Feature: allow the use of TURN to connect client and server together

TURN is a last resort, used only if all other methods failed.
TURN is a relay approach to connect client and server together, where
openttd.org (by default) is the middleman.

It is very unlikely either the client or server cannot connect to
the STUN server, as they are both already connected to the Game
Coordinator. But in the odd case it does fail, estabilishing the
connection fails without any further possibility to recover.

1 files changed, 79 insertions, 0 deletions

diff --git a/src/network/core/tcp_turn.h b/src/network/core/tcp_turn.h
new file mode 100644
index 000000000..082373199
--- /dev/null
+++ b/src/network/core/tcp_turn.h
@@ -0,0 +1,79 @@
+/*
+ * 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_turn.h Basic functions to receive and send TCP packets to/from the TURN server.
+ */
+
+#ifndef NETWORK_CORE_TCP_TURN_H
+#define NETWORK_CORE_TCP_TURN_H
+
+#include "os_abstraction.h"
+#include "tcp.h"
+#include "packet.h"
+#include "game_info.h"
+
+/** Enum with all types of TCP TURN packets. The order MUST not be changed. **/
+enum PacketTurnType {
+	PACKET_TURN_TURN_ERROR,     ///< TURN server is unable to relay.
+	PACKET_TURN_SERCLI_CONNECT, ///< Client or server is connecting to the TURN server.
+	PACKET_TURN_TURN_CONNECTED, ///< TURN server indicates the socket is now being relayed.
+	PACKET_TURN_END,            ///< Must ALWAYS be on the end of this list!! (period)
+};
+
+/** Base socket handler for all TURN TCP sockets. */
+class NetworkTurnSocketHandler : public NetworkTCPSocketHandler {
+protected:
+	bool ReceiveInvalidPacket(PacketTurnType type);
+
+	/**
+	 * TURN server was unable to connect the client or server based on the
+	 * token. Most likely cause is an invalid token or the other side that
+	 * hasn't connected in a reasonable amount of time.
+	 *
+	 * @param p The packet that was just received.
+	 * @return True upon success, otherwise false.
+	 */
+	virtual bool Receive_TURN_ERROR(Packet *p);
+
+	/**
+	 * Client or servers wants to connect to the TURN server (on request by
+	 * the Game Coordinator).
+	 *
+	 *  uint8   Game Coordinator protocol version.
+	 *  string  Token to track the current TURN request.
+	 *
+	 * @param p The packet that was just received.
+	 * @return True upon success, otherwise false.
+	 */
+	virtual bool Receive_SERCLI_CONNECT(Packet *p);
+
+	/**
+	 * TURN server has connected client and server together and will now relay
+	 * all packets to each other. No further TURN packets should be send over
+	 * this socket, and the socket should be handed over to the game protocol.
+	 *
+	 *  string  Hostname of the peer. This can be used to check if a client is not banned etc.
+	 *
+	 * @param p The packet that was just received.
+	 * @return True upon success, otherwise false.
+	 */
+	virtual bool Receive_TURN_CONNECTED(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.
+	 * @param address IP etc. of the client.
+	 */
+	NetworkTurnSocketHandler(SOCKET s = INVALID_SOCKET) : NetworkTCPSocketHandler(s) {}
+
+	bool ReceivePackets();
+};
+
+#endif /* NETWORK_CORE_TCP_TURN_H */