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

This protocol varies a lot from earlier ones and will
hopefully give cleaner code and enable more features.

Common header:

 7654 3210
+----+----+
|CCCC|UUUU|
+----+----+

CCCC = Command
UUUU = User id

Commands:
0: Version
1: Login
2: Case check
3: Codec switch
4: Data
5: Ping
6: -
7: -
8: -
9: -
A: -Reserved- (So header byte will never encode to a v)
B: -
C: -
D: - 
E: -
F: -

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

Version:
Client sends:
	Command = 0x0, User = 0xF
	Data is 4 bytes big endian protocol version
	Ends with CMC
Server replies:
	Command = 0x0, User = userid
	Then 4 chars, followed by big endian int:
		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
	
Login:
Command = 0x1, User = userid from version reply
Client sends:
	16 bytes MD5 hash of: (first 32 bytes of password) xor (8 repetitions of login challenge)
	Ends with CMC
Server replies:
	4 chars, then maybe three ints
	LACK serverip clientip mtu means login accepted
	LNAK means not accepted

Case check:
Command = 0x2, User = userid from version reply
Client sends: 
	Lots of data that should not be decoded
Server replies:
	The requested domain copied raw

Switch codec:
Command = 0x03, User = userid
Client sends:
	One byte, with value 5 or 6, representing number of bits per byte in encoding
Server sends:
	Name of codec if accepted. After this all upstream packets must be encoded with the new codec.
	BADCODEC if not accepted. Client must then revert to Base64

Data:
Command = 0x04, User = userid
Data header:
	 76543210 7 6 543210
	+--------+-+-+------+
	|SSSSSSSS|L|C|FFFFFF|
	+--------+-+-+------+

SSSSSSSS = Packet sequence number
L = Last fragment in packet flag
C = Compression used flag
FFFFFF = Fragment index in packet

The data header is used both by the server and the client, followed by a fragment.
Packet and fragment numbers are used to detect retransmits by dns relay.
When a fragment arrives with L bit set, the packet should be pushed to the tun device.
If the C bit is set, it should be decompressed before sent to tun device.

Ping:
Command = 0x04, User = userid
Client sends:
	Only a CMC
Server replies:
	With a Data packet or 0 bytes.