NETWORKED PROPERTIES
====================

Networked properties is network protocol which allows to get and set
properties values over network.   Property is named typed value.
Property with the same name but different type treated as different
properties.

Typical session includes connection setup, property subscription,
cycles of receiving properties values, setting properties and finally
subscription canceling.

Transport protocol is TCP.


0. CONNECTION SETUP
-------------------

In order to setup connection client should establish TCP connection to
server and send string 'NP1\n' without quotes, \n is carriedge
return character.

In response server will send the same characters back and random
sequence of 16 bytes.  Client should calculate MD5 checksum over them
and password, and send result to server.  If authentication will be
OK, server will send word PASS or DENY otherwise and close connetion
immediatelly.


1. SUBSCRIPTION
---------------

Subscription to property has following format:

Field         Size      Description
============= ========= ============================
command       1 byte    equals to 0x01 or 0x05
type          1 byte    type of property
id            1 byte    unique property ID
size          1 byte    length of property name
name          size      property name

Server doesn't return anything in reply, but value of property should
be sent on next update command.

If commands equals to 0x05 and proerty doesn't exists, it will be created.

Allowed properties types are:  

Code  C++ Name   Description
===== ========== =====================================
1     int        32 bit signed integer in network order
2     float      IEEE float
3     double     IEEE double


2. SET PROPERTY VALUE
---------------------

In order to set property value client have to sent following packet:

Field         Size      Description
============= ========= ============================
command       1 byte    equals to 0x02
id            1 byte    property ID
type          1 byte    type of property
serial        2 bytes   number of set request
data          variable  property value

Each set request has serial number.  It must equals to previous set request
serial number plus one.  First set request must have serial number equals 
to 1.  After request number 0xFFFF next request will be 0x0000.

Data format depends on property type.  For integer properties it is 4-bytes
integer in network byte order.  Float and Double properties transfered
in corresponding IEEE formats.

Server will not reply for set property message but it will send property
new value on next update.


3. GET PROPERTIES VALUES
------------------------

Server sends values of all changed properties after get values request.
Get values request consists of single byte equals to 0x03:

Field         Size      Description
============= ========= ============================
command       1 byte    equals to 0x03

Response to this command consist of header and properties data:

Field         Size      Description
============= ========= ============================
command       1 byte    equals to 0x04
count         1 byte    number of properties in reply
serial        2 bytes   last seen set seral number
data          variable  properies values

Each reply has last seen set property number.  If there are wasn't any set
property requests yet serial number equals to 0.

Each property sent in following format:

Field         Size      Description
============= ========= ============================
id            1 byte    property ID
data          variable  property value

data format depends on property type.  For integer properties it is 4-bytes
integer in network byte order.  Float and Double properties transfered
in corresponding IEEE formats.  Type is always the same as in property
subscription request.


