The key needs to be changed manually in the source code to something secret to prevent people from hacking the server.
The protocol is as follows:
If $KEY PING $SERVER
is sent, $KEY PONG
is returned, and the $SERVER value will be stored.
If $KEY PING
is sent, $KEY PONG
is returned and the IP address will be stored.
If $KEY LS
is sent, a list of servers (e.g. $KEY LS SERVER1 SERVER2 SERVER3 ...
) is returned.