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.

Simon Coulter.
FlyByNight Software OS/400, i5/OS Technical Specialists

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