY_HOLDER);
    return v.isObject() ? &v.toObject() : nullptr;
}

JSObject*
XrayTraits::ensureHolder(JSContext* cx, HandleObject wrapper)
{
    RootedObject holder(cx, getHolder(wrapper));
    if (holder) {
        return holder;
    }
    holder = createHolder(cx, wrapper); // virtual trap.
    if (holder) {
        js::SetProxyReservedSlot(wrapper, JSSLOT_XRAY_HOLDER, ObjectValue(*holder));
    }
    return holder;
}

static inline JSObject*
GetCachedXrayExpando(JSObject* wrapper)
{
    JSObject* holder = XrayTraits::getHolder(wrapper);
    if (!holder) {
        return nullptr;
    }
    Value v = JS_GetReservedSlot(holder, XrayTraits::HOLDER_SLOT_EXPANDO);
    return v.isObject() ? &v.toObject() : nullptr;
}

static inline void
SetCachedXrayExpando(JSObject* holder, JSObject* expandoWrapper)
{
    MOZ_ASSERT(js::GetObjectCompartment(holder) ==
               js::GetObjectCompartment(expandoWrapper));
    JS_SetReservedSlot(holder, XrayTraits::HOLDER_SLOT_EXPANDO, ObjectValue(*expandoWrapper));
}

static nsGlobalWindowInner*
AsWindow(JSContext* cx, JSObject* wrapper)
{
  // We want to use our target object here, since we don't want to be
  // doing a security check while unwrapping.
  JSObject* target = XrayTraits::getTargetObject(wrapper);
  return WindowOrNull(target);
}

static bool
IsWindow(JSContext* cx, JSObject* wrapper)
{
    return !!AsWindow(cx, wrapper);
}

static bool
wrappedJSObject_getter(JSContext* cx, unsigned argc, Value* vp)
{
    CallArgs args = CallArgsFromVp(argc, vp);
    if (!args.thisv().isObject()) {
        JS_ReportErrorASCII(cx, "This value not an object");
        return false;
    }
    RootedObject wrapper(cx, &args.thisv().toObject());
    if (!IsWrapper(wrapper) || !WrapperFactory::IsXrayWrapper(wrapper) ||
        !WrapperFactory::AllowWaiver(wrapper)) {
        JS_ReportErrorASCII(cx, "Unexpected object");
        return false;
    }

    args.rval().setObject(*wrapper);

    return WrapperFactory::WaiveXrayAndWrap(cx, args.rval());
}

bool
XrayTraits::resolveOwnProperty(JSContext* cx, HandleObject wrapper, HandleObject target,
                               HandleObject holder, HandleId id,
                               MutableHandle<PropertyDescriptor> desc)
{
    desc.object().set(nullptr);
    RootedObject expando(cx);
    if (!getExpandoObject(cx, target, wrapper, &expando)) {
        return false;
    }

    // Check for expando properties first. Note that the expando object lives
    // in the target compartment.
    bool found = false;
    if (expando) {
        JSAutoRealm ar(cx, expando);
        JS_MarkCrossZoneId(cx, id);
        if (!JS_GetOwnPropertyDescriptorById(cx, expando, id, desc)) {
            return false;
        }
        found = !!desc.object();
    }

    // Next, check for ES builtins.
    if (!found && JS_IsGlobalObject(target)) {
        JSProtoKey key = JS_IdToProtoKey(cx, id);
        JSAutoRealm ar(cx, target);
        if (key != JSProto_Null) {
            MOZ_ASSERT(key < JSProto_LIMIT);
            RootedObject constructor(cx);
            if (!JS_GetClassObject(cx, key, &constructor)) {
                return false;
            }
            MOZ_ASSERT(constructor);
            desc.value().set(ObjectValue(*constructor));
            found = true;
        } else if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_EVAL)) {
            RootedObject eval(cx);
            if (!js::GetRealmOriginalEval(cx, &eval)) {
                return false;
            }
            desc.value().set(ObjectValue(*eval));
            found = true;
        }
    }

    if (found) {
        if (!JS_WrapPropertyDescriptor(cx, desc)) {
            return false;
        }
        // Pretend the property lives on the wrapper.
        desc.object().set(wrapper);
        return true;
    }

