XMPP Presense

Presense is the technology allowing you choose what informations of your network availability you want to share. This is happening by subscription “handshake”

To request someone’s presence you send him a subscruption request:

<presence from="george@im.company.org"
        to="mary@im.company.org"
        type="subscribe" />

The recepient can approve it or denied by sending presence stanza of type subscribed or unsubscribed:

<presence from="mary@im.company.org"
        to="george@im.company.org"
        type="subscribed" />

This is bidirectional process. So the recepient also send you a subscription request and you also can subscrube or unsubscrbe to it.

<presence from="mary@im.company.org"
        to="george@im.company.org"
        type="subscribe" />

<presence from="george@im.company.org"
        to="mary@im.company.org"
        type="subscribed" />

After success handshake you will be automaticaly notified when someone’s network awailability changed with presence stanza without type attribute.

<presence from="mary@im.company.org"
        to="george@im.company.org">
    <show>xa</show>
    <status>On the meeting...</status>
</presence>

How Presence Is Propagated

open xml stream
send initial presence stanza:

<presence />

Server check roster ( contact list ) and sends a presence notification to each person who subscribed to you with full JID with resource portion:

<presence from="george@im.company.org/office"
        to="patric@im.company.org"/>

<presence from="george@im.company.org/office"
        to="mary@im.company.org"/>

Now, everyone of your contact list ( who subscribe to you presence ) know about your availability. But you do not know about THEIR availability. To achieve that server sends presence of type probe:

<presence from="george@im.company.org/office"
        to="patric@im.company.org"
        type="probe" />

<presence from="george@im.company.org/office"
        to="mary@im.company.org"
        type="probe" />

Once contacts receive probes they check permissions according to their records. If your contact is offline the presence stanza will be of type unavailable often with information when it was online last time. Like this:

<!-- contact is offline -->
<presence from="george@im.company.org/office"
        to="patric@im.company.org"
        type="unavailable">
    <delay xmlns="urn:xmpp:delay" stamps="2024-06-24T08:04:00+03:00" />
</presence>

<!-- contact is online -->
<presence from="mary@im.company.org/accounting"
        to="george@im.company.org/office" />

( basicaly delay element is the time when presence was last time changed - when presence was chanded to “unavailable” )

If contact has more then one connected resource you will receive more than one presence stanza from this contact.

Status

Precense stanzas can contain more information than just un/available. As you was see before there also <show/> and <status/> elements.

Show element is limited to four predefined values:

chat - you are available for communication
away - you AFK. This is often triggered automaticaly after some timeout without activity.
xa - “eXtended Away`; more extended version of “away”.
dnd - “Do ot disturb”

Status element is for short text string describing your show status.

Priority

Presence stanza can include one more element <priority />. It used for prioritize availability statuses between connected resources:


<presence from="george@im.company.org/office">
    <priority>7</priority>
</presence>

<presence from="george@im.company.org/store">
    <priority>-1</priority>
</presence>

Value can be in range between -127 and +128 numbers. Higher priority resource will more likely receive message from bare JID ( JID without resource portion ).

Direct Presence

All previously examples was broadcasted messages. For example if you need to chat a little with some one but without permantent precense subscribtion.

<message from="george@im.company.org/office"
        to="garry.tech@im.company.org"
        type="chat">
    <body>I need the printer to fix. Can you help me?</body>
</message>

<presence from="george@im.company.org/office"
        to="garry.tech@im.company.org">
</presence>

And contact can respond with stanza like this:

<presence from="garry.tech@im.company.org"
        to="george@im.company.org/office"
        type="available" />

Offline

To set your network status as offline you need to send stanza:

<presence type="unavailable" />

Rich Presence

With precense you can also just change your status text, without changing network availability:

<presence>
    <status>At the coffe machine</status>
</presence>

Presence and Rosters

When you send iq stanza to server to get roster list:

<iq from="george@im.company.org/office"
    id="un1qu31D"
    to="george@im.company.org"
    type="get">
    <query xmlns="jabber:iq:roster" />
</iq>

you will receive this kind of responce:

<iq from="george@im.company.org"
    id="un1qu31D"
    to="george@im.company.org/office"
    type="result">
    <query xmlns="jabber:iq:roster">
        <item jid="patric@im.company.org"/>
        <item jid="stuart@im.company.org"/>
        <item jid="Garry@im.company.org"/>
        <item jid="Potter@im.company.org"/>
    </query>
</iq>

In a real applications response will be more extended:

<iq from="george@im.company.org"
    id="un1qu31D"
    to="george@im.company.org/office"
    type="result">
    <query xmlns="jabber:iq:roster">
        <item jid="patric@im.company.org" name="Patric" subsciption="none" />
        <item jid="stuart@im.company.org" name="Stuart" subsciption="to" />
        <item jid="Garry@im.company.org" name="Garry" subsciption="from" />
        <item jid="Potter@im.company.org" name="Potter" subsciption="both" />
    </query>
</iq>

Also you can group contact list and the roster will look like this:

<iq from="george@im.company.org"
    id="un1qu31D"
    to="george@im.company.org/office"
    type="result">
    <query xmlns="jabber:iq:roster">
        <item jid="patric@im.company.org" name="Patric" subsciption="none">
            <group>Coworker</group>
        </item>
        <item jid="stuart@im.company.org" name="Stuart" subsciption="to">
            <group>Coworker</group>
        </item>
        <item jid="garry@im.company.org" name="Garry" subsciption="from">
            <group>Coworker</group>
        </item>
        <item jid="potter@im.company.org" name="Potter" subsciption="both">
            <group>Friends</group>
        </item>
    </query>
</iq>

Roster groups can be edited with next:

<iq id="32984723984" type="set">
    <query xmlns="jabber:iq:roster">
        <item jid="stuart@im.company.org">
            <group>Friends</group>
        </item>
    </query>
</iq>

After that server will push that change for all connected clients. Basicaly synchronization requests which is called roster push.

<iq from="george@im.company.org"
    id="df987239f"
    to="george@im.company.org/office"
    type="set">
    <query xmlns="jabber:iq:roster">
        <item jid="stuart@im.company.org">
            <group>Friends</group>
        </item>
    </query>
</iq>

Notes and examples used from XMPP The Definitive Guide by Peter Saint-Andre

How Presence Is Propagated#

Status#

Priority#

Direct Presence#

Offline#

Rich Presence#

Presence and Rosters#