WebContent+WebDriver: Make the element locator endpoints asynchronous

We currently spin the event loop to wait for the specified element to
become available. As we've seen with other endpoints, this can result
in dead locks if another web component also spins the event loop.

This patch makes the locator implementations asynchronous.

Userland/Services/WebContent/WebDriverConnection.cpp

@@ -203,6 +203,7 @@ void WebDriverConnection::visit_edges(JS::Cell::Visitor& visitor)
     visitor.visit(m_current_browsing_context);
     visitor.visit(m_current_parent_browsing_context);
     visitor.visit(m_current_top_level_browsing_context);
+    visitor.visit(m_element_locator);
     visitor.visit(m_action_executor);
     visitor.visit(m_document_observer);
     visitor.visit(m_navigation_observer);
@@ -810,29 +811,41 @@ Messages::WebDriverClient::ConsumeUserActivationResponse WebDriverConnection::co
     return consume;
 }
 
+static Web::WebDriver::Response extract_first_element(Web::WebDriver::Response result)
+{
+    auto array = TRY(result);
+    VERIFY(array.is_array());
+
+    if (!array.as_array().is_empty())
+        return array.as_array().take(0);
+
+    return Web::WebDriver::Error::from_code(Web::WebDriver::ErrorCode::NoSuchElement, "The requested element does not exist"sv);
+}
+
 // 12.3.2 Find Element, https://w3c.github.io/webdriver/#dfn-find-element
 Messages::WebDriverClient::FindElementResponse WebDriverConnection::find_element(JsonValue const& payload)
 {
-    // 1. Let location strategy be the result of getting a property called "using".
+    // 1. Let location strategy be the result of getting a property named "using" from parameters.
     auto location_strategy_string = TRY(Web::WebDriver::get_property(payload, "using"sv));
     auto location_strategy = Web::WebDriver::location_strategy_from_string(location_strategy_string);
 
-    // 2. If location strategy is not present as a keyword in the table of location strategies, return error with error code invalid argument.
+    // 2. If location strategy is not present as a keyword in the table of location strategies, return error with error
+    //    code invalid argument.
     if (!location_strategy.has_value())
         return Web::WebDriver::Error::from_code(Web::WebDriver::ErrorCode::InvalidArgument, ByteString::formatted("Location strategy '{}' is invalid", location_strategy_string));
 
-    // 3. Let selector be the result of getting a property called "value".
+    // 3. Let selector be the result of getting a property named "value" from parameters.
     // 4. If selector is undefined, return error with error code invalid argument.
     auto selector = TRY(Web::WebDriver::get_property(payload, "value"sv));
 
-    // 5. If the current browsing context is no longer open, return error with error code no such window.
+    // 5. If session's current browsing context is no longer open, return error with error code no such window.
     TRY(ensure_current_browsing_context_is_open());
 
-    // 6. Handle any user prompts and return its value if it is an error.
+    // 6. Try to handle any user prompts with session.
     TRY(handle_any_user_prompts());
 
-    auto start_node_getter = [this]() -> StartNodeGetter::ReturnType {
+    auto get_start_node = JS::create_heap_function(current_browsing_context().heap(), [this]() -> ErrorOr<JS::NonnullGCPtr<Web::DOM::ParentNode>, Web::WebDriver::Error> {
-        // 7. Let start node be the current browsing context’s document element.
+        // 7. Let start node be session's current browsing context's document element.
         auto* start_node = current_browsing_context().active_document();
 
         // 8. If start node is null, return error with error code no such element.
@@ -840,41 +853,41 @@ Messages::WebDriverClient::FindElementResponse WebDriverConnection::find_element
             return Web::WebDriver::Error::from_code(Web::WebDriver::ErrorCode::NoSuchElement, "document element does not exist"sv);
 
         return *start_node;
-    };
+    });
-
-    // 9. Let result be the result of trying to Find with start node, location strategy, and selector.
-    auto result = TRY(find(move(start_node_getter), *location_strategy, selector));
 
+    // 9. Let result be the result of trying to Find with session, start node, location strategy, and selector.
+    find(*location_strategy, move(selector), get_start_node, JS::create_heap_function(current_browsing_context().heap(), [this](Web::WebDriver::Response result) {
         // 10. If result is empty, return error with error code no such element. Otherwise, return the first element of result.
-    if (result.is_empty())
+        async_find_elements_complete(extract_first_element(move(result)));
-        return Web::WebDriver::Error::from_code(Web::WebDriver::ErrorCode::NoSuchElement, "The requested element does not exist"sv);
+    }));
 
