Add: use Game Coordinator to annouce public servers

13 files changed, 569 insertions, 39 deletions

diff --git a/src/lang/english.txt b/src/lang/english.txt
index bd5cff8d3..2e84d4b3a 100644
--- a/src/lang/english.txt
+++ b/src/lang/english.txt
@@ -1995,7 +1995,7 @@ STR_FACE_TIE                                                    :Tie:
 STR_FACE_EARRING                                                :Earring:
 STR_FACE_TIE_EARRING_TOOLTIP                                    :{BLACK}Change tie or earring
 
-STR_NETWORK_SERVER_VISIBILITY_PRIVATE                           :Private
+STR_NETWORK_SERVER_VISIBILITY_LOCAL                             :Local
 STR_NETWORK_SERVER_VISIBILITY_PUBLIC                            :Public
 
 # Network server list
@@ -2136,6 +2136,8 @@ STR_NETWORK_CLIENT_LIST_SERVER_NAME_EDIT_TOOLTIP                :{BLACK}Edit the
 STR_NETWORK_CLIENT_LIST_SERVER_NAME_QUERY_CAPTION               :Name of the server
 STR_NETWORK_CLIENT_LIST_SERVER_VISIBILITY                       :{BLACK}Visibility
 STR_NETWORK_CLIENT_LIST_SERVER_VISIBILITY_TOOLTIP               :{BLACK}Whether other people can see your server in the public listing
+STR_NETWORK_CLIENT_LIST_SERVER_CONNECTION_TYPE                  :{BLACK}Connection type
+STR_NETWORK_CLIENT_LIST_SERVER_CONNECTION_TYPE_TOOLTIP          :{BLACK}Whether and how your server can be reached by others
 STR_NETWORK_CLIENT_LIST_PLAYER                                  :{BLACK}Player
 STR_NETWORK_CLIENT_LIST_PLAYER_NAME                             :{BLACK}Name
 STR_NETWORK_CLIENT_LIST_PLAYER_NAME_TOOLTIP                     :{BLACK}Your player name
@@ -2154,6 +2156,12 @@ STR_NETWORK_CLIENT_LIST_PLAYER_ICON_SELF_TOOLTIP                :{BLACK}This is
 STR_NETWORK_CLIENT_LIST_PLAYER_ICON_HOST_TOOLTIP                :{BLACK}This is the host of the game
 STR_NETWORK_CLIENT_LIST_CLIENT_COMPANY_COUNT                    :{BLACK}{NUM} client{P "" s} / {NUM} compan{P y ies}
 
+############ Begin of ConnectionType
+STR_NETWORK_CLIENT_LIST_SERVER_CONNECTION_TYPE_UNKNOWN          :{BLACK}Local
+STR_NETWORK_CLIENT_LIST_SERVER_CONNECTION_TYPE_ISOLATED         :{RED}Remote players can't connect
+STR_NETWORK_CLIENT_LIST_SERVER_CONNECTION_TYPE_DIRECT           :{BLACK}Public
+############ End of ConnectionType
+
 STR_NETWORK_CLIENT_LIST_ADMIN_CLIENT_KICK                       :Kick
 STR_NETWORK_CLIENT_LIST_ADMIN_CLIENT_BAN                        :Ban
 STR_NETWORK_CLIENT_LIST_ADMIN_COMPANY_RESET                     :Delete
@@ -2281,6 +2289,10 @@ STR_NETWORK_MESSAGE_SERVER_SHUTDOWN                             :{WHITE}The serv
 STR_NETWORK_MESSAGE_SERVER_REBOOT                               :{WHITE}The server is restarting...{}Please wait...
 STR_NETWORK_MESSAGE_KICKED                                      :*** {RAW_STRING} was kicked. Reason: ({RAW_STRING})
 
+STR_NETWORK_ERROR_COORDINATOR_REGISTRATION_FAILED               :{WHITE}Server registration failed
+STR_NETWORK_ERROR_COORDINATOR_ISOLATED                          :{WHITE}Your server doesn't allow remote connections
+STR_NETWORK_ERROR_COORDINATOR_ISOLATED_DETAIL                   :{WHITE}Other players won't be able to connect to your server
+
 # Content downloading window
 STR_CONTENT_TITLE                                               :{WHITE}Content downloading
 STR_CONTENT_TYPE_CAPTION                                        :{BLACK}Type
diff --git a/src/network/CMakeLists.txt b/src/network/CMakeLists.txt
index 1c27d6206..bf89b5c1d 100644
--- a/src/network/CMakeLists.txt
+++ b/src/network/CMakeLists.txt
@@ -14,6 +14,8 @@ add_files(
     network_content.h
     network_content_gui.cpp
     network_content_gui.h
+    network_coordinator.cpp
+    network_coordinator.h
     network_func.h
     network_gamelist.cpp
     network_gamelist.h
diff --git a/src/network/core/CMakeLists.txt b/src/network/core/CMakeLists.txt
index bf713be99..6eb255f6f 100644
--- a/src/network/core/CMakeLists.txt
+++ b/src/network/core/CMakeLists.txt
@@ -20,6 +20,8 @@ add_files(
     tcp_content.cpp
     tcp_content.h
     tcp_content_type.h
+    tcp_coordinator.cpp
+    tcp_coordinator.h
     tcp_game.cpp
     tcp_game.h
     tcp_http.cpp
diff --git a/src/network/core/config.h b/src/network/core/config.h
index 6d6038ec7..e0ec63a0c 100644
--- a/src/network/core/config.h
+++ b/src/network/core/config.h
@@ -14,6 +14,8 @@
 
