From a7862696876e610690820246fbae96c10521e788 Mon Sep 17 00:00:00 2001
From: Ali Mohammad Pur <ali.mpfard@gmail.com>
Date: Tue, 22 Apr 2025 11:17:48 +0200
Subject: [PATCH] LibWeb/WebAssembly: Implement Module::customSections(module)

---
 Libraries/LibWeb/WebAssembly/Module.cpp | 24 ++++++++++++++++++++++++
 Libraries/LibWeb/WebAssembly/Module.h   |  1 +
 Libraries/LibWeb/WebAssembly/Module.idl |  2 +-
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/Libraries/LibWeb/WebAssembly/Module.cpp b/Libraries/LibWeb/WebAssembly/Module.cpp
index 16c3a487af9..080bc50b486 100644
--- a/Libraries/LibWeb/WebAssembly/Module.cpp
+++ b/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))
diff --git a/Libraries/LibWeb/WebAssembly/Module.h b/Libraries/LibWeb/WebAssembly/Module.h
index 347fa2deb77..1205d7f75cd 100644
--- a/Libraries/LibWeb/WebAssembly/Module.h
+++ b/Libraries/LibWeb/WebAssembly/Module.h
@@ -42,6 +42,7 @@ public:
     static WebIDL::ExceptionOr<GC::Ref<Module>> construct_impl(JS::Realm&, GC::Root<WebIDL::BufferSource>& bytes);
     static WebIDL::ExceptionOr<Vector<ModuleImportDescriptor>> imports(JS::VM&, GC::Ref<Module>);
     static WebIDL::ExceptionOr<Vector<ModuleExportDescriptor>> exports(JS::VM&, GC::Ref<Module>);
+    static WebIDL::ExceptionOr<GC::RootVector<GC::Ref<JS::ArrayBuffer>>> custom_sections(JS::VM&, GC::Ref<Module>, String section_name);
 
     NonnullRefPtr<Detail::CompiledWebAssemblyModule> compiled_module() const { return m_compiled_module; }
 
diff --git a/Libraries/LibWeb/WebAssembly/Module.idl b/Libraries/LibWeb/WebAssembly/Module.idl
index 77d5e49a690..25996f6da3c 100644
--- a/Libraries/LibWeb/WebAssembly/Module.idl
+++ b/Libraries/LibWeb/WebAssembly/Module.idl
@@ -23,5 +23,5 @@ interface Module {
 
     static sequence<ModuleExportDescriptor> exports(Module moduleObject);
     static sequence<ModuleImportDescriptor> imports(Module moduleObject);
-    [FIXME] static sequence<ArrayBuffer> customSections(Module moduleObject, DOMString sectionName);
+    static sequence<ArrayBuffer> customSections(Module moduleObject, DOMString sectionName);
 };