-    return result.take(0);
+    return JsonValue {};
 }
 
 // 12.3.3 Find Elements, https://w3c.github.io/webdriver/#dfn-find-elements
 Messages::WebDriverClient::FindElementsResponse WebDriverConnection::find_elements(JsonValue const& payload)
 {
-    // 1. Let location strategy be the result of getting a property called "using".
+    // 1. Let location strategy be the result of getting a property named "using" from parameters.
     auto location_strategy_string = TRY(Web::WebDriver::get_property(payload, "using"sv));
     auto location_strategy = Web::WebDriver::location_strategy_from_string(location_strategy_string);
 
-    // 2. If location strategy is not present as a keyword in the table of location strategies, return error with error code invalid argument.
+    // 2. If location strategy is not present as a keyword in the table of location strategies, return error with error
+    //    code invalid argument.
     if (!location_strategy.has_value())
         return Web::WebDriver::Error::from_code(Web::WebDriver::ErrorCode::InvalidArgument, ByteString::formatted("Location strategy '{}' is invalid", location_strategy_string));
 
-    // 3. Let selector be the result of getting a property called "value".
+    // 3. Let selector be the result of getting a property named "value" from parameters.
     // 4. If selector is undefined, return error with error code invalid argument.
     auto selector = TRY(Web::WebDriver::get_property(payload, "value"sv));
 
-    // 5. If the current browsing context is no longer open, return error with error code no such window.
+    // 5. If session's current browsing context is no longer open, return error with error code no such window.
     TRY(ensure_current_browsing_context_is_open());
 
-    // 6. Handle any user prompts and return its value if it is an error.
+    // 6. Try to handle any user prompts with session.
     TRY(handle_any_user_prompts());
 
-    auto start_node_getter = [this]() -> StartNodeGetter::ReturnType {
+    auto get_start_node = JS::create_heap_function(current_browsing_context().heap(), [this]() -> ErrorOr<JS::NonnullGCPtr<Web::DOM::ParentNode>, Web::WebDriver::Error> {
-        // 7. Let start node be the current browsing context’s document element.
+        // 7. Let start node be session's current browsing context's document element.
         auto* start_node = current_browsing_context().active_document();
 
         // 8. If start node is null, return error with error code no such element.
@@ -882,16 +895,20 @@ Messages::WebDriverClient::FindElementsResponse WebDriverConnection::find_elemen
             return Web::WebDriver::Error::from_code(Web::WebDriver::ErrorCode::NoSuchElement, "document element does not exist"sv);
 
         return *start_node;
-    };
+    });
 
-    // 9. Return the result of trying to Find with start node, location strategy, and selector.
+    // 9. Return the result of trying to Find with session, start node, location strategy, and selector.
-    return TRY(find(move(start_node_getter), *location_strategy, selector));
+    find(*location_strategy, move(selector), get_start_node, JS::create_heap_function(current_browsing_context().heap(), [this](Web::WebDriver::Response result) {
+        async_find_elements_complete(move(result));
+    }));
+
+    return JsonValue {};
 }
 
 // 12.3.4 Find Element From Element, https://w3c.github.io/webdriver/#dfn-find-element-from-element
 Messages::WebDriverClient::FindElementFromElementResponse WebDriverConnection::find_element_from_element(JsonValue const& payload, String const& element_id)
 {
-    // 1. Let location strategy be the result of getting a property called "using".
+    // 1. Let location strategy be the result of getting a property named "using" from parameters.
     auto location_strategy_string = TRY(Web::WebDriver::get_property(payload, "using"sv));
     auto location_strategy = Web::WebDriver::location_strategy_from_string(location_strategy_string);
 
@@ -899,35 +916,34 @@ Messages::WebDriverClient::FindElementFromElementResponse WebDriverConnection::f
     if (!location_strategy.has_value())
         return Web::WebDriver::Error::from_code(Web::WebDriver::ErrorCode::InvalidArgument, ByteString::formatted("Location strategy '{}' is invalid", location_strategy_string));
 
-    // 3. Let selector be the result of getting a property called "value".
+    // 3. Let selector be the result of getting a property named "value" from parameters.
     // 4. If selector is undefined, return error with error code invalid argument.
     auto selector = TRY(Web::WebDriver::get_property(payload, "value"sv));
 
-    // 5. If the current browsing context is no longer open, return error with error code no such window.
+    // 5. If session's current browsing context is no longer open, return error with error code no such window.
     TRY(ensure_current_browsing_context_is_open());
 
-    // 6. Handle any user prompts and return its value if it is an error.
+    // 6. Try to handle any user prompts with session.
     TRY(handle_any_user_prompts());
 
