feat(Core): Linux: Support systemd socket activation for the worldserver game socket (#21998)

src/common/Utilities/Systemd.cpp

@@ -0,0 +1,59 @@
+/*
+ * This file is part of the AzerothCore Project. See AUTHORS file for Copyright information.
+ *
+ * Portions of this file are derived from systemd, licensed under:
+ * - GPL-2.0-or-later (if the original systemd file was GPL-2.0+)
+ *   OR
+ * - LGPL-2.1-or-later, relicensed under GPL-2.0-or-later as permitted by LGPL-2.1+
+ *
+ * Original systemd copyright:
+ *   Copyright (c) the systemd contributors.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#if defined(__linux__)
+#include "Log.h"
+#include "StringConvert.h"
+#include <cstdlib>
+#include <unistd.h>
+#include <string>
+
+int get_listen_fd()
+{
+    char* const listen_pid = std::getenv("LISTEN_PID");
+    char* const listen_fds = std::getenv("LISTEN_FDS");
+    if (!listen_pid || !listen_fds)
+        return 0;
+
+    pid_t pid = Acore::StringTo<int>(listen_pid).value_or(0);
+    if (pid != getpid())
+        return 0;
+
+    int fds = Acore::StringTo<int>(listen_fds).value_or(0);
+    if (fds <= 0)
+        return 0;
+
+    if (fds > 1)
+        LOG_WARN("network", "Multiple file descriptors received from systemd socket activation, only the first will be used");
+
+    return 3;
+}
+#else
+// On non-Linux systems, just return 0 (no socket activation)
+int get_listen_fd()
+{
+    return 0;
+}
+#endif

src/common/Utilities/Systemd.h

@@ -0,0 +1,31 @@
+/*
+ * This file is part of the AzerothCore Project. See AUTHORS file for Copyright information.
+ *
+ * Portions of this file are derived from systemd, licensed under:
+ * - GPL-2.0-or-later (if the original systemd file was GPL-2.0+)
+ *   OR
+ * - LGPL-2.1-or-later, relicensed under GPL-2.0-or-later as permitted by LGPL-2.1+
+ *
+ * Original systemd copyright:
+ *   Copyright (c) the systemd contributors.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _SYSTEMD_H_
+#define _SYSTEMD_H_
+
+int get_listen_fd();
+
+#endif

src/server/apps/worldserver/Main.cpp

@@ -48,6 +48,7 @@
 #include "SecretMgr.h"
 #include "SharedDefines.h"
 #include "SteadyTimer.h"
+#include "Systemd.h"
 #include "World.h"
 #include "WorldSessionMgr.h"
 #include "WorldSocket.h"
@@ -406,7 +407,8 @@ int main(int argc, char** argv)
     sScriptMgr->OnShutdown();
 
     // set server offline
-    LoginDatabase.DirectExecute("UPDATE realmlist SET flag = flag | {} WHERE id = '{}'", REALM_FLAG_OFFLINE, realm.Id.Realm);
+    if (!sConfigMgr->GetOption<bool>("Network.UseSocketActivation", false))
+        LoginDatabase.DirectExecute("UPDATE realmlist SET flag = flag | {} WHERE id = '{}'", REALM_FLAG_OFFLINE, realm.Id.Realm);
 
     LOG_INFO("server.worldserver", "Halting process...");
 

src/server/apps/worldserver/worldserver.conf.dist

@@ -397,6 +397,20 @@ Network.TcpNodelay = 1
 
 Network.EnableProxyProtocol = 0
 
+#
+#    Network.UseSocketActivation
+#        Description: Enable systemd socket activation support for the worldserver.
+#                     When enabled and the process is started by systemd socket activation,
+#                     the server will use the socket passed by systemd instead of
+#                     creating and binding its own listening socket. Disabled by default.
+#
+#                     When enabled the realm is not automatically set as offline on shutdown.
+#
+#        Example:     1 - (Enabled)
+#        Default:     0 - (Disabled)
+
+Network.UseSocketActivation = 0
+
 #
 ###################################################################################################
 

src/server/shared/Network/AsyncAcceptor.h

@@ -20,6 +20,7 @@
 
 #include "IpAddress.h"
 #include "Log.h"
+#include "Systemd.h"
 #include <atomic>
 #include <boost/asio/ip/tcp.hpp>
 #include <functional>
@@ -33,10 +34,20 @@ class AsyncAcceptor
 public:
     typedef void(*AcceptCallback)(tcp::socket&& newSocket, uint32 threadIndex);
 
