C++ PropertySlot::disableCaching方法代码示例

// Property access sequence is:
// (1) indexed properties,
// (2) regular own properties,
// (3) named properties (in fact, these shouldn't be on the window, should be on the NPO).
bool JSDOMWindow::getOwnPropertySlotByIndex(JSObject* object, ExecState* state, unsigned index, PropertySlot& slot)
{
    auto* thisObject = jsCast<JSDOMWindow*>(object);
    auto* frame = thisObject->wrapped().frame();

    // Indexed getters take precendence over regular properties, so caching would be invalid.
    slot.disableCaching();

    // (1) First, indexed properties.
    // These are also allowed cross-orgin, so come before the access check.
    if (frame && index < frame->tree().scopedChildCount()) {
        slot.setValue(thisObject, ReadOnly | DontDelete | DontEnum, toJS(state, frame->tree().scopedChild(index)->document()->domWindow()));
        return true;
    }

    // Hand off all cross-domain/frameless access to jsDOMWindowGetOwnPropertySlotRestrictedAccess.
    String errorMessage;
    if (!frame || !BindingSecurity::shouldAllowAccessToDOMWindow(*state, thisObject->wrapped(), errorMessage))
        return jsDOMWindowGetOwnPropertySlotRestrictedAccess(thisObject, frame, state, Identifier::from(state, index), slot, errorMessage);

    // (2) Regular own properties.
    return Base::getOwnPropertySlotByIndex(thisObject, state, index, slot);
}

//.........这里部分代码省略.........
    } else if (propertyName == exec->propertyNames().close) {
        if (!allowsAccess) {
            slot.setCustom(thisObject, ReadOnly | DontDelete | DontEnum, nonCachingStaticFunctionGetter<jsDOMWindowPrototypeFunctionClose, 0>);
            return true;
        }
    } else if (propertyName == exec->propertyNames().focus) {
        if (!allowsAccess) {
            slot.setCustom(thisObject, ReadOnly | DontDelete | DontEnum, nonCachingStaticFunctionGetter<jsDOMWindowPrototypeFunctionFocus, 0>);
            return true;
        }
    } else if (propertyName == exec->propertyNames().postMessage) {
        if (!allowsAccess) {
            slot.setCustom(thisObject, ReadOnly | DontDelete | DontEnum, nonCachingStaticFunctionGetter<jsDOMWindowPrototypeFunctionPostMessage, 2>);
            return true;
        }
    } else if (propertyName == exec->propertyNames().showModalDialog) {
        if (!DOMWindow::canShowModalDialog(thisObject->impl().frame())) {
            slot.setUndefined();
            return true;
        }
    } else if (propertyName == exec->propertyNames().toString) {
        // Allow access to toString() cross-domain, but always Object.prototype.toString.
        if (!allowsAccess) {
            slot.setCustom(thisObject, ReadOnly | DontDelete | DontEnum, objectToStringFunctionGetter);
            return true;
        }
    }

    const HashTableValue* entry = JSDOMWindow::info()->propHashTable(exec)->entry(exec, propertyName);
    if (entry) {
        slot.setCacheableCustom(thisObject, allowsAccess ? entry->attributes() : ReadOnly | DontDelete | DontEnum, entry->propertyGetter());
        return true;
    }

#if ENABLE(USER_MESSAGE_HANDLERS)
    if (propertyName == exec->propertyNames().webkit && thisObject->impl().shouldHaveWebKitNamespaceForWorld(thisObject->world())) {
        slot.setCacheableCustom(thisObject, allowsAccess ? DontDelete | ReadOnly : ReadOnly | DontDelete | DontEnum, jsDOMWindowWebKit);
        return true;
    }
#endif

    // Do prototype lookup early so that functions and attributes in the prototype can have
    // precedence over the index and name getters.  
    JSValue proto = thisObject->prototype();
    if (proto.isObject()) {
        if (asObject(proto)->getPropertySlot(exec, propertyName, slot)) {
            if (!allowsAccess) {
                thisObject->printErrorMessage(errorMessage);
                slot.setUndefined();
            }
            return true;
        }
    }

    // After this point it is no longer valid to cache any results because of
    // the impure nature of the property accesses which follow. We can move this 
    // statement further down when we add ways to mitigate these impurities with, 
    // for example, watchpoints.
    slot.disableCaching();

    // Check for child frames by name before built-in properties to
    // match Mozilla. This does not match IE, but some sites end up
    // naming frames things that conflict with window properties that
    // are in Moz but not IE. Since we have some of these, we have to do
    // it the Moz way.
    if (thisObject->impl().frame()->tree().scopedChild(propertyNameToAtomicString(propertyName))) {
        slot.setCustom(thisObject, ReadOnly | DontDelete | DontEnum, childFrameGetter);
        return true;
    }

    // FIXME: Search the whole frame hierarchy somewhere around here.
    // We need to test the correct priority order.

    // allow window[1] or parent[1] etc. (#56983)
    unsigned i = propertyName.asIndex();
    if (i < thisObject->impl().frame()->tree().scopedChildCount()) {
        ASSERT(i != PropertyName::NotAnIndex);
        slot.setValue(thisObject, ReadOnly | DontDelete | DontEnum,
            toJS(exec, thisObject->impl().frame()->tree().scopedChild(i)->document()->domWindow()));
        return true;
    }

    if (!allowsAccess) {
        thisObject->printErrorMessage(errorMessage);
        slot.setUndefined();
        return true;
    }

    // Allow shortcuts like 'Image1' instead of document.images.Image1
    Document* document = thisObject->impl().frame()->document();
    if (document->isHTMLDocument()) {
        AtomicStringImpl* atomicPropertyName = findAtomicString(propertyName);
        if (atomicPropertyName && toHTMLDocument(document)->hasWindowNamedItem(*atomicPropertyName)) {
            slot.setCustom(thisObject, ReadOnly | DontDelete | DontEnum, namedItemGetter);
            return true;
        }
    }

    return Base::getOwnPropertySlot(thisObject, exec, propertyName, slot);
}