LibWeb: Introduce the FormData interface from the XHR specification

Userland/Libraries/LibWeb/HTML/FormControlInfrastructure.cpp

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2023, Kenneth Myhra <kennethmyhra@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/HTML/FormControlInfrastructure.h>
+#include <LibWeb/Infra/Strings.h>
+
+namespace Web::HTML {
+
+// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#create-an-entry
+WebIDL::ExceptionOr<Entry> create_entry(JS::Realm& realm, String const& name, Variant<JS::NonnullGCPtr<FileAPI::Blob>, String> const& value, Optional<String> const& filename)
+{
+    auto& vm = realm.vm();
+
+    // 1. Set name to the result of converting name into a scalar value string.
+    auto entry_name = TRY_OR_THROW_OOM(realm.vm(), Infra::convert_to_scalar_value_string(name));
+
+    auto entry_value = TRY(value.visit(
+        // 2. If value is a string, then set value to the result of converting value into a scalar value string.
+        [&](String const& string) -> WebIDL::ExceptionOr<Variant<JS::NonnullGCPtr<FileAPI::File>, String>> {
+            return TRY_OR_THROW_OOM(vm, Infra::convert_to_scalar_value_string(string));
+        },
+        // 3. Otherwise:
+        [&](JS::NonnullGCPtr<FileAPI::Blob> const& blob) -> WebIDL::ExceptionOr<Variant<JS::NonnullGCPtr<FileAPI::File>, String>> {
+            // 1. If value is not a File object, then set value to a new File object, representing the same bytes, whose name attribute value is "blob".
+            // 2. If filename is given, then set value to a new File object, representing the same bytes, whose name attribute is filename.
+            String name_attribute;
+            if (filename.has_value())
+                name_attribute = filename.value();
+            else
+                name_attribute = TRY_OR_THROW_OOM(vm, String::from_utf8("blob"sv));
+            return TRY(FileAPI::File::create(realm, { JS::make_handle(*blob) }, name_attribute.to_deprecated_string(), {}));
+        }));
+
+    // 4. Return an entry whose name is name and whose value is value.
+    return Entry {
+        .name = move(entry_name),
+        .value = move(entry_value),
+    };
+}
+
+}