state machine

events = receive_bytes(data)
send(request)
bytes_to_send()


current broker connection methods:

    check state:
        blacked_out
        connected
        connecting
        disconnected
        can_send_more

    connect
    close
    send
    recv
    check_version

connection state transitions:

    connecting
        handshake
        authenticating
        connected
        disconnected
    handshake
        authenticating
        connected
        disconnected
    authenticating
        connected
        disconnected
    connected
        disconnected

    


consumer:
    coordinator_unknown
    coordinator_check_pending
    coordinator_known
    join_group_needed
    join_group_pending
    join_group_follower
    join_group_leader
    join_group_sync
    group_active
    leave_group_pending