From e8d162c293fbdf9a40a1369b60b80fa286aceb0f Mon Sep 17 00:00:00 2001
From: Stefan Boberg <stefan.boberg@epicgames.com>
Date: Wed, 21 Jan 2026 09:38:16 +0100
Subject: zen hub (#574)

Initial implementation of zenserver "hub" mode. This is an experimental feature.

zenserver can be started in hub mode by specifying `hub` as the first argument to zenserver
---
 src/zenserver/hub/hydration.cpp | 119 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)
 create mode 100644 src/zenserver/hub/hydration.cpp

(limited to 'src/zenserver/hub/hydration.cpp')

diff --git a/src/zenserver/hub/hydration.cpp b/src/zenserver/hub/hydration.cpp
new file mode 100644
index 000000000..52c17fe1a
--- /dev/null
+++ b/src/zenserver/hub/hydration.cpp
@@ -0,0 +1,119 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+
+#include "hydration.h"
+
+#include <zencore/filesystem.h>
+#include <zencore/fmtutils.h>
+
+namespace zen {
+
+///////////////////////////////////////////////////////////////////////////
+
+struct FileHydrator : public HydrationStrategyBase
+{
+	virtual void Configure(const HydrationConfig& Config) override;
+	virtual void Hydrate() override;
+	virtual void Dehydrate() override;
+
+private:
+	HydrationConfig		  m_Config;
+	std::filesystem::path m_StorageModuleRootDir;
+};
+
+void
+FileHydrator::Configure(const HydrationConfig& Config)
+{
+	m_Config = Config;
+
+	std::filesystem::path ConfigPath(Utf8ToWide(m_Config.TargetSpecification));
+
+	if (!std::filesystem::exists(ConfigPath))
+	{
+		throw std::invalid_argument(fmt::format("Target does not exist: '{}'", ConfigPath.string()));
+	}
+
+	m_StorageModuleRootDir = ConfigPath / m_Config.ModuleId;
+
+	CreateDirectories(m_StorageModuleRootDir);
+}
+
+void
+FileHydrator::Hydrate()
+{
+	ZEN_INFO("Hydrating state from '{}' to '{}'", m_StorageModuleRootDir, m_Config.ServerStateDir);
+
+	// Ensure target is clean
+	ZEN_DEBUG("Wiping server state at '{}'", m_Config.ServerStateDir);
+	const bool ForceRemoveReadOnlyFiles = true;
+	CleanDirectory(m_Config.ServerStateDir, ForceRemoveReadOnlyFiles);
+
+	bool WipeServerState = false;
+
+	try
+	{
+		ZEN_DEBUG("Copying '{}' to '{}'", m_StorageModuleRootDir, m_Config.ServerStateDir);
+		CopyTree(m_StorageModuleRootDir, m_Config.ServerStateDir, {.EnableClone = true});
+	}
+	catch (std::exception& Ex)
+	{
+		ZEN_WARN("Copy failed: {}. Will wipe any partially copied state from '{}'", Ex.what(), m_Config.ServerStateDir);
+
+		// We don't do the clean right here to avoid potentially running into double-throws
+		WipeServerState = true;
+	}
+
+	if (WipeServerState)
+	{
+		ZEN_DEBUG("Cleaning server state '{}'", m_Config.ServerStateDir);
+		CleanDirectory(m_Config.ServerStateDir, ForceRemoveReadOnlyFiles);
+	}
+
+	// Note that we leave the storage state intact until next dehydration replaces the content
+}
+
+void
+FileHydrator::Dehydrate()
+{
+	ZEN_INFO("Dehydrating state from '{}' to '{}'", m_Config.ServerStateDir, m_StorageModuleRootDir);
+
+	const std::filesystem::path TargetDir = m_StorageModuleRootDir;
+
+	// Ensure target is clean. This could be replaced with an atomic copy at a later date
+	// (i.e copy into a temporary directory name and rename it once complete)
+
+	ZEN_DEBUG("Cleaning storage root '{}'", TargetDir);
+	const bool ForceRemoveReadOnlyFiles = true;
+	CleanDirectory(TargetDir, ForceRemoveReadOnlyFiles);
+
+	bool CopySuccess = true;
+
+	try
+	{
+		ZEN_DEBUG("Copying '{}' to '{}'", m_Config.ServerStateDir, TargetDir);
+		CopyTree(m_Config.ServerStateDir, TargetDir, {.EnableClone = true});
+	}
+	catch (std::exception& Ex)
+	{
+		ZEN_WARN("Copy failed: {}. Will wipe any partially copied state from '{}'", Ex.what(), m_StorageModuleRootDir);
+
+		// We don't do the clean right here to avoid potentially running into double-throws
+		CopySuccess = false;
+	}
+
+	if (!CopySuccess)
+	{
+		ZEN_DEBUG("Removing partially copied state from '{}'", TargetDir);
+		CleanDirectory(TargetDir, ForceRemoveReadOnlyFiles);
+	}
+
+	ZEN_DEBUG("Wiping server state '{}'", m_Config.ServerStateDir);
+	CleanDirectory(m_Config.ServerStateDir, ForceRemoveReadOnlyFiles);
+}
+
+std::unique_ptr<HydrationStrategyBase>
+CreateFileHydrator()
+{
+	return std::make_unique<FileHydrator>();
+}
+
+}  // namespace zen
-- 
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