IBM - CGIDEV2 Interview Questions & Answers

Question 1. What If My System I Runs With System Value Qccsid 65535?

Answer :

System value QCCSID 65535 inhibits automatic character conversion from a CCSID to another CCSID. That is general a big problem with CGI programs.

For instance, the external HTML of a CGI program is not translated to the CCSID of the CGI job when loaded in memory from it. If this HTML contains special characters, these characters are pratically corrupted and when output-ted to the browser they may cause problems, such as some piece of Javascript no longer running.

Fortunately, CGIDEV2 service program cares for this problem. The service program checks the job CCSID and, if it is found to be 65535, it is changed to its default value.

However, this may be not enough. The HTTP server assumes that the CGI is running with the CCSID of system value QCCSID, and this can also cause problems in character conversion.

In order to have your HTTP instance jobs running with a CCSID other than the one specified in system value QCCSID, just add the following directive to the configuration file of your HTTP instance:

DefaultFsCCSID nnn

where nnn is the desired CCSID value.

Question 2. How Can I Start A Page In A New Window?

Answer :

The tag <A> supports the keyword target which lets you specify the destination of a page.

• <A HREF="..." target="_blank"> 

starts a page in a new window

• <A HREF="..." target="xxx"> 

starts a page in an existing window named xxx; if this doesn't exist yet, it is created.

• <A HREF="..." target="_top"> 

starts a page in the current window, after clearing it; this is used when you work with frames and you want to get back to the full window. If you do not specify the target keyword, the page is started in the current window or frame. 

The keyword target may be also specified in the form tag. As an example:

<form method="post" action="/mypath/mypgm.pgm" target="_blank">

Question 3. How Can I Control From My Cgis The Cache Of A Remote Browser?

Answer :

If an internet browser (Netscape, MS Internet Explorer, etc.) does use the cache, it is most likely that the next time this browser is requested to call a CGI, it shows the previous response instead of issuing a new request.

In such a case the user would see the cached response instead of the new one.

Question 4. How Can I Control The Way A Remote Browser Uses Its Cache?

Answer :

You have two ways to avoid that a browser fetches a previous version of a page from the cache, instead of asking a fresher version of a page to the remote server. 

Technique 1- Avoid to cache a page
Technique 2- Make your response a unique page.

Question 5. When Should I Use Method Get, And When Should I Use Method Post In My Cgis?

Answer :

There are two ways you may invoke a CGI from your html.

• When you use the anchor technique

   <A> ... </A>

you implicitly use the GET method.

• When you use the form technique

   <form method=get/post  ... >

you may choose between the GET or the POSTmethod.

Therefore your question makes sense only for the form technique.

Your CGI's, using Mel's service program, are not sensitive to the GET or POST method, but the remote browser is.

The GET method: 

The query string (the string starting by ? and containing the request parameters) is visible in the browser command line.

This is useful for testing purposes, because you can easily detect some flaw in the string.

But it is dangerous once you release your CGIs, because the user may try to alter some parameters in your request.

The POST method: There is no way the user may see the query string, therefore the query string is more protected against undue manipulations.

Another interesting control mastered by the browser when you use the POST method, is the protection against a back page which is not in the cache: a dialog box would appear askingwhether you want to re-post your previous request. An educated user, who previously submitted an order, would understand that doing this would re-enter the same order a second time, and would not go back page. If you used instead the GET method, no such dialog box would appear for aback page which is not in the cache. 

In conclusion my suggestion is:

• -in your forms, use the GET method to perform the test
• -but, before releasing your htmls, substitute the GET with the POST method.

Question 6. Can You Summarize The Steps I Have To Go Through In Writing My First Cgi?

Answer :

Suppose the following:

• your images (gif's, jpg's, etc.) will reside in an IFS directory named myobjlib
• your source library is named mysrclib
• your object library (the one to contain your dynamic HTML scripts, your CGI programs, and Mel Rothman's service program CGISRVPGM) is named myobjlib
• your first CGI program is named MYCGI1

Proceed as follow:

1. Set up your CGI source and object libraries

by entering command
CGIDEV2/SETCGILIB SRCLIB(mysrclib) PRDLIB(myobjlib) .

