TechTip: Validating HTML Forms with Message Subfiles

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I like message subfiles. As a user, I like them because they give me a good, easy overview of one or more errors that might have occurred on a screen. As a programmer, I like them because they offer great functionality and are pretty easy to handle once you get in the habit. So I have created a similar function using HTML, JavaScript, Cascading Style Sheets (CSS), and a CGI-RPG program. If you think this sounds interesting, please read on.

The CGI-RPG program is about 650 lines and because I have limited space here, I will not go into detail about every program line, subroutine and prototype in the code. You might find more clever ways to write the code and feel free to do so; the objective of the tip is to give you an idea of what you can do with a little HTML and JavaScript.

First, a few things must be in place in order to make it all work.

  1. Your i5 must be able to run and execute CGI programs.
  2. A little knowledge about HTML forms, JavaScript, and CSS will not do you any harm.
  3. My CGI library is named CGILIB. If you have something different, you have to do a search/replace in program FORM002 and insert your own library name. Search for "yourlib" and please note that the library name must be replaced in three places (including the compile instructions).
  4. To parse the input from the HTML form, I like to use the QZHBCGIPARSE API instead of the obsolete QTMHCVTDB and QTMHRDSTIN APIs. Instead of reinventing the wheel, download and compile program CGIPARSEZ. This great program was originally written by Craig Pelkie and was called CGIPARSE. I call my program CGIPARSEZ because you might already have a version of the program running, and I have made one small change in the original program because a counter was not reset in Craig's program, which caused trouble in my setup.
  5. The record length of your QRPGSRC source file must be at least 112 bytes. Please note that I store all my RPG programs in QRPGSRC. In this example, I also store the HTML skeleton member called FORM002H in QRPGSRC. If you want to change this to something else, make the appropriate changes on the F-spec in program FORM002.

Note: Throughout out the program, two prototypes are called repeatedly: MakeHTML writes the HTML to the browser using the QTMHWRSTOUT API. ReplaceIt replaces the keywords in the skeleton code in member FORM002H.
Below is a snippet of the code:


The keyword %%errorbox%% in program FORM002 scans for and replaces some HTML code; in this case, this is where the dropdown box will be placed. FORM002 also uses other keywords, such as %%focus%% and %%err1%%. This is a very flexible way to write code. If you want the drop-down box somewhere else, simply move the line. The %% symbols indicate an invariant character, which means that it always has the same tagging, no matter what CCSID you use. (Yes, yes, I know about CCSID 420.) You can read more about invariant characters here.

When you have all the above in place, download programs FORM002 and HTML skeleton FORM002H into QRPGSRC in your CGI library. Compile FORM002 following the compile instructions in the header of the program. Then, open your browser of choice and enter the following URL:


The screen shown in Figure 1 will be displayed:

Figure 1: This is a typical HTML form into which you enter data. (Click images to enlarge.)

This is a typical HTML form: You type information into the input fields and click Submit Data. And then, something will happen.

Try clicking Submit Data without entering anything in the form. This will call the CGI-RPG program, and the following will occur (Figure 2):

Figure 2: Trying to "submit data" without entering data first generates a drop-down box.

As you see, all the fields change to yellow and a drop-down box appears on the screen. This is "my" message subfile.

If you select an entry in the drop-down box, the cursor will automatically jump to the field in error and you can start typing right away. If you already wrote something in the field, it will be selected too.

Let me briefly explain what happens: The first time the program is called, it checks whether the Submit Data button was pressed. If not, subroutine subrLoadForm is called. Member FORM002H will be opened and used as a skeleton to load the HTML form in the browser. Some search/replace will occur to prevent the drop-down box to be displayed and to place the cursor in the name input field. When you press Submit Data, FORM002 is called again. The HTML form is parsed, and because the Submit Data button was pressed, subroutines subrFindErrors and subrCrtHTMLreply are called. The subrFindErrors subroutine will find the fields in error and place an error message in an array, which will be used in subrCrtHTMLreply to build the drop-down box. In this program, the messages are hard-coded, but they should of course be retrieved from a message- or database file. That's the cycle of the program. There's nothing more to it.

The way I give the fields red borders and yellow backgrounds is by using the following CSS code:


If you do not like the colors or border types, change the code. The correct way would of course be to soft-code it and read the attributes from a database or data area.

To make the cursor jump to the field in error, I use the JavaScript OnChange event and places it on the