-    AsyncAcceptor(Acore::Asio::IoContext& ioContext, std::string const& bindIp, uint16 port) :
+    AsyncAcceptor(Acore::Asio::IoContext& ioContext, std::string const& bindIp, uint16 port, bool supportSocketActivation = false) :
         _acceptor(ioContext), _endpoint(Acore::Net::make_address(bindIp), port),
-        _socket(ioContext), _closed(false), _socketFactory([this](){ return DefaultSocketFactory(); })
+        _socket(ioContext), _closed(false), _socketFactory([this](){ return DefaultSocketFactory(); }),
+        _supportSocketActivation(supportSocketActivation)
     {
+        int const listen_fd = get_listen_fd();
+        if (_supportSocketActivation && listen_fd > 0)
+        {
+            LOG_DEBUG("network", "Using socket from systemd socket activation");
+            boost::system::error_code errorCode;
+            _acceptor.assign(boost::asio::ip::tcp::v4(), listen_fd, errorCode);
+            if (errorCode)
+                LOG_WARN("network", "Failed to assign socket {}", errorCode.message());
+        }
     }
 
     template<class T>
@@ -72,27 +83,31 @@ public:
     bool Bind()
     {
         boost::system::error_code errorCode;
-        _acceptor.open(_endpoint.protocol(), errorCode);
-        if (errorCode)
+        // with socket activation the acceptor is already open and bound
+        if (!_acceptor.is_open())
         {
-            LOG_INFO("network", "Failed to open acceptor {}", errorCode.message());
-            return false;
-        }
+            _acceptor.open(_endpoint.protocol(), errorCode);
+            if (errorCode)
+            {
+                LOG_INFO("network", "Failed to open acceptor {}", errorCode.message());
+                return false;
+            }
 
 #if AC_PLATFORM != AC_PLATFORM_WINDOWS
-        _acceptor.set_option(boost::asio::ip::tcp::acceptor::reuse_address(true), errorCode);
-        if (errorCode)
-        {
-            LOG_INFO("network", "Failed to set reuse_address option on acceptor {}", errorCode.message());
-            return false;
-        }
+            _acceptor.set_option(boost::asio::ip::tcp::acceptor::reuse_address(true), errorCode);
+            if (errorCode)
+            {
+                LOG_INFO("network", "Failed to set reuse_address option on acceptor {}", errorCode.message());
+                return false;
+            }
 #endif
 
-        _acceptor.bind(_endpoint, errorCode);
-        if (errorCode)
-        {
-            LOG_INFO("network", "Could not bind to {}:{} {}", _endpoint.address().to_string(), _endpoint.port(), errorCode.message());
-            return false;
+            _acceptor.bind(_endpoint, errorCode);
+            if (errorCode)
+            {
+                LOG_INFO("network", "Could not bind to {}:{} {}", _endpoint.address().to_string(), _endpoint.port(), errorCode.message());
+                return false;
+            }
         }
 
         _acceptor.listen(ACORE_MAX_LISTEN_CONNECTIONS, errorCode);
@@ -124,6 +139,7 @@ private:
     tcp::socket _socket;
     std::atomic<bool> _closed;
     std::function<std::pair<tcp::socket*, uint32>()> _socketFactory;
+    bool _supportSocketActivation;
 };
 
 template<class T>

src/server/shared/Network/SocketMgr.h

@@ -19,6 +19,7 @@
 #define SocketMgr_h__
 
 #include "AsyncAcceptor.h"
+#include "Config.h"
 #include "Errors.h"
 #include "NetworkThread.h"
 #include <boost/asio/ip/tcp.hpp>
@@ -42,7 +43,8 @@ public:
         std::unique_ptr<AsyncAcceptor> acceptor;
         try
         {
-            acceptor = std::make_unique<AsyncAcceptor>(ioContext, bindIp, port);
+            bool supportSocketActivation = sConfigMgr->GetOption<bool>("Network.UseSocketActivation", false);
+            acceptor = std::make_unique<AsyncAcceptor>(ioContext, bindIp, port, supportSocketActivation);
         }
         catch (boost::system::system_error const& err)
         {