Core/PacketIO: implement a legacy connection mode which uses only the first connection socket to allow older pre-patched clients to connect

src/server/game/Handlers/CharacterHandler.cpp

@@ -752,7 +752,10 @@ void WorldSession::HandlePlayerLoginOpcode(WorldPackets::Character::PlayerLogin&
         return;
     }
 
-    SendConnectToInstance(WorldPackets::Auth::ConnectToSerial::WorldAttempt1);
+    if (_legacyConnectionModeEnabled)
+        HandleContinuePlayerLogin();
+    else
+        SendConnectToInstance(WorldPackets::Auth::ConnectToSerial::WorldAttempt1);
 }
 
 void WorldSession::HandleContinuePlayerLogin()
@@ -770,7 +773,8 @@ void WorldSession::HandleContinuePlayerLogin()
         return;
     }
 
-    SendPacket(WorldPackets::Auth::ResumeComms(CONNECTION_TYPE_INSTANCE).Write());
+    if (!_legacyConnectionModeEnabled)
+        SendPacket(WorldPackets::Auth::ResumeComms(CONNECTION_TYPE_INSTANCE).Write());
 
     AddQueryHolderCallback(CharacterDatabase.DelayQueryHolder(holder)).AfterComplete([this](SQLQueryHolderBase const& holder)
     {

src/server/game/Server/Protocol/Opcodes.cpp

@@ -16,13 +16,16 @@
  */
 
 #include "Opcodes.h"
-#include "Log.h"
-#include "WorldSession.h"
-#include "Packets/AllPackets.h"
+
 #include <iomanip>
 #include <sstream>
 
-template<class PacketClass, void(WorldSession::*HandlerFunction)(PacketClass&)>
+#include "Log.h"
+#include "Packets/AllPackets.h"
+#include "World.h"
+#include "WorldSession.h"
+
+template <class PacketClass, void(WorldSession::*HandlerFunction)(PacketClass&)>
 class PacketHandler : public ClientOpcodeHandler
 {
 public:
@@ -128,6 +131,10 @@ void OpcodeTable::ValidateAndSetServerOpcode(OpcodeServer opcode, char const* na
         return;
     }
 
+    // If the legacy connection mode has been enabled, all packets will get sent on one connection
+    if (sWorld->getBoolConfig(CONFIG_LEGACY_CONNECTION_MODE))
+        conIdx = CONNECTION_TYPE_REALM;
+
     if (_internalTableServer[opcode] != nullptr)
     {
         TC_LOG_ERROR("network", "Tried to override server handler of %s with %s (opcode %u)", opcodeTable[opcode]->Name, name, opcode);

src/server/game/Server/WorldSession.cpp

@@ -140,7 +140,8 @@ WorldSession::WorldSession(uint32 id, std::string&& name, uint32 battlenetAccoun
     _timeSyncClockDeltaQueue(std::make_unique<boost::circular_buffer<std::pair<int64, uint32>>>(6)),
     _timeSyncClockDelta(0),
     _pendingTimeSyncRequests(),
-    _gameClient(new GameClient(this))
+    _gameClient(new GameClient(this)),
+    _legacyConnectionModeEnabled(sWorld->getBoolConfig(CONFIG_LEGACY_CONNECTION_MODE))
 {
     memset(m_Tutorials, 0, sizeof(m_Tutorials));
 

src/server/game/Server/WorldSession.h

@@ -1420,6 +1420,7 @@ class TC_GAME_API WorldSession
         ConnectToKey _instanceConnectKey;
 
         GameClient* _gameClient;
+        bool _legacyConnectionModeEnabled;
 
         WorldSession(WorldSession const& right) = delete;
         WorldSession& operator=(WorldSession const& right) = delete;

src/server/game/World/World.cpp

@@ -1644,6 +1644,9 @@ void World::LoadConfigSettings(bool reload)
     // Anti movement cheat measure. Time each client have to acknowledge a movement change until they are kicked
     m_int_configs[CONFIG_PENDING_MOVE_CHANGES_TIMEOUT] = sConfigMgr->GetIntDefault("AntiCheat.PendingMoveChangesTimeoutTime", 0);
 
+    // Legacy connection mode
+    m_bool_configs[CONFIG_LEGACY_CONNECTION_MODE] = sConfigMgr->GetBoolDefault("LegacyConnectionModeEnabled", false);
+
     // call ScriptMgr if we're reloading the configuration
     if (reload)
         sScriptMgr->OnConfigLoad(reload);

src/server/game/World/World.h

@@ -186,6 +186,7 @@ enum WorldBoolConfigs : uint8
     CONFIG_CHECK_GOBJECT_LOS,
     CONFIG_RESPAWN_DYNAMIC_ESCORTNPC,
     CONFIG_CACHE_DATA_QUERIES,
+    CONFIG_LEGACY_CONNECTION_MODE,
     BOOL_CONFIG_VALUE_COUNT
 };
 

src/server/worldserver/worldserver.conf.dist

@@ -266,6 +266,15 @@ ProcessPriority = 0
 
 Compression = 1
 
+#
+#    LegacyConnectionModeEnabled
+#        Description: Enables/Disables the legacy connection handling in which only one connection socket
+#                     is being used to send and receive packets. This allows older pre-patched clients to connect.
+#        Default:     0   - (Disabled, Both sockets are used and required)
+#                     1   - (Enabled, One the first socket is being used)
+
+LegacyConnectionModeEnabled = 0
+
 #
 #    PlayerLimit
 #        Description: Maximum number of players in the world. Excluding Mods, GMs and Admins.