2011-08-13 00:33:32 +00:00
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.. index:: XMLStream, BaseXMPP, ClientXMPP, ComponentXMPP
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2014-07-17 12:19:04 +00:00
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Slixmpp Architecture
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2011-08-13 00:33:32 +00:00
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======================
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The core of Slixmpp is contained in four classes: ``XMLStream``,
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``BaseXMPP``, ``ClientXMPP``, and ``ComponentXMPP``. Along side this
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stack is a library for working with XML objects that eliminates most
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of the tedium of creating/manipulating XML.
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.. image:: _static/images/arch_layers.png
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:height: 300px
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:align: center
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.. index:: XMLStream
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The Foundation: XMLStream
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-------------------------
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:class:`~slixmpp.xmlstream.xmlstream.XMLStream` is a mostly XMPP-agnostic
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class whose purpose is to read and write from a bi-directional XML stream.
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It also allows for callback functions to execute when XML matching given
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patterns is received; these callbacks are also referred to as :term:`stream
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handlers <stream handler>`. The class also provides a basic eventing system
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which can be triggered either manually or on a timed schedule.
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The Main Threads
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~~~~~~~~~~~~~~~~
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:class:`~slixmpp.xmlstream.xmlstream.XMLStream` instances run using at
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least three background threads: the send thread, the read thread, and the
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scheduler thread. The send thread is in charge of monitoring the send queue
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and writing text to the outgoing XML stream. The read thread pulls text off
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of the incoming XML stream and stores the results in an event queue. The
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scheduler thread is used to emit events after a given period of time.
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Additionally, the main event processing loop may be executed in its
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own thread if Slixmpp is being used in the background for another
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application.
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Short-lived threads may also be spawned as requested for threaded
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:term:`event handlers <event handler>`.
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How XML Text is Turned into Action
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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To demonstrate the flow of information, let's consider what happens
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when this bit of XML is received (with an assumed namespace of
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``jabber:client``):
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.. code-block:: xml
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<message to="user@example.com" from="friend@example.net">
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<body>Hej!</body>
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</message>
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1. **Convert XML strings into objects.**
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Incoming text is parsed and converted into XML objects (using
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ElementTree) which are then wrapped into what are referred to as
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:term:`Stanza objects <stanza object>`. The appropriate class for the
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new object is determined using a map of namespaced element names to
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classes.
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Our incoming XML is thus turned into a :class:`~slixmpp.stanza.Message`
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:term:`stanza object` because the namespaced element name
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``{jabber:client}message`` is associated with the class
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:class:`~slixmpp.stanza.Message`.
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2. **Match stanza objects to callbacks.**
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These objects are then compared against the stored patterns associated
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with the registered callback handlers. For each match, a copy of the
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:term:`stanza object` is paired with a reference to the handler and
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placed into the event queue.
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Our :class:`~slixmpp.stanza.Message` object is thus paired with the message stanza handler
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:meth:`BaseXMPP._handle_message` to create the tuple::
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('stanza', stanza_obj, handler)
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3. **Process the event queue.**
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The event queue is the heart of Slixmpp. Nearly every action that
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takes place is first inserted into this queue, whether that be received
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stanzas, custom events, or scheduled events.
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When the stanza is pulled out of the event queue with an associated
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callback, the callback function is executed with the stanza as its only
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parameter.
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.. warning::
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The callback, aka :term:`stream handler`, is executed in the main event
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processing thread. If the handler blocks, event processing will also
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block.
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4. **Raise Custom Events**
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Since a :term:`stream handler` shouldn't block, if extensive processing
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for a stanza is required (such as needing to send and receive an
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:class:`~slixmpp.stanza.Iq` stanza), then custom events must be used.
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These events are not explicitly tied to the incoming XML stream and may
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be raised at any time. Importantly, these events may be handled in their
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own thread.
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When the event is raised, a copy of the stanza is created for each
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handler registered for the event. In contrast to :term:`stream handlers
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<stream handler>`, these functions are referred to as :term:`event
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handlers <event handler>`. Each stanza/handler pair is then put into the
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event queue.
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2011-11-22 23:25:24 +00:00
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The code for :meth:`BaseXMPP._handle_message` follows this pattern, and
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raises a ``'message'`` event::
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self.event('message', msg)
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The event call then places the message object back into the event queue
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paired with an :term:`event handler`::
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('event', 'message', msg_copy1, custom_event_handler_1)
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('event', 'message', msg_copy2, custom_evetn_handler_2)
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5. **Process Custom Events**
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The stanza and :term:`event handler` are then pulled from the event
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queue, and the handler is executed, passing the stanza as its only
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argument. If the handler was registered as threaded, then a new thread
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will be spawned for it.
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.. note::
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Events may be raised without needing :term:`stanza objects <stanza object>`.
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For example, you could use ``self.event('custom', {'a': 'b'})``.
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You don't even need any arguments: ``self.event('no_parameters')``.
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However, every event handler MUST accept at least one argument.
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Finally, after a long trek, our message is handed off to the user's
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custom handler in order to do awesome stuff::
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msg.reply()
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msg['body'] = "Hey! This is awesome!"
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msg.send()
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.. index:: BaseXMPP, XMLStream
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Raising XMPP Awareness: BaseXMPP
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--------------------------------
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While :class:`~slixmpp.xmlstream.xmlstream.XMLStream` attempts to shy away
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from anything too XMPP specific, :class:`~slixmpp.basexmpp.BaseXMPP`'s
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sole purpose is to provide foundational support for sending and receiving
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XMPP stanzas. This support includes registering the basic message,
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presence, and iq stanzas, methods for creating and sending stanzas, and
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default handlers for incoming messages and keeping track of presence
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notifications.
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The plugin system for adding new XEP support is also maintained by
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:class:`~slixmpp.basexmpp.BaseXMPP`.
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.. index:: ClientXMPP, BaseXMPP
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ClientXMPP
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----------
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:class:`~slixmpp.clientxmpp.ClientXMPP` extends
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:class:`~slixmpp.clientxmpp.BaseXMPP` with additional logic for connecting
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to an XMPP server by performing DNS lookups. It also adds support for stream
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features such as STARTTLS and SASL.
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.. index:: ComponentXMPP, BaseXMPP
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ComponentXMPP
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-------------
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:class:`~slixmpp.componentxmpp.ComponentXMPP` is only a thin layer on top of
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:class:`~slixmpp.basexmpp.BaseXMPP` that implements the component handshake
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protocol.
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