 /** DNS hostname of the masterserver */
 static const char * const NETWORK_MASTER_SERVER_HOST            = "master.openttd.org";
+/** DNS hostname of the Game Coordinator server */
+static const char * const NETWORK_COORDINATOR_SERVER_HOST       = "coordinator.openttd.org";
 /** DNS hostname of the content server */
 static const char * const NETWORK_CONTENT_SERVER_HOST           = "content.openttd.org";
 /** DNS hostname of the HTTP-content mirror server */
@@ -23,14 +25,15 @@ static const char * const NETWORK_CONTENT_MIRROR_URL            = "/bananas";
 /** Message sent to the masterserver to 'identify' this client as OpenTTD */
 static const char * const NETWORK_MASTER_SERVER_WELCOME_MESSAGE = "OpenTTDRegister";
 
-static const uint16 NETWORK_MASTER_SERVER_PORT    = 3978;         ///< The default port of the master server (UDP)
-static const uint16 NETWORK_CONTENT_SERVER_PORT   = 3978;         ///< The default port of the content server (TCP)
-static const uint16 NETWORK_CONTENT_MIRROR_PORT   =   80;         ///< The default port of the content mirror (TCP)
-static const uint16 NETWORK_DEFAULT_PORT          = 3979;         ///< The default port of the game server (TCP & UDP)
-static const uint16 NETWORK_ADMIN_PORT            = 3977;         ///< The default port for admin network
-static const uint16 NETWORK_DEFAULT_DEBUGLOG_PORT = 3982;         ///< The default port debug-log is sent to (TCP)
+static const uint16 NETWORK_MASTER_SERVER_PORT      = 3978;           ///< The default port of the master server (UDP)
+static const uint16 NETWORK_COORDINATOR_SERVER_PORT = 3976;           ///< The default port of the Game Coordinator server (TCP)
+static const uint16 NETWORK_CONTENT_SERVER_PORT     = 3978;           ///< The default port of the content server (TCP)
+static const uint16 NETWORK_CONTENT_MIRROR_PORT     =   80;           ///< The default port of the content mirror (TCP)
+static const uint16 NETWORK_DEFAULT_PORT            = 3979;           ///< The default port of the game server (TCP & UDP)
+static const uint16 NETWORK_ADMIN_PORT              = 3977;           ///< The default port for admin network
+static const uint16 NETWORK_DEFAULT_DEBUGLOG_PORT   = 3982;           ///< The default port debug-log is sent to (TCP)
 
-static const uint16 UDP_MTU                       = 1460;         ///< Number of bytes we can pack in a single UDP packet
+static const uint16 UDP_MTU                         = 1460;           ///< Number of bytes we can pack in a single UDP packet
 /*
  * Technically a TCP packet could become 64kiB, however the high bit is kept so it becomes possible in the future
  * to go to (significantly) larger packets if needed. This would entail a strategy such as employed for UTF-8.
@@ -45,40 +48,42 @@ static const uint16 UDP_MTU                       = 1460;         ///< Number of
  * Send_uint16(GB(size, 16, 14) | 0b10 << 14)
  * Send_uint16(GB(size,  0, 16))
  */
-static const uint16 TCP_MTU                       = 32767;        ///< Number of bytes we can pack in a single TCP packet
-static const uint16 COMPAT_MTU                    = 1460;         ///< Number of bytes we can pack in a single packet for backward compatibility
+static const uint16 TCP_MTU                         = 32767;          ///< Number of bytes we can pack in a single TCP packet
+static const uint16 COMPAT_MTU                      = 1460;           ///< Number of bytes we can pack in a single packet for backward compatibility
 
-static const byte NETWORK_GAME_ADMIN_VERSION      =    1;         ///< What version of the admin network do we use?
-static const byte NETWORK_GAME_INFO_VERSION       =    4;         ///< What version of game-info do we use?
-static const byte NETWORK_COMPANY_INFO_VERSION    =    6;         ///< What version of company info is this?
-static const byte NETWORK_MASTER_SERVER_VERSION   =    2;         ///< What version of master-server-protocol do we use?
+static const byte NETWORK_GAME_ADMIN_VERSION        =    1;           ///< What version of the admin network do we use?
+static const byte NETWORK_GAME_INFO_VERSION         =    4;           ///< What version of game-info do we use?
+static const byte NETWORK_COMPANY_INFO_VERSION      =    6;           ///< What version of company info is this?
+static const byte NETWORK_MASTER_SERVER_VERSION     =    2;           ///< What version of master-server-protocol do we use?
+static const byte NETWORK_COORDINATOR_VERSION       =    1;           ///< What version of game-coordinator-protocol do we use?
 
