src/murmur/Messages.cpp: Warn older clients about ChannelListener fea…

…ture

ChannelListener will be introduced with Mumble 1.4.0 but older clients
will not know what these are. Thus they won't show them in their UI
which could lead to users being listened to without noticing.

In order to solve this issue, this commit implements a logic on the
Server that'll inform older clients about this possibility by sending
them a TextMessage right after they have authenticated (and after they
have received the server's welcome text).

src/murmur/Messages.cpp

@@ -508,6 +508,27 @@ void Server::msgAuthenticate(ServerUser *uSource, MumbleProto::Authenticate &msg
 		sendMessage(uSource, mpsug);
 	}
 
+	if (uSource->uiVersion < 0x010400 && Meta::mp.iMaxListenersPerChannel > 0 && Meta::mp.iMaxListenerProxiesPerUser > 0) {
+		// The server has the ChannelListener feature enabled but the client that connects doesn't have version 1.4.0 or newer
+		// meaning that this client doesn't know what ChannelListeners are. Thus we'll send that user a text-message informing
+		// about this.
+		MumbleProto::TextMessage mptm;
+
+		QLatin1String msg();
+
+		if (Meta::mp.bAllowHTML) {
+			mptm.set_message("<b>[WARNING]</b>: This server has the <b>ChannelListener</b> feature enabled but your client version does not support it. "
+				"This means that users <b>might be listening to what you are saying in your channel without you noticing!</b> "
+				"You can solve this issue by upgrading to Mumble 1.4.0 or newer.");
+		} else {
+			mptm.set_message("[WARNING]: This server has the ChannelListener feature enabled but your client version does not support it. "
+				"This means that users might be listening to what you are saying in your channel without you noticing! "
+				"You can solve this issue by upgrading to Mumble 1.4.0 or newer.");
+		}
+
+		sendMessage(uSource, mptm);
+	}
+
 	log(uSource, "Authenticated");
 
 	emit userConnected(uSource);