WebContent: Add more IPC endpoints for getting Elements

This patch adds `get_document_element()` and `query_selector_all()`
which return Node's IDs.

    `get_document_element` returns the ID of the document element

    `query_selector_all` returns the IDs of all elements matching the
    selector starting at the Node associated with the start_node_id

Userland/Services/WebContent/ConnectionFromClient.cpp

@@ -2,6 +2,7 @@
  * Copyright (c) 2020-2022, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
  * Copyright (c) 2021-2022, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2022, Tobias Christiansen <tobyase@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -19,6 +20,7 @@
 #include <LibWeb/Bindings/MainThreadVM.h>
 #include <LibWeb/Cookie/ParsedCookie.h>
 #include <LibWeb/DOM/Document.h>
+#include <LibWeb/DOM/NodeList.h>
 #include <LibWeb/Dump.h>
 #include <LibWeb/HTML/BrowsingContext.h>
 #include <LibWeb/HTML/Scripting/ClassicScript.h>
@@ -438,6 +440,39 @@ void ConnectionFromClient::js_console_request_messages(i32 start_index)
         m_console_client->send_messages(start_index);
 }
 
+Messages::WebContentServer::GetDocumentElementResponse ConnectionFromClient::get_document_element()
+{
+    auto* document = page().top_level_browsing_context().active_document();
+    if (!document)
+        return { {} };
+    return { document->id() };
+}
+
+Messages::WebContentServer::QuerySelectorAllResponse ConnectionFromClient::query_selector_all(i32 start_node_id, String const& selector)
+{
+    auto* start_node = Web::DOM::Node::from_id(start_node_id);
+    if (!start_node)
+        return { {} };
+
+    if (!start_node->is_element() && !start_node->is_document())
+        return { {} };
+
+    auto& start_element = verify_cast<Web::DOM::ParentNode>(*start_node);
+
+    auto result = start_element.query_selector_all(selector);
+    if (result.is_error())
+        return { {} };
+
+    auto element_list = result.release_value();
+    Vector<i32> return_list;
+    for (u32 i = 0; i < element_list->length(); i++) {
+        auto node = element_list->item(i);
+        return_list.append(node->id());
+    }
+
+    return { return_list };
+}
+
 Messages::WebContentServer::GetSelectedTextResponse ConnectionFromClient::get_selected_text()
 {
     return page().focused_context().selected_text();

Userland/Services/WebContent/ConnectionFromClient.h

@@ -79,6 +79,9 @@ private:
     virtual void run_javascript(String const&) override;
     virtual void js_console_request_messages(i32) override;
 
+    virtual Messages::WebContentServer::GetDocumentElementResponse get_document_element() override;
+    virtual Messages::WebContentServer::QuerySelectorAllResponse query_selector_all(i32 start_node_id, String const& selector) override;
+
     virtual Messages::WebContentServer::GetLocalStorageEntriesResponse get_local_storage_entries() override;
     virtual Messages::WebContentServer::GetSessionStorageEntriesResponse get_session_storage_entries() override;
 

Userland/Services/WebContent/WebContentServer.ipc

@@ -37,6 +37,9 @@ endpoint WebContentServer
     js_console_input(String js_source) =|
     js_console_request_messages(i32 start_index) =|
 
+    get_document_element() => (Optional<i32> node_id)
+    query_selector_all(i32 start_node_id, String selector) => (Optional<Vector<i32>> elements_ids)
+
     run_javascript(String js_source) =|
 
     dump_layout_tree() => (String dump)