Domains

Every JabberID (JID) contain domain portion. It’s an server address. Every JID looks like this:

test@test.com
worker@chat.company.org
admin@chat.application.com

Users

User name is case insensetive ACII characters string without special characters

Resources

When you connect your client to an XMPP server server ( or manualy ) assign resoirce id for that particular connection. This is using for routing trafic to connection instead of any other open connection ( if exists ). It looks like this:

alex@jabber.org/home
manager@chat.company.org/office

XMPP URIs

see RFC5122 or XEP-0147

Streaming XML

To start streaming xml you need to open long live TCP connection with XMPP server. Main an the only message types exists in this stream are:

  • <message />
  • <presense />
  • <iq />

This snippets called stanza .

Stanza

Message

Messages not asknowladged. Used in groupchat, alerts and notifications etc. Message stanzas came in five types ( determin by the type attribute ):

  • normal - This is simple message simular to email message
  • chat - exchanged in real-time “sessions” between two entities, such as IM between two users
  • groupchat - exchanged in multi-user chat room
  • headline - this type of message used to send alerts and notifications without expecting response at all. ( client should not able a user to reply )
  • error - server send this type of messages if something was wrong

Also <message> contain to and from required attributes.

Messages also contain some payload elements: <body/> and <subject />. So in overal basic message can looks like this:

<message from="madhatter@wonderland.lit/foo"
        to="alice@wonderland.lit"
        type="chat">
    <body>Who are you?</body>
    <subject>Query</subject>
</message>

Presense

Presense stanzas used for udpating avaliability status in the network. But not every user on server can see your status. At first he should be subscribed to see your status updates. This is broader topic for discussion than the current artice. But basic presence message can look’s like this:

<presence from="george@im.company.org/office">
    <show>xa</show>
    <status>Making coffe on the kitched</status>
</presense>

IQ

The “Info Query” stanza used to get or set some information or settings on the XMPP server. This type of stanzas should return replyes tracked by id attribute. It also has type attribute:

  • get - for requesting some information
  • set - for changing
  • result - responging entity after request
  • error - if response with some errors

Basic iq stanza can look like this:

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

( George asked for contact list ) . The response can be liike 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"/>
        <item jid="stuart@im.company.org"/>
        <item jid="Garry@im.company.org"/>
        <item jid="Potter@im.company.org"/>
    </query>
</iq>

Adding new contact to list:

<iq from="george@im.company.org/office"
    id="n3wun1qu31D"
    to="george@im.company.org"
    type="set">
    <query xmlns="jabber:iq:roster">
        <item jid="joseph@im.company.org"/>
    </query>
</iq>

In this case server will return empty result iq:

<iq from="george@im.company.org"
    id="n3wun1qu31D"
    to="george@im.company.org/office"
    type="result" />

Did you notice how resource portion of address work’s in this type of messages?

To be continued…

In the next articles we will deep dive into XMPP messaging mechanism with more interesting examples :)

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