Re: Flex & RPG

[Simon Coulter <shc@xxxxxxxxxxxxxxxxx>]

On 13/03/2010, at 11:38 PM, Aaron Bartell wrote:

> > However, your comment was prompted by a reference to RPG Open I/O  
> > and that
> has nothing to do with the 5250 data stream itself.
>
> Well, it somewhat does because it gives you access to things that  
> before, as
> I understand it, were only available to certain vendors.  For  
> example, I
> could have a display file with input fields in it.  I could do an  
> EXFMT and
> dynamically intercept and process the layout of that display file  
> and put it
> to the web page.  Then on the way back in, after a user event, I  
> could map
> those values to the display file input fields, and those fields are  
> already
> readily available to the RPG program - no need to call CGI API's to  
> load
> data.  That is a nice feature to save on lines of code and thus save  
> on
> program complexity.
>
> I am not an expert on the front of 5250 or work station controllers  
> but only
> make comments as to how I see them work.  Please correct my  
> understanding
> where I am wrong.

Still nothing to do with the 5250 data stream. Open I/O will present a  
buffer of program data to user or vendor written plug-in code. That  
code can certainly interrogate a display file via an API but that's  
also not the 5250 data stream but either a list of field information  
(QUSLFLD) or direct access to the compiled guts of a display file  
(QDFRTVFD). The plug-in code can merge the data and the file  
information and generate a new data stream such as XML, HTML, JSON, or  
whatever.

This technique will allow typical RPG programmers to communicate with  
new world devices such as a browser by using traditional display I/O  
operation codes but no 5250 data is involved. Indeed the "5250  
subsystem"  (i.e., Workstation Function Management) isn't even  
involved in the transaction at all. Therefore no display device is  
required and thus no 5250 data stream.

The current method used by most vendors is either via Virtual Terminal  
APIs to intercept display file I/O (raw 5250 data stream) or via pre- 
processing the RPG/COBOL code to replace display file I/O with program  
or procedure calls. Both of these methods are available to non-vendors  
but obviously require quite a bit of work to implement properly. An  
alternative is to write CGI applications either directly or via a  
framework such as CGIDEV2 but even that seems more work than typical  
RPG developers are prepared to embrace.

Regards,
Simon Coulter.
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