network_coordinator.cpp

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/*
 * This file is part of OpenTTD.
 * OpenTTD 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, version 2.
 * OpenTTD 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 OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */
 
#include "../stdafx.h"
#include "../debug.h"
#include "../error.h"
#include "../rev.h"
#include "../settings_type.h"
#include "../strings_func.h"
#include "../window_func.h"
#include "../window_type.h"
#include "network.h"
#include "network_coordinator.h"
#include "network_gamelist.h"
#include "network_gui.h"
#include "network_internal.h"
#include "network_server.h"
#include "network_stun.h"
#include "table/strings.h"
 
#include "../safeguards.h"
 
static const auto NETWORK_COORDINATOR_DELAY_BETWEEN_UPDATES = std::chrono::seconds(30); 
ClientNetworkCoordinatorSocketHandler _network_coordinator_client; 
ConnectionType _network_server_connection_type = CONNECTION_TYPE_UNKNOWN; 
std::string _network_server_invite_code = ""; 
 
class NetworkDirectConnecter : public TCPConnecter {
private:
  std::string token;     
  uint8_t tracking_number; 
 
public:
  NetworkDirectConnecter(const std::string &hostname, uint16_t port, const std::string &token, uint8_t tracking_number) : TCPConnecter(hostname, port), token(token), tracking_number(tracking_number) {}
 
  void OnFailure() override
  {
    _network_coordinator_client.ConnectFailure(this->token, this->tracking_number);
  }
 
  void OnConnect(SOCKET s) override
  {
    NetworkAddress address = NetworkAddress::GetPeerAddress(s);
    _network_coordinator_client.ConnectSuccess(this->token, s, address);
  }
};
 
class NetworkReuseStunConnecter : public TCPConnecter {
private:
  std::string token;     
  uint8_t tracking_number; 
  uint8_t family;          
 
public:
  NetworkReuseStunConnecter(const std::string &hostname, uint16_t port, const NetworkAddress &bind_address, std::string token, uint8_t tracking_number, uint8_t family) :
    TCPConnecter(hostname, port, bind_address),
    token(token),
    tracking_number(tracking_number),
    family(family)
  {
  }
 
  void OnFailure() override
  {
    /* Close the STUN connection too, as it is no longer of use. */
    _network_coordinator_client.CloseStunHandler(this->token, this->family);
 
    _network_coordinator_client.ConnectFailure(this->token, this->tracking_number);
  }
 
  void OnConnect(SOCKET s) override
  {
    NetworkAddress address = NetworkAddress::GetPeerAddress(s);
    _network_coordinator_client.ConnectSuccess(this->token, s, address);
  }
};
 
class NetworkCoordinatorConnecter : public TCPConnecter {
public:
  NetworkCoordinatorConnecter(const std::string &connection_string) : TCPConnecter(connection_string, NETWORK_COORDINATOR_SERVER_PORT) {}
 
  void OnFailure() override
  {
    _network_coordinator_client.connecting = false;
    _network_coordinator_client.CloseConnection(true);
  }
 
  void OnConnect(SOCKET s) override
  {
    assert(_network_coordinator_client.sock == INVALID_SOCKET);
 
    _network_coordinator_client.sock = s;
    _network_coordinator_client.last_activity = std::chrono::steady_clock::now();
    _network_coordinator_client.connecting = false;
  }
};
 
bool ClientNetworkCoordinatorSocketHandler::Receive_GC_ERROR(Packet &p)
{
  NetworkCoordinatorErrorType error = (NetworkCoordinatorErrorType)p.Recv_uint8();
  std::string detail = p.Recv_string(NETWORK_ERROR_DETAIL_LENGTH);
 
  switch (error) {
    case NETWORK_COORDINATOR_ERROR_UNKNOWN:
      this->CloseConnection();
      return false;
 
    case NETWORK_COORDINATOR_ERROR_REGISTRATION_FAILED:
      ShowErrorMessage(GetEncodedString(STR_NETWORK_ERROR_COORDINATOR_REGISTRATION_FAILED), {}, WL_ERROR);
 
