Provided by: libnet-xmpp-perl_1.02-3_all bug

NAME

       Net::XMPP::Namespaces - In depth discussion on how namespaces are handled

SYNOPSIS

         Net::XMPP::Namespaces provides an depth look at how Net::XMPP handles
         namespacs, and how to add your own custom ones.  It also serves as the
         storage bin for all of the Namespace information Net::XMPP requires.

DESCRIPTION

         XMPP as a protocol is very well defined.  There are three main top
         level packets (message, iq, and presence).  There is also a way to
         extend the protocol in a very clear and strucutred way, via namespaces.

         Two major ways that namespaces are used in Jabber is for making the
         <iq/> a generic wrapper, and as a way for adding data to any packet via
         a child tag <x/>.  We will use <x/> to represent the packet, but in
         reality it could be any child tag: <foo/>, <data/>, <error/>, etc.

         The Info/Query <iq/> packet uses namespaces to determine the type of
         information to access.  Usually there is a <query/> tag in the <iq/>
         that represents the namespace, but in fact it can be any tag.  The
         definition of the Query portion, is the first tag that has a namespace.

           <iq type="get"><query xmlns="..."/></iq>

             or

           <iq type="get"><foo xmlns="..."/></iq>

         After that Query stanza can be any number of other stanzas (<x/> tags)
         you want to include.  The Query packet is represented and available by
         calling GetQuery() or GetChild(), and the other namespaces are
         available by calling GetChild().

         The X tag is just a way to piggy back data on other packets.  Like
         embedding the timestamp for a message using jabber:x:delay, or signing
         you presence for encryption using jabber:x:signed.

         To this end, Net::XMPP has sought to find a way to easily, and clearly
         define the functions needed to access the XML for a namespace.  We will
         go over the full docs, and then show two examples of real namespaces so
         that you can see what we are talking about.

   Overview
         To avoid a lot of nasty modules populating memory that are not used,
         and to avoid having to change 15 modules when a minor change is
         introduced, the Net::XMPP modules have taken AUTOLOADing to the
         extreme.  Namespaces.pm is nothing but a set of function calls that
         generates a big hash of hashes.  The hash is accessed by the Stanza.pm
         AUTOLOAD function to do something.  (This will make sense, I promise.)

         Before going on, I highly suggest you read a Perl book on AUTOLOAD and
         how it works.  From this point on I will assume that you understand it.

         When you create a Net::XMPP::IQ object and add a Query to it (NewChild)
         several things are happening in the background.  The argument to
         NewChild is the namespace you want to add. (custom-namespace)

         Now that you have a Query object to work with you will call the GetXXX
         functions, and SetXXX functions to set the data.  There are no defined
         GetXXX and SetXXXX functions.  You cannot look in the Namespaces.pm
         file and find them.  Instead you will find something like this:

         &add_ns(ns    => "mynamespace",
                 tag   => "mytag",
                 xpath => {
                           JID       => { type=>'jid', path => '@jid' },
                           Username  => { path => 'username/text()' },
                           Test      => { type => 'master' }
                          }
                );

         When the GetUsername() function is called, the AUTOLOAD function looks
         in the Namespaces.pm hash for a "Username" key.  Based on the "type" of
         the field (scalar being the default) it will use the "path" as an XPath
         to retrieve the data and call the XPathGet() method in Stanza.pm.

         Confused yet?

   Net::XMPP private namespaces
         Now this is where this starts to get a little sticky.  When you see a
         namespace with __netxmpp__, or __netjabber__ from Net::Jabber, at the
         beginning it is usually something custom to Net::XMPP and NOT part of
         the actual XMPP protocol.

         There are some places where the structure of the XML allows for
         multiple children with the same name.  The main places you will see
         this behavior is where you have multiple tags with the same name and
         those have children under them (jabber:iq:roster).

         In jabber:iq:roster, the <item/> tag can be repeated multiple times,
         and is sort of like a mini-namespace in itself.  To that end, we treat
         it like a separate namespace and defined a __netxmpp__:iq:roster:item
         namespace to hold it.  What happens is this, in my code I define that
         the <item/>s tag is "item" and anything with that tag name is to create
         a new Net::XMPP::Stanza object with the namespace
         __netxmpp__:iq:roster:item which then becomes a child of the
         jabber:iq:roster Stanza object.  Also, when you want to add a new item
         to a jabber:iq:roster project you call NewQuery with the private
         namespace.