    // Handle .wrappedJSObject for subsuming callers. This should move once we
    // sort out own-ness for the holder.
    if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_WRAPPED_JSOBJECT) &&
        WrapperFactory::AllowWaiver(wrapper))
    {
        if (!JS_AlreadyHasOwnPropertyById(cx, holder, id, &found)) {
            return false;
        }
        if (!found && !JS_DefinePropertyById(cx, holder, id, wrappedJSObject_getter, nullptr,
                                             JSPROP_ENUMERATE)) {
            return false;
        }
        if (!JS_GetOwnPropertyDescriptorById(cx, holder, id, desc)) {
            return false;
        }
        desc.object().set(wrapper);
        return true;
    }

    return true;
}

bool
DOMXrayTraits::resolveOwnProperty(JSContext* cx, HandleObject wrapper, HandleObject target,
                                  HandleObject holder, HandleId id,
                                  MutableHandle<PropertyDescriptor> desc)
{
    // Call the common code.
    bool ok = XrayTraits::resolveOwnProperty(cx, wrapper, target, holder, id, desc);
    if (!ok || desc.object()) {
        return ok;
    }

    // Check for indexed access on a window.
    uint32_t index = GetArrayIndexFromId(cx, id);
    if (IsArrayIndex(index)) {
        nsGlobalWindowInner* win = AsWindow(cx, wrapper);
        // Note: As() unwraps outer windows to get to the inner window.
        if (win) {
            nsCOMPtr<nsPIDOMWindowOuter> subframe = win->IndexedGetter(index);
            if (subframe) {
                subframe->EnsureInnerWindow();
                nsGlobalWindowOuter* global = nsGlobalWindowOuter::Cast(subframe);
                JSObject* obj = global->FastGetGlobalJSObject();
                if (MOZ_UNLIKELY(!obj)) {
                    // It's gone?
                    return xpc::Throw(cx, NS_ERROR_FAILURE);
                }
                ExposeObjectToActiveJS(obj);
                desc.value().setObject(*obj);
                FillPropertyDescriptor(desc, wrapper, true);
                return JS_WrapPropertyDescriptor(cx, desc);
            }
        }
    }

    if (!JS_GetOwnPropertyDescriptorById(cx, holder, id, desc)) {
        return false;
    }
    if (desc.object()) {
        desc.object().set(wrapper);
        return true;
    }

    bool cacheOnHolder;
    if (!XrayResolveOwnProperty(cx, wrapper, target, id, desc, cacheOnHolder)) {
        return false;
    }

    MOZ_ASSERT(!desc.object() || desc.object() == wrapper, "What did we resolve this on?");

    if (!desc.object() || !cacheOnHolder) {
        return true;
    }

    return JS_DefinePropertyById(cx, holder, id, desc) &&
           JS_GetOwnPropertyDescriptorById(cx, holder, id, desc);
}

bool
DOMXrayTraits::delete_(JSContext* cx, JS::HandleObject wrapper,
                       JS::HandleId id, JS::ObjectOpResult& result)
{
    RootedObject target(cx, getTargetObject(wrapper));
    return XrayDeleteNamedProperty(cx, wrapper, target, id, result);
}

bool
DOMXrayTraits::defineProperty(JSContext* cx, HandleObject wrapper, HandleId id,
                              Handle<PropertyDescriptor> desc,
                              Handle<PropertyDescriptor> existingDesc,
                              JS::ObjectOpResult& result, bool* defined)
{
    // Check for an indexed property on a Window.  If that's happening, do
    // nothing but claim we defined it so it won't get added as an expando.
    if (IsWindow(cx, wrapper)) {
        if (IsArrayIndex(GetArrayIndexFromId(cx, id))) {
            *defined = true;
            return result.succeed();
        }
    }

    JS::Rooted<JSObject*> obj(cx, getTargetObject(wrapper));
    return XrayDefineProperty(cx, wrapper, obj, id, desc, result, defined);
}

bool
DOMXrayTraits::enumerateNames(JSContext* cx, HandleObject wrapper, unsigned flags,
                              AutoIdVector& props)
{
    // Put the indexed properties for a window first.
    nsGlobalWindowInner* win = AsWindow(cx, wrapper);
    if (win) {
        uint32_t length = win->Length();
        if (!props.reserve(props.length() + length)) {
            return false;
        }
        JS::RootedId indexId(cx);
        for (uint32_t i = 0; i < length; ++i) {
            if (!JS_IndexToId(cx, i, &indexId)) {
                return false;
            }
            props.infallibleAppend(indexId);
        }
    }