      /* To prevent that we constantly try to reconnect, switch to local game. */
      _settings_client.network.server_game_type = SERVER_GAME_TYPE_LOCAL;
 
      this->CloseConnection();
      return false;
 
    case NETWORK_COORDINATOR_ERROR_INVALID_INVITE_CODE: {
      auto connecter_pre_it = this->connecter_pre.find(detail);
      if (connecter_pre_it != this->connecter_pre.end()) {
        connecter_pre_it->second->SetFailure();
        this->connecter_pre.erase(connecter_pre_it);
      }
 
      /* Mark the server as offline. */
      NetworkGameList *item = NetworkGameListAddItem(detail);
      item->status = NGLS_OFFLINE;
 
      UpdateNetworkGameWindow();
      return true;
    }
 
    case NETWORK_COORDINATOR_ERROR_REUSE_OF_INVITE_CODE:
      ShowErrorMessage(GetEncodedString(STR_NETWORK_ERROR_COORDINATOR_REUSE_OF_INVITE_CODE), {}, WL_ERROR);
 
      /* To prevent that we constantly battle for the same invite-code, switch to local game. */
      _settings_client.network.server_game_type = SERVER_GAME_TYPE_LOCAL;
 
      this->CloseConnection();
      return false;
 
    default:
      Debug(net, 0, "Invalid error type {} received from Game Coordinator", error);
      this->CloseConnection();
      return false;
  }
}
 
bool ClientNetworkCoordinatorSocketHandler::Receive_GC_REGISTER_ACK(Packet &p)
{
  /* Schedule sending an update. */
  this->next_update = std::chrono::steady_clock::now();
 
  _settings_client.network.server_invite_code = p.Recv_string(NETWORK_INVITE_CODE_LENGTH);
  _settings_client.network.server_invite_code_secret = p.Recv_string(NETWORK_INVITE_CODE_SECRET_LENGTH);
  _network_server_connection_type = (ConnectionType)p.Recv_uint8();
 
  if (_network_server_connection_type == CONNECTION_TYPE_ISOLATED) {
    ShowErrorMessage(
      GetEncodedString(STR_NETWORK_ERROR_COORDINATOR_ISOLATED),
      GetEncodedString(STR_NETWORK_ERROR_COORDINATOR_ISOLATED_DETAIL),
      WL_ERROR);
  }
 
  /* Users can change the invite code in the settings, but this has no effect
   * on the invite code as assigned by the server. So
   * _network_server_invite_code contains the current invite code,
   * and _settings_client.network.server_invite_code contains the one we will
   * attempt to re-use when registering again. */
  _network_server_invite_code = _settings_client.network.server_invite_code;
 
  SetWindowDirty(WC_CLIENT_LIST, 0);
 
  if (_network_dedicated) {
    std::string connection_type;
    switch (_network_server_connection_type) {
      case CONNECTION_TYPE_ISOLATED: connection_type = "Remote players can't connect"; break;
      case CONNECTION_TYPE_DIRECT:   connection_type = "Public"; break;
      case CONNECTION_TYPE_STUN:     connection_type = "Behind NAT"; break;
      case CONNECTION_TYPE_TURN:     connection_type = "Via relay"; break;
 
      case CONNECTION_TYPE_UNKNOWN: // Never returned from Game Coordinator.
      default: connection_type = "Unknown"; break; // Should never happen, but don't fail if it does.
    }
 
    std::string game_type;
    switch (_settings_client.network.server_game_type) {
      case SERVER_GAME_TYPE_INVITE_ONLY: game_type = "Invite only"; break;
      case SERVER_GAME_TYPE_PUBLIC: game_type = "Public"; break;
 
      case SERVER_GAME_TYPE_LOCAL: // Impossible to register local servers.
      default: game_type = "Unknown"; break; // Should never happen, but don't fail if it does.
    }
 
