The fundamental problem in the example:

    leader_host = bigdata.example.org:10443

is ":10443" is not part of the hostname. The field is called "leader_host"; if a port is needed, it should use it's own field instead of trying to overload the host field.

    leader_host = bigdata.example.org
    leader_port = 10443

(and as as others have already mentioned, don't write your own parser when they already exist in your stdlib/etc)