    JS::Rooted<JSObject*> obj(cx, getTargetObject(wrapper));
    if (JS_IsGlobalObject(obj)) {
        // We could do this in a shared enumerateNames with JSXrayTraits, but we
        // don't really have globals we expose via those.
        JSAutoRealm ar(cx, obj);
        if (!JS_NewEnumerateStandardClassesIncludingResolved(
          cx, obj, props, !(flags & JSITER_HIDDEN))) {
            return false;
        }
    }
    return XrayOwnPropertyKeys(cx, wrapper, obj, flags, props);
}

bool
DOMXrayTraits::call(JSContext* cx, HandleObject wrapper,
                    const JS::CallArgs& args, const js::Wrapper& baseInstance)
{
    RootedObject obj(cx, getTargetObject(wrapper));
    const js::Class* clasp = js::GetObjectClass(obj);
    // What we have is either a WebIDL interface object, a WebIDL prototype
    // object, or a WebIDL instance object.  WebIDL prototype objects never have
    // a clasp->call.  WebIDL interface objects we want to invoke on the xray
    // compartment.  WebIDL instance objects either don't have a clasp->call or
    // are using "legacycaller", which basically means plug-ins.  We want to
    // call those on the content compartment.
    if (clasp->flags & JSCLASS_IS_DOMIFACEANDPROTOJSCLASS) {
        if (JSNative call = clasp->getCall()) {
            // call it on the Xray compartment
            if (!call(cx, args.length(), args.base())) {
                return false;
            }
        } else {
            RootedValue v(cx, ObjectValue(*wrapper));
            js::ReportIsNotFunction(cx, v);
            return false;
        }
    } else {
        // This is only reached for WebIDL instance objects, and in practice
        // only for plugins.  Just call them on the content compartment.
        if (!baseInstance.call(cx, wrapper, args)) {
            return false;
        }
    }
    return JS_WrapValue(cx, args.rval());
}

bool
DOMXrayTraits::construct(JSContext* cx, HandleObject wrapper,
                         const JS::CallArgs& args, const js::Wrapper& baseInstance)
{
    RootedObject obj(cx, getTargetObject(wrapper));
    MOZ_ASSERT(mozilla::dom::HasConstructor(obj));
    const js::Class* clasp = js::GetObjectClass(obj);
    // See comments in DOMXrayTraits::call() explaining what's going on here.
    if (clasp->flags & JSCLASS_IS_DOMIFACEANDPROTOJSCLASS) {
        if (JSNative construct = clasp->getConstruct()) {
            if (!construct(cx, args.length(), args.base())) {
                return false;
            }
        } else {
            RootedValue v(cx, ObjectValue(*wrapper));
            js::ReportIsNotFunction(cx, v);
            return false;
        }
    } else {
        if (!baseInstance.construct(cx, wrapper, args)) {
            return false;
        }
    }
    if (!args.rval().isObject() || !JS_WrapValue(cx, args.rval())) {
        return false;
    }
    return true;
}

bool
DOMXrayTraits::getPrototype(JSContext* cx, JS::HandleObject wrapper,
                            JS::HandleObject target,
                            JS::MutableHandleObject protop)
{
    return mozilla::dom::XrayGetNativeProto(cx, target, protop);
}

void
DOMXrayTraits::preserveWrapper(JSObject* target)
{
    nsISupports* identity = mozilla::dom::UnwrapDOMObjectToISupports(target);
    if (!identity) {
        return;
    }
    nsWrapperCache* cache = nullptr;
    CallQueryInterface(identity, &cache);
    if (cache) {
        cache->PreserveWrapper(identity);
    }
}

JSObject*
DOMXrayTraits::createHolder(JSContext* cx, JSObject* wrapper)
{
    return JS_NewObjectWithGivenProto(cx, &HolderClass, nullptr);
}

const JSClass*
DOMXrayTraits::getExpandoClass(JSContext* cx, HandleObject target) const
{
    return XrayGetExpandoClass(cx, target);
}

namespace XrayUtils {

bool
HasNativeProperty(JSContext* cx, HandleObject wrapper, HandleId id, bool* hasProp)
{
    MOZ_ASSERT(WrapperFactory::IsXrayWrapper(wrapper));
    XrayTraits* traits = GetXrayTraits(wrapper);
    MOZ_ASSERT(traits);
    RootedObject target(cx, XrayTraits::getTargetObject(wrapper));
    RootedObject holder(cx, traits->ensureHolder(cx, wrapper));
    NS_ENSURE_TRUE(holder, false);
    *hasProp = false;
    Rooted<PropertyDescriptor> desc(cx);