    Debug(net, 3, "----------------------------------------");
    Debug(net, 3, "Your server is now registered with the Game Coordinator:");
    Debug(net, 3, "  Game type:       {}", game_type);
    Debug(net, 3, "  Connection type: {}", connection_type);
    Debug(net, 3, "  Invite code:     {}", _network_server_invite_code);
    Debug(net, 3, "----------------------------------------");
  } else {
    Debug(net, 3, "Game Coordinator registered our server with invite code '{}'", _network_server_invite_code);
  }
 
  return true;
}
 
bool ClientNetworkCoordinatorSocketHandler::Receive_GC_LISTING(Packet &p)
{
  uint8_t servers = p.Recv_uint16();
 
  /* End of list; we can now remove all expired items from the list. */
  if (servers == 0) {
    NetworkGameListRemoveExpired();
    return true;
  }
 
  for (; servers > 0; servers--) {
    std::string connection_string = p.Recv_string(NETWORK_HOSTNAME_PORT_LENGTH);
 
    /* Now we know the connection string, we can add it to our list. */
    NetworkGameList *item = NetworkGameListAddItem(connection_string);
 
    /* Clear any existing GRFConfig chain. */
    ClearGRFConfigList(item->info.grfconfig);
    /* Read the NetworkGameInfo from the packet. */
    DeserializeNetworkGameInfo(p, item->info, &this->newgrf_lookup_table);
    /* Check for compatibility with the client. */
    CheckGameCompatibility(item->info);
    /* Mark server as online. */
    item->status = NGLS_ONLINE;
    /* Mark the item as up-to-date. */
    item->version = _network_game_list_version;
  }
 
  UpdateNetworkGameWindow();
  return true;
}
 
bool ClientNetworkCoordinatorSocketHandler::Receive_GC_CONNECTING(Packet &p)
{
  std::string token = p.Recv_string(NETWORK_TOKEN_LENGTH);
  std::string invite_code = p.Recv_string(NETWORK_INVITE_CODE_LENGTH);
 
  /* Find the connecter based on the invite code. */
  auto connecter_pre_it = this->connecter_pre.find(invite_code);
  if (connecter_pre_it == this->connecter_pre.end()) {
    this->CloseConnection();
    return false;
  }
 
  /* Now store it based on the token. */
  this->connecter[token] = {invite_code, connecter_pre_it->second};
  this->connecter_pre.erase(connecter_pre_it);
 
  return true;
}
 
bool ClientNetworkCoordinatorSocketHandler::Receive_GC_CONNECT_FAILED(Packet &p)
{
  std::string token = p.Recv_string(NETWORK_TOKEN_LENGTH);
  this->CloseToken(token);
 
  return true;
}
 
bool ClientNetworkCoordinatorSocketHandler::Receive_GC_DIRECT_CONNECT(Packet &p)
{
  std::string token = p.Recv_string(NETWORK_TOKEN_LENGTH);
  uint8_t tracking_number = p.Recv_uint8();
  std::string hostname = p.Recv_string(NETWORK_HOSTNAME_LENGTH);
  uint16_t port = p.Recv_uint16();
 
  /* Ensure all other pending connection attempts are killed. */
  if (this->game_connecter != nullptr) {
    this->game_connecter->Kill();
    this->game_connecter = nullptr;
  }
 
  this->game_connecter = TCPConnecter::Create<NetworkDirectConnecter>(hostname, port, token, tracking_number);
  return true;
}
 
bool ClientNetworkCoordinatorSocketHandler::Receive_GC_STUN_REQUEST(Packet &p)
{
  std::string token = p.Recv_string(NETWORK_TOKEN_LENGTH);
 
  this->stun_handlers[token][AF_INET6] = ClientNetworkStunSocketHandler::Stun(token, AF_INET6);
  this->stun_handlers[token][AF_INET] = ClientNetworkStunSocketHandler::Stun(token, AF_INET);
  return true;
}
 
bool ClientNetworkCoordinatorSocketHandler::Receive_GC_STUN_CONNECT(Packet &p)
{
  std::string token = p.Recv_string(NETWORK_TOKEN_LENGTH);
  uint8_t tracking_number = p.Recv_uint8();
  uint8_t family = p.Recv_uint8();
  std::string host = p.Recv_string(NETWORK_HOSTNAME_PORT_LENGTH);
  uint16_t port = p.Recv_uint16();
 
