LibWeb/CSS: Implement "fetch a style resource" algorithm

Author: https://github.com/AtkinsSJ
Commit: https://github.com/LadybirdBrowser/ladybird/commit/ae943965dc2
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/2998

Libraries/LibWeb/CMakeLists.txt

@@ -74,6 +74,7 @@ set(SOURCES
     CSS/ComputedProperties.cpp
     CSS/Display.cpp
     CSS/EdgeRect.cpp
+    CSS/Fetch.cpp
     CSS/FontFace.cpp
     CSS/FontFaceSet.cpp
     CSS/Flex.cpp

Libraries/LibWeb/CSS/Fetch.cpp

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2024, Sam Atkins <sam@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibURL/Parser.h>
+#include <LibWeb/CSS/CSSStyleSheet.h>
+#include <LibWeb/CSS/Fetch.h>
+#include <LibWeb/Fetch/Fetching/Fetching.h>
+
+namespace Web::CSS {
+
+// https://drafts.csswg.org/css-values-4/#fetch-a-style-resource
+void fetch_a_style_resource(String const& url_value, CSSStyleSheet const& sheet, Fetch::Infrastructure::Request::Destination destination, CorsMode cors_mode, Fetch::Infrastructure::FetchAlgorithms::ProcessResponseConsumeBodyFunction process_response)
+{
+    auto& vm = sheet.vm();
+
+    // 1. Let environmentSettings be sheet’s relevant settings object.
+    auto& environment_settings = HTML::relevant_settings_object(sheet);
+
+    // 2. Let base be sheet’s stylesheet base URL if it is not null, otherwise environmentSettings’s API base URL. [CSSOM]
+    auto base = sheet.base_url().value_or(environment_settings.api_base_url());
+
+    // 3. Let parsedUrl be the result of the URL parser steps with urlValue’s url and base. If the algorithm returns an error, return.
+    auto parsed_url = URL::Parser::basic_parse(url_value, base);
+    if (!parsed_url.is_valid())
+        return;
+
+    // 4. Let req be a new request whose url is parsedUrl, whose destination is destination, mode is corsMode,
+    //    origin is environmentSettings’s origin, credentials mode is "same-origin", use-url-credentials flag is set,
+    //    client is environmentSettings, and whose referrer is environmentSettings’s API base URL.
+    auto request = Fetch::Infrastructure::Request::create(vm);
+    request->set_url(parsed_url);
+    request->set_destination(destination);
+    request->set_mode(cors_mode == CorsMode::Cors ? Fetch::Infrastructure::Request::Mode::CORS : Fetch::Infrastructure::Request::Mode::NoCORS);
+    request->set_origin(environment_settings.origin());
+    request->set_credentials_mode(Fetch::Infrastructure::Request::CredentialsMode::SameOrigin);
+    request->set_use_url_credentials(true);
+    request->set_client(&environment_settings);
+    request->set_referrer(environment_settings.api_base_url());
+
+    // 5. Apply any URL request modifier steps that apply to this request.
+    // FIXME: No specs seem to define these yet. When they do, implement them.
+
+    // 6. If req’s mode is "cors", set req’s referrer to sheet’s location. [CSSOM]
+    if (request->mode() == Fetch::Infrastructure::Request::Mode::CORS) {
+        // FIXME: sheet's location is an optional string, what do we do here?
+    }
+
+    // 7. If sheet’s origin-clean flag is set, set req’s initiator type to "css". [CSSOM]
+    if (sheet.is_origin_clean())
+        request->set_initiator_type(Fetch::Infrastructure::Request::InitiatorType::CSS);
+
+    // 8. Fetch req, with processresponseconsumebody set to processResponse.
+    Fetch::Infrastructure::FetchAlgorithms::Input fetch_algorithms_input {};
+    fetch_algorithms_input.process_response_consume_body = move(process_response);
+
+    (void)Fetch::Fetching::fetch(environment_settings.realm(), request, Fetch::Infrastructure::FetchAlgorithms::create(vm, move(fetch_algorithms_input)));
+}
+
+}

Libraries/LibWeb/CSS/Fetch.h

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2024, Sam Atkins <sam@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <LibWeb/Fetch/Infrastructure/FetchAlgorithms.h>
+#include <LibWeb/Fetch/Infrastructure/HTTP/Requests.h>
+
+namespace Web::CSS {
+
+enum class CorsMode {
+    NoCors,
+    Cors,
+};
+
+// https://drafts.csswg.org/css-values-4/#fetch-a-style-resource
+void fetch_a_style_resource(String const& url, CSSStyleSheet const&, Fetch::Infrastructure::Request::Destination, CorsMode, Fetch::Infrastructure::FetchAlgorithms::ProcessResponseConsumeBodyFunction process_response);
+
+}