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, 71 insertions, 0 deletions

diff --git a/src/network/core/tcp_turn.cpp b/src/network/core/tcp_turn.cpp
new file mode 100644
index 000000000..026b64194
--- /dev/null
+++ b/src/network/core/tcp_turn.cpp
@@ -0,0 +1,71 @@
+/*
+ * 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.cpp Basic functions to receive and send TURN packets.
+ */
+
+#include "../../stdafx.h"
+#include "../../date_func.h"
+#include "../../debug.h"
+#include "tcp_turn.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 if we should immediately handle further packets, false otherwise
+ */
+bool NetworkTurnSocketHandler::HandlePacket(Packet *p)
+{
+	PacketTurnType type = (PacketTurnType)p->Recv_uint8();
+
+	switch (type) {
+		case PACKET_TURN_TURN_ERROR:     return this->Receive_TURN_ERROR(p);
+		case PACKET_TURN_SERCLI_CONNECT: return this->Receive_SERCLI_CONNECT(p);
+		case PACKET_TURN_TURN_CONNECTED: return this->Receive_TURN_CONNECTED(p);
+
+		default:
+			Debug(net, 0, "[tcp/turn] Received invalid packet type {}", type);
+			return false;
+	}
+}
+
+/**
+ * Receive a packet at TCP level
+ * @return Whether at least one packet was received.
+ */
+bool NetworkTurnSocketHandler::ReceivePackets()
+{
+	Packet *p;
+	static const int MAX_PACKETS_TO_RECEIVE = 4;
+	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 NetworkTurnSocketHandler::ReceiveInvalidPacket(PacketTurnType type)
+{
+	Debug(net, 0, "[tcp/turn] Received illegal packet type {}", type);
+	return false;
+}
+
+bool NetworkTurnSocketHandler::Receive_TURN_ERROR(Packet *p) { return this->ReceiveInvalidPacket(PACKET_TURN_TURN_ERROR); }
+bool NetworkTurnSocketHandler::Receive_SERCLI_CONNECT(Packet *p) { return this->ReceiveInvalidPacket(PACKET_TURN_SERCLI_CONNECT); }
+bool NetworkTurnSocketHandler::Receive_TURN_CONNECTED(Packet *p) { return this->ReceiveInvalidPacket(PACKET_TURN_TURN_CONNECTED); }