  /* Check if we know this token. */
  auto stun_it = this->stun_handlers.find(token);
  if (stun_it == this->stun_handlers.end()) return true;
  auto family_it = stun_it->second.find(family);
  if (family_it == stun_it->second.end()) return true;
 
  /* Ensure all other pending connection attempts are killed. */
  if (this->game_connecter != nullptr) {
    this->game_connecter->Kill();
    this->game_connecter = nullptr;
  }
 
  /* We now mark the connection as closed, but we do not really close the
   * socket yet. We do this when the NetworkReuseStunConnecter is connected.
   * This prevents any NAT to already remove the route while we create the
   * second connection on top of the first. */
  family_it->second->CloseConnection(false);
 
  /* Connect to our peer from the same local address as we use for the
   * STUN server. This means that if there is any NAT in the local network,
   * the public ip:port is still pointing to the local address, and as such
   * a connection can be established. */
  this->game_connecter = TCPConnecter::Create<NetworkReuseStunConnecter>(host, port, family_it->second->local_addr, token, tracking_number, family);
  return true;
}
 
bool ClientNetworkCoordinatorSocketHandler::Receive_GC_NEWGRF_LOOKUP(Packet &p)
{
  this->newgrf_lookup_table_cursor = p.Recv_uint32();
 
  uint16_t newgrfs = p.Recv_uint16();
  for (; newgrfs> 0; newgrfs--) {
    uint32_t index = p.Recv_uint32();
    DeserializeGRFIdentifierWithName(p, this->newgrf_lookup_table[index]);
  }
  return true;
}
 
bool ClientNetworkCoordinatorSocketHandler::Receive_GC_TURN_CONNECT(Packet &p)
{
  std::string token = p.Recv_string(NETWORK_TOKEN_LENGTH);
  uint8_t tracking_number = p.Recv_uint8();
  std::string ticket = p.Recv_string(NETWORK_TOKEN_LENGTH);
  std::string connection_string = p.Recv_string(NETWORK_HOSTNAME_PORT_LENGTH);
 
  /* Ensure all other pending connection attempts are killed. */
  if (this->game_connecter != nullptr) {
    this->game_connecter->Kill();
    this->game_connecter = nullptr;
  }
 
  this->turn_handlers[token] = ClientNetworkTurnSocketHandler::Turn(token, tracking_number, ticket, connection_string);
 
  if (!_network_server) {
    auto connecter_it = this->connecter.find(token);
    if (connecter_it == this->connecter.end()) {
      /* Make sure we are still interested in connecting to this server. */
      this->ConnectFailure(token, 0);
      return true;
    }
 
    switch (_settings_client.network.use_relay_service) {
      case URS_NEVER:
        this->ConnectFailure(token, 0);
        break;
 
      case URS_ASK:
        ShowNetworkAskRelay(connecter_it->second.first, connection_string, token);
        break;
 
      case URS_ALLOW:
        this->StartTurnConnection(token);
        break;
    }
  } else {
    this->StartTurnConnection(token);
  }
 
  return true;
}
 
void ClientNetworkCoordinatorSocketHandler::StartTurnConnection(std::string &token)
{
  auto turn_it = this->turn_handlers.find(token);
  if (turn_it == this->turn_handlers.end()) return;
 
  turn_it->second->Connect();
}
 
void ClientNetworkCoordinatorSocketHandler::Connect()
{
  /* We are either already connected or are trying to connect. */
  if (this->sock != INVALID_SOCKET || this->connecting) return;
 
  this->Reopen();
 
  this->connecting = true;
  this->last_activity = std::chrono::steady_clock::now();
 
