From 4ad9543a654a2b8d5c965aec2d099c025bfd510b Mon Sep 17 00:00:00 2001
From: Timothy Flynn <trflynn89@pm.me>
Date: Wed, 4 Feb 2026 10:07:32 -0500
Subject: [PATCH] LibCore: Add helpers to share arbitrary versions between
 processes

This will allow sharing e.g. document cookie versions between the UI and
WebContent processes, and safely accessing those versions.

Core::AnonymousBuffer internally creates a minimum buffer of PAGE_SIZE
bytes. This is much more than the size of a single version, but this
affords us the opportunity to share multiple versions in a single buffer
between processes. With a PAGE_SIZE of 4096, we can share up to 512
versions in a single buffer.
---
 Libraries/LibCore/CMakeLists.txt    |  1 +
 Libraries/LibCore/SharedVersion.cpp | 49 +++++++++++++++++++++++++++++
 Libraries/LibCore/SharedVersion.h   | 26 +++++++++++++++
 3 files changed, 76 insertions(+)
 create mode 100644 Libraries/LibCore/SharedVersion.cpp
 create mode 100644 Libraries/LibCore/SharedVersion.h

diff --git a/Libraries/LibCore/CMakeLists.txt b/Libraries/LibCore/CMakeLists.txt
index e48bddb825..e027380c1c 100644
--- a/Libraries/LibCore/CMakeLists.txt
+++ b/Libraries/LibCore/CMakeLists.txt
@@ -53,6 +53,7 @@ set(SOURCES
     Resource.cpp
     ResourceImplementation.cpp
     ResourceImplementationFile.cpp
+    SharedVersion.cpp
     SystemServerTakeover.cpp
     ThreadEventQueue.cpp
     Timer.cpp
diff --git a/Libraries/LibCore/SharedVersion.cpp b/Libraries/LibCore/SharedVersion.cpp
new file mode 100644
index 0000000000..60852e2976
--- /dev/null
+++ b/Libraries/LibCore/SharedVersion.cpp
@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2026, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Platform.h>
+#include <LibCore/SharedVersion.h>
+
+namespace Core {
+
+static size_t SHARED_VERSION_BUFFER_SIZE = PAGE_SIZE;
+static size_t SHARED_VERSION_BUFFER_COUNT = SHARED_VERSION_BUFFER_SIZE / sizeof(SharedVersion);
+
+AnonymousBuffer create_shared_version_buffer()
+{
+    return MUST(AnonymousBuffer::create_with_size(SHARED_VERSION_BUFFER_SIZE));
+}
+
+bool initialize_shared_version(AnonymousBuffer& shared_version_buffer, SharedVersionIndex shared_version_index)
+{
+    if (!shared_version_buffer.is_valid() || shared_version_index >= SHARED_VERSION_BUFFER_COUNT)
+        return false;
+
+    auto* shared_versions = shared_version_buffer.data<SharedVersion>();
+    shared_versions[shared_version_index] = INITIAL_SHARED_VERSION;
+
+    return true;
+}
+
+void increment_shared_version(AnonymousBuffer& shared_version_buffer, SharedVersionIndex shared_version_index)
+{
+    if (!shared_version_buffer.is_valid() || shared_version_index >= SHARED_VERSION_BUFFER_COUNT)
+        return;
+
+    auto* shared_versions = shared_version_buffer.data<SharedVersion>();
+    ++shared_versions[shared_version_index];
+}
+
+Optional<SharedVersion> get_shared_version(AnonymousBuffer const& shared_version_buffer, SharedVersionIndex shared_version_index)
+{
+    if (!shared_version_buffer.is_valid() || shared_version_index >= SHARED_VERSION_BUFFER_COUNT)
+        return {};
+
+    auto const* shared_versions = shared_version_buffer.data<SharedVersion>();
+    return shared_versions[shared_version_index];
+}
+
+}
diff --git a/Libraries/LibCore/SharedVersion.h b/Libraries/LibCore/SharedVersion.h
new file mode 100644
index 0000000000..cf064435f7
--- /dev/null
+++ b/Libraries/LibCore/SharedVersion.h
@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2026, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Optional.h>
+#include <AK/Types.h>
+#include <LibCore/AnonymousBuffer.h>
+
+namespace Core {
+
+using SharedVersion = u64;
+using SharedVersionIndex = u32;
+
+constexpr inline SharedVersion INVALID_SHARED_VERSION = 0;
+constexpr inline SharedVersion INITIAL_SHARED_VERSION = 1;
+
+[[nodiscard]] AnonymousBuffer create_shared_version_buffer();
+[[nodiscard]] bool initialize_shared_version(AnonymousBuffer&, SharedVersionIndex);
+void increment_shared_version(AnonymousBuffer&, SharedVersionIndex);
+Optional<SharedVersion> get_shared_version(AnonymousBuffer const&, SharedVersionIndex);
+
+}