Chat: new settings to prevent spam

Added the following chat coreside features
* Chat messages length limit
* Message rate limiting
* Message rate kicking

Note:
* handleChat now takes RemotePlayer pointer instead of u16 to remove useless
  lookups

8 files changed, 125 insertions, 11 deletions

diff --git a/builtin/settingtypes.txt b/builtin/settingtypes.txt
index 15fab0f30..95cc826a0 100644
--- a/builtin/settingtypes.txt
+++ b/builtin/settingtypes.txt
@@ -774,6 +774,15 @@ time_speed (Time speed) int 72
 #    Interval of saving important changes in the world, stated in seconds.
 server_map_save_interval (Map save interval) float 5.3
 
+#    Set the maximum character length of a chat message sent by clients.
+# chat_message_max_size int 500
+
+#    Limit a single player to send X messages per 10 seconds.
+# chat_message_limit_per_10sec float 10.0
+
+#    Kick player if send more than X messages per 10 seconds.
+# chat_message_limit_trigger_kick int 50
+
 [**Physics]
 
 movement_acceleration_default (Default acceleration) float 3
diff --git a/minetest.conf.example b/minetest.conf.example
index 9c8015625..b1b202786 100644
--- a/minetest.conf.example
+++ b/minetest.conf.example
@@ -933,6 +933,18 @@
 #    type: float
 # server_map_save_interval = 5.3
 
+#    Set the maximum character length of a chat message sent by clients. (0 to disable)
+#    type: integer
+# chat_message_max_size = 500
+
+#    Limit a single player to send X messages per 10 seconds. (0 to disable)
+#    type: float
+# chat_message_limit_per_10sec = 8.0
+
+#    Kick player if send more than X messages per 10 seconds. (0 to disable)
+#    type: integer
+# chat_message_limit_trigger_kick = 50
+
 ### Physics
 
 #    type: float
@@ -1523,7 +1535,7 @@
 # profiler.default_report_format = txt
 
 #    The file path relative to your worldpath in which profiles will be saved to.
-#    
+#
 #    type: string
 # profiler.report_path = ""
 
diff --git a/src/defaultsettings.cpp b/src/defaultsettings.cpp
index 4520bac2f..00c233a42 100644
--- a/src/defaultsettings.cpp
+++ b/src/defaultsettings.cpp
@@ -285,6 +285,9 @@ void set_default_settings(Settings *settings)
 	settings->setDefault("server_unload_unused_data_timeout", "29");
 	settings->setDefault("max_objects_per_block", "49");
 	settings->setDefault("server_map_save_interval", "5.3");
+	settings->setDefault("chat_message_max_size", "500");
+	settings->setDefault("chat_message_limit_per_10sec", "8.0");
+	settings->setDefault("chat_message_limit_trigger_kick", "50");
 	settings->setDefault("sqlite_synchronous", "2");
 	settings->setDefault("full_block_send_enable_min_time_from_building", "2.0");
 	settings->setDefault("dedicated_server_step", "0.1");
diff --git a/src/network/serverpackethandler.cpp b/src/network/serverpackethandler.cpp
index 1bcb78a8a..a8bfd9068 100644
--- a/src/network/serverpackethandler.cpp
+++ b/src/network/serverpackethandler.cpp
@@ -1065,7 +1065,7 @@ void Server::handleCommand_ChatMessage(NetworkPacket* pkt)
 	std::wstring wname = narrow_to_wide(name);
 
 	std::wstring answer_to_sender = handleChat(name, wname, message,
-		true, pkt->getPeerId());
+		true, dynamic_cast<RemotePlayer *>(player));
 	if (!answer_to_sender.empty()) {
 		// Send the answer to sender
 		SendChatMessage(pkt->getPeerId(), answer_to_sender);
@@ -1656,16 +1656,16 @@ void Server::handleCommand_Interact(NetworkPacket* pkt)
 		}
 
