public int activeLocalPort(SessionProtocol protocol) {
        return activeLocalPort0(requireNonNull(protocol, "protocol"));
    }
Returns the local {@link ServerPort} which serves the given {@link SessionProtocol}.

@throws IllegalStateException if there is no active local port available for the given
                              {@link SessionProtocol} or the server is not started yet
core/src/main/java/com/linecorp/armeria/server/Server.java