• Note 1- Command SETCGILIB - when run from a user profile with *CHANGEauthority on the HTTP configuration file ( QUSRSYS/QATMHTTPC) - will show you a list of the configuration files for the existing HTTP instances. If you select with a "1" a given HTTP instance, the program will add - to the configuration file of that HTTP instance - the HTTP directives needed to run your CGI programs in library myobjlib.

2. Obtain a sample external html source and a sample CGI RPG source by using command

CGIDEV2/CRTCGISRC SRCMBR(mycgi1) SRCLIB(mysrclib) PRDLIB(myobjlib) 

You may compile the module, create the CGI program and run it. Afterwards you may change both the external HTML and the CGI program to fit your needs.

Question 7. How Can I Predict The Performance Of My Cgis?

Answer :

SC41-0607-02 AS/400 Performance Capabilities Reference - Version 4, Release 4 

You should read Chapter 6, Web serving performance

(click -> to display this manual in PDF format).
(click -> to display this chapter in HTML format).

In this chapter they report a benchmark done on a simple non-persistent CGI, rather different from the ones one could develop with our CGI service program method.

Question 8. How Can I Give More Performance To Some Selected Pages?

Answer :

I obtained surprising improvements on the performance of my welcome page (/easy400/welcome.htm), adding the following directives:

CacheLocalMaxBytes 2 M 
CacheLocalMaxFiles 200 
CacheLocalFile /easy400/welcome.htm

and adding a CacheLocalFile directive for each image used in the welcome page, such as

CacheLocalFile /easy400/ibm_logo.gif

I also added CacheLocalFile directives for other images frequently used in other pages.

Loading images into local AS/400 cache provides a superbous performance, even better than loading into cache text pages.

Question 9. How Can A Cgi Check Whether An Ifs Object Is Available?

Answer :

You may use CGISRVPGM2 subprocedure chkIfsObj2() or subprocedure chkIfsObj3() 

Question 10. How To Develop Some Simple Graphs (bar Charts) Using Just Html?

Answer :

What you need is some sample gif, that you may stretch according to the value you want to show. 

For instance, the following html

<table cellspacing=0 cellpadding=0>
<tr><td><img src="/cgidev/blue.gif" alt="blue line" height=5 width=80></td></tr>
<tr><td><img src="/cgidev/blue.gif" height=5 width=125></td></tr>
<tr><td><img src="/cgidev/blue.gif" height=5 width=300></td></tr>
<tr><td><img src="/cgidev/blue.gif" height=5 width=193></td></tr>
</table>

If you like, you may run a sample CGI that displays this kind of graphs,

or you may run an Easy400 program displaying the number of downloaders of the Easy400.net CGIDEV2 version.

Question 11. Some Special Characters I Key In My Html Source Members Show Different On My Web Pages. Why? How Can I Solve This?

Answer :

The following special characters,

    #  @  ! 
    {  }  [  ]  |  

which have special meanings for HTML and JavaScript, will not show correctly in your Web pages, unless you make sure that, before entering SEU, your job CCSID matches the language of your keyboard.

Do the following:

• Step 1- Check out system value qccsid.
• Step 2- Make sure that your HTML source or stream file contains the correct characters
• Step 3- Make sure that your HTML contains the following <meta ... > tag
• Step 4- Make sure that the HTML from your CGIs is not translated from a CCSID to another CCSID

Question 12. How Can I Automatically Refresh A Web Page?

Answer :

You may use some JavaScript to have a Web page automatically refreshed after a given number of seconds (milliseconds, to be correct).

Please read about the setTimeout method of object window:

       setTimeout(function, msec[, arg1[, ..., argN]])

For example, to refresh your page every 25 seconds, add the following to your page source:

<head> 
<script language=JavaScript> 
function reloadPage() { 
        window.location=window.location 
} 
function refreshPage() { 
        setTimeout('reloadPage()',25000)
} 
</script> 
</head> 
<body   onLoad=refreshPage()>

Question 13. Is There Any Way I Can Ease My Rpg Controls On Numeric Input Fields? How About An Input Date Field?