-    auto start_node_getter = [&]() -> StartNodeGetter::ReturnType {
+    auto get_start_node = JS::create_heap_function(current_browsing_context().heap(), [this, element_id]() -> ErrorOr<JS::NonnullGCPtr<Web::DOM::ParentNode>, Web::WebDriver::Error> {
-        // 7. Let start node be the result of trying to get a known connected element with url variable element id.
+        // 7. Let start node be the result of trying to get a known element with session and URL variables["element id"].
-        return TRY(Web::WebDriver::get_known_element(current_browsing_context(), element_id));
+        return Web::WebDriver::get_known_element(current_browsing_context(), element_id);
-    };
+    });
-
-    // 8. Let result be the value of trying to Find with start node, location strategy, and selector.
-    auto result = TRY(find(move(start_node_getter), *location_strategy, selector));
 
+    // 8. Let result be the value of trying to Find with session, start node, location strategy, and selector.
+    find(*location_strategy, move(selector), get_start_node, JS::create_heap_function(current_browsing_context().heap(), [this](Web::WebDriver::Response result) {
         // 9. If result is empty, return error with error code no such element. Otherwise, return the first element of result.
-    if (result.is_empty())
+        async_find_elements_complete(extract_first_element(move(result)));
-        return Web::WebDriver::Error::from_code(Web::WebDriver::ErrorCode::NoSuchElement, "The requested element does not exist"sv);
+    }));
 
-    return result.take(0);
+    return JsonValue {};
 }
 
 // 12.3.5 Find Elements From Element, https://w3c.github.io/webdriver/#dfn-find-elements-from-element
 Messages::WebDriverClient::FindElementsFromElementResponse WebDriverConnection::find_elements_from_element(JsonValue const& payload, String const& element_id)
 {
-    // 1. Let location strategy be the result of getting a property called "using".
+    // 1. Let location strategy be the result of getting a property named "using" from parameters.
     auto location_strategy_string = TRY(Web::WebDriver::get_property(payload, "using"sv));
     auto location_strategy = Web::WebDriver::location_strategy_from_string(location_strategy_string);
 
@@ -935,23 +951,27 @@ Messages::WebDriverClient::FindElementsFromElementResponse WebDriverConnection::
     if (!location_strategy.has_value())
         return Web::WebDriver::Error::from_code(Web::WebDriver::ErrorCode::InvalidArgument, ByteString::formatted("Location strategy '{}' is invalid", location_strategy_string));
 
-    // 3. Let selector be the result of getting a property called "value".
+    // 3. Let selector be the result of getting a property named "value" from parameters.
     // 4. If selector is undefined, return error with error code invalid argument.
     auto selector = TRY(Web::WebDriver::get_property(payload, "value"sv));
 
-    // 5. If the current browsing context is no longer open, return error with error code no such window.
+    // 5. If session's current browsing context is no longer open, return error with error code no such window.
     TRY(ensure_current_browsing_context_is_open());
 
-    // 6. Handle any user prompts and return its value if it is an error.
+    // 6. Try to handle any user prompts with session.
     TRY(handle_any_user_prompts());
 
-    auto start_node_getter = [&]() -> StartNodeGetter::ReturnType {
+    auto get_start_node = JS::create_heap_function(current_browsing_context().heap(), [this, element_id]() -> ErrorOr<JS::NonnullGCPtr<Web::DOM::ParentNode>, Web::WebDriver::Error> {
-        // 7. Let start node be the result of trying to get a known connected element with url variable element id.
+        // 7. Let start node be the result of trying to get a known element with session and URL variables["element id"].
-        return TRY(Web::WebDriver::get_known_element(current_browsing_context(), element_id));
+        return Web::WebDriver::get_known_element(current_browsing_context(), element_id);
-    };
+    });
 
-    // 8. Return the result of trying to Find with start node, location strategy, and selector.
+    // 8. Return the result of trying to Find with session, start node, location strategy, and selector.
-    return TRY(find(move(start_node_getter), *location_strategy, selector));
+    find(*location_strategy, move(selector), get_start_node, JS::create_heap_function(current_browsing_context().heap(), [this](Web::WebDriver::Response result) {
+        async_find_elements_complete(move(result));
+    }));
+
+    return JsonValue {};
 }
 
 // 12.3.6 Find Element From Shadow Root, https://w3c.github.io/webdriver/#find-element-from-shadow-root
@@ -969,25 +989,24 @@ Messages::WebDriverClient::FindElementFromShadowRootResponse WebDriverConnection
     // 4. If selector is undefined, return error with error code invalid argument.
     auto selector = TRY(Web::WebDriver::get_property(payload, "value"sv));
 
-    // 5. If the current browsing context is no longer open, return error with error code no such window.
+    // 5. If the ssession's current browsing context is no longer open, return error with error code no such window.
     TRY(ensure_current_browsing_context_is_open());
 
     // 6. Handle any user prompts and return its value if it is an error.
     TRY(handle_any_user_prompts());
 
