.. index:: XMLStream, BaseXMPP, ClientXMPP, ComponentXMPP SleekXMPP Architecture ====================== The core of SleekXMPP is contained in four classes: ``XMLStream``, ``BaseXMPP``, ``ClientXMPP``, and ``ComponentXMPP``. Along side this stack is a library for working with XML objects that eliminates most of the tedium of creating/manipulating XML. .. image:: _static/images/arch_layers.png :height: 300px :align: center .. index:: XMLStream The Foundation: XMLStream ------------------------- ``XMLStream`` is a mostly XMPP-agnostic class whose purpose is to read and write from a bi-directional XML stream. It also allows for callback functions to execute when XML matching given patterns is received; these callbacks are also referred to as :term:`stream handlers `. The class also provides a basic eventing system which can be triggered either manually or on a timed schedule. The Main Threads ~~~~~~~~~~~~~~~~ ``XMLStream`` instances run using at least three background threads: the send thread, the read thread, and the scheduler thread. The send thread is in charge of monitoring the send queue and writing text to the outgoing XML stream. The read thread pulls text off of the incoming XML stream and stores the results in an event queue. The scheduler thread is used to emit events after a given period of time. Additionally, the main event processing loop may be executed in its own thread if SleekXMPP is being used in the background for another application. Short-lived threads may also be spawned as requested for threaded :term:`event handlers `. How XML Text is Turned into Action ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ To demonstrate the flow of information, let's consider what happens when this bit of XML is received (with an assumed namespace of ``jabber:client``): .. code-block:: xml Hej! 1. **Convert XML strings into objects.** Incoming text is parsed and converted into XML objects (using ElementTree) which are then wrapped into what are referred to as :term:`Stanza objects `. The appropriate class for the new object is determined using a map of namespaced element names to classes. Our incoming XML is thus turned into a ``Message`` :term:`stanza object` because the namespaced element name ``{jabber:client}message`` is associated with the class ``sleekxmpp.stanza.Message``. 2. **Match stanza objects to callbacks.** These objects are then compared against the stored patterns associated with the registered callback handlers. For each match, a copy of the :term:`stanza object` is paired with a reference to the handler and placed into the event queue. Our ``Message`` object is thus paired with the message stanza handler ``BaseXMPP._handle_message`` to create the tuple:: ('stanza', stanza_obj, handler) 3. **Process the event queue.** The event queue is the heart of SleekXMPP. Nearly every action that takes place is first inserted into this queue, whether that be received stanzas, custom events, or scheduled events. When the stanza is pulled out of the event queue with an associated callback, the callback function is executed with the stanza as its only parameter. .. warning:: The callback, aka :term:`stream handler`, is executed in the main processing thread. If the handler blocks, event processing will also block. 4. **Raise Custom Events** Since a :term:`stream handler` shouldn't block, if extensive processing for a stanza is required (such as needing to send and receive an ``Iq`` stanza), then custom events must be used. These events are not explicitly tied to the incoming XML stream and may be raised at any time. Importantly, these events may be handled in their own thread. When the event is raised, a copy of the stanza is created for each handler registered for the event. In contrast to :term:`stream handlers `, these functions are referred to as :term:`event handlers `. Each stanza/handler pair is then put into the event queue. .. note:: It is possible to skip the event queue and process an event immediately by using ``direct=True`` when raising the event. The code for ``BaseXMPP._handle_message`` follows this pattern, and raises a ``'message'`` event:: self.event('message', msg) The event call then places the message object back into the event queue paired with an :term:`event handler`:: ('event', 'message', msg_copy1, custom_event_handler_1) ('event', 'message', msg_copy2, custom_evetn_handler_2) 5. **Process Custom Events** The stanza and :term:`event