-static const uint NETWORK_NAME_LENGTH             =   80;         ///< The maximum length of the server name and map name, in bytes including '\0'
-static const uint NETWORK_COMPANY_NAME_LENGTH     =  128;         ///< The maximum length of the company name, in bytes including '\0'
-static const uint NETWORK_HOSTNAME_LENGTH         =   80;         ///< The maximum length of the host name, in bytes including '\0'
-static const uint NETWORK_HOSTNAME_PORT_LENGTH    =   80 + 6;     ///< The maximum length of the host name + port, in bytes including '\0'. The extra six is ":" + port number (with a max of 65536)
-static const uint NETWORK_SERVER_ID_LENGTH        =   33;         ///< The maximum length of the network id of the servers, in bytes including '\0'
-static const uint NETWORK_REVISION_LENGTH         =   33;         ///< The maximum length of the revision, in bytes including '\0'
-static const uint NETWORK_PASSWORD_LENGTH         =   33;         ///< The maximum length of the password, in bytes including '\0' (must be >= NETWORK_SERVER_ID_LENGTH)
-static const uint NETWORK_CLIENTS_LENGTH          =  200;         ///< The maximum length for the list of clients that controls a company, in bytes including '\0'
-static const uint NETWORK_CLIENT_NAME_LENGTH      =   25;         ///< The maximum length of a client's name, in bytes including '\0'
-static const uint NETWORK_RCONCOMMAND_LENGTH      =  500;         ///< The maximum length of a rconsole command, in bytes including '\0'
-static const uint NETWORK_GAMESCRIPT_JSON_LENGTH  = COMPAT_MTU-3; ///< The maximum length of a gamescript json string, in bytes including '\0'. Must not be longer than COMPAT_MTU including header (3 bytes)
-static const uint NETWORK_CHAT_LENGTH             =  900;         ///< The maximum length of a chat message, in bytes including '\0'
-static const uint NETWORK_CONTENT_FILENAME_LENGTH =   48;         ///< The maximum length of a content's filename, in bytes including '\0'.
-static const uint NETWORK_CONTENT_NAME_LENGTH     =   32;         ///< The maximum length of a content's name, in bytes including '\0'.
-static const uint NETWORK_CONTENT_VERSION_LENGTH  =   16;         ///< The maximum length of a content's version, in bytes including '\0'.
-static const uint NETWORK_CONTENT_URL_LENGTH      =   96;         ///< The maximum length of a content's url, in bytes including '\0'.
-static const uint NETWORK_CONTENT_DESC_LENGTH     =  512;         ///< The maximum length of a content's description, in bytes including '\0'.
-static const uint NETWORK_CONTENT_TAG_LENGTH      =   32;         ///< The maximum length of a content's tag, in bytes including '\0'.
+static const uint NETWORK_NAME_LENGTH               =   80;           ///< The maximum length of the server name and map name, in bytes including '\0'
+static const uint NETWORK_COMPANY_NAME_LENGTH       =  128;           ///< The maximum length of the company name, in bytes including '\0'
+static const uint NETWORK_HOSTNAME_LENGTH           =   80;           ///< The maximum length of the host name, in bytes including '\0'
+static const uint NETWORK_HOSTNAME_PORT_LENGTH      =   80 + 6;       ///< The maximum length of the host name + port, in bytes including '\0'. The extra six is ":" + port number (with a max of 65536)
+static const uint NETWORK_SERVER_ID_LENGTH          =   33;           ///< The maximum length of the network id of the servers, in bytes including '\0'
+static const uint NETWORK_REVISION_LENGTH           =   33;           ///< The maximum length of the revision, in bytes including '\0'
+static const uint NETWORK_PASSWORD_LENGTH           =   33;           ///< The maximum length of the password, in bytes including '\0' (must be >= NETWORK_SERVER_ID_LENGTH)
+static const uint NETWORK_CLIENTS_LENGTH            =  200;           ///< The maximum length for the list of clients that controls a company, in bytes including '\0'
+static const uint NETWORK_CLIENT_NAME_LENGTH        =   25;           ///< The maximum length of a client's name, in bytes including '\0'
+static const uint NETWORK_RCONCOMMAND_LENGTH        =  500;           ///< The maximum length of a rconsole command, in bytes including '\0'
+static const uint NETWORK_GAMESCRIPT_JSON_LENGTH    = COMPAT_MTU - 3; ///< The maximum length of a gamescript json string, in bytes including '\0'. Must not be longer than COMPAT_MTU including header (3 bytes)
+static const uint NETWORK_CHAT_LENGTH               =  900;           ///< The maximum length of a chat message, in bytes including '\0'
+static const uint NETWORK_CONTENT_FILENAME_LENGTH   =   48;           ///< The maximum length of a content's filename, in bytes including '\0'.
+static const uint NETWORK_CONTENT_NAME_LENGTH       =   32;           ///< The maximum length of a content's name, in bytes including '\0'.
+static const uint NETWORK_CONTENT_VERSION_LENGTH    =   16;           ///< The maximum length of a content's version, in bytes including '\0'.
+static const uint NETWORK_CONTENT_URL_LENGTH        =   96;           ///< The maximum length of a content's url, in bytes including '\0'.
+static const uint NETWORK_CONTENT_DESC_LENGTH       =  512;           ///< The maximum length of a content's description, in bytes including '\0'.
+static const uint NETWORK_CONTENT_TAG_LENGTH        =   32;           ///< The maximum length of a content's tag, in bytes including '\0'.
+static const uint NETWORK_ERROR_DETAIL_LENGTH        = 100;           ///< The maximum length of the error detail, in bytes including '\0'
 