  TCPConnecter::Create<NetworkCoordinatorConnecter>(NetworkCoordinatorConnectionString());
}
 
NetworkRecvStatus ClientNetworkCoordinatorSocketHandler::CloseConnection(bool error)
{
  NetworkCoordinatorSocketHandler::CloseConnection(error);
 
  this->CloseSocket();
  this->connecting = false;
 
  _network_server_connection_type = CONNECTION_TYPE_UNKNOWN;
  this->next_update = {};
 
  this->CloseAllConnections();
 
  SetWindowDirty(WC_CLIENT_LIST, 0);
 
  return NETWORK_RECV_STATUS_OKAY;
}
 
void ClientNetworkCoordinatorSocketHandler::Register()
{
  _network_server_connection_type = CONNECTION_TYPE_UNKNOWN;
  this->next_update = {};
 
  SetWindowDirty(WC_CLIENT_LIST, 0);
 
  this->Connect();
 
  auto p = std::make_unique<Packet>(this, PACKET_COORDINATOR_SERVER_REGISTER);
  p->Send_uint8(NETWORK_COORDINATOR_VERSION);
  p->Send_uint8(_settings_client.network.server_game_type);
  p->Send_uint16(_settings_client.network.server_port);
  if (_settings_client.network.server_invite_code.empty() || _settings_client.network.server_invite_code_secret.empty()) {
    p->Send_string("");
    p->Send_string("");
  } else {
    p->Send_string(_settings_client.network.server_invite_code);
    p->Send_string(_settings_client.network.server_invite_code_secret);
  }
 
  this->SendPacket(std::move(p));
}
 
void ClientNetworkCoordinatorSocketHandler::SendServerUpdate()
{
  Debug(net, 6, "Sending server update to Game Coordinator");
 
  auto p = std::make_unique<Packet>(this, PACKET_COORDINATOR_SERVER_UPDATE, TCP_MTU);
  p->Send_uint8(NETWORK_COORDINATOR_VERSION);
  SerializeNetworkGameInfo(*p, GetCurrentNetworkServerGameInfo(), this->next_update.time_since_epoch() != std::chrono::nanoseconds::zero());
 
  this->SendPacket(std::move(p));
 
  this->next_update = std::chrono::steady_clock::now() + NETWORK_COORDINATOR_DELAY_BETWEEN_UPDATES;
}
 
void ClientNetworkCoordinatorSocketHandler::GetListing()
{
  this->Connect();
 
  _network_game_list_version++;
 
  auto p = std::make_unique<Packet>(this, PACKET_COORDINATOR_CLIENT_LISTING);
  p->Send_uint8(NETWORK_COORDINATOR_VERSION);
  p->Send_uint8(NETWORK_GAME_INFO_VERSION);
  p->Send_string(_openttd_revision);
  p->Send_uint32(this->newgrf_lookup_table_cursor);
 
  this->SendPacket(std::move(p));
}
 
void ClientNetworkCoordinatorSocketHandler::ConnectToServer(const std::string &invite_code, TCPServerConnecter *connecter)
{
  assert(invite_code.starts_with("+"));
 
  if (this->connecter_pre.find(invite_code) != this->connecter_pre.end()) {
    /* If someone is hammering the refresh key, one can sent out two
     * requests for the same invite code. There isn't really a great way
     * of handling this, so just ignore this request. */
    connecter->SetFailure();
    return;
  }
 
  /* Initially we store based on invite code; on first reply we know the
   * token, and will start using that key instead. */
  this->connecter_pre[invite_code] = connecter;
 
  this->Connect();
 
  auto p = std::make_unique<Packet>(this, PACKET_COORDINATOR_CLIENT_CONNECT);
  p->Send_uint8(NETWORK_COORDINATOR_VERSION);
  p->Send_string(invite_code);
 
  this->SendPacket(std::move(p));
}
 
void ClientNetworkCoordinatorSocketHandler::ConnectFailure(const std::string &token, uint8_t tracking_number)
{
  /* Connecter will destroy itself. */
  this->game_connecter = nullptr;
 
  auto p = std::make_unique<Packet>(this, PACKET_COORDINATOR_SERCLI_CONNECT_FAILED);
  p->Send_uint8(NETWORK_COORDINATOR_VERSION);
  p->Send_string(token);
  p->Send_uint8(tracking_number);
 
  this->SendPacket(std::move(p));
 