-    auto start_node_getter = [&]() -> StartNodeGetter::ReturnType {
+    auto get_start_node = JS::create_heap_function(current_browsing_context().heap(), [this, shadow_id]() -> ErrorOr<JS::NonnullGCPtr<Web::DOM::ParentNode>, Web::WebDriver::Error> {
-        // 7. Let start node be the result of trying to get a known shadow root with url variable shadow id.
+        // 7. Let start node be the result of trying to get a known shadow root with session and URL variables["shadow id"].
-        return TRY(Web::WebDriver::get_known_shadow_root(shadow_id));
+        return Web::WebDriver::get_known_shadow_root(current_browsing_context(), shadow_id);
-    };
+    });
-
-    // 8. Let result be the value of trying to Find with start node, location strategy, and selector.
-    auto result = TRY(find(move(start_node_getter), *location_strategy, selector));
 
+    // 8. Let result be the value of trying to Find with session, start node, location strategy, and selector.
+    find(*location_strategy, move(selector), get_start_node, JS::create_heap_function(current_browsing_context().heap(), [this](Web::WebDriver::Response result) {
         // 9. If result is empty, return error with error code no such element. Otherwise, return the first element of result.
-    if (result.is_empty())
+        async_find_elements_complete(extract_first_element(move(result)));
-        return Web::WebDriver::Error::from_code(Web::WebDriver::ErrorCode::NoSuchElement, "The requested element does not exist"sv);
+    }));
 
-    return result.take(0);
+    return JsonValue {};
 }
 
 // 12.3.7 Find Elements From Shadow Root, https://w3c.github.io/webdriver/#find-elements-from-shadow-root
@@ -1005,19 +1024,23 @@ Messages::WebDriverClient::FindElementsFromShadowRootResponse WebDriverConnectio
     // 4. If selector is undefined, return error with error code invalid argument.
     auto selector = TRY(Web::WebDriver::get_property(payload, "value"sv));
 
-    // 5. If the current browsing context is no longer open, return error with error code no such window.
+    // 5. If session's current browsing context is no longer open, return error with error code no such window.
     TRY(ensure_current_browsing_context_is_open());
 
     // 6. Handle any user prompts and return its value if it is an error.
     TRY(handle_any_user_prompts());
 
-    auto start_node_getter = [&]() -> StartNodeGetter::ReturnType {
+    auto get_start_node = JS::create_heap_function(current_browsing_context().heap(), [this, shadow_id]() -> ErrorOr<JS::NonnullGCPtr<Web::DOM::ParentNode>, Web::WebDriver::Error> {
-        // 7. Let start node be the result of trying to get a known shadow root with url variable shadow id.
+        // 7. Let start node be the result of trying to get a known shadow root with session and URL variables["shadow id"].
-        return TRY(Web::WebDriver::get_known_shadow_root(shadow_id));
+        return Web::WebDriver::get_known_shadow_root(current_browsing_context(), shadow_id);
-    };
+    });
 
-    // 8. Return the result of trying to Find with start node, location strategy, and selector.
+    // 8. Return the result of trying to Find with session, start node, location strategy, and selector.
-    return TRY(find(move(start_node_getter), *location_strategy, selector));
+    find(*location_strategy, move(selector), get_start_node, JS::create_heap_function(current_browsing_context().heap(), [this](Web::WebDriver::Response result) {
+        async_find_elements_complete(move(result));
+    }));
+
+    return JsonValue {};
 }
 
 // 12.3.8 Get Active Element, https://w3c.github.io/webdriver/#get-active-element
@@ -1043,13 +1066,13 @@ Messages::WebDriverClient::GetActiveElementResponse WebDriverConnection::get_act
 // 12.3.9 Get Element Shadow Root, https://w3c.github.io/webdriver/#get-element-shadow-root
 Messages::WebDriverClient::GetElementShadowRootResponse WebDriverConnection::get_element_shadow_root(String const& element_id)
 {
-    // 1. If the current browsing context is no longer open, return error with error code no such window.
+    // 1. If session's current browsing context is no longer open, return error with error code no such window.
     TRY(ensure_current_browsing_context_is_open());
 
     // 2. Handle any user prompts and return its value if it is an error.
     TRY(handle_any_user_prompts());
 
-    // 3. Let element be the result of trying to get a known connected element with url variable element id.
+    // 3. Let element be the result of trying to get a known element with session and URL variables[element id].
     auto element = TRY(Web::WebDriver::get_known_element(current_browsing_context(), element_id));
 
     // 4. Let shadow root be element's shadow root.
@@ -1059,8 +1082,8 @@ Messages::WebDriverClient::GetElementShadowRootResponse WebDriverConnection::get
     if (!shadow_root)
         return Web::WebDriver::Error::from_code(Web::WebDriver::ErrorCode::NoSuchShadowRoot, ByteString::formatted("Element with ID '{}' does not have a shadow root", element_id));
 
