New protocol spec

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Erik Ekman 2008-12-06 13:20:47 +00:00 committed by Erik Ekman
parent ae942ac542
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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.