  /* We do not close the associated connecter here yet, as the
   * Game Coordinator might have other methods of connecting available. */
}
 
void ClientNetworkCoordinatorSocketHandler::ConnectSuccess(const std::string &token, SOCKET sock, NetworkAddress &address)
{
  assert(sock != INVALID_SOCKET);
 
  /* Connecter will destroy itself. */
  this->game_connecter = nullptr;
 
  if (_network_server) {
    if (!ServerNetworkGameSocketHandler::ValidateClient(sock, address)) return;
    Debug(net, 3, "[{}] Client connected from {} on frame {}", ServerNetworkGameSocketHandler::GetName(), address.GetHostname(), _frame_counter);
    ServerNetworkGameSocketHandler::AcceptConnection(sock, address);
  } else {
    /* The client informs the Game Coordinator about the success. The server
     * doesn't have to, as it is implied by the client telling. */
    auto p = std::make_unique<Packet>(this, PACKET_COORDINATOR_CLIENT_CONNECTED);
    p->Send_uint8(NETWORK_COORDINATOR_VERSION);
    p->Send_string(token);
    this->SendPacket(std::move(p));
 
    /* Find the connecter; it can happen it no longer exist, in cases where
     * we aborted the connect but the Game Coordinator was already in the
     * processes of connecting us. */
    auto connecter_it = this->connecter.find(token);
    if (connecter_it != this->connecter.end()) {
      connecter_it->second.second->SetConnected(sock);
      this->connecter.erase(connecter_it);
    }
  }
 
  /* Close all remaining connections. */
  this->CloseToken(token);
}
 
void ClientNetworkCoordinatorSocketHandler::StunResult(const std::string &token, uint8_t family, bool result)
{
  auto p = std::make_unique<Packet>(this, PACKET_COORDINATOR_SERCLI_STUN_RESULT);
  p->Send_uint8(NETWORK_COORDINATOR_VERSION);
  p->Send_string(token);
  p->Send_uint8(family);
  p->Send_bool(result);
  this->SendPacket(std::move(p));
}
 
void ClientNetworkCoordinatorSocketHandler::CloseStunHandler(const std::string &token, uint8_t family)
{
  auto stun_it = this->stun_handlers.find(token);
  if (stun_it == this->stun_handlers.end()) return;
 
  if (family == AF_UNSPEC) {
    for (auto &[family, stun_handler] : stun_it->second) {
      stun_handler->CloseConnection();
      stun_handler->CloseSocket();
    }
 
    this->stun_handlers.erase(stun_it);
  } else {
    auto family_it = stun_it->second.find(family);
    if (family_it == stun_it->second.end()) return;
 
    family_it->second->CloseConnection();
    family_it->second->CloseSocket();
 
    stun_it->second.erase(family_it);
  }
}
 
void ClientNetworkCoordinatorSocketHandler::CloseTurnHandler(const std::string &token)
{
  CloseWindowByClass(WC_NETWORK_ASK_RELAY, NRWCD_HANDLED);
 
  auto turn_it = this->turn_handlers.find(token);
  if (turn_it == this->turn_handlers.end()) return;
 
  turn_it->second->CloseConnection();
  turn_it->second->CloseSocket();
 
  /* We don't remove turn_handler here, as we can be called from within that
   * turn_handler instance, so our object cannot be free'd yet. Instead, we
   * check later if the connection is closed, and free the object then. */
}
 
void ClientNetworkCoordinatorSocketHandler::CloseToken(const std::string &token)
{
  /* Close all remaining STUN / TURN connections. */
  this->CloseStunHandler(token);
  this->CloseTurnHandler(token);
 