    // Try resolveOwnProperty.
    if (!traits->resolveOwnProperty(cx, wrapper, target, holder, id, &desc)) {
        return false;
    }
    if (desc.object()) {
        *hasProp = true;
        return true;
    }

    // Try the holder.
    return JS_AlreadyHasOwnPropertyById(cx, holder, id, hasProp);
}

} // namespace XrayUtils


template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::preventExtensions(JSContext* cx, HandleObject wrapper,
                                             ObjectOpResult& result) const
{
    // Xray wrappers are supposed to provide a clean view of the target
    // reflector, hiding any modifications by script in the target scope.  So
    // even if that script freezes the reflector, we don't want to make that
    // visible to the caller. DOM reflectors are always extensible by default,
    // so we can just return failure here.
    return result.failCantPreventExtensions();
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::isExtensible(JSContext* cx, JS::Handle<JSObject*> wrapper,
                                        bool* extensible) const
{
    // See above.
    *extensible = true;
    return true;
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::getPropertyDescriptor(JSContext* cx, HandleObject wrapper, HandleId id,
                                                 JS::MutableHandle<PropertyDescriptor> desc)
                                                 const
{
    // CrossOriginXrayWrapper::getOwnPropertyDescriptor calls this.

    assertEnteredPolicy(cx, wrapper, id, BaseProxyHandler::GET | BaseProxyHandler::SET |
                                         BaseProxyHandler::GET_PROPERTY_DESCRIPTOR);
    RootedObject target(cx, Traits::getTargetObject(wrapper));
    RootedObject holder(cx, Traits::singleton.ensureHolder(cx, wrapper));

    if (!holder) {
        return false;
    }

    // Ordering is important here.
    //
    // We first need to call resolveOwnProperty, even before checking the holder,
    // because there might be a new dynamic |own| property that appears and
    // shadows a previously-resolved non-own property that we cached on the
    // holder. This can happen with indexed properties on NodeLists, for example,
    // which are |own| value props.
    //
    // resolveOwnProperty may or may not cache what it finds on the holder,
    // depending on how ephemeral it decides the property is. This means that we have to
    // first check the result of resolveOwnProperty, and _then_, if that comes up blank,
    // check the holder for any cached native properties.

    // Check resolveOwnProperty.
    if (!Traits::singleton.resolveOwnProperty(cx, wrapper, target, holder, id, desc)) {
        return false;
    }

    // Check the holder.
    if (!desc.object() && !JS_GetOwnPropertyDescriptorById(cx, holder, id, desc)) {
        return false;
    }
    if (desc.object()) {
        desc.object().set(wrapper);
        return true;
    }

    // We need to handle named access on the Window somewhere other than
    // Traits::resolveOwnProperty, because per spec it happens on the Global
    // Scope Polluter and thus the resulting properties are non-|own|. However,
    // we're set up (above) to cache (on the holder),
    // which we don't want for something dynamic like named access.
    // So we just handle it separately here.  Note that this is
    // only relevant for CrossOriginXrayWrapper, which calls
    // getPropertyDescriptor from getOwnPropertyDescriptor.
    nsGlobalWindowInner* win = nullptr;
    if (!desc.object() &&
        JSID_IS_STRING(id) &&
        (win = AsWindow(cx, wrapper)))
    {
        nsAutoJSString name;
        if (!name.init(cx, JSID_TO_STRING(id))) {
            return false;
        }
        if (nsCOMPtr<nsPIDOMWindowOuter> childDOMWin = win->GetChildWindow(name)) {
            auto* cwin = nsGlobalWindowOuter::Cast(childDOMWin);
            JSObject* childObj = cwin->FastGetGlobalJSObject();
            if (MOZ_UNLIKELY(!childObj)) {
                return xpc::Throw(cx, NS_ERROR_FAILURE);
            }
            ExposeObjectToActiveJS(childObj);
            FillPropertyDescriptor(desc, wrapper, ObjectValue(*childObj),
                                   /* readOnly = */ true);
            return JS_WrapPropertyDescriptor(cx, desc);
        }
    }