-    // 6. Let serialized be the shadow root reference object for shadow root.
+    // 6. Let serialized be the shadow root reference object for session and shadow root.
-    auto serialized = Web::WebDriver::shadow_root_reference_object(*shadow_root);
+    auto serialized = Web::WebDriver::shadow_root_reference_object(current_browsing_context(), *shadow_root);
 
     // 7. Return success with data serialized.
     return serialized;
@@ -2587,54 +2610,126 @@ void WebDriverConnection::wait_for_visibility_state(JS::NonnullGCPtr<JS::HeapFun
     }));
 }
 
-// https://w3c.github.io/webdriver/#dfn-find
+class ElementLocator final : public JS::Cell {
-// FIXME: Update this AO to the latest spec steps.
+    JS_CELL(ElementLocator, JS::Cell);
-ErrorOr<JsonArray, Web::WebDriver::Error> WebDriverConnection::find(StartNodeGetter&& start_node_getter, Web::WebDriver::LocationStrategy using_, StringView value)
+    JS_DECLARE_ALLOCATOR(ElementLocator);
-{
-    // 1. Let end time be the current time plus the session implicit wait timeout.
-    auto end_time = MonotonicTime::now() + AK::Duration::from_milliseconds(static_cast<i64>(m_timeouts_configuration.implicit_wait_timeout.value_or(0)));
 
-    // 2. Let location strategy be equal to using.
+public:
-    auto location_strategy = using_;
+    ElementLocator(
+        Web::HTML::BrowsingContext const& browsing_context,
+        Web::WebDriver::LocationStrategy location_strategy,
+        ByteString selector,
+        WebDriverConnection::GetStartNode get_start_node,
+        WebDriverConnection::OnFindComplete on_complete,
+        JS::NonnullGCPtr<Web::WebDriver::HeapTimer> timer)
+        : m_browsing_context(browsing_context)
+        , m_location_strategy(location_strategy)
+        , m_selector(move(selector))
+        , m_get_start_node(get_start_node)
+        , m_on_complete(on_complete)
+        , m_timer(timer)
+    {
+    }
 
-    // 3. Let selector be equal to value.
+    void search_for_element()
-    auto selector = value;
+    {
+        if (auto result = perform_search(); result.has_value()) {
+            m_on_complete->function()(result.release_value());
+            return;
+        }
 
-    ErrorOr<JS::GCPtr<Web::DOM::NodeList>, Web::WebDriver::Error> maybe_elements { nullptr };
+        if (m_timer->is_timed_out())
+            return;
 
-    auto try_to_find_element = [&]() -> decltype(maybe_elements) {
+        Web::HTML::queue_a_task(Web::HTML::Task::Source::Unspecified, nullptr, nullptr, JS::create_heap_function(heap(), [this]() {
-        // 4. Let elements returned be the result of trying to call the relevant element location strategy with arguments start node, and selector.
+            search_for_element();
-        auto elements = Web::WebDriver::invoke_location_strategy(location_strategy, *TRY(start_node_getter()), selector);
-
-        // 5. If a DOMException, SyntaxError, XPathException, or other error occurs during the execution of the element location strategy, return error invalid selector.
-        if (elements.is_error())
-            return Web::WebDriver::Error::from_code(Web::WebDriver::ErrorCode::InvalidSelector, ByteString::formatted("The location strategy could not finish: {}", elements.error().message));
-
-        return elements.release_value();
-    };
-
-    Web::Platform::EventLoopPlugin::the().spin_until(JS::create_heap_function(current_top_level_browsing_context()->heap(), [&]() {
-        maybe_elements = try_to_find_element();
-        if (maybe_elements.is_error())
-            return true;
-
-        // 6. If elements returned is empty and the current time is less than end time return to step 4. Otherwise, continue to the next step.
-        return maybe_elements.value()->length() != 0 || MonotonicTime::now() >= end_time;
         }));
+    }
 
-    auto elements = TRY(maybe_elements);
+private:
-    VERIFY(elements);
+    Optional<Web::WebDriver::Response> perform_search()
+    {
+        // 1. Set elements returned to the result of trying to call the relevant element location strategy with arguments
+        //    start node, and selector.
+        auto maybe_elements = Web::WebDriver::invoke_location_strategy(m_location_strategy, TRY(m_get_start_node->function()()), m_selector);
 
