[JDEV] Howto add middleware!

Bernino Lind lind at hlgroup.dk
Sat Sep 6 10:03:19 CDT 2003

Dear sirs,

During the last couple of months I have been doing a game utilizing jabber
as the stream infrastructure.

I have repeatedly asked questions with respect to xdb_sql (Benoit has been
very helpfull!), since storing, selecting and manipulating is a big part
of any project.

In these questions I have repeatedly seen how I miss a middleware method,
in the terms of som sort of programming language/logical layer between the
data storage and the jabber server.

First I have been using PL/SQL via PostgreSQL by the usage of xdb_sql
(xdb_sql needs a lot of tweaking before it runs smoothly on

xdb_sql has many problems which relates to a) configuration file in XML
(eliminates the possibility to use > < operators) and b) no way of post
processing data.

In a way PL/SQL gives you exactly that post processing thingy - in
relation to a rescent INSERT/DELETE vs UPDATE discussion one could for
example define a function in PL/SQL and let PL/SQL handle it all...

However PL/SQL is not really that nice to work with even though it has C
and Perl and more at its disposal. So I didnt like it and wanted the
complete Perl artellery at my disposal due to scalability issues: I want
to be able to tweak any foreseen and unforeseen data possibly and
impossibly existing (definition of Perl ;-)).

Then I thought, ah bugger what the hell I must write a new component and
have it connected under the XDB method, just like the xdb_perl project

I quickly hit the wall of IQ-GET and SET packets.

The jabber protocol people have appearently defined IQ-GET packets as
packets which can only contain one subelement, namely a query with some
xmlns attribute.

The set packet can contain any subelements holding data for the set at hand.


This means that if one takes DJ Adams words in his book Programming Jabber
seriously and uses jabber as an XML socket streaming infrastructure, which
I do, one must make a namespace with static coded variables in each and
every namespace.

I have four games I service. I want to find out the highscore for game #3.

<iq type="get">
  <query xmlns="highscore">

Then my idea was to catch the variable gameid and do a SELECT with this
data aka SELECT bla bla FROM TABLE WHERE gameid=$gameid.

This will not work as jabber will simply just wipe out anything below

So I need to do 4 namespaces which staticly have the gameid set:

<iq type="get">
  <query xmlns="highscore:3"/>



Any way I figured that if IQ-SET packets are allowed to carry as much data
as I like I might as well use the SET packet as a data carrier for my

<iq type="set">
  <query xmlns="highscore">

Which works in the backend, I can see the data being outputted to jabber
for resend to the jid who asked.

But since this is a SET packet jabber simply deletes all data after the
"type='result'" and I see nothing!!!

IT DOESNT WORK! Only GET packets allows for data sets to be resend...Ok, I
could of course construct with Nodefactory a message with all the data
etc. - but hey, thats not the way to do it properly seen from the backend:
the problem is that GET packets cant carry data!

So back to static hardcoding...?!?!?

To me it seems that Jabber is a good IM system but to claim that it can be
used as scalable XML socket infrastructure is perhaps a bit exaggerated.

There are so many unchangeable defaults in the protocol that jabber cant
be used for anything but IM systems.

I have added a middleware component via XDB - but due to limitations in
the jabber protocol it doesnt really change a goddamn thing.

If its true that its actually not possible to extent jabber in this way,
then be carefull if you think of choosing jabber as your XML
infrastructure - if you think this attitude is wrong, then please solve my
problem before actually discussing anything so I can be proven wrong.

Howto add data to an IQ-GET packet via XDB?

Best regards, Bernino Lind

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