 	} // action == 4
-	
+
 	/*
 		5: rightclick air
 	*/
 	else if (action == 5) {
 		ItemStack item = playersao->getWieldedItem();
-		
-		actionstream << player->getName() << " activates " 
+
+		actionstream << player->getName() << " activates "
 				<< item.name << std::endl;
-		
+
 		if (m_script->item_OnSecondaryUse(
 				item, playersao)) {
 			if( playersao->setWieldedItem(item)) {
diff --git a/src/player.cpp b/src/player.cpp
index 5949712a5..fd72d63b6 100644
--- a/src/player.cpp
+++ b/src/player.cpp
@@ -227,10 +227,25 @@ void Player::clearHud()
 	}
 }
 
+// static config cache for remoteplayer
+bool RemotePlayer::m_setting_cache_loaded = false;
+float RemotePlayer::m_setting_chat_message_limit_per_10sec = 0.0f;
+u16 RemotePlayer::m_setting_chat_message_limit_trigger_kick = 0;
+
 RemotePlayer::RemotePlayer(IGameDef *gamedef, const char *name):
 	Player(gamedef, name),
-	m_sao(NULL)
+	m_sao(NULL),
+	m_last_chat_message_sent(time(NULL)),
+	m_chat_message_allowance(5.0f),
+	m_message_rate_overhead(0)
 {
+	if (!RemotePlayer::m_setting_cache_loaded) {
+		RemotePlayer::m_setting_chat_message_limit_per_10sec =
+				g_settings->getFloat("chat_message_limit_per_10sec");
+		RemotePlayer::m_setting_chat_message_limit_trigger_kick =
+				g_settings->getU16("chat_message_limit_trigger_kick");
+		RemotePlayer::m_setting_cache_loaded = true;
+	}
 	movement_acceleration_default   = g_settings->getFloat("movement_acceleration_default")   * BS;
 	movement_acceleration_air       = g_settings->getFloat("movement_acceleration_air")       * BS;
 	movement_acceleration_fast      = g_settings->getFloat("movement_acceleration_fast")      * BS;
@@ -304,3 +319,42 @@ void RemotePlayer::setPosition(const v3f &position)
 		m_sao->setBasePosition(position);
 }
 
+const RemotePlayerChatResult RemotePlayer::canSendChatMessage()
+{
+	// Rate limit messages
+	u32 now = time(NULL);
+	float time_passed = now - m_last_chat_message_sent;
+	m_last_chat_message_sent = now;
+
+	// If this feature is disabled
+	if (m_setting_chat_message_limit_per_10sec <= 0.0) {
+		return RPLAYER_CHATRESULT_OK;
+	}
+
+	m_chat_message_allowance += time_passed * (m_setting_chat_message_limit_per_10sec / 8.0f);
+	if (m_chat_message_allowance > m_setting_chat_message_limit_per_10sec) {
+		m_chat_message_allowance = m_setting_chat_message_limit_per_10sec;
+	}
+
+	if (m_chat_message_allowance < 1.0f) {
+		infostream << "Player " << m_name
+				<< " chat limited due to excessive message amount." << std::endl;
+
+		// Kick player if flooding is too intensive
+		m_message_rate_overhead++;
+		if (m_message_rate_overhead > RemotePlayer::m_setting_chat_message_limit_trigger_kick) {
+			return RPLAYER_CHATRESULT_KICK;
+		}
+
+		return RPLAYER_CHATRESULT_FLOODING;
+	}
+
+	// Reinit message overhead
+	if (m_message_rate_overhead > 0) {
+		m_message_rate_overhead = 0;
+	}
+
+	m_chat_message_allowance -= 1.0f;
+	return RPLAYER_CHATRESULT_OK;
+}
+
diff --git a/src/player.h b/src/player.h
index eab00bb04..f38effa9d 100644
--- a/src/player.h
+++ b/src/player.h
@@ -439,7 +439,11 @@ private:
 	Mutex m_mutex;
 };
 
-
+enum RemotePlayerChatResult {
+	RPLAYER_CHATRESULT_OK,
+	RPLAYER_CHATRESULT_FLOODING,
+	RPLAYER_CHATRESULT_KICK,
+};
 /*
 	Player on the server
 */
@@ -457,8 +461,18 @@ public:
 	{ m_sao = sao; }
 	void setPosition(const v3f &position);
 