    // We found nothing, we're done.
    MOZ_ASSERT(!desc.object());
    return true;
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::getOwnPropertyDescriptor(JSContext* cx, HandleObject wrapper, HandleId id,
                                                    JS::MutableHandle<PropertyDescriptor> desc)
                                                    const
{
    assertEnteredPolicy(cx, wrapper, id, BaseProxyHandler::GET | BaseProxyHandler::SET |
                                         BaseProxyHandler::GET_PROPERTY_DESCRIPTOR);
    RootedObject target(cx, Traits::getTargetObject(wrapper));
    RootedObject holder(cx, Traits::singleton.ensureHolder(cx, wrapper));
    if (!holder) {
        return false;
    }

    if (!Traits::singleton.resolveOwnProperty(cx, wrapper, target, holder, id, desc)) {
        return false;
    }
    if (desc.object()) {
        desc.object().set(wrapper);
    }
    return true;
}

// Consider what happens when chrome does |xray.expando = xray.wrappedJSObject|.
//
// Since the expando comes from the target compartment, wrapping it back into
// the target compartment to define it on the expando object ends up stripping
// off the Xray waiver that gives |xray| and |xray.wrappedJSObject| different
// identities. This is generally the right thing to do when wrapping across
// compartments, but is incorrect in the special case of the Xray expando
// object. Manually re-apply Xrays if necessary.
//
// NB: In order to satisfy the invariants of WaiveXray, we need to pass
// in an object sans security wrapper, which means we need to strip off any
// potential same-compartment security wrapper that may have been applied
// to the content object. This is ok, because the the expando object is only
// ever accessed by code across the compartment boundary.
static bool
RecreateLostWaivers(JSContext* cx, const PropertyDescriptor* orig,
                    MutableHandle<PropertyDescriptor> wrapped)
{
    // Compute whether the original objects were waived, and implicitly, whether
    // they were objects at all.
    bool valueWasWaived =
        orig->value.isObject() &&
        WrapperFactory::HasWaiveXrayFlag(&orig->value.toObject());
    bool getterWasWaived =
        (orig->attrs & JSPROP_GETTER) && orig->getter &&
        WrapperFactory::HasWaiveXrayFlag(JS_FUNC_TO_DATA_PTR(JSObject*, orig->getter));
    bool setterWasWaived =
        (orig->attrs & JSPROP_SETTER) && orig->setter &&
        WrapperFactory::HasWaiveXrayFlag(JS_FUNC_TO_DATA_PTR(JSObject*, orig->setter));

    // Recreate waivers. Note that for value, we need an extra UncheckedUnwrap
    // to handle same-compartment security wrappers (see above). This should
    // never happen for getters/setters.

    RootedObject rewaived(cx);
    if (valueWasWaived && !IsCrossCompartmentWrapper(&wrapped.value().toObject())) {
        rewaived = &wrapped.value().toObject();
        rewaived = WrapperFactory::WaiveXray(cx, UncheckedUnwrap(rewaived));
        NS_ENSURE_TRUE(rewaived, false);
        wrapped.value().set(ObjectValue(*rewaived));
    }
    if (getterWasWaived && !IsCrossCompartmentWrapper(wrapped.getterObject())) {
        MOZ_ASSERT(CheckedUnwrap(wrapped.getterObject()));
        rewaived = WrapperFactory::WaiveXray(cx, wrapped.getterObject());
        NS_ENSURE_TRUE(rewaived, false);
        wrapped.setGetterObject(rewaived);
    }
    if (setterWasWaived && !IsCrossCompartmentWrapper(wrapped.setterObject())) {
        MOZ_ASSERT(CheckedUnwrap(wrapped.setterObject()));
        rewaived = WrapperFactory::WaiveXray(cx, wrapped.setterObject());
        NS_ENSURE_TRUE(rewaived, false);
        wrapped.setSetterObject(rewaived);
    }

    return true;
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::defineProperty(JSContext* cx, HandleObject wrapper,
                                          HandleId id, Handle<PropertyDescriptor> desc,
                                          ObjectOpResult& result) const
{
    assertEnteredPolicy(cx, wrapper, id, BaseProxyHandler::SET);

    Rooted<PropertyDescriptor> existing_desc(cx);
    if (!JS_GetPropertyDescriptorById(cx, wrapper, id, &existing_desc)) {
        return false;
    }

