5. CGI debugging tips

Though debugging always comes last in a tutorial, it should rank first in a programmer's interest. This is why we dedicate a separate page to this topic.

6. Error number values

In some circumstances some subprocedures of the service programs may end with non-zero return codes. Usually such error codes are also reported in the CGIDEBUG file. The guess would be about the meaning of such codes. To find out about them:

• Go to the following page of the iSeries Information Center: Errno Values for UNIX-Type Functions.

7. Performance tips

In order to obtain the best performance from your CGI's, you may want to adopt the following tips:

1. use a named activation group (a different activation group for each CGI, see FAQ number 26)
2. return without setting LR on

   Note. By returning with LR set to *off provides you with another great performance advantage. The next time the program is called and tries to reload the external HTML, the service program will find that the HTML is still in core, and will skip its loading, thus saving some relevant amount of time.

3. open files just the first time through, never close them
4. each time the program runs
   • re-initialize variables
   • do not rely on files being positioned on the first record; reposition with SETLL, or SETGT, or any other appropriate way
5. After programs are thoroughly tested, use CALLP SetNoDebug(*ON) to turn all debugging off.

   Note.SetNoDebug sets a global variable in the service program. If multiple CGI programs are running in the same named activation group, all those programs are affected in the same way by the most recent execution of SetNoDebug.

8. About persistent CGI

So far, without mentioning them, we have being talking about non persistent CGI. Traditionally, CGI programs are not persistent, that is, a CGI program, the next time it is called, does not remember (or, better, must not remember - as no guarantee exists that it is called by the same client as before) what values where left in its variables, and where files are positioned. This fact of course has a relevant impact in program design, because the values of the variables which are important for a program at the time it is invoked must be saved in the previous response HTML (usually as hidden fields) and sent with the program invocation request.

Since V4R3, however, persistent CGI have been implemented for OS/400 HTTP.
A persistent CGI returns without raising LR, that is, the next time it is called, it finds its status as it was left.
The obvious problem with persistent CGI, is that for a given program there are potentially several copies waiting to be called back, and each copy is related to a different user. You would not like to have such responsibilities be randomly mixed up. To solve this problem, it is a program responsibility to give a "ticket" (technically speaking, a "handle") to each next program invocation.
The next problem is that a persistent CGI cannot wait forever to be called back. An HTTP controlled timeout will kill any persistent CGI session waiting over a given number of seconds. At this point, the user may need to re-start his transaction cycle from the beginning.

Because of this second problem, the implementation of persistent CGI is not very frequent and left to cases where a COMMIT technique is mandatory.

Our recommendation is not to use persistent CGI, unless strictly necessary. Persistent CGI

• do not perform faster than non-persistent CGI
• require much more skill and testing
• may not provide a user-friendly solution

However, should you like to know more on this subject, this is your page.

9. ZIP and UNZIP commands

Library CGIDEV2 includes commands ZIP and UNZIP.
These commands allow to compress and decompress IFS stream files using standard .zip files.
The requests entered from commands ZIP and UNZIP are transformed to QSHELL commands, that are run in batch mode.
Results from ZIP and UNZIP commands can optionally be displayed.

10. CGIDEV2 updates

Some releases of CGIDEV2 may include new subprocedures for service program CGIDEV2/CGISRVPGM2.

Since March 25, 2009 service program CGIDEV2/CGISRVPGM2 has a zero signature.

If you already have installed CGIDEV2 and you are going to install a new release of it, you should first check the release date of the existing CGIDEV2. You do that by running command CGIDEV2/RELEASED.

1. If the existing CGIDEV2 carries a release date equal to or higher than March 25, 2009, your CGI programs bounded to service program CGIDEV2 will have no problem with the new CGIDEV2 release, as there will be no signature check with the new service program CGIDEV2/CGISRVPGM2.
2. If you have a CGIDEV2 version released prior to March 25, 2009 , after installing the new version of CGIDEV2 you must run command CGIDEV2/REBIND library_name for each library containing programs bound to service program CGIDEV2/CGISRVPGM2.
   Command CGIDEV2/REBIND rebinds all service programs and CBLLE/RPGLE programs in the user specified library.
3. If you duplicated service program CGIDEV2/CGISRVPGM2 to several CGI program libraries (to make them independent from service program CGIDEV2/CGISRVPGM2, and be free to update library CGIDEV2 in any moment), and you want to replace some of those duplicated CGISRVPGM2 service programs with a more recent version available in library CGIDEV2, then you may use command CGIDEV2/DUPSRVPGM.
   This command:
   1. retrieves the libraries containing service program CGISRVPGM2
   2. lets you select the libraries to be processed
   3. for each selected library
      • replaces service program CGISRVPGM2 in that library with a copy of service program CGIDEV2/CGISRVPGM2
      • rebinds all service programs of that library
      • rebinds all CBLLE and RPGLE programs in that library.