XMPP multiplayer gaming: should I store opponents as roster contacts?

Question

I've read all 484 pages of Professional XMPP and read countless forum threads regarding rosters + XMPP and this question is still something I am struggling to solve. I'm looking for insight on best practices, so I at least know which direction to go in.

I'm building a cross-platform (web, iOS & Xbox), turn-based board game. Every player can have up to 100 different matches active at any given moment -- so they could easily skip from one game where it's not there turn to one where it is.

The game will feature a lobby where your list of active games are displayed, along with the name and online status of each opponent for that game (you may have up to 3 opponents, 4 total players per game).

Additionally, each player will have a friends list accessible from a different area which also lists online status.

I am using XMPP behind the scenes, completely transparent to the players, no one will ever sign in with a Jabber client or anything of the sort. I have complete control over how the information is displayed and utilized.

The main aspects I am using XMPP to solve are: notifications when an opponent has made a move, seeing my friends online statuses, and seeing my opponents online statuses, and in-game text chat.

So here's where I start having trouble: obviously your friends list will be contacts in your roster, so you can see their online status. But what about opponents? These are usually random opponents you will only play a single match with and never again -- yet your game with them may last up to 2 weeks.

Keeping in mind that everything is behind the scenes (ex: automatic subscription confirmations, etc) -- would the best course of action be to add each opponent to another group in your roster while the game is in progress and then remove them after the game is complete? That way you get presence notifications when that player is online? Or is this a case where PubSub could be utilized?

I've also considered using multi-user chat so I'd always have access to every users online status without subscriptions, but that seems far from efficient when there could be up to 20k players online at any given moment. Definitely sounds like a battery hog on mobile devices as well.

My other solution is to used share roster lists. Create a roster list for each game and assign that list to each player. Then delete the shared roster list once the game is complete.

Answer 1

I would choose Pubsub here. Of course, this means that you have to do some server side work too.

Send a directed presence to the opponents. This will allow them to see your presence.