-static const uint NETWORK_GRF_NAME_LENGTH         =   80;         ///< Maximum length of the name of a GRF
+static const uint NETWORK_GRF_NAME_LENGTH           =   80;           ///< Maximum length of the name of a GRF
 
 /**
  * Maximum number of GRFs that can be sent.
  * This limit is reached when PACKET_UDP_SERVER_RESPONSE reaches the maximum size of UDP_MTU bytes.
  */
-static const uint NETWORK_MAX_GRF_COUNT           =   62;
+static const uint NETWORK_MAX_GRF_COUNT             =   62;
 
 /**
  * The number of landscapes in OpenTTD.
@@ -88,6 +93,6 @@ static const uint NETWORK_MAX_GRF_COUNT           =   62;
  * there is a compile assertion to check that this NUM_LANDSCAPE is equal
  * to NETWORK_NUM_LANDSCAPES.
  */
-static const uint NETWORK_NUM_LANDSCAPES          =    4;
+static const uint NETWORK_NUM_LANDSCAPES            =    4;
 
 #endif /* NETWORK_CORE_CONFIG_H */
diff --git a/src/network/core/tcp_coordinator.cpp b/src/network/core/tcp_coordinator.cpp
new file mode 100644
index 000000000..1cf5cd676
--- /dev/null
+++ b/src/network/core/tcp_coordinator.cpp
@@ -0,0 +1,80 @@
+/*
+ * 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/>.
+ */
+
+/**
+ * @file tcp_coordinator.cpp Basic functions to receive and send Game Coordinator packets.
+ */
+
+#include "../../stdafx.h"
+#include "../../date_func.h"
+#include "../../debug.h"
+#include "tcp_coordinator.h"
+
+#include "../../safeguards.h"
+
+/**
+ * Handle the given packet, i.e. pass it to the right.
+ * parser receive command.
+ * @param p The packet to handle.
+ * @return True iff we should immediately handle further packets.
+ */
+bool NetworkCoordinatorSocketHandler::HandlePacket(Packet *p)
+{
+	PacketCoordinatorType type = (PacketCoordinatorType)p->Recv_uint8();
+
+	switch (type) {
+		case PACKET_COORDINATOR_GC_ERROR:        return this->Receive_GC_ERROR(p);
+		case PACKET_COORDINATOR_SERVER_REGISTER: return this->Receive_SERVER_REGISTER(p);
+		case PACKET_COORDINATOR_GC_REGISTER_ACK: return this->Receive_GC_REGISTER_ACK(p);
+		case PACKET_COORDINATOR_SERVER_UPDATE:   return this->Receive_SERVER_UPDATE(p);
+
+		default:
+			Debug(net, 0, "[tcp/coordinator] Received invalid packet type {}", type);
+			return false;
+	}
+}
+
+/**
+ * Receive a packet at TCP level.
+ * @return Whether at least one packet was received.
+ */
+bool NetworkCoordinatorSocketHandler::ReceivePackets()
+{
+	/*
+	 * We read only a few of the packets. This allows the GUI to update when
+	 * a large set of servers is being received. Otherwise the interface
+	 * "hangs" while the game is updating the server-list.
+	 *
+	 * What arbitrary number to choose is the ultimate question though.
+	 */
+	Packet *p;
+	static const int MAX_PACKETS_TO_RECEIVE = 42;
+	int i = MAX_PACKETS_TO_RECEIVE;
+	while (--i != 0 && (p = this->ReceivePacket()) != nullptr) {
+		bool cont = this->HandlePacket(p);
+		delete p;
+		if (!cont) return true;
+	}
+
+	return i != MAX_PACKETS_TO_RECEIVE - 1;
+}
+
+/**
+ * Helper for logging receiving invalid packets.
+ * @param type The received packet type.
+ * @return Always false, as it's an error.
+ */
+bool NetworkCoordinatorSocketHandler::ReceiveInvalidPacket(PacketCoordinatorType type)
+{
+	Debug(net, 0, "[tcp/coordinator] Received illegal packet type {}", type);
+	return false;
+}
+
+bool NetworkCoordinatorSocketHandler::Receive_GC_ERROR(Packet *p) { return this->ReceiveInvalidPacket(PACKET_COORDINATOR_GC_ERROR); }
+bool NetworkCoordinatorSocketHandler::Receive_SERVER_REGISTER(Packet *p) { return this->ReceiveInvalidPacket(PACKET_COORDINATOR_SERVER_REGISTER); }
+bool NetworkCoordinatorSocketHandler::Receive_GC_REGISTER_ACK(Packet *p) { return this->ReceiveInvalidPacket(PACKET_COORDINATOR_GC_REGISTER_ACK); }
+bool NetworkCoordinatorSocketHandler::Receive_SERVER_UPDATE(Packet *p) { return this->ReceiveInvalidPacket(PACKET_COORDINATOR_SERVER_UPDATE); }
diff --git a/src/network/core/tcp_coordinator.h b/src/network/core/tcp_coordinator.h
new file mode 100644
index 000000000..a438f07aa
--- /dev/null
+++ b/src/network/core/tcp_coordinator.h
@@ -0,0 +1,115 @@
+/*
+ * 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/>.
+ */
+
+/**
+ * @file tcp_coordinator.h Basic functions to receive and send TCP packets to/from the Game Coordinator server.
+ */
+
+#ifndef NETWORK_CORE_TCP_COORDINATOR_H
+#define NETWORK_CORE_TCP_COORDINATOR_H
+
