LibWeb: Add {,de}serialization steps for FileList

Tests/LibWeb/Text/expected/HTML/StructuredClone-serializable-FileList.txt

@@ -0,0 +1,5 @@
+Select files...4 files selected.   input1:
+file1: text/plain: Contents for file1
+file2: text/plain: Contents for file2
+file3: text/plain: Contents for file3
+file4: text/plain: Contents for file4

Tests/LibWeb/Text/input/HTML/StructuredClone-serializable-FileList.html

@@ -0,0 +1,32 @@
+<input id="input1" type="file" multiple />
+<script src="../include.js"></script>
+<script>
+    const runTest = async id => {
+        let input = document.getElementById(id);
+
+        return new Promise(resolve => {
+            input.addEventListener("input", async () => {
+                println(`${id}:`);
+
+                let files = structuredClone(input.files);
+
+                for (let file of input.files) {
+                    const text = await file.text();
+
+                    println(`${file.name}: ${file.type}: ${text}`);
+                }
+
+                resolve();
+            });
+
+            internals.dispatchUserActivatedEvent(input, new Event("mousedown"));
+            input.showPicker();
+        });
+    }
+
+    asyncTest(async done => {
+        await runTest("input1");
+
+        done();
+    });
+</script>

Userland/Libraries/LibWeb/FileAPI/FileList.cpp

@@ -18,6 +18,11 @@ JS::NonnullGCPtr<FileList> FileList::create(JS::Realm& realm, Vector<JS::Nonnull
     return realm.heap().allocate<FileList>(realm, realm, move(files));
 }
 
+JS::NonnullGCPtr<FileList> FileList::create(JS::Realm& realm)
+{
+    return realm.heap().allocate<FileList>(realm, realm);
+}
+
 FileList::FileList(JS::Realm& realm, Vector<JS::NonnullGCPtr<File>>&& files)
     : Bindings::PlatformObject(realm)
     , m_files(move(files))
@@ -25,6 +30,12 @@ FileList::FileList(JS::Realm& realm, Vector<JS::NonnullGCPtr<File>>&& files)
     m_legacy_platform_object_flags = LegacyPlatformObjectFlags { .supports_indexed_properties = 1 };
 }
 
+FileList::FileList(JS::Realm& realm)
+    : Bindings::PlatformObject(realm)
+{
+    m_legacy_platform_object_flags = LegacyPlatformObjectFlags { .supports_indexed_properties = 1 };
+}
+
 FileList::~FileList() = default;
 
 void FileList::initialize(JS::Realm& realm)
@@ -59,4 +70,34 @@ void FileList::visit_edges(Cell::Visitor& visitor)
         visitor.visit(file);
 }
 
+WebIDL::ExceptionOr<void> FileList::serialization_steps(HTML::SerializationRecord& serialized, bool for_storage, HTML::SerializationMemory& memory)
+{
+    auto& vm = this->vm();
+
+    // 1. Set serialized.[[Files]] to an empty list.
+    // 2. For each file in value, append the sub-serialization of file to serialized.[[Files]].
+    HTML::serialize_primitive_type(serialized, m_files.size());
+    for (auto& file : m_files)
+        serialized.extend(TRY(HTML::structured_serialize_internal(vm, file, for_storage, memory)));
+
+    return {};
+}
+
+WebIDL::ExceptionOr<void> FileList::deserialization_steps(ReadonlySpan<u32> const& serialized, size_t& position, HTML::DeserializationMemory& memory)
+{
+    auto& vm = this->vm();
+    auto& realm = *vm.current_realm();
+
+    // 1. For each file of serialized.[[Files]], add the sub-deserialization of file to value.
+    auto size = HTML::deserialize_primitive_type<size_t>(serialized, position);
+    for (size_t i = 0; i < size; ++i) {
+        auto deserialized_record = TRY(HTML::structured_deserialize_internal(vm, serialized, realm, memory, position));
+        if (deserialized_record.value.has_value() && is<File>(deserialized_record.value.value().as_object()))
+            m_files.append(dynamic_cast<File&>(deserialized_record.value.release_value().as_object()));
+        position = deserialized_record.position;
+    }
+
+    return {};
+}
+
 }

Userland/Libraries/LibWeb/FileAPI/FileList.h

@@ -15,12 +15,16 @@
 
 namespace Web::FileAPI {
 
-class FileList : public Bindings::PlatformObject {
+class FileList
+    : public Bindings::PlatformObject
+    , public Bindings::Serializable {
     WEB_PLATFORM_OBJECT(FileList, Bindings::PlatformObject);
     JS_DECLARE_ALLOCATOR(FileList);
 
 public:
     [[nodiscard]] static JS::NonnullGCPtr<FileList> create(JS::Realm&, Vector<JS::NonnullGCPtr<File>>&&);
+    [[nodiscard]] static JS::NonnullGCPtr<FileList> create(JS::Realm&);
+
     virtual ~FileList() override;
 
     // https://w3c.github.io/FileAPI/#dfn-length
@@ -41,8 +45,13 @@ public:
     virtual bool is_supported_property_index(u32 index) const override;
     virtual WebIDL::ExceptionOr<JS::Value> item_value(size_t index) const override;
 
+    virtual StringView interface_name() const override { return "FileList"sv; }
+    virtual WebIDL::ExceptionOr<void> serialization_steps(HTML::SerializationRecord& serialized, bool for_storage, HTML::SerializationMemory&) override;
+    virtual WebIDL::ExceptionOr<void> deserialization_steps(ReadonlySpan<u32> const& serialized, size_t& position, HTML::DeserializationMemory&) override;
+
 private:
     FileList(JS::Realm&, Vector<JS::NonnullGCPtr<File>>&&);
+    explicit FileList(JS::Realm&);
 
     virtual void initialize(JS::Realm&) override;
     virtual void visit_edges(Cell::Visitor&) override;

Userland/Libraries/LibWeb/HTML/StructuredSerialize.cpp

@@ -36,6 +36,7 @@
 #include <LibWeb/Crypto/CryptoKey.h>
 #include <LibWeb/FileAPI/Blob.h>
 #include <LibWeb/FileAPI/File.h>
+#include <LibWeb/FileAPI/FileList.h>
 #include <LibWeb/Geometry/DOMMatrix.h>
 #include <LibWeb/Geometry/DOMMatrixReadOnly.h>
 #include <LibWeb/Geometry/DOMPoint.h>
@@ -974,6 +975,8 @@ private:
             return FileAPI::Blob::create(realm);
         if (interface_name == "File"sv)
             return FileAPI::File::create(realm);
+        if (interface_name == "FileList"sv)
+            return FileAPI::FileList::create(realm);
         if (interface_name == "DOMMatrixReadOnly"sv)
             return Geometry::DOMMatrixReadOnly::create(realm);
         if (interface_name == "DOMMatrix"sv)