Re: RPG Web Service Architecture -- WEB400

As I was running a CGI page today that loads an absolute boatload of records
(because I haven't taken the time to implement paging - yet) I thought of
another reason why large result sets are problematic/dangerous.

As soon as I clicked submit I realized I had specified the wrong criteria in
the submit form, so I hit stop in the browser, changed my criteria and
resubmitted the form. Note that the first CGI job on the AS400 is *still*
running as it doesn't know I no longer want the first request. At this
point there are two jobs consuming a fair amount of CPU.

I could repeatedly hit the submit button and enact a pseudo
denial-of-cpu-attack (new term? DOCPUA :-). As developers we get to help
shield users from themselves by building software that will perform even
when users don't use our applications responsibly.

It sounds like you have your hands tied somewhat in that you don't get to
make the final decision, but you will be in a good position to say "I told
you so" and wash your hands of the mistake when it does fail, but also have
the solution to fix it when they ask how.

HTH,
Aaron Bartell
http://mowyourlawn.com

On Wed, Dec 10, 2008 at 12:26 PM, <Dean.Eshleman@xxxxxxxxxxxxxx> wrote:

Hi,

I have some questions about web services and how we are designing them. We
are using web services to provide data from our system i to our .NET web
application. These web services are not intended to be used outside of our
own application. One of our reasons for using web services was to avoid
storing a user id and password on the .NET side.

Our current approach has been to create the RPG program to return the data
and then use the functionality in WDSC to create the web service front end
for the RPG program. Overall, this approach works pretty well for most
situations. The only thing we don't like about this approach is when we
are returning multiple records from the RPG. We set the size of the output
multiple occurrence data structure to be large enough to handle what we
think is the highest number we will run into. In one case it needs to
handle close to 10,000 records. Personally, I think that is to large of a
number to return at one time, but the web developers don't want to call
the web service multiple times, so I'm stuck with finding a solution.

The generated Java code from WDSC will return an XML document matching the
number of occurrences output from the RPG. We would like it to only return
the number of occurrences that actually contain data.

Since I don't know Java, my initial thought solve this problem was to
create an RPG program to replace the Java in this situation. The RPG would
receive the input XML document, parse it and then call the RPG data
retrieval program. Next it would build the XML response document and
return that result. I thought I could do this using CGIDEV2 and Scott
Klement's port of the Expat parser (thanks Scott). This way, I can control
the XML document that is output. Does this seem like a reasonable
solution?

I was able to test out the XML parsing and that seems to work okay. Right
now, I'm trying to use CGIDEV2 to read the input XML and I'm not sure how
to do that. All the examples I see involve reading input from a web page.
Does anyone know what field would contain the XML after using the
zhbgetinput procedure?

One concern I have about the CGIDEV2 approach is how will I secure the web
service? Only our application should be authorized to call it.

We are on V5R3 and won't be going to V5R4 until sometime next year and
this needs to be solved before then.

Dean Eshleman,
MMA, Inc.

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