+#include "os_abstraction.h"
+#include "tcp.h"
+#include "packet.h"
+#include "game_info.h"
+
+/**
+ * Enum with all types of TCP Game Coordinator packets. The order MUST not be changed.
+ *
+ * GC     -> packets from Game Coordinator to either Client or Server.
+ * SERVER -> packets from Server to Game Coordinator.
+ * CLIENT -> packets from Client to Game Coordinator.
+ **/
+enum PacketCoordinatorType {
+	PACKET_COORDINATOR_GC_ERROR,        ///< Game Coordinator indicates there was an error.
+	PACKET_COORDINATOR_SERVER_REGISTER, ///< Server registration.
+	PACKET_COORDINATOR_GC_REGISTER_ACK, ///< Game Coordinator accepts the registration.
+	PACKET_COORDINATOR_SERVER_UPDATE,   ///< Server sends an set intervals an update of the server.
+	PACKET_COORDINATOR_END,             ///< Must ALWAYS be on the end of this list!! (period).
+};
+
+/**
+ * The type of connection the Game Coordinator can detect we have.
+ */
+enum ConnectionType {
+	CONNECTION_TYPE_UNKNOWN,  ///< The Game Coordinator hasn't informed us yet what type of connection we have.
+	CONNECTION_TYPE_ISOLATED, ///< The Game Coordinator failed to find a way to connect to your server. Nobody will be able to join.
+	CONNECTION_TYPE_DIRECT,   ///< The Game Coordinator can directly connect to your server.
+};
+
+/**
+ * The type of error from the Game Coordinator.
+ */
+enum NetworkCoordinatorErrorType {
+	NETWORK_COORDINATOR_ERROR_UNKNOWN,             ///< There was an unknown error.
+	NETWORK_COORDINATOR_ERROR_REGISTRATION_FAILED, ///< Your request for registration failed.
+};
+
+/** Base socket handler for all Game Coordinator TCP sockets. */
+class NetworkCoordinatorSocketHandler : public NetworkTCPSocketHandler {
+protected:
+	bool ReceiveInvalidPacket(PacketCoordinatorType type);
+
+	/**
+	 * Game Coordinator indicates there was an error. This can either be a
+	 * permanent error causing the connection to be dropped, or in response
+	 * to a request that is invalid.
+	 *
+	 *  uint8   Type of error (see NetworkCoordinatorErrorType).
+	 *  string  Details of the error.
+	 *
+	 * @param p The packet that was just received.
+	 * @return True upon success, otherwise false.
+	 */
+	virtual bool Receive_GC_ERROR(Packet *p);
+
+	/**
+	 * Server is starting a multiplayer game and wants to let the
+	 * Game Coordinator know.
+	 *
+	 *  uint8   Game Coordinator protocol version.
+	 *  uint8   Type of game (see ServerGameType).
+	 *  uint16  Local port of the server.
+	 *
+	 * @param p The packet that was just received.
+	 * @return True upon success, otherwise false.
+	 */
+	virtual bool Receive_SERVER_REGISTER(Packet *p);
+
+	/**
+	 * Game Coordinator acknowledges the registration.
+	 *
+	 *  uint8   Type of connection was detected (see ConnectionType).
+	 *
+	 * @param p The packet that was just received.
+	 * @return True upon success, otherwise false.
+	 */
+	virtual bool Receive_GC_REGISTER_ACK(Packet *p);
+
+	/**
+	 * Send an update of the current state of the server to the Game Coordinator.
+	 *
+	 *  uint8   Game Coordinator protocol version.
+	 *  Serialized NetworkGameInfo. See game_info.hpp for details.
+	 *
+	 * @param p The packet that was just received.
+	 * @return True upon success, otherwise false.
+	 */
+	virtual bool Receive_SERVER_UPDATE(Packet *p);
+
+	bool HandlePacket(Packet *p);
+public:
+	/**
+	 * Create a new cs socket handler for a given cs.
+	 * @param s The socket we are connected with.
+	 */
+	NetworkCoordinatorSocketHandler(SOCKET s = INVALID_SOCKET) : NetworkTCPSocketHandler(s) {}
+
+	bool ReceivePackets();
+};
+
+#endif /* NETWORK_CORE_TCP_COORDINATOR_H */
diff --git a/src/network/network.cpp b/src/network/network.cpp
index c05634e00..361517c96 100644
--- a/src/network/network.cpp
+++ b/src/network/network.cpp
@@ -19,6 +19,7 @@
 #include "network_udp.h"
 #include "network_gamelist.h"
 #include "network_base.h"
+#include "network_coordinator.h"
 #include "core/udp.h"
 #include "core/host.h"
 #include "network_gui.h"
@@ -591,6 +592,8 @@ void NetworkClose(bool close_admins)
 		}
 		ServerNetworkGameSocketHandler::CloseListeners();
 		ServerNetworkAdminSocketHandler::CloseListeners();
+
+		_network_coordinator_client.CloseConnection();
 	} else if (MyClient::my_client != nullptr) {
 		MyClient::SendQuit();
 		MyClient::my_client->CloseConnection(NETWORK_RECV_STATUS_CLIENT_QUIT);
@@ -932,6 +935,10 @@ bool NetworkServerStart()
 
