LibWeb/WebAssembly: Implement Module::customSections(module)

Author: https://github.com/alimpfard
Commit: a786269687
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4423
Reviewed-by: https://github.com/ADKaster ✅

Libraries/LibWeb/WebAssembly/Module.cpp

@@ -5,6 +5,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <LibJS/Runtime/ArrayBuffer.h>
 #include <LibJS/Runtime/Realm.h>
 #include <LibJS/Runtime/VM.h>
 #include <LibWeb/Bindings/Intrinsics.h>
@@ -95,6 +96,29 @@ WebIDL::ExceptionOr<Vector<ModuleExportDescriptor>> Module::exports(JS::VM&, GC:
     return export_objects;
 }
 
+// https://webassembly.github.io/threads/js-api/index.html#dom-module-customsections
+WebIDL::ExceptionOr<GC::RootVector<GC::Ref<JS::ArrayBuffer>>> Module::custom_sections(JS::VM& vm, GC::Ref<Module> module_object, String section_name)
+{
+    // 1. Let bytes be moduleObject.[[Bytes]].
+    // 2. Let customSections be « ».
+    GC::RootVector<GC::Ref<JS::ArrayBuffer>> array_buffers { vm.heap() };
+
+    // 3. For each custom section customSection of bytes, interpreted according to the module grammar,
+    auto& custom_sections = module_object->m_compiled_module->module->custom_sections();
+    for (auto& section : custom_sections) {
+        // 3.1. Let name be the name of customSection, decoded as UTF-8.
+        // 3.2. Assert: name is not failure (moduleObject.[[Module]] is valid).
+        auto name = MUST(String::from_utf8(section.name().bytes()));
+        // 3.3. If name equals sectionName as string values,
+        if (section_name == name) {
+            // 3.3.1. Append a new ArrayBuffer containing a copy of the bytes in bytes for the range matched by this customsec production to customSections.
+            array_buffers.append(JS::ArrayBuffer::create(module_object->realm(), section.contents()));
+        }
+    }
+    // 4. Return customSections.
+    return array_buffers;
+}
+
 Module::Module(JS::Realm& realm, NonnullRefPtr<Detail::CompiledWebAssemblyModule> compiled_module)
     : Bindings::PlatformObject(realm)
     , m_compiled_module(move(compiled_module))