-    // 7. Let result be an empty JSON List.
+        // 2. If a DOMException, SyntaxError, XPathException, or other error occurs during the execution of the element
+        //    location strategy, return error invalid selector.
+        if (maybe_elements.is_error())
+            return Web::WebDriver::Error::from_code(Web::WebDriver::ErrorCode::InvalidSelector, ByteString::formatted("The location strategy could not finish: {}", maybe_elements.error().message));
+
+        if (auto elements = maybe_elements.release_value(); elements->length() > 0) {
+            // 8. Let result be an empty List.
             JsonArray result;
             result.ensure_capacity(elements->length());
 
-    // 8. For each element in elements returned, append the web element reference object for element, to result.
+            // 9. For each element in elements returned, append the web element reference object for session and element,
+            //    to result.
             for (size_t i = 0; i < elements->length(); ++i)
-        TRY(result.append(Web::WebDriver::web_element_reference_object(current_browsing_context(), *elements->item(i))));
+                result.must_append(Web::WebDriver::web_element_reference_object(m_browsing_context, *elements->item(i)));
 
-    // 9. Return success with data result.
+            // 10. Return success with data result.
-    return result;
+            return JsonValue { move(result) };
+        }
+
+        return {};
+    }
+
+    virtual void visit_edges(Cell::Visitor& visitor) override
+    {
+        Base::visit_edges(visitor);
+        visitor.visit(m_browsing_context);
+        visitor.visit(m_get_start_node);
+        visitor.visit(m_on_complete);
+        visitor.visit(m_timer);
+    }
+
+    JS::NonnullGCPtr<Web::HTML::BrowsingContext const> m_browsing_context;
+
+    Web::WebDriver::LocationStrategy m_location_strategy;
+    ByteString m_selector;
+
+    WebDriverConnection::GetStartNode m_get_start_node;
+    WebDriverConnection::OnFindComplete m_on_complete;
+
+    JS::NonnullGCPtr<Web::WebDriver::HeapTimer> m_timer;
+};
+
+JS_DEFINE_ALLOCATOR(ElementLocator);
+
+// https://w3c.github.io/webdriver/#dfn-find
+void WebDriverConnection::find(Web::WebDriver::LocationStrategy location_strategy, ByteString selector, GetStartNode get_start_node, OnFindComplete on_complete)
+{
+    auto& realm = current_browsing_context().active_document()->realm();
+
+    // 1. Let location strategy be equal to using.
+    // 2. Let selector be equal to value.
+
+    // 3. Let timeout be session's session timeouts' implicit wait timeout.
+    auto timeout = m_timeouts_configuration.implicit_wait_timeout;
+
+    // 4. Let timer be a new timer.
+    auto timer = realm.heap().allocate<Web::WebDriver::HeapTimer>(realm);
+
+    auto wrapped_on_complete = JS::create_heap_function(realm.heap(), [this, on_complete, timer](Web::WebDriver::Response result) {
+        m_element_locator = nullptr;
+        timer->stop();
+
+        on_complete->function()(move(result));
+    });
+
+    // 5. If timeout is not null:
+    if (timeout.has_value()) {
+        // 1. Start the timer with timer and timeout.
+        timer->start(*timeout, JS::create_heap_function(realm.heap(), [wrapped_on_complete]() {
+            wrapped_on_complete->function()({ JsonArray {} });
+        }));
+    }
+
+    // 6. Let elements returned be an empty List.
+    // 7. While elements returned is empty and timer's timeout fired flag is not set:
+    m_element_locator = realm.heap().allocate<ElementLocator>(realm, current_browsing_context(), location_strategy, move(selector), get_start_node, wrapped_on_complete, timer);
+    m_element_locator->search_for_element();
 }
 
 // https://w3c.github.io/webdriver/#dfn-json-deserialize

Userland/Services/WebContent/WebDriverConnection.h

@@ -9,7 +9,6 @@
 #pragma once
 
 #include <AK/ByteString.h>
-#include <AK/Function.h>
 #include <AK/HashMap.h>
 #include <AK/String.h>
 #include <LibGfx/Rect.h>
@@ -28,6 +27,8 @@
 
 namespace WebContent {
 
+class ElementLocator;
+
 class WebDriverConnection final
     : public IPC::ConnectionToServer<WebDriverClientEndpoint, WebDriverServerEndpoint> {
     C_OBJECT_ABSTRACT(WebDriverConnection)
@@ -133,8 +134,9 @@ private:
     Gfx::IntPoint calculate_absolute_position_of_element(JS::NonnullGCPtr<Web::Geometry::DOMRect> rect);
     Gfx::IntRect calculate_absolute_rect_of_element(Web::DOM::Element const& element);
 
