solana/rfcs/rfc-004-tictactoe-program.md

Two players want to play tic-tac-toe with each other on Solana.

The tic-tac-toe program has already been provisioned on the network, and the program author has advertised the following information to potential gamers:

• tictactoe_publickey - the program's public key
• tictactoe_gamestate_size - the number of bytes needed to maintain the game state

The game state is a well-documented data structure consisting of:

• Player 1's public key
• Player 2's public key
• Game status. An 8-bit value where:
  • 0 = game uninitialized
  • 1 = Player 1's turn
  • 2 = Player 2's turn
  • 3 = Player 1 won
  • 4 = Player 2 won
• Current board configuration. A 3x3 character array containing the values '\0', 'X' or 'O'

Game Setup

1. Two players want to start a game. Player 2 sends Player 1 their public key, player2_publickey off-chain (IM, email, etc)

2. Player 1 creates a new keypair to represent the game state, (gamestate_publickey, gamestate_privatekey).

3. Player 1 issues an allocate_memory transaction, assigning that memory page to the tic-tac-toe program. The memory_fee is used to rent the memory page for the duration of the game and is subtracted from current account balance of Player 1:

allocate_memory(gamestate_publickey, tictactoe_publickey, tictactoe_gamestate_size, memory_fee)

4. Game state is then initialized by issuing a new call transaction to the tic-tac-toe program. This transaction is signed by gamestate_privatekey, known only to Player 1.

call(tictactoe_publickey, gamestate_publickey, 'new', player1_publickey, player2_publickey)

5. Once the game is initialized, Player 1 shares gamestate_publickey with Player 2 off-chain (IM, email, etc)

Note that it's likely each player prefer to generate a game-specific keypair rather than sharing their primary public key (player1_publickey, player2_publickey) with each other and the tic-tac-toe program.

Game Play

Both players poll the network, via a TBD off-chain RPC API, to read the current game state from the gamestate_publickey memory page.

When the Game status field indicates it's their turn, the player issues a move call transaction passing in the board position (1..9) that they want to mark as X or O:

call(tictactoe_publickey, gamestate_publickey, 'move', position)

The program will reject the transaction if it was not signed by the player whose turn it is.

The outcome of the move call is also observed by polling the current game state via the TBD off-chain RPC API.

Game Cancellation

At any time Player 1 may conclude the game by issuing:

call(tictactoe_publickey, gamestate_publickey, 'abort')

causing any remaining rent tokens assigned to the gamestate_publickey page to be transferred back to Player 1 by the tic-tac-toe program. Lastly, the network recognizes the empty account and frees the gamestate_publickey memory page.