How to Process Inputs to a REBOL CGI Web Page
Processing HTML Forms in a REBOL Internet Based Application
Jul 24, 2009 Mark Alexander Bain
If a programmer needs to implement business rules across an organisation then REBOL is a suitable solution. The business rules can be mapped to a custom REBOL dialects and REBPOL itself is available in a number of versions, both free and commercial. For example anyone can download:
- REBOL/View - this provides a GUI (Graphical User Interface) that enables the programmer to write and test business rules
- REBOL/Core - this has no GUI and has been designed for use on server
Therefore, if the programmer has access to a web server (such as Apache) then they can produce quickly produce REBOL CGI web pages for all of their users to view. Of course the next stage is for the developer to create REBOL CGI applications that can both display information for the users, and to accept information from them. For that to happen the REBOL must be able to process data sent from HTML forms.
An Example HTML Form
A user will enter information into an HTML form in a web page. The programmer must create such a form, for example:
Here the form will call the "process_input.r" script file when the user clicks on the submit button.
Identifying the Request Method with REBOL
There are two methods that the web programmer can use to send information from the form to the CGI application:
- GET - information is passed as part of the URL. This is visible to the user
- POST - information is passes via the standard input and is invisible to the user
The CGI application must, therefore, be able to identify which method is being used and then to handle the inputs accordingly. The first step is to add the first three obligatory lines that must appear at the start of every REBOL CGI file. These lines are:
- the shebang line - this tells the server where to find the REBOL interpretor
- the REBOL header line
- the CGI header line
They will look like:
And, in this example, the request method being used is displayed in the browser:
Figure 1 (at the bottom of this article) shows the results when using the GET method, and figure 2 shows the results of using the POST method. The next step is to process the inputs according to the sending method being used.
Processing the CGI Inputs with REBOL
The CGI variables will start life as a string, either read in from the string sent as part of the URL (in the case of the GET method) or it will be read in from the standard input (in the case of the POST method). The first step, therefore, is to create the variable that will store this information. In this case it's been given and initial size of 1 KB:
The CGI input is then read into this string:
At the moment the string is not in a usable form;
- all the variables input will form part of the string
- the string will contain control characters
However, all of that can be resolved in a single statement:
This new object (named "cgi") will contain a field for each of the CGI variables, for example:
Figure 3 shows this simple process in operation, and that's the important thing for any programmer to remember: it is a very simple procedure, but it enables the REBOL programmer to create highly sophisticated business rules based applications.
How to Process Inputs to a REBOL CGI Web Page
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Figure 1: Processing a GET Form
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Figure 2: Processing a POST Form
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Figure 3: Processing the CGI Variables
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