iodine/doc/proto_00000403.txt

Detailed specification of protocol in version 00000403
======================================================

CMC = 2 byte Cache Miss Counter, increased every time it is used

Version:
Client sends:
	First byte v or V
	Rest encoded with base32:
	4 bytes big endian protocol version
	CMC
Server replies:
	4 chars:
		VACK (version ok), followed by login challenge
		VNAK (version differs), followed by server protocol version
		VFUL (server has no free slots), followed by max users
	4 byte value: means login challenge/server protocol version/max users
	1 byte userid of the new user, or any byte if not VACK
	
Login:
Client sends:
	First byte l or L
	Rest encoded with base32:
	1 byte userid
	16 bytes MD5 hash of: (first 32 bytes of password) xor (8 repetitions of login challenge)
	CMC
Server replies:
	LNAK means not accepted
	x.x.x.x-y.y.y.y-mtu means accepted (server ip, client ip, mtu)

Case check:
Client sends: 
	First byte z or Z
	Lots of data that should not be decoded
Server replies:
	The requested domain copied raw

Switch codec:
Client sends:
	First byte s or S
	One byte ASCII digit, meaning userid
	One byte ASCII digit, with value 5 or 6, representing number of raw
	bits per encoded byte
Server sends:
	Name of codec if accepted. After this all upstream data packets must 
	be encoded with the new codec.
	BADCODEC if not accepted. Client must then revert to Base32

Data:
Upstream data header (encoded as 4 bytes Base32):
	 4321 0 432 10 43 210 4321 0
	+----+-+---+--+--+---+----+-+
	|UUUU|L|SSS|FF|FF|DDD|GGGG|C|
	+----+-+---+--+--+---+----+-+

Downstream data header:
	 7 654 3210 765 4321 0
	+-+---+----+---+----+-+
	|L|SSS|FFFF|DDD|GGGG|C|
	+-+---+----+---+----+-+

UUUU = Userid
L = Last fragment in packet flag
SSS = Upstream packet sequence number
FFFF = Upstream fragment number
DDD = Downstream packet sequence number
GGGG = Downstream fragment number
C = Compression enabled for this packet

Upstream data packet starts with 4 bytes Base32 encoded header, then comes 
the payload data, encoded with chosen codec.

Downstream data starts with 2 byte header. Then payload data, which may be
compressed.

Ping:
Client sends:
	First byte p or P
	Rest encoded with Base32:
	1 byte userid
	CMC

The server response to Ping and Data packets is a DNS NULL type response:
If server has nothing to send, data length is 0 bytes.
If server has something to send, it will send a downstream data packet, 
prefixed with 2 bytes header as shown above.