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cc633123ca
`<iframe>` and `<img>` tags share the same spec for several aspects of lazy-loading: how the `loading` attribute works, the "will lazy load element" steps, and a member for storing the lazy-load resumption steps. So let's share the implementation by using a base class. This mostly involves moving things around. However, we also change the `start_intersection_observing_a_lazy_loading_element()` method to take a LazyLoadingElement, and operate on one, instead of always casting to HTMLImageElement. We do unfortunately have to do some shenanigans to make the cast work, by adding a virtual function stub in DOM::Element.
91 lines
3.7 KiB
C++
91 lines
3.7 KiB
C++
/*
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* Copyright (c) 2018-2023, Andreas Kling <kling@serenityos.org>
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* Copyright (c) 2023, Sam Atkins <atkinssj@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <LibWeb/Forward.h>
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#include <LibWeb/HTML/AttributeNames.h>
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namespace Web::HTML {
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// Lazy-loaded elements should invoke this macro to inject overridden LazyLoadingElement methods.
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#define LAZY_LOADING_ELEMENT(ElementClass) \
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private: \
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virtual JS::GCPtr<JS::HeapFunction<void()>> take_lazy_load_resumption_steps(Badge<DOM::Document>) override \
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{ \
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return take_lazy_load_resumption_steps_internal(); \
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} \
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\
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virtual bool is_lazy_loading() const override { return true; }
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enum class LazyLoading {
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Lazy,
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Eager,
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};
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template<typename T>
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class LazyLoadingElement {
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public:
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// https://html.spec.whatwg.org/multipage/urls-and-fetching.html#lazy-loading-attributes
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[[nodiscard]] LazyLoading lazy_loading_attribute() const
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{
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auto& element = static_cast<T const&>(*this);
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auto value = element.attribute(HTML::AttributeNames::loading);
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if (value.has_value() && value->equals_ignoring_ascii_case("lazy"sv))
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return LazyLoading::Lazy;
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return LazyLoading::Eager;
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}
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// https://html.spec.whatwg.org/multipage/urls-and-fetching.html#will-lazy-load-element-steps
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[[nodiscard]] bool will_lazy_load_element() const
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{
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auto& element = static_cast<T const&>(*this);
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// 1. If scripting is disabled for element, then return false.
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// Spec Note: This is an anti-tracking measure, because if a user agent supported lazy loading when scripting is
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// disabled, it would still be possible for a site to track a user's approximate scroll position throughout
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// a session, by strategically placing images in a page's markup such that a server can track how many
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// images are requested and when.
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if (element.is_scripting_disabled())
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return false;
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// 2. If element's lazy loading attribute is in the Lazy state, then return true.
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// 3. Return false.
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return lazy_loading_attribute() == LazyLoading::Lazy;
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}
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void set_lazy_load_resumption_steps(Function<void()> steps)
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{
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auto& element = static_cast<T&>(*this);
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m_lazy_load_resumption_steps = JS::create_heap_function(element.vm().heap(), move(steps));
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}
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void visit_lazy_loading_element(JS::Cell::Visitor& visitor)
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{
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visitor.visit(m_lazy_load_resumption_steps);
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}
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protected:
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LazyLoadingElement() = default;
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virtual ~LazyLoadingElement() = default;
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JS::GCPtr<JS::HeapFunction<void()>> take_lazy_load_resumption_steps_internal()
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{
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auto lazy_load_resumption_steps = m_lazy_load_resumption_steps;
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m_lazy_load_resumption_steps = nullptr;
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return lazy_load_resumption_steps;
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}
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private:
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// https://html.spec.whatwg.org/multipage/urls-and-fetching.html#lazy-load-resumption-steps
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// Each img and iframe element has associated lazy load resumption steps, initially null.
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JS::GCPtr<JS::HeapFunction<void()>> m_lazy_load_resumption_steps;
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};
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}
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