  /* Close the caller of the connection attempt. */
  auto connecter_it = this->connecter.find(token);
  if (connecter_it != this->connecter.end()) {
    connecter_it->second.second->SetFailure();
    this->connecter.erase(connecter_it);
  }
}
 
void ClientNetworkCoordinatorSocketHandler::CloseAllConnections()
{
  /* Ensure all other pending connection attempts are also killed. */
  if (this->game_connecter != nullptr) {
    this->game_connecter->Kill();
    this->game_connecter = nullptr;
  }
 
  /* Mark any pending connecters as failed. */
  for (auto &[token, it] : this->connecter) {
    this->CloseStunHandler(token);
    this->CloseTurnHandler(token);
    it.second->SetFailure();
 
    /* Inform the Game Coordinator he can stop trying to connect us to the server. */
    this->ConnectFailure(token, 0);
  }
  this->stun_handlers.clear();
  this->turn_handlers.clear();
  this->connecter.clear();
 
  /* Also close any pending invite-code requests. */
  for (auto &[invite_code, it] : this->connecter_pre) {
    it->SetFailure();
  }
  this->connecter_pre.clear();
}
 
void ClientNetworkCoordinatorSocketHandler::SendReceive()
{
  /* Private games are not listed via the Game Coordinator. */
  if (_network_server && _settings_client.network.server_game_type == SERVER_GAME_TYPE_LOCAL) {
    if (this->sock != INVALID_SOCKET) {
      this->CloseConnection();
    }
    return;
  }
 
  static int last_attempt_backoff = 1;
  static bool first_reconnect = true;
 
  if (this->sock == INVALID_SOCKET) {
    static std::chrono::steady_clock::time_point last_attempt = {};
 
    /* Don't auto-reconnect when we are not a server. */
    if (!_network_server) return;
    /* Don't reconnect if we are connecting. */
    if (this->connecting) return;
    /* Throttle how often we try to reconnect. */
    if (std::chrono::steady_clock::now() < last_attempt + std::chrono::seconds(1) * last_attempt_backoff) return;
 
    last_attempt = std::chrono::steady_clock::now();
    /* Delay reconnecting with up to 32 seconds. */
    if (last_attempt_backoff < 32) {
      last_attempt_backoff *= 2;
    }
 
    /* Do not reconnect on the first attempt, but only initialize the
     * last_attempt variables.  Otherwise after an outage all servers
     * reconnect at the same time, potentially overwhelming the
     * Game Coordinator. */
    if (first_reconnect) {
      first_reconnect = false;
      return;
    }
 
    Debug(net, 1, "Connection with Game Coordinator lost; reconnecting...");
    this->Register();
    return;
  }
 
  last_attempt_backoff = 1;
  first_reconnect = true;
 
  if (_network_server && _network_server_connection_type != CONNECTION_TYPE_UNKNOWN && std::chrono::steady_clock::now() > this->next_update) {
    this->SendServerUpdate();
  }
 
  if (!_network_server && std::chrono::steady_clock::now() > this->last_activity + IDLE_TIMEOUT) {
    this->CloseConnection();
    return;
  }
 
  if (this->CanSendReceive()) {
    if (this->ReceivePackets()) {
      this->last_activity = std::chrono::steady_clock::now();
    }
  }
 
  this->SendPackets();
 
  for (const auto &[token, families] : this->stun_handlers) {
    for (const auto &[family, stun_handler] : families) {
      stun_handler->SendReceive();
    }
  }
 
  /* Check for handlers that are not connecting nor connected. Destroy those objects. */
  for (auto turn_it = this->turn_handlers.begin(); turn_it != this->turn_handlers.end(); /* nothing */) {
    if (turn_it->second->connect_started && turn_it->second->connecter == nullptr && !turn_it->second->IsConnected()) {
      turn_it = this->turn_handlers.erase(turn_it);
    } else {
      turn_it++;
    }
  }
 
  for (const auto &[token, turn_handler] : this->turn_handlers) {
    turn_handler->SendReceive();
  }
}