Answer :

You may add some JavaScript to have this done. Also in this case, however, we recommend your CGI performs the appropriate checks (some Web users disable JavaScript from their browsers).

In your JavaScript evaluation you should also consider advantages ("pros") and disadvantages ("cons").

• pro. User errors are more quickly communicated through JavaScript (it runs on the client) than through CGI response. JavaScript makes users more happy in terms of faster diagnosis.
• con. Imbedding JavaScript in your HTML would increase the size of your page, and this might result to a slightly slower response, expecially in cases were the user connects through a slow line.

As to examples of JavaScript for controlling input fields, you may look at our page JavaScript examples: regular expressions. A little further you'll find a link (Validating form numeric fields) to a CGI performing through JavaScript exactly what you're looking for.

Should you be interested, just download and install on your AS/400 our library js2.

With regard to the checks your CGI should in any case, here are our tips:

• If your CGI did initialize the input field, on the next "call" it might just check whether its new value is equal to initialized one. If so, the field was not changed by the user.
• You might check numeric data through the Mel's service program chkNbr subprocedure. If you like to use subprocedure c2n2 instead, please note that it ignores slashes but treats dashes as minus signs.
• Another method would be to output the date as three fields in the form: month, day, and year with separators as constants between them.
• Another method would be to output the date twice: once in edited form ( modifiable) and once as pure numerics (as an input field).

Question 14. Netscape 6 Does Not Display Any Images, Gif's Or Jpg's. How Can I Fix This?

Answer :

Do the following:

1. Go to page PTF Cover Letters
2. Click on your system's release
3. Search for Netscape 6

There is also a bypass, at least for gif's:

1. add the following HTTP directive

       AddType .gif image/gif 8bit

2. re-start your HTTP server

Question 15. The Output From My Cgi Is Correctly Interpreted By Ms Internet Explorer, Whereas Netscape Navigator Would Display It As A Plain Text. What Should I Do To Have Also Netscape Interpreting The Html Output From My Cgi?

Answer :

A CGI should always start the HTML response in the following way:

Content-type: text/html 
<html>

The " Content-type: text/html" line contains a so called "HTTP header". This header MUST be followed by a blank line. See also our page Externally defined HTML.

This header tells the remote browser that the response contains an HTML script to be interpreted.

While MS Internet Explorer, in absence of such a header, assumes it by default, Netscape Navigator assumes a text default. Apparently the two products didn't agree on a standard approach. But this is just one of the many examples of disagreement.

Question 16. Is It Possible, In The Same Cgi, To Run More Than One Gethtml Or Gethtmlifs?

Answer :

Yes. There are several ways you can do this.

Using multiple gethtml or gethtmlifs

However you should be aware of the following:

1. Each time a different external HTML is read, the previous external HTML is discarded. Therefore sections of a given HTML are no longer available when a subsequent HTML has been loaded.
2. CGI performance will not be as good as with one HTML file used over and over.

If you care, we have an example of this approach:

• Run our example
• Display the first external HTML used by our example
• Display the second external HTML used by our example
• Display the source of the CGI used in our example

Using gethtmlifsmult: This subprocedure allows to load in memory several external IFS files containing html code. This subprocedure is highly recommended whenever several CGI's share some HTML code. 

Using Server Side Includes: This allows to merge pieces of static HTML code into the HTML output buffer once it has already been sent from the CGI.

Question 17. Is There Any Way To Dynamically Merge Other Html Scripts Into A Given Html?

Answer :

In a sense you are requesting something like a /copy pre-compiler function. This could be extremely useful when you have many html pages sharing some pieces of html/javascript. A /copy-like function would allow to keep these common pieces external, and to include them wherever needed, thus reducing both html scripts development time and maintenance.

