The closest to your BB interface above is the
Nagios Service Check Acceptor NSCA.
It accepts a plain text format on a TCP socket.
Besides the binary send_ncsa there is Net::NSCA::Client, which I do _not_ know.
in reply to Pure Perl Big Brother and Nagios clients: ideas? code bits?
But keep in mind that pure passive checks are a bit at odds with Nagios' state polling philosophy.
If you are not allowed to add an agent like NRPE or the excellent check_mk, you may consider check_by_ssh.
Since years OpenSSH offers the ControlMaster option to re-use existing connections.
Without the very expensive key exchange phase, the transfer performance is not much different from raw TCP such as with NRPE.
It just needs a bit of thought with your templates to coordinate master and slave.