-    using StartNodeGetter = Function<ErrorOr<JS::NonnullGCPtr<Web::DOM::ParentNode>, Web::WebDriver::Error>()>;
+    using GetStartNode = JS::NonnullGCPtr<JS::HeapFunction<ErrorOr<JS::NonnullGCPtr<Web::DOM::ParentNode>, Web::WebDriver::Error>()>>;
-    ErrorOr<JsonArray, Web::WebDriver::Error> find(StartNodeGetter&& start_node_getter, Web::WebDriver::LocationStrategy using_, StringView value);
+    using OnFindComplete = JS::NonnullGCPtr<JS::HeapFunction<void(Web::WebDriver::Response)>>;
+    void find(Web::WebDriver::LocationStrategy, ByteString, GetStartNode, OnFindComplete);
 
     struct ScriptArguments {
         ByteString script;
@@ -166,6 +168,9 @@ private:
 
     size_t m_pending_window_rect_requests { 0 };
 
+    friend class ElementLocator;
+    JS::GCPtr<ElementLocator> m_element_locator;
+
     JS::GCPtr<JS::Cell> m_action_executor;
 
     JS::GCPtr<Web::DOM::DocumentObserver> m_document_observer;

Userland/Services/WebContent/WebDriverServer.ipc

@@ -3,6 +3,7 @@
 endpoint WebDriverServer {
     navigation_complete(Web::WebDriver::Response response) =|
     window_rect_updated(Web::WebDriver::Response response) =|
+    find_elements_complete(Web::WebDriver::Response response) =|
     script_executed(Web::WebDriver::Response response) =|
     actions_performed(Web::WebDriver::Response response) =|
     dialog_closed(Web::WebDriver::Response response) =|

Userland/Services/WebDriver/Client.cpp

@@ -442,7 +442,7 @@ Web::WebDriver::Response Client::find_element(Web::WebDriver::Parameters paramet
 {
     dbgln_if(WEBDRIVER_DEBUG, "Handling POST /session/<session_id>/element");
     auto session = TRY(find_session_with_id(parameters[0]));
-    return session->web_content_connection().find_element(payload);
+    return session->find_element(payload);
 }
 
 // 12.3.3 Find Elements, https://w3c.github.io/webdriver/#dfn-find-elements
@@ -451,7 +451,7 @@ Web::WebDriver::Response Client::find_elements(Web::WebDriver::Parameters parame
 {
     dbgln_if(WEBDRIVER_DEBUG, "Handling POST /session/<session_id>/elements");
     auto session = TRY(find_session_with_id(parameters[0]));
-    return session->web_content_connection().find_elements(payload);
+    return session->find_elements(payload);
 }
 
 // 12.3.4 Find Element From Element, https://w3c.github.io/webdriver/#dfn-find-element-from-element
@@ -460,7 +460,7 @@ Web::WebDriver::Response Client::find_element_from_element(Web::WebDriver::Param
 {
     dbgln_if(WEBDRIVER_DEBUG, "Handling POST /session/<session_id>/element/<element_id>/element");
     auto session = TRY(find_session_with_id(parameters[0]));
-    return session->web_content_connection().find_element_from_element(payload, move(parameters[1]));
+    return session->find_element_from_element(move(parameters[1]), move(payload));
 }
 
 // 12.3.5 Find Elements From Element, https://w3c.github.io/webdriver/#dfn-find-elements-from-element
@@ -469,7 +469,7 @@ Web::WebDriver::Response Client::find_elements_from_element(Web::WebDriver::Para
 {
     dbgln_if(WEBDRIVER_DEBUG, "Handling POST /session/<session_id>/element/<element_id>/elements");
     auto session = TRY(find_session_with_id(parameters[0]));
-    return session->web_content_connection().find_elements_from_element(payload, move(parameters[1]));
+    return session->find_elements_from_element(move(parameters[1]), move(payload));
 }
 
 // 12.3.6 Find Element From Shadow Root, https://w3c.github.io/webdriver/#find-element-from-shadow-root
@@ -478,7 +478,7 @@ Web::WebDriver::Response Client::find_element_from_shadow_root(Web::WebDriver::P
 {
     dbgln_if(WEBDRIVER_DEBUG, "Handling POST /session/<session_id>/shadow/<shadow_id>/element");
     auto session = TRY(find_session_with_id(parameters[0]));
-    return session->web_content_connection().find_element_from_shadow_root(payload, move(parameters[1]));
+    return session->find_element_from_shadow_root(move(parameters[1]), move(payload));
 }
 
 // 12.3.7 Find Elements From Shadow Root, https://w3c.github.io/webdriver/#find-elements-from-shadow-root
@@ -487,7 +487,7 @@ Web::WebDriver::Response Client::find_elements_from_shadow_root(Web::WebDriver::
 {
     dbgln_if(WEBDRIVER_DEBUG, "Handling POST /session/<session_id>/shadow/<shadow_id>/elements");
     auto session = TRY(find_session_with_id(parameters[0]));
-    return session->web_content_connection().find_elements_from_shadow_root(payload, move(parameters[1]));
+    return session->find_elements_from_shadow_root(move(parameters[1]), move(payload));
 }
 
