Detecting other clients using the same account in XMPP

XMPP allows users to connect to the server from multiple clients simultaneously, using the same account. I built an application that does this but if the desktop client is enabled, I do not want the users to be able to connect using a mobile client. This is for a game and being connected to both causes problems.

So what I'm wondering is: Is it possible to detect if there are other clients connected using the same account. If I can check for other 开发者_开发百科clients, I can auto logout the user.

@Flow was on the right track. If all of your client instances use the same resource, in most servers, the later-connecting client will replace the older session. The older session will get a conflict stream error, and be disconnected. You MUST be careful not to auto-reconnect with the older client, or you will have written the "dueling resources" bug.

If you had control over your server, you have a chance at configuring it to allow a maximum of one resource for a given user, in which case the newer connection will fail with a conflict error, but you'll have worse user interface problems if you head down that path; there will be no way to get the second client logged in, even if you wanted to.

Finally, all resources for a given user are subscribed to that user's presence. As long as your client sends presence in:

<presence/>

you will receive presence from each of your other devices:

<presence to='user@example.com/resource1' from='user@example.com/resource2'/>
<presence to='user@example.com/resource1' from='user@example.com/resource3'/>
<presence to='user@example.com/resource1' from='user@example.com/resource4'/>

You could use this to decide which client is current, perhaps by adding an extension to the presence like XEP-0115.

Give the desktop and mobile client a fixed but different resource string. If the mobile client logs in, it can detect the presence of the desktop client by looking up the presence/availability of the resource of the desktop client and vice versa.

Then you only need to implement an custom XMPP ad-hoc command (XEP-0050) that tells the conflicting resource to log out.

It would be the servers responsibility: to reject a login from a client that is not accepted. I don't know if servers are able to blacklist xmpp clients but, in case you use openfire, you should be able to write an extension.