    // Note that the check here is intended to differentiate between own and
    // non-own properties, since the above lookup is not limited to own
    // properties. At present, this may not always do the right thing because
    // we often lie (sloppily) about where we found properties and set
    // desc.object() to |wrapper|. Once we fully fix our Xray prototype semantics,
    // this should work as intended.
    if (existing_desc.object() == wrapper && !existing_desc.configurable()) {
        // We have a non-configurable property. See if the caller is trying to
        // re-configure it in any way other than making it non-writable.
        if (existing_desc.isAccessorDescriptor() || desc.isAccessorDescriptor() ||
            (desc.hasEnumerable() && existing_desc.enumerable() != desc.enumerable()) ||
            (desc.hasWritable() && !existing_desc.writable() && desc.writable()))
        {
            // We should technically report non-configurability in strict mode, but
            // doing that via JSAPI used to be a lot of trouble. See bug 1135997.
            return result.succeed();
        }
        if (!existing_desc.writable()) {
            // Same as the above for non-writability.
            return result.succeed();
        }
    }

    bool defined = false;
    if (!Traits::singleton.defineProperty(cx, wrapper, id, desc, existing_desc, result, &defined)) {
        return false;
    }
    if (defined) {
        return true;
    }

    // Grab the relevant expando object.
    RootedObject target(cx, Traits::getTargetObject(wrapper));
    RootedObject expandoObject(cx, Traits::singleton.ensureExpandoObject(cx, wrapper,
                                                                         target));
    if (!expandoObject) {
        return false;
    }

    // We're placing an expando. The expando objects live in the target
    // compartment, so we need to enter it.
    JSAutoRealm ar(cx, target);
    JS_MarkCrossZoneId(cx, id);

    // Wrap the property descriptor for the target compartment.
    Rooted<PropertyDescriptor> wrappedDesc(cx, desc);
    if (!JS_WrapPropertyDescriptor(cx, &wrappedDesc)) {
        return false;
    }

    // Fix up Xray waivers.
    if (!RecreateLostWaivers(cx, desc.address(), &wrappedDesc)) {
        return false;
    }

    return JS_DefinePropertyById(cx, expandoObject, id, wrappedDesc, result);
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::ownPropertyKeys(JSContext* cx, HandleObject wrapper,
                                           AutoIdVector& props) const
{
    assertEnteredPolicy(cx, wrapper, JSID_VOID, BaseProxyHandler::ENUMERATE);
    return getPropertyKeys(cx, wrapper, JSITER_OWNONLY | JSITER_HIDDEN | JSITER_SYMBOLS, props);
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::delete_(JSContext* cx, HandleObject wrapper,
                                   HandleId id, ObjectOpResult& result) const
{
    assertEnteredPolicy(cx, wrapper, id, BaseProxyHandler::SET);

    // Check the expando object.
    RootedObject target(cx, Traits::getTargetObject(wrapper));
    RootedObject expando(cx);
    if (!Traits::singleton.getExpandoObject(cx, target, wrapper, &expando)) {
        return false;
    }

    if (expando) {
        JSAutoRealm ar(cx, expando);
        JS_MarkCrossZoneId(cx, id);
        bool hasProp;
        if (!JS_HasPropertyById(cx, expando, id, &hasProp)) {
            return false;
        }
        if (hasProp) {
            return JS_DeletePropertyById(cx, expando, id, result);
        }
    }

    return Traits::singleton.delete_(cx, wrapper, id, result);
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::get(JSContext* cx, HandleObject wrapper,
                               HandleValue receiver, HandleId id,
                               MutableHandleValue vp) const
{
    // Skip our Base if it isn't already ProxyHandler.

    // This uses getPropertyDescriptor for backward compatibility with
    // the old BaseProxyHandler::get implementation.
    Rooted<PropertyDescriptor> desc(cx);
    if (!getPropertyDescriptor(cx, wrapper, id, &desc)) {
        return false;
    }
    desc.assertCompleteIfFound();

    if (!desc.object()) {
        vp.setUndefined();
        return true;
    }

    // Everything after here follows [[Get]] for ordinary objects.
    if (desc.isDataDescriptor()) {
        vp.set(desc.value());
        return true;
    }