+	const RemotePlayerChatResult canSendChatMessage();
+
 private:
 	PlayerSAO *m_sao;
+
+	static bool m_setting_cache_loaded;
+	static float m_setting_chat_message_limit_per_10sec;
+	static u16 m_setting_chat_message_limit_trigger_kick;
+
+	u32 m_last_chat_message_sent;
+	float m_chat_message_allowance;
+	u16 m_message_rate_overhead;
 };
 
 #endif
diff --git a/src/server.cpp b/src/server.cpp
index fb241f179..c615aee13 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -358,6 +358,7 @@ Server::Server(
 	add_legacy_abms(m_env, m_nodedef);
 
 	m_liquid_transform_every = g_settings->getFloat("liquid_update");
+	m_max_chatmessage_length = g_settings->getU16("chat_message_max_size");
 }
 
 Server::~Server()
@@ -2734,8 +2735,7 @@ void Server::handleChatInterfaceEvent(ChatEvent *evt)
 }
 
 std::wstring Server::handleChat(const std::string &name, const std::wstring &wname,
-	const std::wstring &wmessage, bool check_shout_priv,
-	u16 peer_id_to_avoid_sending)
+	const std::wstring &wmessage, bool check_shout_priv, RemotePlayer *player)
 {
 	// If something goes wrong, this player is to blame
 	RollbackScopeActor rollback_scope(m_rollback,
@@ -2753,6 +2753,26 @@ std::wstring Server::handleChat(const std::string &name, const std::wstring &wna
 	if (ate)
 		return L"";
 
+	switch (player->canSendChatMessage()) {
+		case RPLAYER_CHATRESULT_FLOODING: {
+			std::wstringstream ws;
+			ws << L"You cannot send more messages. You are limited to "
+			   << g_settings->getFloat("chat_message_limit_per_10sec")
+			   << " messages per 10 seconds.";
+			return ws.str();
+		}
+		case RPLAYER_CHATRESULT_KICK:
+			DenyAccess_Legacy(player->peer_id, L"You have been kicked due to message flooding.");
+			return L"";
+		case RPLAYER_CHATRESULT_OK: break;
+		default: FATAL_ERROR("Unhandled chat filtering result found.");
+	}
+
+	if (m_max_chatmessage_length > 0 && wmessage.length() > m_max_chatmessage_length) {
+		return L"Your message exceed the maximum chat message limit set on the server. "
+			"It was refused. Send a shorter message";
+	}
+
 	// Commands are implemented in Lua, so only catch invalid
 	// commands that were not "eaten" and send an error back
 	if (wmessage[0] == L'/') {
@@ -2787,6 +2807,7 @@ std::wstring Server::handleChat(const std::string &name, const std::wstring &wna
 
 		std::vector<u16> clients = m_clients.getClientIDs();
 
+		u16 peer_id_to_avoid_sending = (player ? player->peer_id : PEER_ID_INEXISTENT);
 		for (u16 i = 0; i < clients.size(); i++) {
 			u16 cid = clients[i];
 			if (cid != peer_id_to_avoid_sending)
diff --git a/src/server.h b/src/server.h
index 7ee15a463..3ad894b38 100644
--- a/src/server.h
+++ b/src/server.h
@@ -487,7 +487,7 @@ private:
 	std::wstring handleChat(const std::string &name, const std::wstring &wname,
 		const std::wstring &wmessage,
 		bool check_shout_priv = false,
-		u16 peer_id_to_avoid_sending = PEER_ID_INEXISTENT);
+		RemotePlayer *player = NULL);
 	void handleAdminChat(const ChatEventChat *evt);
 
 	v3f findSpawnPos();
@@ -522,6 +522,7 @@ private:
 	// If true, do not allow multiple players and hide some multiplayer
 	// functionality
 	bool m_simple_singleplayer_mode;
+	u16 m_max_chatmessage_length;
 
 	// Thread can set; step() will throw as ServerError
 	MutexedVariable<std::string> m_async_fatal_error;