What, at least in my opinion, would be needed is some include function to be interpreted / executed from the client browser at page load time. Unluckily, nothing like this -- as far as I know -- is available. This means that any include function must be carried over from the server site.

There are two ways you can obtain this dynamic merging:

1. using subprocedure gethtmlifsmult in your CGI. This subprocedure allows to load in memory several external IFS files containing html code. This subprocedure is highly recommended whenever several CGI's share some HTML code. 
2. including external JavaScript code
3. using Server Side Includes.

Question 18. What Is The Favicon.ico Request That My Site Receives Now And Then?

Answer :

This request comes from your Internet browser.

When an user visiting a page of yours asks the browser to take a favorite (bookmark), the browser tries to find whether your site provides a favicon.ico to be associated with favorites.

If such icon is found, the browser associates it to the favorite (bookmark).

For instance, if you bookmark this page, you'll find that your favorite (bookmark) is associated with our computer icon.

Question 19. Under Given Circumstances, My Cgi Should Link To Another Site. How To Implement This?

Answer :

Usually the response from your CGI looks as follow:

Content-type: text/html
blank line
<html>
... etc. ...
</html>

A very simple way to have your CGI response linking to another site is that of providing just the following response:

Location: http://URL
blank line

If you whish, you may run our example and display its sources.

Question 20. How May A Cgi Control Duplicate Inputs?

Answer :

When you have a CGI (like an Order Entry) receiving input from a form, the danger always exists that the user incorrectly sends duplicate inputs.

There are two main cases where this is possible.

Case 1: The user enters by mistake an order line equal to the last previously submitted.

This can be controlled in this way:

1. Have the CGI resending the last processed data in a hidden input field of the form
2. Have some javascript to submit the form. This javascript --before submitting the form-- would check that the new input data are different from the previous ones.

Case 2: The user by mistake presses the Refresh / Reload button of the browser (I.E. supports also F5 for page reload). In this case, the browser would resend the last transaction. 

One way a CGI could control this would be to:

1. Have the CGI assigning a transaction sequence number and storing it in a hidden input field of the form
2. Once the CGI receives the transaction, it could check whether this transaction sequence number was already processed. If so, it would ignore the request and issue an error message. Otherwise, it would process the transaction and file this transaction sequence number. This of course requires a transaction sequence number file to be available.

Question 21. Http Default Port 80 Is Used By Some Other Production Http Service. How Can I Create An Http Instance On Another Port To Run Cgidev2 And My Future Cgi Developments?

Answer :

Use command cgidev2/http8000.

It creates a (traditional) HTTP server instance for port 8000. The instance name is CGIDEV2.

• Enter command
  strtcpsvr httpsvr(cgidev2)
  to start that instance.
• Enter command
  wrkhttpcfg cgidev2
  to edit its HTTP directives.

Note 1 - To run command CGIDEV2/HTTP8000, you must have full authority on filesQUSRSYS/QATMHINSTC and QUSRSYS/QATMHTTPC.

Note 2 - Command CGIDEV2/HTTP8000 can be run just once.

Question 22. Is It There An Easy Way To Determine If An Html Section Is Available To Issue A Wrtsection Upon?

Answer :

After reading the external html (GetHtml, GetHtmlIfs, or GetHtmlIfsMult you can use the RtvHtmlRcd subprocedure (see member XXXWRKHTML in CGIDEV2/QRPGLESRC). Ask it to retrieve the first record from the section of interest. For example, if 'top' exists and 'xxx' doesn't:

eval rcd = RtvHtmlRcd('top':1:rc) gives rc = 0 
eval rcd = RtvHtmlRcd('xxx':1:rc) gives rc = -1

If you don't care about the contents or the rcd, you can use callp inst of eval:

callp RtvHtmlRcd('top':1:rc) gives rc = 0 
callp RtvHtmlRcd('xxx':1:rc) gives rc = -1

I would recommending using WrtSection for the section only if rc = 0. Return codes -1 and -2 are obvious. You can get return code -3 only if the first parameter is *NONE and the relative record number is within a duplicate section.