    MOZ_ASSERT(desc.isAccessorDescriptor());
    RootedObject getter(cx, desc.getterObject());

    if (!getter) {
        vp.setUndefined();
        return true;
    }

    return Call(cx, receiver, getter, HandleValueArray::empty(), vp);
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::set(JSContext* cx, HandleObject wrapper, HandleId id, HandleValue v,
                               HandleValue receiver, ObjectOpResult& result) const
{
    MOZ_CRASH("Shouldn't be called");
    return false;
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::has(JSContext* cx, HandleObject wrapper,
                               HandleId id, bool* bp) const
{
    // This uses getPropertyDescriptor for backward compatibility with
    // the old BaseProxyHandler::has implementation.
    Rooted<PropertyDescriptor> desc(cx);
    if (!getPropertyDescriptor(cx, wrapper, id, &desc)) {
        return false;
    }

    *bp = !!desc.object();
    return true;
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::hasOwn(JSContext* cx, HandleObject wrapper,
                                  HandleId id, bool* bp) const
{
    // Skip our Base if it isn't already ProxyHandler.
    return js::BaseProxyHandler::hasOwn(cx, wrapper, id, bp);
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::getOwnEnumerablePropertyKeys(JSContext* cx,
                                                        HandleObject wrapper,
                                                        AutoIdVector& props) const
{
    // Skip our Base if it isn't already ProxyHandler.
    return js::BaseProxyHandler::getOwnEnumerablePropertyKeys(cx, wrapper, props);
}

template <typename Base, typename Traits>
JSObject*
XrayWrapper<Base, Traits>::enumerate(JSContext* cx, HandleObject wrapper) const
{
    MOZ_CRASH("Shouldn't be called");
    return nullptr;
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::call(JSContext* cx, HandleObject wrapper, const JS::CallArgs& args) const
{
    assertEnteredPolicy(cx, wrapper, JSID_VOID, BaseProxyHandler::CALL);
    // Hard cast the singleton since SecurityWrapper doesn't have one.
    return Traits::call(cx, wrapper, args, Base::singleton);
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::construct(JSContext* cx, HandleObject wrapper, const JS::CallArgs& args) const
{
    assertEnteredPolicy(cx, wrapper, JSID_VOID, BaseProxyHandler::CALL);
    // Hard cast the singleton since SecurityWrapper doesn't have one.
    return Traits::construct(cx, wrapper, args, Base::singleton);
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::getBuiltinClass(JSContext* cx, JS::HandleObject wrapper, js::ESClass* cls) const
{
    return Traits::getBuiltinClass(cx, wrapper, Base::singleton, cls);
}

template <typename Base, typename Traits>
const char*
XrayWrapper<Base, Traits>::className(JSContext* cx, HandleObject wrapper) const
{
    return Traits::className(cx, wrapper, Base::singleton);
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::getPrototype(JSContext* cx, JS::HandleObject wrapper,
                                        JS::MutableHandleObject protop) const
{
    // We really only want this override for non-SecurityWrapper-inheriting
    // |Base|. But doing that statically with templates requires partial method
    // specializations (and therefore a helper class), which is all more trouble
    // than it's worth. Do a dynamic check.
    if (Base::hasSecurityPolicy()) {
        return Base::getPrototype(cx, wrapper, protop);
    }

    RootedObject target(cx, Traits::getTargetObject(wrapper));
    RootedObject expando(cx);
    if (!Traits::singleton.getExpandoObject(cx, target, wrapper, &expando)) {
        return false;
    }

    // We want to keep the Xray's prototype distinct from that of content, but
    // only if there's been a set. If there's not an expando, or the expando
    // slot is |undefined|, hand back the default proto, appropriately wrapped.

    if (expando) {
        RootedValue v(cx);
        { // Scope for JSAutoRealm
            JSAutoRealm ar(cx, expando);
            v = JS_GetReservedSlot(expando, JSSLOT_EXPANDO_PROTOTYPE);
        }
        if (!v.isUndefined()) {
            protop.set(v.toObjectOrNull());
            return JS_WrapObject(cx, protop);
        }
    }

    // Check our holder, and cache there if we don't have it cached already.
    RootedObject holder(cx, Traits::singleton.ensureHolder(cx, wrapper));
    if (!holder) {
        return false;
    }

