* TODO:

Response length field needs further testing. At least bytes 2 and 3 belong to it, but
I have not seen a clear confirmation of 4 and 5 also belonging to it.

I tested it with trying to transfer big map files, but they might be compressed for
transfer (message begins with "fI" instead of "fH") and the map file transfers I tried
failed with the receiving end crashing.


* Packet types
** General

So far I have seen the first two bytes of the messages be either "fH" or "fI". The
latter seems to be used with turn data related messages and might indicate a compressed
message body (length of message is less than the size of the corresponding file on disk).

Bytes 3-6 are a little-endian 32bit integer telling how many more bytes the message
contains after it. So for example in the general info and mod list requests, it's
value is 1.

7th byte looks like a message type. Values seen so far:

 0x01  client           probably "I am playing these nations"
 0x02  server  no body  reply to 0x01
 0x03  client  no body  request general info 
 0x04  server           general info
 0x05  client  no body  probably "Which nations are in the game?"
 0x06  server           reply to 0x05
 0x07  client           turn file request
 0x0b  client  no body  bye
 0x0c  server  no body  bye
 0x0d  client           map file request
 0x11  client  no body  request mod list
 0x12  server           mod list

 0x34  client           pretender upload
 0x36  client           start game




** General info response, 0x04

There are some bytes I don't know the meaning of yet (no variation seen so far)
after the type code: 0x23, 0x01, 0x00, 0x00

Byte 12 might be game state code:
 0x01  waiting for pretenders
 0x02  running

The name begins at byte 13 and is nullterminated.

The byte after that is the game's era:
  0x00  unknown, the game loses the era information once the process ends for the first
        time in running mode and always has 0x00 for era value after that point
  0x01  EA
  0x02  MA
  0x03  LA

Constant 0x2d

Time to host, as 32-bit little-endian value. Special values:
  0x00000000  the timer is off in running mode
  0xffffffff  the timer is off in waiting mode

Constant 0x00

Next comes information about the nation slots (of which there are 95):
First, the status of each nation slot, 1 byte per:
  0x00  empty
  0x01  human
  0x02  AI
  0x03  only ever occurs with nation slot 25 (independents)
  0xfd  closed
  0xfe  defeated this turn
  0xff  defeated earlier

Second, whether the turn for a nation has been submitted, 1 byte per:
  0x00  not submitted
  0x01  submitted

Third, whether the player for a nation is currently connected, 1 byte per:
  0x00  not connected, always this in waiting mode
  0x01  connected

Next, turn number as 32-bit little-endian integer.
The value is 0xffffffff in games in waiting mode.

Last, whether clients are allowed to start the game, 1 byte:
  0x00  not allowed
  0x01  allowed



** Turn file request, 0x07

Byte 8 is number of the nation whose turn file is being requested. The rest of the
message body is the nation password as a nullterminated string.

TODO: What of the case where user selects more than one nation?


The response to this request begins with "fI" and the response body looks compressed.


** Mods info response, 0x12

If there are no mods, bytes 8 and 9 are 0xff

Otherwise the 8th byte is number of mods - 1 and 9th byte is 0x00. Or the mods count
might be a 2 byte little-endian integer.

After that come mod descriptors, which contain:
 Mod version: 2 2-byte little-endian integers, in order major, minor
 The mod file name string, nullterminated


** Bye messages 0x0b and 0x0c

The 0x0b message is sent by the client when disconnecting from server in the game. The
server responds with a 0x0c response. Both messages have an empty body.

This is probably not necessary, considering GGS hasn't made games blow up yet.