handler` are then pulled from the event queue, and the handler is executed, passing the stanza as its only argument. If the handler was registered as threaded, then a new thread will be spawned for it. .. note:: Events may be raised without needing :term:`stanza objects `. For example, you could use ``self.event('custom', {'a': 'b'})``. You don't even need any arguments: ``self.event('no_parameters')``. However, every event handler MUST accept at least one argument. Finally, after a long trek, our message is handed off to the user's custom handler in order to do awesome stuff:: msg.reply() msg['body'] = "Hey! This is awesome!" msg.send() .. index:: BaseXMPP, XMLStream Raising XMPP Awareness: BaseXMPP -------------------------------- While ``XMLStream`` attempts to shy away from anything too XMPP specific, ``BaseXMPP``'s sole purpose is to provide foundational support for sending and receiving XMPP stanzas. This support includes registering the basic message, presence, and iq stanzas, methods for creating and sending stanzas, and default handlers for incoming messages and keeping track of presence notifications. The plugin system for adding new XEP support is also maintained by ``BaseXMPP``. .. index:: ClientXMPP, BaseXMPP ClientXMPP ---------- ``ClientXMPP`` extends ``BaseXMPP`` with additional logic for connecting to an XMPP server by performing DNS lookups. It also adds support for stream features such as STARTTLS and SASL. .. index:: ComponentXMPP, BaseXMPP ComponentXMPP ------------- ``ComponentXMPP`` is only a thin layer on top of ``BaseXMPP`` that implements the component handshake protocol. .. index:: double: object; stanza Stanza Objects: A Brief Look ---------------------------- .. seealso:: See :ref:`api-stanza-objects` for a more detailed overview. Almost worthy of their own standalone library, :term:`stanza objects ` are wrappers for XML objects which expose dictionary like interfaces for manipulating their XML content. For example, consider the XML: .. code-block:: xml A very plain element to start with, but we can create a :term:`stanza object` using ``sleekxmpp.stanza.Message`` as so:: msg = Message(xml=ET.fromstring("")) The ``Message`` stanza class defines interfaces such as ``'body'`` and ``'to'``, so we can assign values to those interfaces to include new XML content:: msg['body'] = "Following so far?" msg['to'] = 'user@example.com' Dumping the XML content of ``msg`` (using ``msg.xml``), we find: .. code-block:: xml Following so far? The process is similar for reading from interfaces and deleting interface contents. A :term:`stanza object` behaves very similarly to a regular ``dict`` object: you may assign to keys, read from keys, and ``del`` keys. Stanza interfaces come with built-in behaviours such as adding/removing attribute and sub element values. However, a lot of the time more custom logic is needed. This can be provided by defining methods of the form ``get_*``, ``set_*``, and ``del_*`` for any interface which requires custom behaviour. Stanza Plugins ~~~~~~~~~~~~~~ Since it is generally possible to embed one XML element inside another, :term:`stanza objects ` may be nested. Nested :term:`stanza objects ` are referred to as :term:`stanza plugins ` or :term:`substanzas `. A :term:`stanza plugin` exposes its own interfaces by adding a new interface to its parent stanza. To demonstrate, consider these two stanza class definitions using ``sleekxmpp.xmlstream.ElementBase``: .. code-block:: python class Parent(ElementBase): name = "the-parent-xml-element-name" namespace = "the-parent-namespace" interfaces = set(('foo', 'bar')) class Child(ElementBase): name = "the-child-xml-element-name" namespace = "the-child-namespace" plugin_attrib = 'child' interfaces = set(('baz',)) If we register the ``Child`` stanza as a plugin of the ``Parent`` stanza as so, using ``sleekxmpp.xmlstream.register_stanza_plugin``:: register_stanza_plugin(Parent, Child) Then we can access content in the child stanza through the parent. Note that the interface used to access the child stanza is the same as ``Child.plugin_attrib``:: parent = Parent() parent['foo'] = 'a' parent['child']['baz'] = 'b' The above code would produce: .. code-block:: xml

It is also possible to allow a :term:`substanza` to appear multiple times by using ``iterable=True`` in the ``register_stanza_plugin`` call. All iterable :term:`substanzas ` can be accessed using a standard ``substanzas`` interface.