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Miniature/Development/Phase 2.0: Real-time P2P Miniature/P2P-Protocol

Revision as of 10:04, 15 April 2010

Protocol draft for Miniature-P2P
================================

We will assume that P1 and P2 have already found each other and are able to
chat ("match nick" in FICS).

>>jukey>>
We also should assume that both players are using Miniature. One
example what happens if not is described in one of my comments below
(automatc/manual acceptance of games).
<<jukey<<

A Chat
======

* "tell [nick|#channel] msg"
  Why nick and #channel? Because later we migt want observers in P2P (so
  there'd be a channel #obs, because you dont want the players so see the chat
  of kibitzs).

* http://www.freechess.org/Help/HelpFiles/tell.html

* This command is the *only* one that will work in every situation, without
  exception. It does not change the current game state.


B Game mode negotiation
=======================

* Both of the players can now propose a game mode, similar to
  http://www.freechess.org/Help/HelpFiles/seek.html

* We can skip the parameters we dont support yet, so we need at least be able
  to send/parse this:

  "seek [time inc] [rated|unrated] [white|black]"

>>jukey>> It makes sense to make the [white|black] value optional. If it's not
available the game can be accepted by people who had choosen black, white or
nothing. I personally like the possibility to play "random colored" games.
<<jukey<<

* Examples:
  "seek 5 0 r w":         5 minutes, no incr, rated, seeker wants white,
  "seek 5 0 rated white": same as above,
  "seek 2 10 u b":        2 minutes, 10s incr, unrated, seeker wants black
>>jukey>>
  "seek 2 12 r":	2 minutes, 12s incr, rated, seeker wants black or white
<<jukey<<


* When the other player receives a seek, he can either accept the offer or
  ignore it. Both players could propose game modes sending as many seeks as
  they want, and at any time! But that would be silly in our case, so let's
  simplify this dramatically:

  1 host player (P1) sends seek,
    A client player (P2) accepts seek: send "play" → 2
    B P2 ignores seek: P2 can now send a seek
      A P1 accepts seek: send "play" → 2
      B P1 ignores seek: → 1
  2 game starts (http://www.freechess.org/Help/HelpFiles/play.html)

>>jukey>>
There is possible a special situation if you opponent is not using
Miniature (which not allows the players to choose if they want to start the game
manually or automaticly) and don't automaticly accept games. See fourth
paragraph in http://www.freechess.org/Help/HelpFiles/play.html :
"If the ad calls
for a manual start, the other user will be notified that you are challenging
him/her to a match; he/she then can accept or decline your offer to play that
match."
In this case the description above changes into:
  1 host player (P1) sends seek,
    A client player (P2) accepts seek: send "play" → 2
    B P2 ignores seek: P2 can now send a seek
      A P1 accepts seek: send "play" → 2
      	A P2 using manual as seek parameter accepts the offer to play from P1 → 2
      	B P2 using manual as seek parameter declines the offer to play from P1 → 1
      	C P2 using manual as seek parameter accepts the offer to play from P1
						 but P1 is no more available (for example in an other game) → 3
      B P1 ignores seek: → 1
  2 game starts (http://www.freechess.org/Help/HelpFiles/play.html)
  3 P1 is shown as not ready to play
<<jukey<< 


C Moves
=======

* In FICS, once it is your turn, it is sufficient to enter "e2-e4" to move your
  pawn, for example.

* FICS sends the new position to each player, obviously this simplifies sync
  issues. So I think we should send sth like "move e2-e4; fen
  rnbqkbnr/pppppppp/8/8/4/P/3/8/PPPP1PPP/RNBQKBNR b". The FEN position string
  can be seen as checksum for the move, so we are able to always detect sync
  issues.  In case of an sync issue, the FEN position *overrides* the move, and
  the error is logged (maybe even send "sync error" back to sender, so both
  peers are aware). How to handle that beyond logging the error, I do not know.
  Let's see if it really happens first. The more general approach is to have
  the receiving peer always confirm a move with a checksum, based on the
  position info it was able to compute, and the sending peer then compares this
  checksum, and complains.

* The peers compute the status (check, checkmate, ...) themselves, based on the
  position info send

* Move requests that are sent when it is not the player's turn should
  be silently discarded.
>>jukey>>
Maybe the client also should not be able to send a request if it is
the opponents move.
<<jukey<<

D Takeback
==========
* FICS is a bit funny here, showing its age wrt verbose & racy protocol
  implementation "takeback 2 - accept - withdraw", note how accept and withdraw
  can happen at the same time.
  http://www.freechess.org/Help/HelpFiles/takeback.html

* Again, let's simplify:
  "takeback n", request to take back n moves, answered by "takeback n" (the
  same n) to accept. Now it doesn't even matter who sends it first.
  1 P1 sends "takeback n",
    A P2 accepts: send "takeback n" → 2
    B P2 declines: nothing happens → 3.
  2 N half-moves are taken back.
  3 P2 or P1 sends his next move (notice how this can clash with a "takeback n"
    confirmation in case it was P1's turn, in which case the takeback
    confirmation should win, as P2 is free to ignore P1's move after confirming
    the takeback).

* Same as with moves, we send: "takeback n; fen current/fen/pos/ w|b", so that
  the fen position is the one to be expected after takeback n would be
  performed (assuming we go without the general approach of sending checksums
  after every position change).

* A takeback request can be simply ignored without further actions.


E Draw
======
* http://www.freechess.org/Help/HelpFiles/draw.html

* We don't support claiming a draw yet, but that will be easy to implement:
  before the other peer gets chance to say ok, "draw", we query the logic
  analyzer, which is entitled to enforce a technical "draw".

* Otherwise, same as in takeback, without position sending:
  1 P1 sends "draw",
    A P2 accepts: send "draw" → 2
    B P2 declines: nothing happens → 3.
  2 Game ends in draw.
  3 P1 sends his next move (P2 is not allowed to demand a draw if it is not his
    turn, also, same conflict resolution as in takeback: draw confirmation wins
    over P1's move, and P2 is free to ignore the move).


F Resign
========
* http://www.freechess.org/Help/HelpFiles/resign.html

* Players can resign at any time, I guess? No confirmation by other player
  needed, game ends.


G Adjourn
=========
* http://www.freechess.org/Help/HelpFiles/adjourn.html

* I like the 2 cases presented on FICS, esp. the courtesy adjourn which handles
  time-outs gracefully.

* Similar to draw and takeback:
  1 P1 ran out of time, unresponsive
    A P2 sends "adjourn" → 3
    (B P2 claims the win, not important yet for our case)
  2 P1 sends "adjourn"
    A P2 accepts: send "adjourn" → 3
    B P2 declines: nothing happens
  3 Game is adjourned, both sides save the current position locally, game ends.