LibWeb: Add Storage interface and window.localStorage

This is a naive-but-somewhat-functional initial implementation of
HTML Storage.

Note that there is no persistence yet, everything is in-process only,
and one local Storage object per origin.

Userland/Libraries/LibWeb/HTML/Storage.cpp

@@ -0,0 +1,149 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/String.h>
+#include <LibWeb/HTML/Storage.h>
+
+namespace Web::HTML {
+
+NonnullRefPtr<Storage> Storage::create()
+{
+    return adopt_ref(*new Storage);
+}
+
+Storage::Storage()
+{
+}
+
+Storage::~Storage()
+{
+}
+
+// https://html.spec.whatwg.org/multipage/webstorage.html#dom-storage-length
+size_t Storage::length() const
+{
+    // The length getter steps are to return this's map's size.
+    return m_map.size();
+}
+
+// https://html.spec.whatwg.org/multipage/webstorage.html#dom-storage-key
+String Storage::key(size_t index)
+{
+    // 1. If index is greater than or equal to this's map's size, then return null.
+    if (index >= m_map.size())
+        return {};
+
+    // 2. Let keys be the result of running get the keys on this's map.
+    auto keys = m_map.keys();
+
+    // 3. Return keys[index].
+    return keys[index];
+}
+
+// https://html.spec.whatwg.org/multipage/webstorage.html#dom-storage-getitem
+String Storage::get_item(String const& key) const
+{
+    // 1. If this's map[key] does not exist, then return null.
+    auto it = m_map.find(key);
+    if (it == m_map.end())
+        return {};
+
+    // 2. Return this's map[key].
+    return it->value;
+}
+
+// https://html.spec.whatwg.org/multipage/webstorage.html#dom-storage-setitem
+DOM::ExceptionOr<void> Storage::set_item(String const& key, String const& value)
+{
+    // 1. Let oldValue be null.
+    String old_value;
+
+    // 2. Let reorder be true.
+    bool reorder = true;
+
+    // 3. If this's map[key] exists:
+    if (auto it = m_map.find(key); it != m_map.end()) {
+        // 1. Set oldValue to this's map[key].
+        old_value = it->value;
+
+        // 2. If oldValue is value, then return.
+        if (old_value == value)
+            return {};
+
+        // 3. Set reorder to false.
+        reorder = false;
+    }
+
+    // FIXME: 4. If value cannot be stored, then throw a "QuotaExceededError" DOMException exception.
+
+    // 5. Set this's map[key] to value.
+    m_map.set(key, value);
+
+    // 6. If reorder is true, then reorder this.
+    if (reorder)
+        this->reorder();
+
+    // 7. Broadcast this with key, oldValue, and value.
+    broadcast(key, old_value, value);
+
+    return {};
+}
+
+// https://html.spec.whatwg.org/multipage/webstorage.html#dom-storage-removeitem
+void Storage::remove_item(String const& key)
+{
+    // 1. If this's map[key] does not exist, then return null.
+    // FIXME: Return null?
+    auto it = m_map.find(key);
+    if (it == m_map.end())
+        return;
+
+    // 2. Set oldValue to this's map[key].
+    auto old_value = it->value;
+
+    // 3. Remove this's map[key].
+    m_map.remove(it);
+
+    // 4. Reorder this.
+    reorder();
+
+    // 5. Broadcast this with key, oldValue, and null.
+    broadcast(key, old_value, {});
+}
+
+// https://html.spec.whatwg.org/multipage/webstorage.html#dom-storage-clear
+void Storage::clear()
+{
+    // 1. Clear this's map.
+    m_map.clear();
+
+    // 2. Broadcast this with null, null, and null.
+    broadcast({}, {}, {});
+}
+
+// https://html.spec.whatwg.org/multipage/webstorage.html#concept-storage-reorder
+void Storage::reorder()
+{
+    // To reorder a Storage object storage, reorder storage's map's entries in an implementation-defined manner.
+    // NOTE: This basically means that we're not required to maintain any particular iteration order.
+}
+
+// https://html.spec.whatwg.org/multipage/webstorage.html#concept-storage-broadcast
+void Storage::broadcast(String const& key, String const& old_value, String const& new_value)
+{
+    (void)key;
+    (void)old_value;
+    (void)new_value;
+    // FIXME: Implement.
+}
+
+Vector<String> Storage::supported_property_names() const
+{
+    // The supported property names on a Storage object storage are the result of running get the keys on storage's map.
+    return m_map.keys();
+}
+
+}