StanzaExtension Class Reference

This class abstracts a stanza extension, which is usually an element in a specific namespace. More...

#include <stanzaextension.h>

Inherited by Adhoc::Command, AMP, Capabilities, ChatState, Client::ResourceBind, Client::SessionCreation, ClientBase::Ping, DataForm, DelayedDelivery, Disco::Info, Disco::Items, Disco::SoftwareVersion, Error, FeatureNeg, GPGEncrypted, GPGSigned, InBandBytestream::IBB, Session::Jingle, MessageEvent, MUCRoom::MUCAdmin, MUCRoom::MUCOwner, MUCRoom::MUCUser, Nickname, NonSaslAuth::Query, OOB, PrivateXML::Query, Event, Receipt, Registration::Query, RosterManager::Query, Search::Query, UniqueMUCRoom::Unique, VCard, VCardUpdate, and XHtmlIM.

Inheritance diagram for StanzaExtension:

[legend]List of all members.

Public Member Functions
	StanzaExtension (int type)
virtual	~StanzaExtension ()
virtual const std::string &	filterString () const =0
virtual StanzaExtension *	newInstance (const Tag *tag) const =0
virtual Tag *	tag () const =0
int	extensionType () const

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Detailed Description

This class abstracts a stanza extension, which is usually an element in a specific namespace.

This class is the base class for almost all protocol extensions in gloox. As such, it should be used whenever an add-on to the core XMPP spec needs to be made. For simple protocols it may suffice to create a sub-class of StanzaExtension. For protocols which require keeping of state, an additional persistent object acting like a manager may be needed.

A Stanza can be extended by additional namespaced child elements. Obviously, it is not viable to include all the kinds of extensions possible. To avoid hard-coding of such extensions into gloox, StanzaExtension can be used to inform the core of gloox about additional supported extensions without it needing to know about the exact implementation.

Note that a StanzaExtension can be used for both sending and receiving of custom protocols. When receiving, gloox requires an appropriate implementation of the pure virtuals filterString() and newInstance(). To be able to properly use the encapsulation, some getters may be necessary. Note that the object you will be dealing with usually is const. For sending StanzaExtensions, a custom constructor (as well as some setters, possibly) is needed. Additionally, an implementation of tag() is required.

• Sub-class StanzaExtension and re-implement filterString(). filterString() is supposed to return an XPath expression that matches the child element of a stanza that the protocol-to-implement uses. For example, consider this hypothetical XML format: The protocol is encapsulated inside a <stats> element in the 'ext:stats' namespace. It uses IQ stanzas for transmission.

   <iq from='...' to='...' id='id1' type='get'>
     <stats xmlns='ext:stats'/>
   </iq>
  
   <iq from='...' to='...' id='id1' type='result'>
     <stats xmlns='ext:stats'>
       <users>10</users>
     </stats>
   </iq>
  

  The idea of filterString() and its XPath expression is to match the <stats> element such that it can be fed to your StanzaExtension-derived class' constructor when creating a new instance of it. For our stats protocol, filterString() would return something like: /iq/stats[@xmlns='ext:stats']

• When subclassing StanzaExtension, you have to initialize it with an int, the extension's type. You should choose a value that is not yet used in gloox, and unique to the given extension you implement. In general, you are free to use values above ExtUser . See StanzaExtensionType for existing values.

• The next step is to implement newInstance(). Whenever filterString()'s XPath expression matches a child element of an incoming stanza, newInstance() is called with the matched Tag. For our example above, this is the <stats> element (including its children):

   <stats xmlns='ext:stats'>
     <users>10</users>
   </stats>
  

  The purpose of newInstance() is to return a new instance of your specialized StanzaExtension (implicitly cast to StanzaExtension). This way, gloox can deal entirely with the abstract base, StanzaExtension, and never ever needs to know which kind of extension it deals with. The most common implementation of newInstance() looks like this:

   StanzaExtension* StatsExtension::newInstance( const Tag* tag ) const
   {
     return new StatsExtension( tag );
   }
  

  This of course implies that a constructor exists that takes a const Tag* as the only parameter.

• Finally, gloox must be able to serialize the StanzaExtension back into string'ified XML. This is done by means of the tag() function which must be reimplemented. The output Tag should -- like the input Tag -- be embeddable into the respective stanza.

Author:

Jakob Schroeter <js@camaya.net>

Since:

0.9

Definition at line 167 of file stanzaextension.h.

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Constructor & Destructor Documentation

StanzaExtension (  int  type  )  [inline]

Constructs an empty StanzaExtension. Parameters: type  Designates the extension's type. It should be one of StanzaExtensionType for built-in extensions, and it should be higher than ExtUser for custom types. Definition at line 175 of file stanzaextension.h.

virtual ~StanzaExtension (   )  [inline, virtual]

Virtual destructor. Definition at line 180 of file stanzaextension.h.

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Member Function Documentation

int extensionType (   )  const [inline]

Returns the extension's type. Returns: The extension's type. Definition at line 213 of file stanzaextension.h.

virtual const std::string& filterString (   )  const [pure virtual]

Returns an XPath expression that describes a path to child elements of a stanza that an extension handles. Returns: The extension's filter string. Implemented in Adhoc::Command, AMP, Capabilities, ChatState, DataForm, DelayedDelivery, Disco::Info, Disco::Items, Error, FeatureNeg, GPGEncrypted, GPGSigned, Session::Jingle, MessageEvent, Nickname, OOB, Event, Receipt, Registration::Query, VCard, VCardUpdate, and XHtmlIM.

virtual StanzaExtension* newInstance (  const Tag *  tag  )  const [pure virtual]

Returns a new Instance of the derived type. Usually, for a derived class FooExtension, the implementation of this function looks like: StanzaExtension* FooExtension::newInstance( const Tag* tag ) const { return new FooExtension( tag ); } Returns: The derived extension's new instance. Implemented in Adhoc::Command, AMP, Capabilities, ChatState, DataForm, DelayedDelivery, Disco::Info, Disco::Items, Error, FeatureNeg, GPGEncrypted, GPGSigned, Session::Jingle, MessageEvent, Nickname, OOB, Event, Receipt, Registration::Query, VCard, VCardUpdate, and XHtmlIM.

virtual Tag* tag (   )  const [pure virtual]

Returns a Tag representation of the extension. Returns: A Tag representation of the extension. Implemented in Adhoc::Command, AMP, Capabilities, ChatState, DataForm, DelayedDelivery, Disco::Info, Disco::Items, Error, FeatureNeg, GPGEncrypted, GPGSigned, Session::Jingle, MessageEvent, Nickname, OOB, Event, Receipt, Registration::Query, VCard, VCardUpdate, and XHtmlIM.

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The documentation for this class was generated from the following file:

• stanzaextension.h

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