 	NetworkInitGameInfo();
 
+	if (_settings_client.network.server_advertise) {
+		_network_coordinator_client.Register();
+	}
+
 	/* execute server initialization script */
 	IConsoleCmdExec("exec scripts/on_server.scr 0");
 	/* if the server is dedicated ... add some other script */
@@ -1032,6 +1039,7 @@ static void NetworkSend()
 void NetworkBackgroundLoop()
 {
 	_network_content_client.SendReceive();
+	_network_coordinator_client.SendReceive();
 	TCPConnecter::CheckCallbacks();
 	NetworkHTTPSocketHandler::HTTPReceive();
 
diff --git a/src/network/network_coordinator.cpp b/src/network/network_coordinator.cpp
new file mode 100644
index 000000000..3e4079740
--- /dev/null
+++ b/src/network/network_coordinator.cpp
@@ -0,0 +1,234 @@
+
+/*
+ * 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/>.
+ */
+
+/** @file network_coordinator.cpp Game Coordinator sending/receiving part of the network protocol. */
+
+#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 "table/strings.h"
+
+#include "../safeguards.h"
+
+static const auto NETWORK_COORDINATOR_DELAY_BETWEEN_UPDATES = std::chrono::seconds(30); ///< How many time between updates the server sends to the Game Coordinator.
+ClientNetworkCoordinatorSocketHandler _network_coordinator_client; ///< The connection to the Game Coordinator.
+ConnectionType _network_server_connection_type = CONNECTION_TYPE_UNKNOWN; ///< What type of connection the Game Coordinator detected we are on.
+
+/** Connect to the Game Coordinator server. */
+class NetworkCoordinatorConnecter : TCPConnecter {
+public:
+	/**
+	 * Initiate the connecting.
+	 * @param address The address of the Game Coordinator server.
+	 */
+	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.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:
+			SetDParamStr(0, detail);
+			ShowErrorMessage(STR_NETWORK_ERROR_COORDINATOR_REGISTRATION_FAILED, STR_JUST_RAW_STRING, WL_ERROR);
+
+			/* To prevent that we constantly try to reconnect, switch to private game. */
+			_settings_client.network.server_advertise = false;
+
+			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();
+
+	_network_server_connection_type = (ConnectionType)p->Recv_uint8();
+
+	if (_network_server_connection_type == CONNECTION_TYPE_ISOLATED) {
+		ShowErrorMessage(STR_NETWORK_ERROR_COORDINATOR_ISOLATED, STR_NETWORK_ERROR_COORDINATOR_ISOLATED_DETAIL, WL_ERROR);
+	}
+
+	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_UNKNOWN: // Never returned from Game Coordinator.
+			default: connection_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:       Public");
+		Debug(net, 3, "  Connection type: {}", connection_type);
+		Debug(net, 3, "----------------------------------------");
+	}
+
+	return true;
+}
+
+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;
+	new NetworkCoordinatorConnecter(NETWORK_COORDINATOR_SERVER_HOST);
+}
+
+NetworkRecvStatus ClientNetworkCoordinatorSocketHandler::CloseConnection(bool error)
+{
+	NetworkCoordinatorSocketHandler::CloseConnection(error);
+
+	this->CloseSocket();
+	this->connecting = false;
+
+	_network_server_connection_type = CONNECTION_TYPE_UNKNOWN;
+	this->next_update = {};
+
+	SetWindowDirty(WC_CLIENT_LIST, 0);
+
+	return NETWORK_RECV_STATUS_OKAY;
+}
+
+/**
+ * Register our server to receive our join-key.
+ */
+void ClientNetworkCoordinatorSocketHandler::Register()
+{
+	_network_server_connection_type = CONNECTION_TYPE_UNKNOWN;
+	this->next_update = {};
+
+	SetWindowDirty(WC_CLIENT_LIST, 0);
+
+	this->Connect();
+
+	Packet *p = new Packet(PACKET_COORDINATOR_SERVER_REGISTER);
+	p->Send_uint8(NETWORK_COORDINATOR_VERSION);
+	p->Send_uint8(SERVER_GAME_TYPE_PUBLIC);
+	p->Send_uint16(_settings_client.network.server_port);
+
+	this->SendPacket(p);
+}
+
+/**
+ * Send an update of our server status to the Game Coordinator.
+ */
+void ClientNetworkCoordinatorSocketHandler::SendServerUpdate()
+{
+	Debug(net, 6, "Sending server update to Game Coordinator");
+	this->next_update = std::chrono::steady_clock::now() + NETWORK_COORDINATOR_DELAY_BETWEEN_UPDATES;
+
+	Packet *p = new Packet(PACKET_COORDINATOR_SERVER_UPDATE);
+	p->Send_uint8(NETWORK_COORDINATOR_VERSION);
+	SerializeNetworkGameInfo(p, GetCurrentNetworkServerGameInfo());
+
+	this->SendPacket(p);
+}
+
+/**
+ * Check whether we received/can send some data from/to the Game Coordinator server and
+ * when that's the case handle it appropriately.
+ */
+void ClientNetworkCoordinatorSocketHandler::SendReceive()
+{
+	/* Private games are not listed via the Game Coordinator. */
+	if (_network_server && !_settings_client.network.server_advertise) {
+		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 (this->CanSendReceive()) {
+		this->ReceivePackets();
+	}
+
+	this->SendPackets();
+}
diff --git a/src/network/network_coordinator.h b/src/network/network_coordinator.h
new file mode 100644
index 000000000..1dbce063b
--- /dev/null