    Value cached = js::GetReservedSlot(holder,
                                       Traits::HOLDER_SLOT_CACHED_PROTO);
    if (cached.isUndefined()) {
        if (!Traits::singleton.getPrototype(cx, wrapper, target, protop)) {
            return false;
        }

        js::SetReservedSlot(holder, Traits::HOLDER_SLOT_CACHED_PROTO,
                            ObjectOrNullValue(protop));
    } else {
        protop.set(cached.toObjectOrNull());
    }
    return true;
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::setPrototype(JSContext* cx, JS::HandleObject wrapper,
                                        JS::HandleObject proto, JS::ObjectOpResult& result) const
{
    // Do this only for non-SecurityWrapper-inheriting |Base|. See the comment
    // in getPrototype().
    if (Base::hasSecurityPolicy()) {
        return Base::setPrototype(cx, wrapper, proto, result);
    }

    RootedObject target(cx, Traits::getTargetObject(wrapper));
    RootedObject expando(cx, Traits::singleton.ensureExpandoObject(cx, wrapper, target));
    if (!expando) {
        return false;
    }

    // The expando lives in the target's realm, so do our installation there.
    JSAutoRealm ar(cx, target);

    RootedValue v(cx, ObjectOrNullValue(proto));
    if (!JS_WrapValue(cx, &v)) {
        return false;
    }
    JS_SetReservedSlot(expando, JSSLOT_EXPANDO_PROTOTYPE, v);
    return result.succeed();
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::getPrototypeIfOrdinary(JSContext* cx, JS::HandleObject wrapper,
                                                  bool* isOrdinary,
                                                  JS::MutableHandleObject protop) const
{
    // We want to keep the Xray's prototype distinct from that of content, but
    // only if there's been a set.  This different-prototype-over-time behavior
    // means that the [[GetPrototypeOf]] trap *can't* be ECMAScript's ordinary
    // [[GetPrototypeOf]].  This also covers cross-origin Window behavior that
    // per <https://html.spec.whatwg.org/multipage/browsers.html#windowproxy-getprototypeof>
    // must be non-ordinary.
    *isOrdinary = false;
    return true;
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::setImmutablePrototype(JSContext* cx, JS::HandleObject wrapper,
                                                 bool* succeeded) const
{
    // For now, lacking an obvious place to store a bit, prohibit making an
    // Xray's [[Prototype]] immutable.  We can revisit this (or maybe give all
    // Xrays immutable [[Prototype]], because who does this, really?) later if
    // necessary.
    *succeeded = false;
    return true;
}

template <typename Base, typename Traits>
bool
XrayWrapper<Base, Traits>::getPropertyKeys(JSContext* cx, HandleObject wrapper, unsigned flags,
                                           AutoIdVector& props) const
{
    assertEnteredPolicy(cx, wrapper, JSID_VOID, BaseProxyHandler::ENUMERATE);

    // Enumerate expando properties first. Note that the expando object lives
    // in the target compartment.
    RootedObject target(cx, Traits::getTargetObject(wrapper));
    RootedObject expando(cx);
    if (!Traits::singleton.getExpandoObject(cx, target, wrapper, &expando)) {
        return false;
    }

    if (expando) {
        JSAutoRealm ar(cx, expando);
        if (!js::GetPropertyKeys(cx, expando, flags, &props)) {
            return false;
        }
    }
    for (size_t i = 0; i < props.length(); ++i) {
        JS_MarkCrossZoneId(cx, props[i]);
    }

    return Traits::singleton.enumerateNames(cx, wrapper, flags, props);
}

/*
 * The Permissive / Security variants should be used depending on whether the
 * compartment of the wrapper is guranteed to subsume the compartment of the
 * wrapped object (i.e. - whether it is safe from a security perspective to
 * unwrap the wrapper).
 */

template<typename Base, typename Traits>
const xpc::XrayWrapper<Base, Traits>
xpc::XrayWrapper<Base, Traits>::singleton(0);

template class PermissiveXrayDOM;
template class SecurityXrayDOM;
template class PermissiveXrayJS;
template class PermissiveXrayOpaque;

/*
 * This callback is used by the JS engine to test if a proxy handler is for a
 * cross compartment xray with no security requirements.
 */
static bool
IsCrossCompartmentXrayCallback(const js::BaseProxyHandler* handler)
{
    return handler == &PermissiveXrayDOM::singleton;
}

js::XrayJitInfo gXrayJitInfo = {
    IsCrossCompartmentXrayCallback,
    CompartmentHasExclusiveExpandos,
    JSSLOT_XRAY_HOLDER,
    XrayTraits::HOLDER_SLOT_EXPANDO,
    JSSLOT_EXPANDO_PROTOTYPE
};

} // namespace xpc