[JDEV] Howto add middleware!

[Joe Hildebrand]

http://www.jabber.org/jeps/jep-0004.html

-- 
Joe Hildebrand

 

> -----Original Message-----
> From: Bernino Lind [mailto:lind at hlgroup.dk] 
> Sent: Saturday, September 06, 2003 9:03 AM
> To: jdev at jabber.org
> Subject: [JDEV] Howto add middleware!
> Importance: High
> 
> 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 FreeBSD/PostgreSQL).
> 
> 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 does.
> 
> 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.
> 
> WHAT THE FUCK!?!!!
> 
> 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.
> 
> EXAMPLE:
> I have four games I service. I want to find out the highscore 
> for game #3.
> 
> <iq type="get">
>   <query xmlns="highscore">
>     <gameid>3</gameid>
>   </query>
> </iq>
> 
> 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 xmlns...
> 
> So I need to do 4 namespaces which staticly have the gameid set:
> 
> <iq type="get">
>   <query xmlns="highscore:3"/>
> </iq>
> 
> AKA SELECT bla bla FROM TABLE WHERE gameid=3
> 
> WHY NOT ALLOW FOR DATA TO BE CARRIED BY IQ-GET????
> 
> 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
> query...so:
> 
> <iq type="set">
>   <query xmlns="highscore">
>     <gameid>3</gameid>
>   </query>
> </iq>
> 
> 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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