It is quite common to play games over IM networks. Since Tic-tac-toe is a well known game, XMPP needs a protocol to support it.
This protocol should provide all means to play a regular game of Tic-tac-toe over XMPP.
Tic-tac-toe is also one of the simplest games and played "just for fun". Therefore no validation support is needed. The typical duration is below one minute and the matches are not of great interest for non-players. Therefore spectators do not have to be supported as well. That is why this document only describes the protocol to play a Tic-tac-toe as a One-to-One match without support for game saving and resuming.
An entity implementing this protocol MUST also support Instant Gaming  and answer to disco requests accordingly including both the Instant Gaming and the game <feature/> elements in the response.
When inviting to a game of Tic-tac-toe, an entity SHOULD use Data Forms (XEP-0004)  to specify game options in the REQUIRED <game/> element. Possible options are "role" (of the inviting player), "rows" (height), "cols" (width) and "strike" (number of marks in a row needed to win). If these options are missing, all but role default to '3' and role defaults to 'x'. An implementation MUST be able to handle the default values. Everything beyond that is OPTIONAL.
When sending an invitation of type "renew", the role option MUST be changed to the opposite of the role the inviting player had in the previous match with that match ID. So both players essentially switch their roles. All other options MUST stay the same.
During the game, players change in turn, each of them sending one move at a time. The player with the role 'x' makes the first move. A game move is represented as a <message/> stanza addressed to the full JID of the other player. It MUST have a <thread/> child element which specifies the match ID. Furthermore, the <message/> stanza contains a <turn/> element which in turn contains exactly one <move/> element qualified by 'http://jabber.org/protocol/games/tictactoe'. It MUST possess these attributes:
|'id'||REQUIRED||The number of the move. First move is 1.|
|'row'||REQUIRED||The horizontal position of the mark.|
|'col'||REQUIRED||The vertical position of the mark.|
Notifying the players whether they have won or lost is in responsibility of the game client. The game is considered terminated when the board is full, i.e. nine moves have been made. For further termination conditions see the appropriate section of Instant Gaming .
The author is not aware of any security issues introduced by this protocol extension.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) .
The XMPP Registrar  shall include 'http://jabber.org/protocol/games/tictactoe' in its registry of protocols.
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1. XEP-xxxx: Instant Gaming <http://pidgin-games.sourceforge.net/xep/instant-gaming.html>.
3. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.
4. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.
Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/