Debugging an RPG CGI Program


Debugging an RPG CGI Program

Debugging a normal interactive program is pretty straightforward.  But, what if we want to debug a web program running our on IBM i (AS/400)?   These programs normally run under "Batch" jobs are are initiated from a web browser, not from us just calling the program from a command line.

The only real difference in debugging a web application is using the Start Service Program (STRSRVPGM) command to identify the job that we want to start debugging on.  But sometimes finding that job can be tricky

Method 1 - Start the HTTP Server with a Maximum of 1 Processing Job
If you have the option (for example, if you have a testing/development environment) you should be able to start the HTTP server so that only one job will be started that will be used to process the CGI Program requests.  This is done by adding a couple of keywords to the STRTCPSVR command as such:


These parameters tell the HTTP server to start a MINimum of 1 job and a MAXimum of 1 job.  This way we can find the single job, normally with a status of PGM-QZSRCGI, that we can use the STRSRVJOB command on.

Now, depending on our OS level, this may not always work.  If you're wondering why, ask IBM, not me.  I'm just the messenger.  But, if you do have issues you could try using the uiMin and uiMax paramters instead to see if that works.  While I've found these work fine when you have a very busy server and need to make sure you have enough jobs running to handle requests, specifying a min and max of 1 has mixed results.

Method 2 - Get Lucky
The second method, and one that I use when I need to, is the "Get Lucky" method by guessing which job to start a service on.  This can be by running a CGI program and watching the CPU for the jobs using WRKACTJOB to see which one is being used, or just guessing that it's most likely the 1st or 2nd job in the PGM-QZSRCGI status.  

Once you've determined which job you want to start a servicing in order to debug a CGI program, we can enter the appropriate job identifying data into the STRSRVJOB command.

One trick that I used, since it's never fun to try and remember all of those variables, is using the STRSRVJOB command from the command line while viewing the job properties.  So it goes something like this:

  1. User WRKACTJOB JOB(servername)
  2. Determine which job you want to service/debug
  3. Use option 5 next to that particular job.  You should see something like the following:
                                    Work with Job                                 
                                                                System:   S216709W
    Job:   BVSCOMP        User:   QTMHHTTP       Number:   381889                 

    Select one of the following:                                                  
         1. Display job status attributes                                         
         2. Display job definition attributes                                     
         3. Display job run attributes, if active                                 
         4. Work with spooled files                                               
        10. Display job log, if active, on job queue, or pending                  
        11. Display call stack, if active                                         
        12. Work with locks, if active                                            
        13. Display library list, if active                                       
        14. Display open files, if active                                         
        15. Display file overrides, if active                                     
        16. Display commitment control status, if active                          
    Selection or command                                                          

  4. Now, at the top of this display we we see the Job Name, User Name and Job Number.  If we just remember to enter these in reverse order, we can use the STRSRVJOB command quite easily from the command line provided.


Once this is complete it's as simple as issuing the Start Debug (STRDBG) command for the program in question and initiating the program from the browser.  When we get to the appropriate break points the job that we issued the STRSRVJOB command on should go into debug mode.

Last edited 02/01/2024 at 15:09:09


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