Fix OpenTTD#12076: Do not allow 'join' command on dedicated servers

src/console_cmds.cpp

@@ -155,6 +155,21 @@ DEF_CONSOLE_HOOK(ConHookNeedNetwork)
 	return CHR_ALLOW;
 }
 
+/**
+ * Check whether we are in a multiplayer game and are playing, i.e. we are not the dedicated server.
+ * @return Are we a client or non-dedicated server in a network game? True when yes, false otherwise.
+ */
+DEF_CONSOLE_HOOK(ConHookNeedNonDedicatedNetwork)
+{
+	if (!NetworkAvailable(echo)) return CHR_DISALLOW;
+
+	if (_network_dedicated) {
+		if (echo) IConsolePrint(CC_ERROR, "This command is not available to a dedicated network server.");
+		return CHR_DISALLOW;
+	}
+	return CHR_ALLOW;
+}
+
 /**
  * Check whether we are in singleplayer mode.
  * @return True when no network is active.
@@ -2693,7 +2708,7 @@ void IConsoleStdLibRegister()
 	IConsole::CmdRegister("reconnect",               ConNetworkReconnect, ConHookClientOnly);
 	IConsole::CmdRegister("rcon",                    ConRcon,             ConHookNeedNetwork);
 
-	IConsole::CmdRegister("join",                    ConJoinCompany,      ConHookNeedNetwork);
+	IConsole::CmdRegister("join",                    ConJoinCompany,      ConHookNeedNonDedicatedNetwork);
 	IConsole::AliasRegister("spectate",              "join 255");
 	IConsole::CmdRegister("move",                    ConMoveClient,       ConHookServerOnly);
 	IConsole::CmdRegister("reset_company",           ConResetCompany,     ConHookServerOnly);