+++ b/src/network/network_coordinator.h
@@ -0,0 +1,51 @@
+
+/*
+ * 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/>.
+ */
+
+/** @file network_coordinator.h Part of the network protocol handling Game Coordinator requests. */
+
+#ifndef NETWORK_COORDINATOR_H
+#define NETWORK_COORDINATOR_H
+
+#include "core/tcp_coordinator.h"
+
+/**
+ * Game Coordinator communication.
+ *
+ * For servers:
+ *  - Server sends SERVER_REGISTER.
+ *  - Game Coordinator probes server to check if it can directly connect.
+ *  - Game Coordinator sends GC_REGISTER_ACK with type of connection.
+ *  - Server sends every 30 seconds SERVER_UPDATE.
+ */
+
+/** Class for handling the client side of the Game Coordinator connection. */
+class ClientNetworkCoordinatorSocketHandler : public NetworkCoordinatorSocketHandler {
+private:
+	std::chrono::steady_clock::time_point next_update; ///< When to send the next update (if server and public).
+
+protected:
+	bool Receive_GC_ERROR(Packet *p) override;
+	bool Receive_GC_REGISTER_ACK(Packet *p) override;
+
+public:
+	bool connecting; ///< Are we connecting to the Game Coordinator?
+
+	ClientNetworkCoordinatorSocketHandler() : connecting(false) {}
+
+	NetworkRecvStatus CloseConnection(bool error = true) override;
+	void SendReceive();
+
+	void Connect();
+
+	void Register();
+	void SendServerUpdate();
+};
+
+extern ClientNetworkCoordinatorSocketHandler _network_coordinator_client;
+
+#endif /* NETWORK_COORDINATOR_H */
diff --git a/src/network/network_gui.cpp b/src/network/network_gui.cpp
index e3e05db92..6f48bf022 100644
--- a/src/network/network_gui.cpp
+++ b/src/network/network_gui.cpp
@@ -62,7 +62,7 @@ static CompanyID _admin_company_id = INVALID_COMPANY; ///< For what company a co
  * do not.
  */
 static const StringID _server_visibility_dropdown[] = {
-	STR_NETWORK_SERVER_VISIBILITY_PRIVATE,
+	STR_NETWORK_SERVER_VISIBILITY_LOCAL,
 	STR_NETWORK_SERVER_VISIBILITY_PUBLIC,
 	INVALID_STRING_ID
 };
@@ -1607,21 +1607,26 @@ static const NWidgetPart _nested_client_list_widgets[] = {
 			NWidget(WWT_FRAME, COLOUR_GREY), SetDataTip(STR_NETWORK_CLIENT_LIST_SERVER, STR_NULL), SetPadding(4, 4, 0, 4), SetPIP(0, 2, 0),
 				NWidget(NWID_HORIZONTAL), SetPIP(0, 3, 0),
 					NWidget(WWT_TEXT, COLOUR_GREY), SetMinimalTextLines(1, 0), SetDataTip(STR_NETWORK_CLIENT_LIST_SERVER_NAME, STR_NULL),
-					NWidget(NWID_SPACER), SetMinimalSize(20, 0),
+					NWidget(NWID_SPACER), SetMinimalSize(10, 0),
 					NWidget(WWT_TEXT, COLOUR_GREY, WID_CL_SERVER_NAME), SetFill(1, 0), SetMinimalTextLines(1, 0), SetResize(1, 0), SetDataTip(STR_BLACK_RAW_STRING, STR_NETWORK_CLIENT_LIST_SERVER_NAME_TOOLTIP), SetAlignment(SA_VERT_CENTER | SA_RIGHT),
 					NWidget(WWT_PUSHIMGBTN, COLOUR_GREY, WID_CL_SERVER_NAME_EDIT), SetMinimalSize(12, 14), SetDataTip(SPR_RENAME, STR_NETWORK_CLIENT_LIST_SERVER_NAME_EDIT_TOOLTIP),
 				EndContainer(),
 				NWidget(NWID_HORIZONTAL), SetPIP(0, 3, 0),
 					NWidget(WWT_TEXT, COLOUR_GREY), SetMinimalTextLines(1, 0), SetDataTip(STR_NETWORK_CLIENT_LIST_SERVER_VISIBILITY, STR_NULL),
-					NWidget(NWID_SPACER), SetMinimalSize(20, 0), SetFill(1, 0), SetResize(1, 0),
+					NWidget(NWID_SPACER), SetMinimalSize(10, 0), SetFill(1, 0), SetResize(1, 0),
 					NWidget(WWT_DROPDOWN, COLOUR_GREY, WID_CL_SERVER_VISIBILITY), SetDataTip(STR_BLACK_STRING, STR_NETWORK_CLIENT_LIST_SERVER_VISIBILITY_TOOLTIP),
 				EndContainer(),
+				NWidget(NWID_HORIZONTAL), SetPIP(0, 3, 0),
+					NWidget(WWT_TEXT, COLOUR_GREY), SetMinimalTextLines(1, 0), SetDataTip(STR_NETWORK_CLIENT_LIST_SERVER_CONNECTION_TYPE, STR_NULL),
+					NWidget(NWID_SPACER), SetMinimalSize(10, 0),
+					NWidget(WWT_TEXT, COLOUR_GREY, WID_CL_SERVER_CONNECTION_TYPE), SetFill(1, 0), SetMinimalTextLines(1, 0), SetResize(1, 0), SetDataTip(STR_BLACK_STRING, STR_NETWORK_CLIENT_LIST_SERVER_CONNECTION_TYPE_TOOLTIP), SetAlignment(SA_VERT_CENTER | SA_RIGHT),
+				EndContainer(),
 			EndContainer(),
 		EndContainer(),
 		NWidget(WWT_FRAME, COLOUR_GREY), SetDataTip(STR_NETWORK_CLIENT_LIST_PLAYER, STR_NULL), SetPadding(4, 4, 4, 4), SetPIP(0, 2, 0),
 			NWidget(NWID_HORIZONTAL), SetPIP(0, 3, 0),
 				NWidget(WWT_TEXT, COLOUR_GREY), SetMinimalTextLines(1, 0), SetDataTip(STR_NETWORK_CLIENT_LIST_PLAYER_NAME, STR_NULL),
-				NWidget(NWID_SPACER), SetMinimalSize(20, 0),
+				NWidget(NWID_SPACER), SetMinimalSize(10, 0),
 				NWidget(WWT_TEXT, COLOUR_GREY, WID_CL_CLIENT_NAME), SetFill(1, 0), SetMinimalTextLines(1, 0), SetResize(1, 0), SetDataTip(STR_BLACK_RAW_STRING, STR_NETWORK_CLIENT_LIST_PLAYER_NAME_TOOLTIP), SetAlignment(SA_VERT_CENTER | SA_RIGHT),
 				NWidget(WWT_PUSHIMGBTN, COLOUR_GREY, WID_CL_CLIENT_NAME_EDIT), SetMinimalSize(12, 14), SetDataTip(SPR_RENAME, STR_NETWORK_CLIENT_LIST_PLAYER_NAME_EDIT_TOOLTIP),
 			EndContainer(),
@@ -2050,6 +2055,10 @@ public:
 				SetDParam(0, _server_visibility_dropdown[_settings_client.network.server_advertise]);
 				break;
 