         I know this sounds complicated.  And if after reading this entire
         document it is still complicated, email me, ask questions, and I will
         monitor it and adjust these docs to answer the questions that people
         ask.

   add_ns()
         To repeat, here is an example call to add_ns():

           &add_ns(ns    => "mynamespace",
                   tag   => "mytag",
                   xpath => {
                             JID       => { type=>'jid', path => '@jid' },
                             Username  => { path => 'username/text()' },
                             Test      => { type => 'master' }
                            }
                  );

         ns - This is the new namespace that you are trying to add.

         tag - This is the root tag to use for objects based on this namespace.

         xpath - The hash reference passed in the add_ns call to each name of
         entry tells Net::XMPP how to handle subsequent GetXXXX(), SetXXXX(),
         DefinedXXXX(), RemoveXXXX(), AddXXXX() calls.  The basic options you
         can pass in are:

            type - This tells Stanza how to handle the call.  The possible
                   values are:

                  array - The value to set and returned is an an array
                          reference.  For example, <group/> in jabber:iq:roster.

                  child - This tells Stanza that it needs to look for the
                          __netxmpp__ style namesapced children.  AddXXX() adds
                          a new child, and GetXXX() will return a new Stanza
                          object representing the packet.

                  flag - This is for child elements that are tags by themselves:
                         <foo/>.  Since the presence of the tag is what is
                         important, and there is no cdata to store, we just call
                         it a flag.

                  jid - The value is a Jabber ID.  GetXXX() will return a
                        Net::XMPP::JID object unless you pass it "jid", then it
                        returns a string.

                  master - The GetXXX() and SetXXX() calls return and take a
                           hash representing all of the GetXXX() and SetXXX()
                           calls.  For example:

                             SetTest(foo=>"bar",
                                     bar=>"baz");

                           Translates into:

                             SetFoo("bar");
                             SetBar("baz");

                           GetTest() would return a hash containing what the
                           packet contains:

                             { foo=>"bar",  bar=>"baz" }

                  raw - This will stick whatever raw XML you specify directly
                        into the Stanza at the point where the path specifies.

                  scalar - This will set and get a scalar value.  This is the
                           main workhorse as attributes and CDATA is represented
                           by a scalar.  This is the default setting if you do
                           not provide one.

                  special - The special type is unique in that instead of a
                            string "special", you actually give it an array:

                              [ "special" , <subtype> ]

                            This allows Net::XMPP to be able to handle the
                            SetXXXX() call in a special manner according to your
                            choosing.  Right now this is mainly used by
                            jabber:iq:time to automatically set the time info in
                            the correct format, and jabber:iq:version to set the
                            machine OS and add the Net::Jabber version to the
                            return packet.  You will likely NOT need to use
                            this, but I wanted to mention it.

                  timestamp - If you call SetXXX() but do not pass it anything,
                              or pass it "", then Net::XMPP will place a
                              timestamp in the xpath location.

            path - This is the XPath path to where the bit data lives.  The
                   difference.  Now, this is not full XPath due to the nature
                   of how it gets used.  Instead of providing a rooted path
                   all the way to the top, it's a relative path ignoring what
                   the parent is.  For example, if the "tag" you specified was
                   "foo", and the path is "bar/text()", then the XPath will be
                   rooted in the XML of the <foo/> packet.  It will set and get
                   the CDATA from:

                      <foo><bar>xxxxx</bar></foo>

                   For a flag and a child type, just specify the child element.
                   Take a look at the code in this file for more help on what
                   this means.  Also, read up on XPath if you don't already know
                   what it is.

            child - This is a hash reference that tells Net::XMPP how to handle
                    adding and getting child objects.  The keys for the hash are
                    as follows:

                    ns - the real or custom (__netxmpp__) namesapce to use for
                         this child packet.

                    skip_xmlns => 1 - this tells Net::XMPP not to add an
                                      xmlns='' into the XML for the child
                                      object.

                    specify_name => 1 - allows you to call NewChild("ns","tag")
                                        and specify the tag to use for the child
                                        object.  This, IMHO, is BAD XML
                                        practice.  You should always know what
                                        the tag of the child is and use an
                                        attribute or CDATA to change the type
                                        of the stanza.  You do not want to use
                                        this.

                    tag - If you use specify_name, then this is the default tag
                          to use.  You do not want to use this.

            calls - Array reference telling Net::XMPP what functions to create
                    for this name.  For most of the types above you will get
                    Get, Set, Defined, and Remove.  For child types you need to
                    decide how you API will look and specify them yourself:

                      ["Get","Defined"]
                      ["Add"]
                      ["Get","Add","Defined"]

                   It all depends on how you want your API to look.

         Once more... The following:

           &add_ns(ns    => "mynamespace",
                   tag   => "mytag",
                   xpath => {
                             JID       => { type=>'jid', path => '@jid' },
                             Username  => { path => 'username/text()' },
                             Test      => { type => 'master' }
                            }
                  );

         generates the following API calls:

           GetJID()
           SetJID()
           DefinedJID()
           RemoveJID()
           GetUsername()
           SetUsername()
           DefinedUsername()
           RemoveUsername()
           GetTest()
           SetTest()

   Wrap Up
         Well.  I hope that I have not scared you off from writing a custom
         namespace for you application and use Net::XMPP.  Look in the
         Net::XMPP::Protocol manpage for an example on using the add_ns()
         function to register your custom namespace so that Net::XMPP can
         properly handle it.

AUTHOR

       Ryan Eatmon

COPYRIGHT

       This module is free software, you can redistribute it and/or modify it under the LGPL.