Control commands is ascii encoded.
Client requests(70 Bytes, fixed-length):

HELO.$UID.$KEY # tell server that client process is up
GBYE.$UID.$KEY # tell server that client is offline

Server response(4 Bytes, fixed-length):

NKEY # key invalid
FULL # no sparing slot
NCMD # invalid command
GOOD # good to go
THNX # bye bye

/db

Get current database, including all key, uid, last_seen, and max.

/gen
/gen/:max

Generate new key, where max is optional.

/del/:key

Delete one existing key.

/del/:key/:uid

Delete one existing uid