ZMTP-PLAIN

plain = C:hello ( S:welcome | S:error )
        C:initiate ( S:ready | S:error )
     *( C:message | S:message )

hello = command-size %d5 "HELLO" username password
username = OCTET *VCHAR
password = OCTET *VCHAR

welcome = command-size %d7 "WELCOME"

initiate = command-size %d8 "INITIATE" metadata

ready = command-size %d5 "READY" metadata