+			case WID_CL_SERVER_CONNECTION_TYPE:
+				SetDParam(0, STR_NETWORK_CLIENT_LIST_SERVER_CONNECTION_TYPE_UNKNOWN + _network_server_connection_type);
+				break;
+
 			case WID_CL_CLIENT_NAME:
 				SetDParamStr(0, _settings_client.network.client_name);
 				break;
diff --git a/src/network/network_internal.h b/src/network/network_internal.h
index 67e97bb07..c1e6aa7b9 100644
--- a/src/network/network_internal.h
+++ b/src/network/network_internal.h
@@ -11,6 +11,7 @@
 #define NETWORK_INTERNAL_H
 
 #include "network_func.h"
+#include "core/tcp_coordinator.h"
 #include "core/tcp_game.h"
 
 #include "../command_type.h"
@@ -82,6 +83,7 @@ extern NetworkJoinStatus _network_join_status;
 extern uint8 _network_join_waiting;
 extern uint32 _network_join_bytes;
 extern uint32 _network_join_bytes_total;
+extern ConnectionType _network_server_connection_type;
 
 extern uint8 _network_reconnect;
 
diff --git a/src/network/network_type.h b/src/network/network_type.h
index fb9953695..6e6fe33de 100644
--- a/src/network/network_type.h
+++ b/src/network/network_type.h
@@ -35,6 +35,15 @@ enum NetworkVehicleType {
 	NETWORK_VEH_END
 };
 
+/**
+ * Game type the server can be using.
+ * Used on the network protocol to communicate with Game Coordinator.
+ */
+enum ServerGameType : uint8 {
+	SERVER_GAME_TYPE_LOCAL = 0,
+	SERVER_GAME_TYPE_PUBLIC,
+};
+
 /** 'Unique' identifier to be given to clients */
 enum ClientID : uint32 {
 	INVALID_CLIENT_ID = 0, ///< Client is not part of anything
diff --git a/src/widgets/network_widget.h b/src/widgets/network_widget.h
index a96a56fa8..a665afdb7 100644
--- a/src/widgets/network_widget.h
+++ b/src/widgets/network_widget.h
@@ -101,6 +101,7 @@ enum ClientListWidgets {
 	WID_CL_SERVER_NAME,                ///< Server name.
 	WID_CL_SERVER_NAME_EDIT,           ///< Edit button for server name.
 	WID_CL_SERVER_VISIBILITY,          ///< Server visibility.
+	WID_CL_SERVER_CONNECTION_TYPE,     ///< The type of connection the Game Coordinator detected for this server.
 	WID_CL_CLIENT_NAME,                ///< Client name.
 	WID_CL_CLIENT_NAME_EDIT,           ///< Edit button for client name.
 	WID_CL_MATRIX,                     ///< Company/client list.