 // 12.3.8 Get Active Element, https://w3c.github.io/webdriver/#get-active-element

Userland/Services/WebDriver/Session.cpp

@@ -237,6 +237,48 @@ Web::WebDriver::Response Session::fullscreen_window() const
     });
 }
 
+Web::WebDriver::Response Session::find_element(JsonValue payload) const
+{
+    return perform_async_action(web_content_connection().on_find_elements_complete, [&]() {
+        return web_content_connection().find_element(move(payload));
+    });
+}
+
+Web::WebDriver::Response Session::find_elements(JsonValue payload) const
+{
+    return perform_async_action(web_content_connection().on_find_elements_complete, [&]() {
+        return web_content_connection().find_elements(move(payload));
+    });
+}
+
+Web::WebDriver::Response Session::find_element_from_element(String element_id, JsonValue payload) const
+{
+    return perform_async_action(web_content_connection().on_find_elements_complete, [&]() {
+        return web_content_connection().find_element_from_element(move(payload), move(element_id));
+    });
+}
+
+Web::WebDriver::Response Session::find_elements_from_element(String element_id, JsonValue payload) const
+{
+    return perform_async_action(web_content_connection().on_find_elements_complete, [&]() {
+        return web_content_connection().find_elements_from_element(move(payload), move(element_id));
+    });
+}
+
+Web::WebDriver::Response Session::find_element_from_shadow_root(String shadow_id, JsonValue payload) const
+{
+    return perform_async_action(web_content_connection().on_find_elements_complete, [&]() {
+        return web_content_connection().find_element_from_shadow_root(move(payload), move(shadow_id));
+    });
+}
+
+Web::WebDriver::Response Session::find_elements_from_shadow_root(String shadow_id, JsonValue payload) const
+{
+    return perform_async_action(web_content_connection().on_find_elements_complete, [&]() {
+        return web_content_connection().find_elements_from_shadow_root(move(payload), move(shadow_id));
+    });
+}
+
 Web::WebDriver::Response Session::execute_script(JsonValue payload, ScriptMode mode) const
 {
     return perform_async_action(web_content_connection().on_script_executed, [&]() {

Userland/Services/WebDriver/Session.h

@@ -70,6 +70,13 @@ public:
     Web::WebDriver::Response minimize_window() const;
     Web::WebDriver::Response fullscreen_window() const;
 
+    Web::WebDriver::Response find_element(JsonValue) const;
+    Web::WebDriver::Response find_elements(JsonValue) const;
+    Web::WebDriver::Response find_element_from_element(String, JsonValue) const;
+    Web::WebDriver::Response find_elements_from_element(String, JsonValue) const;
+    Web::WebDriver::Response find_element_from_shadow_root(String, JsonValue) const;
+    Web::WebDriver::Response find_elements_from_shadow_root(String, JsonValue) const;
+
     Web::WebDriver::Response element_click(String) const;
     Web::WebDriver::Response element_send_keys(String, JsonValue) const;
     Web::WebDriver::Response perform_actions(JsonValue) const;

Userland/Services/WebDriver/WebContentConnection.cpp

@@ -32,6 +32,12 @@ void WebContentConnection::window_rect_updated(Web::WebDriver::Response const& r
         on_window_rect_updated(response);
 }
 
+void WebContentConnection::find_elements_complete(Web::WebDriver::Response const& response)
+{
+    if (on_find_elements_complete)
+        on_find_elements_complete(response);
+}
+
 void WebContentConnection::script_executed(Web::WebDriver::Response const& response)
 {
     if (on_script_executed)

Userland/Services/WebDriver/WebContentConnection.h

@@ -24,6 +24,7 @@ public:
     Function<void()> on_close;
     Function<void(Web::WebDriver::Response)> on_navigation_complete;
     Function<void(Web::WebDriver::Response)> on_window_rect_updated;
+    Function<void(Web::WebDriver::Response)> on_find_elements_complete;
     Function<void(Web::WebDriver::Response)> on_script_executed;
     Function<void(Web::WebDriver::Response)> on_actions_performed;
     Function<void(Web::WebDriver::Response)> on_dialog_closed;
@@ -33,6 +34,7 @@ private:
 
     virtual void navigation_complete(Web::WebDriver::Response const&) override;
     virtual void window_rect_updated(Web::WebDriver::Response const&) override;
+    virtual void find_elements_complete(Web::WebDriver::Response const&) override;
     virtual void script_executed(Web::WebDriver::Response const&) override;
     virtual void actions_performed(Web::WebDriver::Response const&) override;
     virtual void dialog_closed(Web::WebDriver::Response const&) override;