XMPP: how to request server for presence status of a user's contacts ?

Question

We have a site and we developed a chat system for it using strophe.js library and ejabberd XMPP server. We use session attachment that was initiated with PHP (using an in-house library). What we do is get the RID and SID from the PHP script, then use strophe's session attachment. The said RID and SID is stored on a cookie and the RID value on the cookie is updated every update of the RID on strophe.js.

This works fine, after logging in we receive the presence status of each of our contacts. The problem with this is, when you go to another page on the site, and attach using the said RID (we use the incremented value produced by strophe) and SID, the server wouldn't send presence information of your contacts anymore as opposed to when you logged in. This caused our contacts area to appear all invisible even though they are online. They would only appear online if you (or your contact) log out on the chat, then log in again (since you will receive a presence update from the XMPP server).

I have written a workaround where the presence status of your contacts is saved on a cookie (all online contacts will have their JIDs saved on the cookie) when a presence is received from the server. This is checked every page load, if the cookie is set, it will be read, and all JIDs on the cookie will be marked as online. This is working fine but there might be some better ways to solve this, using XMPP's default behaviors.

Answer 1

XMPP servers send presence probes to all your contacts on your behalf when you send your own initial presence to the server. From then on, you will only receive presence status changes from your contacts.

If you lose the presence state of your contacts, you will need to send your own presence probes to re-establish that state. However, this is probably not something you want to do a lot, and passing around the presence state is probably preferred in most cases.

You could try passing the state via XMPP. For example, you could use Private XML Storage (XEP-0049), Pubsub (XEP-0060), or PEP (XEP-0163).

Another option instead of cookies for passing it client side is to use an HTML5 SharedWorker object to hold the state.

Answer 2

I shudder to think of the scale properties associated with storing all of the presence you just received from the server back to the server in private storage. Private storage almost always is backed to long-term storage rather than stored in memory, so you're going to grind your server's disk to dust.

If you want to store more state in the browser, and insulate yourself from browser version, and you're already using jQuery, then jStore is pretty sweet.