Correspondence chess built on top of the scuttlebutt platform. More information about scuttlebutt here: https://staltz.com/an-off-grid-social-network.html and https://www.scuttlebutt.nz/

It is built to allow it to be integrated into scuttlebutt viewers (such as patchbay, patchwork using depject so that they can take care of things like discovering friends to play with, etc.

ssb-chess is currently integrated into patchbay. You can find it in the menu at the top right (the blue dot) and then the 'chess' menu item.

• Mithriljs is used for rendering the pages.
• Chessground is used for the board and pieces widget and animating the moves.
• Scalachessjs is used for move validation and check / end condition detection.
• Embedded Chat is used for the chatroom to allow the players to chat during their game.

Note: since this is built on a peer 2 peer protocol, messages may be corrupted or deliberately misleading to cheat. ssb-chess doesn't validate that the client agrees a post is valid yet as it assumes your friends can be trusted.

The documentation below documents the 'content' section of the scuttlebutt messages. The 'author' field of the outer object containing the content field is the ID of person who posted the message (made the chess move, posted the chat message, invited another player to a game, etc.)

For example, the entire scuttlebutt message for a move could look like this:

{
  "key": "%mbTncS4L6NkmWbUu28SYFR+gkS+EBXtv69qw1Nys+GA=.sha256",
  "value": {
    "previous": "%tAgOzYHfdUDjTCtL/WPdBFikGpi7FF1y5yluIa0L70c=.sha256",
    "author": "@RJ09Kfs3neEZPrbpbWVDxkN92x9moe3aPusOMOc4S2I=.ed25519",
    "sequence": 2467,
    "timestamp": 1512721788946,
    "hash": "sha256",
    "content": {
      "type": "chess_move",
      "ply": 35,
      "root": "%GplJjfQtF931QBN/QLb5Dbkkn7p6vPDa6GlArwx7lXs=.sha256",
      "orig": "d6",
      "dest": "e7",
      "pgnMove": "dxe7",
      "fen": "r1b2rk1/pp1pPppp/6q1/8/2Pp1B2/1Q1P2P1/PP4BP/R3R1K1 b - - 0 18",
      "branch": "%FvjrSmC/02bneFhr1/xZz9K5HQezQBTI4nEyG3rQ7FM=.sha256"
    },
    "signature": "0SpisCR/celfcZsc9Bc0Ikq/12bAp2B3sNh5q0lPqTB1JsMT56rtVzxq75ly1eE3+bp+vj+XfZ262wDCNLjhDw==.sig.ed25519"
  },
  "timestamp": 1513461650805.013
}

Type chess_invite

• Inviting - the ID of the player being invited.
• myColor - the colour of the inviting player (white or black.)

{
  "type": "chess_invite",
  "inviting": "@RJ09Kfs3neEZPrbpbWVDxkN92x9moe3aPusOMOc4S2I=.ed25519",
  "myColor": "black"
}

The key of the message inviting a player to play then becomes the game ID which subsequent messages link back to.

Type chess_invite_accept

• root - the key of the invitiation message that is being accepted.
• branch - the key of the invitiation message that is being accepted. This is used to support ssb-ooo, which allows clients to request messages that are not visible in their follow graph. This helps clients observe the game, even if the user isn't close to one of the players in the follow graph.

{
      "type": "chess_invite_accept",
      "root": "%JJis5OErved3kJu2q9tpPyd+hjFq4EnqHUusy6LJ+OE=.sha256",
      "branch": "%JJis5OErved3kJu2q9tpPyd+hjFq4EnqHUusy6LJ+OE=.sha256"
    }

A player may accept an invite they have received by sending a message of type chess_invite_accept linking back to the key of the original game invitation message.

The game is then 'in progress.'

Type chess_move

• root - the original game invite message key.
• branch - the key of the previous move that the move is being made in response to. This is used to support ssb-ooo, which allows clients to request messages that are not visible in their follow graph. This helps clients observe the game, even if the user isn't close to one of the players in the follow graph.
• ply - the move number
• orig - the origin square
• dest - the destination square
• pgnMove - the PGN of the move.
• fen - the position of the board after the move in FEN notation.
• promotion (optional) - A letter donating the piece a pawn should be promoted to (b,n,q,r denoting bishop, knight, queen and rook respectively.)

{
  "type": "chess_move",
  "ply": 26,
  "root": "%WbzP0UxevK8j4g6CdLmgFnsjblnW0EVp/u6phVD5Y/4=.sha256",
  "branch": "%FvjrSmC/02bneFhr1/xZz9K5HQezQBTI4nEyG3rQ7FM=.sha256",
  "orig": "b2",
  "dest": "c1",
  "pgnMove": "bxc1=B",
  "fen": "r2qkbnr/p3pppp/3p4/6B1/4P3/5Q2/b2N1PPP/2b1KB1R w kq - 0 14",
  "promotion": "b"
}

Type chess_game_end

• root - the original game invite message key.
• branch - the key of the previous move that the end of the game is in response to. This is used to support ssb-ooo, which allows clients to request messages that are not visible in their follow graph. This helps clients observe the game, even if the user isn't close to one of the players in the follow graph.
• status - the status the game ended with. May be one of the following: mate | draw | resigned.
• ply (optional - may be omitted for resignations) - the move number
• orig (optional - may be omitted for resignations) - the origin square
• dest (optional - may be omitted for resignations) - the destination square
• pgnMove (optional - may be omitted for resignations) - the PGN of the move.
• fen (optional - may be omitted for resignations) - the position of the board after the move in FEN notation.
• promotion (optional) - A letter donating the piece a pawn should be promoted to (b,n,q,r denoting bishop, knight, queen and rook respectively.)

Note: The client should work out the winner for display based on who posted the message. For resign messages, the opposite player is the winner. For 'mate' messages, the player authoring the message is the winner and for a draw there are no winners.

{
 "type": "ssb_chess_game_end",
  "status": "mate",
  "ply": 20,
  "fen": "rnb2rk1/ppp2ppp/3p4/4p1qK/2P1n3/8/P2P1PPP/RNB2BNR w - - 2 11",
  "root": "%HGPn7yS2bjpWZndXtuusOjGXrirIIGu0XS18aY8YoFM=.sha256",
  "branch": "%FvjrSmC/02bneFhr1/xZz9K5HQezQBTI4nEyG3rQ7FM=.sha256",
  "orig": "f6",
  "dest": "g5",
  "pgnMove": "Qg5#"
}

Type ssb_chess_chat

Note: If this is a private message between the two players in the game, the content of the message is encrypted using sbot.private.publish with an array of the IDs of the players of the game as the recipients parameter.

If it is not a private message, it is a public message in the observer chat between spectators of the game. This shouldn't be displayed to the two players playing (or only displayed after the game has finished) so that the game isn't interfered with. Obviously a player could look at the raw feed to see what other people are saying about the game, but it's better to not make the chat easily visible.

• root - the original game invite message key.
• msg - The chat message contents.

{
  msg: "Chat testarooni"
  root: "%YQktCnxwY0rQyljO6BLrD7AQwRpf13HzbsVAZV19vlo=.sha256"
  type: "chess_chat"
}

• Requires the ssb-chess-db which is used to index the state of all the known games.

You can read more about depject here

The strategy for this was recently updated. I need to document the new approach :)