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

Protocol draft for Miniature-P2P (by Michael Hasselmann) ================================ We will assume that P1 and P2 have already found each other and are able to chat ("match nick" in FICS). 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]" * 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 * 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) 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. 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. -- Initial source: https://garage.maemo.org/pipermail/chess-developer/2010-April/000133.html